Formation of zirconium molybdate sludge from an irradiated fuel and its dissolution into mixture of nitric acid and hydrogen peroxide

摘要

In the dissolution step of the PUREX process, a sludge of zirconium molybdate can be generated from zirconium and molybdenum dissolved in the solution. In order to avoid accumulation of sludge, a new cleaning method using a mixture of nitric acid and hydrogen peroxide was developed. In this work, the cleaning method was verified using an irradiated fuel. Cubic crystals of the zirconium molybdate ZrMo_2O_7(OH)_2 were formed upon dissolution of an irradiated PWR fuel. The sludge deposition continued after the completion of the fuel dissolution. A small amount of fissile material was incorporated into the sludge. Although almost the same amount of insoluble residue was present, the sludge could be dissolved with a HNO_3-H _2O_2 solution at 80 °C within 5 h. The sludge formation on the clean Zr surface is inhibited.