Pd‐catalyzed surface reactions of importance in radiation induced dissolution of spent nuclear fuel involving H${}_2$

To assess the influence of metallic inclusions (ϵ‐particles) on the dissolution of spent nuclear fuel under deep repository conditions, Pd‐catalyzed reactions of H${}_2$O${}_2$, O${}_2$ and UO${}_2$${}^{2+}$ with H${}_2$ were studied using Pd‐powder suspensions. U(VI) can efficiently be reduced to less soluble U(IV) on Pd‐particles in the presence of H${}_2$. The kinetics of the reaction was found to depend on the H${}_2$ partial pressure at p${}_{H2}$≤5.1×10${}^{-2}$ bar. In comparison, the H${}_2$ pressure dependence for the reduction of H${}_2$O${}_2$ on Pd also becomes evident below 5.1×10${}^{-2}$ bar. Surface bound hydroxyl radicals are formed as intermediate species produced during the catalytic decomposition of H${}_2$O${}_2$ on oxide surfaces. While a significant amount of surface bound hydroxyl radicals were scavenged during the catalytic decomposition of H${}_2$O${}_2$ on ZrO${}_2$, no scavenging was observed in the same reaction on Pd. This indicates a different reaction mechanism for H${}_2$O${}_2$ decomposition on Pd compared to metal oxides and is in contrast to current literature. While Pd is an excellent catalyst for the synthesis of H${}_2$O${}_2$ from H${}_2$ and O${}_2$, a similar catalytic activity that was previously proposed for ZrO${}_2$ could not be confirmed. (© 2019 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)