MAAP5 Simulation of the PWR Severe Accident Induced by Pressurizer Safety Valve Stuck-Open Accident

Abstract

The Modular Accident Analysis Program version 5 (MAAP5) is a computer code that can simulate the response of light water reactor power plants during severe accident sequences. The present work aims to simulate the severe accident of a typical Chinese pressure water reactor (PWR) induced by the he pressurizer safety valve stuck-open accident with MAAP5. Three cases corresponding to 1, 2 and 3 pressurizer safety valves stuck open accidents without high pressure injection (HPI) and the auxiliary feed water (AFW) of steam generator (SG) were analyzed. The results showed that the pressure safety valve stuck open with HPI and AFW failure accident would lead to a severe accident. And the severe accident sequence was correlated with the number of the stuck open valve. In the case of 1 valve stuck open, the coolant lost slowly and the primary system depressurized slowly which delayed the activation of the low pressure injection (LPI). The reactor pressure vessel (RPV) failed at this case. On the contrary, in the case of 2 and 3 valves stuck open, the coolant lost faster and the pressure decreased rapidly to the critical pressure of the LPI. Thus, the consequences of the two cases were much slighter. The results are meaningful and significant for comprehending the detailed process of PWR severe accident, which is the basic standard for establishing the severe accident management guidelines.

ASTEC–MAAP Comparison of a 2 Inch Cold Leg LOCA until RPV Failure

“…Similar but less severe overshooting is observed in the ASTEC results as shown in Figures 6 and 8. Similar observation is reported in several published works including [47]. This phenomenon occurs when partially uncovered and overheated core is quenched from below by core inlet flow.…”