Wylfa Nuclear Power Station - History

History

The construction of the power station, which was undertaken by British Nuclear Design & Construction (BNDC), a consortium backed by English Electric, Babcock International Group and Taylor Woodrow Construction, began in 1963. The reactors were supplied by The Nuclear Power Group (TNPG) and the turbines by English Electric.

It was the second nuclear power station to be built in Wales, after Trawsfynydd. Following the closure of Trawsfynydd in 1991, Wylfa is the only nuclear power station in Wales.

Wylfa houses two 490 MW Magnox nuclear reactors, "Reactor 1" and "Reactor 2", which were built from 1963 and became operational in 1971. Wylfa typically supplied 23 GW h of electricity daily when they were both in service. These were the largest and last Magnox-type reactors to be built in the UK. Wylfa was the second British nuclear power station, following Oldbury, to have a pre-stressed concrete pressure vessel instead of steel for easier construction and enhanced safety.

The original design output was 1,190 MW but unexpected accelerated ("breakaway") corrosion of mild steel components of the gas circuit in hot CO₂ was detected even before the first reactor began operating. The channel gas outlet temperature, the temperature at which the CO₂ leaves the fuel channels in the reactor core, had to be reduced, initially dropping the power output to 840 MW, which was later raised to 980 MW as more experience accumulated.

The graphite cores each weigh 3,800 tonnes (3,700 long tons); 6,156 vertical fuel channels contain over 49,248 natural uranium magnox-clad fuel elements, hence the name magnox reactor. A further 200 channels allow boron control rods to enter the reactor and control the nuclear reaction. The primary coolant in the reactors is carbon dioxide gas.

The power station is operated by Magnox Ltd, formerly Magnox North, formerly British Nuclear Group, formerly Magnox Electric, formerly Nuclear Electric, formerly National Power, formerly the Central Electricity Generating Board (CEGB). The site is owned by the Nuclear Decommissioning Authority (NDA). Its purpose is to oversee and manage the decommissioning and clean-up of the UK's civil nuclear legacy.

During its operational life substantial works have been needed to strengthen the reactors against deteriorating welds discovered in the safety review in April 2000. Amid public controversy, Greenpeace issued an independent safety appraisal by the nuclear engineering consultancy Large Associates, but the permit to restart operation was given in August 2001. In addition to welding weaknesses, radiolytic depletion of the graphite moderator blocks was still of concern and PAWB continue to campaign for early shut-down of the plant as well as against any nuclear replacement.

On 20 July 2006 the NDA announced that the station would be shut down in 2010 because operation beyond then would be uneconomic given plans to shut down the Magnox spent fuel reprocessing plant at Sellafield. However, in 2010 the NDA announced an extension to 2012, beyond Wylfa's 40th anniversary as a generating power station in January 2011.

The ONR 2011 Q3 report states Reactor 1's lifetime will be extended to September 2014, but it is anticipated that remaining fuel will be used up before the end of the operator’s allocated extension period. Reactor 2 ceased generating on 25 April 2012 at 19:02 BST.