What is tritium? Why does tritium-containing water occur? November 18, 21:49
At the Fukushima Daiichi nuclear power plant, the water injected to cool down the melted nuclear fuel comes into contact with the nuclear fuel and becomes contaminated water containing radioactive materials.
We collect and remove radioactive materials with a device called “ALPS” (Alps), but some of the radioactive materials such as tritium that are difficult to remove remain, and a tank is built on the site of the nuclear power plant. The state of storage continues.
What is "tritium"
Tritium is a radioactive substance called "tritium" in Japanese and is a member of hydrogen.
It is also present in nature such as being contained in water vapor, rainwater, and seawater in the atmosphere.
The radiation that tritium emits is a kind of beta ray that has low energy and travels only about 5 mm in the air.
The amount of tritium decreases as it emits radiation and changes to helium.
It will be half of the original amount in over 12 years.
Since it is a friend of hydrogen, it is difficult to separate it from the water and remove it. Fukushima Daiichi nuclear power plant will remain after treating the contaminated water.
Tritium is also generated at nuclear power plants in operation, and is released into the environment below the standard.
At the nuclear power plant in Japan, it is released to the sea after confirming that it is below the standard value of 60,000 becquerel per liter.
Even overseas, standards are set and released in each country.
The NRA has expressed the view that scientifically, even in the case of the Fukushima Daiichi nuclear power plant, it is a reasonable disposal method to dilute below the standard and release it to the sea.
However, more than eight and a half years have passed since the accident, and while there are signs of recovery and the path to Fukushima's industries such as fishing, agriculture, and tourism, there are strong opinions against the reputational damage again. .
The country and electric power companies say that the radiation energy of tritium is weak, so there is almost no impact from external exposure.
In addition, if it is below the standard, internal exposure that occurs when taken into the body is said to be sufficiently small compared to radioactive cesium, and there have been no reports of health damage caused by tritium until now.
On the other hand, some experts point out that, depending on the concentration and amount, there are parts that have not been clarified as to how they will affect the substance when taken into the body.
Six proposals “How to treat tritium water”
There are currently six options for what to do with this tritium-mixed water.
▽ First, it is a plan to lower the concentration of tritium below the standard and release it to the ocean.
Internationally, tritium generated at nuclear facilities such as nuclear power plants is approved for ocean release and is being carried out in various countries. The cost is the cheapest, and it is said that the disposal will be completed in the shortest time.
▽ The second is to make the concentration below the standard, then evaporate it at a high temperature of about 1000 degrees and release it into the atmosphere from the exhaust stack.
This method was carried out at the Three Mile Island nuclear plant in the United States where meltdown occurred 40 years ago, but it is said that there are issues such as the incineration ash with radioactivity remaining.
▽ The third method is to make hydrogen by electrolysis and release it to the atmosphere below the standard.
This requires some technical development.
▽ The fourth is a plan to pour into the formation with a pipe that has been driven to a depth of about 2500 meters.
This is based on a method for storing carbon dioxide underground, which has been put to practical use overseas as a measure against global warming. Is an issue.
▽ Fifth is a method of mixing in cement and making it into a plate and filling it underground.
There is no track record, and the issue is that a vast area is required in the basement.
▽ And, sixthly, by adding more tanks etc. and storing it for a long time, there was also an option to wait for the tritium to decay and the amount to decrease, or to wait for technological development to remove tritium.
Each issue
Five of the options, including ocean release, are all put into the environment, and many oppositions were raised at public hearings held by the country in Fukushima Prefecture and Tokyo.
Even if the concentration is below the standard,
▽ A fatal blow to the fishery in Fukushima Prefecture
▽ We are worried about the reputational damage that the import restrictions of neighboring countries spread and may affect the tourism industry.
▽ Also, regarding the sixth plan to store tanks for a long time, TEPCO has a limit to the site inside the nuclear power plant, so residents will need to add tanks outside the site. It is said that the risk of transportation increases.
In addition, as the number of tanks increases, there is a risk that a large amount of leakage will occur due to the effects of tsunami and aging.
It seems that there is a need for more wisdom and more discussion than ever to determine whether there is a way to solve the problems faced by each option.