@article{dong_doster_mayo_2008, title={Steam generator control in nuclear power plants by water mass inventory}, volume={238}, ISSN={["0029-5493"]}, DOI={10.1016/j.nucengdes.2007.09.001}, abstractNote={Control of water mass inventory in Nuclear Steam Generators is important to insure sufficient cooling of the nuclear reactor. Since downcomer water level is measurable, and a reasonable indication of water mass inventory near steady-state, conventional feedwater control system designs attempt to maintain downcomer water level within a relatively narrow operational band. However, downcomer water level can temporarily react in a reverse manner to water mass inventory changes, commonly known as shrink and swell effects. These complications are accentuated during start-up or low power conditions. As a result, automatic or manual control of water level is difficult and can lead to high reactor trip rates. This paper introduces a new feedwater control strategy for Nuclear Steam Generators. The new method directly controls water mass inventory instead of downcomer water level, eliminating complications from shrink and swell all together. However, water mass inventory is not measurable, requiring an online estimator to provide a mass inventory signal based on measurable plant parameters. Since the thermal-hydraulic response of a Steam Generator is highly nonlinear, a linear state-observer is not feasible. In addition, difficulties in obtaining flow regime and density information within the Steam Generator make an estimator based on analytical methods impractical at this time. This work employs a water mass estimator based on feedforward neural networks. By properly choosing and training the neural network, mass signals can be obtained which are suitable for stable, closed-loop water mass inventory control. Theoretical analysis and simulation results show that water mass control can significantly improve the operation and safety of Nuclear Steam Generators.}, number={4}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Dong, Wei and Doster, J. Michael and Mayo, Charles W.}, year={2008}, month={Apr}, pages={859–871} }
 @article{guo_gardner_mayo_2005, title={A study of the real-time deconvolution of digitized waveforms with pulse pile up for digital radiation spectroscopy}, volume={544}, ISSN={["1872-9576"]}, DOI={10.1016/j.nima.2004.12.036}, abstractNote={Two new real-time approaches have been developed and compared to the least-squares fit approach for the deconvolution of experimental waveforms with pile-up pulses. The single pulse shape chosen is typical for scintillators such as LSO and NaI(Tl). Simulated waveforms with pulse pile up were also generated and deconvolved to compare these three different approaches under cases where the single pulse component has a constant shape and the digitization error dominates. The effects of temporal separation and amplitude ratio between pile-up component pulses were also investigated and statistical tests were applied to quantify the consistency of deconvolution results for each case. Monte Carlo simulation demonstrated that applications of these pile-up deconvolution techniques to radiation spectroscopy are effective in extending the counting-rate range while preserving energy resolution for scintillation detectors.}, number={3}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT}, author={Guo, WJ and Gardner, RP and Mayo, CW}, year={2005}, month={Jun}, pages={668–678} }
 @article{metwally_mayo_han_gardner_2005, title={Coincidence counting for PGNAA applications: Is it the optimum method?}, volume={265}, ISSN={["1588-2780"]}, DOI={10.1007/s10967-005-0826-2}, number={2}, journal={JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY}, author={Metwally, WA and Mayo, CW and Han, X and Gardner, RP}, year={2005}, month={Aug}, pages={309–314} }
 @article{metwally_gardner_mayo_2004, title={Two-dimensional diagonal summing of coincidence spectra for bulk PGNAA applications}, volume={525}, ISSN={["1872-9576"]}, DOI={10.1016/j.nima.2004.02.012}, abstractNote={Abstract In the past 10 years, new electronic devices have been developed that allow fast coincidence measurements to be performed that are capable of simultaneously recording the individual spectra as well as the coincidence spectra of multiple detectors. Utilizing these devices with computer software allows multiparameter data acquisition which adds much more flexibility in data analysis. One of the capabilities that is enabled is that of obtaining two-dimensional spectra. In this work, the use of this equipment and the two-dimensional spectra obtained with it are used to allow two-dimensional diagonal summing. The main advantages of this approach are improved peak resolution and very low background (Compton continuum). Possible uses of the two-dimensional diagonal summing are identifying coincidence schemes, performing elemental analysis, and identifying trace elements in bulk samples. The spectra obtained are very promising for these applications.}, number={3}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT}, author={Metwally, WA and Gardner, RP and Mayo, CW}, year={2004}, month={Jun}, pages={511–517} }
 @article{metwally_gardner_mayo_2004, title={Elemental PGNAA analysis using gamma-gamma coincidence counting with the library least-squares approach}, volume={213}, ISSN={["1872-9584"]}, DOI={10.1016/S0168-583X(03)01660-4}, abstractNote={Abstract An accurate method for determining elemental analysis using gamma–gamma coincidence counting is presented. To demonstrate the feasibility of this method for PGNAA, a system of three radioisotopes (Na-24, Co-60 and Cs-134) that emit coincident gamma rays was used. Two HPGe detectors were connected to a system that allowed both singles and coincidences to be collected simultaneously. A known mixture of the three radioisotopes was used and data was deliberately collected at relatively high counting rates to determine the effect of pulse pile-up distortion. The results obtained, with the library least-squares analysis, of both the normal and coincidence counting are presented and compared to the known amounts. The coincidence results are shown to give much better accuracy. It appears that in addition to the expected advantage of reduced background, the coincidence approach is considerably more resistant to pulse pile-up distortion.}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS}, author={Metwally, WA and Gardner, RP and Mayo, CW}, year={2004}, month={Jan}, pages={394–399} }
 @article{gardner_mayo_el-sayyed_metwally_zheng_poezart_2000, title={A feasibility study of a coincidence counting approach for PGNAA applications}, volume={53}, ISSN={["0969-8043"]}, DOI={10.1016/S0969-8043(00)00206-2}, abstractNote={Prompt gamma-ray nutron activation analysis (PGNAA) has an inherently low signal-to-noise (S/N) ratio primarily because of the large background (noise) associated with it. Most elements emit a significant fraction of their prompt gamma rays in coincidence with one or more other prompt gamma rays. This paper reports on initial efforts to use coincidence counting in PGNAA to significantly reduce the several sources of background and thereby increase the S/N ratio. An added benefit is the elimination of the often dominant hydrogen prompt gamma-ray spectrum which emits only a single prompt gamma ray with an energy of 2.223 MeV. Preliminary results are given for both in situ bulk analysis applications with a 252Cf neutron source and for nuclear reactor thermal neutron beam applications for small laboratory samples.}, number={4-5}, journal={APPLIED RADIATION AND ISOTOPES}, author={Gardner, RP and Mayo, CW and El-Sayyed, ES and Metwally, WA and Zheng, Y and Poezart, M}, year={2000}, pages={515–526} }
 @article{gardner_sayyed_zheng_hayden_mayo_2000, title={NaI detector neutron activation spectra for PGNAA applications}, volume={53}, ISSN={["0969-8043"]}, DOI={10.1016/S0969-8043(00)00198-6}, abstractNote={When NaI detectors are used in prompt gamma-ray neutron activation analysis devices, they are activated by neutrons that penetrate the detector. While thermal neutron filters like boron or lithium can be used to reduce this activation, it can never be completely eliminated by this approach since high energy neutrons can penetrate the detector and thermalize inside it. This activation results in the emission of prompt gamma rays from both the I and Na and the production of the radioisotopes 128I and 24Na that subsequently decay and emit their characteristic beta particles and gamma rays. The resulting three spectra represent a background for this measurement. An experimental method for obtaining these three spectra is described and results are reported for 2" x 2", 5" x 5", 6" x 6", and 1" x 6" NaI detectors using the thermal neutron beam of the NCSU PULSTAR nuclear reactor. In addition, Monte Carlo simulation programs have been developed and used for simulating these spectra. Good results have been obtained by the Monte Carlo method for the two radioisotope spectra, and it is anticipated that good results will also be obtained for the prompt gamma-ray spectrum when the I and Na coincidence schemes are known.}, number={4-5}, journal={APPLIED RADIATION AND ISOTOPES}, author={Gardner, RP and Sayyed, E and Zheng, YS and Hayden, S and Mayo, CW}, year={2000}, pages={483–497} }
 @article{shi_doster_mayo_2000, title={Numerical simulation of accumulated steam generator tube sheet damage and loose part impact distributions}, volume={129}, ISSN={["0029-5450"]}, DOI={10.13182/NT00-A3066}, abstractNote={An experimental research program into the loose part damage process identified important mechanisms that govern accumulated loose part damage to steam generator tube sheets. Relationships were developed to quantify damage due to single and multiple impacts, including such effects as tube end open diameter reduction and tube end contour deformation. These experimental investigations have led to the development of a computational model for estimating loose part impact damage on steam generator tube ends. Comparisons to experimental data show the loose part damage model to be a good approximation of actual loose part impact damage and provide a convenient and quantitative linkage between loose part impact properties and damage. Impact damage effects are local effects that depend only on the single impacts and impact overlaps in a small region of interest. The damage can be directly related to local impact density. Since in general the local impact density on a steam generator tube sheet is unknown, a model developed to simulate loose part impact distributions as a function of operating conditions is described.}, number={3}, journal={NUCLEAR TECHNOLOGY}, author={Shi, L and Doster, JM and Mayo, CW}, year={2000}, month={Mar}, pages={338–355} }
 @article{shi_doster_mayo_1999, title={Drag coefficients for reactor loose parts}, volume={127}, ISSN={["0029-5450"]}, DOI={10.13182/NT99-A2981}, abstractNote={To estimate the range of impact velocities of potential reactor loose parts (LPs) requires information on regional flow velocities, LP mass, and LP drag coefficients. Flow velocities and the mass of potential LPs can generally be bounded and therefore are assumed to be known. In this work, drag coefficients for prototype LP shapes, including objects such as bolts, nuts, pins, and hand tools, were measured in the fluid velocity range typical of reactor coolant systems. Unlike drag coefficients measured for stationary objects, or by moving a body through a stagnant fluid, these experiments are performed on objects moving freely in a turbulent flow stream. In general, the measured drag coefficients for all tested LP shapes are shown to be close to the standard drag coefficient for a sphere, especially in the low-Reynolds-number region. However, significant differences exist in the wake transition region, which indicates that the drag coefficient for a freely moving body in turbulent flow is different from the drag coefficient for a confined body under the same flow conditions or for a body moving in a stagnant fluid.}, number={1}, journal={NUCLEAR TECHNOLOGY}, author={Shi, L and Doster, JM and Mayo, CW}, year={1999}, month={Jul}, pages={24–37} }
 @article{shi_mayo_doster_1999, title={Loose-part damage}, volume={34}, ISSN={["0149-1970"]}, DOI={10.1016/S0149-1970(98)00009-2}, abstractNote={Experiments and analytical methods were used to develop models that describe loose part impact damage. Single impact damage volume was characterized as a function of impact energy and contact shape. The deformation volume for multiple, overlapping impacts was used to define work hardening. Integrated impact damage experiments were conducted at representative pressurized water reactor steam generator inlet flow velocity using a target plate that represented a section of a steam generator tube sheet. Data from the integrated impact tests were used to develop an empirical relationship for tube end open diameter reduction as a function of loose part energy and accumulated impact density. Monte-Carlo programs were developed to investigate the tube sheet impact density distribution and the penetration of tube end welds. The results provide insight with respect to single and multiple impact damage mechanisms and methods that can be used to predict steam generator tube sheet accumulated impact damage.}, number={3}, journal={PROGRESS IN NUCLEAR ENERGY}, author={Shi, L and Mayo, CW and Doster, JM}, year={1999}, pages={231–261} }
 @article{mayo_1999, title={Loose-part mass and energy estimation}, volume={34}, ISSN={["0149-1970"]}, DOI={10.1016/S0149-1970(98)00010-9}, abstractNote={Expressions for loose-part momentum and impact force were derived as functions of plate bending wave surface acceleration and primary frequency content. These relationships were used to constrain the loose-part diagnostic problem so that loose part mass and impact energy can be determined for credible values of contact radius. Uncertainties associated with unknown contact radius were evaluated by simulation, and experimental data were analyzed for multiple energy impacts by metal spheres having mass between 0.15 and 32 lbs. Significant biases were found to exist when using apparent impact contact time information based on the two-dimensional Lamb wave model. Using the mass estimation method and bias estimates, an iterative technique was developed that converges to close to the theoretical contact time. The results provide methods for loose-part mass and energy estimation and for evaluating the effects of uncertainty in loose part location and signal transmission attenuation.}, number={3}, journal={PROGRESS IN NUCLEAR ENERGY}, author={Mayo, CW}, year={1999}, pages={263–282} }
 @article{gardner_mayo_1999, title={NaI detector nonlinearity for PGNAA applications}, volume={51}, ISSN={["0969-8043"]}, DOI={10.1016/S0969-8043(98)00183-3}, abstractNote={The nonlinearity of a 6″×6″ NaI detector used for PGNAA has been measured. The prompt γ-rays from pure element samples mixed with graphite were used for this determination in the range from 1.712 to 10.829 MeV and γ-rays from radioisotope sources were used in the range from 0.356 to 1.333 MeV. A surprising result is that the pulse height per unit absorbed energy is slightly higher from single escape as opposed to full energy peaks. One explanation for this is that the light production efficiency for positrons may be different than that for electrons. By interpolation a value for the coincidence spectral full energy peak exhibited by NaI detectors that are neutron activated is obtained. The value reported is 6.885 MeV which is slightly higher than the cross section weighted value of 6.834 MeV. (The reported SN values for I and Na are 6.826 and 6.959 MeV, respectively.)}, number={2}, journal={APPLIED RADIATION AND ISOTOPES}, author={Gardner, RP and Mayo, CW}, year={1999}, month={Aug}, pages={189–195} }
 @article{shi_mayo_doster_1999, title={Reactor loose-part activity}, volume={34}, ISSN={["0149-1970"]}, DOI={10.1016/S0149-1970(98)00011-0}, abstractNote={Measured Loose-Part drag coefficients were used to calculate reactor loose-part activity as a function of mass and reactor coolant flow conditions for prototype loose-part shapes. The maximum loose-part mass that could be levitated in vertical flow and the maximum loose-part mass that could impact a recirculating steam generator tube sheet were calculated as a function of flow velocity for Pressurized Water Reactor (PWR) cold and operating primary coolant water properties. The energy of steam generator tube sheet impacts was calculated as a function of mass at cold and operating conditions for a 1130 MW Pressurized Water Reactor. Substantial decreases in active loose-part mass and impact energy occurred between cold and hot flow conditions due to the decrease in water density and viscosity. Loose-parts with higher surface area to mass ratios had higher maximum levitation masses and impact energy. These calculations provide insight into the range of active loose-part mass and impact energy as a function of flow conditions. The associated range in detected signal amplitude can assist in the screening and evaluation of unknown loose-part signals. The loose-part activity modeling methods can be used to extend the results to other reactor coolant system flow conditions and geometries.}, number={3}, journal={PROGRESS IN NUCLEAR ENERGY}, author={Shi, L and Mayo, CW and Doster, JM}, year={1999}, pages={283–298} }
 @article{gardner_guo_sood_mayo_gehrke_dobbs_1998, title={Monte Carlo aided treatments of the nonlinear inverse PGNAA measurement problem for various continuous on-line applications}, volume={233}, ISSN={["0236-5731"]}, DOI={10.1007/BF02389655}, number={1-2}, journal={JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY}, author={Gardner, RP and Guo, P and Sood, A and Mayo, CW and Gehrke, RJ and Dobbs, CL}, year={1998}, month={Jul}, pages={105–107} }
 @article{mayo_verghese_huo_1997, title={Mixed enrichment core design for the NC State University PULSTAR reactor}, DOI={10.2172/319770}, abstractNote={The North Carolina State University PULSTAR Reactor license was renewed for an additional 20 years of operation on April 30, 1997. The relicensing period added additional years to the facility operating time through the end of the second license period, increasing the excess reactivity needs as projected in 1988. In 1995, the Nuclear Reactor Program developed a strategic plan that addressed the future maintenance, development, and utilization of the facility. Goals resulting from this plan included increased academic utilization of the facility in accordance with its role as a university research facility, and increased industrial service use in accordance with the mission of a land grant university. The strategic plan was accepted, and it is the intent of the College of Engineering to operate the PULSTAR Reactor as a going concern through at least the end of the current license period. In order to reach the next relicensing review without prejudice due to low excess reactivity, it is desired to maintain sufficient excess reactivity so that, if relicensed again, the facility could continue to operate without affecting users until new fuel assistance was provided. During the NC State University license renewal, the operation of the PULSTAR Reactor at the State University of New York at Buffalo (SUNY Buffalo) was terminated. At that time, the SUNY Buffalo facility had about 240 unused PULSTAR Reactor fuel pins with 6% enrichment. The objective of the work reported here was to develop a mixed enrichment core design for the NC State University PULSTAR reactor which would: (1) demonstrate that 6% enriched SUNY buffalo fuel could be used in the NC State University PULSTAR Reactor within the existing technical specification safety limits for core physics parameters; (2) show that use of this fuel could permit operating the NC State University PULSTAR Reactor to 2017 with increased utilization; and (3) assure that the decision whether or not to relicense the facility would not be prejudiced by reduced operations due to low excess reactivity.}, number={1997 Dec. 31}, journal={Dept. of Energy NTIS Report #DOE/NE/38004-1(12/97)  Contract #FG05-95NE38004}, author={Mayo, C.W. and Verghese, K. and Huo, Y.G.}, year={1997} }