Adding prefilters to French containment venting systems

The sand-bed filters installed on all French Pressurized Water Reactors were intended to retain the source term of radioactivity for 24h after the beginning of a core meltdown. But because of its size the sand filter is outside the containment and therefore the source term, which may be inside the sand filter, could produce very high radiation levels on site. To solve this problem a prefilter has been designed. This is to be located inside the containment and aims to retain the source term there. (author)