Analysis of extreme scenarios and sensitive cases of the Peach Bottom 2 BWR Turbine Trip by coupled Relap5/Parcs

A research activity started at the end of 80’s was substantiated within the context of the participation of the TMI-1 (Three Mile –Unit 1) Benchmark in 1998. A coupled thermal-hydraulic neutron physics code was developed. This was used for the Boiling Water Reactor (BWR) Turbine Trip (TT) experiment planned and executed in the Peach Bottom Nuclear Power Plant (NPP) in the USA. The test was originated by the quick closing of the turbine inlet valve, followed by the quick opening of the condenser bypass line and, in the core region, by the arrival of a pressure wave. The pressure wave cause void collapse and increase of fission core power for a factor 5 in a few seconds after the turbine trip. The overall scenario was successfully reproduced by the coupled Relap5/Parcs code. This document discusses the results of additional accident scenarios in the ‘now-qualified’ Peach Bottom NPP scenario. The analysis demonstrated, among the other things, the role and the importance of SRV (Steam Relief Valves) opening in preventing code damage