The accumulator effects on in-vessel severe accident progression of a three loop PWR nuclear power plant in a SBLOCA without safety injection system

Highlights: • Simulation of three-loop Westinghouse nuclear power plant using RELAP5/SCDAP code. • Investigation of postpone accident by accumulator coolant injection effects. • Simulation of SBLOCA event in the station blackout condition. • Investigation of in-vessel core melting progression. • Analysis of the melt core concrete interaction using CONTAIN2.0 code. • Investigation of IVR strategy using RELAP5/SCDAP code. - Abstract: This paper aims to evaluate the effects of coolant injection into a three-loop Westinghouse plant reactor vessel by the accumulators during small break loss of coolant accident, under severe accident condition. Using RELAP5/SCDAP mod3.4 computer code, a best estimate simulation from initiating SBLOCA event of 2, 3, and 4-in. without active part of the emergency core cooling system, in conditions with and without accumulators, is conducted until the rector pressure vessel failure. The results show that, the actuation of the accumulators lead to postponing the reactor vessel failure. Therefore, although the accumulators are designed for a large break LOCA, their actuation is very effective on the delay of a vessel failure. In this paper, the melt core concrete interaction is analyzed using CONTAIN2.0 code for the 4-in. break size without ACCs case as the most serious cases for the time of lower plenum failure. The result for 52.8 h is reported. The in-vessel molten material retention strategy for this case is studied using RELAP5/SCDAP code. The results show that lower plenum integrity is preserved during the severe accident that causes reactor core melt.