On Mo-Ru-Tc-Pd-Rh-Te alloy particles extracted from spent fuel and their leaching behavior under Ar and H-2 atmospheres

In the present work. we extracted Mo-Tc-Ru-Pd-Rh-Te alloy particles from spent fuel by a non-oxidative selective leaching of the fuel matrix, characterized them and studied their leaching behavior under different redox conditions. After selecting the optimal experimental conditions by using a synthetic alloy, the radioactive alloy particles were extracted from spent fuel and characterized by using SEM (scanning electron rnicroscopy)-WDS (wavelength dispersive spectra). Micrometer sized alloy particles display very similar compositions, on average (wt. %): 32.7% Mo, 40.5% Ru, 7% Tc, 4.4% Rh, 12.2% Pd and 3.8% Te. The alloy particles were leached in 10 mM NaCl and 2 mM NaHCO3 solutions, purged with two kinds of gas mixtures. It was observed that, under purging with Ar + 0.03% CO2, the leaching rates of Tc-99 and Mo-100 were similar, about 1.5 ppb/day. The results obtained under purging with 89.97% Ar + 0.03% CO2 + 10% H-2 indicate that the 4d alloy particles are very effective catalysts for reduction caused by hydrogen: the concentrations of Tc-99 and Mo-100 dropped to levels below 1 ppb. No significant leaching of Ru, Rh, Pd and Te was observed during purging with both gas mixtures.