Synthesis and characterisation of Ca1-xCexZrTi2-2xCr2xO7: Analogue zirconolite wasteform for the immobilisation of stockpiled UK plutonium

Lewis R Blackburn,Shi-Kuan Sun,Sebastian M Lawson,Laura J Gardner,Hao Ding,Claire L Corkhill,Ewan R Maddrell,Martin C Stennett,Neil C Hyatt

doi:10.1016/j.jeurceramsoc.2020.05.066

Lewis R Blackburn, Shi-Kuan Sun + Show 7 more

Open Access

https://doi.org/10.1016/j.jeurceramsoc.2020.05.066

Copy DOI

Abstract

A series of Ca1-xCexZrTi2-2xCr2xO7 zirconolite ceramics (0 ≤ x ≤ 0.35) were reactively sintered in air at 1350 °C for 20 h. Single phase zirconolite-2M was formed for x ≤ 0.15, with Cr2O3 and an undesirable Ce-bearing perovskite phase present above x = 0.20. Electron diffraction analysis confirmed that the zirconolite-2M polytype was maintained over the solid solution. X-ray absorption near edge structure (XANES) data determined that between 10–20% Ce was speciated as Ce3+, and Cr was present uniformly as Cr3+ with near edge features consistent with occupation of octahedral sites within the zirconolite-2M structure. A sample corresponding to x = 0.20 was processed by reactive spark plasma sintering (RSPS), with a rapid processing time of less than 1 h. XANES data confirmed complete reduction to Ce3+ during RSPS, promoting the formation of a Ce-bearing perovskite, comprising 19.3 ± 0.4 wt. % of the phase assemblage.

Highlights

The safe handling and conditioning of highly radioactive materials derived from nuclear fuel reprocessing operations is an issue of scientiic and socioeconomic importance
It was determined from powder X-ray difraction data (Fig. 1) that zirconolite-2M crystallised as the major phase for each composition in the range 0 ≤ x ≤ 0.35
The densiication achieved by a cold-press and sinter method was poor, and this is not a practical choice of solid solution for Pu4+ immobilisation from the perspective of the ceramic microstructure, despite the eicacy of Cr as a charge compensator

Summary

Introduction

The safe handling and conditioning of highly radioactive materials derived from nuclear fuel reprocessing operations is an issue of scientiic and socioeconomic importance. In the United Kingdom, a large stockpile of separated civil plutonium oxide (PuO2) has amassed from spent fuel reprocessing via the PUREX (Plutonium-Uranium-ReductionExtraction) process [1]. This stockpile is forecast to peak at 140 teHM (tonnes of heavy metal equivalent), following cancellation of the Fast Neutron Reactor programme in 1994, which has led to the need for other Pu management strategies, for example reuse as mixed oxide (U, Pu)O2 (MOX) fuel in light water reactors [2]. An alternative approach is the conditioning of the Pu stockpile and waste material via immobilisation within a ceramic matrix

Objectives

Results

Conclusion