Reactor vessel

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In a nuclear power plant, the reactor vessel is a pressure vessel containing the coolant and reactor core.

Not all power reactors have a reactor vessel. Power reactors are generally classified by the type of coolant rather than the by the configuration of the reactor vessel used to contain the coolant. The classifications are:

• Light-Water Reactors - Includes the PWR, BWR. The Chernobyl Reactor RBMK was a light water reactor, but of vastly different design than the United States light-water reactors.
• Gas Cooled Thermal Reactor - Includes the AGR,the GCFR, and the HTGR. An example of a Gas Cooled Reactor is the British Magnox.
• Heavy Water Reactors - Utilize deuterium in some manner, however it should be noted that D20 is more expensive and may be used as a main component, but not necessarily as a coolant in this case. An example of a Heavy-Water reactor is Canada's CANDU reactor.
• Liquid Metal Cooled Reactors - Utilize a liquid metal, such as sodium or a lead-bismuth alloy to cool the reactor core.
• Molten Salt Reactors - Special organic coolants are used in this unique design, such as the MSBR.

Of the main classes of reactor with a pressure vessel, the PWR is unique in that the pressure vessel suffers significant neutron irradiation (called fluence) during operation, and may become brittle over time as a result. In particular, the larger pressure vessel of the BWR is better shielded from the neutron flux, so although more expensive to manufacture in the first place because of this extra size, it has an advantage in not needing annealing to extend its life.

Annealing of PWR reactor vessels to extend their working life is a complex and high-value technology being actively developed by both nuclear service providers (AREVA) and operators of PWRs.