Analysis of oxidation influence on steam explosion energetics

• Different oxidation influence in ZREX and OECD SERENA experiments explained.
• Hydrogen film hypothesis proposed to explain experimental observations.
• MC3D simulations provided additional insight and support hypothesis.
• Oxidation during premixing phase typically reduces explosion strength.
• Oxidation during explosion phase increases explosion strength.

When during a severe reactor accident the corium melt comes into contact with the coolant water a steam explosion may occur. If non-oxidized zirconium is present in the corium melt the oxidation of zirconium may significantly affect the steam explosion energetics, as observed in experiments. In the ZREX experiments the steam explosion strength was largely increased by the oxidation of 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 the article, the performed analysis of the influence of oxidation 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 sub-cooled water conditions and that the remaining non-oxidized 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 qualitatively explains the observed experimental findings.