H2 inhibition of radiation induced dissolution of spent nuclear fuel

In order to elucidate the effect of noble metal clusters in spent nuclear fuel on the kinetics of radiation induced spent fuel dissolution we have used Pd particle doped UO ₂ pellets. The catalytic effect of Pd particles on the kinetics of radiation induced dissolution of UO ₂ during γ-irradiation in HCO 3 - containing solutions purged with N ₂ and H ₂ was studied in this work. Four pellets with Pd concentrations of 0%, 0.1%, 1% and 3% were produced to mimic spent nuclear fuel. The pellets were placed in 10 mM HCO 3 - aqueous solutions and γ-irradiated, and the dissolution of UO 2 2 + was measured spectrophotometrically as a function of time. Under N ₂ atmosphere, 3% Pd prevent the dissolution of uranium by reduction with the radiolytically produced H ₂, while the other pellets show a rate of dissolution of around 1.6 × 10 ⁻⁹ mol m ⁻² s ⁻¹. Under H ₂ atmosphere already 0.1% Pd effectively prevents the dissolution of uranium, while the rate of dissolution for the pellet without Pd is 1.4 × 10 ⁻⁹ mol m ⁻² s ⁻¹. It is also shown in experiments without radiation in aqueous solutions containing H ₂O ₂ and O ₂ that ϵ -particles catalyze the oxidation of the UO ₂ matrix by these molecular oxidants, and that the kinetics of the catalyzed reactions is close to diffusion controlled.