What is tritium? Why "release into the sea or the atmosphere"? Dec 23, 18:13
How do we dispose of water containing tritium and the like that continues to accumulate at the Fukushima Daiichi Nuclear Power Station?
The National Sub-Committee has drafted a proposal to dilute below the standards and proceed with a discussion centered on "release into the sea" or "release into the atmosphere."
Locals concerned about reputational damage are expected to have a strong rebound and attention will be paid to future discussions.
What kind of substance is "tritium" in the first place? And what do we mean by "release into the sea" and "release into the atmosphere"? I summarized it in detail.
What is "tritium" in the first place?
What kind of substance is tritium, a radioactive substance?
The nature and effects on the body are summarized in the draft of the national sub-committee as follows.
"Tritium" is a radioactive substance called "tritium" (sanju) in Japanese and is a kind of hydrogen.
Because it is also generated in the natural world by cosmic rays flying from space, it is contained in atmospheric water vapor, rainwater, seawater, and tap water, and a small amount of tritium is taken into our bodies. .
It also introduces the fact that tritium generated at nuclear power plants in Japan and overseas is diluted and released into the sea and air based on the standards of each country.
What is the effect on the human body?
Regarding the effect on the human body, the draft of the national subcommittee points to the magnitude of the concentration.
The radiation emitted by tritium is weak beta radiation, and the effects of internal exposure when taken into the body should be considered rather than external exposure.
Based on that risk, we collected reproducible data and research papers and summarized the results of the examination as a subcommittee, and argued that some tritium might bind to proteins and other organic substances in the body and concentrate. He concludes that the body has the ability to repair DNA, and animal and epidemiological studies did not confirm that tritium had a greater health effect than other radioactive materials.
Carcinogenicity experiments in mice are similar to the frequency of occurrence in the natural world, and no examples of effects that could be attributed to tritium have been found around nuclear power plants.
We asked Prof. Hiroshi Tauchi of Ibaraki University, who is a member of the subcommittee about the nature of radioactive materials, how he thinks about the risks of tritium.
According to Professor Tauchi, "There is certainly a mechanism by which tritium is taken into the body and damages DNA, but DNA has a function of repairing, and it is common to repair it even if it is broken by ultraviolet rays or stress. The effect on cells was observed, but the effect on cells could not be confirmed at a concentration lower than the standard. Therefore, in experiments, the concentration was intentionally higher than the standard. " Risk indicates a low radioactive material view.
From "five plans" to "two plans" this time
The national task force team, which has been discussing the disposal method of tritium-containing water after treating contaminated water from the Fukushima Daiichi Nuclear Power Plant from a scientific and technical viewpoint, presented five plans in 2016. .
▼ A plan to dilute below the standard and release it to the sea ▼ A plan to heat and evaporate and release it to the atmosphere ▼ A plan to electrolyze it to hydrogen and release it to the atmosphere ▼ A plan to inject it into a deep underground stratum ▼ It is a plan to mix it with cement and make it into a plate shape and bury it underground.
In this draft of the Sub-Committee, which took over the task force discussions,
It was suggested that discussions be made focusing on two proposals, one for release to the ocean and one for evaporation and release to the atmosphere.
The main reason is proven and realistic.
What is "marine release"?
Of these, the ocean release is to mix the seawater pumped up and dilute it below the standard and release it to the ocean. Nuclear power plants, including Japan, have set standards in each country and have released them to the sea, and have confirmed that monitoring is possible.
In addition, the task force is said to be able to be stably thinned and diffused by flowing into the sea. The cost is the lowest, and a large amount of treated water can be disposed of in the shortest time.
What is "Atmospheric Release"?
Also, another plan to release to the atmosphere is to evaporate at a high temperature of about 1000 degrees and release it from the exhaust stack to the atmosphere.
This method was also proven 40 years ago at a nuclear power plant on Three Mile Island in the United States that caused a meltdown.
In addition, the two proposals were evaluated by the government and TEPCO based on the model of the United Nations Scientific Committee, and were evaluated to be sufficiently small compared to the exposures of the general public in nature. That's why I was chosen.
The remaining three plans
On the other hand, the remaining three plans ▼ need to search for a suitable site for geological injection, and no monitoring method has been established. ▼ The plan to release hydrogen into the atmosphere requires further technological development. The possibility of hydrogen explosion remains, ▼ In addition, underground burial requires new regulations and secures a disposal site, etc. did.
In addition, regarding plans for long-term storage for tanks that were given out at public participation hearings and added to discussions on the way, there is limited room for additional tanks on the site of the nuclear power plant, A negative opinion was expressed that the leakage amount would be enormous if the capacity tank was damaged, ▼ In addition to transport problems to store outside the site, it would take time to understand and approve local governments etc. .
Experts "should face all concerns and concerns"
`` This issue is a concrete solution to the issue of ocean and atmospheric emissions among experts, as if it were a market view, '' said Associate Professor Kota Souraku of Tokyo Denki University, which is familiar with nuclear and social relations. It is an impression that the discussion has been made somewhat linear as a result of the common understanding. "
He added that experts from the subcommittee three years ago, such as psychology and sociology, and local stakeholders should have been involved earlier. More flexible, if we take early and serious feedback from experts, such as psychology and economics, who consider the reactions and effects that can actually occur in society, and the opinions of local parties at an early stage, Various ideas and solutions were on top of it, and we could have a rich discussion. "
As for the future, "Scientifically and technically, there is such a solution, so it is not easy to get local consent simply by asking them to be satisfied. The part that can be corrected will improve the sense of satisfaction by making repeated corrections, etc., '' the government and TEPCO will discuss in the future from a more flexible and complex viewpoint. Is required to do so.
"Tritium" Can't be separated from water?
Tritium and tritium are difficult to remove from water. We interviewed experts to see if there was any technology to separate them.
Dr. Toshihiko Yamanishi of the Research and Development Agency for Quantum Science and Technology, who is a leader in this field and also serves as a member of the subcommittee, says that although there is technology to separate it, it is difficult to completely separate it at present, Needs to be solved and is not realistic.
In addition to overseas, such as Korea and Canada, there have been cases where the new converter "Fugen" developed in Japan has already been put to practical use, but in all cases, the amount was small and the concentration was much higher than required in Fukushima.
For this reason, the Ministry of Economy, Trade and Industry recruited domestic and foreign businesses from 2014 to 2016 to conduct verification experiments.
Among them, a Russian company has constructed and verified a full-scale facility that combines technology that uses a slight difference in boiling point with technology that uses a chemical reaction.
The facilities are large, such as a distillation column with a height of about 43 meters and a device that removes tritium by a chemical reaction. Some of the data obtained from the tests are less concentrated than national standards.
However, it was concluded that the technology was not immediately applicable because the test period was short and data acquisition was not sufficient.
In addition, it is said that even with these latest technologies, complete separation cannot be achieved, and some tritium remains.
In addition, the separation causes the removed tritium to collect and become highly concentrated, creating new issues such as how to handle it.
Dr. Yamanishi said, "Practical application in Fukushima requires a device capable of processing more than three orders of magnitude more than that currently being developed, and practical application is far from being possible. We need to discuss the risks of managing the intensified ones. "
However, Dr. Yamanishi says that continuing research as one of the future technologies is necessary.
Kinki University is working on the development of technology to adsorb and remove tritium.
It is aiming to remove by passing steam containing tritium into a substance called `` porous body '' with multiple small holes, and at present it is a laboratory level, but it is possible to remove about half. Says.
The university wants to increase the rate of further removal in the future.
Professor Hiroki Yamanishi of Kinki University's Nuclear Research Institute said, "I don't think it would be possible to gain local understanding if tritium wastewater was simply diluted and released. We need a convincing form, and we are working on developing one of the options, "he said.
However, he said that in order to continue development, it would be necessary to increase the size of the equipment and verify its performance, etc., and said, "The challenge is how to procure expenses for facilities and experiments."