2023-08-17 07:05:26
Twelve years after the triple disaster – earthquake, tsunami, nuclear accident – Japan will begin to discharge part of the treated water from the Fukushima Daiichi power plant into the sea from the end of August, unveiled the Japanese daily Asahi Shimbun on August 7without giving a specific date.
In the pipeline since 2018 but regularly stopped or postponed, the project led by the Tokyo electricity company, Tepco, had finally obtained authorization from the International Atomic Energy Agency (IAEA) at the beginning of July. After more than two years of investigation, five field missions and six technical reports, the organization had concluded that these discharges into the sea complied with the agency’s safety standards and that they would only have an impact “negligible on the population and the environment”, thus officially paving the way for the realization of the project. A green light, however, was greeted with skepticism by some members of the scientific community and with animosity by many local fishermen who fear that their products will be shunned by consumers.
Storage capacities soon to be saturated
On March 11, 2011, the cores of the three reactors of the Fukushima Daiichi power plant had gone into meltdown, leaving northeastern Japan devastated. Since then, astronomical quantities of water have had to be used to cool the damaged reactors daily, while hundreds of thousands of liters of rainwater or groundwater have accumulated around the plant. Radioactive water that the Japanese authorities had initially decided to store in huge tanks.
First problem: while 1,000 tanks have already been filled, i.e. 1.33 million tonnes of water, storage capacities are now reaching their limit and will reach saturation by 2024, warn the Japanese authorities. Second problem: in this area with high seismic risks, an earthquake could cause these tanks to leak.
See alsoIn Fukushima, the challenge of managing radioactive water
filtered water
To avoid any accident, the Japanese government has therefore decided to gradually discharge – over three decades – these millions of tons of water into the sea. The process is simple: a pipe is to carry water up to a kilometer off Fukushima Prefecturewhere it will be released.
The discharge of water from nuclear power plants into the natural environment is a widely used and generalized process all over the planet. Usually, this water circulates around the nuclear reactor, where it heats up. This is what makes it possible to trigger turbines and produce electricity. During the operation, the water becomes loaded with radioactive compounds. But it is then treated before being discharged into the sea or rivers.
“In Fukushima, however, we are in a very different situation since it is a damaged plant”, explains Jean-Christophe Gariel, Deputy Director General in charge of the environment and health at the Institute of Radiation Protection. and nuclear safety (IRSN). “Part of the stored water, this time, was poured directly onto the reactors, with the aim of cooling them. Unlike the water from our power stations, it was thus loaded with many radioactive compounds, radionuclides.”
Before discharging the water into the sea, the big challenge is therefore to get rid of these radioactive substances. To do this, the operator Tepco has set up a powerful filtration system called ALPS (Advanced Liquid Processing System). “This makes it possible to eliminate a large part of these radioactive compounds, which only remain in the state of traces.”
“On the other hand, as in our own power plants, there is one component left: tritium, which cannot be eliminated“, continues Jean-Christophe Gariel. This substance is systematically produced by nuclear reactors and rejected by power plants around the world. If it is considered relatively harmless, it is often blamed for increasing the risk of cancer. ” To further limit the risks, the water will then be diluted in a large quantity of seawater to lower this level of tritium as much as possible”, specifies the specialist.
When water was last drawn from one of the reservoirs in March, the Japan Atomic Energy Agency detected 40 radionuclides. After treatment, the concentration in the water was lower than the standards in force for 39 of them – all except tritium. The rate of the latter reached 140,000 becquerels per liter (Bq/l) – while the regulatory threshold for discharge into the sea is set in Japan at 60,000 Bq/l. After the last dilution step, the level had decreased to 1,500 Bq/l.
“In summary, if the water from the Fukushima reservoirs is more contaminated than that which comes out of our power stations, after treatment and dilution, it is the same as elsewhere”, concludes Jean-Christophe Gariel.
“It’s like diluting whiskey in Coke”
However, these standards and figures must be nuanced and taken with caution, as the thresholds set vary greatly from one country to another. For tritium for example, France sets its limit at 100 Bq/lthe WHO at 10,000 Bq/l.
Beyond this question of figures, faced with the dilution of tritium, some environmentalists point out that it’s like “diluting whiskey in coke” – just because there’s coke doesn’t mean there’s less alcohol. The quantity of tritium indeed remains the same, it is simply distributed in a greater quantity of water.
Within the scientific community, the validity of the project is thus widely debated. For several years, the Woods Hole Oceanographic Institution (WHOI), based in the United States, has regularly worried about the real impact on the environment. In December 2022, she again expressed her opposition to the projectdeploring this time that the concentration rates measured had not been measured in all the reservoirs of the plant.
In reverse, Jim Smith, professor of environmental sciences at the University of Portsmouth, in the United Kingdom, who has been studying the consequences of radioactive pollutants for several years, assured in an article published in January in The Conversation that this rejection in the sea was “the best option”. “On the scale of the environmental problems we face, the discharge of wastewater from Fukushima is relatively minor,” he says, highlighting the low levels of radioactivity after water treatment.
An eminently political subject
“Basically, this subject is eminently political. It is part of the Japanese government’s desire to make the Fukushima region an example of resilience after a nuclear accident”, analyzes Cécile Asanuma-Brice, researcher at the CNRS and co-director of the laboratory Mitate who studies the consequences of the Fukushima disaster. “It is in this perspective that the Japanese government’s reconstruction policy is in line, which includes, in fact, the dismantling of the plant and the reopening of the area to habitation. However, this dismantling can only be done by getting rid of these contaminated waters, according to the latest statements by the Minister of Economy and Industry, Yasutoshi Nishimura.
But to carry out this project, the government must also regularly face the reluctance of the population, in particular that of the fishermen’s unions. “For the latter, who represent an important part of the country’s economy, the question is not so much whether the concerns are justified or not”, continues the specialist. “After the accident, they spent years suffering from a negative image, both in the region and internationally. They had just started to recover and regain a dynamic economic activity. With this water discharge project, they fear seeing their image wither again and their products shunned by consumers.”
Over the years, several alternatives had been studied with varying degrees of attention by the authorities. “Among them, one seemed to have the preference of the local population: build new reservoirs or even install them underground and continue to store contaminated water until it loses radioactivity in the coming years”, says Cécile Asanuma-Brice. . An idea swept away by the government, because officially deemed too expensive.
In addition to this mistrust of the population, the Japanese government will also have to deal with the mistrust of other Pacific countries, particularly China. Following the green light from the IAEA in early July, Beijing has already announced the forthcoming ban on the import of food products from certain prefectures in Japan, including Fukushima, for “security reasons”.
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