THERMAL RECOVERY OF SELF-RADIATION DAMAGE IN URANINITE AND THORIANITE

Thermal recovery studies on single crystals of naturally self-irradiat ed uraninite and thorianite, (U, Th)O2, have indicated lattice expansi on of congruent-to 0.5%, which is greater by a factor of congruent-to 5 from lattice dilatation in < 100-degrees-C reactor-irradiated UO2 an d ThO2, and by a factor of congruent-to 1.6 from saturated lattice dil atation in self-irradiated PuO2, AmO2 and CmO2. Mineral alpha-decay-in duced lattice expansion is partly controlled by radiogenic Pb. Micro s train in uraninite and thorianite, congruent-to 0.3%, is twice the str ain in fission-damaged UO2. These ancient minerals simulate the correc t material, radiation and the extended time scale for the production o f structural damage in actinide-containing UO2 and ThO2 wastes. Thus, depending on the nature and abundance of impurity elements, long-term accumulation of alpha-decay damage in unreprocessed, spent nuclear rea ctor fuel elements may cause about 1 to 2.5% macroscopic volume expans ion, that may cause microfracturing and thereby enhanced leachability of the primary UO2/ThO2 waste containment.