Pressure increas during severe accidents is one of the major problems of nuclear power plant safety. Containment filter venting systems are designed in order to deal with such issue by reducng pressure build-up in containment. In severe accidents conditions, passive containment filtered venting systems (PCFV) have been shown as the most effective, while they have no need for electrical power, operator intervention or any other support system. They are activated independently by bursting rupture disc if containment pressure reachs certain set point and besides decreasing pressure their main goal is to filter contaminated venting gas flow before its release in the atmosphere. There are few different filter venting sytems whose main purpose is to retain radioactive aerosols and fission products such as iodine (both elemental and organic) from venting gas. In order to ensure exceptional filtration efficiency, the process is carried out in several steps. Rapid pressurization of containment can be also caused by explosions of gas mixtures such as hydrogen and carbon monoxide, so one of key procedures for preserving containment itegrity is to keep their concentration low. This is achieved by passive autocatalytic recombiner (PAR) which, by chemical reaction between hydrogen / carbon monoxide and oxygen release heat with formation of aerated watter.