Best-estimate calculation plus uncertainty analysis of SBLOCA transient for the scale-down passive test facility

Abstract

CAP1400 has been developed as a new passive nuclear power plant in China based on AP1000 technique. In order to support the CAP1400 licensing, a scale-down integral test facility named ACME (Advanced Core-cooling Mechanism Experiment) has been designed and constructed. In this study, best-estimate calculation using RELAP5/MOD3.4 code plus uncertainty quantification and sensitivity analysis of the small break loss of coolant accident (SBLOCA) transient were carried out for the ACME test facility. The important thermal-hydraulic phenomena during the SBLOCA transient were investigated through the comparing calculations between the ACME and CAP1400. Thereafter, uncertainty quantification process was demonstrated including the selection of input uncertain parameters, the application of Wilks’ nonparametric statistics and the propagation of uncertainty through the SNAP interface coupling RELAP5 and DAKOTA codes. Furthermore, the results of uncertainty and sensitivity analysis were discussed. Through the comparison of the thermal-hydraulic modeling results between ACME and CAP1400, the results show that the ACME test facility is able to reproduce the important thermal-hydraulic phenomena of CAP1400 by reasonable scaling design. The 95/95 uncertainty bands of some key output parameters are obtained through uncertainty quantification. The lower band of the minimum core level is maintained still above the top of the active core section, thus the core uncover will not occur with 95% confidence level. Important input uncertain contributors for the minimum core level are identified through the measure of Spearman rank correlation coefficients in sensitivity analysis. The demonstration of best-estimate plus uncertainty analysis (BEPU) application will provide some guidance for the safety analysis of advanced passive nuclear power plants.