Mechanisms and kinetics of leaching of UO(2) in water
Interaction of UO(2) with water leads to the formation of nonstoichiometric oxides and is of interest both in mineralogy and for the envisaged technique of disposal of spent nuclear fuel elements in deep geological repositories. In the present study, UO(2) single crystals and sinters were leached in distilled water between room temperature and 200 C, for time periods between about 1 and 1000 h. Rutherford backscattering of 2 MeV He(+) ions, with and without the channelling effect technique, was used to determine the thickness and O/U-ratio of the surface layers, and elastic recoil detection analysis (ERDA) was used to measure the hydrogen concentration of the surface layers. Following a first formation of thin layers of essentially water-free oxides of compositions between U(3)O(7) and U(2)O(5), thick layers of UO(3).nH(2)O were formed at temperatures above about 150 C. The value of n was low, indicating that the expected equilibrium composition of schoepite was either not formed or that schoepite was not covering all of the surface. Islands of basaltic-type crystals of redeposited uranium oxide were also found. The kinetics of U(3)O(7) or U(2)O(5) layer formation were controlled either by the reaction at the UO(2)/U(3)O(7)-U(2)O(5) interface or by oxygen diffusion through the oxidised layer, depending on the temperature.
Bibliographic Reference: Paper presented: International Conference on Non-Stoichiometric Compounds, Tokyo (JP), Dec. 3-5, 1990
Availability: Available from (1) as Paper EN 35890 ORA
Record Number: 199110128 / Last updated on: 1994-12-02
Original language: en
Available languages: en