Large break LOCA Calculations for the AP600 Design

This paper presents the application of RELAP5 to the calculation of a Large Break (200% doubled-ended rupture) Loss-of-Colant-Accident (LBLOCA) at the reactor vessel inlet for the proposed Westinghouse AP600 design. A parametric calculation was also performed to determine effects of loss of a complete Emergency Core Cooling system (ECCS) train. These calculations were performed over the core blowdown, refill, and reflood phases of the LBLOCA and did not address long term cooling. RELAP5 was shown to be adequate for system response calculation over the period of interest. The passive safety systems were predicted to effectively mitigate the consequences of LBLOCAs; the calculations showed less severe thermal responses than for a current generation Pressurized Water Reactor (PWR) plant. The two primary differences between the AP600 design and a current generation plant that affect LBLOCA response are the lower core thermal power, which results in lower temperatures during the blowdown phase, and the long duration accumulator injection, which provides ample core inventory makeup for final quenching.