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0985-NN04-02

An Evaluation of Single Phase Ceramic Formulations for Plutonium Disposition Martin C. Stennett1, Ewan R. Maddrell2, Charlie R. Scales2, Francis R. Livens3, Matthew Gilbert3, and Neil C. Hyatt1 1 Engineering Materials, University of Sheffield, Mappin Street, Sheffield, S1 3JD, United Kingdom 2 Nexia Solutions Ltd., Sellafield, Seascale, CA20 1PG, United Kingdom 3 Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL, United Kingdom ABSTRACT Ceramics are promising potential hosts for the immobilization of actinide containing wastes. Work has been reported in the literature on multiphase systems, such as SYNROC [1], and on single phase systems such as pyrochlores [2] and zirconia [3], but assessment of the different wasteforms by direct comparison of literature data is not always easy due to the different processing and fabrication routes employed. In this study a potential range of different ceramic systems were investigated for plutonium disposition using the same processing scheme. Durable actinide containing minerals exist in nature and provided excellent target phases for the titanate, zirconate, silicate and phosphate based formulations examined here [4]. The Ce solid solution limits for each particular substitution mechanism were established and the processing parameters required to produce high quality ceramic specimens were optimised. Importantly, this was achieved within the constraints of a generic processing route suitable for fabrication of Pu bearing samples. INTRODUCTION A legacy of civilian and military nuclear programmes is a considerable stockpile of separated PuO2. This material is considered both an asset for future energy generation and a proliferation risk, the balance between these factors depending on national policy. Irrespective of the proportion of PuO2 stocks that may be consumed by nuclear fission, in mixed oxide (MOX) or inert matrix (IMF) fuels, there will remain a quantity of waste PuO2 unsuitable for fuel manufacture, requiring immobilisation. Single phase ceramic systems rather than multiphase systems have been proposed because the waste stream is pure PuO2. We have initiated a research programme to investigate the potential of four ceramic formulations for the disposition of waste plutonium, using cerium as a plutonium surrogate (table I). The ceramic formulations Table I. Ceramics formulations for plutonium immobilisation. Phase Pyrochlore Zirconolite Britholite Kosnarite

Composition Gd2(Zr1.6Ce0.2Hf0.2)O7 (Ca0.9Gd0.1)(Zr1.5Ce0.2Hf0.2Gd0.1)Ti2O7 (Ca3Y5CeGd)Si6O26 Na1.2(Zr1.4Ce0.2Gd0.2Hf0.2)P3O12

were chosen based on cerium solid solution limits in the host phases Gd2Zr2O7, CaZrTi2O7, Ca2Y8Si6O26 and NaZr2P3O12. A generic processing route that was compatible with the restraints

imposed when processing active samples was developed. Optimisation of the sintering process was performed and the phase assemblages and morphologies of the sintered samples were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spe