This study was initiated because licensees appeared to be submitting licensee event reports involving dampers regularly. These devices are used throughout the plant to provide system realignment for emergency ventilation in the control room, the containment building, the diesel generator building, the auxiliary building, and other locations. They are also used as barriers to prevent the spread of fire through the ventilation system. Ventilation dampers include louvered, butterfly, blade, and bladder types that can be air actuated or motor driven.
Fire dampers are generally a curtain type with a fusible link that is heat sensitive.
The damper is closed, after the link melts, by gravity or is spring assisted. Damper installation problems included interferences, upside down installation, installation in the middle of a duct instead of at the wall, and no installation at all. Problems with ventilation dampers include mispositioning, single failures, absence of backdraft dampers, and actuator problems. Problems with dampers in ventilation systems could go undetected because damper positions are not monitored during surveillance tests. NRR is considering the need for developing a generic letter on control room emergency ventilation systems to address these types of problems.