Boiling Water Reactor - 
Typical of Russian Nuclear Power Plants

A Boiling Water Reactor (BWR) is a nuclear reactor in which the design permits steam to be in contact with the nuclear fuel rods. This diagram is a schematic of a RMBK-1000 reactor which is in wide use in Russia and countries of the former Soviet Union and their allies to whom they supplied this type of plant. In this design, the individual fuel rods are inside individual water pipes. Water is pumped through the pipes past the fuel rods, which heat the water to boiling. The mixture of boiling water and steam is separated in a tank (steam separator). The steam is then sent directly to the turbine which drives the electric generator. There is no separation of radioactive steam from the turbines. This system is simple in overall concept. But there is less safety margin in containing radioactivity in the event of a plumbing failure. The reactor core has all the moderator which controls neutron flux outside the water system. The variable part of the moderator system is a set of moveable Boron rods which are geometrically interspersed between the vertical array of water channels which contain the fuel rods. Instead of stationary control rods this reactor design has a massive pile of graphite bricks. Water channels and control rods pass through vertical holes through the graphite pile. Graphite has a problem. It will burn if expoed to air at the temperature in the pile in an operating reactor. Thus the reactor is enclosed in an air-tight and water tight concrete shell. This shell is filled with an oxygen-free gas mixtures, primarily helium and nitrogen.


C. D. Sigwart 1999