Abstract
Reactive spark plasma sintering has been utilised as a high-throughput processing route for the synthesis of two simulant zirconolite wasteform materials, targeting Ca0.80Ce0.20ZrTi1.60M0.40O7 (M = Fe3+ and Al3+). Materials were processed under 15 MPa uniaxial pressure, with heating/cooling rates of 100 °C/min to 1320 °C, maintained under vacuum. Despite moderate yield (> 80 wt%) of zirconolite-2M, a considerable Ce-rich perovskite phase was formed in both formulations, attributed to complete reduction of the Ce inventory to Ce3+, as determined by Ce L3-edge XANES analysis. The composition charge balanced with Al3+ was favoured on the basis of lower accompanying perovskite fraction.Graphical abstract
Highlights
A strategy combining reuse, immobilisation and disposal has been proposed as a long-term solution for at least some portion of the United Kingdom civil P uO2 inventory, which is forecast to reach ~ 140 teHM once domestic reprocessing operations cease [1]
The simultaneous synthesis and consolidation of ceramic materials via RSPS are achieved by rapid DC current pulsing through a compressed powder compact, maintained under uniaxial pressure
Analysis of powder X-ray diffraction (XRD) data (Fig. 2) revealed, for both Al3+ and F e3+-doped compositions, intense reflections consistent with the zirconolite-2M polytype occupying the dominant fraction of the phase assemblage
Summary
A strategy combining reuse, immobilisation and disposal has been proposed as a long-term solution for at least some portion of the United Kingdom civil P uO2 inventory, which is forecast to reach ~ 140 teHM (tonnes equivalent heavy metal) once domestic reprocessing operations cease [1]. On the basis of high chemical durability and radiation stability, crystalline titanate materials (including hollandite, pyrochlore, perovskite, brannerite and zirconolite) are suitable phases for the sequestration of partitioned. With Ce utilised as a surrogate for Pu, reactive spark plasma sintering (RSPS) has been deployed as a high-throughput synthesis route to fabricate zirconolite ceramics with the formulation Ca0.80Ce0.20ZrTi1.60M0.40O7 where M = Fe3+ or Al3+. The simultaneous synthesis and consolidation of ceramic materials via RSPS are achieved by rapid DC current pulsing through a compressed powder compact, maintained under uniaxial pressure. This allows the production of monoliths of near theoretical density, even in short processing times, due to heating/cooling rates typically of the order 100 °C/min [11]. The process has previously been demonstrated as suitable for the effective immobilisation of 129I in lead vanadophosphate iodoapatite Pb10(VO4)4.8(PO4)O1.2I2) [12], Cs in hollandite (nominally BaAl2Ti6O16) [13], and more recently Ce in zirconolite [9]
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