A meeting of the Sellafield Local Liaison Committee (SLLC) on 4th December was told of the Environment Agency’s concerns about the increasing spread of Technetium 99 (Tc-99) in groundwater outside the Sellafield site. In its six-monthly review, the Agency reports its dissatisfaction with BNFL’s progress in dealing with the off-site leakage which it describes as ‘potentially significant contamination’. The Agency has indicated to BNFL a number of areas where improvement to their monitoring of the contamination is required.
The leakage of Tc-99 into groundwater was first admitted by BNFL in November 2001 (Sellafield Newsletter 23.11.01) when concentrations of Tc-99 and Tritium were discovered in sampling boreholes on the site. The company stated at the time that there was no threat to safety and there was no indication that the material had moved off site. Some months later HSE’s Nuclear Safety Directorate (Statement of Nuclear Incidents 8.4.02. E069:02) reported that Tc-99 had been detected in samples from boreholes located outside the site. The suspected source was the old B241 building containing tanks of reprocessing wastes which ‘have been suspected of leaking for some years…’ [see CORE Briefing 07/02]
Of the recent and worsening developments, information from within Sellafield suggests that the concentration and spread of contamination outside the plant is more serious than indicated by the Agency’s review, involving radionuclides other than TC-99 and possible sources other than B241, including B38. Concentrations of Tc-99 now being found in boreholes outside the plant are understood to be at a level of many thousands of Becquerels, and that similar concentrations of Strontium-90 and Caesium-137 are also being found along with Tritium. The plume of leaking material now appears to have reached the sandstone aquifer below Sellafield – with potential implications for drinking water supplies.
An Environment Agency spokesman has confirmed that, with groundwater as a resource requiring protection, BNFL is being urged to provide a groundwater protection strategy to control the spread of contamination on similar lines to those adopted at the Hanford site in the US. Since the problem first came to light two years ago, a number of 30-metre deep boreholes have been sunk by BNFL in farmland and sand dunes around Sellafield. The Agency is now pressing for an inner ring of boreholes, possibly deeper than before, to be sunk inside the site around the Magnox (reprocessing) Separation area so that the sources of the leaks can be better identified and controlled. This area is likely to be heavily contaminated from past reprocessing operations.
B241, built in the early 1950’s, contains a number of concrete tanks used for ‘settling out’ treated reprocessing wastes from the plutonium product and finishing streams. An HSE/Environment Agency audit in 1995 showed the tank complex to then hold 7400 cubic metres of waste, with a solids content of 3000 tonnes.
B38 consists of a number of ponds and Highly Active silos for storing unconditioned wastes from decanned Magnox fuel rods. A 1986 HSE Safety Audit of B38 referred to an original silo as having previously leaked into the ground. A 1992 report by the Advisory Committee on the Safety of Nuclear Installations (ACSNI) describes the plant as being contaminated with fission products, mainly caesium released from corroded irradiated fuel which has dissolved in the waters of the ponds and silos.