Multicycle Adaptive Simulation of Boiling Water Reactor Core Simulators

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dc.contributor.advisor Dr. Semyon V. Tsynkov, Committee Member en_US
dc.contributor.advisor Dr. Paul J. Turinsky, Committee Co-Chair en_US
dc.contributor.advisor Dr. Hany S. Abdel-Khalik, Committee Co-Chair en_US Briggs, Christopher Michael en_US 2010-04-02T18:05:40Z 2010-04-02T18:05:40Z 2007-04-25 en_US
dc.identifier.other etd-04202007-145700 en_US
dc.description.abstract Adaptive simulation (AS) is an algorithm utilizing a regularized least squares methodology to correct for the discrepancy between core simulators predictions and actual plant measurements. This is an inverse problem that will adjust the cross sections input to a core simulator within their range of uncertainty to obtain better agreement with the plant measurements. The cross section adjustments are constrained to their range of uncertainty using the covariance matrix of the few-group cross sections and in imposing the regularization on the least squares solution. This few-group covariance matrix is obtained using the covariance matrix of the multi-group cross sections and the corresponding lattice physics sensitivity matrix. To perform the adaption, one must also have the sensitivity matrix of the core simulator. Constructing the sensitivity matrix of both the lattice physics code and core simulator would be a daunting task using the traditional brute-force method of computing a forward solve for a perturbation of every input. To avoid this, a singular value decomposition (SVD) is used to construct a low rank approximation of the covariance matrices, thus drastically reducing the number of required forward solves. Until now, AS has been used on a single depletion cycle to correct for discrepancies resulting from errors introduced by incorrect cross sections only. Adapting to a single depletion cycle means that the cross sections of cycle m were adjusted so that the core simulator better predicts the actual measurements of cycle m (and future cycles if the algorithm is robust). This, however, does not account for the reloaded burnt fuel number density errors at the beginning-of-cycle (BOC) m. By definition a burnt assembly has been used and depleted in a previous cycle. If adaption changes the cross sections of that burnt assembly in cycle m, those cross sections should have also been changed in any cycle preceding m which would have resulted in different BOC m number densities. This means that the number densities obtained using the original cross sections are not consistent with the newly adapted cross sections. Hence, the number densities input to a core simulator are not the actual values in the reactor's fuel assemblies for the burnt fuel. This discrepancy in isotopics is another component to the discrepancy between the core simulator and actual observables. This means that the adaption algorithm is adjusting cross sections to account for number density errors. It is the goal of this research to 1) remove these inconsistencies between the adapted cross sections and the burnt fuel BOC n number densities, and 2) ensure that adjusting cross sections to make up for number density errors does not corrupt the adaption. To do this, we assume that to best predict cycle n (by correcting both cross sections and BOC number densities of cycle n), one must adapt cycles m through n-1 simultaneously, where cycle m is the cycle in which the oldest assembly in cycle n is a fresh assembly. After adaption, the cross sections must be used to deplete from cycle m to n. This will remove the number density errors in two ways: 1) burnup healing, and 2) beginning the depletion of fresh assemblies in cycles m through n-1 with the correct cross sections. To ensure the cross sections adjustments are not overcompensating for the number density errors, we restrain their adjustment to stay near one standard deviation of their a prior values. en_US
dc.rights I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dis sertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. en_US
dc.subject regularization en_US
dc.subject inverse theory en_US
dc.subject uncertainty en_US
dc.subject cross section uncertainty en_US
dc.subject cross section adjustment en_US
dc.subject least squares en_US
dc.subject adaptive simulation en_US
dc.subject data adjustment en_US
dc.title Multicycle Adaptive Simulation of Boiling Water Reactor Core Simulators en_US MS en_US thesis en_US Nuclear Engineering en_US

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