RWMAC's Advice to Ministers on the Restoration of the UKAEA Dounreay Nuclear Site

Annex B

A Short History of the Dounreay site

The Dounreay site is built on a former Admiralty airfield. The complex initially comprised the Dounreay Materials Test Reactor (DMTR) followed by the Dounreay Fast Reactor (DFR) with its characteristic "golf ball" containment building, and facilities for fuel manufacture, reprocessing and storage of radioactive waste. Construction began in March 1955 and criticality was first achieved in DMTR in May 1958 and in DFR in November 1959. The Fast Reactor Fuel Reprocessing Plant was completed in July 1959.

DMTR was shut down in 1969: all of its fuel has since been removed and reprocessed and it is now in a care and maintenance regime. A second fast reactor, the Prototype Fast Reactor (PFR), became operational in 1974, whilst DFR continued in operation until 1977. DFR is now in the process of being decommissioned, but a fuel assembly remains stuck in the reactor awaiting removal, with shipping to Sellafield for reprocessing as the preferred disposal route.

In 1988, the UK Government decided that there was no short term need for fast reactors and the research and development programme was run down, being finally terminated in 1993. PFR closed down, to programme, on 31 March 1994. All used fuel and breeder assemblies have since been removed from the reactor vessel itself, but some fuel remains in facilities in the PFR building. A small number of unirradiated fuel assemblies are also held in store in the PFR building.

Within the Fuel Cycle Area (FCA), a wide variety of operations have been carried out. These ranged from the manufacture of fuel for research reactors and for the DFR, and the fabrication of targets for medical isotope production, to the reprocessing of spent MTR and fast reactor fuel and the storage and treatment of radioactive waste. Reprocessing of fast reactor fuel in the FCA ceased in September 1996 following the detection of a small leak into the cooling water circuit of the plant's irradiated fuel dissolver. In May 1998, following an incident which caused damage to an underground power cable, NII issued a Direction prohibiting all activities in the FCA, other than those essential for safety, until improvements had been made. On 5 June 1998, the Government announced that any future commercial reprocessing activities would be confined to the fuel already on the site and that for which there were existing contracts. On 18 July 2001, the Minister for Energy announced that the Dounreay reprocessing facility for irradiated PFR fuel would not be refurbished and that no further PFR fuel would be reprocessed.

In June 1998, the HSE and SEPA undertook a comprehensive Safety Audit of Dounreay. The Audit Report was published in August 1998 and contained 143 recommendations covering all aspects of work on the site. One of the key recommendations was that the decommissioning and radioactive waste strategies should be integrated. This has led to the production of the Dounreay Site Restoration Plan.

Beyond these main facilities, there is a range of other buildings that formerly supported fast reactors and research, and which currently support present FCA operations and decommissioning work, and which store waste awaiting further treatment, storage or disposal.

The site also includes two facilities previously authorised for the disposal of intermediate and low level radioactive wastes (ILW and LLW): these are the ILW Shaft and the Low Level Waste Pits. The Shaft was the scene of a chemical explosion in 1977 which blew off, and displaced, its heavy concrete lid. Use of the Shaft for disposal of radioactive waste had ceased, except for large items, in 1971 when the Wet Silo, a concrete vault in which ILW is stored underwater, came into operation. After the 1977 explosion, the use of the Shaft for disposal of any radioactive waste was immediately halted, although the disposal authorisation remained in force.

The LLW pits (a complex of trenches excavated five metres into bedrock and located about 30 metres from the cliff edge) are now, in effect, full and can no longer be used for routine disposals. LLW is being stored in other facilities pending a decision on final disposal. The route for LLW disposal in the future now poses a significant problem for restoration of the Dounreay site.

In 1998, the Government announced its decision that UKAEA should implement a programme to retrieve the ILW from the Shaft and from the Wet Silo.

Another issue associated with the Dounreay site has been the finding of two types of radioactive particle on the nuclear site itself, on the site foreshore and a nearby public beach, and in the offshore sediments. These particles originated from historic reprocessing operations of MTR and DFR fuel on the Dounreay site. UKAEA believes that particles escaped onto some of the road verges on the site during historic transport operations in which particles were moved from the fuel ponds to the Shaft and Silo. In addition, it is believed that particles also entered the active effluent system and were discharged to sea through the site main discharge pipeline. A regular programme of work is underway to monitor local beaches, establish the extent of the offshore contamination, understand the magnitude of the risk to the public from these particles, and explore options for intervening to reduce this risk.