RELAP5 code analysis of LSTF small break LOCA tests with steam generator intentional depressurization as an accident management procedure; Investigation on base case result appropriate for the best estimate plus uncertainty (BEPU) application

Kinoshita, Ikuo*; Torige, Toshihide*; Murase, Michio*; Yoshida, Yoshitaka*; Takeda, Takeshi ; Satou, Akira ; Nakamura, Hideo 

A BEPU method is to be used for reactor safety analysis to quantitatively estimate uncertainties in the analysis results. However, the accuracy depends primarily on the code capability in simulating the system response. In this study, the predictive capability of RELAP5 code was studied against three ROSA LSTF small break LOCA experiments with assumptions of intentional depressurization of steam generator (SG) secondary side as an accident management procedure and high-pressure injection failure. The RELAP5 code was then confirmed to predict well the major event progressions characteristic to this accident scenario, which include such important phenomena as formation and clearing of loop seal and CCFL at the inlet of SG U-tubes.