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Wylfa Nuclear Power Station
Cemaes Bay, Anglesey, Wales, UK
associated engineer
Not known
date  September 1963 - 1st November 1969
era  Modern  |  category  Power Generation  |  reference  SH350939
Wylfa is the last and largest of the Magnox reactor nuclear power stations to be built in the UK. It was one of the first to dry-store spent fuel. Wylfa supplies more than 40 percent of Wales' electricity.
There are two reactors, each providing 490MW or a combined output of 980MW through a total of four turbine generating units. Reactor 1 went critical on 1st November 1969, was connected to the UK's National Grid on 24th January 1971 and started supplying electricity commercially on 1st November 1971.
Reactor 2 achieved criticality on 1st September 1970, with grid connection 21st July 1971 and commercial electricity supplies beginning 3rd January 1972.
The original design was for a combined output of 1,190 MW. However, as the output increases, so does the temperature of the reactor core and therefore the temperature of the coolant as it absorbs heat from the core.
The coolant at Wylfa is carbon dioxide, which can be corrosive at high temperatures and could cause metal fatigue. To avoid the problem, the power output was restricted initially to 840MW and later increased to the present 980MW.
It was only the second UK nuclear power station to have a pressure vessel made from prestressed concrete rather than steel. The first one was at Oldbury. There are two pressure vessels at Wylfa, each containing a reactor. The vessels are spherical and some 30m in diameter.
Each graphite reactor core weighs 3,800 tonnes, and has vertical channels built in to contain fuel and control rods. There are 6,156 fuel channels and 200 control channels. The fuel channels contain 49,248 Magnox fuel elements. The control channels contain boron rods, which can control the nuclear reaction and shut down the reactor.
At earlier Magnox power stations, there had been problems storing the spent fuel while it cooled and became less radioactive. Used fuel rods were normally put into a water-filled cooling pond, but the magnesium alloy casing around the uranium fuel corroded in water.
At Wylfa, the spent fuel is stored in a dry magazine cooled by carbon dioxide gas the same gas used for cooling inside the reactor core. This new method proved so successful that two air-cooled storage units were constructed.
Deteriorating welds were discovered in the reactors in April 2000 and the reactors were shut down until August 2001.
In July 2009, Wylfa was awarded five stars in the British Safety Council's Five Star Environmental Award Scheme. Operated originally by BNFL, the 21 hectare Wylfa site is now run by Magnox North Ltd and is owned by the Nuclear Decommissioning Authority. Its decommissioning date was expected to be 2010, or possibly 2016.
In April 2009, Bow Bidco Wylfa an equal joint venture between E.ON and RWE npower bought 178 hectares of land at Wylfa in anticipation of building a new nuclear power station. Money from the sale will offset decommissioning costs.
On 9th November 2009, the government announced their intention to build ten new nuclear power stations. Wylfa was one of the sites selected.
Reactors: The Nuclear Power Group
Turbine and generator supply: English Electric
Research: ECPK
"Going Critical An Unofficial History of British Nuclear Power"
by Walter C. Patterson, Paladin Books, 1985

Wylfa Nuclear Power Station