(A) combination of generalized equivalence theory and super-homogenization for cross-section corrections in pin-wise PWR diffusion analysis

Abstract

In this thesis, a new leakage correction method called GET plus SPH (GPS) method has been introduced to correct the pin-wise homogenized two-group cross-sections by taking into account the neutron leakage information. In order to improve the accuracy in the conventional two-step core analysis, the pin-wise cross-section (XS)-dependent SPH factors are introduced and functionalized in terms of the integrated pin-wise albedo information, i.e., current-to-flux ratio (CFR), via the GPS method. To acquire the relationship between the CFR information and the corresponding XS-dependent SPH factors, small color-set models were considered. These color-set problems are comprised of several fuel assemblies (FAs) to obtain physically meaningful pin-wise CFR values for various lattice environments. The proposed GPS method was implemented to an in-house pin-by-pin nodal expansion method (NEM)-based solver with the pin-wise CMFD acceleration. To evaluate the performance of the GPS method, various benchmark problems based on an SMR initial core and a large PWR core were analyzed. In order to demonstrate the general applicability of the GPS functions, several modified core configurations were also solved by using the same GPS functions. In addition, fully rodded benchmark problems were examined to test the GPS method in the extremely abnormal core configurations. Finally, the GPS method was applied to various partially MOX-loaded PWR cores to demonstrate its applicability to extremely difficult reactor problems. The comprehensive results of this research illustrate that the GPS method can substantially enhance the accuracy of the pin-wise reactor analyses with a reasonably small additional computational costs.