The United Kingdom’s nuclear legacy has arisen from a variety of nuclear facilities operated across the country over the past ~60 years. These contribute to the production of nuclear material for nuclear reactors or weapons, the use of this material in reactor plants and the re-processing of spent nuclear fuel. Construction on the UK’s first nuclear power plant, Calder Hall, began in 1953 and in 1956 it was connected to the national grid becoming the world’s first commercial nuclear power station. The site was also expanded over the fol­lowing decades, to result in the present Sellafield site (see section 2.1.1). Between 1953 and 1971 a total of 26 reactors were built at nuclear research and devel­opment sites across the UK.3 A substantial part of the UK’s electricity supply has come from the first generation of Magnox nuclear power stations over the past 60 years. Just two of the eleven Magnox stations are still operational.

The Atomic Weapons Establishment (AWE) is responsible for providing and maintaining the UK’s nuclear deterrent and has held this responsibility for over 50 years. AWE operates over two sites, Aldermaston which is a former airfield and Burghfield, a former munitions factory. Although the Aldermaston site is radiologically safe there are areas where soils contain higher than background levels of various radionuclides, including plutonium. Levels of 239 + 240Pu have been found to range from 15 to 155Bqkg-1 in certain settled sediments (sludge)4 compared to background levels due to global fallout of 0.02 to 0.7Bqkg-1.5

The Nuclear Decommissioning Authority (NDA), a Non-Departmental Public Body (NDPB), was established in 2005 to manage the decommissioning and clean up of the UK’s civil public sector nuclear legacy sites. The restoration program tasked to the NDA relates to 19 sites covering the length and breadth of the UK with certain sites not expected to reach their planned end state for decades. The discounted lifetime cost for completing their contracted work, the Nuclear Liabilities Estimate (NLE), stands at £44.5 billion.3 A detailed overview of the NDA’s planned approach for decommissioning and clean up is provided in their recent draft strategy published for consultation.3

Although there are a number of sites in the UK where nuclear operations have occurred, the majority of the legacy waste and contamination is located at a few principal facilities. Two key sites (Sellafield and Dounreay) involved in the UK’s nuclear waste inventory and which suffer from the greatest contamination concerns are discussed here in more detail.

2.1.1 Sellafield

Sellafield (formerly Windscale), West Cumbria, is the UK’s largest nuclear complex covering 262 hectares and has supported the nuclear power program

since the 1940s with the site containing the world’s first commercial nuclear power station, Calder Hall. Operations at the Sellafield site include spent fuel reprocessing, mixed oxide fuel fabrication (MOX) and nuclear waste storage and management. Discharges into the environment from Sellafield began in 1951 and first became subject to formal authorisation in August 1954 under the ‘‘Atomic Energy Authority Act 1954’’. Prior to 1954, discharges were subjected to controls derived from consultation with site operators and government departments. Current disposal of radioactive waste is regulated under the “Environmental Permitting (England and Wales) Regulations 2010’’ (EPR).

During reprocessing, plutonium, uranium and highly radioactive fission pro­ducts are separated by a series of solvent extractions which results in some of these products being concentrated in aqueous waste. Highly radioactive aqueous waste is added to an acid effluent stream for evaporation and storage and is now being converted into vitrified waste. Low level aqueous waste is discharged into the Irish Sea via pipelines extending 2.5 km from the high water mark. These low level discharges have created an environmental inventory, over the period of 1952-1990, of around 1.1 x 102 TBq of 238Pu, 6.1 x 102 TBq of 239,240Pu, 1.3 x 104 TBq of 241Pu and 9.4 x 102 TBq of 241Am (with about 3.6 x 102 TBq of the americium having been derived from decay of 241Pu released).6 Around 90% of the Pu, in its insoluble Pu(iv) state, was retained rapidly by the sediment in the Irish Sea along with the vast majority of the discharged Am. The remaining 10% of plutonium, in the more soluble Pu(v) state, remained in solution and was transported out of the Irish Sea.7 Since 2006, beach monitoring has detected a number of contaminated sites resulting from the Sellafield discharges, although they are generally less active than those found in Dounreay.8

Approximately 1600 m3 of soil around the centre of Sellafield has been contaminated by spillage and reprocessing and will have to be treated as intermediate level waste (ILW).8 This area overlies an aquifer in the underlying sandstone geology, which is significantly contaminated to the southwest due to leaching of the contaminated soil from above. An estimated 1 000 000 m3 of soil will require treatment as low level waste (LLW). Sellafield is also responsible for the storage of the majority of the UK’s nuclear waste products and, as such, a large inventory of varying levels of radioactive waste is stored on site either awaiting disposal9 or for the activity to decrease.

Two site investigations have been conducted at Sellafield over the past decade in an attempt to identify and develop conceptual models of below ground contamination. The first phase of the report was completed in 2004 and exam­ined contamination outside of the Sellafield ‘‘Separation Area’’, where fuel re-processing and fabrication took place, with the second report focussing on contamination within the Separation Area expected to be completed in 2010.

Soil sample records from over 2000 boreholes have demonstrated that radioactively contaminated ground exists beneath and, occasionally, outside the Separation Area. Groundwater monitoring throughout the site has revealed that radioactive contamination is present in distinct plumes in the groundwater which are migrating in the direction of the hydraulic gradient. These con­taminants include 90Sr, 137Cs, 3H and 99Tc, with actinides also expected.10

The maximum activity of the most mobile contaminant, tritium, is around 1.0 x 107 Bqm-3 in contaminated groundwater found in boreholes close to the Separation Area. The activity decreases down the hydraulic gradient towards the River Ehen, until it becomes undetectable (below 1.0 x 105Bqm-3).10 Technetium-99, although derived from a different source, becomes a co­contaminant with the tritium in a common plume as they both migrate downgradient. The 99Tc is known to be a contaminant in the upper strata of the sandstone bedrock and has also been found in monitoring wells as far as the site boundary. The maximum concentration of 99Tc found in this plume during the phase 1 site investigation was 2.3 x 105 Bqm-3, located near to the site main gate.10 Strontium-90, which has limited solubility and readily adsorbs to sedi­ments at Sellafield, is detectable in monitoring wells inside the Separation Area where it is mostly contained. Beta activity from the 90Sr is also detected in two plumes, including the plume contaminated with 3H and 99Tc.10 Caesium-137, the only other radioactive isotope detected in the groundwater plumes, was found to be present only in very low concentrations and only in filtered solids.

Monitoring of 137 boreholes was conducted for the Sellafield Ltd Ground­water Annual Report11 and is summarised in Table 2. Although the majority of boreholes contain activity below the WHO drinking standard for total alpha, tritium and technetium activity, there are a significant number of boreholes with total beta activity above the WHO drinking standard. Strontium-90 makes up the bulk of the total beta activity, with caesium-137 also contributing sig­nificant activity. However, when both isotopes are examined on an individual

basis, then fewer samples exceed the WHO drinking standard for 90Sr and no samples exceed the 137Cs safe drinking limit. The majority of boreholes with values above the WHO standard are located within the Separation Area with a number also located to its south-west.

The former storage and de-canning facility, known as B-30, houses a pond used for the storage of spent nuclear fuel until its replacement facility, the Fuel Handling Plant, was commissioned in 1986. Although now closed, the storage pond is thought to contain 300 to 450 tonnes of spent nuclear fuel. Fuel was stored in the pond for longer than was anticipated due to an accident at the Magnox reprocessing facility in 1974 causing corrosion of the fuel cans and leakage of radiation into the pond.