Pressurizer models for loft experiment LP-FW-1

The primary system pressure response in all operational and fault transients is largely determined by the flow into or out of the pressurizer, and by the functional response of the pressure control systems (spray, PORV, etc) and the processes that take place within the pressurizer. It is important that these processes be adequately modeled if the pressure response, and hence the ensuing transient are to be correctly calculated. The present study investigates the RETRAN-02/MOD 4 representation of pressurizer behavior during the early stages of the OECD LOFT loss of feedwater experiment LP-FW-1. Attention is focused on the pressurizer itself by treating the surge line flow as a boundary condition. Sensitivity studies are performed to evaluate the importance of the following processes: heat transfer to/from the pressurizer walls; heat transfer between the vapor and liquid regions; thermal stratification in the liquid region; and desuperheating and condensation of the vapor by the spray