Dose Rate Effects on the Accumulation of Radiation Damage

During storage, spent fuel and other waste forms accumulate alpha-decay damage (and He). The dose rates and the temperatures experienced during storage are lower than during in-pile operation: however, the duration of the storage is much longer (of the order of up to a few hundred years if extended interim storage concepts are considered); if final disposal in the repository is considered, the time interval in which radiation damage accumulates is open-ended. In order to simulate within timeframes suitable for laboratory experiments long-term accumulation of alpha-decay damage, the so-called alpha-doped materials can be used, i.e. materials loaded with short-lived alpha-emitters (like e.g. Pu-238, U-233, etc.). The question is often posed if the accelerated accumulation of decay damage and He obtained using alpha-doped materials does cause some artefact related to the rate of accumulation rather than by the integrated dose. This work presents evidence that, at least within the range of alpha-activities considered, there is no dose rate effect. By comparing property evolution as a function of accumulated dpa for alpha-doped materials with activities of ∼1010 and ∼108 Bq/g, respectively, the same trends and levels of alteration are observed. In particular, macroscopic properties like hardness (measured by Vickers indentation) or swelling (evolution of lattice parameter derived from XRD), and microstructural formation and accumulation of defects in the lattice of the alpha-doped material are investigated, showing a remarkable similarity of behaviour vs. dpa independently not only from the dose rate, but also from the composition (namely, Pu and U are considered).