An assessment of effectiveness of core exit temperatures with respect to PWR core damage state using RELAP/SCDAPSIM/MOD3.4

Core exit temperature measurements play a very important role in the development and implementation of Severe Accident Management Guidelines. For example, the transition from Emergency Operating Procedures to the Severe Accident Management Guidelines may be triggered by core exit temperatures exceeding set limits. Core exit temperatures may also be used to determine if core cooling has been re-established when different management techniques have been applied. However, core exit temperatures may not always be reliable indicators of the state of the core. For that reason, a systematic study of the relationship between core exit temperatures and the state of the core for different accident conditions and different reactor designs has been started using the detailed system thermal hydraulic and severe accident analysis code package, RELAP/SCDAPSIM. In this paper, the results of the first part of the study is presented and discussed. The paper includes (a) a brief description of the RELAP/SCDAPSIM package, (b) insights from two full plant calculations, a Station Blackout transient for the Surry PWR and the TMI-2 accident analysis, and (c) the results from a series of sensitivity studies to relate core exit temperatures to core damage states for idealized core uncovery, heating, and reflooding scenarios for a typical PWR fuel assembly