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 (SB WR) carried out at ENEL (the Italian Electricity Board) are discussed. The SBWR is a medium-size [600 MW(electric)] new generation reactor developed by GE, whose safety is ensured by means of passive systems (water 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 SBWR RELAP5/MOD2 model was developed and a selected number of transients were analyzed. The typical phenomena related to the SBWR 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 SBWR safety systems was also evaluated.