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

Abstract

The production of H 2 in the γ-ray and 5 MeV helium ion radiolyses of water adsorbed on 0.4 and 1 μm particles of UO 2 has been examined. The yields of H 2 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 CeO 2 particles. Radiation chemical yields of H 2 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 H 2 per 100 eV energy directly absorbed by four layers of water on UO 2 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 UO 2 have been combined with data on ZrO 2 and CeO 2 to give H 2 yields for a wide range of water loading. H 2 is mainly produced from chemisorbed water in the γ-radiolysis of ZrO 2, and its yield decreases in the presence of O 2 to values comparable to those for UO 2 and CeO 2 . The yields of H 2 in the 5 MeV helium ion radiolysis of water on UO 2, CeO 2, and ZrO 2 are similar, indicating that these materials may be suitable for estimating H 2 production in transuranic waste.