Synroc-C containing 10wt% simulated PW-4b-D HLW including 0.62 wt% 239Pu was
subjected to MCC-1 type leach tests at 70°C in deionised water, silicate and
carbonate leachates for 53 d and deionised water for 2472 d. The normalised
total (i.e. unfiltered leachate + vessel wall) Pu leach rates in deionised
water, silicate and carbonate leachates for periods up to 53 d were found to
be of the order of 10-5, 10-4 and 10-4 g
m-2 d-1 respectively. After 2472 d, the
differential, normalised, Pu leach rate in deionised water dropped to ∼5 ×
10-6 (total) and ∼5 × 10-8 (solution - after
filtration through a 1000NMW filter) g m-2 d-1. SEM
and AEM were used to characterise our starting material and investigate the
secondary phases on the surfaces of leached Synroc-C discs. Calculated and
measured normalised Pu leach rates are compared and the partitioning of Pu
between zirconolite and perovskite is discussed.