Towards a Single Host Phase Ceramic Formulation for UK Plutonium Disposition
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Towards a Single Host Phase Ceramic Formulation for UK Plutonium Disposition Martin C. Stennett1, Neil C. Hyatt1, Matthew Gilbert2, Francis R. Livens2, and Ewan R. Maddrell3 1 Immobilization Science Laboratory, Department of Engineering Materials, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD, UK. 2 Centre for Radiochemistry Research, School of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL. 3 Nexia Solutions Ltd., Sellafield, Seascale, Cumbria, CA20 1PG, UK ABSTRACT The UK has a considerable stockpile of separated plutonium; a legacy of over 50 years of civilian nuclear programmes. This material has been considered both as an asset for future energy generation and a liability due to the proliferation threat. A proportion of the PuO2 stocks may be consumed by nuclear fission, in mixed oxide (MOx) or inert matrix (IMF) fuels but a quantity of waste PuO2 will remain which is unsuitable for fuel manufacture and will require immobilisation. A research program is currently underway to investigate the potential of various single phase ceramic formulations for the immobilisation of this waste PuO2 fraction. In this work a number of synthetic mineral systems have been considered including titanate, zirconate, phosphate and silicate based matrices. Although a wealth of information on plutonium disposition in some of the systems exists in the literature, the data is not always directly comparable which hinders comparison between different ceramic hosts. The crux of this research has been to compile a database of information on the proposed hosts to allow impartial comparison of the relative merits and shortcomings in each system. INTRODUCTION The potential for utilising ceramic matrices to immobilise radioactive waste has been recognised for many decades. Ringwood et al. [1] first developed SYNROC (SYNthetic Rock) in the late 1970’s as a multiphase ceramic alternative to borosilicate glass for the immobilisation of high level radioactive waste arising from reprocessing of light water reactor fuel. In the mid 1990’s a research program was initiated to look at SYNROC based options for disposal of separated plutonium [2]. A multiphase pyrochlore-rich variant of SYNROC was developed to incorporate plutonium and the significant levels of feedstock impurities in the wastestream. Whilst composite ceramics are required for wastestreams with a variety of constituent elements, a number of single host phase ceramic options have been highlighted for pure actinide wastestreams [3-5]. The remit of this research was to evaluate the various ceramic options for the immobilisation of ‘pure’ PuO2 containing only actinide impurities arising as a result of the decay of the shorter lived plutonium isotopes. This allowed the focus of the work to be aimed at single host phase ceramic formulations.
WASTEFORM SELECTION Research into the partitioning behaviour of multiphase wasteforms such as SYNROC [6] and the study of naturally occurring actinide bearing minerals [7] has lead to a ran
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