Synthesis and study of 239Pu-doped ceramics based on zircon, (Zr,Pu)Sio4, and hafnon, (Hf,Pu)SiO4

Zircon, ZrSiO(4), as well as its Hf-analogue hafnon, HfSiO(4), have been proposed for use as durable Pu host phases for the immobilization of weapons grade Pu and other actinides. Four samples of Pu-doped ceramics based on the zircon and hafnon structures were synthesized through sintering in air using precursors containing 5-6 and 10 wt% (239)Pu. Synthesized ceramic samples were studied by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), microprobe method, MCC-1 leach test at 25 and 90 degreesC. Inclusions of separated a PuO(2) phase in the matrix of zircon-based ceramic and presumably, (Pu,Hf)O(2) phase in the hafnon-based ceramic were observed for samples obtained from precursors doped with 10 wt% Pu. No separated Pu-phases in significant amounts were identified in the matrices of both ceramics obtained from the precursors doped with 5-6 wt% Pu. It was found that normalized Pu mass losses (without correction on ceramic porosity) for samples doped with 10 wt% Pu which contain separated inclusions of PuO(2) or (Pu,Hf)O(2) after 14/28 days were approximately (in g/m(2)) - for zircon: 0.2/0.2 - at 90 degreesC and 0.03/0.04 - at 25 degreesC and for hafnon: 0.02/0.04 - at 90 degreesC and 0.01/0.01 - at 25 degreesC. The losses of Pu from samples doped with 5-6 wt% are 1-2 order of magnitude less. It was suggested that optimal amount of Pu which could be incorporated by zircon and hafnon lattices does not exceed 7 wt%. An important additional conclusion is that Pu-doped ceramic based on zircon or hafnon can be successfully fabricated excluding hot pressing method.