Why does Japan have an excess of contaminated water from the Fukushima nuclear reactors?
During the meltdown of the Fukushima Dai-ichi Nuclear plants in 2011 after an earthquake and tsunami, the reactors were flooded with sea water in order to cool the melted cores and slow the meltdown. Even today, the melted fuel elements are still thermally hot and radioactive. So, water is still pumped and flows through the melted reactor core and is then recovered before it finds its way to the sea.
What are the contaminants?
The main contaminants are isotopes of strontium, cesium, iodine, and some technetium and selenium, and tritium. Different treatment systems were developed for decontamination, and the systems were efficient as measured by decontamination factors. The decontamination factors are on a scale of 100 – 1000, which is high. In one case, they evidently reached 10,000 which is very good. There can be problems, even a very high decontamination factor, by definition, still leaves some of the contaminant in the water. The way that this is normally handled is to recycle the water through the treatment plant but that wasn’t always done. The other difficulty that the Japanese face is that certainly in the beginning, the decontamination process depended on exchange columns – that is materials that would pull these elements out of the solution. But these exchange columns have a lifetime. There is a point where they will reach a limit of how much of a particular radionuclide can be removed and, much like the air and oil filters in your car, they have to be replaced. If they are not replaced often enough, then the contaminants will remain in the water.
Is the current Japanese removal process thorough enough to remove radioactive particles?
The recent realization is that there is more radioactivity in some of the water than expected, namely that there are radionuclides besides the tritium in the water. This reflects a failure in the processing of some of the water.
Is the remaining tritium harmful?
That’s the controversy. Tritium has two things going for it that make it less harmful than other kinds of radioactivity. First, it decays by a “soft” beta emission, that is a very low energy beta decay. Hence, the energy is so low that it’s not very penetrating. It would travel only a few millimeters in air or even much shorter distances in water; hence it will not penetrate the skin from external sources. However, ingestion or inhalation of tritium in food or water is a radiation hazard. Extreme dilution, say in the ocean, reduces the hazard. The second aspect of tritium that is very important is that the half-life is a little over twelve years. Compared to other radioactive nuclides, it decays rapidly so that the total radioactivity is constantly decreasing. As a rule of thumb, over 99% of the tritium will have decayed away in 125 years.
Tritium is naturally formed in the environment and has no proven adverse health effects to humans. Is the worry about the Fukushima water then coming from a misunderstanding of tritium or a lack of understanding?
It would be too simple to say that public does not understand the risk of releasing tritium to the environment. There are two issues: on the one hand, there is the physics side, and on the other hand, the social side. From the physics perspective, tritium has a short half-life and the beta-particle is not very penetrating. When released into the ocean, where dilution will be great, a physicist might argue that it is not a serious source of radiation exposure. However, on the social side, the released tritium is a serious concern because consumers will not buy fish from a tritium-contaminated area. The economic and social aspects of releasing the tritium to the environment have to be considered. Having an expert or an expert panel say that releasing tritium is safe, whether true or not, we must still consider the consequences on the social system.
An advisory panel to the Japanese government has recommended that the contaminated water be released into the ocean. While the expert panel has stated that this plan is the most feasible option, other nuclear policy experts disagree, calling it “industrial vandalism.” Coastal nuclear plants commonly dump water that contains tritium into the ocean. Why is there opposition to the Japanese plan?
The scale of the release of tritium contaminated water is a legitimate concern, as well as the issue of what other radionuclides remain in the water. The filtering systems did not always remove all of the other types of radioactivity. The difficulty is that we can talk about tritium and its dilution in water, which may be a good idea; but if the public discovers there are other radionuclides in the water, a lack of trust makes moving forward even more difficult.
An alternative to disposing the contaminated water into the ocean is releasing it into the atmosphere or burying it under ground in either liquid or solid form. Given these alternatives, in your opinion, why has the advisory panel recommended that the water be released into the ocean?
The ocean, because of the dilution factor, is an attractive place to put the tritium. One thing that I haven’t seen discussed is that evaporation of tritium as water vapor would leave most of the other radionuclides, if present, behind. That could be an attractive aspect of evaporation and release to the atmosphere of tritium – without the release of other radioactive contaminants.
I would be really curious to understand how the local Japanese people have been involved in the decision making. One lesson that I have learned in the radioactive waste disposal field is that public engagement is critical. By public engagement, we don’t mean education in the sense that if the public only understood, they would agree. Rather I mean public engagement that allows the public to shape the policy. Every country has its own culture, but looking around the world at successful nuclear operations, the most successful plans are those where the public has important input into the decision.
This is obviously a very time-sensitive topic; water storage will run out in 2022. What do you think is the most feasible option going forward?
The answer to this question hinges on a better understanding of exactly which radionuclides in addition to tritium are the contaminants in the water. Does the water need to be processed again? Are there samples of each container so the public knows exactly the types of radionuclides that will be released? There’s no clear answer to your question because it really depends on a precise knowledge of what is in the water.
Fukushima_1_Nuclear_Power_Plant_07.jpg: kawamoto takuoderivative work: PM3 / CC BY (https://creativecommons.org/licenses/by/2.0)