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[ Safety Question on Fukushima Anniversary: Should Plants of the Same Design Have Filtered Vents? ]

When the giant winter storm Nemo hit New England in February, the Pilgrim Nuclear Power Generating Station in Plymouth, Massachusetts, lost outside power for seven days. Diesel backups took over operating the reactors’ cooling system. (Related Quiz: “What Do You Know About Nuclear Power?“)

Pilgrim has the same kind of reactors that failed at Fukushima, Japan, after an earthquake and tsunami two years ago today crippled offsite power and emergency back-ups. The Pilgrim incident came as the U.S. nuclear industry is fighting proposed new safety measures meant for a crisis that might begin exactly this way. (Related: “Rare Video: Japan Tsunami“)

Of the 104 reactors in the U.S., 31 are very like those in Fukushima. Here is a map of those 31 U.S. sites.

After Fukushima, the U.S. Nuclear Regulatory Commission (NRC) studied what happened. Should it require new safety measures here, even though a crisis is very unlikely?

“It’s not zero,” says Charles Casto, director of NRC Region III, which oversees plants in the Midwest. “The probability’s not zero; it’s something.”

Region III has about two dozen reactors. We spoke at Casto’s office. Nuclear regulation, he said, is about possibility more than probability.

“You take your best – based on history…you know, what has history shown you that the probability would be?” Casto said. “But that doesn’t mean zero.”

Gas Build-Up

The Fukushima reactors, and their 31 U.S. cousins, including the Pilgrim Station, are old boiling water reactors with “Mark I” and “Mark II” containment systems, built by General Electric. The safety enclosures for the reactors are too small. If their cores start to melt down, the containments could fail in several ways, including a build-up of hydrogen gas with radioactive particles and explosion, as at Fukushima. (Related: “Japan Reactor Crisis: Satellite Pictures Reveal Damage“) There’s an increasingly politicized dispute between the industry and the NRC over how to make preventing meltdowns safer.

I visited one of those 31 sites—the Dresden Nuclear Station, about an hour southwest of Chicago. (Listen to Alex Chadwick’s report from Dresden at BURN: An Energy Journal)

Dresden—the first privately financed commercial nuclear plant in the country—is operated by Exelon Generation, the largest nuclear energy company in the United States. (Related: “Ten Oldest U.S. Nuclear Plants-Post-Japan Risks“) It looks dated, but extremely well maintained. It hums.

Gregory Roach, the senior NRC inspector here, showed me back-ups on backups on backups. Flood protection, fire protection. An hour into the tour, we came to the part I most wanted to see: the venting system.

“We showed you where the hardened vents were for the dry well, so now this is downstream,” Roach said.

He was pointing to a pipe overhead that exits the container wall. The vent system: If power fails, and the back-ups fail, and hydrogen builds up, you can probably save the reactors by venting the gas.

“And this pipe goes up to the main stack, 300 feet, and then releases into the environment,” Roach said.

The Japanese vents mostly didn’t work. That’s what caused the explosions.

“So you learn a lesson of Fukushima Daiichi,” Casto said. “And then you put in standards and say your vent must be able to operate under those conditions.” (Related: “Photos: Rare Look Inside Fukushima Daiichi“)

A year ago, the NRC issued a new order aimed at increasing the reliability of the vents.

“Does that mean during an accident you have to be able to get access to it?” Casto asked. “Does that mean you have to do it remotely?

The industry and the NRC are working on it; the industry has until the end of 2016.

Now, here’s what the fight is about: do the vents at these 31 plants also need filters? Because, in the best of conditions, some radioactive gas and particles may escape in venting – and in the very, very unlikely worst of conditions, a lot could escape.

“You have to establish the ‘What if?’,” Casto said. “What if it does happen? What if the improbable happens?”

Reactor cores hold dozens of tons of radioactive material. At Pennsylvania’s Three Mile Island in 1979, about half the core melted, but the containment held, and the venting was relatively minor.

We don’t yet know how much escaped from Fukushima. It’s too dangerous to go look. But there are scenarios in which it’s possible to lose a good part of those dozens of tons through the vents. With filters, virtually all of it is captured.

Costs, Benefits, Safety

To a layperson, nuclear regulation can be almost as daunting as nuclear physics. The Dresden plant is a wonder of machine technology— in it, I got reacquainted with the idea of awe.

The NRC process for new rules— that’s messier.

The chances of a reactor ever needing a filter are so small that you can’t justify the cost. But the NRC staff concluded that the consequences of no-filter could be so bad, they should be required anyway. By NRC procedures, if the staff wants to override normal cost-benefit standards, the five commissioners have to vote to approve, and the fight is on.

A week after the NRC staff testified for filters in January, 21 House Republicans on the Energy and Commerce Committee sent the NRC a letter admonishing the staff. There is plenty of money at stake.

“External filter vents would be an additional approximately $15 million to $20 million per unit,” said David Czufin, an engineer who runs the Dresden plant for Exelon.

Exelon has 10 more of these reactors, so filters could cost the company more than $200 million—on top of many other precautions, he said.

“Additional connections, additional equipment, stored equipment for readiness,” said Czufin.

Exelon does plan to spend $400 million in the next three years for post-Fukushima modifications, some of that for vents—but not filters.

“The one thing I would tell you is that the Fukushima event, we have learned a lot from it,” Czufin said. “We continue to look at how the plant in Japan was operated differently from my plant.”

He’s right. They are different. The independent Japanese commission on Fukushima says so: U.S. plants are much better regulated, run and prepared. And nuclear is already at a competitive disadvantage, according to Bloomberg New Energy Finance; natural gas plants can produce electricity for about 40 percent less. If the industry loses this one, it’s going to hurt.

A last question for the director of NRC Region III, Charles Casto. Is he satisfied now that under circumstances like Fukushima Daiichi, he has the technology to operate vents at the stations that are under his authority?

“Yes,” Casto said, “we believe that we have reliable vents and that the operators can do a controlled vent in a reliable way during an accident.”

But unusual things do happen, as at the Pilgrim Station. Without the filters, there is a very small chance that those vents might become a kind of radioactive fire hose. That’s what the fight is about.

Since our report aired, The New York Times also ran a story on the vent filter issue. The Times report included an important detail: Vent filters are now required in Japan and most of Europe.

The NRC Commissioners are voting on this issue now—a process that can take weeks, or longer.

What do you think? Given a very, very low probability event with very, very high consequences, do you think that vent filters should be required in these reactors?

Alex Chadwick is the host of the public radio series, BURN: An Energy Journal, from SoundVision productions and American Public Media’s Marketplace, produced with funding from the Alfred P. Sloan Foundation.

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