Investigation of SAM measures during selected MBLOCA sequences along with Station Blackout in a generic Konvoi PWR using ASTECV2.0

Abstract

The Fukushima accidents have shown that further improvement of Severe Accident Management Guidelines (SAMGs) is necessary for the current fleet of Light Water Reactors. The elaboration of SAMGs requires a broad database of deterministic analyses performed with state-of-the art simulation tools. Within this work, the ASTECV2.0 integral severe accident code is used to study the efficiency of core reflooding (as a SAM measure) during postulated Medium Break LOCA (MBLOCA) scenarios in a German Konvoi PWR.In a first step, the progression of selected MBLOCA sequences without SAM measures has been analysed. The sequences postulate a break in the cold leg of the pressurizer loop and the total loss of AC power at a given stage of the accident. Results show the existence of a 40min grace time up to the detection of a Core Exit Temperature (CET) of 650°C providing that the AC power has been maintained at least 1h after SCRAM.In a second step, an extensive analysis on core reflooding has been carried out. The sequences assume that the plant remains in Station Blackout (SBO) and that reflooding occurs at different times with different mobile pumps. The simulations yield the following results:•Reflooding mass flow rates above 60kg/s have to be supplied as soon as the CET exceeds 650°C in order to prevent core melting.•Reflooding mass flow rates ranging from 25–40kg/s at CET=650°C mitigate the accident without major core damage depending on when the plant enters in SBO.•Reflooding mass flow rates lower than 10kg/s cannot prevent RPV failure.The performed investigations elucidate the ASTECV2.0 capabilities to describe the in-vessel phase of a severe accident in a German Konvoi PWR and to assess the performance of core reflooding for slightly degraded cores. Moreover, they form the basis of future analysis on sequences with a higher contribution to the overall risk of such nuclear plant.