38,39 The radiation effects recover upon annealing to room temperature, a few percent of the damage remaining. Of course this is also reflected in other properties such as electrical resistivity. In contrast, the (Ti-stabilised) β phase shows a slight, and the (Al-stabilised) δ phase a substantial contraction, the latter saturating at 15 vol%. 35,36Īs discussed by Hecker and Martz 37 the expansion of the lattice of α-Pu is significant due to self-irradiation, when held at cryogenic temperatures, saturating at about 10 vol%.
34 In addition to the radiation damage, helium ingrowth takes place, leading to the formation of pressurized helium gas bubbles, which coalesce with time (aging of the material) and at elevated temperature. Computer simulations of the radiation effects in fcc plutonium have shown that the defect recombination stage is much longer than in other metals and that the vacancies do not seem to form clusters. 33 Although recombination will take place, point defects and eventually extended defects (dislocations, dislocation loops) will survive in the crystal lattice, resulting in changes in the properties of the materials. The α particle has a path of about 10 µm, with a cascade of about 265 displacements at the end of its range. The recoil atom produced has a range of about 12 nm, and causes a dense collision cascade with typically about 2300 displacements (Frenkel pairs) within a short distance, around 7.5 nm in size.
The α-decay of the actinides taking place in the crystal lattice creates an alpha particle and a recoil atom. Jean-Christophe Griveau, in Comprehensive Nuclear Materials (Second Edition), 2020 7.01.3.4 Effects of Radiation 23 The studies on α-damage also at determining the long-term evolution of spent nuclear fuel during storage and more specifically what has to be expected from its integrity or behavior against corrosion on contact with water. 20–22 The formation of point defects and their evolution into extended defects, and also the consequences on the UO 2 lattice (e.g., lattice swelling) and on the modification of thermophysical properties have been assessed. The effects of α-damage in UO 2 have been studied for decades either by external irradiations with α-particles or heavy ions simulating the recoil nucleus 19 or by doping UO 2 with strong α-emitters (e.g., 238Pu). Source: © European Atomic Energy Community. Fraction of energy lost by elastic (nuclear)/inelastic collisions (electronic)
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