Pressurized Thermal Shock Preliminary Analyses of a 2-Loop Pressurized Water Reactor under Loss-Of-Coolant Accident Scenarios

The lifetime of a nuclear power plant strongly depends on the ability of the reactor pressure vessel (RPV) to safely endure reactor transients that may jeopardise its structural integrity. Examples of such transients are loss-of-coolant accidents (LOCA) followed by pressurized thermal shock (PTS) events which are characterized by rapid cooling of the internal RPV surface in combination with repressurization. As the RPV gets embrittled due to neutron irradiation, this ability decreases together with its material's resistance to crack propagation. Therefore, it is of interest to investigate available margins, in terms of embrittlement referencetemperature shifts, under PTS conditions. In this paper, preliminary PTS analyses of a 2-loop pressurized water reactor under selected LOCA scenarios are performed and the methodology to evaluate temperature margins is developed. The thermal-hydraulic and structural analyses are performed, respectively, with RELAP5 and FAVOR computer codes. The results of the preliminary analyses suggest that temperature margins are probably sufficient for the safe and long-term operation of the plant. Nevertheless, the margins obtained for a 12 inch break are rather close to regulatory limits.