Pyrochemical processes for LWR spent fuel

Pyrochemical processes are under development at Argonne National Laboratory for recovery of transuranium (TRU) elements from light water reactor spent fuel. The recovered TRU elements will be used as fuel in the integral fast reactor (IFR). Burning these long-lived isotopes for electrical power generation has the additional benefit of reducing the burden on the geological repository for their long-term containment. The goals for the process include: greater than 99.90% recovery of TRU elements, a metal product that is compatible with the IFR fuel cycle, retention of some fission products in the TRU product to enhance proliferation resistance, and a simple process that is economically attractive. The TRU product will be inserted into the IFR fuel cycle for fission product decontamination and incorporation into the fuel. Based on research and development at ANL in the 1960 and 1970 and a comparison of known processes for separation of TRU elements from uranium fuel, three conceptual processes were identified that seem to offer high potential for achieving the desired goals. All three conceptual processes include a reduction step to convert the oxide fuel to metal, an electrochemical step to recover the reductant (calcium) from its oxide, a TRU extraction step to separate TRU elements from the bulk uranium, and a retort step to recover the TRU product from a solvent metal. The candidate processes differ primarily in the methods used to separate the TRU elements from uranium. The salt transport process effects this separation by molten salt extraction; the magnesium extraction process uses the differential solubility of TRU elements in magnesium relative to that of uranium; and the zinc-magnesium process uses phase separation to recover TRU elements, which are soluble in a Zn-Mg alloy. The chemical feasibility of each step of the three concepts has been demonstrated in small-scale experiments. Candidate containment materials have been selected and tested at the temperature and environmental conditions of the processes. The data from these small-scale experiments are summarized in this paper. The emphasis of current work is on selection of a single process concept for further development and scale-up of the process to a size that will address many of the design issues of a large system. This engineering-scale process system is being designed for 20-kg batch size, and fabrication of the process equipment and the containment glovebox are well underway. (authors)