Safety System Design Concept and Performance Evaluation of the Long Operating Cycle Simplified BWR

The long operating cycle simplified BWR (LSBWR) is a reactor concept that pursues both safety and economy by employing natural circulation core without refueling, passive decay heat removal, and integrated building for reactor and turbine. Throughout the entire spectrum of design base accident, the core is kept covered by passive ECCS. The decay heat is removed by conventional active low pressure RHR system. As for postulated severe accident, the suppression pool water floods the lower part of RPV in case core damage occurs, and in-vessel retention (IVR) that keeps the melt inside the RPV is achieved by serving coolant. The containment hull structure as PCCS enables coolant between inner and outer walls to absorb heat transferred from inside atmosphere, and eventually transfers the decay heat to ultimate heat sink in the form of clean steam without containment venting. This paper describes the PCCS performance evaluation using TRAC code as one of the characteristic plant features. The core damage frequency for internal event at power operation was also evaluated to examine safety level and balance of design. (authors)