Around 4:45 a.m. on March 12, 2011, barely 12 hours after the Great East Japan Earthquake and tsunami hit, a central control room at the Fukushima No. 1 nuclear power plant, where operators of the No. 1 and No. 2 reactors were based, received a special delivery.
It comprised full-face masks and “alarm pocket dosimeters (APDs),” or personal dosimeters with alarm functions, adjusted to sound an alarm only at a radiation dose of 80 millisieverts so that those wearing them could continue working until the dose limit of 100 millisieverts was reached.
Fukushima nuclear crisis: major events, radiation levels per hour near main gate to Fukushima No. 1 nuclear plant
Question: What did you think this white mist was when you heard about it?
Yoshida: I thought it was steam.
Q: So you were under the impression that something could be leaking from somewhere, right?
Q: Later, at around 4:30 a.m., the written record says the central control room had to stop on-site operations for fear of potential tsunami from aftershocks. Was that (decision), in brief, affected by aftershocks?
Yoshida: Yes, it was. I just don’t happen to remember the data, but many aftershocks occurred that night that measured upper 5 or nearly 6 on the Japanese seismic intensity scale (of 7). I ordered workers to take shelter from their posts every time. Such was the situation where we were working.
Q: And if you look at this, it says that at around 4:45 a.m., the plant’s response headquarters delivered APDs set at 100 millisieverts and all-face masks to the central control room. Maybe I shouldn’t say “suicide squads,” but it appears things were developing into that direction around that time, right? And afterward, teams were organized--three pairs of workers--and those who should go were named. This shows that, anyway, seniors--shift supervisors and their deputies, team leaders ... maybe I shouldn’t say “elderly,” but anyway, those who were more aged than young people were prioritized in organizing the teams, right?
Q: Did you leave it up to people on the shift to organize these teams?
Yoshida: I left it up to them.
Photo: Hoses are seen in the Fukushima No. 1 nuclear plant’s No. 2 turbine building at around 11 a.m. on June 11, 2011. They are connected to apparatus for removing radioactive substances from the reactor building. (Provided by Tokyo Electric Power Co.)
The No. 1 reactor, where workers failed to notice nonoperating isolation condensers, remained uncooled for many hours. It was already in a critical state early on March 12.
Pressure in the reactor containment vessel stood at 840 kilopascals, about double the maximum operative pressure, at 2:30 a.m.
Any higher pressure could cause the vessel to crack and spew its content of radioactive substances to the outside.
A white mist filled the interior of the reactor building. Hydrogen and water vapor, which both have small molecules, might already be leaking from the containment vessel. It meant that the pressure was rising to a critical level.
The only way to prevent a disaster was to vent gas from the interior of the containment vessel. Very simple operations by workers in the central control room would have sufficed to perform the venting under normal conditions.
But doing so in the No. 1 reactor, which had lost its entire power supply following the strong seismic shocks and the tsunami, presented an enormous difficulty.
Two valves need to be opened, each with a different method, to perform venting. When pressure in the containment vessel reaches a predetermined level, with both valves open, a component called a “rupture disk” is broken, enabling the venting.
One of the pair of valves, called the “air-operated valve,” is designed to open when workers in the central control room operate a switch to activate an electromagnetic valve, which sends compressed air stored in an accumulator toward the AOV. But it was not possible to open the electromagnetic valve as long as the power supply was out.
The other of the pair, called the “motor-operated valve,” is designed to open simply by the force of an electric motor. With no power available, it, too, could not open.
Desperate to find out a solution, workers studied valve structures on blueprints and other materials removed from the damaged main office building. They discovered that the MOV was equipped with a handle that could be rotated manually to open the valve in every one of the No. 1, No. 2 and No. 3 reactors.
They also found the AOV had a similar handle on its reserve valve component, known as the “smaller valve,” in the No. 1 reactor, though not elsewhere. That meant the valve could only be opened if someone went there.
Easier said than done, however.
Photo: White smoke, believed to be steam, rises from the Fukushima No. 1 nuclear plant’s No. 3 reactor building on the afternoon of March 16, 2011. On the right of this photo, taken by a Tokyo Electric Power Co. employee aboard a Self-Defense Forces aircraft, is the No. 2 reactor building. (Provided by Tokyo Electric Power Co.)
Question: When you say you couldn’t, what exactly is it that you could not do?
Yoshida: As I said earlier, we had no power supply. And we had no accumulator, so we tried a lot of things. Workers, in the meantime, went to add pressure and tried to restore the power supply, but the only thing we were told was that all efforts had failed.
We agreed it all had to be done manually in the end, so we went manual, but a valve called the MOV on the drywell side is quite heavy to turn. As a result, the workers were exposed to radiation, but somehow they managed to open it. But when they tried to access a valve along a line that comes out of the drywell’s suppression chamber, radiation levels were so high that they could not even approach it and came back.
As the situation was like that, we were, like, telling workers to try to do it all over again from the step of activating the accumulator. A compressor vehicle finally arrived around that time, which turned out to be useful. We were in such a state, and we tried various things--even though there was a limited availability of tools. What we did was seldom successful.
In discussions now, those who believe that venting could be done right away understand nothing about the hardships we had. That is quite unnerving, but in reality, those who worked on the front lines had a much harder time than I did. Some of them, in fact, got doses of nearly 100 (millisieverts) there.
Photo: An inpatient, airlifted aboard a helicopter from an evacuation zone, arrives at the Fukushima Medical University in the prefectural capital of Fukushima at 8:40 p.m. on March 14, 2011. (Toru Nakata)
Workers learned that both vent valves could be opened if only somebody went there in person.
But it appeared dangerous to approach the valves as aftershocks continued. The Great East Japan Earthquake, which itself was a massive magnitude-9.0, was followed by three magnitude-7.0 or greater, 48 magnitude-6.0 or greater, and 281 magnitude-5.0 or greater aftershocks during March 11-12 alone. As a matter of fact, Yoshida, the plant general manager, had ordered workers to take shelter on several occasions. Before anything else, an alarming radiation level of 300 millisieverts per hour had been measured on the site.
—— ‘RADIATION LEVELS WERE TERRIBLY HIGH’
Operators in the central control room decided to organize three pairs of workers. The six members were picked from among shift supervisors and their deputies, or senior leaders of operators, but not from among the younger staff. Skills were evidently not the only criterion.
The operators decided to organize the three pairs because they believed the task would take nearly an hour to complete. Workers had to end their tasks when their exposure to radiation reached 80 millisieverts so as not to exceed the dose limit of 100 millisieverts.
That meant each pair had only a maximum of 16-17 minutes to work. A single pair was not enough to complete the task.
The first pair of workers left for the MOV at 9:04 a.m. They turned its heavy handle and opened the valve at 25 percent.
The second pair of workers subsequently left to open the “smaller valve” component of the AOV. But they had to turn back when their portable dosimeters sounded an alarm before they even arrived there.
The AOV was close to the suppression chamber in the lower part of the reactor containment vessel, which made it more difficult to reach than the MOV.
The third pair gave up on going there at all. The venting efforts were back to square one, so workers switched to plan B, whereby they would connect a powerful air compressor in an area of low radiation levels and pump air from a distance to open the valve.
Again, it was tough going. It seemed likely there was possible damage from the quake to either the accumulator itself or the piping for sending compressed air. It was only at 2:30 p.m., five and a half hours after the first “suicide squad” was dispatched, that Tokyo Electric Power Co., the plant operator, decided that venting had been achieved successfully.
The high radiation levels and the potential of explosions blocked all sorts of tasks and delayed work to bring the situation under control.
Photo: Beds that were once used to evacuate inpatients are left unattended on the grounds of the Futaba Hospital in Okuma, Fukushima Prefecture, at 10:53 a.m. on July 23, 2012. (Asahi Shimbun file photo)
Question: Following the explosion (of the No. 3 reactor building) at 11:01 a.m. (on March 14), work was temporarily...
Yoshida: All suspended.
Q: So you withdrew workers from their posts. And then, you resumed work at some point in time. What information did you get, and what judgment did you make when you decided to get going?
Yoshida: It was not so much about what information we got. (The No. 3 reactor building) had exploded after all, so using an analogy for the No. 1 reactor building, it appeared likely that different lines, including water injection lines, were dead.
We were pumping water into the No. 1 and No. 3 reactors, but that was suspended. It appeared likely that various other components had also failed. So we did a round of checks and confirmed nobody had been killed. We arranged for the sick and injured to be sent to J-Village for treatment. Everybody was in a daze and could hardly think about anything.
So I assembled all the workers and told them we had resumed work in such and such state, and we had ended up like that, and my judgment was to blame, so I was sorry, but I said no water was probably being pumped in at that moment, and we had to prepare for pumping water into the No. 2 reactor, because it would only turn for the worse if we did nothing about it.
I asked workers to go back to the front lines to clear rubble, because there must be mountains of rubble at the site, and the rubble was highly radioactive. So I asked them to have that in mind in measuring radiation levels properly, removing rubble, and replacing water injection hoses to a minimum required extent. I bowed my head to ask them to get ready promptly for water injection.
And I was really moved when everybody came out willing to go back to the front lines.
I called for restraint, on the contrary, so they would not go out at random. We arranged things like, this team and that team should be doing this, construction guys should use backhoes to clear rubble. We worked out plans before they left. And most of them at that time got almost excessive radiation doses when they were, like, replacing hoses.
That allowed us to be in time finally, and we managed to resume seawater injection at 4:30 p.m., but while all that was going on, quite a number of people went out to the front lines, like, for removing highly radioactive rubble.
It is annoying that nothing is written in here between 11:01 a.m. and 12:30 p.m. I did order workers to take shelter before that, but that is not written here, either. I have no idea what kind of “time series” this is.
Photo: Members of a “hyper rescue” unit of the Tokyo Fire Department are lined up in the Moriya service area along the Joban Expressway in Ibaraki Prefecture at 7:44 a.m. on March 19, 2011, before leaving for the Fukushima No. 1 nuclear power plant as replacement staff. (Toshiyuki Takeya)
None of the emergency core cooling systems provided in the No. 1 through No. 3 reactors was activated after the Fukushima No. 1 nuclear plant lost all of its alternating-current power supply. Workers used fire engines and hoses to pump water into those reactors to cool nuclear fuel.
The water was being taken from a depression on the immediate seaside of the No. 3 reactor building, called a reversing valve pit, as of the morning of March 14. Fire engines were pumping up that water, and hoses were being used to pump it into the No. 1 and No. 3 reactors via their water inlets.
Workers had planned to reduce the water pumped into the No. 3 reactor and increase the water pumped into the No. 1 reactor from 11:30 a.m. But the plan was aborted by an explosion of the No. 3 reactor building that took place at 11:01 a.m.
One worker was cited as saying that he saw a ripped hose while he was fleeing from the site.
Map: Location of the quake-proof control center building, where Masao Yoshida was taking command, on the grounds of the Fukushima No. 1 nuclear power plant.
At 12:37 p.m., Masao Yoshida, general manager of the Fukushima No. 1 nuclear power plant, ordered plant staff, visibly let down by the two explosions, to alter the rates of water injection, inspect hoses, and go to remove rubble that had fallen into the reversing valve pit, the water source.
“I do feel bad about it, given the circumstances,” he said as he gave the instruction.
The rubble was not just any rubble. Part of it was highly radioactive.
At 2:13 p.m., Yoshida additionally ordered an increase in the work force to clear highly radioactive rubble. In doing so, he used the wording: “organize a special team.”
Yoshida was growing impatient, because he received few reports from an advance team, possibly because of poor telecommunications. He only thought the rubble, if left uncleared, could pose a serious obstacle to subsequent efforts to pump water into nuclear reactors.
The word “suicide squad” is registered twice in the records of TEPCO’s teleconferencing system by the night of March 14, 2011, alone.
It was first uttered at 3:49 p.m. on March 13, 2011, when Yoshida ordered plant staff to return to their posts on the front lines to rebuild a seawater injection line for the No. 2 reactor. He said, during discussions on the matter: “a suicide squad of oldies.”
People working outdoors at the Fukushima No. 1 nuclear plant had withdrawn to the quake-proof control center building by that time, following the confirmation of some sort of mist inside the No. 3 reactor building, similar to the one that immediately preceded a hydrogen explosion in the No. 1 reactor building. But Yoshida sent them back to the front lines in the belief that their tasks definitely had to be accomplished.
The other occasion took place at 6:10 p.m. on March 14.
Workers were trying in vain to open valves for releasing steam, called safety relief valves, to lower pressure in the No. 2 reactor pressure vessel. They suspected weakened pressure of the nitrogen gas that was essential for opening the valves.
An official with the TEPCO head office used the word “suicide squad” in explaining that workers had left to replace a nitrogen gas cylinder despite high radiation levels.
The dose limit for workers applicable to an emergency was set at 100 millisieverts when the Fukushima nuclear disaster began. Following coordination with the Nuclear and Industrial Safety Agency, however, the government raised that limit at a stretch to 250 millisieverts at 2:03 p.m. on March 14, three days after the crisis broke out.
Sakae Muto, a TEPCO executive vice president in charge of nuclear power, instantly responded when he heard of the limit hike: “Two hundred and fifty is a pretty critical figure, so I think it is essential to abide by it.”
The government’s ceiling made it possible, in institutional terms, for workers nearing their dose limits to stay on the front lines a while longer. But the step did not make human bodies more resistant to radiation.
Efforts to bring the situation under control continued at the expense of increased health risks on the part of workers.