Photo: The Fukushima No. 1 nuclear power plant is seen in Okuma, Fukushima Prefecture, on Dec. 15, 2013. (Satoru Semba)
At around 11 p.m. on March 14, 2011, three days after the Great East Japan Earthquake and tsunami triggered a crisis at the Fukushima No. 1 nuclear power plant, U.S. Ambassador to Japan John Roos asked Chief Cabinet Secretary Yukio Edano over the phone to allow a U.S. expert in nuclear power to be stationed permanently at the prime minister’s office in Tokyo.
The request showed Washington’s distrust of the way Japan was dealing with the nuclear crisis.
Officials back in the United States also summoned Ichiro Fujisaki, Japan’s ambassador to Washington, on several occasions to convey their concerns, which centered on the nuclear fuel storage pool in the No. 4 reactor building at the crippled nuclear plant.
The U.S. Embassy in Japan on March 17, 2011, advised American citizens living within 50 miles, or 80 kilometers, of the Fukushima No. 1 nuclear plant to evacuate the area. The recommendation targeted four times the distance and 16 times the coverage area of the Japanese government’s evacuation order effective at the time.
While the U.S. advisory was tantamount to labeling Japan’s evacuation measures as insufficient, it was not without grounds of its own. Gregory Jaczko, chairman of the U.S. Nuclear Regulatory Commission, had said on March 16 that the storage pool was devoid of water.
Fukushima nuclear crisis: major events, radiation levels per hour near main gate to Fukushima No. 1 nuclear plant
The nuclear fuel storage pool in the No. 4 reactor building contained 204 unused fuel assemblies and 1,331 spent nuclear fuel assemblies. Of that number, 548 had been in use in the nuclear reactor until only four months earlier. The nuclear fuel in the No. 4 reactor building’s storage pool therefore had, say, four times the decay heat of the nuclear fuel in the No. 3 reactor building’s storage pool.
Unlike when mounted in a reactor, nuclear fuel in the storage pool has no steel pressure vessel or containment vessel to protect it. In addition, a hydrogen explosion had blown off the exterior reactor building on March 15, so highly toxic radioactive substances, such as plutonium and uranium, could be spewed directly into the outer environment if the fuel were to stop being cooled and catch fire.
That could leave not only the Fukushima No. 1 nuclear plant but also the Fukushima No. 2 nuclear plant, only 10 km away, out of human access and render uncontrollable all reactors and fuel storage pools at the two plants that contained nuclear fuel, experts feared.
Graphic: Evacuation zoning in worst-case scenario
It was only on March 25 that the government of Japan ordered Shunsuke Kondo, chairman of the Japan Atomic Energy Commission, to work out a worst-case scenario, whereby the area of compulsory human displacement could extend to a radius of 170 km or more, and displacement could be presented as an option within a radius of 250 km, including Tokyo, if the nuclear reactors were to spiral out of human control.
But Washington had concluded by March 16 that the nuclear fuel storage pool in the No. 4 reactor building had already reached that critical stage.
Tokyo’s worst-case scenario never turned into a reality. Washington’s conclusion was also wrong.
Why, then, were Tokyo’s worst-case scenario and Washington’s central concerns both averted?
This article will present in-depth viewpoints, along with citations from the testimony of Masao Yoshida, then general manager of the Fukushima No. 1 nuclear plant.
This epilogue concludes the series on the Yoshida Testimony, which has addressed questions such as who is there to halt nuclear reactors, if residents can really be evacuated, and if it is in the power of humans to halt nuclear reactors. But analysis and reviews of the Yoshida Testimony will, and should, continue.
Photo: Nuclear fuel assemblies are seen in the fuel storage pool in the No. 4 reactor building, cleared of rubble from an explosion, at the Fukushima No. 1 nuclear plant on Nov. 6, 2013. (Soichiro Yamamoto)
Question: I just wanted to make one point clear. The No. 4 reactor building’s fuel storage pool had a rising water temperature, so you could have thought that had to be cooled or, for that matter, when (water) was yet to be checked from aboard a helicopter, you could have thought that the water levels could be falling. Discussions were being focused on the No. 4 reactor, and when we checked the order of priority a moment ago, the first entry said, “1F4” (Fukushima No. 1 plant’s No. 4 reactor), but during the operations of March 17--we are at No. 91 here--this here says that the purpose was to cool the spent fuel storage pool in the No. 3 reactor building. Why did the focus shift from the No. 4 reactor building to the No. 3 reactor building?
Yoshida: A helicopter flew on the morning of (March) 17, though I don’t remember what time. The helicopter was not for dropping water but for air reconnaissance. I think it belonged to the Self-Defense Forces, and it flew, and one of our employees was aboard it to take video footage. And (the footage showed) water likely was, remained, in the No. 4 reactor building’s fuel storage pool. We saw a water level.
Video: Silent video footage taken by a Tokyo Electric Power Co. employee shows the Fukushima No. 1 nuclear plant’s No. 4 reactor building
Video footage taken slightly before 5 p.m. on March 16, 2011, five days after the quake and tsunami, by an employee of Tokyo Electric Power Co., operator of the crippled nuclear plant, from aboard a Self-Defense Forces helicopter was screened from 11:33 p.m. that day at the joint response headquarters of the government and TEPCO for dealing with the nuclear disaster. The joint headquarters was located in the TEPCO head office in Tokyo.
Yoshida erroneously said the helicopter flew on the morning of March 17. It flew on the evening of March 16.
The heavily shaking video footage was hastily put to analysis after one watcher said some of its frames showed a water surface in the No. 4 reactor building’s nuclear fuel storage pool, which Washington said was empty.
Akiyoshi Minematsu, a TEPCO adviser, was the first among the viewers of the video footage at the joint headquarters to assert that water remained in the No. 4 reactor building’s fuel storage pool.
“One portion of a truss groove is seen reflected on a water surface,” he said. “That shows there is water up to that level.”
Minematsu, a nuclear plant engineer, joined TEPCO as early as 1968, the year after construction began for the Fukushima No. 1 nuclear plant’s No. 1 reactor. He is exactly a dozen years senior to Yoshida.
Ichiro Takekuro, a senior TEPCO official, doubted that water remained.
“How could there be so much water in the spent fuel storage pool, which has one order of magnitude more heat than elsewhere, and after so many days?” Takekuro asked.
But Minematsu began using a diagram to explain himself.
Graphic: How water flowed into the nuclear fuel storage pool in Fukushima No. 1 nuclear plant’s No. 4 reactor building
Minematsu said that water filling the reactor well, a space directly above the reactor, and water in the dryer/separator (DS) pit, a pool connected to the reactor well and designed for underwater storage of equipment tainted with radioactivity, had flowed into the nuclear fuel storage pool through an opening in a gate that separated the fuel storage pool and the reactor well.
Water pressure would have held the separator gate tight in its position, and no opening could have formed if the nuclear fuel storage pool had been full of water. In fact, the gate was slightly off position and allowed for an opening, possibly because of reduced pressure from a loss of water due to decay heat of the nuclear fuel, and possibly because of the explosion, Minematsu said.
The reactor well and the DS pit contained a combined 1,440 tons of water, more than enough to fill the nuclear fuel storage pool. If Minematsu had it right, the crisis over the No. 4 reactor building’s fuel storage pool, Washington’s central concern, was gone. Analysis and discussions concluded that enough water remained in the No. 4 reactor building’s nuclear fuel storage pool.
Goshi Hosono, then a special adviser to the prime minister, said he was holding his breath watching the development. He said he remembers how cheers were heard in the joint response headquarters when the water surface was confirmed present.
But the reactor well is seldom filled with water. How did it happen to be filled with water at the time?
Photo: The reactor well remains filled with water in the Fukushima No. 1 nuclear plant’s No. 4 reactor building on June 29, 2011. (Provided by Tokyo Electric Power Co.)
Work began on replacing the No. 4 reactor’s core shroud, the largest structure inside the reactor, at the Fukushima No. 1 nuclear plant on Dec. 29, 2010, three months before the quake and tsunami.
The core shroud was being replaced for the first time after 32 years of continued use since the reactor entered service in 1978.
Given the immense size of the core shroud--6.8 meters in height and 4.3 to 4.7 meters across--a plan was worked out to cut it into pieces inside the reactor before pulling up those pieces one by one and moving them into the DS pit.
Workers also decided to fill the reactor well and the DS pit both with water so that all the pieces would stay underwater as they were carried, because the core shroud, which had long stayed inside the reactor, had itself become radioactive. The spaces were filled with water on Dec. 3.
It turned out, soon after the work began, that a jig, equipment for guiding and controlling a shroud-cutting tool into the reactor, had a slightly wrong design. Workers decided to quickly retool the jig on the site, but they had to push back the overall work period by about two weeks.
The workers had planned to remove water from the reactor well and restore it to its original state, once the old core shroud had been cut and taken out, so that a new core shroud could be fit in, but that plan ended up being postponed to late March 2011.
The initial plan would have restored the reactor well to a dry state on March 7, 2011, four days before the giant earthquake.
Investigations by Tomomi Miyazaki and Hideaki Kimura
Production by Morihiro Sakuma, Shinya Uemura, Akahiko Suefusa, Masayuki Shirai and Madoka Kimura
Translations in English by Taku Tada and Roy K. Akagawa