Hot Isostatically Pressed Zirconolite Wasteforms for Actinide Immobilisation

L R Blackburn,M C Stennett,E R Maddrell,S K Sun,C L Corkhill,N C Hyatt,L J Gardner

doi:10.1088/1757-899x/818/1/012010

L R Blackburn, M C Stennett + Show 5 more

Open Access

https://doi.org/10.1088/1757-899x/818/1/012010

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Abstract

In order to demonstrate the deployment of Hot Isostatic Pressing (HIP) for the immobilisation of Pu stocks and residues, a series of active and inactive zirconolite formulations have been processed and characterised. In this instance, Ce, U, and Th have been applied as chemical surrogates for Pu4+. A range of formulations targeting isovalent Zr4+ site substitution (i.e. to simulate CaZr1-xPuxTi2O7) have been processed by HIP and characterised by powder X-ray diffraction, and scanning electron microscopy, in order to determine surrogate partitioning between the host zirconolite phase, and accessory phases that may have formed during the HIP process.

Highlights

The United Kingdom holds a stockpile of civil separated plutonium that is forecast to exceed 140 teHM, subsequent to the completion of domestic reprocessing operations [1]
We report laboratory scale trials for zirconolite wasteforms processed by Hot Isostatic Pressing (HIP)
Refinement of the powder diffraction profile determined that zirconolite-2M was formed as the major crystalline phase – these reflections are indexed by relevant values

Summary

Introduction

The United Kingdom holds a stockpile of civil separated plutonium that is forecast to exceed 140 teHM (tonnes equivalent heavy metal), subsequent to the completion of domestic reprocessing operations [1]. Zirconolite has demonstrated extensive chemical flexibility with regards to feedstock chemistry, and as such is the dominant actinide-bearing phase in the Synroc formulation, developed for the immobilisation of high level waste (HLW) [2]. The preferred final wasteform for Pu would require a robust processing route, insensitive to feed chemistry, with high throughput and waste loading. The HIP process is insensitive to the chemical properties of the feedstock, and produces minimal secondary waste, and is a good candidate thermal treatment for the immobilisation of Pu stocks and residues [5]. We report laboratory scale trials for zirconolite wasteforms processed by HIP. In this instance, CeO2, UO2 and ThO2 were employed as chemical surrogates for PuO2.

Materials synthesis and characterisation

Results

Conclusions