Filtered Containment Venting System
Filtered Containment Venting System (FCVS) is a system to retain fission products in case of a nuclear accident.
In the event of a nuclear power plant accident the pressure within the nuclear reactors containment building can increase. A FCVS allows for the release of the over-pressure through a scrubber normally containing water, stones and chemicals, where most of the fission products are contained. This reduces the radioactive release to the environment with up to 99%.
Historically in terms of accident usage, a primitive scrubber on a first generation gas cooled reactor, reduced the emission of radioisotopes from the Windscale fire in 1957. The scrubber, which prior to its scrubbing services being called upon, was derisively known as Cockroft's folly after the scientist John Cockroft, who had insisted on its incorporation with the facility. Following the fire and Cockroft's scrubber reducing the quantity of material that escaped into the greater environment, "the word folly did not seem appropriate after the accident".
Fukushima nuclear disaster
The plant involved in the 2011 Fukushima Daiichi nuclear disaster did not contain FCVS.
Many countries require FCVS: for example, Sweden, Germany and France.