Inhibition of radiation induced dissolution of UO2 by sulfide – A comparison with the hydrogen effect

Abstract

In this work we have studied the influence of H2S on radiation induced dissolution of spent nuclear fuel using simple model systems. The reaction between H2O2 and H2S/HS− has been studied experimentally as well as the effect of H2S/HS− on γ-radiation induced dissolution of a UO2 pellet. The experiments clearly show that the reaction of H2O2 and H2S/HS− is fairly rapid and that H2O2 and H2S/HS− stoichiometry is favorable for inhibition. Radiolysis experiments show that H2S/HS− can effectively protect UO2 from oxidative dissolution. The effect depends on sulfide concentration in combination with dose rate. Autoclave experiments were also conducted to study the role of H2S/HS− in the reduction of U(VI) in the presence and absence of H2 and Pd particles in anoxic aqueous solution. The aqueous solutions were pressurized with H2 or N2 and two different concentrations of H2S/HS− were used in the presence and absence of Pd. No catalytic effect of Pd on the U(VI) reduction by H2S/HS− could be found in N2 atmosphere. U(VI) reduction was found to be proportional to H2S/HS− concentration in H2 and N2 atmosphere. It is clearly shown the Pd catalyzed H2 effect is more powerful than the effect of H2S/HS−. H2S/HS− poisoning of the Pd catalyst is not observed under the present conditions.