A containment building, in its most common usage, is a reinforced steel or lead structure enclosing a nuclear reactor. It is designed, in any emergency, to contain the escape of radioactive steam or gas to a maximum pressure in the range of 275 to 550 kPa (40 to 80 psi) .
Control rods thereby find their use as an effective method for combating these time-dependent changes in reactors. Control rods are essentially a highly effective neutron-absorbing mechanical structure, which can be actively inserted or withdrawn from the reactor core while the fission process is occurring.
A nuclear reactor coolant is a coolant in a nuclear reactor used to remove heat from the nuclear reactor core and transfer it to electrical generators and the environment. Frequently, a chain of two coolant loops are used because the primary coolant loop takes on short-term radioactivity from the reactor.
Nuclear fuel is a substance that is used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission. Most nuclear fuels contain heavy fissile elements that are capable of nuclear fission, such as Uranium-235 or Plutonium-239.
Commonly used moderators include regular (light) water (roughly 75% of the world's reactors), solid graphite (20% of reactors) and heavy water (5% of reactors). Beryllium has also been used in some experimental types, and hydrocarbons have been suggested as another possibility.
Boiling water reactors (BWR) do not use steam generators, as turbine steam is produced directly in the reactor core. Activation of oxygen and dissolved nitrogen in the water means that the turbine hall is inaccessible during reactor operation and for some time afterwards.