Safety study for HTR concepts under German site conditions. Main volume for phase I B

Within the spectrum of accidents, core heat-up, caused by failure of the power supplies to the reactor or by interruption of the cooling system, is of major significance. This accident causes no serious effects to the environment if the reactor containment building remains intact; however, in certain infrequent events the containment building could fail due to overpressure after about one week at the earliest and a significant environmental hazard would ensue. The other accidents - depressurisation, water and air ingress - are by comparison of distinctly lower importance to the overall risk. A common feature of all the significant accidents is that within the first five hours the maximum release of radioactivity to the reactor containment building is the inventory of the primary circuit, while the fission product inventory of the core is securely retained. The accidents investigated are characterised in the study by the probability of occurrence, by the types and quantities of the fission products released and by the period of release. It was stipulated that in this phase of the study the health risk to the neighbouring population should not be determined. However, the estimated quantities of released nuclides and their associated time of release lead to the conclusion that the worst possible damage to the environment is very limited. This arises from the inherent safety characteristics of the HTR and the comparatively long period available for counter measures. (orig./HP)