Decommissioning aims to take a plant which has been washed out at the end of operations and leave the site in its planned end state. End states could range from buildings containing waste entombed in concrete in their current location * Corresponding author

Issues in Environmental Science and Technology, 32 Nuclear Power and the Environment Edited by R. E. Hester and R. M. Harrison © Royal Society of Chemistry 2011

Published by the Royal Society of Chemistry, www. rsc. org to completely clear sites available for another use. Intermediate states might include building foundations left in place while above ground structures are removed from the site.

Materials which are exported from the site must be treated to make them acceptable for final disposal. The UK presently has a near-surface, low level waste repository (LLWR) and is planning to build a Geological Disposal Facility (GDF) to contain intermediate and high level wastes. In some cir­cumstances materials will be sufficiently inactive that they are suitable for free- release and do not require disposal to one of these facilities. Disposal to one of the repositories typically requires wastes to be boxed and filled with grout, or other encapsulant. Waste boxes are stacked in the repository and then further material will be introduced to surround the boxes and provide a controlled local chemical environment. One goal of decommissioning is to minimise the amount of waste going to the GDF and LLWR.

The drivers for decommissioning are both varied and interrelated. Decom­missioning can therefore proceed for a number of reasons. These include:

• Reduction of the hazard associated with legacy radioactive inventory in ageing facilities.2

• Completion of decommissioning allows sale or reuse of the site.

• Continued existence of the site requires conformance to safety legislation and so requires care and maintenance that will incur ongoing costs that could be avoided by completion of decommissioning.

• There is a duty to future generations to avoid leaving them to clean up the waste generated by the current generation.

• To remove visual intrusion caused by large facilities.

Given that a facility is to be decommissioned, there is then a decision as to when this shall take place. The factors above will strongly influence the prioritisation of decommissioning but a number of other factors should also be considered: •

• Enhanced technology may be developed during the deferral period which improves the process.