RBMK

RBMK reactor class
View of the Smolensk Nuclear Power Plant site, with three operational RBMK-1000 reactors. A fourth reactor was cancelled before completion.
Generation	Generation II reactor
Reactor concept	Graphite-moderated light water-cooled reactor
Reactor line	RBMK (Reaktor Bolshoy Moshchnosti Kanalniy)
Reactor types	RBMK-1000 RBMK-1500 RBMKP-2400 (never built)
Status	26 blocks: 7 operational 1 involved in accident 1 partially damaged 9 cancelled 10 decommissioned 3 small EGP-6 graphite moderated BWR operational (as of December 2021)[1][2]
Main parameters of the reactor core
Fuel (fissile material)	235U (NU/SEU/LEU)
Fuel state	Solid
Neutron energy spectrum	Thermal
Primary control method	Control rods
Primary moderator	Graphite
Primary coolant	Liquid (light water)
Reactor usage
Primary use	Generation of electricity
Power (thermal)	RBMK-1000: 3,200 MWth RBMK-1500: 4,800 MWth RBMKP-2400: 6,500 MWth
Power (electric)	RBMK-1000: 1,000 MWe RBMK-1500: 1,500 MWe RBMKP-2400: 2,400 MWe

The RBMK (Russian: реа́ктор большо́й мо́щности кана́льный, РБМК; reaktor bolshoy moshchnosti kanalnyy, "high-power channel-type reactor") is a class of graphite-moderated nuclear power reactor designed and built by the Soviet Union. It is somewhat like a Boiling water reactor as water boils in the pressure tubes. It is one of two reactor types to be developed in the Soviet Union during the 1970s, the other being the VVER reactor. ^[3] The name refers to its design^[4] where instead of a large steel pressure vessel surrounding the entire core, the core is surrounded by a cylindrical annular steel tank inside a concrete vault and each fuel assembly is enclosed in an individual 8 cm (inner) diameter pipe (called a "technological channel"). The channels also contain the coolant, and are surrounded by graphite.

The RBMK is an early Generation II reactor and the oldest commercial reactor design still in wide operation, although reactor units of the first generation type have all been decomissioned. Certain aspects of the original RBMK reactor design had several shortcomings,^[5] such as the large positive void coefficient, the 'positive scram effect' of the control rods^[6] and instability at low power levels—which contributed to the 1986 Chernobyl disaster, in which an RBMK experienced an uncontrolled nuclear chain reaction, leading to a steam and hydrogen explosion, large fire, and subsequent core meltdown. Radioactive material was released over a large portion of northern and southern Europe—including Sweden—where evidence of the nuclear disaster was first registered outside of the Soviet Union, and before the Chernobyl accident was finally communicated by the Soviet Union to the rest of the world.^[7][8] The disaster prompted worldwide calls for the reactors to be completely decommissioned; however, there is still considerable reliance on RBMK facilities for power in Russia. Most of the flaws in the design of RBMK-1000 reactors were corrected after the Chernobyl accident and a dozen reactors have since been operating without any serious incidents for over thirty years.^[9]

RBMK reactors may be classified as belonging to one of 3 distinct generations, according to when the particular reactor was built and brought online:^[10][11]

• Generation 1 - during the early-to-mid 1970's, before OPB-82 General Safety Provisions were introduced in the Soviet Union
• Generation 2 - during the late 1970's and early 1980's, conforming to the OPB-82 standards issued in 1982
• Generation 3 - post Chernobyl accident in 1986, where Soviet safety standards were revised to OPB-88, of which only Smolensk-3 was built to these standards

Nine RBMK blocks under construction were cancelled after the Chernobyl disaster, and the last of three remaining RBMK blocks at the Chernobyl Nuclear Power Plant was shut down in 2000.

As of April 2024, there are still seven RBMK reactors (Leningrad units 3 & 4; Smolensk units 1,2,3; Kursk units 3 & 4—all generation 2 unit apart from Smolensk-3), and three small EGP-6 graphite moderated light-water reactors (Bilibino units 2,3,4) operating in Russia.^[1][12] All have been retrofitted with a number of safety updates. Only two RBMK blocks were started after 1986: Ignalina-2 (located in Lithuania, now decommissioned) and Smolensk-3.