On March 14, the government agreed to raise the maximum allowable radiation dose for workers in an emergency from ten rem (100 millisieverts) per year to twenty-five rem (250 millisieverts) per year. The decision, announced the following day, was based, in part, on fear that soon everyone at Fukushima Daiichi might exceed the existing exposure limit and thus be required to leave. Already workers had to perform tasks in short bursts to stay within cumulative dose limits.8
That evening, TEPCO president Shimizu was told that, because of the worsening conditions, Yoshida was considering evacuating about 650 nonessential personnel from the plant. Shimizu telephoned the head of NISA before dawn on March 15 to apprise him of the grave conditions at Unit 2 and noted that if things continued to worsen, the company might pull out some personnel. In another instance of bungled communication, Shimizu apparently did not make it clear that essential workers would remain.
Officials in the prime minister’s office feared a total abandonment of the plant, in which case the dangers would grow exponentially. At around 4:00 a.m., an angry Kan summoned Shimizu to his office, where the utility chief told him there was no plan to abandon the plant. (The media reported that Kan, irate that he was not informed of events at the plant, shouted at Shimizu, “What the hell is going on?”) The encounter apparently convinced both Kan and Shimizu that the lines of communication—and cooperation—needed to improve quickly. The two men agreed to establish a government-TEPCO integrated response center at the utility headquarters.
About ninety minutes later, Kan visited TEPCO headquarters to make it clear that the government was asserting a stronger role in the accident response. En route, he said later, he considered a worst-case scenario in which evacuations could extend as far as metropolitan Tokyo, population 13 million. (Indeed, mass evacuations might have been necessary, according to a worst-case assessment prepared at Kan’s request by the chairman of the Japan Atomic Energy Commission and presented to the prime minister on March 25.)
The TEPCO showdown coincided with the arrival of the latest bad news from Fukushima Daiichi: the possible containment rupture at Unit 2, followed by the blast in the Unit 4 spent fuel pool.
When the Japanese finally did ask for help from the United States on March 14, they were looking for heavy-duty pumping equipment that could deliver seawater to pits from which it could then be injected into the reactor cores via fire engines. U.S. military forces in Japan had firefighting equipment that would fit the bill, and discussions already were under way with TEPCO.
Over the course of that day, NRC staffers began arriving in Tokyo, including Tony Ulses and Jim Trapp, both experts in boiling water reactors. Finally, the NRC’s emergency operations center at White Flint had eyes and ears on the ground. The NRC team joined experts arriving from other government agencies, most of them based at the U.S. Embassy.
Later on Monday, Jack Grobe, the NRC’s deputy director for engineering, was manning the White Flint Operations Center when Chairman Jaczko telephoned for an update. Grobe had worrisome news: the prevailing winds in Japan, which had been carrying radiation out to sea, were about to shift to the southwest—toward Tokyo. With three reactors and the Unit 4 spent fuel pool in trouble, “that changes the dynamic of the protective measures aspects of this,” Grobe told his boss. Vast numbers of people could now be downwind. As a result, the Operations Center had summoned additional staff experts on radiation dose assessments and meteorology. But so far, Grobe told Jaczko, Japan’s 12.4-mile (twenty-kilometer) evacuation zone around Fukushima Daiichi was “consistent with what we would recommend.”
Marty Virgilio then called Grobe to tell him U.S. nuclear industry officials now speculated that there was a crack in the torus at Unit 2. If true, this could dramatically change the team’s assessment of the situation. The torus was part of the primary containment. Up to that time, as bad as things had gotten, the NRC was not aware of evidence that the primary containments at any of the reactors had experienced a major rupture. Such a breach could release dozens of times as much radioactive material as the minor leakage that had previously occurred. Given the projected wind shift inland, a Unit 2 containment failure could have catastrophic consequences for a large segment of the Japanese population.
“I mean, this is beginning to feel like an emergency drill where everything goes wrong and you can’t, you know, you can’t imagine how these things, all of them, can go wrong,” said Grobe. No drill had ever come close to this.
But the bad news hadn’t stopped arriving. Jim Trapp called to say that an admiral at the U.S. naval base at Yokosuka, south of Tokyo and 188 miles from Fukushima Daiichi, was reporting radiation measurements of 1.5 millirem (0.015 millisievert) per hour, apparently because of the wind shift. The NRC team was astonished that such a high dose rate would be detected at such a great distance from the plant.
Trapp added one more ominous bit of information from Japanese officials about the blast inside Unit 2: “[T]hey do believe they breached the primary containment.” Tony Ulses, also on the phone, raised an even more frightening prospect: the loud noise heard in Unit 2 “was probably when the core went X-up”—meaning when it had melted through the bottom of the reactor vessel. “Landing in the water under the vessel, it would have caused a little steam explosion,” said Ulses.
“Believe it or not, Jack, we’re telling you the good news,” Trapp told Grobe. Then he launched another dire litany, based on information gleaned from NISA officials in Tokyo. No one was certain of the water level in the spent fuel pool at Unit 3; as a result of the explosion, the reactor building “really collapsed into the fuel pool.” Radiation of ten rem (one hundred millisieverts) per hour was being measured near Unit 4, which could prove lethal after a day or two of exposure. (For context, workers at U.S. nuclear reactors are limited to five rem per year and generally receive far less than that.)
In an attempt to find some good news to pass along to his exhausted colleagues in Tokyo, Grobe told Trapp and Ulses that additional NRC staff members were en route. But that prompted a word of warning from Trapp: “[W]e’ve got to think about . . . whether we want them to come.”
“I mean,” added Ulses,” we’re getting to the point where this is just more bodies to have to get back out of here possibly.”
4
MARCH 15 THROUGH 18, 2011: “IT’S GOING TO GET WORSE . . .”
Jim Trapp and Tony Ulses were back on the phone with their colleagues at White Flint before dawn East Coast time on March 15. The original plan for the pair to spell each other off until reinforcements arrived had fallen apart; there was just too much going on. Both were exhausted; it had been a roller-coaster day.
At first, it had seemed that the flood of bad news from Fukushima Daiichi was slowing. The latest pressure readings indicated that the core of the Unit 2 reactor had not breached the reactor vessel, and operators were able to reestablish water injection. Other pressure readings contradicted the assumption that the mysterious noise heard at Unit 2 had been a rupture of the torus, although the data were inconsistent, suggesting an instrument failure. Units 1 and 3 were stable, with seawater injections proceeding smoothly.
The details even elicited a bit of optimism from Brian McDermott a short time later when he briefed his boss, Gregory Jaczko. “[L]ast night we thought we had a big problem,” he told Jaczko, referring to Unit 2. “And this morning, it, it suggests we have less of a problem.”
That assessment was short-lived.
Overnight, concern about the status of Unit 2 had led the NRC’s Protective Measures Team to run computer simulations for that unit based on worst-case assumptions: a fully molten core and a ruptured containment. The simulations projected levels of radiation exposure based on the prevailing winds blowing toward Tokyo. Readings picked up at the Yokosuka naval base and elsewhere seemed to suggest that the release was worse than everyone had thought.
Because the NRC’s RASCAL program can only estimate radiation doses within fifty miles of a release site, it was of little use in
interpreting the data collected at Yokosuka, about 190 miles from the plant. Even so, the findings were passed along to the State Department and the U.S. Embassy in Japan. The calculations indicated that, if winds continued to blow steadily in one direction, then evacuation would be warranted for everyone up to fifty miles downwind of the plant. This was based on the U.S. Environmental Protection Agency’s (EPA) protective action guides, or PAGs. (According to the PAGs, members of the public should be evacuated from any area where they could receive more than one rem, or ten millisieverts, of radiation exposure in a four-day period.) Based on the RASCAL estimate, the NRC was recommending to State that U.S. citizens evacuate if they were within fifty miles of the plant, four times the distance the Japanese were recommending. Approximately three hundred Americans resided inside this fifty-mile zone, along with about 2 million Japanese.
From a health standpoint, it seemed a prudent call. Politically, however, a recommendation so at odds with what Japan was telling its citizens was sure to upset Tokyo. The State Department was in an awkward position diplomatically, hoping the NRC might find a way to support the twelve-mile evacuation with a press release—even suggesting the language it wanted the NRC to use, reaffirming the Japanese evacuation recommendations. The NRC’s experts stuck by their guns: ask Japan to tell us why we’re wrong, they countered.
For the NRC, a fifty-mile evacuation advisory for Japan could also have political ramifications at home. The commission currently requires that emergency evacuation plans be developed only for the area within ten miles of a nuclear reactor. Safely evacuating an area twenty-five times as large would be difficult, if not impossible, at many reactor sites without detailed advance preparation—and plenty of time.
While debate continued about the status of Fukushima Daiichi Unit 2 and its implications, Trapp and Ulses had more bad news to report: the crisis at the Unit 4 spent fuel pool. It appeared, they said, that the situation could be just as dangerous—and baffling—as that in Unit 2, if not more so.
The hydrogen explosion at Unit 4 had occurred almost simultaneously with the suspected explosion in Unit 2 (about 6:00 a.m. March 15, Japan time), but the NRC heard nothing about a problem at Unit 4 until a couple of hours after the report of a possible containment breach at Unit 2. (Masao Yoshida at the plant also had been late in learning. He had not known of the explosion for almost two hours—until his workers made it back to the Seismic Isolation Building.) The Unit 4 reactor, out of service with its fuel in the pool, had not even been on anyone’s radar. In fact, only a few hours before the Unit 4 explosion, Marty Virgilio had reported in a status briefing that there were no concerns about any of the spent fuel pools, although given the extended loss of power, the team needed to “keep an eye on” them. Even after information about the Unit 4 crisis began trickling in, Unit 2 remained at the top of the priority list—but not for long.
As the NRC staffers pieced together data from a variety of sources, a disturbing picture began to emerge that challenged the team’s complacency toward the spent fuel pools. The massive blast that had blown off the Unit 4 reactor building’s roof and damaged walls there looked like yet another hydrogen explosion. But where had the hydrogen come from? The most obvious source would be a chemical reaction between steam and overheating fuel rods in the spent fuel pool. But that would mean that the water level had dropped to expose the fuel much more quickly than anyone anticipated.
The spent fuel pool was designed to hold 1,300 to 1,400 tons of water, approximately half the volume of an Olympic-sized swimming pool. If the pool lost cooling, it would have taken a couple of days for the water to reach the boiling point. When the water began boiling away, the pool would lose around one hundred tons of it per day. About one thousand tons of water would have to boil off before the fuel would be exposed. By a back-of-the-envelope calculation, it should take well over a week to get to that point. At the time of the explosion, the cooling pumps for the Unit 4 pool had lacked power for less than four days. If the spent fuel had become uncovered in such a short time, then more than eight hundred tons of water must have been lost in some way other than boiling. This could have been a result of shaking during the earthquake. (One worker who was on the Unit 4 refueling floor when the quake struck later reported seeing waves in the pool and being drenched as water sloshed out.) There was another possibility: a leak or crack in the pool itself, caused by the earthquake or the explosion in Unit 3.
No one could verify what was actually going on in Unit 4, or in any of the other spent fuel pools for that matter, because the gauges that measured the water level and temperature in the pools were useless without electrical power.
The worst case seemed to be confirmed when the NRC started to receive reports that a few hours after the blast a fire was observed burning in the Unit 4 reactor building. Initial fears were that this showed the zirconium cladding on the fuel had indeed ignited, making it possible that the fuel itself was melting and releasing a massive amount of radioactive cesium. With the roof and walls of the Unit 4 reactor building blown apart, the radiation would go straight into the atmosphere. No one could get close enough to investigate; however, the fire burned itself out shortly before noon. Its source was subsequently identified by NISA as lubricating oil used in a generator on a level below the fuel pool. The quake might have damaged piping or a storage tank, and a spark apparently set the oil ablaze. If the zirconium cladding had been burning, the fire would have lasted for days.
Radiation measurements between the Units 3 and 4 reactor buildings had soared to forty rem per hour, making even brief forays near the buildings extremely dangerous. They also seemed to indicate that, even if there had not been a zirconium fire in the Unit 4 spent fuel pool, something bad had happened there: perhaps pieces of spent fuel had been dispersed by the explosion, or there was no water left in the pool to shield the fuel.
Meanwhile, in the hours after the mysterious event at Unit 2 and the explosion at Unit 4, radiation at the plant gate had spiked to its highest level since the accident began, and an ominous cloud of “white smoke” was seen drifting from Unit 2. The prevailing winds continued blowing inland, toward populated areas. News that the wind direction was rotating clockwise, away from Tokyo but toward smaller cities and agricultural areas northwest of the plant, was small consolation. Since it was no longer clear that there had been a containment rupture at Unit 2, reports of white smoke notwithstanding, it was looking more plausible that Unit 4 was the source of the increased emissions.
Now the NRC had a new challenge: trying to understand what was going on with the Unit 4 spent fuel pool. The question of whether the pool still held any water had serious implications for estimating the amount of radiation that potentially could be released. This would soon become a thorny issue for the NRC team.
There was no doubt at White Flint that water had to be added to the Unit 4 pool immediately. That meant plant operators would have to figure out a way to deliver tons of water per hour into a spent fuel pool five stories off the ground, filled with rubble, and emitting levels of radiation that could be lethal within minutes. In the NRC’s view, getting water into the spent fuel pools should become the number one priority at Fukushima Daiichi. However, the Japanese did not yet see it that way.
WHERE FUKUSHIMA DAIICHI GOT THINGS RIGHT
Fukushima Daiichi focused world attention on spent fuel pools and their associated risks. Fukushima also demonstrated a safer means of managing the spent fuel risk: dry storage.
There were 408 spent fuel assemblies in dry storage at Fukushima. Although jostled by the earthquake and submerged temporarily by the tsunami, these assemblies survived without the need for helicopters dropping water from above or fire trucks spraying water from below.
Damage inside the dry cask storage building at Fukushima Daiichi was extensive. Although the casks (one is visible, center) were jostled and submerged by the tsunami, they remained unharmed. Tokyo Electric Power Company
Dry storage was first used in the United Sta
tes in 1986, and it is now practiced at plants across the country. After spent fuel assemblies have stayed in a pool for an initial period, workers transfer them into dry storage on-site. Typically, about fifteen tons of spent fuel are placed inside a sealed metal canister, then placed within a concrete and steel cask (the core at a large reactor holds nearly one hundred tons of fuel). Passive cooling—air flow from the chimney effect—removes the heat produced by the fuel.
Passive cooling does not work for densely packed spent fuel pools. The heat produced by the fuel assemblies—particularly those discharged from the reactor core within the past five years—requires continual cooling of the water in the pools.
A large radiation release from a pool could result in thousands of cancer deaths and hundreds of billions of dollars in decontamination costs and economic damage.
The crowded spent fuel pools at U.S. reactors pose hazards. An accident or terrorist attack could cause a loss of water from a pool or interrupt vital cooling systems. As Fukushima Daiichi demonstrated, it can be challenging to pump water up five levels into a pool for a boiling water reactor. And unless a hydrogen explosion rips apart walls and roofs, it can be difficult to drop water into a pool from above or spray water in from the side.
Transferring more assemblies into dry storage is the better way to manage risks posed by spent fuel. Reducing the spent fuel pool inventory accomplishes four things: It (1) reduces the heat load in the pool, (2) adds more water to the pool for every assembly removed, (3) allows the remaining assemblies to be spread out, and (4) reduces the amount of radioactive material in the pool.
The first two of these give workers more time to intervene in the event of a problem, increasing their chances of success. The third restores margin against inadvertent criticality within a spent fuel pool and provides additional space between assemblies for cooling air or water flow. And the fourth limits the size of the radioactive cloud that can be emitted from a pool. Thus, both the probability and the consequences of a spent fuel pool accident are lowered by moving fuel assemblies into dry storage.
Fukushima: The Story of a Nuclear Disaster Page 11
