It is the highest fine for a prosecution brought by the Environment Agency since early 2000 when Thames Water Utilities Ltd was fined the same amount for polluting the River Thames.

Judge Peter Fenn today (Tues) passed sentence at Chelmsford Crown Court, 11 days after Magnox Electric Ltd (formerly Nuclear Electric Plc) was found guilty by a jury of three offences of failing to carry out any inspections of a holding tank from which liquid radioactive waste had been leaking since 1990.

The company was also sentenced today for two offences to which they had earlier pleaded guilty of failing to maintain plant, namely, a sump – a type of holding tank – in the decontamination bay at the site for a period between 1 January 1993 and 4 February 2004, when the leak was discovered.

Judge Fenn said he was surprised that the integrity of the sump had not been checked in 2001 when it was upgraded.

At the earlier hearing the jury had heard that as part of its normal regulation of nuclear sites, the Environment Agency monitors the environment outside a site’s boundaries. Over the period of the leak no pollution of the type which would have been caused by it was detected and the leak did not cause any risk to local people or the environment.

The court heard that the breaches came to light because of a voluntary disclosure by Magnox to the Nuclear Regulation Group (NRG) of the Environment Agency and the Nuclear Installations Inspectorate (NII) of the Health and Safety Executive (HSE) in 2004.

Staff working to clear sludge from the sump realised that when full of water, levels in the sump fell and when empty, the sump was backfilling by a couple of inches a day. A pump was immediately brought in and all liquid and sludge carefully removed from the sump.

Prosecuting on behalf of the Environment Agency, Mark Harris told the court that prior to the work to clear sludge, no inspection of the sump had been carried out and no tests had been undertaken to check the integrity of the sump.

He said liquid leaked onto the ground because of a combination of poor original design when the sump was modified in 1976 and the lack of any routine inspection and maintenance afterwards until the leak was discovered.

Magnox Electric Ltd maintained that all the contamination took place between 1988 and 1990, but an Environment Agency expert stated that scum marks on the wall of the sump indicated that leakage occurred over many years.

Raymond Jepps, a former site manager for Bradwell told investigating officers that no routine maintenance or inspection would have been undertaken on the sump before February 2004 but it now was.

Phil Heaton, Team Leader of the Environment Agency’s Nuclear Regulation Group said: ‘This has been a complex investigation for the Environment Agency. We have demonstrated that the company failed to appreciate, properly or at all, that the sump was part of the system for discharging relevant waste, and so failed to take the proper precautions.

‘Our prosecution of the company sends a clear message to the nuclear industry that we require the highest standards of operation at all such sites and will take firm action, even if the environment beyond a site’s boundaries are not affected.’