About a third of the country's 104 operating nuclear reactors should be required to install filtering systems that cost up to $45 million each to limit how much radioactive material is sent up into the atmosphere after a severe accident, staff at the Nuclear Regulatory Commission said yesterday.

The equipment would allow operators to release steam and pressure from a damaged nuclear power plant while using filters to better protect the public and workers from radiation, John Monninger, deputy director of the NRC's Division of Risk Analysis, told the Advisory Committee on Reactor Safeguards.

"We believe it would provide improved confidence to operators to make that decision," he told the independent panel, which advises the NRC on reactor safety, radiation and license applications.

Filtered vents are systems of water-filled tanks, sand or other materials that scrub the gas of radioactive material before it leaves the plant.

The systems cost $15 million to $45 million, according to industry sources.

The NRC staff is looking into the issue as part of the agency's review of the disaster that erupted last year at Japan's Fukushima Daiichi power plant. Three reactors at the site on Japan's northeastern coast melted down after being slammed by a magnitude-9 earthquake and tsunami that disabled emergency diesel generators needed to keep the units cool, triggering explosions and radioactive leaks.

The draft recommendation focuses solely on General Electric boiling water reactors with Mark I and Mark II designs, which have smaller containment volumes and are more vulnerable to excessive buildup of pressure during severe accidents, Monninger said. Containment systems are steel-lined concrete shells that prevent radioactive materials generated by reactor accidents from reaching the environment.

NRC staff will give the five-member commission a formal recommendation by the end of the month. The ACRS will make a separate recommendation based on staff and stakeholder input.

Anti-nuclear groups applauded the staff's comments, calling the decision a "no-brainer."

Jim Riccio, nuclear policy analyst for Greenpeace, said nuclear operators around the world either have the vents or are installing them and that his group would reach out to Congress if the ACRS didn't agree to require filtered vents once the "silly season" of the elections was over.

"The further you get up this building, the harder it is to trust what's being done," Riccio told the panel. "You should learn your lessons from Fukushima rather than being forced to do the right thing."

But the industry opposes mandatory filtered vents and says the boiling water reactors in question already include internal equipment that can be used to scrub radioactive gas before it is released.

"To suggest that there's no filtering being done is incorrect," said Tony Pietrangelo, the Nuclear Energy Institute's senior vice president and chief nuclear officer.

Pietrangelo dismissed the staff's assertion that requiring filtered vents would give operators more confidence during a severe accident. Unlike Japanese operators that didn't vent the Fukushima plant quickly enough -- leading to hydrogen buildup and explosions -- U.S. operators follow detailed procedures during severe accidents that would direct them when to vent early, he said. Having filters on the Fukushima reactors wouldn't have prevented radioactive release, he added.

Operators are "going to vent when the procedures tell them to vent," he said. "If that's what you're basing your decision on to move forward with a decision or recommendation to the commission, it's very, very tenuous."

Pietrangelo pointed to a report the Electric Power Research Institute released in September that found filters would be useless if operators didn't first find ways to cool a crippled reactor and the containment structure failed.

Instead, NEI is asking the NRC to consider strategies that involve adding new hardware and adopting new procedures to prevent any release or the need for filters. Plant operators should also be allowed to decide whether filters are the best option, NEI says.

"This is not a simple 'add a filter, no filter' decision," Pietrangelo said. "It's much more complex than that. Ultimately, what you're trying to do is prevent land contamination."

Monninger said that although he's open to more research, he doesn't see a commitment across the nuclear industry to move forward on the issue and questioned NEI's approach.

"We have less confidence in those filtering strategies," he said.