Of all the crucial decisions that Tepco engineers faced at the Fukushima Power Plant in the frenzied hours after the March 11 earthquake, none was more agonizing or difficult than this: should the company intentionally vent gas from the overheating reactors even though doing so would release radioactivity into the atmosphere?
The decision took time—and caused dissent among company and government officials—but it was eventually agreed that doing so was the only way to prevent hydrogen that had accumulated in the reactor containment vessel from exploding. What happened next will be scrutinized by nuclear safety experts for years.
According to various press reports that cite internal Tepco documents, when officials decided to begin authorized venting, they found that the venting system did not work. It relied on the same source of electricity as the rest of the plant: backup generators that had been decimated by a 50 ft tsunami that followed shortly after the earthquake. They then decided to try to manually open the vents, but again were thwarted, perhaps because the vents had been damaged during the earthquake. What eventually happened is now well-known: hydrogen in reactors 1, 2 and 3 exploded, blowing the roof off the containment buildings and spewing a radioactive plume that spread for miles.
There are two main questions that the Fukushima venting problems raise. The first is whether existing Bioling Water Reactors (BWRs) in the U.S. and elsewhere have adequate venting systems to handle serious loss of coolant accidents. The U.S. Nuclear Regulatory Commission mandated in the 1980s that an enhanced venting system be installed at boiling water reactors that use the same containment system as Fukushima. Early on after the Japanese quake, U.S. experts had said that U.S. plants were safer because of these improvements. But this week it emerged that Tepco had installed the new venting system at Fukushima, and it still malfunctioned.
So should the NRC require U.S. plants to redesign their venting systems? “It’s still too soon to start drawing conclusions on either the events at Fukushima or how our task force will examine/evaluate verified information from the incident to provide possible recommendations to the Commission,” NRC spokesman Scott Burnell told Ecocentric. Of course, that doesn’t mean the NRC won’t be looking closely at the issue.
The second question is whether plant operators should be given the freedom to decide when to vent to prevent hydrogen explosions. Should there be a set trigger point that sets off the mandatory release of pressure? Currently, U.S. regulations allow plant operators to take actions during an emergency that might technically “violate” NRC regulations, as long as those actions work to control or mitigate the overall situation. Perhaps the NRC should codify this process. The Wall Street Journal reported on Wednesday that one of the delays to venting efforts at Fukushima was the result of:
Tepco officials’ concern that an intentional radiation release would sharply elevate the accident’s severity. At the time, Tepco still hoped the accident could be contained without venting, given that release of radioactivity in the atmosphere would instantly rank Fukushima among the world’s worst accidents.
So maybe the NRC needs to make explicitly clear when plant operators must vent to prevent them from taking on high risks in an effort to keep situations under control. We trust plant operators to make safe decisions because the stakes for their industry are so high: cynically put, nuclear accidents are very bad for business. But perhaps this cynical truth might also lead to risky behavior in certain circumstances.
While the NRC mulls over such questions, Britain became the first country to publish a report stating that Fukushima should not be a game changer for the nuclear industry. On Wednesday, the UK’s Office for Nuclear Regulation published a preliminary report that found that Fukushima provided no warnings that should curtail nuclear power in the U.K, which has plans for the construction of 8 new reactors. The report pointed out that the UK has no boiling water reactors and all but one of its fleet use gas-cooled techonology so would not face the same issues as Fukushima’s reactors during a loss of coolant accident. What’s more, the report pointed out, “the extreme natural events that preceded the accident at Fukushima – the magnitude 9 earthquake and subsequent huge tsunami – are not credible in the UK.”
However, the report did lay out 25 areas—including improved communication by the IAEA and national nuclear bodies, better facilites to deal with the flooding of radioactive water, and more robust electricity supplies—in which the nuclear industry should take instruction from the experience at Fukushima.
“We should recognize that to achieve sustained high standards of nuclear safety we all need to adhere to the principle of continuous improvement. This means that, no matter how high the standards of nuclear design and subsequent operation are, the question for improvement should never stop,” the report states.
Three cheers to that.