Formation of Zirconium Molybdate Sludge from an Irradiated Fuel and Its Dissolution into Mixture of Nitric Acid and Hydrogen Peroxide

Abstract 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 2 O 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 2 O 2 solution at 80 °C within 5 h. The sludge formation on the clean Zr surface is inhibited.