Читать книгу Meltdown - Yoichi Funabashi - Страница 9

2:46 P.M., MARCH 11, 2011. The Tokyo Electric Power Company (TEPCO) Fukushima Daiichi Nuclear Power Station.

At the time, there were twenty-four employees in the Central Control Room that managed the Unit 1 and Unit 2 reactors. The Central Control Room was the size of about two classrooms. The stainless steel, moss-green walls were crammed with instrumentation.

“460,000 kilowatts.”

That number was displayed on a large digital panel on the Unit 1 side. It was the output generated by Unit 1.

The Central Control Room was situated in the Control Wing, which was attached in hinge-like fashion to the Unit 1 and Unit 2 turbine buildings. Outside were the reactor buildings. Behind them were the radioactive waste treatment buildings for the Unit 1 and Unit 2 reactors.

There was not a single window connecting the room to the outside world. The instruments lining the wall shook with a creaking sound.

“Is that an earthquake?!”

The shaking became even stronger. The operations manual and documents flew from the desk of Ikuo Izawa (age 52), the duty manager of Unit 1 and Unit 2 Central Control Room, and scattered all over the floor.

The operators could not remain on their feet. They held on to the levers attached to the control panel. The levers were mounted so that they could still be operated and not shaken loose by an earthquake. Some of the operators sat down on the floor still clinging to the levers.

The shaking stopped after a little while. Red alarm lights started to flash. It was not just the red lights. White lights, orange lights, everything started to light up like a Christmas tree. Next came the fire alarm.

Izawa remembered an operator who worked in the control room of the TEPCO Kashiwazaki-Kariwa Station at the time of the 2007 Chuetsu earthquake, who said the fire alarm had been triggered by a mere flurry of dust in the control room.

“Try resetting it.”

The alarm stopped ringing when one of the staff reset it. Apparently, there was no fire.

The loud voice of Izawa rang out, “Everyone, calm down! First, check the SCRAM! Don’t operate the plant. Don’t do anything until the quaking calms down.”¹

When an earthquake strikes, the first thing that has to be done is stopping the fission reaction of the reactor. If this is not stopped, the temperature in the reactor would rise, the fuel would melt, and a large amount of radioactive material would leak out.

In order to stop the fission reaction, rod-like devices called “control rods” were inserted into the reactor. Each control rod was about four meters long. They contained boron. They were inserted between the fuel rods in the reactor to allow the boron to absorb the neutrons and stop a nuclear fission chain reaction.

Following the assistant shift supervisor’s instructions, the control panel workers started checking the situation in Units 1 and 2. They were able to ascertain that all control rods had been fully inserted and the two reactors had been automatically scrammed (SCRAM).

Finally, the tremors subsided. An alarm was ringing loudly. After a short time, one of the operators cried out, “Shift supervisor, we’ve lost external power!”

“Emergency power check.” Izawa gave the instruction immediately.

The emergency power was a diesel generator (D/G) that ran on heavy fuel oil in an emergency. Nuclear power plants generated electricity, but several hundred of the devices in the facilities were powered by electricity provided by external transmission lines. This was what had been hit.

“The MSIV is off!”

“Roger, MSIV off!”

The main steam isolation valve (MSIV) was the valve that isolated the main steam going to the turbines from the reactors. Turning it off prevents any radioactive main steam from reaching the turbines and leaking.

Already a loss of electricity meant there was no external power coming in. An operator was soon heard to say, “We’ve started the D/G! Both A and B are firing up.”

They felt a low reverberation inside the Central Control Room. The emergency diesel generator had started to operate. Up until this point, everything was going according to the operation manual. But it was a very short-lived moment of peace.

A young worker in the Central Control Room shouted out, “D/G trip!”

“What?”

“The D/G has tripped!”

The emergency diesel generator had gone offline. Alternating current (AC) power had already been lost from the quake. If the D/G was down, it meant that they had lost the power to cool the reactors down. If that was so, it meant the situation was hopeless.

One of the workers whispered, “The lights are flickering.” The lights on the control room’s power panel blinked, then, one by one, went out. The only light that remained was the emergency light for Unit 1. The alarms could no longer be heard and the room was enveloped in a bottomless silence.

The voice of Izawa, the duty manager, rang out, cutting the silence.

“SBO!”

Station blackout—that is, the total loss of AC power. One after the other, the workers all repeated, “SBO! SBO!”

Izawa placed a call to the operational manager at the Emergency Response Center.

“We have SBO. The D/G has failed. The emergency generator is down.”

“This makes it a Special Measures [Act on Special Measures Concerning Nuclear Emergency Preparedness] article 10 event. We are currently checking what is functioning.”

Izawa was surprised himself at how matter-of-fact he sounded when declaring an article 10 event.

I’m much calmer than during the training drill.

However, the person on the other end of the phone could not say anything but “Ahh!” He appeared to be thoroughly shaken and stunned.²

Immediately after that the four operators who had been outside to check the situation came back into the control room in two pairs, shouting at the top of their voices:

“We’re in trouble! We’re being flooded with seawater!”

“The basement of the turbine building is flooded up to around waist-height!”

“I heard a roaring growl from afar! I’d never heard such a noise before!”

“Seawater came flooding into the basement from the first floor! I managed to come up against the flow!”

All of them were soaked to the skin.

Is it a tsunami? Could a tsunami make it up to here?

This was something they had never imagined.³

The first tsunami hit the Fukushima Daiichi Station at 3:27 p.m., and the second and larger sometime between 3:35–3:37 p.m.⁴ Ten and thirteen meter–high waves hit the reactor and turbine buildings. The emergency seawater pump installed at four meters above sea level was swallowed up.

The staff who went to see if the Service Building had electricity tried to enter the building, but were trapped in the entrance area. They tried to contact site security, but could not get through.

Water started seeping in from below. They thought it was all over, but an older member of the staff broke the glass from outside and they escaped with their lives just as the water was already up to their chins.

Staff who had gone to the site to restore the electric motor at Unit 2 ran up the stairs in a hurry. From below the ground came a roaring sound the likes of which they had never heard before. Water came suddenly pouring in from the entrance of the Service Building.

For some reason, the door connecting Units 1 and 2 closed, and one person could no longer open it; it required two people pushing on it. The moment it opened, a huge volume of water came surging in. They walked up to their waists in water.

That was when they realized for the first time: It’s a tsunami.

Another member of the staff emerging from the Service Building saw a tsunami rolling in from the direction of the Unit 4 reactor. It was crashing violently into the steel plates of the water inlet in front of Unit 4, sending up columns of water. It looked like it was higher than ten meters. He froze in his tracks. Looking over to the sea, he saw the breakwaters tumbling down like a pack of dominoes. A construction crane was impaled on one of the pumps. He could hear the endless ringing of car horns below.

The Anti-Seismic Building and the various control rooms were separated by several hundred meters as the crow flies. The twenty- or thirty-meter flight of stairs linked to the Anti-Seismic Building, built on high ground, had been destroyed by a landslide and could not be used. Pipes above the ground had ruptured and water was spewing out in fountains.

The tsunami pounded in. It could well continue its attack. Izawa gathered the operators inside the Central Control Room. Only the emergency light on the Unit 1 side was dimly lit.

“Everyone, listen up. I have no idea what’s happening onsite. From now on, we’ll follow the rules when going to the site.”

Izawa spoke looking them in the eye, one by one.

“You’re to get my permission when going to the site, and I’m imposing a two-hour limit. You’re not to go alone but in pairs; meaning, you’re to move in twos. I want you to stick to this. If you’re not back in two hours, I’ll send out a rescue. Even if you don’t make it to your destination, check the time, and if it looks like going over two hours, turn back then. And write on the whiteboard the time you set out.”

Izawa then looked around at everyone and said, “If you don’t follow these rules, then it’s your lives on the line. So make sure of it. You’ve got that, right?”

“Roger that.”

“Understood.”⁵

Two of the workers headed to Unit 1 and another two to Unit 2 to check for damage to the emergency diesel generators in the turbine building basement. They took the stairs, but by the time they reached the first floor, another tsunami wave had hit. The workers just about managed to run back to the control room soaking wet. Two other young workers in the Unit 4 turbine buildings were not as lucky. They drowned as the waves came crashing in through the parking lot, seeping into all of the surrounding buildings.⁶

The Fukushima Daiichi Nuclear Power Station (NPS) had a two-stage structure from the sea level. The seawater intake and emergency seawater pumps were four meters above the sea level. The reactor buildings, turbine buildings, control buildings, and radioactive waste treatment buildings were located ten meters above sea level.

The operators called them the “4 disk” and “10 disk,” respectively. They used to be called the “4M board” and the “10M board,” but over time this had evolved into “disk.”⁷

Site Superintendent Masao Yoshida had been in his onsite office. Although he could not stay on his feet when the quake struck, he thought, The plant can withstand it. He then ran immediately to the Anti-Seismic Building.⁸

The turbine buildings were on the seaside and the reactors toward the hillside. Units 1 through 4 on the Okuma site were painted blue in a seascape motif, while Units 5 and 6 on the Futaba site were decorated in a green mosaic. Blue represented the sea and green the hills. The sales pitch was: “A nuclear plant at one with its environment.”

To the southern side of the Unit 4 reactor was a disposal complex for both handling radioactive liquid waste and incinerating solid waste. The entire station with its six reactor units was capable of generating 4.696 gigawatts of electricity (GWe).

There were two unit managers and three deputy site superintendents working under Masao Yoshida, the site superintendent. The operation of the reactor facilities was handled by the TEPCO shift supervisor. Shift supervisor was a career post. Training a full-fledged shift supervisor was said to cost 60 million yen. The shift supervisor acted something like the facility’s pilot. Shift supervisors, who reported to the operational manager, were separated into those in charge of Units 1 and 2, 3 and 4, and 5 and 6. Each shift team consisted of eleven members: a shift supervisor, two assistant shift supervisors, two senior operators, one assistant senior operator, two main equipment shift operators, and four auxiliary equipment shift operators. There were five such teams rostered to operate the reactors around the clock. This meant a nucleus of fifty to fifty-five key personnel.

TEPCO had some 1,100 workers in operations at Fukushima Daiichi NPS. There were a further 2,000 workers from TEPCO-associated companies, who looked after plant manufacturing, fire protection, and site security. At the time of the quake, there was a total of 5,600 workers onsite, of whom 750 were TEPCO employees. The number of associated workers was so large because the quake coincided with a periodical inspection of Units 4, 5, and 6 reactors.

The emergency response center (ERC) was on the second floor of the Anti-Seismic Building. With the earthquake, the room’s lights had gone out, only the glowing red light indicating the emergency exit. There were no windows overlooking the site in this room. There were no surveillance cameras, either.

3:37 P.M. One or two minutes had passed since the second tsunami hit.

A report came in via the hotline from the Units 1 and 2 Central Control Room.

“Both the Unit 1 emergency diesel generator and the DC power supply have stopped. We’ve lost all power! The tsunami is rapidly flooding the building.”

Around 3:38 p.m., a hotline report was received, this time from the Units 3 and 4 Central Control Room.

“Both Units 3 and 4 have lost power!”

Around 3:41 p.m., emergency contact was again received from the Units 1 and 2 Central Control Room. A woeful voice reported:

“Unit 2 has also lost all power.”⁹ Four reactors had now all lost power.

Yoshida was at a loss for words.

What? The D/G is not working?

This is not good. This could be a severe accident. Isn’t there any way to get the D/G to function properly again? If that is impossible, it might take hours for the IC and RCIC to cool. If we can’t do that, what else can be done …?

The DC power. We will be waiting eight hours for it. Even having said that, because DC power runs on batteries, there is only that capacity. When it does run out, will we be able to charge it? This could well fall under an article 15 for DC power.

Yoshida’s thoughts spun around and around the possible scenarios that could unfold.¹⁰

The operators took out the emergency operating procedures manual that TEPCO had prepared in-house and started to read it by portable battery lights and LED torches.

“Event-based?”

“State-based?”

None of this corresponded to what they were directly facing. An outage of both AC and DC power had not been foreseen.

In the first place, the manuals all assumed that plant information could be ascertained via the instrumentation in the respective control rooms. But those very control rooms were currently in the dark. None of the instruments were showing anything.¹¹

Still, the veteran shift supervisor and his team had a mental picture of where everything was on the power panel. They knew by instinct which meter was where even in the dark. In the words of a Toshiba engineer, “They were fellows who knew where even the mouse holes were.”¹²

Even for such old hands as these, a total power outage was unimaginable. What’s more, a total loss of DC power—also known as a station blackout—had never been conducted in training scenarios. The drills always ended before reaching such a severe point, with an instructor calling out, “Freeze!” Despite all the mayhem, one of the operators turned to Izawa and said, “Isn’t this where the instructors say, ‘Freeze’?” They both laughed.¹³

3:42 P.M. In accordance with section 1, article 10 of the Act on Special Measures Concerning Nuclear Emergency Preparedness (NEPA), Yoshida reported to the government that a specific event requiring notification (the total loss of all AC power sources) had occurred.¹⁴ This measure was taken after receiving the report from Izawa in the Central Control Room. When Izawa called, he reported that the loss of power supplies and emergency core cooling systems mandated an article 15. Upon hearing this, the person on the other end of the phone in the ERC began to mumble and then fell speechless, Izawa recalls.¹⁵ It had taken staff in the ERC somewhere between thirty minutes to an hour to decide whether to report an article 10 or 15, with article 15 representing the most serious condition: red. Although they had chosen to go with article 10, it was only one hour and three minutes later, at 4:45 p.m., that they would upgrade the incident to an article 15.¹⁶

By around 3:50 p.m., they were no longer able to read the reactor water level or pressure meters. What was happening inside the reactors? Was the cooling equipment working? They had lost their parameters for identifying this.

The control rooms had lost their five senses.