How the Nuclear Reactor Works
Return to Main
The nuclear reactors in Chernobyl, were RBMK reactors. Unlike most nuclear reactors, the coolant system is boiling water, or steam, rather that water. Before we continue on with the cooling system, we need to talk about how they work.
All about RBMK Reactors
RBMK reactors have a huge graphite structure, known as the Moderator. The moderator's job is to slows down the fission produced by neutrons. Vertical tubes, about 3.5 inches in diameter circulate water as the Coolant, go through the Reactor Core. The coolant's job is to remove all heat produced by the Fuel Assemblies, which consist of 18 horizontal rods, mounted in the vertical tubes. The fuel rods are about .5 inch in diameter. A helium-nitrogen mixture is used to improve heat transfer from the graphite to the coolant channels and reduce the probability of graphite oxidation.
This diagram is use by permission of Howstuffworks.com
In the RBMK design, boiling occurs. The steam produced goes into the Steam Separator, which separates the steam from the water. Then the steam continues on into the Turbine as in the Boiling Water Reactor design. Similar to the BWR case, the steam is radioactive, though, the steam separator has a delay time so the radiation levels near the turbine may not be as high as in the BWR case.
RBMK vs. Other Reactor Types
|The low power core density of RBMKs provides a unique ability to withstand station blackout and loss of power in event of up to an hour with no expected core damage||Lack of massive steel and concrete containment structure as the final barrier against large releases of radiation in an accident.|
|Ability to be refueled while operating, permitting a high level of availability||Power increases when cooling water is lost, i.e. Positive Void Coefficient|
|The graphite moderator design allows the use of fuel that is not suitable for use in conventional water-moderated reactors||Accident mitigation systems are limited|
|Flawed separation and redundancy of electrical and safety systems|
|Limited capability for steam suppression in the graphite stack|