Qu Ai,Shi-Kuan Sun,Peng-Wei Hao,Yuan-Bin Chen,Yi Zhao,Sheng-Heng Tan,Wei-Ming Guo,Hua-Tay Lin
The aqueous reprocessing of spent nuclear fuel generates a considerable amount of plutonium alongside contaminated stainless steel, necessitating meticulous handling for safe decommission and long-term management. The present work investigated the co-immobilization of CeO 2 (as an inactive surrogate for PuO 2 ) with metallic Fe and Cr (representing a simplified stainless steel) within a zirconolite ceramic wasteform, nominally targeting Ca 1− x Ce x ZrTi 2−2 x Fe x Cr x O 7 . After sintering at 1400°C under an air atmosphere, the zirconolite phase constituted 90.8–95.1 wt.% of the product across the solid solution range of 0.05 ≤ x ≤ 0.25, alongside perovskite and baddeleyite secondary phases in varying proportion; no evidence of the unincorporated CeO 2 or metallic and oxidized Fe or Cr were identified. Above x = 0.30 CeO 2 was detected inferring, the solubility limit was reached. A polytype transformation from zirconolite 2M to 3T was confirmed by X -ray diffraction and selected area electron diffraction results, with the relative fraction of the 3T phase gradually increasing to 49.5 wt.% at x = 0.30. Deconvolution of X-ray photoelectron spectroscopy data revealed the partial reduction of Ce 4+ –Ce 3+ , whereas Fe and Cr species maintained trivalent, in agreement with the targeted substitution scheme. Benefitting from the excellent chemical flexibility of zirconolite structured compounds, the co-immobilization approach may be an effective disposal pathway for Pu-containing wastes and contaminated stainless steel residues.
Zirconolite wasteforms were designed for the co-immobilisation of CeO 2 (as a PuO 2 surrogate) and metallic iron, chromium, and aluminum , simulating contaminated FeCrAl alloy cladding. Zirconolite ceramics with the target composition Ca (1-3.87x) Ce 3.87x ZrTi (2-7.73x) Fe 5.73x Cr x Al x O 7 (x = 0–0.11), were synthesised via solid state reaction sintering at 1400 °C. Phase and microstructural evolution were investigated to ensure the oxidation of the metals, formation of zirconolite phase and densification of the final ceramics. It was found that both oxidation and solid-state reaction could be accomplished by processing at 900 °C and 1400 °C under ambient atmosphere, accompanied by the overall yield of zirconolite in the range 92.4–94.0 wt % between x = 0.01–0.07 f.u., with a dense microstructure observed. Polytype transitions from zirconolite-2M to -3T were evidenced, where the solubility limit was reached at substitution level of x = 0.11 and precipitation of CeO 2 was apparent. XPS analysis confirmed that an elevation in dopant concentration resulted in the partial reduction of Ce 4+ to Ce 3+ , whereas Fe, Cr and Al metals were oxidised to the trivalent state. This study demonstrated the feasibility for designing advanced ceramic wasteforms for the co-immobilisation of actinides and metallic cladding residues.
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