The Benefits of Cementitious Encapsulation Matrices for the Conditioning of Intermediate Level Waste

The UK has significant quantities of radioactive waste, which have arisen over the past fifty years or so, largely as a result of nuclear power, reprocessing and defence programmes. The intermediate level wastes arising as a result of these activities, exhibit a high level of physical and chemical diversity, and must be managed safely in a way that protects existing and future generations and the environment. Development work has been conducted since the early 1980s to identify suitable conditioning materials and techniques that are compatible with the needs of safe long-term management, including interim storage, transport and future deep geological disposal. From these studies cementation emerged as the one medium which could satisfy all the key waste management criteria. Other materials were not ruled out and may offer benefits in specific applications. The advantages of conditioning ILW with cement include: • the extensive experience of its use in a wide variety of contexts; • the raw materials are relatively cheap and have a long shelf life; • cement is processed in relatively simple plant at room temperature, with safety and cost benefits for plant operators; • the product is fire resistant and of relatively low toxicity; • cement is capable of immobilising a wide range of wastes ranging from solids to aqueous slurries; • cement provides desirable product properties. Desirable properties include: • suitable strength, • chemical control of radionuclide leading to enhanced retention, • good corrosion protection for steels, • low permeability, • tolerance to radiation, • durability over extended timescales, and • good radiation self-shielding properties. Several waste packaging plants are now operational in the UK using cement-based encapsulants. These are currently conditioning ILW for interim storage, in a manner suitable for future transport and compatible with the Nirex phased deep disposal concept. This paper will describe the development of cement-based encapsulants to meet the needs of UK radioactive wastes, and will provide examples of the supporting product quality data.