Vent Filters Eyed for 31 Nukes

Monday, November 5, 2012 @ 04:11 PM gHale

A new requirement is in the works for the 31 nuclear reactors similar in design to those that experienced core melting at Japan’s Fukushima-1 to undergo a retrofit for containment vent filters that could cost $16 million each to install.

A paper is in development for the five-member Nuclear Regulatory Commission (NRC) by the end of November, said John Monninger, associate director of the agency’s Japan lessons learned directorate, during a meeting at agency headquarters in Rockville, MD. There is no timetable for the commission to take action on the measure.

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Commissioners told the staff to include the issue of filtered vents in the agency’s immediate response to the Fukushima accident, instead of waiting to decide later.

NRC staff believes the filters provide a “substantial safety enhancement” that provides additional defenses for the containment structures in some General Electric-designed boiling water reactors. Those GE Mark I and Mark II containment designs, because they have generally smaller containment volumes than other GE-designed units and pressurized water reactors, are more vulnerable to excessive pressure during a severe accident, Monninger said.

The containment structure for a nuclear unit encloses the reactor and key safety systems, and is sealed from the exterior environment. The containment structure is the third of the three main barriers to the release of radioactive fission products.

Containments at Fukushima ended up subjected to pressure beyond their design limit and there were delays in venting them, in part because of concern about exposure to the public in the vicinity of the plant, Japanese officials have said.

The nuclear industry opposes the requirement, which it believes could cost even more than NRC estimates, said Steven Kraft, the Nuclear Energy Institute’s senior director of Fukushima response coordination, during the meeting.

“There’s this aura built up around external filters that is unwarranted,” Kraft said.

The industry has proposed that NRC set heightened requirements for additional protection from the release of radioactive materials in an accident, and allow individual plants to determine whether the filters or another strategy is the best approach.

Representatives of environmental groups welcomed the agency staff recommendation.

Requiring filtered containment vents for the reactors in question is “a no-brainer,” said Mary Lambert, head of the group Pilgrim Watch in Massachusetts. Entergy’s 728-MW Pilgrim reactor in Plymouth, MA, is one of the 31 units covered by the proposed order.

Filtered vents would make it easier for reactor operators to make the decision to vent the containment structures at the right time, Lambert said. Without them, operators would be “hesitant” because they know the venting would likely release radioactive materials into the community where they and their families live, she said.

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