@article{chen_jiang_spencer_2024, title={A mixed formulation of the plane-stress problem to facilitate reuse of constitutive models in finite-element programs}, volume={139}, ISSN={["1873-3972"]}, DOI={10.1016/j.mechrescom.2024.104307}, journal={MECHANICS RESEARCH COMMUNICATIONS}, author={Chen, Hailong and Jiang, Wen and Spencer, Benjamin W.}, year={2024}, month={Aug} }
 @article{recuero_singh_jiang_2024, title={Fracture mechanics approach to TRISO fuel particle failure analysis}, volume={596}, ISSN={["1873-4820"]}, url={https://doi.org/10.1016/j.jnucmat.2024.155083}, DOI={10.1016/j.jnucmat.2024.155083}, abstractNote={Weibull stress-based methods for failure probability assessment have been developed and analyzed to assess the integrity of tristructural isotropic (TRISO) fuel particles during fuel life cycles and accident operating conditions. While simple, these methods entail a number of drawbacks when stress concentrates near crack tips, including finite element mesh size dependency when the Weibull stress is averaged over the finite element domain. Fracture mechanics approaches involving the use of interaction integrals eliminate this lack of mesh convergence and produce consistent fracture predictions. In this work, we use an interaction integral approach to computing stress intensity factors for a crack in the inner pyrolytic carbon layer perpendicular to the silicon carbide layer, which is simplified representation of a failure mode in TRISO particles. The interface between these two TRISO layers has been shown to become porous, which we simulate by considering a transition of mechanical properties over such porous length, i.e. the layers are modeled as a functionally graded material. Aspects such as porosity and thermal and irradiation eigenstrains are considered in computing the stress intensity factor from a fracture mechanics approach and compared with the known Weibull stress failure approach. The methodology introduced in this paper enables a more general fracture probability assessment in TRISO particles and eliminates the need to identify best suited parameters when using local or averaged stress-based failure criterion. Finally, the numerical sensitivity studies show how parameters such as the porous transition zone length, the material stiffness, and creep affect the probability of TRISO fuel particle failure.}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Recuero, Antonio M. and Singh, Gyanender and Jiang, Wen}, year={2024}, month={Aug} }
 @article{hales_jiangb_2024, title={Versatile TRISO fuel particle modeling in Bison}, volume={428}, ISSN={["1872-759X"]}, url={https://doi.org/10.1016/j.nucengdes.2024.113515}, DOI={10.1016/j.nucengdes.2024.113515}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Hales, Jason D. and Jiangb, Wen}, year={2024}, month={Nov} }
 @article{bognarova_jiang_schwen_tonks_2023, title={A comparative study of two numerical approaches for solving Kim–Kim–Suzuki phase-field models}, url={https://doi.org/10.1016/j.commatsci.2023.112375}, DOI={10.1016/j.commatsci.2023.112375}, abstractNote={Among the standard multi-phase multi-component phase-field (PF) methods, the Kim–Kim–Suzuki (KKS) method has the advantage of decoupling interfacial energy from bulk energy and solving concentration as the conserved variable. There are two approaches to numerically solving a KKS method: the global solution approach (GSA) solves all variables in a global system simultaneously, and the local solution approach (LSA) solves phase concentrations locally using a Newton solver. This work compares the performance of LSA and GSA for solving four KKS models of increasing complexity with the finite element method using the MOOSE framework. The solution accuracy, degrees of freedom (DOFs), memory usage, and computational efficiency are compared. We find that GSA and LSA generate similar solutions, with a maximum difference of only 0.34%. For each model, LSA has a lower number of DOFs, utilizes less memory, and less wall time. The savings of memory and wall time in LSA increase with increasing mesh density of the same model and are more pronounced in models with higher dimensionality and more nodes. However, GSA is easier to implement in existing codes and can better solve highly nonlinear systems by utilizing sophisticated solvers.}, journal={Computational Materials Science}, author={Bognarova, Xueyang and Jiang, Wen and Schwen, Daniel and Tonks, Michael R.}, year={2023}, month={Oct} }
 @article{chakroborty_dhulipala_che_jiang_spencer_hales_shields_2023, title={General Multifidelity Surrogate Models: Framework and Active-Learning Strategies for Efficient Rare Event Simulation}, url={https://doi.org/10.1061/JENMDT.EMENG-7111}, DOI={10.1061/JENMDT.EMENG-7111}, abstractNote={Estimating the probability of failure for complex real-world systems using high-fidelity computational models is often prohibitively expensive, especially when the probability is small. Exploiting low-fidelity models can make this process more feasible, but merging information from multiple low-fidelity and high-fidelity models poses several challenges. This paper presents a robust multifidelity surrogate modeling strategy in which the multifidelity surrogate is assembled using an active-learning strategy using an on-the-fly model adequacy assessment set within a subset simulation framework for efficient reliability analysis. The multifidelity surrogate is assembled by first applying a Gaussian process correction to each low-fidelity model and assigning a model probability based on the model’s local predictive accuracy and cost. Three strategies are proposed to fuse these individual surrogates into an overall surrogate model based on model averaging and deterministic or stochastic model selection. The strategies also dictate which model evaluations are necessary. No assumptions are made about the relationships between low-fidelity models, while the high-fidelity model is assumed to be the most accurate and most computationally expensive model. Through two analytical and two numerical case studies, including a case study evaluating the failure probability of tristructural isotropic-coated (TRISO) nuclear fuels, the algorithm is shown to be highly accurate while drastically reducing the number of high-fidelity model calls (and hence computational cost).}, journal={Journal of Engineering Mechanics}, author={Chakroborty, Promit and Dhulipala, Somayajulu L. N. and Che, Yifeng and Jiang, Wen and Spencer, Benjamin W. and Hales, Jason D. and Shields, Michael D.}, year={2023}, month={Dec} }
 @article{slaughter_prince_german_halvic_jiang_spencer_dhulipala_gaston_2023, title={MOOSE Stochastic Tools: A module for performing parallel, memory-efficient in situ stochastic simulations}, url={https://doi.org/10.1016/j.softx.2023.101345}, DOI={10.1016/j.softx.2023.101345}, abstractNote={Stochastic simulations are ubiquitous across scientific disciplines. The Multiphysics Object-Oriented Simulation Environment (MOOSE) includes an optional module – stochastic tools – for implementing stochastic simulations. It implements an efficient and scalable scheme for performing stochastic analysis in memory. It can be used for building meta models to reduce the computational expense of multiphysics problems as well as perform analyses requiring up to millions of stochastic simulations. To illustrate, we have provided an example that trains a proper orthogonal decomposition reduced-basis model. The impact of the module is detailed by explaining how it is being used for failure analysis in nuclear fuel and reducing the computational burden via dynamic meta model training. The module is unique in that it provides the ability to use a single framework for simulations and stochastic analysis, especially for memory intensive problems and intrusive meta modeling methods.}, journal={SoftwareX}, author={Slaughter, Andrew E. and Prince, Zachary M. and German, Peter and Halvic, Ian and Jiang, Wen and Spencer, Benjamin W. and Dhulipala, Somayajulu L.N. and Gaston, Derek R.}, year={2023}, month={May} }
 @book{simon_aagesen_bhave_jiang_jiang_ke_yang_2023, title={Multi-scale fission product release model with comparison to AGR data}, url={https://doi.org/10.2172/2203700}, DOI={10.2172/2203700}, author={Simon, Pierre-Clement and Aagesen, Larry, Jr. and Bhave, Chaitanya and Jiang, Chao and Jiang, Wen and Ke, Jia-Hong and Yang, Lin}, year={2023}, month={Jun} }
 @article{baghdasaryan_jiang_hales_kozlowski_krajewska_2023, title={TRISO fuel performance analysis: Uncertainty quantification toward optimization}, url={https://doi.org/10.1016/j.nucengdes.2023.112401}, DOI={10.1016/j.nucengdes.2023.112401}, abstractNote={Tri-structural isotropic (TRISO) fuel particles are a fuel form being considered for potential use in next-generation nuclear reactors (i.e., high-temperature gas-cooled reactors). Though the TRISO fuel manufacturing process has continually advanced in recent years, particle comparisons still reveal statistical variations and uncertainties in terms of geometric configurations and material properties. Given that the physical processes ongoing in TRISO fuel particles during reactor operation are highly correlated with each other, a small degree of uncertainty in one model may lead to significant uncertainty in another. This makes appropriate uncertainty quantification of TRISO fuel particles essential. However, one may wonder about the extent to which the current version of TRISO particles has been optimized, and whether any room remains for further improvements. This paper quantifies TRISO fuel performance model uncertainties that stem from geometric and material data. For this analysis, the BISON code was used, and the Advanced Gas Reactor (AGR)-2 experiment served as a reference case. A total of 105 calculations was performed for the uncertainty and optimization analysis, altering the geometric and material data within their uncertainty range. Lastly, the optimization potential of TRISO particles is evaluated from a fuel performance perspective.}, journal={Nuclear Engineering and Design}, author={Baghdasaryan, Nairi and Jiang, Wen and Hales, Jason and Kozlowski, Tomasz and Krajewska, Zuzanna}, year={2023}, month={Aug} }
 @article{jiang_hu_aagesen_biswas_gamble_2022, title={A phase-field model of quasi-brittle fracture for pressurized cracks: Application to UO2 high-burnup microstructure fragmentation}, url={https://doi.org/10.1016/j.tafmec.2022.103348}, DOI={10.1016/j.tafmec.2022.103348}, abstractNote={In this paper, we present a phase-field model of quasi-brittle fracture with pressurized cracks, with dedicated applications for polycrystalline materials. The model is formulated as a minimization problem within the variational framework. The external work done by pressure on the crack surfaces is included in the objective function. Several careful modeling choices lead to a regularization-length-independent critical strength. The model is constructed to give a softening response with an underlying linear traction-separation law. The pressure-dependent softening response and the regularization of the prescribed pressure are demonstrated with a (quasi) one-dimensional numerical analysis. In a two-dimensional numerical analysis under plane strain assumptions, the critical stress corresponding to crack propagation (as predicted by our quasi-brittle fracture model) is compared with linear elastic fracture mechanics (LEFM) analytical solutions. Our model is further utilized to simulate fission-gas-induced fragmentation of the UO2 high-burnup structure (HBS). Simulation results show that pressurized bubbles can cause crack nucleation and propagation, and that the bubble size and the surrounding external pressure affect the critical pressure corresponding to crack nucleation. Simulations of a partial HBS at different recrystallization stages show that different grain structures (due to recrystallization) also influence crack paths and fragmentation morphology.}, journal={Theoretical and Applied Fracture Mechanics}, author={Jiang, Wen and Hu, Tianchen and Aagesen, Larry K. and Biswas, Sudipta and Gamble, Kyle A.}, year={2022}, month={Jun} }
 @article{wu_abdallah_jiang_ullberg_phillpot_couet_perepezko_tonks_2023, title={A phase-field study of stainless-steel oxidation from high-temperature carbon dioxide exposure}, url={https://doi.org/10.1016/j.commatsci.2022.111996}, DOI={10.1016/j.commatsci.2022.111996}, journal={Computational Materials Science}, author={Wu, Xueyang and Abdallah, Iman and Jiang, Wen and Ullberg, Robert S. and Phillpot, Simon R. and Couet, Adrien and Perepezko, John H. and Tonks, Michael R.}, year={2023}, month={Feb} }
 @article{dhulipala_jiang_spencer_hales_shields_slaughter_prince_labouré_bolisetti_chakroborty_2022, title={Accelerated statistical failure analysis of multifidelity TRISO fuel models}, volume={563}, url={https://doi.org/10.1016/j.jnucmat.2022.153604}, DOI={10.1016/j.jnucmat.2022.153604}, abstractNote={Statistical nuclear fuel failure analysis is critical for the design and development of advanced reactor technologies. Although Monte Carlo Sampling (MCS) is a standard method of statistical failure analysis for fuels, the low failure probabilities of some advanced fuel forms and the correspondingly large number of required model evaluations limit its application to low-fidelity (e.g., 1-D) fuel models. In this paper, we present four other statistical methods for fuel failure analysis in Bison, considering tri-structural isotropic (TRISO)-coated particle fuel as a case study. The statistical methods considered are Latin hypercube sampling (LHS), adaptive importance sampling (AIS), subset simulation (SS), and the Weibull theory. Using these methods, we analyzed both 1-D and 2-D representations of TRISO models to compute failure probabilities and the distributions of fuel properties that result in failures. The results of these methods compare well across all TRISO models considered. Overall, SS and the Weibull theory were deemed the most efficient, and can be applied to both 1-D and 2-D TRISO models to compute failure probabilities. Moreover, since SS also characterizes the distribution of parameters that cause TRISO failures, and can consider failure modes not described by the Weibull criterion, it may be preferred over the other methods. Finally, a discussion on the efficacy of different statistical methods of assessing nuclear fuel safety is provided.}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Dhulipala, Somayajulu L.N. and Jiang, Wen and Spencer, Benjamin W. and Hales, Jason D. and Shields, Michael D. and Slaughter, Andrew E. and Prince, Zachary M. and Labouré, Vincent M. and Bolisetti, Chandrakanth and Chakroborty, Promit}, year={2022}, month={May}, pages={153604} }
 @book{toptan_jiang_singh_dhulipala_che_hales_novascone_2022, title={Assessment and Improvement of Fission Product Transport Predictions of Particle Fuel in BISON}, url={https://doi.org/10.2172/1901807}, DOI={10.2172/1901807}, abstractNote={The U.S. Department of Energy’s Nuclear Energy Advanced Modeling and Simulation (NEAMS) program aims to develop predictive capabilities by applying computational methods to the analysis and design of advanced reactor and fuel cycle systems. This program has been providing engineering-scale support for the development of BISON, a high-fidelity and high-resolution fuel performance tool. This study was motivated by the need to incorporate more physics-based models in BISON in order to foster tri-structural isotropic (TRISO) applications. This document details the integration of new modeling capabilities in BISON, including (1) development of pyrolytic carbon (PyC) and silicon carbide (SiC) layer anisotropic thermal and mass transport capabilities, (2) verification of the mass diffusion solution in TRISO modeling, (3) calibration of fission product diffusivity using Advanced Gas Reactor (AGR) experiments, (4) improved fission product release modeling by developing compact diffusion modeling capabilities, and (5) documentation of accelerated failure analysis on the BISON website. Improvements made to the diffusion models and parameters were documented and validated against AGR-1 and -2 experiment data.}, author={Toptan, Aysenur and Jiang, Wen and Singh, Gyanender and Dhulipala, Som and Che, Yifeng and Hales, Jason and Novascone, Stephen}, year={2022}, month={Sep} }
 @article{zhang_jiang_gamble_tonks_2023, title={Comparing the impact of thermal stresses and bubble pressure on intergranular fracture in UO2 using 2D phase field fracture simulations}, url={https://doi.org/10.1016/j.jnucmat.2022.154158}, DOI={10.1016/j.jnucmat.2022.154158}, abstractNote={UO2 fuel fragmentation and pulverization during loss-of-coolant accidents (LOCAs) is an ongoing safety concern that has gained importance due to recent interest in increasing burnup limits for light water reactor fuel. In this work, we investigate the importance of bubble pressure on fragmentation using 2D phase field fracture simulations of UO2 polycrystals. The model includes anisotropic single crystal elastic constants, encourages intergranular fracture, and includes bubble pressure and its impact on crack opening. An external stress is applied that is representative of the internal stresses observed in macroscale BISON simulations of LOCA tests. Cracks do not form under the external applied stress in UO2 polycrystals without porosity. Crack nucleation and propagation do occur under the external applied stress in polycrystals with unpressurized 1 μm radius intergranular voids, and crack propagation accelerates with increasing number of voids. Crack nucleation and propagation also occur in polycrystals without the external applied stress if the intergranular pores are pressurized, and crack propagation is faster with both pressurized pores and the external applied stress. Our 2D results indicate that bubble pressure may not be necessary to initiate fragmentation in polycrystals with intergranular porosity under LOCA conditions, though this should be verified using 3D simulations with fewer assumptions.}, journal={Journal of Nuclear Materials}, author={Zhang, Shuaifang and Jiang, Wen and Gamble, Kyle A. and Tonks, Michael R.}, year={2023}, month={Feb} }
 @article{jiang_singh_hales_toptan_spencer_novascone_dhulipala_prince_2022, title={Efficient high-fidelity TRISO statistical failure analysis using Bison: Applications to AGR-2 irradiation testing}, volume={562}, url={https://doi.org/10.1016/j.jnucmat.2022.153585}, DOI={10.1016/j.jnucmat.2022.153585}, abstractNote={The ability of tri-structural isotropic (TRISO) fuel to contain fission products is largely dictated by the quality of the manufacturing process, since most of the fission product release is expected to occur due to coating layer failure in a small number of particles containing defects. The Bison fuel performance code has capabilities to predict failure in individual particles, accounting for the presence of defects, and to apply statistical analysis methods to compute the probability of failure in a set of fuel particles. Bison has recently undergone significant development both to improve its physical representations of fuel particle behavior and to improve the efficiency of its statistical failure calculations. Physical model improvements include new capabilities to account for the pressure generated by fission gases on inner pyrolytic carbon (IPyC) crack surfaces and to use local material coordinate orientation to accurately incorporate the anisotropy in the material properties in aspherical particles. To improve statistical modeling efficency, a direct integration approach which involves directly integrating the failure probability function associated with statistically varying parameters has been developed. The direct integration approach is much more efficient than the Monte Carlo (MC) schemes commenly employed, and allows Bison to directly run high-dimensional fuel performance models, which improves the accuracy of failure probability calculations. A set of benchmark problems is considered here to compare the MC and direct integration approaches, and a statistical failure analysis of compacts in the Advanced Gas Reactor (AGR)-2 experiments is performed using the direct integration approach.}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Jiang, Wen and Singh, Gyanender and Hales, Jason D. and Toptan, Aysenur and Spencer, Benjamin W. and Novascone, Stephen R. and Dhulipala, Somayajulu L.N. and Prince, Zachary M.}, year={2022}, month={Apr}, pages={153585} }
 @article{mcclenny_butt_abdoelatef_pate_yee_harikrishnan_perez-nunez_jiang_ortega_mcdeavitt_et al._2022, title={Experimentally validated multiphysics modeling of fracture induced by thermal shocks in sintered UO2 pellets}, url={https://doi.org/10.1016/j.jnucmat.2022.153719}, DOI={10.1016/j.jnucmat.2022.153719}, abstractNote={Commercial nuclear power plants extensively rely on fission energy from uranium dioxide (UO2) fuel pellets that provide thermal energy; consequently, generating carbon-free power in current generation reactors. UO2 fuel incurs damage and fractures during operation due to large thermal gradients that develop across the fuel pellet during normal operation. The underlying mechanisms by which these processes take place are still poorly understood. This work is a part of our combined experimental and computational effort for quantifying the UO2 fuel fracture behavior induced by thermal shock. In this work, we describe an experimental study performed to understand the fuel fracturing behavior of sintered powder UO2 pellets when exposed to thermal shock conditions, as well as a multiphysics phase-field fracture model which accurately predicts the experimental results. Parametric studies and sensitivity analysis are used to assess uncertainty. Experimental data was collected from multiple experiments by exposing UO2 pellets to high-temperature conditions (900-1200C), which are subsequently quenched in sub-zero water. We exhibit that the fracture results gathered in the experimental setting can be consistently recreated by this work phase-field fracture model, demonstrating a reliable ability to our model in simulating the thermal shock gradients and subsequent fracture mechanics in the primary fuel source for Light-Water Reactors (LWRs). This model advanced the fundamental understanding of thermal shock and property correlations to advance utilization of UO2 as a fuel for nuclear reactors.}, journal={Journal of Nuclear Materials}, author={McClenny, Levi D. and Butt, Moiz I. and Abdoelatef, M. Gomaa and Pate, Michal J. and Yee, Kay L. and Harikrishnan, R. and Perez-Nunez, Delia and Jiang, W. and Ortega, Luis H. and McDeavitt, Sean M. and et al.}, year={2022}, month={Jul} }
 @book{aagesen_biswas_gamble_jiang_simon_spencer_2022, title={Implementation and testing of physics-based pulverization model in BISON}, url={https://doi.org/10.2172/1984930}, DOI={10.2172/1984930}, abstractNote={This report summarizes lower length scale computational research conducted to improve the pulverization criterion for high-burnup UO 2 fuel in the BISON fuel performance code.This research was sponsored by the NEAMS program during FY22.Efforts to improve the model primarily focus on calculating the current pressure of bubbles in the high-burnup structure (HBS) region, as well as the critical bubble pressure at which pulverization occurs in the HBS.The phase-field model for predicting initial bubble pressure in the HBS was improved by implementing a more realistic model for defect production, and by coupling the phase-field model for inter-granular bubble evolution with the spatially-resolved cluster dynamics code Xolotl to simulate intra-granular fission gas evolution.An evolution equation for current bubble pressure was added to BISON, an improvement over the previous model that assumed that bubble pressure was static following HBS formation.To improve calculations of critical bubble pressure for pulverization, 3-D phase-field fracture simulations were performed, and a function for critical bubble pressure was fit-based on the simulation results-to replace the previous function, which had been determined using 2-D simulations.The impacts of these modifications to the existing pulverization assessment cases will be reported in the forthcoming engineeringscale milestone on high-burnup UO 2 pulverization.A poromechanics-based approach was used to include the effect of bubble overpressurization on the stress state of the pellet at the engineering scale, and the initial strategy for integration of the pulverization criterion with pellet-scale mechanical degradation using a smeared cracking model was developed.This report also describes the initial research that was conducted to inform a forthcoming transient fission gas release (tFGR) model in BISON.Focusing on the fission gas release caused by pulverization of the outer pellet rim, a model for the amount of fission gas release was developed as a function of fuel porosity, bubble size, and fragment size.Implementation of this model in BISON and its impact of engineering-scale predictions will also be described in the aforementioned engineering-scale milestone on high-burnup UO 2 pulverization.}, author={Aagesen, Larry, Jr. and Biswas, Sudipta and Gamble, Kyle and Jiang, Wen and Simon, Pierre-Clément and Spencer, Benjamin}, year={2022}, month={Jun} }
 @article{simon_aagesen_jiang_jiang_ke_2022, title={Mechanistic calculation of the effective silver diffusion coefficient in polycrystalline silicon carbide: Application to silver release in AGR-1 TRISO particles}, volume={563}, url={https://doi.org/10.1016/j.jnucmat.2022.153669}, DOI={10.1016/j.jnucmat.2022.153669}, abstractNote={The silicon carbide (SiC) layer in tristructural isotropic (TRISO) fuel particles serves as a barrier to prevent the escape of fission products produced and not retained in the fuel kernel. The release of silver (Ag) is a concern due to the long half-life of the 110mAg isotope. However, accurately determining the fission gas release rate requires knowing the diffusion coefficient through the SiC layer. In this study, we leverage atomistic calculations of Ag diffusivity in SiC bulk and grain boundaries (GBs) to develop a mesoscale effective Ag diffusion coefficient (Deff) in SiC. Since GBs serve as pathways for Ag diffusion, Deff is defined as a function of temperature and microstructure variables. In particular, the size of SiC grains in the direction perpendicular to diffusion is shown to significantly affect Ag diffusion. The prediction of the mechanistic, mesoscale approach falls within one order of magnitude of empirical values. The temperature and microstructure-dependent effective Ag diffusivity in SiC is implemented in the fuel performance code Bison with a correction factor to predict Ag release from AGR-1 TRISO fuel particles. We hereby quantify the impact of SiC grain size on Ag release and improve Bison's predictions.}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Simon, P.-C.A. and Aagesen, Larry K. and Jiang, Chao and Jiang, Wen and Ke, Jia-Hong}, year={2022}, month={May}, pages={153669} }
 @article{dhulipala_shields_chakroborty_jiang_spencer_hales_labouré_prince_bolisetti_che_2022, title={Reliability estimation of an advanced nuclear fuel using coupled active learning, multifidelity modeling, and subset simulation}, url={https://doi.org/10.1016/j.ress.2022.108693}, DOI={10.1016/j.ress.2022.108693}, abstractNote={Tristructural isotropic (TRISO)-coated particle fuel is a robust nuclear fuel and determining its reliability is critical for the success of advanced nuclear technologies. However, TRISO failure probabilities are small and the associated computational models are expensive. We used coupled active learning, multifidelity modeling, and subset simulation to estimate the failure probabilities of TRISO fuels using several 1D and 2D models. With multifidelity modeling, we replaced expensive high-fidelity (HF) model evaluations with information fusion from two low-fidelity (LF) models. For the 1D TRISO models, we considered three multifidelity modeling strategies: only Kriging, Kriging LF prediction plus Kriging correction, and deep neural network (DNN) LF prediction plus Kriging correction. While the results across these multifidelity modeling strategies compared satisfactorily, strategies employing information fusion from two LF models called the HF model least often. Next, for the 2D TRISO model, we considered two multifidelity modeling strategies: DNN LF prediction plus Kriging correction (data-driven) and 1D TRISO LF prediction plus Kriging correction (physics-based). The physics-based strategy, as expected, consistently required the fewest calls to the HF model. However, the data-driven strategy had a lower overall simulation time since the DNN predictions are instantaneous, and the 1D TRISO model requires a non-negligible simulation time.}, journal={Reliability Engineering & System Safety}, author={Dhulipala, Somayajulu L.N. and Shields, Michael D. and Chakroborty, Promit and Jiang, Wen and Spencer, Benjamin W. and Hales, Jason D. and Labouré, Vincent M. and Prince, Zachary M. and Bolisetti, Chandrakanth and Che, Yifeng}, year={2022}, month={Oct} }
 @article{toptan_jiang_hales_spencer_novascone_2023, title={Verification of Bison fission product species conservation under TRISO reactor conditions}, url={https://doi.org/10.1016/j.jnucmat.2022.154105}, DOI={10.1016/j.jnucmat.2022.154105}, abstractNote={When assessing the reliability and predictive capabilities of a simulation tool, code verification is used to ensure that the implemented numerical algorithm is a faithful representation of its underlying mathematical model, including partial differential or integral equations, initial and boundary conditions, and auxiliary relationships. During this process, numerical results in a discrete solution are compared to the analytical solution of the mathematical model. In this paper, the code verification process is applied to one-dimensional spatiotemporal problems that exercise partial differential equation governing the conservation of fission product species (or mass diffusion). Numerical experiments were performed in the Bison fuel performance code to evaluate its predictive capability under various TRISO reactor conditions such as base irradiation and safety heating test conditions for either short- or long-lived fission product species, as well as a case concerning evaporation from the outer surface of a particle. The code predictions were compared with the expected exact results obtained from the analytical expressions, and the fact that they demonstrate the correct analytical behavior provides strong evidence of proper numerical algorithm implementation.}, journal={Journal of Nuclear Materials}, author={Toptan, Aysenur and Jiang, Wen and Hales, Jason D. and Spencer, Benjamin W. and Novascone, Stephen}, year={2023}, month={Jan} }
 @article{pitts_jiang_pizzocri_barker_zbib_2022, title={A Continuum Dislocation Dynamics Crystal Plasticity Approach to Irradiated Body-Centered Cubic α-Iron}, url={http://dx.doi.org/10.1115/1.4052256}, DOI={10.1115/1.4052256}, abstractNote={Abstract Radiation-induced embrittlement of reactor pressure vessel (RPV) steels can potentially limit the operating life of nuclear power plants. Over extended exposure to radiation doses, these body-centered cubic (BCC) irons demonstrate irradiation damage. Here, we present a continuum dislocation density (CDD) crystal plasticity model to capture the interaction among dislocations and self-interstitial atom (SIA) loops in α-iron. We demonstrate the importance of modeling cross slip using a combined stochastic Monte Carlo approach and the role of slip system strength anisotropy in capturing stochastic cross slip interactions. Through these captured interactions, the CDD crystal plasticity model can capture both the stress response and the physical evolution of dislocations on different slip system planes. Single-crystal verification experiments are used to calibrate the CDD crystal plasticity model, and a set of simplified polycrystalline simulations demonstrates the model’s ability to capture the stress response from tensile experiments on α-iron.}, journal={Journal of Engineering Materials and Technology}, author={Pitts, Stephanie A. and Jiang, Wen and Pizzocri, Davide and Barker, Erin I. and Zbib, Hussein M.}, year={2022}, month={Jan} }
 @book{jiang_simon_jiang_aagesen_ke_2021, title={Atomistic and mesoscale simulations to determine effective diffusion coefficient of fission products in SiC}, url={https://doi.org/10.2172/1825508}, DOI={10.2172/1825508}, abstractNote={The silicon carbide (SiC) layer in tristructural isotropic (TRISO) particles serves as the barrier to prevent escape of fission products produced in the fuel kernel. Knowing the diffusion coefficient of fission products through SiC is critical to determining whether fission gas can escape from the particle. It has been observed in experiments that Ag accumulated in grain boundaries and triple junctions in SiC. It is hypothesized that grain boundary diffusion is the primary pathway by which fission products penetrate the SiC layer. In this report, the effective diffusion coefficient of the fission product Ag through the grain boundary network is calculated using a combination of atomistic and phase-field methods. The grain boundary diffusion coefficient is calculated using molecular dynamics simulations. The bulk diffusion coefficient is determined using a combination of density functional theory and nudged elastic band methods. An effective diffusion coefficient is calculated, accounting for the grain structure using a phase-field method. The effective diffusion coefficient will be incorporated into Bison and fission product release calculations are compared to available experimental data.}, author={Jiang, Chao and Simon, Pierre-Clement and Jiang, Wen and Aagesen, Larry, Jr and Ke, Jia-Hong}, year={2021}, month={Oct} }
 @article{lindsay_stogner_gaston_schwen_matthews_jiang_aagesen_carlsen_kong_slaughter_et al._2021, title={Automatic Differentiation in MetaPhysicL and Its Applications in MOOSE}, volume={207}, url={http://dx.doi.org/10.1080/00295450.2020.1838877}, DOI={10.1080/00295450.2020.1838877}, abstractNote={Abstract Efficient solution via Newton’s method of nonlinear systems of equations requires an accurate representation of the Jacobian, corresponding to the derivatives of the component residual equations with respect to the degrees of freedom. In practice these systems of equations often arise from spatial discretization of partial differential equations used to model physical phenomena. These equations may involve domain motion or material equations that are complex functions of the systems’ degrees of freedom. Computing the Jacobian by hand in these situations is arduous and prone to error. Finite difference approximations of the Jacobian or its action are prone to truncation error, especially in multiphysics settings. Symbolic differentiation packages may be used, but often result in an excessive number of terms in realistic model scenarios. An alternative to symbolic and numerical differentiation is automatic differentiation (AD), which propagates derivatives with every elementary operation of a computer program, corresponding to continual application of the chain rule. Automatic differentiation offers the guarantee of an exact Jacobian at a relatively small overhead cost. In this work, we outline the adoption of AD in the Multiphysics Object Oriented Simulation Environment (MOOSE) via the MetaPhysicL package. We describe the application of MOOSE’s AD capability to several sets of physics that were previously infeasible to model via hand-coded or Jacobian-free simulation techniques, including arbitrary Lagrangian-Eulerian and level-set simulations of laser melt pools, phase-field simulations with free energies provided through neural networks, and metallic nuclear fuel simulations that require inner Newton loop calculation of nonlinear material properties.}, number={7}, journal={Nuclear Technology}, publisher={Informa UK Limited}, author={Lindsay, Alexander and Stogner, Roy and Gaston, Derek and Schwen, Daniel and Matthews, Christopher and Jiang, Wen and Aagesen, Larry K. and Carlsen, Robert and Kong, Fande and Slaughter, Andrew and et al.}, year={2021}, month={Jul}, pages={905–922} }
 @book{aagesen_biswas_jiang_andersson_cooper_matthews_2021, title={BISON microstructure-based pulverization criterion in high burnup structure}, url={https://doi.org/10.2172/1822440}, DOI={10.2172/1822440}, abstractNote={To improve the economics of commercial nuclear power production, utilities are seeking to increase the allowable burnup limit of UO$_2$ fuel. One of the main factors that contributes to the current burnup limit of 62 GWd/MTU in commercial light water reactors (LWRs) is the risk of fine fragmentation or pulverization during a loss of coolant accident (LOCA). Pulverization primarily occurs at high burnups, especially when the high burnup structure (HBS) has formed. To allow the industry to pursue increased burnup and develop mitigation strategies, it is essential to have improved capability to predict the onset of pulverization. However, the mechanism of pulverization is not well understood, and the existing predictive capabilities implemented in the BISON fuel performance code are empirical in nature. In this report, mesoscale simulations are used to improve understanding of the formation mechanism of the HBS and how it responds during a LOCA transient, and inform development of a BISON pulverization criterion. A phase-field model was used to simulate the evolution of bubble pressure as a result of HBS formation. The simulations showed that gas atoms diffuse from grain interiors to the new grain boundaries created during HBS formation, and diffuse rapidly along these grain boundaries to reach existing bubbles. This causes an increase in bubble pressure in existing bubbles, leading to bubble growth during steady-state operation. To simulate the response of HBS bubbles to a LOCA transient, a newly developed phase-field model was used; in agreement with preliminary results from FY20, bubble size did not change significantly during the duration of the transient. A phase-field fracture model was used to study fragmentation patterns in the HBS, including using input from the phase-field model as initial conditions. Phase-field fracture simulations were used to determine a pulverization criterion for BISON. A function for the critical pressure for pulverization to occur was fit to data from the phase-field fracture simulations, and this function was implemented as a material property in BISON. For comparison, an analytical criterion for pulverization was developed and implemented within the same material property.}, author={Aagesen, Larry, Jr. and Biswas, Sudipta and Jiang, Wen and Andersson, David and Cooper, Michael and Matthews, Christopher}, year={2021}, month={Aug} }
 @article{williamson_hales_novascone_pastore_gamble_spencer_jiang_pitts_casagranda_schwen_et al._2021, title={BISON: A Flexible Code for Advanced Simulation of the Performance of Multiple Nuclear Fuel Forms}, volume={207}, url={http://dx.doi.org/10.1080/00295450.2020.1836940}, DOI={10.1080/00295450.2020.1836940}, abstractNote={Abstract BISON is a nuclear fuel performance application built using the Multiphysics Object-Oriented Simulation Environment (MOOSE) finite element library. One of its major goals is to have a great amount of flexibility in how it is used, including in the types of fuel it can analyze, the geometry of the fuel being modeled, the modeling approach employed, and the dimensionality and size of the models. Fuel forms that can be modeled include standard light water reactor fuel, emerging light water reactor fuels, tri-structural isotropic fuel particles, and metallic fuels. BISON is a platform for research in nuclear fuel performance modeling while simultaneously serving as a tool for the analysis of nuclear fuel designs. Recent research in BISON includes techniques such as the extended finite element method for fuel cracking, exploration of high-burnup light water reactor fuel behavior, swelling behavior of metallic fuels, and central void formation in mixed-oxide fuel. BISON includes integrated documentation for each of its capabilities, follows rigorous software quality assurance procedures, and has a growing set of rigorous verification and validation tests.}, number={7}, journal={Nuclear Technology}, publisher={Informa UK Limited}, author={Williamson, Richard L. and Hales, Jason D. and Novascone, Stephen R. and Pastore, Giovanni and Gamble, Kyle A. and Spencer, Benjamin W. and Jiang, Wen and Pitts, Stephanie A. and Casagranda, Albert and Schwen, Daniel and et al.}, year={2021}, month={Jul}, pages={954–980} }
 @article{bayesian inverse uncertainty quantification of a moose-based melt pool model for additive manufacturing using experimental data_2021, year={2021}, month={May} }
 @book{jiang_singh_hales_toptan_spencer_novascone_2021, title={Efficient Failure Probability Calculations and Modeling Interface Debonding in TRISO Particles with BISON}, url={https://doi.org/10.2172/1825512}, DOI={10.2172/1825512}, abstractNote={This document constitutes completion of the NEAMS milestone, which is titled: Demonstrate efficiency improvements in TRISO failure probability calculations and the effect of debonding on fission product transport in TRISO fuel particles in Bison. In this report we present the development of: (1) the anisotropic elasticity model of pyrolytic carbon and extended material models using the local coordinate system for aspherical particle geometry, (2) a capability of modeling interface debonding in TRISO particles , (3) an efficient high-fidelity approach to calculate the failure probability of TRISO particles. Benchmark problems and AGR-2 tests are used to verify the models and demonstrate these new capabilities.}, author={Jiang, Wen and Singh, Gyanender and Hales, Jason and Toptan, Aysenur and Spencer, Benjamin and Novascone, Stephen}, year={2021}, month={Sep} }
 @book{jiang_toptan_hales_casagranda_spencer_novascone_2021, title={Fission Product Transport in TRISO Particles and Pebbles}, url={https://doi.org/10.2172/1818294}, DOI={10.2172/1818294}, abstractNote={This document demonstrates completion of the goals described in the technical narrative of the FOA project titled: ”Modeling and Simulation Development Pathways to Accelerating KP-FHR Licensing” regarding fission product transport in the Kairos-proposed fuel pebble by INL and Kairos Power. Showcased in this report are code developments and simulations in BISON that extend the state of the art in computation and understanding of fission product transport in a TRISO fuel particle and pebble. These enhancements lay the foundation for making predictions of fission product transport that can be used as input in the fuel licensing process. This was achieved by installing existing fuel material models originally used in PARFUME, developing a new failure probability method that is efficient and multi-dimensional, employing material homogenization, and expanding verification and validation simulations to demonstrate the efficacy of the work. All this work is leveraged to spotlight the main deliverable; a three-dimensional model and corresponding demonstration simulation of a pebble, which will serve as the starting point for models used to predict fission product release.}, author={Jiang, Wen and Toptan, Aysenur and Hales, Jason and Casagranda, Albert and Spencer, Benjamin and Novascone, Stephen}, year={2021}, month={Jun} }
 @article{spencer_hoffman_biswas_jiang_giorla_backman_2021, title={Grizzly and BlackBear: Structural Component Aging Simulation Codes}, volume={207}, url={http://dx.doi.org/10.1080/00295450.2020.1868278}, DOI={10.1080/00295450.2020.1868278}, abstractNote={Abstract The operating environment of nuclear reactors imposes extreme challenges on the materials from which the structures within and surrounding the reactor are constructed. Understanding the effects of exposure to this environment is critical for ensuring the safe long-term operation of these reactors. The Grizzly and BlackBear codes are being developed to model the progression of aging mechanisms and their effects on the integrity of critical structures. These codes take advantage of the capabilities of the MOOSE framework to solve the wide range of coupled physics problems that are encountered in predictive simulation of structural degradation. This paper provides an overview of these codes, with a specific focus on two capabilities relevant for light water reactor applications: reactor pressure vessel embrittlement and concrete degradation.}, number={7}, journal={Nuclear Technology}, publisher={Informa UK Limited}, author={Spencer, Benjamin W. and Hoffman, William M. and Biswas, Sudipta and Jiang, Wen and Giorla, Alain and Backman, Marie A.}, year={2021}, month={Jul}, pages={981–1003} }
 @book{toptan_jiang_novascone_hales_2021, title={Matrix Graphite Material Models In Pebbles and Compacts For Bison}, url={https://doi.org/10.2172/1825268}, DOI={10.2172/1825268}, abstractNote={The cores and reflectors in high-temperature gas-cooled reactors (HTGRs) are made of graphite materials, with the graphite acting as a moderator, a fuel host matrix, or the foundation for various structural components. This study aims to survey the models in the literature for graphite materials being used as host matrices in pebble/fuel compacts and to implement those surveyed models into Bison to conduct an early assessment of graphite's thermo-mechanical response under various reactor conditions. In this study, thermal (e.g., thermal conductivity, and specific heat capacity) and mechanical (e.g., elastic properties, thermal expansion, irradiation-induced dimensional changes, and irradiation-induced creep) material models for various graphite grades (e.g., H-451, IG-110, G-348, 2020, A3-3, and A3-27) are incorporated into Bison. Two benchmark problems are then exercised utilizing these new graphite-related capabilities: (1) modeling an Advanced Gas Reactor (AGR)-2 fuel compact, and (2) modeling the debonding of a particle-matrix interface.}, author={Toptan, Aysenur and Jiang, Wen and Novascone, Stephen and Hales, Jason}, year={2021}, month={Sep} }
 @article{bailly-salins_borrel_jiang_spencer_shirvan_couet_2021, title={Modeling of High-Temperature Corrosion of Zirconium Alloys Using the eXtended Finite Element Method (X-FEM)}, url={https://doi.org/10.1016/j.corsci.2021.109603}, DOI={10.1016/j.corsci.2021.109603}, abstractNote={Oxidation modeling in modern nuclear fuel performance codes is currently limited by the lack of coupling with mechanics, thus preventing proper description of how high-temperature oxidation impacts mechanical properties. This is mostly due to the fact that the finite difference formalism adopted in corrosion models is incompatible with the direct coupling with mechanics in the finite element modeling employed in modern nuclear fuel performance codes. In this study, a physically based zirconium alloy corrosion model called the Coupled-Current Charge Compensation (C4) model, which was initially developed for operating temperature conditions, has been updated to include high-temperature corrosion in order to provide additional critical information (e.g., oxygen concentration profile) under loss-of-coolant accident (LOCA) conditions—information lacking in existing empirical models. The C4 model was implemented in the MOOSE finite-element framework developed at Idaho National Laboratory, enabling it to be used in the BISON nuclear fuel performance code based on the MOOSE framework. To precisely track the different interfaces at a relatively low computational cost, the eXtended Finite Element Method (X-FEM) was applied in MOOSE. The model's results were compared to those of existing empirical models as well as metallographic analysis of high-temperature oxidized Zircaloy-4 coupons. Oxygen diffusivities in the α and β phases resulting from this comparison closely agree with those found in the literature. The C4 model implemented with X-FEM in MOOSE now has the capability to accurately predict oxide, oxygen-stabilized α, and prior β phase layer growth kinetics under isothermal exposure at high temperature (1000–1500 °C). Furthermore, in contrast with the empirical models, the C4 model accounts for the finite thickness of the fuel cladding. It can predict the oxygen concentration profile evolution through the whole cladding, enabling evaluation of the remaining ductile thickness—a crucial variable for modeling the mechanical behavior of the fuel cladding under LOCA. This implementation allows direct coupling with mechanics, at a low computing cost, using finite-element-based nuclear fuel performance codes such as BISON.}, journal={Corrosion Science}, author={Bailly-Salins, Louis and Borrel, Léo and Jiang, Wen and Spencer, Benjamin W. and Shirvan, Koroush and Couet, Adrien}, year={2021}, month={Aug} }
 @article{jiang_hales_spencer_collin_slaughter_novascone_toptan_gamble_gardner_2021, title={TRISO particle fuel performance and failure analysis with BISON}, volume={548}, url={https://doi.org/10.1016/j.jnucmat.2021.152795}, DOI={10.1016/j.jnucmat.2021.152795}, abstractNote={Because of its widespread use in multiple advanced reactor concepts, the ability to accurately simulate tri-structural isotropic (TRISO) fuel performance is essential for ensuring the safe operation of these reactors. To that end, the BISON fuel performance code has undergone significant recent development to expand its TRISO particle fuel performance modeling capabilities. This includes the development of material models, such as elastic, creep, swelling, thermal expansion, thermal conductivity, and fission gas release models. The capability to perform statistical failure analysis on large sets of samples has also been developed, utilizing a Monte Carlo scheme to execute fast-running 1-D spherically symmetric models. Stress adjustments are made in those 1-D models to account for multi-dimensional failure phenomena. Stress correlation functions are extracted from multi-dimensional failure simulation results, such as from a particle with cracked inner pyrolytic carbon (IPyC) and an aspherical particle. This paper provides a detailed description of the models used by BISON for TRISO fuel, along with a set of problems that test these models by (favorably) comparing them both with another code and experimental data. These include simulations of the Advanced Gas Reactor (AGR)-2 and AGR-5/6/7 experiments, with predictions for fuel performance parameters, failure probability, and fission product transport.}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Jiang, Wen and Hales, Jason D. and Spencer, Benjamin W. and Collin, Blaise P. and Slaughter, Andrew E. and Novascone, Stephen R. and Toptan, Aysenur and Gamble, Kyle A. and Gardner, Russell}, year={2021}, month={May}, pages={152795} }
 @book{hales_jiang_toptan_gamble_2020, title={BISON TRISO Modeling Advancements and Validation to AGR-1 Data}, url={https://doi.org/10.2172/1711423}, DOI={10.2172/1711423}, abstractNote={BISON is a finite element-based nuclear fuel performance code. Among its unique characteristics are its ability to model 1D, 2D, and 3D geometries and its applicability to a wide variety of nuclear fuels. For the last eight years, BISON has included a beginning capability to model tri-structural isotropic (TRISO) fuel. Recently, interest in TRISO fuel has grown, and a significant effort has been made to improve BISON’s capabilities in this area. Capability development has occurred for each material present in TRISO fuel particles: the buffer, inner pyrolytic carbon, silicon carbide, and outer pyrolytic carbon layers, as well as the fuel kernel. New elastic, creep, swelling, thermal expansion, thermal conductivity, and fission gas release (FGR) models are available. New models for the graphite matrix are also now available. Another important addition is the ability to perform statistical failure analysis of large samples of fuel particles. This new capability, which continues to grow, enables evaluation of failure due to pressure or crack formation by analyzing many thousands of particles. This enables realistic calculations of fission product release from the many particles in a TRISO-fueled reactor. These capabilities were checked via regression and verification tests. A large number of code benchmarking problems were also run, showing that BISON’s results closely match those of other software tools. Finally, a significant validation effort was completed in which fission product release, measured as part of the AGR-1 capsule experiments, was compared to BISON outputs. BISON outputs compared very well to the experimental data and to PARFUME results. Interest in BISON’s TRISO capabilities is growing, with the U.S. Nuclear Regulatory Commission (NRC) and Westinghouse Electric Company receiving training during the past year. Multiple other entities have expressed interest in or are actively using BISON. Kairos Power, LLC, has a strong partnership with Idaho National Laboratory (INL) regarding the use of BISON for TRISO analysis. While its capabilities still continue to grow, BISON has already become a powerful tool for TRISO analysis.}, author={Hales, Jason and Jiang, Wen and Toptan, Aysenur and Gamble, Kyle}, year={2020}, month={Sep} }
 @book{aagesen_biswas_jiang_gamble_2020, title={Mesoscale simulations of High Burnup Fuel Fragmentation: Applying phase-field modeling to understand high burnup fuel fragmentation during loss of coolant accident conditions}, url={https://doi.org/10.2172/2439394}, DOI={10.2172/2439394}, author={Aagesen, Larry, Jr. and Biswas, Sudipta and Jiang, Wen and Gamble, Kyle}, year={2020}, month={Dec} }
 @book{lillo_jiang_2020, title={Quarterly Management Document – FY20, 1st Quarter, Physics-based Creep Simulations of Thick Section Welds in High Temperature and Pressure Applications}, url={https://doi.org/10.2172/1598336}, DOI={10.2172/1598336}, abstractNote={During the first quarter of FY20, efforts focused on calibrating a computational model using experimental data. The experimental creep data obtain from specimens containing weld metal exhibit considerable inherent variability making calibration of the computational difficult and may not result in an accurate model.}, institution={Office of Scientific and Technical Information  (OSTI)}, author={Lillo, Thomas M and Jiang, Wen}, year={2020}, month={Feb} }
 @book{lillo_jiang_2020, title={Quarterly Management Document – FY20, 2nd Quarter, Physics-based Creep Simulations of Thick Section Welds in High Temperature and Pressure Applications}, url={https://doi.org/10.2172/1616583}, DOI={10.2172/1616583}, abstractNote={During the 2nd quarter of FY20, calibration of the creep model was made using experimental creep data on base metal at temperatures between 700-800 C. The model simulated primary and secondary creep behavior at these temperatures but tended to over estimate creep strain in the tertiary regime at 700 C while underestimating it at higher temperatures. Additional issues were also discovered and will be looked at in greater detail in the 3rd quarter of FY20.}, author={Lillo, Thomas M and Jiang, Wen}, year={2020}, month={Apr} }
 @book{casagranda_aagesen_ke_jiang_hales_toptan_gamble_liu_novascone_matthews_et al._2020, title={Summary of BISON Milestones: NEAMS FY2020 Report}, url={https://doi.org/10.2172/1768565}, DOI={10.2172/1768565}, abstractNote={This summary report contains an overview of work performed under the work package entitled "FY2020 NEAMS Advanced Fuels Performance'', which is focused on the development and support of the fuel performance code BISON. The second chapter lists FY20 milestones titles, completion schedule, and milestone level. Subsequent chapters summarize and demonstrate completion of the milestones. The last chapter outlines FY21 proposed future work. In FY20, the NEAMS program emphasized development of BISON for its application to advanced reactors. While there are a variety of advanced fuel concepts, based on interaction with industry and the Nuclear Regulatory Commission, the fuel types we chose to develop were metallic fast reactor, UN/UC and particle fuels. The last chapter of this report documents proposed work for FY21. We plan to continue work on metallic and particle fuel in terms of developing/calibrating models and to begin rigorous validation/assessment for both fuel types. Due to the merger of the NEAMS and CASL programs, FY21 will see a return to light water reactor model development and simulation; this time focused on advanced technology fuels. Additionally, we seek to improve BISON, fundamentally. As such, we plan improvements to BISON and MOOSE in terms of algorithmic robustness, performance, ease-of-use, and quality assurance.}, author={Casagranda, Albert and Aagesen, Larry, Jr and Ke, Jia-Hong and Jiang, Wen and Hales, Jason and Toptan, Aysenur and Gamble, Kyle and Liu, X. and Novascone, Stephen and Matthews, C. and et al.}, year={2020}, month={Sep} }
 @article{kim_jiang_lee_song_yeun_park_2020, title={A Nitsche-type variational formulation for the shape deformation of a single component vesicle}, volume={359}, url={http://dx.doi.org/10.1016/j.cma.2019.112661}, DOI={10.1016/j.cma.2019.112661}, abstractNote={This paper concerns the development of a finite-element formulation using Nitsche’ method for the phase-field model to capture an equilibrium shape of a single component vesicle. The phase-field model derived from the minimization of the curvature energy results in a nonlinear fourth-order partial differential equation. A standard conforming Galerkin formulation thus requires C1-elements. We derive a nonconforming finite-element formulation that can be applied to C0-elements and prove its consistency. Continuity of the first derivatives across interelement boundaries is weakly imposed and stabilization of the method is achieved via Nitsche’s method. The capability of the proposed finite-element formulation is demonstrated through numerical study of the equilibrium shapes of axisymmetric single component vesicles along with budding and fission phenomena.}, journal={Computer Methods in Applied Mechanics and Engineering}, publisher={Elsevier BV}, author={Kim, Tae-Yeon and Jiang, Wen and Lee, Sungmun and Song, Jeong-Hoon and Yeun, Chan Yeob and Park, Eun-Jae}, year={2020}, month={Feb}, pages={112661} }
 @article{zhang_jiang_tonks_2020, title={A new phase field fracture model for brittle materials that accounts for elastic anisotropy}, volume={358}, url={https://doi.org/10.1016/j.cma.2019.112643}, DOI={10.1016/j.cma.2019.112643}, abstractNote={In this manuscript, a new phase field model of brittle fracture is proposed that accounts for any elastic anisotropy using spectral decomposition of the stress. To verify the model, both Mode I and Mode II fracture simulations were performed to ensure that the correct crack paths were predicted. Next, the fracture of face-centered cubic (FCC) and hexagonal close packed (HCP) single crystals was modeled, comparing the impact of crystal orientation on the stress–strain curve. Third, fracture in an HCP bicrystal was simulated and the impact of crystal orientation on the crack paths and stress–strain curves was studied. Finally, a polycrystal structure was simulated to study the impact of crystallographic texture on transgranular fracture.}, journal={Computer Methods in Applied Mechanics and Engineering}, publisher={Elsevier BV}, author={Zhang, Shuaifang and Jiang, Wen and Tonks, Michael R.}, year={2020}, month={Jan}, pages={112643} }
 @article{jiang_spencer_dolbow_2020, title={Ceramic nuclear fuel fracture modeling with the extended finite element method}, volume={223}, url={http://dx.doi.org/10.1016/j.engfracmech.2019.106713}, DOI={10.1016/j.engfracmech.2019.106713}, abstractNote={Ceramic fuel pellets used in nuclear light water reactors experience significant fracture due to the high thermal gradients experienced under normal operating conditions. This has important effects on the performance of the fuel system. Because of this, a realistic, physically based fracture modeling capability is essential to predict fuel behavior in a wide variety of normal and off-normal conditions. The extended finite element method (X-FEM) is a powerful method to represent arbitrary propagating discrete cracks in finite element models, and has many characteristics that make it attractive for nuclear fuel performance analysis. This paper describes the implementation of X-FEM in a multiphysics fuel performance code and presents applications of that capability. These applications include several thermal mechanics fracture benchmark problems, which demonstrate the accuracy of this approach. It also includes application of this capability to study nuclear fuel fracture, both on stationary and propagating cracks. The study on stationary cracks shows the effects of interactions between cracks, and aids in understanding the process of crack propagation during a power ramp. The propagating crack case demonstrates random initiation and subsequent propagation of interacting thermally induced cracks during an initial ramp to full power with fresh fuel.}, journal={Engineering Fracture Mechanics}, publisher={Elsevier BV}, author={Jiang, Wen and Spencer, Benjamin W. and Dolbow, John E.}, year={2020}, month={Jan}, pages={106713} }
 @article{chakraborty_jiang_2019, title={Crystal plasticity-based creep model for solution-strengthened nickel-based alloys}, url={http://dx.doi.org/10.1504/ijmsi.2019.100389}, DOI={10.1504/ijmsi.2019.100389}, abstractNote={Nickel-based alloys are widely used in high temperature applications due to their favourable properties at extreme conditions.However, due to their high cost, efforts are being relentlessly made to extend the useful life of the components made from these alloys.Such life extension requires reliable constitutive models with detailed quantitative understanding of the factors contributing to property variations.Micromechanical analysis along with multi-scale methods can be a key enabler in developing the required high fidelity models.Particularly for properties such as creep that require long term prediction, accelerated tests with empirical models may prove insufficient.Thus, in the present work, a crystal plasticity-based creep model has been developed for solution strengthened nickel-based alloys.Through this model, the effect of microstructural variations in grain orientation, size, etc. on the secondary creep strain rate can be captured.The performance of the model is evaluated against creep data of alloy 617.}, journal={International Journal of Materials and Structural Integrity}, author={Chakraborty, Pritam and Jiang, Wen}, year={2019} }
 @book{lillo_jiang_2019, title={Quarterly Management Document – FY19, 3rd Quarter, Physics-based Creep Simulations of Thick Section Welds in High Temperature and Pressure Applications}, url={https://doi.org/10.2172/1547327}, DOI={10.2172/1547327}, abstractNote={During the 3rd quarter of FY19, a strategy was developed to incorporate creep damage arising from diffusional processes into a computational model describing creep behavior of thick section welds in Alloy 740H. This approach will be followed in the 4th quarter modify the existing creep model to include diffusional damage processes in its predictions of creep behavior and especially the transition to tertiary creep behavior which will allow the prediction of creep rupture time.}, author={Lillo, Thomas M and Jiang, Wen}, year={2019}, month={Aug} }
 @book{lillo_jiang_2019, title={Quarterly Management Document – FY19, 4th Quarter, Physics-based Creep Simulations of Thick Section Welds in High Temperature and Pressure Applications}, url={https://doi.org/10.2172/1596099}, DOI={10.2172/1596099}, abstractNote={During the 4th quarter of FY19, diffusional creep effects, based on the local stress tensor, was incorporated into the modeling and simulation efforts on thick section welds of Alloy 740H. The model is now complete and addresses both dislocation-based creep as well as diffusional creep mechanisms. Preliminary result indicate the model is now capable of predicting a transition from secondary creep to tertiary creep. Calibration of the model using experimental creep data remains to be performed and will be done in the first quarter of FY20.}, author={Lillo, Thomas M and Jiang, Wen}, year={2019}, month={Nov} }
 @book{novascone_casagranda_aagesen_beeler_jiang_jokisaari_mcdowell_lindsay_tompkins_pastore_et al._2019, title={Summary of Bison milestones and activities - NEAMS FY2019 Report}, url={https://doi.org/10.2172/1768049}, DOI={10.2172/1768049}, abstractNote={This summary report contains an overview of work performed under the work package entitled “FY2019 NEAMS Engineering Scale Fuel Performance”, which is focused on the development and support of the fuel performance code Bison [1]. The second chapter lists FY19 milestones titles, completion schedule, and milestone level. Subsequent chapters summarize and demonstrate completion of milestones and activities. The last chapter outlines FY20 proposed future work.}, author={Novascone, Stephen and Casagranda, Albert and Aagesen, Larry, Jr. and Beeler, B. and Jiang, Wen and Jokisaari, Andrea and McDowell, Dylan and Lindsay, Alexander and Tompkins, James and Pastore, Giovanni and et al.}, year={2019}, month={Sep} }
 @book{spencer_pitts_liu_vyas_jiang_casagranda_mcdowell_2019, title={Summary of Grizzly Development for Advanced Reactor Structural Materials}, url={https://doi.org/10.2172/1572400}, DOI={10.2172/1572400}, abstractNote={This summary report contains an overview of work performed during Fiscal Year 2019 under the Nuclear Engineering Advanced Modeling and Simulation (NEAMS) Fuels Product Line work package entitled "MS-19IN020106 - GRIZZLY - INL". Grizzly is a code based on the MOOSE framework that has been under development for several years funded by the US Department of Energy’s Light Water Reactor Sustainability (LWRS) program. Prior to 2019, Grizzly development was focused on development of capabilities needed to simulate the effects of aging mechanisms in light water reactor (LWR) components. The goal of this LWR-focused work has been to develop tools that can be used to assess the ability of existing LWRs to perform safety in long term operation (LTO) scenarios. This LWR-focused work has primarily focused on the effects of reactor pressure vessel (RPV) embrittlement and aging of reinforced concrete structures. Grizzly development to support LWR degradation needs is still ongoing, but starting in 2019, Grizzly’s capabilities are being expanded to also meet growing needs for a tool to address structural component integrity and degradation in advanced reactors. A simulation capability for advanced reactor components has many of the same basic requirements that one for LWRs does, such as the ability to solve coupled systems of partial differential equations that arise from the fact that many of the problems of interest involve multiple coupled physics. The materials issues also inherently involve multiple length scales, with the response at the engineering scale being strongly affected by mechanisms occurring at atomistic and mesoscopic scales.}, institution={Office of Scientific and Technical Information (OSTI)}, author={Spencer, Benjamin and Pitts, Stephanie and Liu, Ling and Vyas, Manu and Jiang, Wen and Casagranda, Albert and McDowell, Dylan}, year={2019}, month={Sep} }
 @article{three-dimensional phase-field modeling of porosity dependent intergranular fracture in uo2_2020, url={http://dx.doi.org/10.1016/j.commatsci.2019.109269}, DOI={10.1016/j.commatsci.2019.109269}, abstractNote={During reactor operation, the formation of bubbles at the grain boundaries can alter the fracture properties and subsequently the thermo-mechanical behavior of nuclear fuels. In this work, we discuss a phase-field fracture model, its implementation in MOOSE (Multiphysics Object-Oriented Simulation Environment), and its application to simulate porosity dependent brittle intergranular fracture. The presence of gas bubbles on grain boundaries has a non-negligible impact on crack initiation and propagation. Three-dimensional simulations are performed to investigate the influence of bubble geometry, porosity and loading conditions on the fracture strength. The correlation between fracture strength and porosity suggested by numerical simulations has a good agreement with experimental measurements.}, journal={Computational Materials Science}, year={2020}, month={Jan} }
 @book{gardner_folsom_jiang_hales_spencer_2018, title={Evaluation of Solver and Time Stepping Options and RIA Demonstration}, url={https://doi.org/10.2172/1484478}, DOI={10.2172/1484478}, abstractNote={This report summarizes Bison development and application in three areas: • Development of the layered 1D approach to permit its use with the reference residual convergence criterion that is widely used for 2D and 3D Bison simulations. For higher-dimensional simulations, this approach has resulted in significant improvements in robustness and solution efficiency, and it is expected to result in similar benefits for 1D simulations of light water reactor (LWR) rods. • A study on the effects of the chosen convergence tolerances on solution difficulty and accuracy was performed for a prototypical layered 1D simulation of an LWR fuel rod. The effect of convergence tolerance on iteration counts, run times, and several quantities of interest in the solution are compared for the various convergence tolerance. This study will be helpful for guiding the choice of convergence tolerances. • A demonstration of a reactivity insertion accident (RIA) simulation with Bison within the coupled VERA code was performed. The MPACT neutron transport code and the CTF thermal-hydraulic code provided inputs to Bison for a postulated control rod ejection scenario. This demonstrates the ability of the VERA environment to consider coupling effects not only for normal operation, but for accident conditions.}, institution={Office of Scientific and Technical Information  (OSTI)}, author={Gardner, Russell J. and Folsom, Charles P. and Jiang, Wen and Hales, Jason D. and Spencer, Benjamin W.}, year={2018}, month={Oct} }
 @book{author_2018, title={Improved Fracture Models for Relocation Modeling}, url={https://doi.org/10.2172/1467403}, DOI={10.2172/1467403}, abstractNote={The BISON fuel performance code is being developed to provide a modern tool that has the flexibility to analyze a wide variety of fuel forms and to model conditions and phenomena that could not be represented in legacy tools. There are a number of motivations for this, including providing support for development of advanced fuel with improved accident tolerance for existing light water (LWR) reactors, improved understanding of mechanisms in fuel designs in current use in a wider variety of conditions, and facilitating the development of fuel for advanced reactor designs. To accomplish these goals, it is clear that BISON must rely on models of fuel behavior that are based on fundamental physical behavior, rather than on empirical correlations that represent that behavior in a simplified fashion. BISON still does employ many empirical models that were originally developed for other fuel performance codes, but efforts are underway to replace these with models that are more physically based. Radial relocation in LWR fuel is an example of a phenomenon that is currently represented by an empirical model, but which is ripe for replacement by physically based models. During normal operation, ceramic LWR fuel experiences significant fracturing that is driven by spatially nonuniform volumetric expansion. This occurs due to the significant thermal gradients within the fuel that occur in fresh and irradiated fuel, as well as nonuniform swelling due to fission products that occurs over longer-term irradiation. Fracture and fragmentation of fuel allows the outer radius of the fuel pellet to expand due to the loss of mechanical constraint and outward radial migration of fragments. This radial expansion has a significant effect on the fuel system response because it decreases the size of the gap between the fuel and cladding. This decreases the thermal resistance across that gap, which leads to decreased fuel centerline temperatures. This report documents recent work to improve the ability of BISON to model radial relocation using the extended finite element method (XFEM). These enhancements include the ability to include cohesive zone models, improved code architecture for propagating cracks based on fracture integrals, and improved handling of fuel and cladding interfaces with XFEM. These capabilities are demonstrated on a simulation of radial relocation including a surface interaction model that enforces residual opening.}, institution={Office of Scientific and Technical Information  (OSTI)}, author={Author, Not Given}, year={2018}, month={Jan} }
 @article{al balushi_jiang_tsogtgerel_kim_2018, title={Adaptivity of a B-spline based finite-element method for modeling wind-driven ocean circulation}, volume={332}, url={https://www.sciencedirect.com/science/article/pii/S0045782517307600}, DOI={https://doi.org/10.1016/j.cma.2017.12.008}, abstractNote={This paper presents an adaptive refinement algorithm of a B-spline based finite-element approximation of the streamfunction formulation for the large scale wind-driven ocean currents. In particular, we focus on a posteriori error analysis of the simplified linear model of the stationary quasi-geostrophic equations, namely the Stommel–Munk model, which is the fourth-order partial differential equation. The analysis provides a posteriori error estimator for the local refinement of the Nitsche-type finite-element formulation. Numerical experiments with several benchmark examples are performed to test the capability of the posteriori error indicator on rectangular and L-shape geometries.}, journal={Computer Methods in Applied Mechanics and Engineering}, author={Al Balushi, Ibrahim and Jiang, Wen and Tsogtgerel, Gantumur and Kim, Tae-Yeon}, year={2018}, pages={1–24} }
 @book{spencer_peterson_jiang_liu_veeraraghavan_casagranda_2017, title={BISON Contact Algorithm Improvements in Support of Pellet Cladding Mechanical Interaction Modeling}, url={https://doi.org/10.2172/1473589}, DOI={10.2172/1473589}, abstractNote={The thermal and mechanical behavior of the gap between the fuel and cladding plays an extremely important role in determining the response of light water reactor (LWR) fuel under irradiation. This is especially true during situations when pellet-cladding mechanical interactions (PCMI) have a significant effect on the behavior of the fuel/cladding system. The BISON code, which is being used as the fuel performance simulation tool for the CASL program, employs contact detection and enforcement algorithms to realistically simulate the thermal and mechanical interactions across the fuel/cladding interaction in LWR fuel. These contact algorithms permit accurate representation of these interactions even when there is significant relative movement between the two surfaces, which is typically the case in many regions of an LWR fuel rod. This report summarizes work done during the 2017 fiscal year to further improve the accuracy and robustness of the contact enforcement algorithms in BISON. This work will benefit all BISON simulations, but will particularly benefit simulations scenarios where PCMI is of interest.}, institution={Office of Scientific and Technical Information  (OSTI)}, author={Spencer, B. W. and Peterson, J. W. and Jiang, W. and Liu, Y. and Veeraraghavan, S. and Casagranda, A.}, year={2017}, month={Sep} }
 @book{spencer_casagranda_pitts_jiang_2017, title={Development of 3D Oxide Fuel Mechanics Models}, DOI={10.2172/1376906}, abstractNote={This report documents recent work to improve the accuracy and robustness of the mechanical constitutive models used in the BISON fuel performance code. These developments include migration of the fuel mechanics models to be based on the MOOSE Tensor Mechanics module, improving the robustness of the smeared cracking model, implementing a capability to limit the time step size based on material model response, and improving the robustness of the return mapping iterations used in creep and plasticity models.}, institution={Office of Scientific and Technical Information  (OSTI)}, author={Spencer, B. W. and Casagranda, A. and Pitts, S. A. and Jiang, W.}, year={2017}, month={Jul} }
 @book{spencer_hoffman_jiang_2017, title={Enhancements to Engineering-scale Reactor Pressure Vessel Fracture Capabilities in Grizzly}, url={https://doi.org/10.2172/1473611}, DOI={10.2172/1473611}, abstractNote={The Grizzly code is being developed to model the effect of aging in nuclear power plant systems, components, and structures. A significant part of this effort has been to develop capabilities to model the effects of embrittlement in reactor pressure vessels on their integrity. This includes both modeling of microstructure and engineering property evolution, and engineering-scale probabilistic fracture mechanics analysis. This report documents recent advances to the engineering-scale fracture mechanics capability for evaluation of RPV integrity under transient loading in Grizzly. These developments are in three areas: probabilistic fracture mechanics, general reduced order models for fracture a flaw locations, and improvements to the XFEM capability used in Grizzly for fracture mechanics analysis. The combination of these developments brings Grizzly closer to a state where it can be applied in production as a general tool for engineering-scale fracture mechanics analysis. The probabilistic fracture mechanics capabilities are included in the 1.5 testing version of Grizzly, and will be further refined in preparation for production use in the 2.0 released planned for fiscal year 2018.}, institution={Office of Scientific and Technical Information  (OSTI)}, author={Spencer, Benjamin W and Hoffman, William M and Jiang, Wen}, year={2017}, month={Sep} }
 @book{jiang_jiang_jaques_charit_fertig_2017, title={FY17 CAES LDRD Annual Report}, url={https://doi.org/10.2172/1472089}, DOI={10.2172/1472089}, abstractNote={Metallic alloys are widely used or planned for use as structural and cladding materials in current and future reactors. Under irradiation, grain boundary (GB) cohesion strength decreases due to interaction with defects and impurities, leading to intergranular fracture and embrittlement of alloys. The objective of this project is to develop a technique for quantifying GB cohesion and its impact on fracture behavior in irradiated alloys, by utilizing transmission electron microscopic (TEM) in situ cantilever testing in concert with multi-scale modeling. The TEM in situ cantilever testing is a novel approach for studying the real-time mechanical response of materials. It will be used in this work for studying intergranular fracture behavior in several irradiated iron-based ferritic alloys and providing key information to link atomistic level events with mesoscale/macroscopic mechanical properties. The Multi-Physics Object-Oriented Simulation Environment (MOOSE)-based cohesive zone model (CZM) and extended finite element method (XFEM) for intergranular fracture of irradiated ferritic alloys will be developed in this work by utilizing atomistic results as inputs and experimental results for validation.}, institution={Office of Scientific and Technical Information  (OSTI)}, author={Jiang, Chao and Jiang, Wen and Jaques, Brian and Charit, Indrajit and Fertig, Ray}, year={2017}, month={Sep} }
 @book{jiang_spencer_2017, title={Modeling 3D PCMI using the Extended Finite Element Method with higher order elements}, DOI={10.2172/1409274}, abstractNote={the goal of improving the fidelity of contact results both adjacent to cut elements as well as away from cut elements, the most impactful development would be to enable the use of higher-order elements with XFEM. This report documents the recent development to enable XFEM to work with higher order elements. It also demon-strates the application of higher order (quadratic) elements to both 2D and 3D models of PCMI problems, where discrete fractures in the fuel are represented using XFEM. The modeling results demonstrate the ability of the higher order XFEM to accurately capture the effects of a crack on the response in the vicinity of the intersecting surfaces of cracked fuel and cladding, as well as represent smooth responses in the regions away from the crack.}, institution={Office of Scientific and Technical Information  (OSTI)}, author={Jiang, W. and Spencer, Benjamin W.}, year={2017}, month={Mar} }
 @article{rotundo_kim_jiang_heltai_fried_2016, title={Error Analysis of a B-Spline Based Finite-Element Method for Modeling Wind-Driven Ocean Circulation}, volume={69}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84963997998&partnerID=MN8TOARS}, DOI={10.1007/s10915-016-0201-1}, number={1}, journal={Journal of Scientific Computing}, author={Rotundo, N. and Kim, T.-Y. and Jiang, W. and Heltai, L. and Fried, E.}, year={2016}, pages={430–459} }
 @book{spencer_backman_chakraborty_schwen_zhang_huang_bai_jiang_2016, title={Grizzly Usage and Theory Manual}, DOI={10.2172/1261013}, abstractNote={Grizzly is a multiphysics simulation code for characterizing the behavior of nuclear power plant (NPP) structures, systems and components (SSCs) subjected to a variety of age-related aging mechanisms. Grizzly simulates both the progression of aging processes, as well as the capacity of aged components to safely perform. This initial beta release of Grizzly includes capabilities for engineering-scale thermo-mechanical analysis of reactor pressure vessels (RPVs). Grizzly will ultimately include capabilities for a wide range of components and materials. Grizzly is in a state of constant development, and future releases will broaden the capabilities of this code for RPV analysis, as well as expand it to address degradation in other critical NPP components.}, institution={Office of Scientific and Technical Information  (OSTI)}, author={Spencer, B. W. and Backman, M. and Chakraborty, P. and Schwen, D. and Zhang, Y. and Huang, H. and Bai, X. and Jiang, W.}, year={2016}, month={Mar} }
 @book{zhang_schwen_chakraborty_jiang_aagesen_ahmed_jiang_biner_bai_tonks_et al._2016, title={MARMOT update for oxide fuel modeling}, DOI={10.2172/1364504}, abstractNote={This report summarizes the lower-length-scale research and development progresses in FY16 at Idaho National Laboratory in developing mechanistic materials models for oxide fuels, in parallel to the development of the MARMOT code which will be summarized in a separate report. This effort is a critical component of the microstructure based fuel performance modeling approach, supported by the Fuels Product Line in the Nuclear Energy Advanced Modeling and Simulation (NEAMS) program. The progresses can be classified into three categories: 1) development of materials models to be used in engineering scale fuel performance modeling regarding the effect of lattice defects on thermal conductivity, 2) development of modeling capabilities for mesoscale fuel behaviors including stage-3 gas release, grain growth, high burn-up structure, fracture and creep, and 3) improved understanding in material science by calculating the anisotropic grain boundary energies in UO$_2$ and obtaining thermodynamic data for solid fission products. Many of these topics are still under active development. They are updated in the report with proper amount of details. For some topics, separate reports are generated in parallel and so stated in the text. The accomplishments have led to better understanding of fuel behaviors and enhance capability of the MOOSE-BISON-MARMOT toolkit.}, institution={Office of Scientific and Technical Information  (OSTI)}, author={Zhang, Yongfeng and Schwen, Daniel and Chakraborty, Pritam and Jiang, Chao and Aagesen, Larry and Ahmed, Karim and Jiang, Wen and Biner, Bulent and Bai, Xianming and Tonks, Michael and et al.}, year={2016}, month={Sep} }
 @book{lillo_jiang_2016, title={Quarterly Management Document – FY16, 4th Quarter, Physics-based Creep Simulations of Thick Section Welds in High Temperature and Pressure Applications}, url={https://doi.org/10.2172/1504929}, DOI={10.2172/1504929}, abstractNote={During the 4th quarter of FY16 welds in Alloy 740H were made and charactrerized. Also, cross weld creep specimens were made and creep tests were initiated in support of the creep modeling and simulation effort. Also, aging of weld material for future characterization was initiated. The creep model was evolved to describe the vacancy concentration that enables the climb of dislocations during power law creep.}, institution={Office of Scientific and Technical Information  (OSTI)}, author={Lillo, Thomas M. and Jiang, Wen}, year={2016}, month={Oct} }
 @article{jiang_annavarapu_dolbow_harari_2015, title={A robust Nitsche's formulation for interface problems with spline-based finite elements}, volume={104}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84943663720&partnerID=MN8TOARS}, DOI={10.1002/nme.4766}, abstractNote={SummaryThe extended finite element method (X‐FEM) has proven to be an accurate, robust method for solving embedded interface problems. With a few exceptions, the X‐FEM has mostly been used in conjunction with piecewise‐linear shape functions and an associated piecewise‐linear geometrical representation of interfaces. In the current work, the use of spline‐based finite elements is examined along with a Nitsche technique for enforcing constraints on an embedded interface. To obtain optimal rates of convergence, we employ a hierarchical local refinement approach to improve the geometrical representation of curved interfaces. We further propose a novel weighting for the interfacial consistency terms arising in the Nitsche variational form with B‐splines. A qualitative dependence between the weights and the stabilization parameters is established with additional element level eigenvalue calculations. An important consequence of this weighting is that the bulk as well as the interfacial fields remain well behaved in the presence of large heterogeneities as well as elements with arbitrarily small volume fractions. We demonstrate the accuracy and robustness of the proposed method through several numerical examples. Copyright © 2015 John Wiley & Sons, Ltd.}, number={7}, journal={International Journal for Numerical Methods in Engineering}, author={Jiang, W. and Annavarapu, C. and Dolbow, J.E. and Harari, I.}, year={2015}, pages={676–696} }
 @book{dolbow_zhang_spencer_jiang_2015, title={Fracture Capabilities in Grizzly with the extended Finite Element Method (X-FEM)}, DOI={10.2172/1244633}, abstractNote={Efforts are underway to develop fracture mechanics capabilities in the Grizzly code to enable it to be used to perform deterministic fracture assessments of degraded reactor pressure vessels (RPVs). A capability was previously developed to calculate three-dimensional interaction- integrals to extract mixed-mode stress-intensity factors. This capability requires the use of a finite element mesh that conforms to the crack geometry. The eXtended Finite Element Method (X-FEM) provides a means to represent a crack geometry without explicitly fitting the finite element mesh to it. This is effected by enhancing the element kinematics to represent jump discontinuities at arbitrary locations inside of the element, as well as the incorporation of asymptotic near-tip fields to better capture crack singularities. In this work, use of only the discontinuous enrichment functions was examined to see how accurate stress intensity factors could still be calculated. This report documents the following work to enhance Grizzly’s engineering fracture capabilities by introducing arbitrary jump discontinuities for prescribed crack geometries; X-FEM Mesh Cutting in 3D: to enhance the kinematics of elements that are intersected by arbitrary crack geometries, a mesh cutting algorithm was implemented in Grizzly. The algorithm introduces new virtual nodes and creates partial elements, and then creates a new mesh connectivity; Interaction Integral Modifications: the existing code for evaluating the interaction integral in Grizzly was based on the assumption of a mesh that was fitted to the crack geometry. Modifications were made to allow for the possibility of a crack front that passes arbitrarily through the mesh; and Benchmarking for 3D Fracture: the new capabilities were benchmarked against mixed-mode three-dimensional fracture problems with known analytical solutions.}, institution={Office of Scientific and Technical Information  (OSTI)}, author={Dolbow, John and Zhang, Ziyu and Spencer, Benjamin and Jiang, Wen}, year={2015}, month={Sep} }
 @article{jiang_kim_2016, title={Spline-based finite-element method for the stationary quasi-geostrophic equations on arbitrary shaped coastal boundaries}, volume={299}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84947924685&partnerID=MN8TOARS}, DOI={10.1016/j.cma.2015.11.003}, abstractNote={This work concerns a B-spline based finite-element algorithm for the stationary quasi-geostrophic equations to treat the large scale wind-driven ocean circulation on arbitrary shaped domains. The algorithm models arbitrary shaped coastal boundaries on intra-element, or embedded boundaries. Dirichlet boundary conditions on the embedded boundaries are weakly imposed and stabilization is achieved via Nitsche's method. We employ a hierarchical local refinement approach to improve the geometrical representation of curved boundaries. Results from several benchmark problems on rectangular and curved domains are provided to demonstrate the accuracy and robustness of the method. We also provide the Mediterranean sea example that illustrates the effectiveness of the approach in the wind-driven ocean circulation simulation.}, journal={Computer Methods in Applied Mechanics and Engineering}, author={Jiang, W. and Kim, T.-Y.}, year={2016}, pages={144–160} }
 @article{jiang_dolbow_2014, title={Adaptive refinement of hierarchical B-spline finite elements with an efficient data transfer algorithm}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84940220143&partnerID=MN8TOARS}, DOI={10.1002/nme.4718}, abstractNote={SummaryWe present an adaptive B‐spline FEM that employs hierarchical refinement and coarsening techniques. Hierarchical B‐spline refinement augments the approximation space through the use of finer, more compactly supported B‐splines. With this approach compatibility is automatic because problematic T‐vertices do not arise. The process of refinement does not change the regularity of the basis functions, and can be easily generalized to arbitrary dimensions. Data transfer during both refinement and coarsening is addressed. The techniques are then applied to several time‐dependent problems for which adaptivity is advantageous, and the performance of the method is evaluated. Copyright © 2014 John Wiley & Sons, Ltd.}, journal={International Journal for Numerical Methods in Engineering}, author={Jiang, W. and Dolbow, J.E.}, year={2014} }
 @article{jiang_yang_2009, title={Energy-absorption behavior of a metallic double-sine-wave beam under axial crushing }, volume={47}, url={http://www.sciencedirect.com/science/article/pii/S0263823109001086}, DOI={http://dx.doi.org/10.1016/j.tws.2009.04.006}, abstractNote={Energy-absorbing behavior of a metallic double-sine-wave beam under axial crushing is studied in this paper. The aims of the study are to improve the energy-absorbing capability of traditional corrugated beams with sine-wave at single direction and reduce the initial peak force by forcing the beam plasticly deformed at the predetermined intervals along the axial direction. The theoretical approach based on a rigid, perfectly plastic model is adopted to predict the mean crushing force under axial crush loading. Besides, the numerical analysis of energy-absorption behavior of aluminium double-sine-wave beams is conducted by using nonlinear finite element code MSC.DYTRAN. The numerical results are compared well with theoretical predictions and show that although the crushing mean force slightly decreases, the double-sine-wave beam produces better uniform load displacement relationship and lower initial peak force.}, number={11}, journal={Thin-Walled Structures}, author={Jiang, W. and Yang, J.L.}, year={2009}, pages={1168–1176} }