Modeling of Safety/Relief Valves With Thermal-Hydraulic System Computer Codes

A generic guideline for thermal-hydraulic (T-H) simulation of multiple bank safety relief valves (SRVs) was developed. To test the guideline, the Full Integral Simulation Test (FIST) 6PMC2 was simulated with the consolidated T-H code of USNRC, TRACE. The FIST 6PMC2 experiment simulates the response of a generic BWR/6 plant to a Main Steam-line Isolation Valve (MSIV) closure without reactor scram. During the test, the HPCS is unavailable and not used. The only inventory make-up system available is the Reactor Core Isolation Cooling (RCIC). This experiment can also be considered proto-typical of a BWR ATWS-like scenario. The simulation is largely dominated by the transient behavior of the SRVs. In this study, the experimental data was analyzed and used to check the modeling guideline for SRVs. The guideline relies on only the data available prior to an experiment or any other analysis, e.g. valve flow coefficients, inlet hydraulic diameters, etc. The study also revealed deficiencies in the “then” current valve model of the TRACE code which were subsequently corrected. The study demonstrates that the T-H models can simulate the operational behavior of SRVs very accurately while rather simple mistakes can be very damaging at the same time.