Investigation at Sizewell B after chemical pollutes groundwater system

The reactor dome of Sizewell B Nuclear Power Station

The reactor dome of Sizewell B Nuclear Power Station - Credit: PA

The Environment Agency is investigating an incident at the Sizewell B nuclear power station in which a diluted chemical over-flowed from a tank and led to groundwater contamination.

The incident was reported to the agency by EDF Energy, the plant’s operator, which claimed last night that there was no risk to the environment or public health.

The chemical involved, sodium hypochlorite , is commonly used within a variety of industries to control bacteria in water systems.

At Sizewell B it is used to deter marine organisms, including mussels, from building up in the seawater cooling systems and blocking pipes.

The ground water conditions were returned to normal within 24 hours and at its peak never exceeded the levels found in tap water.

The incident occurred ten days ago and was revealed yesterday at a meeting of the Sizewell Stakeholder Group, set up as a conduit for public information about the nuclear site.

Martin Cubitt, Sizewell B plant manager, said the use of the chemical was “akin to dosing tap water with chlorine”.

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Groundwater samples had been taken from the company-owned borehole adjacent to the hypochlorite plant and a concentration of only 0.17 parts per million had been detected..

“This can be compared with a value of up to one part per million added to local drinking water as a dosing agent by the local water utility and the World Health Organisation guideline maximum of five parts per million,” Mr Cubitt said.

The chemical was added to seawater stored in the tank at a rate of 1,000 parts per million.

The tank was surrounded by a concrete bund but this failed to prevent an overflow into the surrounding area.

“The cause of the spill is being investigated and engineers at the station will continue to monitor boreholes for traces of the chemical,” Mr Cubitt added.

It is the first “top tier” chemical incident at Sizewell B for more than four years.

The Environment Agency said it was monitoring the situation.