Investigation of radiation swelling in the zirconium-hydrogen system

Conclusions

The radiation swelling of the hydrides ZrH_1.78−ZrH_1.90 at a temperature of 50°C is due to the accumulation of zirconium vacancies and their fine pile-ups. At 430–560°C, swelling is determined by the accumulation of fine (∼10Å) vacancy complexes. In this case, micropores are also formed, with a diameter of 50 Å, but their total volume does not exceed one-tenth of the macroswelling.

The considerable buildup of vacancies in the hydrides studied is related with the substructure of the ε hydride, formed by dislocation voids and the boundaries of twins, which promote an increase of concentration and dispersivity of the injection sinks or themselves serve as these sinks. In samples of the δ hydride obtained by dehydrogenation of the ε phase, the numerous dislocations remaining in the δ hydride after decay of the ε-phase substructure obviously fulfill this function. The weak tendency of the zirconium vacancies in the hydride to amalgamation in the pores during increased irradiation temperature (by comparison with the behavior of vacancies in metals) is explained by the reduction of their surface energy as a result of interaction with hydrogen atoms.

The displacement of hydrogen atoms from the tetrahedral positions during irradiation and their return during annealing changes the periods of the crystal lattice of ε zirconium hydride in the same way as the change of hydrogen content, which enables the number of defects of the hydrogen sublattice to be estimated.