Reactor pressure vessel

A reactor pressure vessel (RPV) in a nuclear power plant is the pressure vessel containing the nuclear reactor coolant, core shroud, and the reactor core.

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

Of the main classes of reactor with a pressure vessel, the pressurized water reactor 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 boiling water reactor 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 pressurized water 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 pressurized water reactors.

All pressurized water reactor pressure vessels share some features regardless of the particular design.

The reactor vessel body is the largest component and is designed to contain the fuel assembly, coolant, and fittings to support coolant flow and support structures. It is usually cylindrical in shape and is open at the top to allow the fuel to be loaded.

This structure is attached to the top of the reactor vessel body. It contains penetrations to allow the control rod driving mechanism to attach to the control rods in the fuel assembly. The coolant level measurement probe also enters the vessel through the reactor vessel head.

The fuel assembly of nuclear fuel usually consisting of uranium or uranium/plutonium mixes. It is usually a rectangular block of gridded fuel rods.

Protecting the inside of the vessel from fast neutron escaping from the fuel assembly is a cylindrical shield wrapped around the fuel assembly. Reflectors send the neutrons back into the fuel assembly to better utilize the fuel. The main purpose though is to protect the vessel from fast neutron induced damage that can make the vessel brittle and reduce its useful life.

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