Hunterston B nuclear power station
Hunterston B Power Station is a nuclear power station in North Ayrshire, Scotland. It is located about 6 miles (9 km) south of Largs and about 2.5 miles (4 km) north-west of West Kilbride, on the Firth of Clyde coast.
|Hunterston B nuclear power station|
The Hunterston B AGR reactor building.
|Official name||Hunterston B|
|Nuclear power station|
|Thermal power station|
|Units operational||2 x 610 MWe (Operating at ~495 MWe  )|
|Nameplate capacity||1220 MWe|
|Commons||Related media on Commons|
It has generated electricity since 1976. It is currently operated by EDF Energy. It currently generates up to 1000 MW and is due to operate until 2023.
Hunterston B is very similar in design to the Hinkley Point B power station which is also due to operate until 2023.
The construction of Hunterston B was undertaken by a consortium known as The Nuclear Power Group (TNPG). The two advanced gas-cooled reactors (AGR) were supplied by TNPG and the turbines by C. A. Parsons & Co. Hunterston B started generating electricity on 6 February 1976.
On 3 December 1977 The Times reported that seawater had entered the reactor through a modification of the secondary cooling system. The secondary cooling system uses fresh water to cool various items including the bearings of the gas circulators, which circulate the carbon dioxide (CO2) coolant through the reactor to the boilers. A small leak of CO2 through a seal had developed, and a bypass pipe was installed to remove the water contaminated with CO2 to the seawater cooling ponds. When maintenance work was carried out on the reactor and the pressure in the gas cooling system was reduced, sea water was able to flow back up this bypass pipe and into the reactor. The residual heat of the reactor was such that the seawater evaporated rapidly, leaving deposits of salt in the reactor around the gas circuit. It was estimated at the time that the reactor could be out of operation for a year, that the repairs could cost £14 million, and that electricity tariffs would have to rise by between 1 and 2 per cent. Extensive modelling work was performed in the Nuclear Power Company's (NPC) Whetstone, Leicestershire, fluid flow laboratories to determine where the salt would have been deposited, and the salt was successfully removed by technicians using vacuum cleaners and the plant returned to operation.
In February 1997 there was concern that contaminated carbon dioxide gas from the plant had got into three road tankers and then entered the food chain via soft drinks and beers. Carlsberg-Tetley withdrew all its gas cylinders in Scotland as a result of finding contamination in one.
In December 1998 an INES 2 incident occurred after severe winds and sea spray disabled all four power lines to the site during the Boxing Day Storm of 1998. After multiple grid failures in a short period of time, emergency diesel generators failed to start. Normally, in the absence of power for the reactor cooling pumps, the reactor would be passively cooled. However, the emergency control system which would have initiated passive cooling failed to act, as it had not been reset. Reactor cooling was reinstated after 4 hours. There was considerable confusion and delay in restoring power as plant schematics and security systems were computerised but were rendered inoperable due to lack of electrical power. Due to the inherent safety margins of the AGR reactor design, there was no reactor damage, and the plant would have tolerated loss of cooling for 20 hours. The subsequent investigation made several recommendations: redesign of the insulators on the 400 kV power lines, installation of an additional 132 kV power line for emergency power, a second diesel generator building remote from the first, installation of an uninterruptible power supply for the reactor safety systems and for essential computer equipment, provision of hard copy plant schematics and emergency protocols, and revised staff training procedures including simulation of multiple simultaneous system failures.
In 2006 there was concern that the graphite moderator core in each of the twin AGRs at Hunterston B might have developed structural problems in the form of cracking of the bricks (as at similar AGRs) but this has not been confirmed.
Its net electrical output was 1,215 MW. In 2007 the reactors were restricted to operating at a reduced level of around 70% of full output (around 850 MWe net). Subsequent work during maintenance shutdowns have resulted in Reactor 3 operating at around 82% (540Mwe net) in early 2011, and Reactor 4 at around 73% (480 MWe net). In total this equates to around 1020MWe gross output from the generators. Internal load of 90MWe brings net output to approximately 930MWe. Hunterston B is capable of supplying the electricity needs of over 1 million homes.
Hunterston B was originally planned to operate until 2011. In 2007 planned operation was extended by 5 years to 2016. In December 2012 EDF said it could (technically and economically) operate until 2023.
Graphite core keyway root cracksEdit
In October 2014 it was reported that cracks had been found in one of the reactors at the plant following routine inspections which began in August 2014. Two of about 3,000 graphite bricks in the core of reactor four at Hunterston were affected. The plant's operator, EDF Energy, said the cracking was predicted to occur as the station ages and said that the issue would not affect the safe operation of the reactor.
In October 2016 it was announced that super-articulated control rods would be installed in the reactor because of concerns about the stability of the reactors' graphite cores. The Office for Nuclear Regulation (ONR) had raised concerns over the number of fractures in keyways that lock together the graphite bricks in the core. An unusual event, such as an earthquake, might destabilise the graphite so that ordinary control rods that shut the reactor down could not be inserted. Super-articulated control rods should be insertable even into a destabilised core.
In early 2018 a higher rate of new keyway root cracks than modelled was observed in Reactor 3 during a scheduled outage, and EDF announced in May 2018 "While Hunterston B Reactor 3 could return to operation from the current outage, it will remain offline while the company works with the regulator to ensure that the longer term safety case reflects the findings of the recent inspections and includes the results obtained from other analysis and modelling."
In December 2018 EDF pushed back their estimated return to service date to March 2019 for Reactor 4 and April 2019 for Reactor 3, to allow for further modelling work and a new seismic analysis. In March 2019 pictures of the cracking were released with EDF stating that it intended to seek permission from the ONR to restart reactor 3 by raising the operational limit for the number of cracks. About 370 fractures have been discovered, on average 2mm wide, in about 10% of the graphite bricks in the reactor core. This was above the operational limit of 350 fractures, and EDF intends to present a new safety case for an operational limit of 700 cracks.
- "Hunterston B EDF Energy". Retrieved 2 Dec 2014.
- Wearne S H & Bird R H (2009). "UK Experience of Consortia Engineering for Nuclear Power Stations, School of Mechanical, Aerospace & Civil Engineering, Dalton Nuclear Institute, University of Manchester" (PDF).[permanent dead link]
- Nuclear Power Plants in the UK - Scotland and Wales Archived 2009-07-19 at the Portuguese Web Archive
- The Times, Saturday, 3 December 1977; pg. 1; Issue 60177; col D
- Wilson, Iain (6 March 1997). "Nuclear chief admits 'failure'. Fear of food risk". Herald Scotland. Retrieved 24 April 2014.
- "Carbon dioxide supply system at Hunterston B Power Station". 6 October 1998. Retrieved 13 October 2016.
- "Brewery recalls CO2 cylinders". The Independent. 8 March 1997. Retrieved 13 October 2016.
- EDF Energy Loss of Off Site Power: An Operator's Perspective
- Large and Associates. Brief Review of the Documents Relating to the Graphite Moderator Cores at Hinkley Point B and Other Advanced Gas-Cooled Reactors, R3154 5 July 2006 Archived November 14, 2006, at the Wayback Machine
- Hunterston B, EDF Energy
- Scotland's Hunterston B to work until 2016, UPI, 11 December 2007][permanent dead link]
- "Hunterston B nuclear power plant will run until 2023". BBC News. 4 December 2012.
- "Cracks found at Hunterston nuclear power station". BBC News. 6 October 2014.
- "Nuclear reactor cracks 'challenge safety case'". BBC News. 31 October 2016. Retrieved 31 October 2016.
- "New cracks delay restart of Hunterston B reactor". World Nuclear News. 3 May 2018. Retrieved 6 May 2018.
- Nina Chestney, Susanna Twidale (9 May 2018). "Cracks in British nuclear reactor ring power alarm bells". Reuters. Retrieved 20 November 2018.
- "Hunterston B restarts delayed by several weeks". World Nuclear News. 21 December 2018. Retrieved 22 December 2018.
- "Footage of cracks in North Ayrshire nuclear reactor released". The Guardian. 8 March 2019. Retrieved 9 March 2019.
- "Hunterston B: Pictures show cracks in Ayrshire nuclear reactor". BBC News. 6 March 2019. Retrieved 6 March 2019.