Untersuchungen zu Störfällen mit massivem Wassereinbruch am Beispiel des Kugelhaufenreaktors PNP-500

摘要

The computer code REACT/THERMIX is used for analyses of massive water ingress accidents in the High-Temperature Gas Cooled Reactor concept PNP-500 with a pebble bed core; the analyses are mainly focussed on graphite corrosion processes. For the investigated accidents a correct reactor shut down is assumed; the mass of water ingressing into the primary circuit is varied between 1000 and 7500 kg (that means up to hypothetical values). The dependence of accident consequences on parameters as intensity and starting time of the afterheat removal system or kinetic values of the chemical processes is examined. The results show, that also under pessimistic assumptions the extent of the graphite corrosion is relatively low; significant damaging of the fuel elements or of the graphite components does not occur. A primary circuit depressurization in combination with a local burning of water gas would probably not affect the fission product retention potential of the (gastight) containment. Summing up, the risk caused by these accidents remains small.