Recycle of Zr Metal From Hull Wastes by Treatment of Chlorination and Metalization

This research evaluated the applicability of chlorination reaction treatment as processing technology to recover Zr metal which becomes reusable resources from radioactive Zr metal wastes. The typical waste generates from reprocessing facilities, and the main component of waste is a zirconium alloy containing 90–95% of Zr. At first, the volatility of ZrCl₄ produced by the chlorination reaction of Zircaloy-2 was theoretically calculated with thermodynamic simulation code. The estimation showed that Zr could be effectively separated and recovered from this alloy by the difference of volatility in each element chloride. The chlorination reaction of metal proceeds as an exothermic reaction and the control of the reaction temperature is an important condition in order to perform optimal Zr separation recovery. The chlorination reaction of Zircaloy-2 was carried out in the low-temperature ranges of 220°C–320°C, and Zr separation performance was experimentally obtained. Zr and Sn (1.5wt% content in Zircaloy-2) volatilize 100% as chlorides at 270°C or higher temperature. The amounts of volatilization of Cr and Ni are 5% and 0.1% or less, respectively. Such volatile ability is well in agreement with the result of thermodynamic calculation quantitatively. The volatile behavior of Fe (0.2wt% or less content) in Zircaloy-2 is influenced by the product of FeCl₂ which is due to the heat decomposition of FeCl₃ with larger volatility, and the experimental volatility is smaller than the theoretical one. ⁶⁰Co produced in the radioactivated Co by neutron radiation is a highest radioactivity source in the hull waste and it should be completely separated and removed from the recovered Zr chloride. In this study, the metal powder of Co was used to measure the volatility, because the content of Co in Zircaloy-2 is very small quantity (20 ppm or less), The obtained volatility was a hundredth of the volatility of thermodynamics calculation. U and Cs also intermingle in the hull wastes by the solid solution or the adhesion of uranium fuel. The volatility of Cs and U in the chlorination reaction at 270°C was measured by using CsCl, and UO₂ in the coexistence of Zircaloy-2. The volatility of UO₂ and CsCl was 4times and thousand times higher than that without the alloy, respectively. The exothermic reaction in the chlorination of metal was inferred. However, the volatility did not influence the effective ability of decontamination for the recovered Zr chloride. In order to recover the high-level decontaminated Zr chloride from radioactive nuclides, it is necessary to efficiently remove radioactive nuclides, which are the sources of high radioactivity due to ⁶⁰Co, ⁶³Ni and ¹³⁷Cs. It was evaluated that a chemical addition treatment in which the amounts of radioactive nuclides relatively decreases by the amounts of radioactive nuclides relatively decreases by the amount of added stable isotopes of chemical compound was a effective treatment, on basis of the calculation of volatility of each element. The addition treatment of chemical compound performs in the distillation of Zr chloride obtained by the chlorination of hull waste. This study showed that a basic process of the high-level decontaminated Zr recovery consists of the two-step process of both chlorination reaction of the hull waste and distillation treatment of Zr chloride in addition of chemical compound.