RBMK Reactor

Lore & Background

The design grew out of the Soviet programme to produce a water-cooled power reactor with dual-use potential, based on military reactors that made plutonium. Using ordinary water for cooling and graphite for moderation allowed fuel of lower enrichment, 1.8% instead of the costlier 4%. It also allowed a very large and powerful reactor to be built quickly, largely from parts made on site. A containment building would have had to be very large and would have doubled the cost of each unit, so it was left out of the original design.

The RBMK was one of two power reactor types to enter serial production in the Soviet Union during the 1970s. Reactors are grouped into three generations by when they were built, and only one unit was completed to the standards revised after the accident.

Reader's Guide

The original design had several shortcomings that contributed to the Chernobyl disaster: a large positive void coefficient, a positive scram effect of the control rods, and instability at low power. In the accident a reactor of this type underwent an uncontrolled chain reaction, followed by a steam and hydrogen explosion, a large fire and a core meltdown. Radioactive material spread over a large part of Europe, and the first evidence outside the Soviet Union was registered in Sweden.

The disaster prompted calls worldwide for the reactors to be decommissioned. Most of the design flaws of the RBMK-1000 were corrected afterwards, and the type remains in use in Russia, with almost 7 GW of installed capacity. Its service life was at first expected to be 30 years and has been extended for some units to 50.

Did You Know?

• It is described as the oldest commercial reactor design still in wide operation.
• All the remaining units are operated by a subsidiary of Rosatom.