• 82.9% (Lifetime) • 63.9% (2021) EDF's strategic target is for a 20-year life extension for Sizewell B PWR, beyond the current accounting closure date of 2035. This would mean the plant remaining in operation until 2055. EDF reaffirmed this plan in December 2024. , the power station is still planned to close in 2035. However, a government official is cited stating that "it probably will be extended", while EDF intends to take a final decision on the estimated investment of £500£700million in 2024.
Design The nuclear island at Sizewell B is based on a
Westinghouse 4-loop plant known as
SNUPPS (Standard Nuclear Unit Power Plant System) initially designed in the 1970s and used at
Wolf Creek and
Callaway but with additional redundancy and diversity in the safety systems, and other modifications such as the addition of a passive Emergency Boration System. The containment design was not based on SNUPPS however, but was designed by NNC (National Nuclear Corporation – bought by
Amec Foster Wheeler in 2005) in conjunction with
Bechtel. The Wolf Creek and Callaway plants each have single half speed, 1,800RPM (60Hz), steam turbine-alternator sets which use the steam produced from the heat generated in the reactor to produce about 1,200MW of electricity at the US grid frequency of 60Hz. Such large turbo-alternator sets were not available in the UK at the time Sizewell B was designed. So that orders could be given to UK manufacturers, and to avoid project risk in dealing with what were at the time newly designed very large turbo-alternator sets, Sizewell B uses two full-speed, 3,000RPM (50Hz), nominal 660MW turbo-alternator sets similar to those used at the AGR power stations Hinkley Point B, Heysham 1, Hartlepool and Torness, and at some fossil-fuel power stations elsewhere, but adapted to cope with the wetter steam conditions produced by the PWR steam supply system. PWR steam supply systems produce saturated steam at lower temperature and pressure than the dry superheated steam produced by AGR reactors or fossil-fuel power stations, and the high- and intermediate-pressure stages of the steam turbines have to be designed cope with this. Sizewell B can run at half power using one turbo-alternator. The major components were supplied by: • Reactor system:
Westinghouse • Reactor vessel:
Framatome (main shell:
Japan Steel Works, domes and other components: Le Creusot Forge) • Core internals: Westinghouse • Steam raising:
Doosan Babcock • Turbines:
GEC-Alsthom • Civil works:
John Laing • Fuel:
Springfields Nuclear Fuel • Architect:
Yorke Rosenberg Mardall A distinctive white hemisphere envelopes the outer shell of the twin-walled containment building that protects the pressurised water reactor and its
steam generators.
History First announced in 1969 as an
advanced gas-cooled reactor (AGR) based power station, and then in 1974 as a
steam-generating heavy water reactor (SGHWR), Sizewell B was eventually announced as a PWR power station in 1980. The initial design submissions to the CEGB and the
Nuclear Installations Inspectorate (NII) were based on the design of the
Trojan plant at
Portland, Oregon. Designed by Westinghouse, construction of Trojan began in 1970 and was completed in 1975. Westinghouse continued to develop the design they had used for the Trojan plant into the SNUPPS design, built first at Callaway, and SNUPPS was adopted as the basis for the design approved by the CEGB in October 1981. Before construction commenced, the design of Sizewell B was subjected to a detailed safety review by the NII, and a lengthy public inquiry. The Pre-Construction Safety Case was submitted to the NII in August 1981. The public inquiry was held between 1982 and 1985, and took over 16million words of evidence, a record at the time. The chairman of the inquiry, Sir Frank Layfield, reported in early 1987 that, subject to a satisfactory safety case, there were no substantive reasons why the project should not proceed. The Nuclear Installations Inspectorate accepted the Pre-Construction Safety Case and issued a licence to proceed with construction in August 1987. Sizewell B was calculated to be economically viable at a 5% discount rate and was approved financially on that basis. The project cost was revised upwards three times to 135% of the original cost, providing a cost-performance of £2,250/kW (2000 prices) not including first of a kind costs and £3,000/kW including them. A post-startup evaluation estimated generating cost were about 6p/kWh (2000 prices, equivalent to £/MWh in ), excluding first-of-kind costs but using an 8% discount rate for the cost of capital, much higher than the expected cost in 1995 of 3.5p/kWh (2000 prices, equivalent to £/MWh in ). Sizewell B was built and commissioned between 1987 and 1995, and first synchronised with the
National Grid on 14 February 1995. The cost of Sizewell B has been quoted as £2billion (1987 prices) with a quarter of that cost being related to civil engineering works. The original rating was for a thermal power of 3,444MW and gross electrical output of 1,250MW, though this is dependent on seawater temperature. As with many other PWRs, Sizewell B operates on an 18-month operating cycle, i.e. at or near 100% output continuously for around 18months, followed by a month's shutdown for maintenance and refuelling. Sizewell B was designed for a commercial life of 40years (i.e. to around 2035) but similar stations elsewhere have been granted extensions to 60years. On 27 May 2008, Sizewell B had an unplanned shutdown, cutting off its supply to the National Grid. A
British Energy spokesman said that the fault involved conventional equipment at the plant rather than any part of the nuclear reactor. On 2 July 2010, just before 21:00, while still offline, a minor fire broke out on the second floor of the building housing the charcoal adsorber at Sizewell B. Numerous emergency services were called to the scene and the fire was brought under control by 3:30 the following day when the charcoal adsorber was flooded. On 2 March 2012, Sizewell B had an unplanned shutdown due to an electrical fault. One and a half weeks later it was restarted at half capacity. , conditions improved and Sizewell B continued under carefully controlled operation. In 2013, a new remote Emergency Response Centre was inaugurated near the power station, following recommendations made after the
Fukushima Daiichi nuclear disaster. The centre provides remote controls and a back-up plant. In January 2014, the building of a
dry spent nuclear fuel store began. The existing
spent fuel pool, which stores spent fuel under water, was expected to reach full capacity in 2015. In April 2016, the building was inaugurated. This will enable
spent nuclear fuel produced from autumn 2016 until at least 2035 to be stored until a
deep geological repository is available. In March 2017, the first cask containing spent nuclear fuel was installed. In 2021, Sizewell B had an extended outage for maintenance and safety related issues.
The Times reported that excessive wear on some stainless steel "thermal sleeves" in the control rod mechanisms had been discovered. The maintenance period was extended to over four months to evaluate the cause and extent of the wear to decide how many to replace. ==Sizewell C==