Crack leakage experiments for concrete containments

The accidents at Chernobyl and Three Mile Island focused world attention on the behavior of nuclear facilities during severe accidents and stimulated interest in the role of containments in mitigating the consequences of such accidents. It is well known that an intact containment is highly effective in limiting fission product releases to the atmosphere, but it is less appreciated that concrete containments can perform well even if their walls are severely cracked. Through-wall cracks will provide pressure relief that can reduce the risk of exceeding the containment's structural limits. They also act as filters and thus present a significant barrier to the release of fission products. It is probable that the postulated consequences of a severe nuclear accident will be greatly reduced when these effects are considered. To take credit for the benefits of cracking in accidents well beyond the design basis, it is necessary to be able to predict the frequency and characteristics of any through-wall cracking, the nature of the resulting relief flow, and the efficacy of the many mechanisms for fission product retention within these cracks. The research required for the formulation and verification of detailed predictive response models is examined in this paper.