Synroc

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Synroc, a portmanteau from "synthetic rock", is a possible means of safely storing and disposing of radioactive waste. It was invented in 1978 by a team led by Dr (A.E.) Ted Ringwood at the Australian National University, with further research being undertaken in collaboration with ANSTO with research laboratories at Lucas Heights.

Unlike borosilicate glass, which is amorphous, Synroc is a ceramic that incorporates the radioactive waste into its crystal structure. Naturally occurring rocks can store radioactive materials for very long times. The aims of the SYNROC project were to imitate this by converting liquid into a crystalline structure and use it as a way of storing radioactive waste. If stored in a liquid form, the waste can enter the environment and the waterways causing widespread damage. As a solid, these risks are greatly minimised. Different types of synroc have been developed for the immobilisation of different types of waste.

Synroc is a highly stable ceramic matrix into which long-life nuclear fission products, such as high-level wastes from nuclear power stations, which generate electricity, can be incorporated. It is a synthetic rock composed of three titanate minerals- hollandite, zirconite and perovskite-plus rutile and a small amount of metal alloy. These are combined into a slurry to which is added a portion of high level liquid nuclear waste. The mixture is dried, calcined at 750 degrees celsius to produce a powder, and then compressed in a bellows-like stainless steel container at temperatures of between 1150 and 1200 degreees celsius. The result is a cylinder of hard, dense, black synthetic rock. The Synroc cylinder is then loaded into a disposal canister.

Problems with this method of disposing of radioactive waste include the fact that that the synroc still has to be stored, often underground. Even though the waste is held in a solid lattice and prevented from spreading, it is still radioactive and can have a negative effect on its surroundings.

Although it has not yet experienced commercial use, in April of 2005, the process was chosen for a multi-million dollar "demonstration" contract to eliminate five tonnes of plutonium-contaminated waste at British Nuclear Fuel's Sellafield plant, on the northwest coast of England.