Magnox

Magnox is a special kind of nuclear power reactor made in the United Kingdom. It was built to make electricity and also to help create materials for nuclear weapons. The reactor uses natural uranium for fuel, with graphite to help control the nuclear reaction and carbon dioxide gas to keep it cool.

The name Magnox comes from the magnesium-aluminium alloy used to protect the fuel rods inside the reactor. This type of reactor was designed to be very efficient with neutrons, which are tiny particles that help control the nuclear reaction. Because of this, it could use natural uranium instead of the enriched uranium needed in many other reactors.

Only a few dozen Magnox reactors were ever built, mostly in the UK between the 1950s and 1970s. The first one to start working was Calder Hall in 1956, which is often called the world's first commercial nuclear power station. The last one in Britain stopped operating in 2015, but as of 2016, North Korea still uses reactors of this type. Later, a new design called the advanced gas-cooled reactor was developed to be more efficient.

General description

Windscale

Main article: Sellafield

The UK's first large nuclear reactor was the Windscale Pile in Sellafield. It was built to make plutonium-239 using natural uranium as fuel. Because natural uranium doesn’t react well on its own, graphite was used to help the reaction.

The reactor was made of a huge cube of graphite blocks with channels for the fuel. Uranium in aluminium containers was placed in these channels. It worked at low temperatures and used air and fans to stay cool. However, graphite can catch fire, and this happened in 1957 when part of the reactor burned.

Magnox

The UK wanted more power from nuclear energy and still needed plutonium, so they changed the Windscale design. The new design, called Magnox, had to work at higher temperatures and use a different cooling method. Instead of air, they used carbon dioxide (CO₂) to keep things cool.

Because aluminium couldn’t handle the higher temperatures, a new material called magnox alloy was used for the fuel containers. The fuel was arranged vertically, and the reactors could keep running while adding new fuel. The whole reactor was placed inside a strong steel container surrounded by a concrete building for safety.

AGR

Main article: Advanced Gas-cooled Reactor

The Magnox design had some problems, so engineers worked on a new version called the advanced gas-cooled reactor (AGR). The goal was to make it more efficient by running it at much higher temperatures. This required new materials and changes to the fuel.

Technical information

Economics

The first Magnox reactors at Calder Hall were built to make materials for nuclear weapons. They also made heat, which was used to create steam. This steam helped make electricity or provided heat for nearby factories like Windscale.

These early reactors were not very efficient. They turned only about 18.8% of their energy into electricity. In 1957, the British government decided to build more nuclear power plants to make electricity. They wanted nuclear power to meet a quarter of the UK’s needs by 1965. Even though nuclear power cost more than coal, the government thought it would help reduce the power that coal workers could demand. By 1960, the plan changed to build less nuclear power, as coal was still cheaper. By 1963, it was clear that nuclear power cost more than twice as much as coal.

After use, the fuel from these reactors was stored in special pools of water to cool down. However, this storage could only last a short time before the fuel needed to be processed again, which added to the cost. Later reviews showed that the project did not stick to one design, which made it more expensive. In the end, the cost of electricity from Magnox reactors was almost 50% more than what coal power plants could have provided.

Safety

Magnox reactors were made to be safe with a simple design and special cooling. They didn’t need extra safety walls because the design could handle most problems. If something went wrong, like losing coolant, the reactor could shut down fast to stop big accidents. These reactors wouldn’t explode because the coolant is a gas.

Even though they were thought to be safe, Magnox reactors were not built near where many people live. Rules were made to keep these reactors far from large groups of people. Some older Magnox designs let out more radiation, but newer ones had better protection to keep people safer.

Reactors built

In the United Kingdom, 11 power stations with 26 units were built. One went to Tōkai in Japan, and another to Latina in Italy. North Korea also made its own reactors using this design, which was shared at an Atoms for Peace meeting.

The first of these power stations, Calder Hall, was the world's first to make electricity on a large scale. It started working on 27 August 1956 and was opened by Queen Elizabeth II on 17 October 1956. It stopped operating on 31 March 2003 after almost 47 years of use.

The first two stations, Calder Hall and Chapelcross, were owned by the UKAEA and were used to help make materials for defense in their early days. Starting in 1964, they mostly provided electricity for everyday use. In April 1995, the UK Government said that making these materials for defense would stop.

Later, bigger stations were owned by the CEGB and used mostly for everyday electricity. However, Hinkley Point A and two other stations could still be changed if needed to help make materials for defense.

Derating to reduce corrosion

When these reactors first started, it was found that some parts got damaged by the hot gas used to keep them cool. This meant they had to lower the temperature and how much power they made. For example, the Latina reactor in Italy had its power lowered by 24% in 1969, from 210 MWe to 160 MWe, by cooling it less.

Last operating magnox reactor

The Nuclear Decommissioning Authority said on 30 December 2015 that Wylfa Unit 1 – the last Magnox reactor still working in the world – had closed. This unit had provided electricity for five years longer than planned. Both units at Wylfa were supposed to stop working at the end of 2012, but Unit 2 was closed early in April 2012 so Unit 1 could keep going and use up the remaining fuel that was no longer being made.

A small experimental reactor in Yongbyon, North Korea, based on the Magnox design, was still operating as of 2016.

Magnox definitions

Magnox alloy

Magnox is also the name of a special mix—mostly magnesium with tiny bits of aluminium and other metals—used to wrap uranium fuel. This mix keeps the fuel safe and stops it from breaking apart. Magnox is short for magnesium non-oxidising. One good thing about this mix is that it doesn’t block the tiny particles that make energy in a special way. But there are two big problems:

• It can’t get very hot, so the plant can’t be as efficient.
• It can’t mix with water, so old fuel can’t be stored underwater for long.

Magnox plants

The word magnox can also mean:

• Three reactors in North Korea, built using plans from British magnox reactors:
  • A small 5 Mwe test reactor at Yongbyon, which worked from 1986 to 1994 and then started again in 2003.
  • A 50 MWe reactor, also at Yongbyon, building started in 1985 but was stopped as part of the 1994 US-North Korea Agreed Framework.
  • A 200 MWe reactor at Taechon, building also stopped in 1994.
• Nine power reactors in France, all now closed. These were similar to British magnox reactors but used a different mix of metals to wrap the fuel and were set up differently.

Decommissioning

The Nuclear Decommissioning Authority is in charge of shutting down the UK's Magnox power plants. This work will cost a lot of money. There are plans to finish this work in either 25 years or 100 years. After about 80 years, dangerous materials inside the reactor will become safer, making it easier to take apart the buildings. A plan called Safestore, which takes about 100 years, is currently being used.

The Sellafield site, which processed used fuel from Magnox reactors, is also being shut down. Fuel for Magnox reactors was made at a place near Preston.

Calder Hall opened in 1956 and was the world's first commercial nuclear power station. The NDA is thinking about turning one of its reactors into a museum. All of the UK's Magnox reactor sites, except Calder Hall, are run by Magnox Ltd, a company owned by the NDA.

In 2008, the company running these sites split into two parts, Magnox North Ltd and Magnox South Ltd. These included sites like Chapelcross, Hunterston A, Oldbury, Trawsfynydd, Wylfa, Berkeley, Bradwell, Dungeness A, and Hinkley Point A. In 2011, the two companies joined back together as Magnox Ltd. Later, in 2019, Magnox Ltd became a part of the NDA again.

List of Magnox reactors in the UK

Magnox reactors exported from the UK