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Sizewell B Nuclear Reactor
Sizewell, east of Leiston, Suffolk
associated engineer
Not known
date  1988 - 14th February 1995
UK era  Modern  |  category  Power Generation  |  reference  TM472635
Sizewell B, located on the Suffolk coast some 3km east of Leiston, is owned and operated by British Energy. It is a pressurised water reactor (PWR) supplying 1188MW — or 3% of the UK's energy requirement — covering the needs of domestic customers in Suffolk and Norfolk. Its coastal location ensures a continual supply of cooling water.
The reactor complex consists of a striking azure blue rectangular building topped by a white hemisphere, which looks from a distance like a giant golf ball. It's situated to the north of Sizewell A, with its twin Magnox reactors, which ceased 40 years of power generation on 31st December 2006 and is now being decommissioned.
Sizewell B is Britain's most-recently built nuclear power station and the only PWR. It was constructed between 1988 and 1994. Fuelling began on 16th October 1994. The reactor first went critical on 31st January 1995 and began generating electricity on 14th February 1995.
The reactor, with its cooling circuit and steam generators, is contained within a 65m high, 45m diameter cylindrical prestressed concrete building. Its walls are 1.4m thick, designed to withstand catastrophic events such as plant failure, earthquake, etc., without leaking. The whole of the interior — floor, walls and dome — is lined with a gas-tight mild steel 6mm thick plate that weighs 2,000 tonnes and is fastened to the concrete. This building is called the primary containment structure, and is enclosed within the blue rectangular building or secondary containment structure. The project cost was some £2b.
Sizewell B was built using American technology and codes of practice. It is equipped with a four-loop Westinghouse 1200MWe Bechtel Standardized Nuclear Unit Power Plant System (SNUPPS). Inside the reactor, controlled nuclear fission is used to produce heat energy in the core. This in turn heats the water in the PWR, up to 325 degrees C, which is pressurised to around 150 atmospheres to prevent the water boiling and turning to steam, and allowing it to be used as a coolant. The hot water leaves the reactor and passes into steam generators, where it drives alternators to produce electricity.
The fission reaction uses neutrons to split the nuclei of slightly enriched uranium dioxide, which initiates a chain reaction producing gamma rays and more neutrons. These neutrons are slowed down by the water in the PWR, increasing the chance of further fission events with the uranium atoms. The rate of the reaction is controlled by the natural slowing effect of rising temperatures (of both fuel and water), and by using neutron-absorbing materials such as boric acid.
The uranium dioxide fuel pellets are packed into vertical tubes of zirconium alloy some 10mm in diameter and 4m long, called fuel rods. There are 193 fuel assemblies in the core, each consisting of 17 x 17 arrays of rods — a total of 55,777 rods.
To ensure safe operation, employees are trained in an exact replica of the power station's control room before they are allowed access to live procedures. Sizewell B was given the President's Award by the Royal Society for the Prevention of Accidents in 2008 for its industrial safety performance.
All local residents in the hamlet of Sizewell are given potassium iodide tablets to take in case of an accident. The idea is to flood the thyroid with iodine, preventing the absorption of radioactive iodine.
Sizewell B has an estimated decommissioning date of 2035.
Main contractor: John Laing plc
Steel plate contractor: Cleveland Bridge
Research: ECPK
Abstract of The Sizewell B Project by J.G. Collier
Nuclear Electric plc, published in Atomwirtschaft, Atomtechnik, vol 41, Handelsblatt GmbH, Dusseldorf, Germany, 1996

Sizewell B Nuclear Reactor