H₂ Production in the Radiolysis of Water on UO₂ and Other Oxides

The production of H2 in the γ-ray and 5 MeV helium ion radiolyses of water adsorbed on 0.4 and 1 μm particles of UO2 has been examined. The yields of H2 determined with respect to the total energy deposited in the oxide−water system is 0.016 molecule/100 eV, which is about the same as similarly sized CeO2 particles. Radiation chemical yields of H2 increase substantially with decreasing number of adsorbed water layers when the yield is determined with respect to the energy deposited directly by γ-rays in the water. A yield of about 40 molecules of H2 per 100 eV energy directly absorbed by four layers of water on UO2 compared to 0.45 molecule/100 eV in bulk liquid water strongly suggests that energy is being transported from the oxide through the water interface. The results with UO2 have been combined with data on ZrO2 and CeO2 to give H2 yields for a wide range of water loading. H2 is mainly produced from chemisorbed water in the γ-radiolysis of ZrO2, and its yield decreases in the presence of O2 to values comparable to those for UO2 and CeO2. The yields of H2 in the 5 MeV helium ion radiolysis of water on UO2, CeO2, and ZrO2 are similar, indicating that these materials may be suitable for estimating H2 production in transuranic waste.