High temperature reaction between sea salt deposit and (U,Zr)O2 simulated corium debris

In order to clarify the possible impacts of seawater injection on the chemical and physical state of the corium debris formed in the severe accident at Fukushima Daiichi Nuclear Power Plants, the high temperature reaction between sea salt deposit and (U,Zr)O2 simulated corium debris (sim-debris) was examined in the temperature range from 1088 to 1668 K. A dense layer of calcium and sodium uranate formed on the surface of a sim-debris pellet at 1275 K under airflow, with the thickness of over 50 μm. When the oxygen partial pressure is low, calcium is likely to dissolve into the cubic sim-debris phase to form solid solution (Ca,U,Zr)O2+x. The diffusion depth was 5–6 μm from the surface, subjected to 1275 K for 12 h. The crystalline MgO remains affixed on the surface as the main residue of salt components. A part of it can also dissolve into the sim-debris.