Interactions between U-Zr-O and concrete near the melting range of concrete

Sudo, Ayako ; Sato, Takumi ; Nagae, Yuji 

Current molten corium concrete interaction codes are based on large-scale tests in which core materials interact with concrete and the initial temperature of the molten pool is below 2000C. Suboxides such as U-Zr-O may react with concrete at lower temperatures near the melting range of concrete. Investigating the reactions between core materials and concrete near the melting range of concrete is essential for advancing severe accident analyses. As a result of small-scale reaction tests between concrete and U-Zr-O under an Ar atmosphere at 1200C and 1300C, held for 2 hours, a Si-Zr-U-O layer was formed at the reaction interface. At 1500C, held for 2 hours, three layers were formed: (i)Si-Zr-U-O layer, (ii) (U,Zr)O and concrete, and (iii) Si-Zr metallic precipitates. The thermodynamic analysis, indicate that Ca dissolves in (U,Zr)O, whereas U is not predicted to be present in the Si-Zr-U-O layer. These discrepancies arise because the calculations assume complete mixing of the core materials and concrete. The present study demonstrated that, within the temperature range of 1200C-1500C, the reaction layer formed between U-Zr-O and concrete became thicker with increasing temperature, and that the composition of the reaction layer could not be adequately predicted by thermodynamic calculations alone.