Old Reactors

Wylfa Nuclear Power Station

Wylfa Nuclear Power Station

Magnox Reactors

In the UK 26 Magnox reactors were built at 11 sites between 1956 and 1971.1 The first Magnox reactor was built at Calder Hall, next to Sellafield, and opened by the Queen on 17th October 1956. It is a British designed reactor – only two were sold abroad – one to Japan and one to Italy. The last Magnox reactor opened at Wylfa on the Isle of Anglesey in 1971.

Reactor 1 at Wylfa is the last remaining operating Magnox reactor. It is expected to close on 30th September 2014 with a possible extendion to December 2015.2

As with most nuclear reactors Magnox reactors are fuelled by uranium. When a uranium atom is split, two or three neutrons fly off at a tremendous speed, splitting more uranium atoms causing a chain reaction. During this chain reaction, the uranium fuel becomes very hot. In Magnox reactors carbon dioxide gas is used to carry the heat away and heat water into steam, which is then used to generate electricity in turbines, just as in a conventional power station.

In order to keep the reaction under control, Magnox reactors have a graphite core or ‘moderator’, which slows down the neutrons. Uranium fuel elements are inserted into vertical channels in this graphite core. (The uranium fuel is clad in a special magnesium alloy ­ hence the name ‘Magnox’). Control rods can also be inserted to absorb the neutrons and stop the chain reaction. These control rods are raised when the operator wants to start up the reactor again. The core is enclosed inside a pressure vessel made out of steel or concrete.

Unlike most other reactors, Magnox reactors use natural uranium. Uranium dug out of the ground, only contains about 0.7% of the split-able (fissile) type of uranium (uranium-235), so 99.3% of the atoms are non-fissile (uranium-238). Most of the world’s nuclear reactors use fuel containing ‘enriched uranium’, which means the uranium-235 content has been increased to about 2 or 3%.

Magnox Electric Ltd is owned by EnergySolutions. It is the management and operations contractor responsible for 10 nuclear sites (all Magnox sites apart from Calder Hall) and one hydroelectric plant (Maentwrog) in the UK. Under contract to the site owner, the Nuclear Decommissioning Authority (NDA), the company is responsible for electricity generation at Wylfa and Maentwrog, defuelling at Chapelcross, Oldbury and Sizewell A, and the decommissioning of Hunterston A, Berkeley, Bradwell, Dungeness A , Hinkley Point A and Trawsfynydd.

A two-year competitive procurement process for ownership of  two Site Licence Companies, Magnox Ltd and Research Sites Restoration Ltd, which operate the 10 Magnox power station sites and two former research centres at Harwell and Winfrith was launched in 2012.

There are four consortia bidding for the contract:

  • Reactor Site Solutions (Bechtel, EnergySolutions)
  • The Babcock Fluor Partnership
  • CAS Restoration Partnership (CH2M Hill, Areva, Serco)
  • UK Nuclear Restoration Ltd (AMEC, Atkins, Rolls Royce)

Tenders are due to be submitted towards the end 2013. These will be evaluated and then the preferred bidder will be announced in March 2014. It is anticipated that shares will be transferred and the contract award confirmed in September 2014.

Dungeness B AGR

Dungeness B AGR

Advanced Gas-cooled Reactors (AGRs)

The Advanced Gas-cooled Reactor design was an attempt to improve on the earlier Magnox design, aiming to achieve higher gas temperatures to improve efficiency. AGRs use uranium in which the fissile part of the uranium (U-235) has been increased or enriched to 2 per cent. Like Magnox reactors, this was a peculiarly British design and no AGRs were sold abroad. Also like Magnox reactors, AGRs have a graphite core. Like the last two Magnox stations (Oldbury and Wylfa), AGRs have a pre-stressed concrete pressure vessel, and use carbon dioxide gas as a coolant.

The AGR programme was a disaster. The first station to be ordered – Dungeness B – was 12 years late, and most of the others were late too with huge cost overruns. Different contractors were used to build different stations, and design changes meant that most of the stations are of a slightly different design.

A long campaign was run against the construction and opening of one of the last AGRs to be built – Torness in East Lothian, near Edinburgh – in the 1970s and 80s. After Torness opened in 1989, the Glasgow Herald quoted a Scottish Office ‘source’ who described it as a £2.5 billion mistake which should never have been built.

Closure dates

Unlike the Magnox reactors, the AGR reactors are all still generating electricity. EDF Energy own and operate 14 AGRs at seven sites. Whilst all of these reactors have closure dates ‘for accountancy purposes’ this does not necessarily mean this is when they will close. These dates are kept under review and can be adjusted (in either direction) at any time to take account of commercial, technical and safety issues. EDF Energy has announced that it would like to extend the life of its AGRs by an average of 7 years. That could mean that instead of decommissioning the AGRs between 2016 and 2023, as previously envisioned, the AGRs would start being decommissioned in 2021, while some would continue operating until 2030.3

EDF Energy’s Stations Station Type Net Capacity (MW) Date Commissioned Closure date for accounting purposes Next PSR
Dungeness B AGR 1,040 1983 2018 2017
Hartlepool AGR 1,180 1983 2019 2018
Heysham 1 AGR 1,155 1983 2019 2018
Hinkley B AGR    880 1976 2023 2016
Hunterston B AGR    880 1976 2023 2016
Heysham 2 AGR 1,220 1988 2023 2019
Torness AGR 1,185 1989 2023 2019
Sizewell B PWR 1,198 1995 2035 2015

On 4th December 2012 EDF Energy announced that it will extend the operating life of two of its nuclear power stations, including Hunterston B, by seven years. Both plants are now expected to remain operational until at least 2023.

The Office for Nuclear Regulation (ONR) says it is working with EDF Energy to extend the life of its nuclear power stations and that it is “content for the plants to continue to operate”, as long as they pass regular safety tests. Hunterston B and its sister station Hinkley Point B in Somerset are both due to undergo a periodic safety review (PSR) in 2015 with a decision on whether to grant EDF Energy a renewed license in 2016. A PSR is carried out for each operating nuclear power station in the UK every ten years. The review requires an operator to prove that its nuclear power plant is safe and complies with site license conditions. So, theoretically ONR could force Hunterston’s closure in 2016, but EDF Energy said the decision “comes after extensive reviews of the plants’ safety cases and continuing work with the independent nuclear regulator”.


UK nuclear waste map (courtesy of CoRWM)

UK nuclear waste map
(courtesy of CoRWM)

There is no opportunity for public intervention in the PSR process, and the ONR is not required to consult the public on issues related to nuclear safety. However, strong local campaigns for the closure of ageing Magnox stations based on health and safety concerns might well have influenced decisions taken by ONR and the nuclear operator in the past, as a number have closed after completion of the PSR process.

EDF Energy’s 15th reactor is the Sizewell B Pressurised Water Reactor (PWR) – the only one in the UK. PWRs have a steel pressure vessel and the primary coolant is water which is pumped under high pressure to the reactor core where it is heated by the energy generated by the fission of atoms. The water also acts as a neutron moderator. The heated water then flows to a steam generator where it transfers its thermal energy to a secondary system where steam is generated and flows to turbines which, in turn, spin an electric generator. In contrast to a boiling water reactor, pressure in the primary coolant loop prevents the water from boiling within the reactor. Although Sizewell is not due to close until 2035, EDF Energy has been discussing the possibility of extending its life for 20 years.

1. A full list of Magnox Reactors
2. Electricity Generation, Magnox Sites Website, accessed 24th June 2013
3. Guardian 22nd May 2012


Published: 13 November 2012
Last updated: 24 June 2013