Oldbury nuclear power station is a Magnox nuclear power station undergoing decommissioning. It is located on the south bank of the River Severn close to the village of Oldbury-on-Severn in South Gloucestershire, England. The ongoing decommissioning process is managed by Magnox Ltd, a subsidiary of the Nuclear Decommissioning Authority (NDA).
Oldbury is one of four former nuclear power stations located close to the mouth of the River Severn and the Bristol Channel, the others being Berkeley, Hinkley Point A, and Hinkley Point B.
History
Opened in 1967, it had two Magnox reactors producing 424megawatts (MWe) in total – enough electricity on a typical day to serve an urban area twice the size of Bristol. Reactor 1 went critical on 18 September 1967 and first generated electricity on 9 November 1967. Reactor 2 started generating electricity in April 1968.
The construction was undertaken by a consortium known as The Nuclear Power Group ('TNPG'). The reactors were supplied by TNPG and the turbines by AEI and C. A. Parsons & Co. The main civil engineering contractor was Sir Robert McAlpine. Construction on the site began in 1961.
Oldbury was the first nuclear power station in the UK to use prestressed concrete pressure vessels, earlier Magnox reactors having used steel pressure vessels more suited to smaller reactors.
The design net power output of the station was 626MWe, but due to steel corrosion problems from the hot carbon dioxide coolant within the reactor, operating temperature had to be reduced soon after operation started causing a large drop in power output. Initially, the power output was set at 424MWe, dropping to 400MWe by 1973. Then as remedial measures were adopted, power was progressively increased to 434MWe by 1983 with a gas outlet temperature of , compared to the design temperature, which was maintained as the normal operational output.
The station had two 216MW turbo-alternator generators giving a gross electrical capability of 439.5MW and a net capability of 416MW. The steam conditions at the turbine stop valves was 43.0bar at .
The generating capacity, electricity output, load factor and thermal efficiency were as shown in the table.
In 1976/77, Oldbury was presented with the Hinton Cup, the CEGB's "good house keeping trophy". The award was commissioned by Sir Christopher Hinton, the first chairman of the CEGB.
In 1992, Reactor one set a world record for the longest continuous period of power generation from a commercial nuclear reactor, of 713days 21hours and 32minutes. Hinkley Point A Nuclear Power Station held the previous world record of 700days and 7hours, set in 1988.
From 2005 until 2012, the power station was protected by armed officers from the Civil Nuclear Constabulary.
Closure and decommissioning
The station was originally to cease generating at the end of 2008, however continued use was licensed in various stages; an additional 2.5years in the case of reactor 2, and four years for reactor 1.
Reactor 2 ceased operating permanently on 30 June 2011, followed by Reactor 1 on 29 February 2012.
Defuelling and removal of most buildings is expected to take until 2027, followed by a care and maintenance phase from 2027 to 2095. Demolition of reactor buildings and final site clearance is planned for 2096 to 2101.
Incidents
On 30 May 2007, only a few days after reopening after safety checks, the power station was shut down as part of standard emergency procedure when a fire broke out on one of the generator transformer HV bushings. No-one was injured in the fire and no radiation was released. Information suggests an insulator overheated, causing it to fail. Minor damage ensued resulting in a standard shutdown. All emergency procedures were commenced, and by 11:30am the situation was stabilised. The power station resumed production for a few days in June then shut down again. Production eventually resumed on 24 August 2007, at which point it had only produced electricity for eight days since August 2006.
On 17 March 2011 at 10:40am, Reactor 2 was automatically shut down after an electrical problem. Magnox stated that workers had been carrying out routine maintenance when a small relay overheated (this failure caused the turbine to shut down). Their spokesman went on to say, "Because the turbine tripped the steam produced in the boilers couldn't be sent to the turbine as it would normally and so was released through relief valves on top of the building." and "To reduce the amount of steam being produced, and in accordance with expectations, the reactor automatically tripped and was safely shut down."