A process of dissolving fuel elements of nuclear reactors

摘要

An element having a core containing uranium dioxide clad with stainless steel or a zirconiumbase metal is immersed in molten lead chloride containing a copper catalyst, e.g. copper, cuprous chloride, or cupric chloride and chlorine is bubbled through to dissolve the element. The quantity of lead chloride used may be three times that of the weight of uranium dioxide present and it may be maintained in the molten state at a temperature between 500 and 550 DEG C. The uranium forms uranyl chloride or uranium tetrachloride and the zirconium forms the tetrachloride which volatilizes if the temperature is 550 DEG C. The concentration of the copper catalyst may be as low as 0.003 M. The amount of chlorine used is in excess of that stoichiometrically required for the total chlorination of the constituents of the element. A chlorine flow rate of from 10 to 130 mg./min. is preferred. Values of the dissolution rates of uranium dioxide and customary cladding materials, e.g. zirconium, stainless steel are given for varying reaction conditions. In a typical example, a zirconium-clad, uranium dioxide-containing fuel rod was dissolved in a molten mixture of lead chloride containing copper through which clorine was passed. The fuel rod was immersed in stepwise fashion, the temperature of the melt being maintained at 550 DEG C. Chlorination was continued until the melt solidified, the final composition of the melt being 20.6 mole per cent uranyl chloride, 11.8 mole per cent cuprous and cupric chlorides, and 67.6 mole per cent lead chloride. Zirconium was separated from the uranium by volatilization as the tetrachloride at 550 DEG C.