FP aerosol trapping effect along the leakage paths of degraded containment penetrations during a severe accident (1)

Fission product (FP) aerosol trapping along the leakage paths of degraded containment penetrations during a severe accident (SA) was investigated. Typical actual electrical penetration assemblies (EPAs) and several actual hatch flange gaskets, were degraded under prototypical severe accident conditions in a reactor containment. No leakage was observed for any test pieces under the Japanese accident management (AM) conditions, that is, a containment ambient temperature less than 200degC and a pressure less than twice the design pressure. Beyond AM conditions, a small leakage was observed from 266 to 324degC for the low-voltage module and from 279 to 349degC for the flange gasket. The temperature condition rather than the pressure condition dominates the failure criteria. The safety margin for temperature was evaluated to be more than about 70degC. The average equivalent leak area of the test piece was around 6 mm2 per 1 unit module for the low-voltage module and around 13 mm2 per 1 m gasket length for the flange gasket. There was no leak for the high-voltage module. The total leak area of a typical BWR plant during SA was estimated at about 2.5 x 103 mm2 and the value was about one order of magnitude smaller than the value used in current severe accident analysis codes. (author)