SIMPLIFIED BOILING WATER-REACTOR THERMAL-HYDRAULIC PERFORMANCE - A RELAP5/MOD2 MODEL SIMULATION

The results of a simulation activity on a General Electric (GE) simplified boiling water reactor (SBWR) carried out at ENEL (the Italian Electricity Board) are discussed. The SE WR is a medium-size [600 MW(electric)] new generation reactor developed by GE, whose safety is ensured by means of passive systems (wafer gravity injection, pressure suppression, and passive heat removal). The RELAP5/MOD2 code is a well-known tool developed at the Idaho National Engineering Laboratories and made available by the U.S. Nuclear Regulatory Commission; it has been widely used and qualified all over the world. To investigate the thermal-hydraulic performance of such an innovative reactor during accident scenarios, a SE WR RELAP5/MOD2 model was developed and a selected number of transients were analyzed. The typical phenomena related to the SEWR accident behavior was investigated. A good agreement was found between the RELAP5/MOD2 code and the licensing code (TRAC-G) results. In all cases, the performance of the SE WR safety systems was also evaluated.