Fission fragment damage in crystalline phases possibly formed in solidified radioactive waste

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Abstract
Radiation damage induced by fission fragments has been studied qualitatively, mainly by powder X-ray diffraction, in several crystalline phases which might occur in radioactive waste solidified by ceramic methods. The phases were synthesized by ceramic techniques and contained depleted or enriched uranium. Reactor irradiation induced fission fragment damage. Oxides such as MgO, α-AI2O3, Fe2O3, ThO2, Y2O3-stabilized ZrO2, and Y2O3 did not show observable structural changes after irradiation with 1015–1016 fission events cm-3.However CaTiO3 CaZrTi2O7, LaPO4, CePO4, ThSiO4 (huttonite), ZrSiO4 and YPO4, all phases which could incorporate actinides, were rendered amorphous after irradiation with 1015-1016 fission events-cm−3. After similar irradiations, TiO2 (rutile) and three of four uranates observed as minor phases, namely U3O8, Sr2U3O11 and MgUO4, were also rendered amorphous; Y2O3-nUO3 (n=l/3 or 2/3) was not noticeably affected. Virtually no structural effects were observed at lower fluences of ∼1014 fission events-cm−3 for SrMoO4, BaAl2TisO14, SrAl2Si2O8 and Ca2La8 (SiO4)6O2. Preliminary studies were made of the action of deionized water at 200°C on unirradiated and X-ray amorphous (irradiated) CaZrTi2O7, CePO4, ThSiO4 (huttonite) and YPO4. The irradiated huttonite and xenotime showed enhanced alteration effects relative to the unirradiated materials, but this was not the case for zircono-lite or monazite. These results are discussed from an atomistic aspect where possible and the relevance of the results to solidified radioactive wastes pointed out.

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