FP aerosol trapping effect along the leakage paths of degraded containment penetrations during a severe accident (2)

Fission product (FP) aerosol trapping along the leakage paths of degraded containment penetrations during a severe accident was investigated. Prior to this aerosol trapping test, several actual electrical penetration assemblies (EPAs) and hatch flange gaskets were degraded under prototypical severe accident conditions in a reactor containment. Then, the aerosol trapping test at the leakage path was conducted. Cesium iodide (CsI) was used as a FP aerosol in the test. The aerosol trapping effect along the leakage paths was expressed as a decontamination factor (DF) and the average values were about 740 for the low-voltage module and about 14 for the flange gaskets. The overall DF value of a typical BWR was estimated at about 450, using the average DF value and a number of containment penetrations of each type. These results were reflected in the severe accident analysis by the MELCOR code. The total amount of FP leaked from containment was reduced to around 50 to 70% compared with that determined by the original MELCOR analysis 1 day after a typical BWR severe accident. (author)