Krypton and helium irradiation damage in neodymium–zirconolite

A leading candidate for the immobilisation of actinides, zirconolite’s suitability as a potential ceramic host for plutonium disposition, both in storage and geological disposal, has been the subject of much research. One key aim of this study is to understand the effects of radiation damage and noble gas accommodation within the zirconolite material. To this end, a series of ex situ irradiations have been performed on polycrystalline (Ca0.8Nd0.2)Zr(Ti1.8Al0.2)O7 zirconolite samples. Zirconolite samples, doped with Nd3+ (as a Pu surrogate) on the Ca-site and charge-balanced by substituting Al3+ onto the Ti-site, were irradiated with 36Kr+ (2 MeV) ions at fluences of 1 × 1014 and 5 × 1015 cm−2 and 4He+ (200 keV) ions at fluences of 1 × 1014, 5 × 1015 and 1 × 1017 cm−2 to simulate the impact of alpha decay on the microstructure. Microstructural analysis revealed no damage present at the lower Kr+ fluence, but that the higher 36Kr+ fluence rendered the zirconolite completely amorphous. Similarly, evidence of helium accumulation was only seen at the highest 4He+ fluence (1 × 1017 cm−2). Monte Carlo simulations using the TRIM code predict the highest concentration of helium accumulating at a depth of 720 nm, in good agreement with the experimental observations.