This is part of IEEE Spectrum's ongoing coverage of Japan's earthquake and nuclear emergency. For more details on how Fukushima Dai-1's nuclear reactors work and what has gone wrong so far, see our explainer.
When Tsuneo Futami felt the ground tremble under his feet on 11 March, his first thoughts were for his family--he hastily got his grandson out of the house. But his next thoughts were for Fukushima Dai-1, the nuclear power plant that he managed from 1997 to 2000. As a former superintendent of the plant, he knew the possible consequences of a major earthquake and tsunami all too well. He flipped on the TV, and watched with the rest of the nation as Japan's nuclear emergency began to unfold.
Futami started working at Tokyo Electric Power Co. (TEPCO) in 1967, and worked his way up to become manager of the nuclear generation department before taking charge of Fukushima Dai-1. He is now a professor at Tokai University and the Tokyo Institute of Technology, and he has lectured on reactor engineering and crisis management. He spoke to IEEE Spectrum about his experiences as plant manager, and about his assessment of TEPCO's response to the current crisis.
Futami: Yes, I worried about earthquakes and tsunami. When I was superintendent, I thought the worst events that could happen were a fire in a radiation control area and station black out (SBO) if there was a loss of external electricity and the diesel generators failed.
All Japanese nuclear power plants use seawater as the final heat sink to cool steam and remove residual heat, so important equipment is located on the power plant's seaside yard. I worried about the loss of that equipment following a tsunami. However I could not imagine such a huge tsunami as occurred on 11 March.
TEPCO's civil engineering group estimates the maximum tsunami risk and maximum earthquake risk for each power plant site. I was informed the maximum tsunami at the Fukushima Dai-1 site might be 10 meters. The turbine buildings and the reactors were built 10 meters above the sea level, so it is beyond my imagination that seawater flowed into the turbine buildings of all units, and that facilities on the basement floor were flooded.
IEEE Spectrum: When you heard about the tsunami on 11 March, what did you think the consequences would be for Fukushima Dai-1?
Futami: The scale of the Fukushima Dai-1 accident was far beyond my imagination. When I was superintendent, I could not have imagined that all electricity including battery power for units 1 through 4 would be completely lost at the same time, and would not be restored for more than 9 days. (On 20 March, a temporary power line was connected to the power center of unit 2 for the first time after the accident. On 22 March, lighting for unit 3's main control room was restored.)
At first, I thought that the diesel generator for each reactor automatically started, so I was sure that they could bring the plant to a cold shut down, although there would be many difficulties. When I watched TV reports of the huge tsunami attacking the coast of the Tohoku area, I thought that major equipment like the condensate water pumps and the residual heat removal sea water pumps, which are on the ground lower than 10 meters above the sea level, must be damaged. That sent a chill down my spine. However I could not imagine that both the diesel generators and the power centers in the turbine buildings were completely covered with seawater by a tsunami that was over 14 meters high.
IEEE Spectrum: Were there safety upgrades while you were head of Fukushima Dai-1?
Futami: In the 1990s, countermeasures against severe accident were taken reflecting NRC and Japanese authorities’ regulations. They included the installation of recirculation pump trips (RIP) and alternate rod-injection systems (ARI) for an event known as anticipated transient without scram (ATWS), installation of automatic depressurization systems (ADS) for the reactor pressure vessels, installation of alternate water injection lines to the reactors and primary containment vessels, and installation of primary containment vessel vents.
IEEE Spectrum: Do you know if those systems failed after the 11 March tsunami?
Futami: I need more plant data obtained by operators and maintenance people from 11 to 14 March to evaluate for certain. But I am afraid some equipment systems did not work smoothly because of the complete loss of electricity including DC battery power.
IEEE Spectrum: Did you experience any serious problems with any of the reactors while you were head of the nuclear plant?
Futami: I did not experience serious operational problems. Instead of that, I was fighting against stress corrosion cracking of internal components in the reactor pressure vessels. Those components are highly radioactive and are inside the reactor pressure vessels. However it was necessary to work inside the reactor pressure vessels in order to replace a component called a shroud, although we used remote and automatic equipment as much as possible. I led the shroud replacement program of unit 1, 2, 3 and 5 and completed the world’s first shroud replacement in 1998.
Stress corrosion cracking is an aging problem. Some Fukushima Dai-1 reactors exceeded 30 years while I was a superintendent. I put my best effort into replace aging equipment based on preventive maintenance philosophy.
IEEE Spectrum: Can you explain what a shroud is?
Futami: The shroud is a large component inside the reactor pressure vessel. It's a very large cylindrical form made of stainless steel. In the space between the shroud and the reactor pressure vessel's outer walls, the water flows down from the top to the bottom of the reactor vessel. Then in the reactor core, which is inside the shroud, the water flows from the bottom to the top.
We found many stress corrosion cracks on the shroud’s welding lines, so we decided to replace the shrouds. We had to stop the plant about a year, and it cost about 8 billion Yen.
Coincidentally, at the number 4 reactor unit at Fukushima Dai-1 they were just replacing the shroud in this year’s annual inspections. That’s why all the core fuel was removed from the reactor pressure vessel, and installed in the spent fuel storage pool. That may have generated more heat than is usual at the spent fuel pools, and may have contributed to the fires that broke out around the spent fuel pool in the number 4 building.
IEEE Spectrum: Do you think the spent fuel storage pools are a hazard?
Futami: Japan is constructing a reprocessing plant in Aomori prefecture, but the construction schedule is very much behind. We cannot remove the spent fuel from the power stations, so a lot of spent fuel is stored inside the spent fuel storage pool of each power station. TEPCO just last year started to construct intermediate storage facilities, also in Aomori prefecture, but these are also behind schedule. So Fukushima Dai-1, Fukushima Dai-2, and all nuclear power stations in TEPCO have a lot of spent fuel stored inside the power stations.
In a normal condition that’s not so dangerous. But in the case of the Fukushima Dai-1 accident, I think such a large amount of spent fuel storage inside the plant increased the difficulties and the risks.
IEEE Spectrum: I know you have lectured on crisis management. Do you think that TEPCO could have responded better to the Fukushima Dai-1 crisis?
Futami: When a station black out occurs, water level drops down very rapidly. So the first several hours to 24 hours are very important. At Fukushima Dai-1, please remember that all diesel generators and power centers were covered with seawater, and that the heat removal seawater system was completely lost. Under these circumstances, I am convinced that no one could have prevented similar damages.
But TEPCO should have taken more serious countermeasures against tsunami.
IEEE Spectrum: Could the Fukushima Dai-1 managers have done anything differently to prevent the partial melting of the nuclear fuel in reactors 1, 2, and 3?
Futami: Residual heat removal seawater systems and condensate seawater pumps are located in the seaside yard. Besides that, TEPCO’s standard layout has the turbine buildings on the sea side and reactor buildings on the mountain side. The turbine buildings have big shutters where we carry in or carry out heavy components. The shutters are facing the sea. The huge tsunami on 11 March broke the shutters and large amounts of seawater flowed into the turbine buildings where the emergency diesel generators and power centers are installed. Judging from that situations, I think it would have been very difficult to find a way to prevent the partial melting of fuel.
IEEE Spectrum: Do you think the other nuclear plants in Japan are safe enough?
Futami: Yes. I am sure that Japanese nuclear power plants will become safe enough by modifications and countermeasures against tsunami based on the lessons learned on 3-11.
IEEE Spectrum: Do you think boiling water reactors are safe enough? Should more boiling water reactors be built in Japan?
Futami: It is difficult question because my experience is only with boiling water reactors. But I wonder if the direct cycle spreads radioactive material and water more easily inside all the buildings. Boiling water reactors use the steam produced in the reactor core directly to rotate the turbine, so all the equipment in the turbine system has radioactivity. In a normal case, that level of radiation is very low, so you don’t worry about it. But in the Fukushima emergency, the higher radioactivity spread in the turbine building. In the case of a pressurized water reactor, they use clean steam produced in steam generator—so the turbine building is not a radiation control area.
IEEE Spectrum: What are the biggest concerns at Fukushima Dai-1 now?
Futami: There are two serious concerns. The first is the highly contaminated water that is leaking in large amounts. I think we should never discharge highly contaminated water to the ocean, because there is no border in seawater.
The second concern is the strength of spent fuel pools’ reinforced concrete. Usually we have to keep the temperature inside the spent fuel pools under 65 degrees Celsius or so. A high temperature decreases the strength of reinforced concrete. Also the hydrogen explosions may have damaged the integrity of the concrete structures of the spent fuel pools. I’m worried about that.
If the spent fuel pools collapse, large amount of radioactive materials in the spent fuel will be released into the air, and a large amount of radioactive water will be released at the same time. So we have to put our best efforts to keep the spent fuel pools intact.
IEEE Spectrum: Will you ever go back to Fukushima Dai-1?
Futami: No. I decided it is my mission to transfer lessons learned from the Fukushima Dai-1 accident to younger people, and to countries that are operating nuclear power plants or planning to introduce nuclear power plants.