Effect of alpha-radiolysis on the dissolution of UO2 doped with alpha emitters under anoxic conditions

The α emissions constitute almost entirely the radiation field of spent nuclear fuel after 500 years in a geological repository. In this work the effect of α-radiolysis on the fuel dissolution in the near field was studied. Pellets of UO2 doped with 10% wt. and 0.1% wt. of ''238 Pu (α-emitter) were prepared using a solgel method which provides homogenous distribution of the dopant in the UO2 matrix. The sintered materials were extensively characterized. Static leaching tests on these materials were carried out under anoxic conditions in deaerated water at room temperature. The results show that the uranium release from the matrix increase for the higher dopant concentration. Under the experimental conditions used it was difficult to observe a clear radiolysis effect on dissolution of the material containing 0.1% wt. of ''238 Pu. In order to study the radiation damage due to α decay in the fluorite type lattice of the UO2, the variation of the lattice parameter as a function of time was measured. An increase of the lattice parameter of approx 0,2% was observed after 1,5 months of storage in the UO2 doped with 10% wt. of plutonium. In the case of the UO2 doped with 0,1% wt. ''238 Pu, the lattice parameter did not vary significantly during the same time interval. The possible effects of damage accumulation on UO2 dissolution are discussed. (Author) 7 refs