Chemical Feasibility of Nuclear Poisons in Uranium-Thorium Fuel Processing Systems

Laboratory experiments have demonstrated the chemical feasibility of incorporating soluble salts of the neutron poisons boron, cadmium, samarium, and gadolinium in solutions associated with the processing of Consolidated Edison reactor fuel (stainless steel-clad 96% ThO₂-4% highly enriched UO₂). At room temperature at least 0.3 M boron or neutron cross section equivalent is soluble in the 6 M H₂SO₄ decladding solution or Thorex dissolvent (13 M HNO₃-0.04 M F-0.1 M Al(NO₃)₃. None of the poisons were volatilized to a significant extent (i.e., <6%) during evaporation for fuel adjustment. Distribution coefficients obtained in batch extraction tests indicated low extraction of these nuclear poisons from nitrate solutions by TBP in Amsco. Single-cycle countercurrent batch extractions with the acid Thorex flowsheet, which uses 30% TBP, gave decontamination factors from uranium for boron, cadmium, and rare earths of ≧1 × 10⁴, > 1.5 × 10³, and > 10⁴, respectively. Countercurrent batch extractions with 2.5% TBP in Amsco resulted in concentrations of boron, rare earths, and cadmium in the uranium product which were at the limits of analytical detection, i.e., 2.5, <4, and <17 ppm, respectively. Two cycles of extraction should decrease the concentration of the nuclear poisons to acceptable levels for fuel recycle.