What is Containment Building

The containment building is a gas-tight (shell) or other enclosure around a nuclear reactor and a primary circuit. The Containment is the most characteristic structure of a nuclear power plant. Practically all nuclear power plants built during the last few decades include a containment building.

The containment building should be designed to ensure or contribute to the achievement of the following safety functions:

Confinement. Confinement of radioactive material in operational states and accident conditions.
Protection. Protection of the power plant against external natural and human-induced events
Shielding. Radiation shielding in operational states and accident conditions.

Containment vs. Confinement

The International Atomic Energy Agency (IAEA) defines Confinement as a prevention or control of releases of radioactive material to the environment in operation or in accidents.

Confinement is closely related in meaning to Containment. Still, confinement is typically used to refer to the safety function of preventing the ‘escape’ of radioactive material, whereas Containment refers to the means for achieving that safety function.

Containment refers to methods or physical structures designed to prevent the dispersion of radioactive substances as low as reasonably achievable.

The containment building is primarily designed to prevent or mitigate the uncontrolled release of radioactive material to the environment in operational states and in accident conditions. Therefore it is considered to be the fourth and final barrier in the in-depth Defence strategy.

While the Containment plays a crucial role in Design Basis Accidents or Design Extension conditions, it is “only” designed to condense steam from primary coolant and contain it inside the building.

In case of Design Basis Accidents such as the Large Break Loss of Coolant Accident (LBLOCA) the pressure increase is usually significant and active containment systems (pressure-suppression systems) must be available in order to maintain the integrity (to keep the pressure and temperature under certain limits) of the containment building.

References:

USNRC Technical Training Center, Pressurized Water Reactor (PWR) Systems, available on www: < http://www.nrc.gov/reading-rm/basic-ref/teachers/04.pdf>.
USNRC Technical Training Center, Boiling Water Reactor (BWR) Systems, available on www: < http://www.nrc.gov/reading-rm/basic-ref/teachers/03.pdf >.
IAEA Safety Standard Series, Design of Reactor Containment Systems for Nuclear Power Plants, NS-G-1.10, Vienna, 2004.
IAEA, Mitigation of hydrogen hazards in water cooled power reactors. IAEA-TECDOC-1196, Vienna, 2001
NEA, Status Report on Filtered Containment Venting, NEA/CSNI/R(2014)7

See above:

Containment Building

See next:

Containment vs. Confinement