Investigation of Strategies for Mitigating Radiological Releases in Severe Accidents

摘要

The Fukushima Dai-ichi accident highlights the need to reduce the magnitude of radioactive fission product releases from BWR Mark I and II containments following beyond-design-basis events. There is no evidence that such accidents have a long-term effect on public health and safety; however, the Fukushima Dai-ichi accident did result in widespread contamination of surrounding areas, both on-site and off-site. This report assesses various strategies that can be used to maintain BWR Mark I and II containment systems as effective barriers and to retain fission products in containment following a beyond-design-basis accident. The best way to avoid radiological release and potential land contamination is to prevent an accident from occurring by improving and augmenting the strategies for preventing core damage. These improvements are described in other assessments and are outside the scope of this report. This report focuses on severe accidents in which the containment vessel provides the chief barrier to fission product release. Various studies have shown that accidents involving long-term loss of electric power and subsequent loss of core cooling capability can significantly challenge the containment barrier. This report evaluates strategies that maintain or enhance the containment function in scenarios involving long-term loss of electric power. The strategies evaluated include water injection (by flooding or spraying), alternative containment heat removal, venting, controlled venting, filtered venting, and combinations.