Thermal recovery of lattice constant and strain in naturally-damaged (Th,U)O2

One of the prominent options considered for long-term disposal of spent nuclear reactor UO2 and future ThO2 fuels is direct burial of unreprocessed burnt fuel elements in deep underground repositories. A potential hazard associated with burial of radioactive wastes in geological strata is leaching of the contained radionuclides by ground water and their subsequent transport and dispersion by the water flow. Moreover, there is concern that accumulation of radiation damage, caused by the intensive radioactive decay within the waste, will significantly increase the leachability of the wasteforms. Of particular importance is the atomic displacement damage created by nuclear stopping of energetic particles. The present investigation is concerned with long-term radiation effects from alpha decay in ancient specimen of mineral thorianite, (Th,U)O2. The mineral has been subjected, since its formation, to radiation from the decay of 232Th,238U,235U and their many intermediate decay products, and may be considered, therefore, as natural analog of UO2 and Th2 wastes. (author)