Systematic Source Term Analyses for Level 3 PSA of a BWR With Mark-II Type Containment With THALES-2 Code

The THALES-2 code is an integrated severe accident analysis code developed at the Japan Atomic Energy Research Institute in order to simulate the accident progression and transport of radioactive material for probabilistic safety assessment (PSA) of a nuclear power plant. As part of a level 3 PSA being performed at JAERI for a 1,100MWe BWR-5 with a Mark-II containment, a series of calculations were performed by THALES-2 to evaluate the source terms for extensive accident scenarios. For some of the containment failure modes not modeled in THALES-2, such as steam explosion, simple models were coupled with the analysis results of THALES-2 to estimate the source terms. This paper presents the methods and insights from the analyses. An insight from the analyses was that the source terms depend more strongly on the differences in the containment function failure scenarios, such as overpressure failure, controlled containment venting, and small leakage to the reactor building, than those core damage sequences.