Abstract
The feedback reactivity caused by the core deformation is one of the most important factors of inherent safety features in sodium-cooled fast reactors (SFRs). To validate the evaluation models of the reactivity feedback, we have been conducting the benchmark analyses in the framework of Generation IV International Forum (GIF) for the unprotected loss of heat sink (ULOHS) tests of BOP-301 and BOP-302R in EBR-II, a pool-type experimental SFR in the United States. In the previous study, coupled analyses with the plant dynamics analysis (1D) code and the computational fluid dynamics analysis (CFD) code for the regions including the cold pool were conducted using the reactor power of the measured data as a boundary condition in the core. By the coupled analyses with the 1D and the CFD codes (1D-CFD coupled analyses), the thermal stratification and the increase of the core inlet temperature could be reproduced successfully. In the previous 1D standalone analyses, it was known that the total reactivity was underestimated. In this study, to validate the reactivity model for ULOHS tests, the renewed 1D-CFD coupled analyses by calculating the core power by using the core reactivity models including the core bowing reactivity in the 1D code were conducted. Through the analysis, the applicability of the modified reactivity model was confirmed in the BOP-301 test. In the BOP-302R test, consideration of the influence of the core restraint system in the core and modeling the control rod driveline expansion reactivity was indicated.
