Small-model tests were performed to examine the integrity of the conta
inment flange gasket in a severe accident. During a severe accident, c
ontainment structures suffer slow pressurization at relatively high te
mperatures. A realistic understanding of containment performance in su
ch conditions is a major concern in developing an accident management
strategy. This paper describes the results of experiments on the seali
ng capability of flange gaskets at high pressures and high temperature
s. Silicone-rubber gaskets, which are used as the sealing material in
BWR plant primary containment vessels (PCV) in Japan, were examined in
small-model tests. The gaskets show sufficient sealing capability up
to 225 degrees C at 20 kgf/cm(2). When applying the leakage characteri
stics specified in this paper to codes for severe accidents, the resul
ts should be examined carefully based on realistic heattransfer phenom
ena.