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)O-7 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 Kr-36(+) (2 MeV) ions at fluences of 1 x 10(14) and 5 x 10(15) cm(-2) and He-4(+) (200 ke) ions at fluences of 1 x 10(14), 5 x 10(15) and 1 x 10(17) 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 Kr-36(+) fluence rendered the zirconolite completely amorphous. Similarly, evidence of helium accumulation was only seen at the highest He-4(+) fluence (1 x 10(17) 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. (C) 2010 Elsevier B.V. All rights reserved.