PNNL

Abstract

This is the second of two papers on the results of radiation-induced damage accumulation in titanate ceramics that potentially could be used for weapons grade plutonium disposition. In the first paper we discussed the results from pyrochlore (betafite) based ceramics. In this paper, we discuss the effects of radiation-induced damage on the density and crystal structure of a nominally phase-pure zirconolite and two other zirconolite-bearing ceramics from the alpha decay of 238Pu. Macro (bulk) and micro (X-ray diffraction) swelling were found to be temperature independent, whereas the density determined with He gas pycnometry was temperature dependent. It took approximately 740 days (2.6?1018 a/g) for the specimens to become X-ray amorphous—longer for the swelling to saturate. Unlike what we observed for the pyrochlore-based ceramics, we did not observe any phase changes associated with storage temperature and damage ingrowth. The forward dissolution rate at a pH value of 2 for material containing essentially all zirconolite is 1.7(4)?10-3 g/(m2?d). Very little pH dependence was observed for zirconolite specimens and, like we observed for the pyrochlore-bearing ceramics in this study, there was no dependence on the amount of radiation-induced damage. As with the pyrochlore, these materials did not become substantially friable with increasing radiation-induced damage. Even after the radiation-induced swelling saturated, the specimens remained physically intact with no evidence for microcracking. Thus, the material remains physically a viable material for the disposition of surplus weapons-grade Pu.