Co‐immobilization of a PuO₂ surrogate and contaminated stainless steel within a zirconolite matrix

Abstract

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 CeO2 (as an inactive surrogate for PuO2) with metallic Fe and Cr (representing a simplified stainless steel) within a zirconolite ceramic wasteform, nominally targeting Ca1−xCexZrTi2−2xFexCrxO7. 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 CeO2 or metallic and oxidized Fe or Cr were identified. Above x = 0.30 CeO2 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 Ce4+–Ce3+, 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.