Abstract

Multiple steam generator tube rupture (MSGTR) accidents are considered in seismic level-1 probabilistic risk assessments (PRAs), because a huge earthquake could cause simultaneous damages to steam generator tubes. Although the occurrence frequency of MSGTR is quite low, the accident may directly lead to a core damage. Therefore, effective recovery actions against MSGTR are essential to avoid the core damage. In order to improve the PRA for MSGTR, the recovery actions should be examined. A MSGTR test with ruptures in multiple loops using the Primärkreisläufe Versuchsanlage (PKL) test facility was conducted in the OECD/NEA-PKL-4 project in order to investigate effectiveness of the recovery actions. The experiment assumed that MSGTR occurred in three out of four loops with a total failure of high-pressure injection system of emergency core cooling system. In the present study, a post-test analysis on the PKL test was carried out with RELAP5/MOD3.3 code (RELAP5). Although discrepancies from the test data appeared in some parameters, the code well predicted the overall trends of the major thermal-hydraulic responses observed in the PKL test. Case studies were also performed to confirm the effects of auxiliary feedwater injection into the secondary side of one or more broken steam generators (SGs) on the core cooling.

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