Sizewell (United Kingdom)

Map of Sizewell

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Unit A: 2 * 290 Magnox GCR; grid connection in 1966, shutdown in 2006.
Unit B: 1200 MW PWR grid connection 1995

Facilities in Sizewell

plantreactor typconstruction startoperation startshut down
Sizewell A-1GCR196119662006
Sizewell A-2GCR196119662006
"Sizewell `ten hours away from serious nuclear accident

12 June 2009

SUFFOLK was only ten hours away from a serious nuclear accident, a consultant's report claimed yesterday as members of a watchdog argued there was a discrepancy in official versions of an incident at the Sizewell A plant more than two years ago.

About 10,000 gallons of radioactively contaminated water was discharged into the North Sea in January 2007 after a pipe - carrying cooling water to an engineered “pond” containing highly radioactive spent fuel rods - burst.

Magnox South, the plant operator, said at the time that it had taken the incident seriously but there had never been any off-site danger or adverse impact on the environment.

However, a consultant's report - commissioned by a local anti-nuclear group and published yesterday - claimed failure to detect the leakage at an early stage could have led to the whole pool draining, a fire and an airborne release of radioactivity

After exhaustive investigations, neither the Nuclear Installations Inspectorate (NII), the UK nuclear safety watchdog, nor the Environment Agency, the country's pollution watchdog, decided to prosecute Magnox South, partly because of the firm's response to the incident.

The company said at the time, and has reiterated since, that the incident was quickly brought under control and that the contaminated water was deliberately discharged into the sea after levels of radioactivity had been found to be less than one percent of the annual limit allowed under the site licence.

The NII announced nearly two years after the accident that it considered it would not be in the public interest to prosecute. Inspectors were satisfied with the Magnox South response to the accident, the replacement of the Sizewell pipework system and inspections and remedial works at its other sites.

However, an interim report into the incident by the NII, put into the public domain yesterday following a request under the Freedom of Information Act, said the contaminated water had found its own way into storm drains and from there into the sea.

The interim report also suggested that lack of staff resources at the NII was a factor in the decision not to prosecute.

The Shut Down Sizewell Campaign, which had condemned the decision by regulators not to prosecute, subsequently commissioned Dr John Large, of Large & Associates, an independent consultant who has carried out a lot of work for anti-nuclear groups, to assess the NII decision-making process.

His conclusion, reported to yesterday's meeting of the Sizewell Stakeholder Group (SSG) - set up to liaise between the nuclear industry, its regulators and the public - was that taking into account the NII's own criteria required the serving of an improvement notice and “most likely” the launching of a prosecution.

Dr Large claimed that if it had not been for the “fortuitous” presence in an adjacent laundry area of a contractor, who had reported flooding, then the leakage” could have completely drained the cooling pond, uncovered the spent fuel and, in all probability, resulted in a fuel fire with an off-site airborne release of highly radioactive fission products.

“This scenario could have developed within ten hours of the initial pipe failure,” he said.

Charles Barnett, chairman of the Shut Down Sizewell Campaign, urged the SSG to examine the evidence surrounding the incident and to take appropriate action. “You've been misled, all of you,” he told members, who are representatives of local authorities and organisations.

Paul Wilkinson, Sizewell A site director, said the storm drains had been “bunged” as a result of the incident and the contaminated

water only released to the sea after calculations had showed that the radioactivity contained was less than one percent of the annual discharge limit.

Only 40,000 gallons of the 800,000 gallons in the pond had leaked. Immediate action had been taken to ensure that no more water escaped from the pond. About 30,000 gallons of the leaked water was contained on site and the rest discharged into the sea after careful assessment.

Mr Wilkinson said the company had “worked closely and in an open and honest manner” with its regulators. “We have addressed every issue and we're willing to be involved in detailed debate on the event itself,” he said.

Ray Jepps, Magnox South chief nuclear operating officer, said the NII report made public was an internal document. “A lot more technical detail will be in the final report,” he said.

Pete Wilkinson, a member of the SSG and a former member of a Government committee on radioactive waste disposal, said the NII's interim report was “at odds” with what the group had been told about the accident. “We believe the information we have received has been economical with what really happened,” he said.

Richard Smith, SSG chairman, said the group needed to hold a meeting to study the incident more fully and both Pete Wilkinson and another member, Joan Girling, said the meeting needed to be held in public.

An NII spokesman said last night that although neither an improvement notice nor a prosecution had been considered appropriate in the case of the Sizewell A incident, a legally binding directive had been served on Magnox South to review safety.

“The site was already undertaking improvements and a prosecution was not deemed to be in the public interest,” he said.

The spokesman said despite the contents of the interim report, lack of staff resources was never a factor in judging whether to launch a prosecution.

He declined to comment on the apparent discrepancy over the discharge of contaminated water into the sea, saying it was an Environment Agency matter. However, there was no-one available at the agency to comment."
(source:, originally reported by channel 4 news)


A degradation of reactor protection systems due to failure to properly categorize a plant modification at Sizewell-B led Nuclear Electric (NE) to declare a Level 2 event on INES.
The error was found on April 21.
Nuclear Electric decided to uprate the event from INES 1 (deviation) because of a deficiency in safety culture. However, the incorrect categorization of the circuit board modification "went unchallenged through several reviewers and the arrangements for implementation of the modification were inadequate in terms of the scope of the testing."


Start of commercial operation delayed for 3 month. Reactor operating at 75%. Delay is caused by secondary side problems (steam & condensate leaks,)


First criticality


Failure of 4 bracketed attachements to a guide tube assembly caused the asssembly used for refueling to drop 75 mm, settling on top of the graphite moderator block (fuel is undamaged).


Embrittlement of RPV welds detected -> pressure reduced. Operating restrictions, e.g. slower startup.


The prospect of Nuclear Electric's (NE) Sizewell-B PWR not being included in the upcoming privatization of the U.K.´s more modern nuclear plants was raised last weekend following the leak of a draft report prepared by Parliament's House of Commons Trade & Industry Select Committee.
Members of Parliament are said to fear that the privatization of Sizewell-B plus the seven advanced gas-cooled reactor stations will not raise more than 2,5-billion pounds - less than it cost to build the 2,9-billion-pound Sizewell-B.