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Sizewell nuclear power stations

From Alfawiki
Sizewell nuclear complex
Company typeNuclear power facilities
IndustryEnergy
Headquarters
Sizewell, Suffolk
,
England, United Kingdom
ProductsElectricity generation

The Sizewell nuclear complex consists of two nuclear power facilities located near the village of Sizewell in Suffolk, England. Sizewell A, which houses two Magnox reactors, is currently undergoing decommissioning. Sizewell B features a single pressurised water reactor (PWR) and holds the distinction of being the most recent nuclear power station commissioned in the UK. Plans are underway for a third facility, Sizewell C, which will include two EPR reactors.

Although Sizewell B is planned to cease operations in 2035, EDF has revealed intentions to prolong its service life by an additional 20 years, potentially extending operations until 2055.

Site

Positioned roughly north of Sizewell on a gently elevated plateau safe from flooding, the Sizewell A site rests on bedrock formations from the Pleistocene epoch, specifically the Norwich Crag Formation and Red Crag Formation, overlying the older Eocene London Clay. These geological layers mainly consist of medium-dense sands interspersed with thin clay and silt deposits. The Crag formations extend approximately below the surface. In recognition of its exemplary maintenance standards, Sizewell A was awarded the Christopher Hinton trophy during 1972/73.

Access to the site is primarily via roadways, with the closest railway connection located about one mile inland at Sizewell Halt. This siding was chiefly utilized for transporting spent fuel to the United Kingdom Atomic Energy Authority facility at Sellafield, Cumbria. Fuel logistics involved a crane loading system positioned at the terminus of the Leiston/Sizewell branch line, which links to the East Suffolk line near Saxmundham station. During the 1980s, this rail line was extended to facilitate construction materials delivery for Sizewell B. Since Sizewell A began decommissioning in 2006, rail transport of irradiated fuel has become infrequent. For future developments, a new branch off the Leiston line has been proposed to support freight operations related to Sizewell C’s construction north of Sizewell B.

Construction

In March 1958, East Suffolk County Council identified Sizewell as a candidate location for a nuclear power station. By September that year, the Central Electricity Generating Board submitted an application seeking approval to proceed with construction. Suffolk County Council recommended granting consent in February 1959 after receiving minimal objections. Subsequently, in January 1960, the Minister of Power formally authorized the project’s commencement.

The primary construction contract was awarded in November 1960 to British Nuclear Design and Construction Ltd ('BNDC'), a consortium composed of English Electric, Babcock & Wilcox, and Taylor Woodrow Construction. The initial budget was set at £56 million but increased to £65 million due to inflationary pressures. Over its four decades of operation, Sizewell A generated enough electricity to meet domestic demand across England and Wales for six months. Unit 1 began commercial operation on 21 March 1966, followed by Unit 2 on 15 September that year. The station was officially inaugurated on 7 April 1967 by the Lord Lieutenant of Suffolk, the Earl of Stradbroke.

Design

Originally designed with a net electrical output capacity of 652MWe, Sizewell A initially operated a single turbo-alternator rated at 324.75MW net (327.7MW gross). In 1967, a second turbo-alternator with a capacity of 275MW was added. However, total generating capacity was reduced to 490MW in 1969 and further curtailed to 420MWe by 1973 as measures were taken to limit oxidation within reactor-core components. Of the gross output at full load (490MWe), approximately 70MWe was allocated for internal station power requirements.

The facility incorporated two Magnox reactors each rated at 1,010MW thermal output. These reactors utilized natural uranium fuel moderated by graphite and cooled with carbon dioxide gas. Steam generated from four boilers per reactor powered two turbo-generators originally rated at 325MW but operated at a reduced output level of around 250MW from 1969 onward.

Both reactors and turbines were supplied by English Electric.

Building specification

The foundations for the reactor and boiler rest on an 8-foot-thick reinforced concrete slab laid on sand, engineered to withstand a net bearing pressure of 3.5 tons per square foot. The biological shields rise to a height of 100 feet and vary in thickness from 10 to 14 feet, topped by a composite cap made of steel and reinforced concrete measuring 12 feet thick. To minimize construction expenses, both reactors are housed within a single building.

The turbine hall is constructed with a steel frame and clad in aluminium, spanning dimensions of 380 by 160 by 90 feet, and includes a reinforced concrete basement that extends 26 feet below ground. Its foundations consist of isolated bases and strip footings designed to support loads up to 3 tons per square foot.

Cooling water for the turbines is supplied by the pumphouse, which draws 27 million imperial gallons per hour from an intake located approximately 1,350 feet offshore through two tunnels each 10 feet in diameter. The water is returned via similar tunnels that discharge at a point 350 feet offshore.

Electricity output

From its commissioning until 1984, Sizewell A’s annual electricity production increased, reaching its highest levels in the mid-1970s with generation surpassing 3,000 GWh before experiencing variable output in subsequent years.

Decommissioning

The plant ceased operations on 31 December 2006. Decommissioning responsibilities are managed by Nuclear Restoration Services, a subsidiary of the Nuclear Decommissioning Authority (NDA) formerly known as Magnox Ltd, with an allocated budget of £1.2 billion. Defuelling was completed in 2014, and the turbine hall was dismantled in 2025. The majority of remaining structures are projected to be removed by 2034, followed by a period of care and maintenance extending until 2092. The demolition of reactor buildings and final site clearance are scheduled between 2088 and 2098.

On 7 January 2007, a contractor identified a leak in the laundry area caused by cooling water escaping from the spent fuel pond. This leakage occurred over several days without activating any alarms. Up to several hundred litres of radioactive water escaped through a ruptured pipe, with some entering the North Sea. The HM Nuclear Installation Inspectorate noted that if the contractor had not intervened, the pond could have emptied prior to inspection, potentially leading to an airborne radiation release if exposed fuel had ignited.

Sizewell B

Sizewell B represents the United Kingdom’s sole commercial pressurised water reactor (PWR) power station. Its single reactor was constructed and brought online between 1987 and 1995, achieving first synchronization with the national grid on 14 February 1995. The primary civil engineering contract was awarded to John Laing, while Yorke Rosenberg Mardall provided architectural design services. EDF Energy operates the facility.

EDF has announced intentions to extend the plant’s operational life by an additional two decades beyond its current planned closure date in 2035, potentially continuing operations until 2055. This commitment was reaffirmed in December 2024. As of 2022, closure remains set for 2035; however, governmental representatives have indicated that an extension is probable. EDF anticipates making a final investment decision valued between £500 million and £700 million in 2024 to facilitate this life extension.

The station delivers a gross electrical capacity of 1,250 MW and has maintained an average lifetime capacity factor of 82.9%. It employs a PWR supplied by Westinghouse alongside turbines manufactured by GEC-Alsthom and utilizes cooling water drawn from the North Sea. In the year 2021 alone, Sizewell B produced roughly 6,709 GWh of electricity.

Design

The nuclear island at Sizewell B is derived from the Westinghouse 4-loop SNUPPS design developed in the 1970s, which was also implemented at Wolf Creek and Callaway. However, Sizewell B incorporates improved safety system redundancies and features a passive Emergency Boration System. Unlike SNUPPS, the containment structure was designed by NNC (later part of Amec Foster Wheeler) in collaboration with Bechtel.

While Wolf Creek and Callaway utilize single steam turbine-alternators running at 1,800 RPM (60 Hz) producing approximately 1,200 MW each, such large turbines were not available in the UK when Sizewell B was designed. To capitalize on British manufacturing capabilities and minimize project risks, Sizewell B employs two full-speed turbo-alternators operating at 3,000 RPM (50 Hz), each rated around 660 MW. These are similar to those used in AGR plants like Hinkley Point B and Heysham 1 but have been modified to handle the pressurized water reactor’s saturated steam conditions. Since PWR steam has lower temperature and pressure than that of AGR or fossil-fuel stations, the turbines include stages specifically engineered for wetter steam. The plant can operate at half power using just one turbo-alternator.

Major contributors to the project included:

  • Westinghouse for the reactor system
  • Framatome for the reactor vessel (with the main shell produced by Japan Steel Works and domes along with other components forged by Le Creusot Forge)
  • Westinghouse for core internals
  • Doosan Babcock for steam generation equipment
  • GEC-Alsthom for turbines
  • John Laing for civil engineering works
  • Springfields Nuclear Fuel for fuel supply
  • Yorke Rosenberg Mardall as architectural designers

The containment building features a twin-walled structure enclosed within a distinctive white hemispherical dome, safeguarding the pressurized water reactor and its steam generators.

History

Initially announced in 1969 as an advanced gas-cooled reactor (AGR) power station and later re-designated in 1974 as a steam-generating heavy water reactor (SGHWR), Sizewell B was ultimately confirmed as a pressurized water reactor (PWR) facility in 1980. Early design proposals submitted to the CEGB and Nuclear Installations Inspectorate (NII) were based on Westinghouse’s Trojan plant located in Portland, Oregon, constructed between 1970 and 1975. This concept evolved into the SNUPPS design, first constructed at Callaway, which received CEGB approval in October 1981.

Prior to construction commencement, Sizewell B underwent an extensive safety assessment by the NII alongside a comprehensive public inquiry held from 1982 to 1985 that compiled over sixteen million words of evidence. The inquiry’s conclusion in 1987 stated that, contingent upon safety clearance, no significant obstacles prevented proceeding with construction. Subsequently, the NII accepted the Pre-Construction Safety Case and granted a construction license in August 1987.

Financially, Sizewell B was judged viable at a discount rate of 5% and received funding accordingly. Nonetheless, actual costs escalated to 135% of initial estimates, resulting in cost-performance figures of £2,250 per kW (in 2000 prices) excluding first-of-a-kind expenses or £3,000 per kW including them. After commissioning, generation costs were estimated at roughly 6p per kWh (2000 prices), significantly exceeding the originally projected 3.5p per kWh.

Constructed and commissioned between 1987 and 1995, Sizewell B first connected to the National Grid on 14 February 1995. The total expenditure amounted to about £2 billion at 1987 prices, with civil engineering representing approximately one-quarter of this sum. Initially rated for a thermal output of 3,444 MW and a gross electrical capacity of 1,250 MW, it supplied a net output of approximately 1,188 MWe to the grid. A thermal power uprate of around 1% implemented in 2013 raised thermal capacity to 3,479 MW and electrical output to around 1,195 MWe, dependent on seawater temperature conditions.

Sizewell B operates on an approximate eighteen-month cycle running near full power followed by about one month dedicated to maintenance and refueling. Designed for an operational lifespan close to forty years—until roughly 2035—comparable PWR plants have been granted extensions up to sixty years.

Operational interruptions have occurred throughout its history: an unplanned shutdown in May 2008 due to failure of conventional equipment; an extended outage starting March 2010 caused by faults in pressuriser electrical heaters; and a minor fire during repair work in July 2010. Another shutdown happened in March 2012 following an electrical fault before restarting at half capacity.

In response to lessons learned from the Fukushima disaster, EDF Energy established a remote Emergency Response Centre near Sizewell B in 2013 to enhance remote operational control capabilities and provide backup support systems.

Construction began in January 2014 on a dry spent fuel storage facility intended to supplement the existing spent fuel pool expected to reach capacity by 2015. This new store opened in April 2016 to accommodate spent fuel generated until at least 2035 pending availability of a deep geological repository. The first fuel cask was installed there in March 2017.

In 2021, Sizewell B experienced a prolonged outage caused by excessive wear on stainless steel "thermal sleeves" inside control rod mechanisms. Maintenance activities extended beyond four months as safety assessments and corrective measures were undertaken.

Sizewell C

Following EDF’s 2009 takeover of British Energy, the initiative to develop a dual-reactor facility at Sizewell has advanced significantly. The site already holds a grid connection agreement for a new station, with the planned 1,600MW Sizewell C reactors anticipated to supply, together with Hinkley Point C, approximately 13% of the United Kingdom’s electricity during the early 2020s. EDF plans to implement Framatome’s EPR technology, aligning with similar projects underway in Finland, France, and China.

In 2010, the UK government designated Sizewell as one of eight viable locations for future nuclear power development. By 2015, Sizewell was included in Strategic Investment Agreements between the UK and China; however, the exact funding arrangements have yet to be finalized. The ultimate investment verdict is contingent upon advancements at Hinkley Point C.

In May 2020, the non-governmental organisation Energy for Humanity called for governmental endorsement of Sizewell C, highlighting nuclear energy’s importance in affordable climate mitigation and urging that procurement lessons from Hinkley Point C and offshore wind projects be applied to ensure timely delivery.

Apprehensions remain regarding consortium stakeholder China General Nuclear Power Group (CGN), a Chinese state-owned enterprise blacklisted by the United States due to concerns over nuclear technology espionage and potential military applications.

EDF lodged its planning application in May 2020, forecasting the creation of 25,000 jobs and pledging that 70% of investment would be sourced from UK suppliers. The design mirrors that of Hinkley Point C closely to capitalize on prior experience and achieve cost efficiencies. The proposal has received endorsement from Unite the Union.

On 27 May 2020, EDF Energy submitted an application for development consent but has yet to secure project financing. To address construction risks and funding obstacles, EDF is seeking UK government backing through a regulated asset base (RAB) framework or equity involvement.

By June 2020, EDF applied to the Office for Nuclear Regulation (ONR) for a licence authorizing construction and operation of Sizewell C—an indispensable regulatory requirement.

In March 2022, an agreement was reached between the UK government and EDF for each party to acquire a 20% ownership stake in Sizewell C, with infrastructure investors and pension funds expected to provide the remaining 60%.

See also

Further reading

  • Wall, Christine (2019). "'Nuclear prospects': the siting and construction of Sizewell A power station 1957–1966". Contemporary British History. 33 (2): 246–273.

External links

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