Photograph: Deposition hole for spent disposal © Steve Barlow
There are no facilities for disposal of higher-activity radioactive wastes in the UK currently and where such wastes exist, they are held in safe interim storage in surface facilities. The UK government reviewed options for the management of these wastes in the long-term in the period 2003-06 and concluded that geological disposal, coupled with safe and secure interim storage, was the best available approach. International consensus supports this view and is already the chosen approach in many countries including Canada, Finland, Sweden, France and Switzerland.
Geological disposal is achieved by:
- isolating the radioactive waste in sealed vaults and tunnels deep underground, between 200 m and 1000 m below the surface
- containing the radioactivity while it decays naturally over time
- preventing the radioactivity from reaching the surface in levels that could cause harm
Liquid radioactive wastes are first solidified and the solidified products packaged into engineered containers typically made of metal or concrete. On receipt at a geological disposal facility the waste containers will be taken underground for emplacement in a vault or tunnel opened up in a stable rock formation. The container will be surrounded by a backfill or buffer material, which will be formulated to be compatible with the host rock and provide a protective environment for the waste container. This is part of the multi-barrier approach.
The multiple barriers are therefore provided in combination by the natural geological barrier and the engineered barrier system comprising the waste, the container, the backfill/buffer and the GDF structure. The exact nature of the barriers and their performance requirements will only be able to be defined with certainty once the geological characteristics of the GDF site have been explored. In other words the engineered barrier system can only be confirmed once the characteristics of the geological barrier are understood. Achieving the requisite understanding of geology and of the characteristics of the geological barrier is referred to as the site characterisation process and is a key component of the disposal safety case.