It took over 12 years to complete the Fukushima I power plant, with the last, Unit 6, starting commercial operation in October of 1979. Although each reactor was a General Electric BWR, no two reactors were just alike. There were constant improvements implemented by GE in the 1970s, and the technical sophistication of the reactor systems increased as units were added to the plant. The TEPCO engineers made certain that the plant met the special requirements for reactors built in a heavy earthquake zone. The earth was bulldozed off the site so that the reactors could be built on solid bedrock, reducing the horizontal earth movement during an earthquake to a minimum, and a tsunami wall was built down on the beach, protecting the plant from an ocean wave as high as 18.7 feet.[270] Two breakwaters, one north and one south, spread out from the beach and onto the sea floor to prevent waves from silting up the water intakes.
Each reactor was equipped with two large water-cooled diesel backup generators, located in the lowest part of the plant, completely underground, in the basement of the turbine building facing the ocean. Electric pumps brought in seawater to cool the engines and dumped it back into the ocean. The battery rooms and the electrical switchgear spaces were also in the basement, on the inboard side of the turbine building. The control room was two stories up, connected to the turbine building. As much equipment as possible was shared between pairs of reactors, especially the vent stacks. Units 3 and 4, for example, shared one 600-foot stack, exceptionally well braced for earthquakes.
There were exceptions. Units 2 and 4 had one water-cooled diesel and one air-cooled diesel. The Unit 4 air-cooled engine was down for maintenance and was in pieces on the floor. Unit 6, the more advanced BWR/5, had two water-cooled diesels in the basement, but there was a third generator located above ground in an auxiliary building. It was air-cooled.
In March 2011, Units 4, 5, and 6 were down for refueling and maintenance. Unit 4 was in the middle of refueling, with the dry-well lid and the reactor vessel cover unbolted and placed aside using the overhead crane in the reactor building. The refueling floor was flooded, and all the fuel had been moved to the adjacent fuel pool for a cool-down period. The only things turned on in the Unit 4 building were the overhead lights and the coolant pumps for the open fuel pool, keeping water moving over the spent fuel as its residual heat tapered off exponentially. Units 5 and 6 had just finished refueling, and Unit 5 was undergoing a reactor-vessel leakage test. Units 1, 2, and 3 were running hot, straight, and normal, and three 275-kilovolt line-sets were humming softly.
On March 9, 2011, 70 miles offshore, the Pacific Plate tried to slip under the Okhotsk Plate, 20 miles under the ocean floor. A magnitude 7.2 earthquake hit Japan. It caused the reactors on the northeast coast to scram due to indications from the ground-motion sensors, including Units 1, 2, and 3 at Fukushima, and it made the news, but nobody was hurt. Three more earthquakes the same day shook the ground. It was just another day in Japan, and life resumed a normal path after the bothersome disturbances. The reactors immediately restarted and resumed power production.
Earthquake prediction is a science in Japan, explored with more enthusiasm than anywhere else on Earth. Accelerometers are spread over Japan and out into the sea floor, and tsunami warning buoys are anchored offshore. These sensors can detect ground or ocean floor movement and send signals back to the Japan Meteorological Agency (JMA) at the speed of light over electrical cables. The earthquake shock travels much slower, at the speed of sound through rock (about 3.7 miles per second), and, depending on how far out the disturbance is, there can be minutes of warning issued by JMA. That is enough time to crawl under something solid or race out the front door of a building. The entire country is wired with earthquake alarms, designed to go off upon ground-movement detection from the array of accelerometers.
On Friday, March 11, at 2:46:43 P.M. Japan Standard Time, two days after the four minor earthquake shocks, Mikoto Nagai, head of the Emergency Response Team in Sendai, was at his desk on the third floor of an earthquake-proof building, sipping coffee. A lot of engineering thought had gone into how to make a building withstand ground accelerations. As Japan rebuilt after having been bombed to the topsoil during World War II, most of the new structures were constructed to sway without the foundation crumbling and the vertical support beams splintering. The early-warning earthquake alarm went off. Nagai put down his cup and looked up at the LED display bolted to the wall. It flashed 100 followed by a 4. In 100 seconds, a hit from a magnitude 4.0 earthquake was expected. The display quickly changed its mind. Make that a 6.0. No, an 8.0. Nagai stood up, and his coffee cup bounced sideways off the desk. Bookshelves collapsed, the internal wall in front of him came down, and people started screaming.
The Pacific plate had successfully relieved the east-west tension and hit Japan with its biggest earthquake ever recorded. It was 9.0 on the dimensionless Moment Magnitude scale.[271] In three minutes, the eastern coastline of Japan fell 2.6 feet, and Japan moved 8 feet closer to California.[272] The rotational axis of the Earth tilted by 10 inches. Roads were churned, high-voltage power lines were downed, and 383,429 buildings were destroyed.
The point in Japan nearest the epicenter of the earthquake was Onagawa in the Oshika District, and on a point of land jutting out into the Pacific Ocean was constructed the Onagawa Nuclear Power Plant by the Tohoku Electric Power Company, down on the beach. It consists of one BWR/4 and two BWR/5s, built by Toshiba under contract with General Electric. The last one started operation on January 30, 2002. As it was the newest reactor of the group, it has the most updated earthquake hardening techniques applied to it, and it has a substantial, 46-foot tsunami wall between it and the surf. The earthquake rolled through Onagawa, scrammed all three reactors, and subsided without doing any damage to the power plant. All the workers’ homes within driving distance of the site, however, were leveled to the ground.
About 22 seconds after it hit Onagawa, the ground-shock hit Fukushima I, which was twice the distance from the epicenter. An inspector for the Nuclear Industrial and Safety Agency, Kazuma Yokata, was permanently stationed in the office building at Fukushima I, in the no-man’s land between Unit 1 and Unit 5. He heard the alarm go off, but he was not overly concerned until the ceiling appeared to be coming down on him. He cringed as the L-shaped brackets holding up the bookshelves ripped out of the wall and his thick binders containing rules and regulations started flying.
There were 6,413 workers on the Fukushima I site that day. One of them, Kazuhiko Matsumoto, was in the turbine building for Unit 6, finishing some work on air ducts. He suddenly found that it was impossible to remain standing on the sparkling clean deck, and he had to cling to a wall to keep from being dribbled on the floor like a basketball. The lights went out, and the windowless expanse of the turbine hall went black. In a few seconds the emergency lights turned on, and over the loudspeaker came a simple instruction: “Get out.”
270
The United States is not above building a nuclear power plant on the beach in the Ring of Fire. The Diablo Canyon Nuclear Power Plant in California is built facing the Pacific Ocean, using it as the source of coolant. Fukushima has an 18.7-foot tsunami wall, but Diablo Canyon has a 32-foot tsunami wall. There is no evidence of a wave this high ever having washed over the Diablo Canyon property.
271
One is tempted to write “Richter scale.” Somehow, it sounds better, but Richter is now considered to be an obsolete relic from 1935. It has been replaced by the Moment Magnitude scale, which expresses the energy released from an earthquake on a base-10 logarithm scale. There are correction factors added to the formula, but it is basically the same value as the old Richter scale, +/-0.6. A 9.0 event is 100 times more powerful than a 7.0 event.
272
The sinking of Japan had an effect on the rotational speed of the Earth. Just as a spinning ice skater speeds up by pulling in her arms, the Earth’s rotation sped up slightly, decreasing the length of a day by 1.8 microseconds as the mass of Honshu Island drew downward, toward the center of the Earth.