More than four years after the Fukushima disaster, no nuclear power plants have operated in Japan. At least that was the case until August 2015, when the Sendai nuclear plant in southern Japan became the first to begin operation since the 2011 Fukushima meltdowns, despite anti-nuclear protests.
An additional 23 units in 14 nuclear power plants are applying for the green light to resume operations. To do this, they must pass a safety review conducted by Japan’s Nuclear Regulation Authority.
But the plan to resume nuclear operations fails to reflect on the lessons we have learned from Fukushima, warns Hiromitsu Ino, a former Tokyo University professor and specialist in metallic material engineering.
“At the moment, the Abe government is attempting to revive nuclear power stations and trying to return the evacuated inhabitants to their home. However, we do not have any clear plan to restore the damaged area yet. We must use our experience of the Fukushima accident as the base when we consider the future,” says Ino, who has already raised major concerns over the risks involved in resuming nuclear operations across the country.
“First of all, I want to emphasize that the common sense of the nuclear power community is senseless for citizens, and the common sense of citizens is senseless for the nuclear power community,” says Ino. “During the Fukushima accident, all the external power was cut down and the internal emergency diesel generators were also damaged. We wonder why they had not made the external power more earthquake resistant, but for them our idea looks senseless.”
Ino points out that cost is also a big factor playing out behind the scenes: “In order to enhance the entire plant’s level of earthquake resistance, you must make the whole system within and around the premises earthquake resistant, including pylons, wiring and the thermal power plant itself, which would cost a huge amount of money. That is why power companies are not willing to do it.”
Nuclear power plants are built taking into consideration not only safety but also the balance of safety, costs (economic efficiency), performance and environmental burden, among other factors. “This sense of balance applies not only to a nuclear power plant, but also to many other things,” says Ino. “However, if and when a nuclear power plant has an accident, the damage is enormous. We need to emphasize safety by all means. But they evaluate the balance at the same level as in any other technology. It is both ridiculous and dangerous to resume a nuclear power plant in this situation.”
Commenting on the nuclear power plants built in the 1970s, Ino says, “The design concept is bad and the materials are also bad. They are built based on the assumption of an operating life of 30 to 40 years. Such common material as stainless steel were used. The material of pressure containers contains copper impurities. When neutrons hit the containers, copper fuses together and forms clusters, making that part stiff, brittle and therefore easier to break.”
The boundary temperature before a material breaks is called “brittle transition temperature.” For example, copper’s brittle transition temperature is usually about minus 20 degrees centigrade, but as the material gets older the brittle transition temperature rises. The worst is 99 degrees in Unit 1 of Takahama Nuclear Power Plant, followed by 98 degrees in Unit 1 of Genkai Nuclear Power Plant.
The higher the brittle transition temperature; the higher the risk of the container breaking. Additionally, when the core cooling system functions as an emergency measure and cold water flows into the container, only the inside part of the container is rapidly cooled down. The temperature difference between inside and outside could generate some force and break the container from inside.
“If the pressure container is broken, we can no longer cool it down with water,” explains Ino. “The meltdown will surely start. If there is hydrogen around, there is a risk of explosion as well. When the containment vessel is blown away, the radioactive substances will disperse in the area of 250 kilometers in radius, causing damage much more serious than the Fukushima Daiichi accident.”
Unit 1 of Genkai Nuclear Power Plant has been officially decommissioned, but there are still hopes that Unit 1 of Takahama Nuclear Power Plant could once again become active. “The reason is that while the output power of Genkai is relatively small, 50 kW, that of Takahama is nearly 100kW,” said Ino. “They do not want to decommission Takahama. These two stations are equally dangerous, but the decision is made based on economic rather than safety reasons.”
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Today, there are approximately 430 nuclear power units in operation in the world. When a nuclear reactor operates for one year, it is called one reactor-year. The global nuclear plant operation amounts to 16,000 reactor-years so far.
“During this period, there have been five major accidents, namely Three Mile in 1979, Chernobyl in 1986, Fukushima Daiichi, Daini and Daisan in 2011. That means a big accident once in every 3,200 reactor-years. If we divide this with 430 units, we have a possibility to have a major accident every 7.4 reactor-years.”
In spite of all this, a power company announced that a severe accident that lets out radioactive substances on a large scale happens only once in a million years. Ino said: “Recently, Kagoshima District Court overruled the petition to prohibit the operation resumption of Sendai Nuclear Power Plant of Kyushu Power Company. The judge certified that level of accident rate as well. That means the nuclear power community’s message of ‘an accident happens almost never’ is very well disseminated.”
In August, Sendai Nuclear Power Plant was the first plant to resume operation after the new regulation standard was put in place by the METI (Ministry of Economics, Trade and Industry). “Though the government and the electric power companies boast that it is ‘the world’s strictest safety standard,’ it is in fact much more lax than those in the U.S. and Europe,” says Ino.
The most serious deficiency of the new regulation standard is, according to Ino, the fact that they deleted the location site evaluation guideline. The old standard strictly regulated the radiation exposure level of the inhabitants of the surrounding areas. The new one deleted that part, he claims.
“It is because they cannot find any location, even a less-populated area, that meets the standard if they deal with the possibility of an accident as grave as Fukushima,” claims Ino. “The new standard also inherits the conventional design criteria which assumes only a malfunction of a single machine. However, we have a significant chance of a simultaneous malfunction of a number of machines caused by earthquakes and tsunami. If it happens, it would be extremely difficult to implement the three principles of a nuclear reactor shutdown; namely shutdown, cooldown and contain. Therefore, I would say this new regulatory standard is set rather to reopen the nuclear power plants which already exist, than to enforce the safety measures.”
At a review meeting of the Nuclear Regulatory Commission in August 2013, members discussed a case based on the assumption that “the coolant is lost due to major damage in the pipework,” “the emergency reactor core cooling system does not function because electricity both from the grid and from emergency generators is knocked out,” and “containment vessel spray does not work.” The director of the Genkai Nuclear Power Plant said, “In such a situation, we currently have no measure to prevent reactor core damage.”
As for the Sendai Nuclear Power Plant, because there are several caldera volcanoes nearby that have a history of large-scale eruptions, it runs a risk of being affected by volcano eruptions. The plant is located, according to the Nankai Trough earthquakes plan, in the area of “over intensity 5.” In addition, both Sendai and Takahama have adopted Pressurized Water Reactor (PWR) made by Mitsubishi. Fukushima used the Boiling Water Reactor (BWR), and nitrogen was filled up inside the containment vessel to prevent hydrogen explosion, which resulted in no explosion in the containment vessel. On the other hand, the PWR containment vessel is filled with air, not nitrogen. If hydrogen, generated by a serious accident, explodes inside a containment vessel, there is a possibility that the containment vessel is destroyed. “The ideal measure is to decommission the reactor. But the realistic measures we can take right away are: to fill the containment vessel with nitrogen, to install a core catcher to receive the melted reactor core, to conduct an assessment, not only by a power company alone but also a cross-check assessment by independent organizations,” adds Ino.
In the 2030s energy target ratio, set by METI, nuclear power represents 20 to 22 percent. “This figure is feasible only by restarting a number of old nuclear power plants,” says Ino. “I think for future energy policy we should establish such a system that citizens can reach a public consensus through discussions based on accurate information, including power companies’ opinions as well as critical opinions.
“In face of the government’s attitude that takes the operation resumptions for granted, if citizens give up, nobody can stop this trend. Citizens’ movements can influence the courts. As scientists, our role is to offer scientific information about what can happen and to validate irresponsible explanations given by government and power companies. It is up to citizens whether to take it seriously or not. The last resort to stop the real danger is, I believe, in the power of citizens.”
Courtesy of INSP News Service www.INSP.ngo / Big Issue Japan