Waste Management Technology Ltd (WMT) has developed the optimal process for immobilizing a solid waste contaminated with thorium dioxide (thoria). The physical and chemical characteristics of the waste present challenges to producing a wasteform acceptable for disposal. Also, high-energy radiation from thorium’s decay progeny requires a treatment plant with shielding and remote handling facilities. Key points of the paper are as follows. 1. Treatment options were investigated and the best practicable means identified as intimate mixing of the waste with cementitious grout. 2. Samples were analysed for particle size and organic contamination. 3. Small-scale active mixes resulted in a single treatment formulation for all the waste. Leach tests confirmed that the organic material is adequately retained within the immobilised waste provided activated carbon is included in the formulation. 4. Active mixes at the two litre scale confirmed that the formulation is mixable and the product acceptable and consistent with expectations from the earlier work. 5. WMT is constructing a treatment plant at its Winfrith site, based on remote grouting in a 200 litre drum with a sacrificial mixer. Inactive full-scale trials with such 200 litre drums were carried out after selection of simulants with the appropriate physical properties.

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