As for TEPCO, dialogue between the utility and the NRC team remained practically nonexistent. And when the NRC experts finally did get the opportunity to sit down with company representatives, the talks weren’t especially productive. “[T]hey said they didn’t need any help and everything’s in full control, under full control,” John Monninger said.
While the Japanese had never anticipated an accident as complex as the one unfolding at Fukushima, neither had the NRC. This didn’t stop the agency from engaging in backseat driving, though. Monninger took issue with what he saw as the utility’s narrow focus in dealing with an unfolding, multipronged crisis that was far from under control. “They have one priority: Unit 3,” he told White Flint. “And once they get done with that, they’ll determine the next priority.”
For the U.S. team, there was no shortage of priorities—and the list seemed to expand with each phone conversation.
Soon, the most contentious issue to confront the NRC would surface as the crisis worsened. High-level officials in Washington wanted to know one thing: how bad could this get? For the NRC, that was a question fraught with all sorts of implications. The agency had spent years downplaying the risks of nuclear accidents, contending that a real “worst case” could never happen. Now, it was being asked to assume the opposite.
The list of federal agencies working on the response to Fukushima in the United States and Japan included familiar names like the DOE, the Department of State, and the EPA. But it also included a small cadre of government entities few Americans have ever heard of, including the National Atmospheric Release Advisory Center. The center, known as NARAC, uses computer models and geographic data to map the spread of hazardous materials that get released into the atmosphere. Its predictions are intended to help decision makers in an emergency, and its models were capable of predicting the movement of radiation plumes with more accuracy and to considerably further distances than the NRC’s RASCAL code.
At the moment, experts across the U.S. government were grappling with these questions: just what could be the worst-case scenario, and how much radiation might escape from Fukushima Daiichi if that scenario occurred? The answer had ramifications not only for Japan and the American citizens there but potentially for the United States itself. To make those predictions, the experts first had to agree on what’s known as a source term, an assessment of how much radioactive material could actually be released from the reactors and fuel pools into the environment. The types of material and the timing of the releases were also key inputs for predicting where the radioactive plumes would travel and the nature of the damage they could cause. The bottom line issue for the U.S. government was this: what threats would such a release pose to Americans, whether at home or abroad, and what measures had to be taken to protect them? Without a more precise understanding of the source term, the answer to that question would remain frustratingly elusive.
SOURCE TERM EXPLAINED
Source term defines the types and amounts of radioactive material released during a nuclear plant accident. The source term depends on many variables, including the initial amount of radioactive material in the nuclear fuel, how much of that radioactivity gets released from damaged fuel, how much of that radioactivity is retained within the plant, and how much is released to the environment, where it can be transported to downwind communities.
Highly radioactive materials like iodine-131 and cesium-137, known as fission products, are by-products of the nuclear chain reaction that drives the nuclear engine. An operating nuclear reactor core contains a mixture of dozens of different radioactive isotopes. The quantities of these isotopes depend on the power level of the reactor and the length of time that the reactor has operated, among other factors.
Radioactive materials are unstable and release radiation seeking to reach a stable form. The time it takes for one-half of a given quantity of radioactive material to decay—called the half-life—varies from a mere fraction of a second to millions of years. In a reactor accident, the longer the onset of reactor core damage is delayed after shutdown, the more time is available for radioactive materials with short half-lives to decay into stable materials, thereby reducing the source term.
Different isotopes have different radioactive properties, which determine the relative hazards they pose to the environment and to humans and other organisms. Certain isotopes, such as plutonium-239, emit alpha particles, which cannot penetrate skin but are particularly hazardous inside the body; thus alpha emitters are very dangerous if inhaled or ingested. Others, like strontium-90, emit beta particles, which are somewhat more penetrating than alpha particles but still do more of their damage if emitted within the body. In contrast, high-energy gamma rays penetrate deeply, and hence gamma emitters like cesium-137 can do their damage from outside the body.
Different radioactive isotopes also have different chemical forms, which determine how they behave within the reactor, in the environment, and in living things. For example, beta-emitting iodine-131 becomes a gas at ambient temperature, can be transported large distances in the environment, and if inhaled or ingested concentrates in the thyroid gland, where it can deliver a high dose. Luckily, though, with a relatively short half-life of eight days, it does not persist in the environment. In contrast, plutonium-239 remains solid up to very high temperatures and is not easy to disperse, but with a 24,000-year half-life and a tendency to deposit in liver and bone, it is very persistent in the environment or in the human body.
These properties determine the relative hazards of the different stages of a radiation release. In the early stages of the accident, people can be immersed in and inhale airborne plumes. In the later stages of the accident, after the plume has passed, people can be exposed to contamination on the ground and other surfaces and in food and water. Contaminated dust particles can also be carried upward by air currents and inhaled.
When an accident causes the fuel rod claddings to overheat and break but is stopped before the fuel pellets are damaged, the release is limited to the radioactive gases trapped in the space between the pellets and cladding, including noble gases, iodine-131, and cesium-137. If overheating is not stopped in time, the fuel pellets themselves can break apart, allowing some of the radioactive materials trapped within the pellets to be released along with the radioactive gases. Ultimately, the pellets themselves can melt, and release an even wider range of isotopes, including plutonium-239 and americium-241. The greater the fraction of the core damaged, the greater the amount of material available for release.
A functioning reactor containment is designed to allow no more than a small fraction of the airborne radioactivity within the reactor—less than 1 percent—from being released. If containment venting is necessary, filters could be used to prevent radioactive materials from escaping into the environment. However, if the containment barrier is breached or bypassed, a far greater amount of radioactivity can escape.
Even if the containment fails, determining the actual amount that may be released over time is difficult because radioactive gases and particles released from damaged fuel may cool down and “plate out”—that is, stick to—various surfaces and be retained within the plant. But even these materials may eventually heat up again and escape.
Once the source term is developed, the weather conditions are defined and populations at risk are identified. Based on this information, the hazard from radioactive materials escaping from a nuclear plant can be estimated. But other variables also play a factor. Wind may blow the radioactive cloud toward or away from densely populated areas. A city forty miles away from a damaged plant may be at greater risk than closer cities if it starts to rain as the plume passes overhead.
Although the source term is used in estimating the risks, the actual hazard depends on questions that cannot be definitively answered during an accident or even long afterward. When was the fuel damaged? How much fuel has been damaged? To what extent has the fuel been damaged? How much radioactive material released from damaged fuel has bee
n retained in the plant? Artful science is applied to estimate the source term based on the most likely answers to these important questions.
President Obama, in an address to the nation on March 17, offered reassurances. “We do not expect harmful levels of radiation to reach the United States, whether it’s the West Coast, Hawaii, Alaska, or U.S. territories in the Pacific,” he said. “That is the judgment of our Nuclear Regulatory Commission and many other experts.” But behind the scenes, those experts were still debating the numbers, even as conditions inside the reactors and fuel pools were unclear.
Radiation monitors at California’s Diablo Canyon and San Onofre nuclear plants had already picked up readings of iodine-131 just slightly above what the NRC described as “the minimal detectable activity level.” It presumably was blowing in from Fukushima, 5,400 miles away. If these levels continued to increase, there was a chance that the president would later have to reverse himself and order countermeasures like banning milk shipments from certain areas. That could result in a major loss of confidence among the public.
Among the scientists and administrators, disparate views on the radiation threat abounded, apparently hashed out in the confidentiality of the White House Situation Room, where officials from a host of agencies gathered. Discussions also were going on at the U.S. Embassy in Tokyo. There had been internal disagreements in both places over the NRC’s recommendation two days earlier for the fifty-mile evacuation for U.S. citizens in Japan. Now, based on aerial measurements between thirteen and twenty miles northwest of the reactors showing exposure rates above one rem over four days, the EPA evacuation standard, the NRC was confident it had made the right call. But the agency continued to take heat for the decision. On March 18, the Nuclear Energy Institute contacted the NRC to complain that the fifty-mile evacuation could undercut the public’s faith in this country’s ten-mile emergency planning zone.
Back at White Flint, Trish Holahan, director of security operations at the NRC’s Office of Nuclear Security and Incident Response, and her colleagues were poring over some alarming dose estimates for U.S. territory that they had received from NARAC. Because the NRC’s own RASCAL model had limited range, the agency had to rely on NARAC to go farther using its more sophisticated plume transport models. Employing source terms supplied by the NRC, NARAC’s models were finding that thyroid doses to one-year-old children in Alaska could be as high as thirty-five rem—seven times the EPA dose threshold that would trigger the need for countermeasures such as potassium iodide administration.
But the NRC thought that some of NARAC’s assumptions seemed a bit far-fetched. The potential radiation exposure of grazing dairy cows in Alaska in mid-March was one example. “The cows are kept indoors,” Holahan told Jaczko over the phone. “Even the water supply is internal because they’re not outside. So we eliminated that dose.”
The assumption of grazing cattle in Alaska in wintertime was just one aspect of a larger issue that the NRC was trying to grapple with: the White House request for a “worst-case” assessment. From the perspective of the president, this approach made sense: if even under the most pessimistic assumptions there was little risk to the American public from Fukushima, then the president could continue to provide reassurances without fear that he would be later accused of underestimating the threat.
Joining the White House in pushing for the worst forecast was Admiral Mike Mullen, chairman of the Joint Chiefs of Staff. “I have been taught by my nuclear power community my whole life to plan around the worst case possibilities,” he wrote to Obama’s top science advisor. “This in great part had a lot to do in keeping our [Navy] plants safe.”
However, the concept of a worst-case scenario was anathema to the NRC’s way of thinking. For decades, NRC regulations and policies had been explicitly designed to avoid accounting for worst-case scenarios, which were believed to be so unlikely as not to merit consideration. Calculating a worst-case source term fell into that same category.
The NRC had already ventured outside its comfort zone when it made the recommendation for a fifty-mile evacuation around Fukushima, based on source-term assumptions that it judged very unlikely. Now it was asked to consider even more extreme cases.
The NRC instead preferred to focus on what it considered more realistic or “best estimate” scenarios. The NRC had just spent several years on a research project called State-of-the-Art Reactor Consequence Analyses meant to calm public fears about nuclear power by calculating “realistic” severe accident source terms. Those numbers were lower than previous estimates, and the NRC was pleased with the initial findings. But now, when a reasoned perspective was needed more than ever—at least in the eyes of the NRC—the White House appeared to be asking the NRC to throw its approach out the window.
The White House wanted the NRC to provide a source term to NARAC that assumed that 100 percent of the fuel in the cores of Units 1, 2, and 3 and in the spent fuel pools of Units 1, 2, 3, and 4 had melted, with the Units 1–3 primary containments failing completely so that the resulting radiation from all seven sources would be released into the environment.
Jaczko was frustrated by this request. He questioned whether the NRC was being asked to hypothesize an accident that was in fact impossible—one that would essentially vaporize all the cores and spent fuel and eject it all into the environment. “[O]bviously, there’s a physical reality at some point that certain things just cannot happen,” Jaczko said. As bad as this accident was, there were no plausible physical mechanisms that could vaporize the entire core of a light-water reactor like those at Fukushima. Even at Chernobyl, a more unstable type of reactor that experienced a runaway chain reaction and massive steam explosions, most of the core material remained within the reactor.
“[T]here’s what’s worst case and then there’s what’s possible,” Jaczko told Holahan and the team at White Flint. “So I think what we should produce [is] a worst-case [scenario] that [is] actually possible.” Instead, he said, the NRC was being asked to envision the nuclear equivalent of a “meteor hitting the earth at the same time as an asteroid strikes.” Holahan agreed to go back and confer again with the reactor safety experts and come up with some new analyses.
Earlier that afternoon, Jaczko had spent forty-five minutes with the Japanese ambassador, making a combined condolence and business call at the embassy on Massachusetts Avenue. The NRC crew hoped the visit might facilitate communications between Washington and Tokyo. “We have a tremendous opportunity here now,” Jaczko had told his team before heading to the meeting. “We have an ambassador who basically wants to be helpful and can pass information to help move a logjam if necessary.”
Chuck Casto, back from a meeting with the chairman of TEPCO and the utility’s chief nuclear officer, called his colleagues at White Flint at about 9:00 p.m. on March 18 to give them an update. “It was a cordial meeting,” he said. In contrast to the few previous encounters, this time TEPCO executives asked for help from the Americans.
Although the NRC was still focused on finding a way to cool the spent fuel pools, TEPCO was more worried about the reactors themselves—in particular, the accumulation of salt inside them. As the fire trucks kept pumping in seawater, large amounts of salt were building up in the bottoms of the reactor vessels, potentially blocking the flow of the water and interfering with efforts to cool down the fuel. In addition, seawater is more corrosive to metal than the freshwater the reactors were built to use. Forced to use seawater at Fukushima, the Japanese wanted to consult about the problems it would create for them down the road. They were now asking for assistance.
Jaczko was listening in. “Do you think that project team should be NRC people or somebody else, like maybe INPO or something like that?” Casto agreed that both the NRC and the Institute of Nuclear Power Operations ought to get involved, along with the DOE, which has expertise in radiation doses and decontamination.
“I think this is a major change in the mission,” Casto told Jaczko. “Sir, I believe that they are lookin
g to us for solutions. . . . I think they were . . . desperate for options.”
Jaczko’s reference to a heightened industry role in the U.S. response to the accident was not hypothetical; the details were being finalized even as the men spoke. The expert industry group was set to gather at NRC headquarters. The weary White Flint team hoped the fresh troops might shift some of the load off the NRC’s shoulders; with luck, the involvement of industry might even encourage TEPCO and Japanese officials to be more forthcoming with information and to accept more help.
Participants with special expertise, such as GE, which had designed the Fukushima Daiichi reactors, would be asked to provide guidance on getting water into the fuel pools, for example. Other industry representatives would be invited to help devise short- and long-term solutions in Japan.
It was not going to be simple. For its part, the NRC planned to work through diplomatic channels in Japan to come up with a cooperative agreement that was politically acceptable to Tokyo, and also to try to obtain better information about the conditions at Fukushima Daiichi and the radiation levels.
But better data would only improve things somewhat; equally important was a definitive plan of action from the Japanese. “[T]hey have shifted almost as frequently as the winds have changed there with respect to what their priorities are,” Virgilio observed. “[I]t’s not a good situation.”
“I’m just trying to figure out who the power player is over here,” Chuck Casto said. For the industry consortium to succeed, it had to be consorting with the real decision makers in Japan, and Casto wasn’t sure who those were. “Is TEPCO the right organization, or should we be going to MOD [Ministry of Defense], or who?”
Fukushima: The Story of a Nuclear Disaster Page 17