12 Mars 2013
Mar. 4, 2013
Manager of TEPCO, Akira Kawano
The 2011 earthquake and tsunami triggered a total blackout at the Fukushima Daiichi Nuclear Power Plant which resulted in the loss of cooling water and melt downs in three of the four operating reactors. Hydrogen explosions severely damaged the unit buildings and all four reactors are to be decommissioned.
Two years on, the operator, Tokyo Electric Power Company or TEPCO, say the plant's situation is stable. They say water circulation systems are keeping the nuclear fuel cool and that the plant is no longer releasing significant amounts of radioactive materials.
The government's roadmap says the decommissioning will end within 40 years.
But details of the plan are yet to be decided.
NHK WORLD's Yoichiro Tateiwa spoke with Akira Kawano, general manager of TEPCO responsible for the decommissioning of reactors at Fukushima Daiichi.
Would you describe the current state of the Fukushima Daiichi reactors ?
The core cooling is the most important thing from the nuclear safety aspect. So we are still now injecting a certain amount of water into the core, reactor core, and also we are cooling the spent fuel pool. The temperature of the reactor pressure vessel and also inside the primary containment vessel is very low now, about 15 to 35 degrees centigrade. It's far below 100 degrees centigrade. It's a very stable status.
Also, the additional release of radioactive materials from the buildings, it's also almost nothing. So it's about 0.03 millisieverts per year at the boundary of our site. It's about 80 million times smaller compared to just after the accident.
It's very difficult to understand the inside situation of the primary containment vessel, and also the reactor pressure vessel. But we have already started to investigate their status. We have already inserted CCD camera to see the inside status. And also we inserted measurement tools to measure the temperature inside, and also the radiation level inside, and it's also very important for us to understand what water level is secured inside the primary containment vessel.
For example in the case of unit 1, it (water level) was 2.8 meters from the bottom of the primary containment vessel, and the temperature is very low. It's around 30-50 degrees centigrade. It means the molten fuel debris are stably cooled down there. But we haven't understood well how those molten fuel debris are distributed and located. We need to know more precisely, so we will continue those efforts for the future retrieval, removal of that debris.
What do you know about the molten fuel debris?
Even we, TEPCO haven't had a really precise information on the debris. In the future, we need to sample the debris, and we need to understand the mechanical characteristics and chemical characteristics of the debris. Otherwise we cannot develop the necessary tool to remove, retrieve the debris.
I hope... we would like to understand something about it within a couple of years. It takes a long time to – it's just difficult to achieve it. It takes time. We need to develop some technology, too. Even for sampling, we need to prepare some container to contain the sample debris. So it takes time.
Can we really say the decommissioning process will finish within 40 years ?
It's very difficult to talk about such a far future. But it really takes time actually. So even just for the removal of the debris, it takes 10 years or more, I think. And you know the half-life of cesium for example is 30 years, so some part of the decommissioning, we need to wait for radiation to be reduced. And then our decommissioning work will be much easier, after the decrease of radiation levels.
We actually have several options for decommissioning the plant, we should wait for a moment, or do something right now, or do something after waiting some time period. That point is the most difficult. And also the point we would like to have some advice on from the international organizations. They have more experience. We actually want to define the kind of end-state of the decommissioning work, after the decommissioning work. But it's really difficult to define the end-state, so we need to have good advice to define it.
We are trying to do decommissioning work as early as possible of course, because we would like people living there to return back to their homeland as early as possible, if it is possible. So we will not stop our efforts to promote decommissioning work as soon as possible. But we need to carefully discuss what the best way is... It's very difficult to say, but it's really a difficult discussion, and we need to do it carefully.
What are you planning to do with the spent fuels stored inside the reactor buildings?
We are focusing to transfer all spent fuels down to the ground, and to transfer to the other, safer storage space that is actually a common fuel storage facility, which is located next to unit 4, as early as possible. In order to achieve it, we have already removed all the rubble, debris at the top part of the unit 4 reactor building last July. And we are now constructing the kind of cover which has a fuel handling machine and also a crane to transfer the spent fuels. So we are planning to start the removal of the spent fuels within this year, regarding unit 4. It's a top priority because there are more than 1,500 fuel bundles there.
Also, some people are concerned about the integrity of the reactor building of unit 4, and the spent fuel pool. We have already reinforced the structure just under the spent fuel pool. We installed some steel pipe structures, and we poured concrete in that place to have a more seismic margin. It's about a 20 percent margin increase.
And also we are measuring the kind of distance between the top floor level and water level at some points around the spent fuel pool, to verify the building is not tilted. And also we are periodically conducting visual inspections to find out any significant cracks in the concrete. We are also doing some concrete integrity confirmation tests.
We call this the Schmidt Hammer method to verify concrete strength. Such are the things we are doing to verify the integrity of the reactor building of unit 4.
So the reactors can withstand a tsunami similar to the one 2 years ago?
We have already made a seismic analysis assuming the same level of earthquake of March 11th, and we have already proved that our seismic resistance for units 1 through 4 are sufficient, enough against a same level of earthquake. And also assuming a same level tsunami, with a 15-meter level tsunami, we have already installed a temporary seawall in front of the ocean side of our units 1 through 4. And also we prepared electric supply trucks and gas turbines also at a high place, it's about 35 meters high, safe place. And also we deployed fire engines in case we need to inject sea water. So we have prepared as much as we can, so I believe we are mostly prepared.
What are you planning to do with the accumulating contaminated water ?
I would say underground water seeping into the reactor buildings is the biggest challenge for us. We really need to have further deep discussion with the stakeholders, like fishermen, and also the local people, and local communities, even with foreign countries.
We have already started it, some part of it. But we need to continue. It's really impossible to just continuously accumulate that water in the tanks, it's not a reasonable way. So we need to think about the possibility of a discharge, or the other alternative ways, like evaporation or something like that. It's really a difficult discussion, I'm very sorry I cannot answer so clearly.
We are recognizing this is the most difficult and challenging issue for us now. 400 tons of groundwater come daily into plant. And the water becomes highly contaminated in turbine building.
So far, we are managing well regarding the highly contaminated water. We are just accumulating that water in the tanks. But a problem exists in the future. We are continuously increasing the capacity of the tanks, and water is accumulating also in parallel. So the difference is always the same. So we cannot continue it. Of course we are managing well now, but we cannot continue eternally, so we have to think about alternative ways.
Is the contaminated water not leaking into the ocean?
What I can say now is, we investigated possible leakage areas and points, and we didn't find any evidence of further additional leakage from the plant side to the ocean. So I believe it's not happening now. But we need to continuously investigate.
We have been continuously monitoring the radiation level of the sea water at several points, especially inside our port. We are doing also the outside ocean with the cooperation from the government. Especially inside the port, actually some part of the radiation level is a bit higher than the legal limit, because you know we had a very bad experience just after the accident. It was in April, and also in May, we inadvertently discharged contaminated water to the ocean. That is still remaining there, so that's the reason why the radiation level there, in the port, is a bit higher. And we are trying to verify that additional leakage is not happening. We investigated the possible portion of the leakage, like the pump pit, or the trench, or even inside, under the soil, sampling the soil to verify whether the ground water is OK or not. So we did as much as possible to verify that additional leakage is not happening. We didn't find any evidence that further leakage is happening.
And we are also making efforts to reduce cesium levels within the port. And also the reason for the high radiation level is kind of the movement of the soil at the bottom of the ocean. So we have already solidified that soil to avoid unnecessary movement.
The other problem is contaminated fish. We are now trying to trap and catch as many fish as possible within the port. We are also installing a kind of net to avoid them going out to the ocean. Various measures are being taken, especially inside the port.
It's a long way work, but we are gradually trying to improve the situation and the atmosphere under the water.
How do you view the importance of sharing information?
After this accident, it was really difficult for TEPCO to understand precisely our plant's situation. That looked a bit like (we were) hiding something, but we have been actually trying to disclose all the information. And also reflecting (back) now, in case we had some concern that this information could be bad information for the public, we have had some hesitation to disclose it. It's not good. From the viewpoint of risk communication, we actually need to disclose all the information as early as possible. That's much better than information coming out later.
So we learned somehow. It was not only the decision of TEPCO, but influenced by the government and also by media. We really need to improve our capability of risk communication in the future. That's also our challenge...regarding also the decommissioning, end-state of decommissioning work. So we need to share that information. After even preparing the minimum information for the stakeholders, it's also necessary.
We will disclose information every time we have it. So we need to have some time to interpret that information and develop strategy options. Of course we disclose all the information whenever we have it, but for a good discussion we need to prepare some clear options for the stakeholders. And that is much better for us and for them, to have a more fruitful discussion to define the end-state.