ANALYSIS OF INFLUENCE OF ZIRCONIUM CONTENT IN OXIDIC CORIUM ON STEAM EXPLOSION ENERGETICS

摘要

A steam explosion, in the frame of nuclear reactor safety, is an energetic fuel coolant interaction process, which may occur when the hot reactor core melt comes into contact with the coolant water. Steam explosions are an important nuclear safety issue because they can potentially jeopardize the primary system and the containment integrity of the nuclear power plant. If metallic zirconium is present in the corium melt the oxidation of zirconium may significantly influence the fuel coolant interaction process, as observed in experiments. In the ZREX (ANL, USA) experiments the steam explosion strength was largely increased by the oxidation of the metallic zirconium, whereas in the recently performed OECD SERENA project KROTOS and TROI experiments it seems that the oxidation had an inhibiting effect. To find out the reasons for this qualitatively different behavior, the experimental results were investigated in comparison and computer simulations were performed. In this paper, the performed analysis of the influence of the zirconium content on the steam explosion energetics is presented and discussed. Based on the experimental findings, the hydrogen film hypothesis is proposed, claiming that only a limiting amount of zirconium may be oxidized during the premixing phase in subcooled conditions and that the remaining amount of unoxidized zirconium is available for the oxidation in the explosion phase. Various computer simulations were performed with the MC3D code to support the hypothesis and to get additional insight. It may be concluded that the proposed hypothesis reasonably well explains the observed experimental differences. Suggestions for further analytical and experimental work are given.