RBMK

The RBMK (Russian: Реактор большой мощности канальный, РБМК; reaktor bolshoy moshchnosti kanalnyy, "high-power channel-type reactor") is a type of graphite-moderated nuclear power reactor created by the Soviet Union. It works in a way similar to a boiling water reactor, where water boils inside special tubes. Unlike other reactors that have one large steel container holding the core, the RBMK design uses a concrete vault with individual pipes for each fuel bundle, and graphite surrounding these pipes.

The RBMK is one of the oldest types of commercial reactors still in use today. However, its original design had some problems, such as how it reacted when power was low, which helped cause the 1986 Chernobyl disaster. During this event, a runaway nuclear chain reaction led to explosions and a fire, releasing radioactive material across much of Europe. Although many people wanted these reactors shut down after the disaster, several still operate in Russia, providing a lot of power.

RBMK reactors are grouped into three generations based on when they were built. The first generation was made in the early-to-mid 1970s, before strict safety rules existed. The second generation followed safety standards introduced in 1982. The third generation was built after the Chernobyl accident, with even stronger safety measures in place.

Lifespan

The RBMK reactor was originally planned to work for 30 years. But with updates, like fixing problems with the core, this time can be longer — up to 45 or even 50 years. Some reactors, like those at Kursk, Leningrad, and Smolensk, are now set to work even longer.

In 2024, the time for Leningrad unit 3 was pushed from 2025 to 2030. In 2026, Leningrad Unit 4 got five more years, so it will work until 2031. All these reactors are run by Rosatom's subsidiary Rosenergoatom.

In 2026, the Kursk plant's RBMK reactors got big safety improvements, making risks almost 100 times smaller.

History

The RBMK was developed by the Soviet nuclear power program to create a water-cooled reactor that could also help make plutonium. The first small reactor, Obninsk AM-1, began working in 1954.

The RBMK used regular water to keep cool and graphite to control the reaction. This design allowed for bigger and more powerful reactors to be built quickly, often using parts made on-site. Because these reactors were so large, they did not have thick outer walls for safety, which made them cheaper but also riskier.

The RBMK-1000, finished in 1968, was the world's largest reactor design at the time. It was chosen because it was easier to build and could produce large amounts of power, helping the Soviet Union meet its goals. However, problems with the RBMK design were found even before the first reactors were built, but construction continued anyway. The first RBMK reactor began operating in 1973.

Reactor design and performance

The RBMK reactor is a special kind of nuclear power reactor made in the Soviet Union. It uses graphite to help control the reaction and water that boils inside the reactor to make steam. This design is different from other reactors because the water boils right inside the reactor’s tubes.

The reactor sits in a strong concrete building. Inside, there is a big block of graphite that helps control the nuclear reaction. The reactor has many tubes where the nuclear fuel sits, and these tubes are cooled by water. The design allows the reactor to keep running even when swapping out fuel, which is helpful for making materials used in nuclear technology. However, this design has some challenges, especially if not watched closely, which showed in serious accidents in the past.

Design flaws and safety issues

The RBMK reactor was created quickly in the Soviet Union, which meant some safety features were not included. One big issue is that when water inside the reactor turns to steam, it can cause the reactor to become unstable. This happened because the reactor uses graphite to help control the reaction, and when water turns to steam, it stops absorbing certain particles, making the reaction faster.

After a serious accident in 1986, changes were made to make these reactors safer. For example, control rods were improved to stop the reaction faster if needed. Workers also fixed parts of the reactors to prevent similar problems from happening again. These changes help keep the reactors running safely today.

Further development

Main article: MKER

After the Soviet Union ended, a new design called the MKER was created from the RBMK. This stands for Multi-loop pressure tube power reactor. The MKER has better safety features and a special building to contain any accidents. Plans were made to build MKER-800, MKER-1000, and MKER-1500 models at the Leningrad nuclear power plant.

List of RBMK reactors

Color key:

Other Graphite Moderated Reactors

There is a graphite-moderated Magnox reactor in North Korea at the Yongbyon Nuclear Scientific Research Center. Some reactors like the AGR and the Dragon reactor at Winfrith also use graphite but they use gases such as carbon dioxide or helium to move heat, which changes how they work.

Four smaller versions of the RBMK called EGP-6 reactors were used at the Bilibino Nuclear Power Plant, which is one of the northernmost nuclear power plants in the world. One of these reactors stopped operating forever in 2020, and the other three stopped in December 2025.

Known incidents

Many problems happened at power plants using the RBMK reactor. Some of these problems were kept secret. Serious issues, like partial meltdowns at the Leningrad and Chernobyl plants, were not fixed properly, which helped cause the big disaster in 1986.

Some of the known problems at RBMK reactors include:

• Explosion of a tank holding gases at the Leningrad Nuclear Power Plant unit 1 in January 1975
• Power outage at the Kursk Nuclear Power Plant in 1980
• Discovery of a safety issue at Ignalina Nuclear Power Plant unit 1 in 1983 and at unit 4 of the Chernobyl Nuclear Power Plant
• Shifting of concrete bars at Chernobyl Nuclear Power Plant units 3 and 4 in 1984
• Chernobyl disaster in 1986
• Turbine fire at Chernobyl unit 2 in 1991
• Melting of cables at Chernobyl unit 1 in 1991
• Release of water at Chernobyl unit 1
• Problems at Chernobyl unit 3 in 1993, 1994, and 1995
• Stop of the third unit of the Leningrad Nuclear Power Plant in 2009 due to a hole in a pump