Leaching behavior of gamma-emitting fission products, calcium, and uranium from simulated MCCI debris in water

Gamma-ray radionuclides (Cs-137, Ba-140, I-131, Ru-103, and Zr-95) were produced by neutron irradiation of simulated molten core–concrete interaction (MCCI) debris, which was synthesized by the heat treatment of a mixture of UO2 with concrete components at a relatively low temperature of 1473 K under reducing and oxidizing conditions. The major uranium solid phases were unreacted UO2 and calcium uranate. The leaching ratio of the radionuclides in the powdered sample of the simulated MCCI debris was investigated under atmospheric conditions at 298 K in 0.1 mol/dm3 NaClO4 after filtration of the leachate through a 0.45-µm pore membrane. The uranium molar concentration in the filtrate was affected by the oxidation state in the solids. In the present study, however, the effect of various solid phase conditions on the leaching ratio normalized to that of uranium matrix could not be clarified. It was found that the leaching ratio of various fission products (RM) was proportional to that of Cs (RCs), and this trend did not depend on the oxidation state of uranium, the type of uranium complex (including a colloidal species), or the presence of Ca, Si, cement, or Zr.