Filtered Containment Venting System ( FCVS ) is an accident management system designed to minimize the release of fission products when releasing the pressure of the containment building in the case of a severe nuclear accident . As a Severe Accident Management Measure ( SAMM ) , containment venting can not prevent a meltdown but can help alleviate its consequences on the environment . Most nuclear power plants feature a containment building whose role is to be the ultimate barrier , as per the defense-in-depth principle , against the release of radionuclides in the environment during accidents involving partial or total reactor core damage , that is , in which the integrity of the nuclear fuel ( first barrier ) is lost . In the most severe of such scenarios , if the fuel remains insufficiently cooled for prolonged periods of time , the integrity of the primary system ( second barrier ) can be threatened as well , for example if a substantial mass of molten fuel ( corium ) reaches the bottom of the reactor pressure vessel and melts through it . At this point most of the cooling water of the primary circuit will have been released into the containment atmosphere if it had not already been released through a pipe rupture ( LOCA ) , along with volatile fission products such as Cesium and Iodine from the molten fuel , thereby increasing containment pressure . Although nuclear power plants are equipped with systems designed to cool the containment atmosphere ( such as containment spray systems ) , these may be unavailable in the case of a severe accident ( for example a Station Blackout in which all power is lost ) . In this case , uncontrolled releases of radionuclides due to containment failure can be avoided by venting its atmosphere to decrease pressure . There are two main types of FCVS : Both allow the removal of most of the aerosols ( including cesium , > 99.9 % ) and iodine ( > 99 % in elemental form ) contained in the vented atmosphere . 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 "
Windscale fire
Windscale fire
Filtered Containment Venting System