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Ensuring Reliability of Nuclear Plant Containment Vents

Enrico Fermi Nuclear Generating Station  Responding to Fukushima: Part 4 of a 5-Part Series

Containment vents play an important role in the overall safety strategy at nuclear energy facilities by preventing the potentially hazardous buildup of pressure from steam and gases inside a reactor. A specially designed vent in the massive containment dome that surrounds a reactor is designed to withstand extreme events by relieving primary containment pressure to a stack or other elevated release point.

Boiling water reactors with Mark I containment structures, the type of reactor at Japan’s Fukushima Daiichi facility, have a proven record of more than 40 years of safe and reliable operations.  Twenty-three of this type of reactor in the United States are equipped with these specially designed vents. Although vent valves are rarely used—they’ve never been needed during five decades of operation at U.S. reactors—the events in Japan highlighted the need to ensure that they would function even in the most unlikely circumstances.

The nuclear energy industry agrees with the Nuclear Regulatory Commission (NRC) that additional steps should be taken to ensure that the vents remain accessible and functional in the event of an extended loss of multiple electricity sources at a nuclear energy facility.

The nuclear energy industry will continue to work with the NRC to determine if changes are needed at America’s reactors. Any changes to Mark I containment vents should be determined only after a thorough understanding of the venting process at the Fukushima Daiichi facility.

The industry recommends that evaluations of boiling water reactors with more recent Mark II containment designs be performed before the NRC takes any action on this issue.

All U.S. boiling water reactors include features that allow operators to vent gases (only Mark I have specially designed vents) from the reactor in an emergency. Motor-operated or air-operated valves are used to open and close vents. There also is a backup manual control for the vent. The vent valves and mechanisms to operate the valves are maintained through the same programs applied to all plant systems and components so that the valves are reliable at all times.

Reactor operators have full authority per plant procedures to vent gases from the primary containment in an emergency. Control room managers do not need additional authorization from either their company’s executive management or government regulators to open vents when they determine it is needed.

U.S. nuclear energy facility operators train on these emergency operations strategies throughout the year at site-specific simulators. Reactor operators spend every fifth week in the classroom and in simulator training to maintain their proficiency. Plant operators must continually undergo requalification training in all safety procedures, including containment venting. Emergency venting also is part of the training for emergency response drills.

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Activity ID: 1002943 Activity Name: NEI Remarketing Safety Activity Group Name: Remarketing Safety First