AVS 50th International Symposium
    Surface Science Thursday Sessions
       Session SS-ThA

Paper SS-ThA4
Thermal and Radiation-Induced Chemistry of Water on Uranium Dioxide Surfaces

Thursday, November 6, 2003, 3:00 pm, Room 328

Session: Oxide Reactions and Catalysis
Presenter: S.A. Joyce, Los Alamos National Laboratory
Authors: J. Stultz, Los Alamos National Laboratory
M.T. Paffett, Los Alamos National Laboratory
S.A. Joyce, Los Alamos National Laboratory
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Most plans for the disposition of surplus nuclear materials involve storage in sealed containers where the evolution of gases from reactions of adsorbed water could present both pressure and flammability hazards. In order to better understand the relative importance of the thermal- and radiation-induced chemistry, we have studied the interactions of water on single crystals of uranium dioxide. Temperature programmed desorption and electron stimulated reaction/desorption are used to examine the chemistry. In the absence of radiation, water adsorbs/desorbs molecularly on nominally pristine oxide surfaces with a binding energy of only a few kcal/mole greater than water with itself. The strength of this interaction is large enough to indicate that UO@sub 2@ surfaces handled outside the driest of environments will be covered with water. External low energy electron irradiation is used to simulate the effects of radiolytic chemistry induced by decay particles. The principle neutral gaseous radiolytic products are H@sub 2@, O@sub 2@, and water. The relative yields are strongly dependent on temperature and coverage. Ion desorption, which is often sensitive to minority species, indicates that surface hydroxyls, presumably formed at defect sites, are stable up to high temperatures (~ 600K).