Separation of Cesium and Strontium from Residues Arising from Fluoride Volatility Processing of Spent Nuclear Fuel

Abstract:

The overall objective of this study was to support an alternative hybrid process to meet Advanced Fuel Cycle Initiative goals, using fluorination and aqueous processing techniques, for treatment of spent nuclear fuel (SNF). The specific goal was to develop a simple aqueous dissolution process to separate two high-heat fission products, cesium and strontium, from SNF fluoride residues. This separation was based on solubility differences examined by modeling using the HSC Chemistry 5.0 program. HSC automatically utilizes an extensive thermochemical database, which contains enthalpy (H), entropy (S), and heat capacity (C) data for more than 17,000 chemical compounds. The work focused on the fluoride residues from the voloxidation and fluorination steps of the fluoride volatility process and was limited to SNF from commercial light-water reactors. Material balances were used to estimate the quantity of residue. A representative SNF was considered to be one with a bumup of 33,000 megawatt days per metric ton initial heavy metal after a 10-yr cooling period, from a pressurized-water reactor. The dry fluorination method was used for uranium removal. The work described in this paper is based solely on computer modeling, which will serve as the basis for any necessary follow-on laboratory validation experiments. Observations from this study showed that water dissolution provided adequate separation of cesium from the fluoride residues but only negligible separation of strontium with cesium. After removal of cesium, a second separation with water provided little additional removal of strontium. For disposal purposes, it would be reasonable to dispose of cesium and strontium together. Therefore, more research is needed to examine the possibility of converting all fluoride residues to hydroxides to increase the solubility of strontium.