Filtered Containment Venting System
A 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 cannot prevent a meltdown but can help alleviate its consequences on the environment.
Source: Wikipedia — Filtered Containment Venting System (CC BY-SA 4.0)