High levels of radioactive cesium remain in the soil near the Fukushima Daiichi nuclear power plant and these radionuclides have migrated at least 5 centimeters down into the ground at several areas since the nuclear accident five years ago, according to preliminary results of a massive sampling project being presented at the JpGU-AGU joint meeting in Chiba, Japan.
In 2016, a team of more than 170 researchers from the Japanese Geoscience Union and the Japan Society of Nuclear and Radiochemical Sciences conducted a large-scale soil sampling project to determine the contamination status and transition process of radioactive cesium five years after a major earthquake and tsunami caused a nuclear accident at the Fukushima Daiichi plant.
The team collected soil samples at 105 locations up to 40 kilometers (25 miles) northwest of the Fukushima Daiichi nuclear power plant in the “difficult-to-return” zone where entry is prohibited. The project seeks to understand the chemical and physical forms of radionuclides in the soil and their horizontal and vertical distribution.
The Japanese government has monitored the state of radioactive contamination in the area near the plant since the 2011 accident by measuring the air dose rate, but scientists can only determine the actual state of contamination in the soil and its chemical and physical forms by direct soil sampling, said Kazuyuki Kita, a professor at Ibaraki University in Japan, who is one of the leaders of the soil sampling effort.
Understanding the radionuclides’ chemical and physical forms helps scientists understand how long they could stay in the soil and the risk they pose to humans, plants and animals, Kita said. The new information could help in assessing the long-term risk of the radionuclides in the soil, and inform decontamination efforts in heavily contaminated areas, according to Kita, one of several researchers will present the team’s preliminary results at the JpGU-AGU joint meeting next week.
Preliminary results show high levels radioactive cesium are still present in the soil near the plant. The levels of radiation are more than 90 percent, on average, of what was found immediately following the accident, according to Kita.
Most of the radiocesium in the soil was found near the surface, down to about 2 centimeters, immediately following the 2011 accident. Five years later, at several sampling points, one-third to one-half of the radiocesium has migrated deeper into the soil, according to Kita. Preliminary results show the radiocesium moved about 0.3 centimeters per year, on average, deeper into the soil and soil samples show the radiocesium has penetrated at least 5 centimeters into the ground at several areas, according to Kita.
The team plans to analyze samples taken at greater depths to see if the radiocesium has migrated even further, he said.
“Most of the radioactive cesium remains after five years, but some parts of the radioactive cesium went from the surface to deeper soil,” he said.
Knowing how much radioactive contamination has stayed on the surface and how deep it has penetrated into the soil helps estimate the risk of the contaminants and determine how much soil should be removed for decontamination. The preliminary results suggest decontamination efforts should remove at least the top 6 to 8 centimeters of soil, Kita said.
The preliminary data also show there are insoluble particles with very high levels of radioactivity on the surface of the soil. Debris from the explosion fused with radiocesium to form small glass particles a few microns to 100 microns in diameter that remain on the ground, according to Kita. The team is currently trying to determine how many of these radiocesium glass particles exist in areas near the nuclear plant, he said.
“We are afraid that if such high radioactive balls remain on the surface, that could be a risk for the environment,” Kita said. “If the radioactivity goes deep into the soil, the risk for people in the area decreases but we are afraid the high radioactive balls remain on the surface.”
— Nanci Bompey is the manager of AGU’s public information office. This research is being presented Thursday, May 25 at the JpGU-AGU joint meeting in Chiba, Japan.
Japan’s Environment Ministry is studying the possibility of using some screened soil cleared from Fukushima Prefecture after the 2011 nuclear power plant accident in public works projects.
The Japanese government says, within the next 30 years, it plans to dispose of some 22 million cubic meters of soil and other waste that will be removed from the prefecture as part of the decontamination effort.
To make the job easier, the Ministry hopes to use soil with acceptable levels of radioactive material to build roads, embankments and parks.
The ministry began testing the feasibility of such projects last month at a temporary storage site in Minami Soma, Fukushima Prefecture. The process was shown to the media on Wednesday.
The experiment involves sifting the soil to remove rocks, leaves and branches, then entering it into a machine that measures the level of radioactive substances. The soil is then piled into mounds.
Ministry officials will monitor radiation levels in the air and groundwater around the mounds.
They plan to draw up guidelines for local governments and construction workers by April next year.
The ministry says it aims to use soil with up to 6,000 becquerels per kilogram of radioactive substances in roads and embankments, and up to 4,000 becquerels in parks.
But residents in Minami Soma have requested that for the experiment, the Ministry only use soil with up to 3,000 becquerels per kilogram.
As a result, the officials are unable to test whether soil with higher levels of contamination is safe for recycling.
The project also raises questions about the long-term monitoring of public works built with contaminated soil, and how the Ministry will win the support of people who live nearby.
Workers move big black plastic bags containing radiated soil. Fukushima prefecture, near Fukushima Daiichi nuclear power plant.
Soil from the Fukushima prefecture may be used as landfill for the creation of “green areas” in Japan, a government panel has proposed, facing potential public backlash over fears of exposure to residual radiation from the decontaminated earth.
The advisory panel of the Environment Ministry on Monday proposed reusing soil that was contaminated during the Fukushima nuclear meltdown of 2011 as part of future landfills designated for public use, Kyodo news reported.
In its proposal, the environmental panel avoided openly using the word “park” and instead said “green space,” apparently to avoid a premature public outcry, Mainichi Shimbun reported.
Following an inquiry from the news outlet, the Ministry of the Environment clarified that “parks are included in the green space.”
In addition to decontaminating and recycling the tainted earth for new parks, the ministry also stressed the need to create a new organization that will be tasked with gaining public trust about the prospects of such modes of recycling.
To calm immediate public concerns, the panel said the decontaminated soil will be used away from residential areas and will be covered with a separate level of vegetation to meet government guidelines approved last year.
In June last year, the Ministry of the Environment decided to reuse contaminated soil with radioactive cesium concentration between 5,000 to 8,000 becquerels per kilogram for public works such as nationwide roads and tidal banks.
Under these guidelines, which can now be extended to be used for the parks, the tainted soil shall be covered with clean earth, concrete or other materials.
Such a landfill, the government said at the time, will not cause harm to nearby residents as they will suffer exposure less than 0.01 mSv a year after the construction is completed.
The Fukushima Daiichi nuclear power plant suffered a blackout and subsequent failure of its cooling systems in March 2011, when it was hit by an earthquake and a killer tsunami that knocked out the facility, spewing radiation and forcing 160,000 people to flee their homes. Three of the plant’s six reactors were hit by meltdowns, making the Fukushima nuclear disaster the worst since the Chernobyl catastrophe in 1986.
Gov’t proposes reusing Fukushima’s decontaminated soil on green land
The Environment Ministry on Monday proposed reusing decontaminated soil from disaster-hit Fukushima Prefecture as landfill for parks and green areas.
At a meeting of an advisory panel, the ministry also called for launching a new organization to map out plans on how to gain public understanding about the reuse of decontaminated soil, ministry officials said.
The proposals come at a time when Fukushima Prefecture faces a shortage of soil due to the decontamination work following the 2011 nuclear meltdown.
The experiment is to be carried out at a temporary storage site in Minamisoma, Fukushima Prefecture, where around 1,000 bags of contaminated soil will be opened, made into construction foundations, and their radiation levels measured. The experiment will be done to check, among other things, whether the radiation exposure dose remains at the yearly limit of 1 millisievert or less. The experiment will cost around 500 million yen. The results are expected to be put together next fiscal year or later.
From soon after the Great East Japan Earthquake in 2011, municipalities including Minamisoma asked the national government to separate out lower-radiation level concrete and other debris for reuse in things like groundwork for coastal forests used to defend against tsunami. At first, the Ministry of the Environment was negative about this, but in December 2011 the ministry allowed such reuse for debris with a limit of 3,000 becquerels per kilogram. According to documents released in response to a release of information request made by the Mainichi Shimbun, some 350,000 metric tons of this kind of debris have been used in Minamisoma and the towns of Namie and Naraha in projects such as groundwork for coastal forests.
Then in June last year, the Ministry of the Environment decided on a policy of reusing contaminated soil with 8,000 becquerels or less per kilogram in structures such as soil foundations for public works projects.
The same month, Minamisoma’s Mayor Katsunobu Sakurai visited then vice-minister of the environment Soichiro Seki, where he questioned Seki about the 3,000 becquerel limit that had been used until being replaced by the 8,000 becquerel limit. Sakurai reportedly called for the 3,000 becquerel limit to be used in the upcoming experiment in Minamisoma.
Sakurai says, “If they don’t use the 3,000 becquerel limit it is inconsistent. It doesn’t make sense for a ministry that is supposed to protect the environment to relax the standards it has set.”
The ministry confirmed to the Mainichi Shimbun that the experiment will only use soil up to the 3,000 becquerel limit, and said that the soil used will on average contain about 2,000 becquerels per kilogram.
Bags containing contaminated soil and other materials produced through decontamination work are seen at a provisional storage site in Tomioka, Fukushima Prefecture.
The Nuclear Regulation Authority (NRA) has raised questions about the Environment Ministry’s proposal to reuse radioactive soil resulting from decontamination work around the crippled Fukushima No. 1 Nuclear Power Plant due to the insufficiency of information on how such material would be managed, it has been learned.
As the ministry has not provided a sufficient amount of information, the nuclear watchdog has not allowed the ministry to seek advice from its Radiation Council — a necessary step in determining standards for radiation exposure associated with the reuse of contaminated materials.
The Ministry of the Environment discussed the reuse of contaminated soil in closed-door meetings with radiation experts between January and May last year. The standard for the reuse of such materials as metal produced in the process of decommissioning nuclear reactors is set at 100 becquerels of radioactive cesium per kilogram. Materials with a contamination level topping 8,000 becquerels are handled as “designated waste” requiring special treatment. In examining the reuse of contaminated soil, the ministry in June decided on a policy of reusing soil containing up to 8,000 becquerels of radioactive cesium per kilogram as a base for roads with concrete coverings.
According to sources close to the matter, the ministry sounded the NRA out on consulting with the Radiation Council over the upper limit of 8,000 becquerels and other issues. An official from the NRA requested the ministry to provide a detailed explanation on how such soil would be handled, including the prospect of when the ministry would end its management of the reused soil, and how it would prevent illegal dumping. The official then told the ministry that the rule of 100-becquerel-per-kilogram rule would need to be guaranteed if contaminated soil were reused without ministry oversight.
The official is also said to have expressed concerns over the ministry plan, questioning the possibility of contaminated soil being used in somebody’s yard in a regular neighborhood. Since the ministry failed to respond with a detailed explanation, the NRA did not allow the ministry to consult with the Radiation Council.
Government bodies are required to consult with the council under law when establishing standards for prevention of radiation hazards. It was the Radiation Council that set up the 8,000-becquerel rule for designated waste.
An official from the NRA’s Radiation Protection and Safeguards Division told the Mainichi Shimbun, “We told the ministry that unless it provides a detailed explanation on how contaminated soil would be used and on how it will manage such material, we cannot judge if its plan would be safe.”