The Challenge of Radioactive Waste March 18, 20:43
It has been 10 years since the accident at TEPCO's Fukushima Daiichi Nuclear Power Station.
On the premises of the nuclear power plant, steady decommissioning work is continuing.
The biggest difficulty is the removal of melted-down nuclear fuel, but in reality there is another difficult problem of how to dispose of "radioactive waste".
The country says it will complete decommissioning in up to 40 years.
However, depending on how the waste is disposed of, it is estimated that it will take 100 to 300 years to complete the decommissioning and reuse the site.
National discussion is required.
A reporter and director interview team closely adhered to the on-site work to find out what the problem of the large amount of radioactive waste that is blocking the road to decommissioning is.
(NHK Special "Road to Decommissioning" coverage group)
"In some cases 300 years" Large amount of radioactive waste
Radioactive waste generated by the decommissioning work of the Fukushima Daiichi nuclear power plant.
In the future, more will occur as the decommissioning work progresses.
Unlike other nuclear power plants, the Fukushima Daiichi nuclear power plant caused an accident, so a large amount of radioactive material diffused.
Not only the inside of the reactor building where the reactor is located, but also the buildings and roads on the site, as well as soil and trees, were contaminated with radioactive materials.
For this reason, if we proceed with the decommissioning of the Fukushima Daiichi nuclear power plant and try to return it to a vacant lot that is not affected by radiation, a large amount of radioactive waste will be generated.
In the first place, how much radioactive waste is there?
Some researchers have tried to estimate that amount.
This is Hideki Kawamura, who was studying the disposal of radioactive waste at a major construction company.
Mr. Kawamura estimated the amount generated based on the materials of the same type of nuclear power plant in the United States and summarized it in a treatise.
According to this, it was estimated that if no measures such as waste reduction were taken, the total amount would amount to about 7.8 million tons.
This is equivalent to about 600 nuclear power plants of the same type as the Fukushima Daiichi nuclear power plant, compared to the decommissioning of a relatively new nuclear power plant with a power generation output of 1.1 million kilowatts.
And the report compiled based on this treatise will be the focus of attention.
This is a report of the Atomic Energy Society of Japan made by experts such as nuclear power who have been discussing the problem of radioactive waste and the final form of decommissioning.
It was announced last July.
The Atomic Energy Society of Japan first presented some scenarios as drafts for the final form of decommissioning.
What kind of scenario did the experts think could be?
In the report, the facilities at the Fukushima Daiichi Nuclear Power Plant are roughly divided into two categories: "when all the facilities are removed and made into a vacant lot" and "when the underground structures are left and managed".
On top of that, he points out that the amount of waste generated will vary greatly depending on how the decommissioning is carried out and how the waste is disposed of, and the period until the site becomes available will also change significantly.
At this point, there is no technical prospect as to whether or not all the melted-down nuclear fuel, so-called fuel debris, can be removed by decommissioning work, but the scenario is based on the assumption that the removal could be completed. Was done.
In the scenario where the building is dismantled immediately after the debris is taken out and all the generated waste is removed, it is estimated that it will take about 100 years before the site can be reused, and the amount of radioactive waste that needs to be disposed of is about 100. It was estimated to be 7.6 million tons.
(Excluding waste generated at water treatment facilities)
On the other hand, if the above-ground part of the building is removed but the contaminated soil in the underground structure and its surroundings is left, the remaining underground structure and its surroundings should be filled with soil or mortar to restrict access and radiation. You will manage it while monitoring the amount.
In this case, the amount of waste can be reduced to about 4.4 million tons, but it will take about 300 years to manage until the radiation amount in the underground part is sufficiently reduced.
Furthermore, it is estimated that the amount of waste can be reduced to about 1.1 million tons if only the above-ground part is removed after a certain period of time has passed to reduce the radiation dose after removing the debris.
The Atomic Energy Society of Japan said that these scenarios are just examples, and that there may be other options, and that where and how to dispose of a large amount of radioactive waste should be considered not only by Fukushima but by the entire nation. is.
In any case, the scenario presented by the Atomic Energy Society of Japan raises the question of what to do with a large amount of radioactive waste before the site of the Fukushima Daiichi nuclear power plant can be used again, and it will take a lot of time and effort. I pointed it out with a certain scientific basis.
How does the country take these scenarios presented by the Atomic Energy Society of Japan?
According to the interview, the roadmap shown by the government and TEPCO is different from that of the academic society in the assumption of the decommissioning procedure, so it is not possible to make a general comparison, and the government responded as follows.
"There are many uncertainties, such as grasping the inside of the furnace and considering the treatment and disposal of waste, and we are not yet in a situation where we can show a concrete picture. It is necessary to deepen the examination in the future. The national government will take responsibility until the end to ensure that waste is properly disposed of. "
The government says that decommissioning will be completed in up to 40 years, but so far the final form of decommissioning, such as how much radioactive waste is generated, where to take it out, and how to dispose of it, has been concrete. Not shown.
Unknown radioactive waste analysis is underway
A large amount of radioactive waste generated at the Fukushima Daiichi nuclear power plant.
It is said that detailed analysis of radioactive substances contained in waste is indispensable for deciding the disposal policy.
Radioactive substances such as cesium, uranium, and plutonium have different periods of continuous radiation depending on the type.
In addition, radioactive substances have the characteristic that the amount of radiation emitted gradually decreases over time.
In a little more detail, the time it takes for the amount of radiation to be reduced to half of its original amount is called the "half-life."
The half-life of cesium-137 is about 30 years.
It will be half of the original radiation dose in 30 years.
Plutonium-239 has a half-life of 24,000 years.
It takes 24,000 years to reduce the radiation dose to half.
The half-life differs depending on the radioactive substance, and the type and intensity of radiation emitted also differ.
After understanding these characteristics, the thickness of the container that traps the waste should be designed, and the depth should be considered when burying it underground.
In other words, unless the radioactive substances contained in each waste are analyzed in detail, it is not possible to make an accurate plan such as what kind of storage is appropriate and how long it needs to be managed.
200 types of analysis every year from now on
The Japan Atomic Energy Agency has been focusing on this analysis.
Engineers have visited the Fukushima Daiichi Nuclear Power Plant since 2011, immediately after the accident, and have collected samples of various radioactive materials.
There are 400 types of samples analyzed so far, such as soil and trees on the site and concrete inside the reactor building.
However, even this is said to be insufficient for analysis.
Mr. Yoshikazu Koma, Director of the Japan Atomic Energy Agency, explained the difficulty of the work related to analysis.
Extremely complex waste generated from contaminated water treatment
One of the wastes that Koma's team is currently working on is the waste that comes out after treating contaminated water.
At the Fukushima Daiichi nuclear power plant, water is constantly being injected to cool the debris remaining in the reactor and containment vessel, and this becomes contaminated water.
Contaminated water removes a lot of radioactive substances such as cesium and strontium through a device that removes radioactive substances.
One of the core devices is the "multi-nuclide removal equipment" commonly known as ALPS.
It has the ability to remove 62 types of radioactive substances.
ALPS is equipped with a multi-layer filter to remove various radioactive substances.
When this filter is used up, it naturally becomes radioactive waste because it has radioactive substances attached to it.
Mr. Koma's team analyzes what kind of radioactive material is attached to the filter one by one.
The sample is dissolved in nitric acid, and each type of radioactive substance is taken out and measured.
It takes more than a week to analyze one sample.
This time, we were also able to cover the work of replacing this filter.
The filters used in ALPS are transferred to a special cylindrical container and stored securely.
Since there is a risk of radiation, the amount of radiation is measured when taking it out.
Then, the special container is further surrounded by a lead plate and transported to the storage location.
This is to shield the radiation.
A container that is stored in such a tightly controlled form.
The filters are already contained in 3702 containers (as of February 4th).
The number of containers will continue to increase as long as contaminated water is treated.
And you have to decide where and how to dispose of it in the future.
Analytical work, which is essential for proper disposal of radioactive waste, takes a lot of time and effort.
Mr. Koma says that there will be various difficulties in the analysis work in the future.
Yoshikazu Koma, Director of the Division, Japan Atomic Energy Agency
"Actually, the radioactive substances contained in the contaminated water at the time of the accident and the contaminated water 10 years later are quite different, which is a challenge for analysis. It is also necessary to obtain samples such as debris inside the storage container where the radiation is measured. This is not easy. Basically, radioactive waste is difficult to access because it emits radiation by itself. Yes, it makes the work difficult. "
The responsibility for "decommissioning" after an accident, which is not a problem only in Fukushima Prefecture, is
This time, the issue of a large amount of radioactive waste generated in the decommissioning that was revealed in the interview.
The local government requires that all radioactive waste be promptly removed and disposed of outside the prefecture.
For nearly half a century, the large amount of electricity generated by the Fukushima Daiichi nuclear power plant has been consumed in the Tokyo metropolitan area and has supported the Japanese economy.
What to do with the cleanup of the nuclear power plant.
It can be said that it is necessary to take it as a problem not only in Fukushima Prefecture but also in society as a whole and face it.
And it may have to continue across generations.
NHK will continue to collect data and convey the real image.
Tomomi Abe,
reporter of the Faculty of Science and Culture
Joined the
station in
2008.
After working at the Fukui and Sapporo stations, he has
been in his current position since 2015 and
is currently in charge of the nuclear field.
Reporter of the Ministry of Science and Culture
Taku Hasegawa
Joined the
station in
2014
Covered the recovery from the earthquake and nuclear accident at the Fukushima Broadcasting Station In
charge of the nuclear field at the Ministry of Science and Culture from 2019
Production Department the third production unit
chief producer
Masahiro Fujikawa
1992 He joined
the incumbent from 2010
related coverage continues in immediately after the Fukushima Daiichi nuclear power plant accident
Sendai Broadcasting Station Chief Director
Akio Suzuki
Joined in 2000
Covered the
incumbent
Fukushima Daiichi Nuclear Power Plant
from 2019