Synthesis of Ca1-xCexZrTi2-2xAl2xO7 zirconolite ceramics for plutonium disposition

Zhong, Min-Xiao; Walkley, Brant; Bailey, Daniel J.; Blackburn, Lewis R.; Ding, Hao; Wang, Shi-Qian; Bao, Weichao; Gardner, Laura J.; Sun, Shi‐Kuan; Stennett, Martin C.; Corkhill, Claire L.; Hyatt, Neil C.

doi:10.1016/j.jnucmat.2021.153198

Cited by 14 publications

(6 citation statements)

References 34 publications

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“…At "x" > 0.15, the 2M polytype is replaced by 4M, which at "x" > 0.6 is displaced by the pyrochlore phase. When studying Pu-containing matrices, cerium is usually used as Pu simulant [97] due to the similar ionic radii of Ce 3+ -Pu 3+ and Ce 4+ -Pu 4+ [98]. According to the data of the review [99], the samples containing tetravalent actinides (An = U/Th/Pu) and cerium CaZr 1−x (Ce/U/Th/Pu) 4+ x Ti 2 O 7 , depending on the value of "x", are composed of zirconolite polytypes 2M, 4M, and (or) pyrochlore (Table 4).…”

Section: Crystal Chemistry Of Zirconolite and Its Polytypementioning

confidence: 99%

“…The study of matrices for the immobilization of plutonium-containing waste continues, for example, in the UK with zirconolite identified as a candidate matrix for Pu [97,99,101,[108][109][110][111][112], separate minor actinides, and whole REE-MA fraction [15,17,88,113]. This is due to the facts that (1) the properties of trivalent REE and MA are similar and they will be separated together into a single fraction during the separation of HLW; (2) in SNF and HLW derived from SNF reprocessing, the relative quantity of REE is 15-20 times greater than that of MA;…”

Section: Crystal Chemistry Of Zirconolite and Its Polytypementioning

confidence: 99%

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Zirconolite Matrices for the Immobilization of REE–Actinide Wastes

et al. 2023

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The structural and chemical properties of zirconolite (ideally CaZrTi2O7) as a host phase for separated REE–actinide-rich wastes are considered. Detailed analysis of both natural and synthetic zirconolite-structured phases confirms that a selection of zirconolite polytype structures may be obtained, determined by the provenance, crystal chemistry, and/or synthesis route. The production of zirconolite ceramic and glass–ceramic composites at an industrial scale appears most feasible by cold pressing and sintering (CPS), pressure-assisted sintering techniques such as hot isostatic pressing (HIP), or a melt crystallization route. Moreover, we discuss the synthesis of zirconolite glass ceramics by the crystallization of B–Si–Ca–Zr–Ti glasses containing actinides in conditions of increased temperatures relevant to deep borehole disposal (DBD).

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Section: Crystal Chemistry Of Zirconolite and Its Polytypementioning

confidence: 99%

Section: Crystal Chemistry Of Zirconolite and Its Polytypementioning

confidence: 99%

Zirconolite Matrices for the Immobilization of REE–Actinide Wastes

et al. 2023

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“…The high solubility of Fe 2 O 3 and Cr 2 O 3 within the zirconolite structure formed the basis to target the use of metallic Fe and Cr (representing a simplified stainless steel) alongside a CeO 2 surrogate fraction. Although the significant differences between Ce and Pu should be acknowledged, particularly in the research topics of their complex ligand formation, radiation, and dissolution response, [27][28][29][30][31][32] Ce served as the most widely used surrogate for both Pu(III) and Pu(IV), 10,21,23,26,[33][34][35][36][37] due to its relative affordability, non-toxicity, and comparable ionic radii corresponding to relevant coordination environment. Regarding the research on material chemistry, the availability of both Ce(III) and Ce(IV) oxidation states made it practical to study mechanisms of element incorporation, phase formation, and defect generation in wasteforms.…”

Section: Introductionmentioning

confidence: 99%

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

Ai,

Sun,

Hao

et al. 2024

J Am Ceram Soc.

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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.

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“…Conventional reactive sintering using component oxides is a common route for the fabrication of ceramic wasteform materials. Whilst the phase assemblage, density and microstructural properties of zirconolite ceramics, as a function of dopants and processing conditions, has been widely studied across a variety of discrete compositions, many samples produced by this sintering route retain moderate porosity [13][14][15]. Pressure-assisted sintering routes such as hot isostatic pressing (HIP) have been proposed as alternative processing routes due to an existing knowledge base from industrial practices [16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Process Development of Zirconolite Ceramics for Pu Disposition: Use of a CuO Sintering Aid

et al. 2023

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Zirconolite-structured ceramics are candidate wasteform materials for the immobilisation of separated Pu. Due to the refractory properties of zirconolite and other titanates, removing residual porosity remains challenging in the final wasteform product when utilising a conventional solid state sintering route. Herein, we demonstrate that the addition of CuO as a sintering aid increases densification and promotes grain growth. Moreover, zirconolite phase formation was enhanced at lower process temperatures than typically required (≥1350 °C). CuO addition allowed an equivalent density to be reached using process temperatures of 250 °C lower than the undoped composition. At 150 °C lower than the undoped zirconolite, the addition of CuO resulted in a favourable microstructure and phase assemblage, as confirmed via X-ray diffraction and scanning electron microscopy. Secondary phases of CaTiO3 and Ca0.25Cu0.75TiO3 were observed at some processing temperatures, which may prove deleterious to wasteform performance. The use of a CuO sintering aid provides an avenue for the further development of the thermal processing of ceramic wasteform materials.

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Synthesis of Ca1-xCexZrTi2-2xAl2xO7 zirconolite ceramics for plutonium disposition

Cited by 14 publications

References 34 publications

Zirconolite Matrices for the Immobilization of REE–Actinide Wastes

Zirconolite Matrices for the Immobilization of REE–Actinide Wastes

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

Process Development of Zirconolite Ceramics for Pu Disposition: Use of a CuO Sintering Aid

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Synthesis of Ca1-xCexZrTi2-2xAl2xO7 zirconolite ceramics for plutonium disposition

Cited by 14 publications

References 34 publications

Zirconolite Matrices for the Immobilization of REE–Actinide Wastes

Zirconolite Matrices for the Immobilization of REE–Actinide Wastes

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

Process Development of Zirconolite Ceramics for Pu Disposition: Use of a CuO Sintering Aid

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