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

The results of a simulation activity on a General Electric (GE) simpli fied boiling water reactor (SBWR) carried out at ENEL (the Italian Ele ctricity Board) are discussed. The SE WR is a medium-size [600 MW(elec tric)] new generation reactor developed by GE, whose safety is ensured by means of passive systems (wafer gravity injection, pressure suppre ssion, and passive heat removal). The RELAP5/MOD2 code is a well-known tool developed at the Idaho National Engineering Laboratories and mad e available by the U.S. Nuclear Regulatory Commission; it has been wid ely used and qualified all over the world. To investigate the thermal- hydraulic performance of such an innovative reactor during accident sc enarios, a SE WR RELAP5/MOD2 model was developed and a selected number of transients were analyzed. The typical phenomena related to the SEW R accident behavior was investigated. A good agreement was found betwe en the RELAP5/MOD2 code and the licensing code (TRAC-G) results. In al l cases, the performance of the SE WR safety systems was also evaluate d.