Fukushima Residents Return Despite Radiation

Evacuees now fear Abe’s determination to put the Daiichi accident behind the nation is jeopardizing public health, especially among children, who are more susceptible. Lifting most evacuations has also ended subsidies for evacuees, forcing many to return despite lingering questions.
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Hiroshi Ueki moved far from the damaged Fukushima power plant and vowed to never return. He now grows grapes in a different region of Japan.
 
Japanese government presses resettlement of Fukushima evacuees back into areas still too radioactive with largest health risks falling on infants, young children and pregnant women.
 
When the Fukushima Daiichi Nuclear Power Plant began spewing radioactive particles after it was clobbered by a tsunami in March 2011Kaori Sakuma fled. She bundled her infant and toddler into a car and left her husband and family in Koriyama, 44 miles west of the ruptured facility. “The truth is, I ran away,” she says. Confronting gas shortages and snarled roads, she transported her children 560 miles away to Hokkaido, about as far as she could get.
 
Radiation from the fuming plant spread over tile-roofed towns and rice paddies across an area the size of Connecticut. The meltdown 150 miles north of Tokyo drove more than 200,000 people out of the region. Most believed they were fleeing for their lives. Now, almost eight years after the accident, the government has lifted most evacuation orders. Nearly 122,000 people have been allowed to return to communities where weeds have overtaken parking lots. Most are elderly, relieved to be resuming their lives. Prime Minister Shinzo Abe is determined to end all evacuations by 2020, when Japan will host the Olympic Summer Games. The events will include baseball and softball competitions in Fukushima City, a mere 55 miles from the ruined reactors.
 
Around 35,000 other citizens still wait to return, but they and many others throughout northeastern Japan worry all of this is too soon. Radiation, which is generally linked to cancer, in some places continues to measure at least 5 millisieverts (mSv) a year beyond natural background radiation, five times the added level Japan had recommended for the general public prior to the incident. In certain spots radioactivity is as high as 20 mSv, the maximum exposure recommended by international safety experts for nuclear power workers.
 
In its haste to address the emergency, two months after the accident the Japanese government raised the allowable exposure from 1 mSv annually, an international benchmark, to 20 mSv. Evacuees now fear Abe’s determination to put the Daiichi accident behind the nation is jeopardizing public health, especially among children, who are more susceptible. Lifting most evacuations has also ended subsidies for evacuees, forcing many to return despite lingering questions.
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Kaori Sakuma, from Koriyama, evacuated her two young sons more than 500 miles from the Fukushima accident. She reluctantly brought them back after the government raised the allowable radiation limits for communities, but she does not trust the government’s radiation readings.
 
As more people inside and outside the country absorb the radiation data, Japanese officials are confronting a collapse of public confidence. Before the accident residents in Japan (and the U.S.) were living with background radiation that averaged 3.1 mSv a year,most of it emanating naturally from the ground and space. In Japan and the U.S. many residents experience an additional 3.1 mSv annually, due mostly to medical testing. But the anxiety of Fukushima residents facing even higher levels is palpable. If the government is going to fully restore lives and livelihoods, it needs to regain their trust, says nuclear engineer Tatsujiro Suzuki, a professor at Nagasaki University and former vice chairman of the Japan Atomic Energy Commission. That, he says, should include respecting international safety standards for radiation and lowering the allowable level at least to 5 mSv, although he acknowledges “even 5 mSv is too high for children.”
Running Away from Radioactivity
 
The tsunami that followed the magnitude 9.0 offshore Tohoku earthquake slammed a 40-foot wall of seawater onto Japan’s northeastern coast. The whole event killed more than 15,000 people. The water surge at Tokyo Electric Power Company’s Daiichi plant led to meltdowns at three reactors.
 
Government officials ordered evacuations in areas called “difficult to return” zones, where radiation was above 50 mSv, enough to cause skin cancer. They quickly added areas between 20 and 50 mSv, then those below 20 mSv. Evacuations continued for months as Japan struggled to find housing for a large population exposed to radioactive iodine 131, cesium 134 and cesium 137. In May 2012 officials reported relocating 164,865 people. Another 26,600 people living outside the evacuation zones left voluntarily, according to Citizens’ Nuclear Information Center, a Tokyo-based organization opposed to the nuclear industry.
 
The evacuations did not go well. Evacuees, many elderly and frail, were moved repeatedly without any plans in place, says Jan Beyea, a physicist with Consulting in the Public Interest who worked on a 2014 U.S. National Academies of Sciences, Engineering and Medicine report about the accident. Disrupted medical care and the trauma of moving were fatal to nearly 2,000 people, according to the World Nuclear Association. Many of those who survived reportedly suffer from alcoholism and clinical depression.
 
As radiation levels declined, the government began allowing evacuees home—one town at a time. By May 2013, coastal communities such as Minamisoma, 25 miles north of Daiichi, were reopening ramen shops, and trains resumed their scheduled runs despite a dearth of customers.
 
Shuzo Sasaki, 56, was one of the first evacuees to return to neighboring Odaka, a quiet seaside village. The long-time employee of Fukushima Prefecture (prefectures are equivalent to states) directs Real Fukushima, a government-sponsored organization providing tours as communities rebuild. In Odaka, where radiation plumes streamed overhead but dropped relatively few radioactive atoms on the ground, levels have stabilized at 1.26 mSv per year, well within the safe range. Today a few rice paddies are productive, with round bales of rice straw drying in the sun. Most, however, are vacant. The market for Fukushima rice is poor, even from farms where contaminated soil has been removed. Some paddies sport solar panels. Many are no longer farmed, instead covered with some of the 16 million bags of contaminated soil removed from other sites.
 
Less than a quarter of Odaka’s 12,800 residentshave returned. Most are over 60, says Sasaki, who wears a starched white shirt and dark blue suit. Some people have found new lives elsewhere; many are afraid to return. “Young people with families—they don’t believe the government radiation measurements,” he says.
 
Concern about children is one of the most controversial issues. When officials raised the allowable level of radiation to 20 mSv, including in schools, it was under the guise of giving people a measure of normalcy. But the May 2011decision became a flash point for opponents of the government’s handling of the accident. They were furious children would be subjected to the maximum radiation allowed for nuclear workers, spending day after day in buildings that increased their cancer risk to one in 200 people.
 
Sakuma was one of those who returned to Koriyama, from her outpost in Hokkaido. She did not want her young children to touch contaminated soil or water along their walk to school, so she carried them both on her small back. “We all want our kids to play in the dirt and pick flowers but I was afraid. We all were,” says Sakuma, now 46.
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Bags of radioactive soil, scraped from certain rice farms, are stored on other farmland.
 
Lack of Public Trust
 
In the year after the accident Koriyama was one of 12 communities where the ongoing radiation rate measured between 3 and 5 mSv above background, but the town had not been evacuated. Today’s levels have stabilized at 1.5 mSv, but doubts remain. Skeptical of the government’s readings, Shigeru Otake, 49, takes his own. A slim man who wears a Dollar Store rope belt to give him “strength like a samurai,” he says he has measured radiation spikes at 15 mSv in Koriyama, where his family has lived for generations. Sakuma walks her sons, now eight and 10 years old, to school past a government monitoring post that she claims reads six times lower than her own dosimeter does.
 
Misgivings about government assurances of safety drove Hiroshi Ueki, 48, to move his family to Nagano Prefecture, where he is now growing “the best grapes in the world.” His parents stayed behind in Fukushima Prefecture. Ueki says he will never move back. “The prime minister says the accident is over but I won’t ever feel safe until the Daiichi plant itself is finally shut down. That will take 100 years.”
 
In spite of these concerns, Japan has continued to showcase repatriation as a barometer of progress toward recovery. By April 2017, the government had lifted all evacuations except for the most contaminated places closest to Daiichi. That decision also ended rent-free housing provided to people who were forced to leave as well as to some 26,600 people like Ueki who vacated voluntarily. Left without the $1,000 monthly subsidy provided by Tokyo Electric Company, some people have been forced to return home despite their safety concerns.* They have no other economic options, says Hajime Matsukubo, general manager of the Citizens’ Nuclear Information Center. Some 16,000 people who refuse to return have been financially abandoned, according to the center.
 
It is unclear if such fear is justified. The danger to people chronically exposed to low levels of radiation is the subject of ongoing scientific debate. “It’s not a bright line where we can say this dose rate is going to kill you,” says Kathryn Higley, a nuclear science professor at Oregon State University.
 
Scientists generally agree on a few basics: The risks of getting leukemia or other cancers are higher for children than adults, and the risks for everyone increase significantly with exposure above 100 mSv annually. Various national agencies have set 20 mSv per year as a maximum for occupational exposure. Public exposure should be no more than 1 mSv per year above background levels, according to the International Commission for Radiological Protection. That raises questions about Japan’s 2011 emergency declaration of 20 mSv per year as the allowable exposure. Five years after the 1986 explosions at Chernobyl, Ukrainian officials lowered the allowable level to 5 mSv per year. Japanese officials note there have been no reported deaths from radiation exposure.
 
The public perception is that the Daiichi nuclear accident continues to pose health risks and, significantly, nuclear power is not safe. More than 80 percent of the Japanese public wants to phase it out, according to an October 2018 study by Suzuki, the former Japan Atomic Energy commissioner. He calls the erosion of public trust “the most unfortunate impact of the accident.”
 
Sakuma, the Koriyama mother, is using the Daiichi accident as a lesson in radical civic involvement. She intends to keep her sons in Koriyama despite radiation concerns. “I want them to grow up here so they can learn what the government does. I want them to tell other people about how it is to live with radiation,” she says. “This accident is not over.”
 
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TEPCO’s refusal to settle money talks prompts center to bow out

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Masakazu Suzuki, 68, head of the group of plaintiffs that filed a damage compensation lawsuit with the Fukushima District Court against Tokyo Electric Power Co. in November 2018, stands in a garden of his home in Namie, Fukushima Prefecture, on Dec. 17.
January 15, 2019
A government body set up to mediate in compensation disputes with Tokyo Electric Power Co. over the 2011 nuclear disaster is throwing in the towel because of the plant operator’s repeated refusal to play ball with aggrieved residents.
Officials of the Nuclear Damage Compensation Dispute Resolution Center complained that TEPCO, operator of the stricken Fukushima No. 1 nuclear power plant, keeps rejecting settlement proposals offered in an alternative dispute resolution process.
The center discontinued trying to offer assistance in 19 cases in 2018 and another one on Jan. 10, affecting 17,000 residents in total.
If the center discontinues its mediation work, residents will have no recourse but to file lawsuits, which take time and money to resolve.
The center was set up in September 2011 to quickly settle disputes between TEPCO and residents who are unhappy with the amounts of compensation offered by the company based on the government’s guidelines.
When residents applied to the center for higher levels of compensation, lawyers working as mediators listened to what they and TEPCO had to say to draw up settlement proposals.
Residents and TEPCO are not legally obliged to accept the proposals.
As a result, some residents resorted to filing lawsuits because they got no joy from TEPCO.
Between 2013 and 2017, the center discontinued mediation work on 72 cases, all of which concerned TEPCO employees or their family members.
The 19 cases that were discontinued last year and the one last week had been mainly brought by groups, each of which consisted of more than 100 residents.
The largest group comprised 16,000 or so residents of Namie, Fukushima Prefecture.
Immediately after the triple meltdown at the Fukushima plant in 2011, all of the town’s residents were ordered to evacuate to other municipalities.
In March 2014, the center offered to add 50,000 yen ($460) to compensation amounts ranging from 100,000 yen to 120,000 yen a month that were offered to each of the 16,000 residents by TEPCO under the government’s guidelines.
It also offered an additional 30,000 yen if any residents were aged 75 or older.
However, TEPCO rejected the proposal, prompting the center to abandon its mediation efforts in the case last April.
Some of the residents filed a lawsuit with the Fukushima District Court in November.
With regard to cases involving groups of residents, the center continued to urge TEPCO to accept its settlement proposals for several years.
As the company kept turning a blind eye to the requests, the center began to discontinue its mediation efforts in those cases from last year.
In its management reconstruction plan, TEPCO says that it will respect settlement proposals made by the center.
However, Masafumi Yokemoto, a professor of environmental policies at Osaka City University, believes it is doubtful that TEPCO will make good on that pledge.
“If TEPCO agrees to offer compensation amounts that exceed the government’s guidelines, people in other areas could also seek increased compensation amounts,” he said.
A TEPCO representative, meantime, said that as settlements (with residents) are closed and individual procedures, “we will refrain from expressing our opinions.”

Schoolchildren co-opted to promote propaganda on Fukushima food safety

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Students tasked with developing dishes using Fukushima produce to promote prefecture’s recovery
Students sample local farm products with the aim of creating their own dishes as part of a campaign to highlight recovery efforts in the prefecture of Fukushima and its capital, on Dec. 16.
January 13, 2019
A group of elementary, junior high and high school students in the city of Fukushima are taking part in an initiative to develop original recipes using local agricultural products as part of a broader project to highlight the city’s recovery from the 2011 Great East Japan Earthquake.
The first phase of the campaign, known as the Fukko Project, whereby the students create new dishes, started Dec. 16. It is designed to help the children learn about local agriculture so they will be able to implement their own action plans to assist Fukushima’s recovery.
“I am convinced that the experiences of thinking about and taking actions to better their hometown will serve as a driving force for these children in the future,” said Kimio Suzuki, the director of the municipal Mikawadai Learning Center, the organizer of the campaign.
The dishes they create will be served at several locations, including the cafeteria in Fukushima City Hall.
Eighteen students ranging from fifth grade in elementary school to second grade in high school from five schools are participating in the initiative. Those schools are Sakura no Seibo High School, Sakura no Seibo Junior High School, Gakuyo Junior High School, Mikawadai Elementary School and an elementary school affiliated with Fukushima University.
In February, a group of judges, including Minoru Honma, the head of the city board of education, will select two dishes that will be served by the students who have been divided into two groups.
In addition to city hall, the Kiichigo restaurant located in the Corasse Fukushima complex will also serve the dishes. The building has a store that features regional products. The hope is the children’s efforts will increase the chances that visitors will want to try dishes made from local produce.
On the initiative’s first day, a city official explained to the students about the harmful rumors related to the Fukushima No. 1 nuclear power plant meltdowns and about regional specialities such as peaches, freeze-dried tofu and gyōza (dumplings). The students, some of whom were just 3 or 4 years old when the 2011 earthquake happened, sampled some of the products before setting off to plan their own dishes.
“I now understand the thoroughness of the (city and prefecture’s) decontamination and inspection processes,” said Ikumi Nakatsuka, 12, a sixth-grader at Mikawadai Elementary School. “I am amazed by the different efforts done up until this point.”
Mariko Chiba, 16, a Sakura no Seibo High School student, said she is enthusiastic about the project.
“I want to guide elementary and middle school students in this project and complete a menu featuring what the city has to offer,” she said.
After the food project is complete, the learning center is hoping to start another similar project wherein students would devise a plan to attract tourists to local festivals and hot spring areas.

Radiation doses underestimated in study of city in Fukushima

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Workers decontaminate land in Date, Fukushima Prefecture, in 2013.
 
January 9, 2019
A nuclear physicist who has drawn attention for tweeting about fallout from the Fukushima nuclear disaster has admitted that he and a colleague underestimated radiation doses in an article for an international scientific journal.
Ryugo Hayano, professor emeritus at the University of Tokyo, said the error, which he recognized on Jan. 8, was “unintentional.”
The article, carried in the Journal of Radiological Protection’s online edition in July 2017, listed average radiation doses that were one-third of the actual levels for people in Date, a city around 60 kilometers northwest of the crippled Fukushima No. 1 nuclear plant, he said.
Hayano’s admission came after an atomic nucleus expert contacted the journal last year to point out unnatural data carried in the report and call for a correction.
The radiation doses in the article were based on figures kept by Date residents after the nuclear accident unfolded in March 2011.
“Even if residents lived in the most contaminated area of Date for 70 years, the median of the doses would not exceed 18 millisieverts,” the article concluded.
However, Shinichi Kurokawa, professor emeritus with the High Energy Accelerator Research Organization, an institute jointly used by national universities, raised doubts about the data presented in some sections of the report.
When Hayano and his colleague re-examined the figures, they found that they mistook a monthly dose recorded on a dosimeter as the figure for three months of exposure.
Hayano said the conclusion of the report still stands.
“Even after the error was fixed, I believe the average of annual doses will be within the 1-millisievert mark,” he said.
The benchmark upper limit for radiation exposure among ordinary people is 1 millisievert a year.
Hayano has frequently tweeted about radiation levels and doses from the nuclear disaster.
He was also involved in another research paper that analyzed radiation doses among people in Date. Kurokawa also questioned the veracity of a chart in the second report.
The second report has often been cited in discussions by the government’s Radiation Council on setting standards for protecting people from radiation.
The two research papers were produced after the Date city government provided Hayano’s research team with data on radiation doses of about 59,000 residents.
But it has emerged that data for 27,000 citizens were provided without their consent.
The city plans to set up an investigation panel to find out why it occurred.
Date has a population of 61,000.

Police officer stays on duty in empty town near Fukushima plant

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Satoru Saeki, a resident police officer at the Okuma police substation, goes on patrol in the difficult-to-return zone in Okuma, Fukushima Prefecture.
 
 
 
January 1, 2019
OKUMA, Fukushima Prefecture–On his rather lonely rounds, Satoru Saeki looks for anything out of place in an empty town center marred by broken windows, uncollected litter and overgrown weeds.
A calendar dated March 2011 is still pinned on a wall of a dilapidated shop.
Saeki, 39, is the only police officer in Okuma, a town that remains largely deserted since an evacuation order was issued following the disaster at the Fukushima No. 1 nuclear power plant in March 2011.
On his daily patrols alone in Okuma, which co-hosts the stricken nuclear plant, Saeki is mainly on the lookout for looters.
Saeki works out of the Futaba Police Station in the neighboring town of Tomioka.
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Officer Satoru Saeki talks to a resident who has temporarily returned home in Okuma, Fukushima Prefecture.
 
 
On Dec. 4, Saeki, whose hobby is working out, eased his well-built physique into a minicar, his police cruiser. He soon arrived in front of the gate to the “difficult-to-return zone,” one of the areas most heavily polluted by radiation that is still essentially off-limits even to residents.
Saeki showed his ID to a security guard before going through the gate. Driving at a speed under 30 kph, the officer looked right and left for unfamiliar cars or any changes to the uninhabited houses.
He arrived at the Okuma town center in about 15 minutes and walked around a shopping district.
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Satoru Saeki patrols an empty shopping district in Okuma, Fukushima Prefecture
Okuma had a population of about 11,000 before the nuclear disaster. Now, it resembles a ghost town.
Construction trucks can be seen going in and out of the town for work to tear down the houses of residents who have decided not to return to Okuma.
Saeki walked some more and found a car parked in front of a house.
“Hello. Has anything changed here?” the smiling officer said to a man in a garden at the home.
“I came back to pick up some things I need because this house is set for demolition,” Hikaru Murai, 69, said.
Murai said he temporarily returned from Aizu-Wakamatsu, also in Fukushima Prefecture, where he has lived since evacuating Okuma, to tidy up his house.
It was only the third time for the two to meet, but they seemed to know each other quite well.
The officer asked Murai what time he started tidying up.
“I got here early because the expressway was so smooth,” Murai replied.
Before the disaster struck, two police officers were assigned to the substation in the Okuma town center. But since it was located in the difficult-to-return zone, the posts were left vacant for a while.
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Officer Satoru Saeki stops by at the unused Okuma police substation in the difficult-to-return zone.
However, evacuees have started staying overnight in their Okuma homes in some areas since spring to prepare for their permanent return. To enforce law and order in the town, Saeki becoming the resident police officer in March this year.
Saeki commutes to the Futaba Police Station from Iwaki, also in the prefecture, where he lives with his family.
A string of break-ins and other crimes have been reported in Okuma.
In 2011, the number of criminal cases in areas under the Futaba Police Station’s jurisdiction was 1,015, more than twice the figure before the nuclear disaster. The number has since been decreasing and stood at 194 in 2017.
“A single case is enough to make residents concerned,” Saeki said.
The officer is adamant about closely liaising with town officials and private security guards, and sharing information no matter how trivial it might seem.
Saeki was born and raised on Shodoshima, an island with a population of about 28,000, in Kagawa Prefecture.
After graduating from college in Kanagawa Prefecture, Saeki became a vocational training school instructor and was assigned to an institution in Iwaki. He married a woman he met in the city and became a member of the Fukushima prefectural police in 2009.
Saeki was on duty when the Great East Japan Earthquake struck and spawned the tsunami that inundated the No. 1 nuclear plant.
He was involved in the search for bodies along the coast.
“It was really hard,” Saeki said. “I made up my mind to support people who made it through even if it means just a little.”
As Saeki continued his patrol in the difficult-to-return zone on Dec. 4, he found many “yuzu” citrus fruit growing on a tree in the garden of a house.
“Oh, it tastes great when you squeeze the juice and pour it into a glass of cocktail,” Saeki said to a resident in the garden.
Citrus fruits are widely cultivated on Shodoshima island.
“Okuma and Shodoshima are similar in the sense that both are rich in nature with the ocean and mountains,” Saeki said.
He said his daily patrols in the town show that recovery will be difficult. But he shared one hope-inspiring event that occurred in early September when the trees started taking on fall colors.
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Satoru Saeki, a resident police officer stationed at the Okuma substation
While on patrol in the Ogawara district, where evacuees have started staying overnight at their homes to prepare for their permanent return, a voice called out to Saeki: “Officer, over here.”
When Saeki looked over, he found about 80 evacuees who had returned to the town to enjoy a barbecue party.
“Let’s take a picture together,” one of them said.
With a slightly shy smile, Saeki joined the group for the photo shoots.

2020 Olympic torches to be made of recycled aluminum from Fukushima temporary housing

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This file photo shows the Tokyo Summer Olympics torch relay held in September 1964.
 
Olympics: 2020 torches to be made of recycled aluminum from Fukushima
Jan 1, 2019
TOKYO (Kyodo) — Recycled aluminum from temporary housing in Fukushima Prefecture, which was devastated by the 2011 earthquake, tsunami and nuclear disaster, is planned to be used in the crafting of Tokyo 2020 Olympic torches, sources close to the matter revealed Monday.
The plan is likely to attract interest in Japan and abroad as being another symbolic effort to uphold one of the main themes of the July 24-Aug. 9 Summer Games as a “reconstruction Olympics.”
More than 10,000 pieces of aluminum are expected to be needed for the torches, used by runners in the nationwide relay beginning after the Olympic flame arrives in Japan from Greece on March 20, 2020.
According to sources, organizers will need to coordinate with local governments in the future in order to determine which metals can be procured from temporary housing that is no longer in use.
Tokyo 2020 organizers are also collecting metals from used electronics handed in by consumers nationwide to forge the approximately 5,000 medals to be awarded at the Games, and said in October they had reached their target for bronzes.
The “flame of reconstruction” will first be displayed in Miyagi, Iwate and Fukushima prefectures, the three most affected by the March 11, 2011, earthquake and tsunami that devastated a large part of northeastern Japan.
The Japan leg of the relay will begin in Fukushima on March 26, and will travel across all 47 prefectures of the country over a period of 121 days before arriving in Tokyo for the opening ceremony.
The design of the torch, which has already been approved by the International Olympic Committee, will be announced next spring.
 
 

Determination and Comparison of the Strontium-90 Concentrations in Topsoil of Fukushima Prefecture before and after the Fukushima Daiichi Nuclear Accident

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Abstract
To precisely understand the status of scattered strontium-90 (90Sr) after the 2011 accident at the Fukushima Daiichi Nuclear Power Plant (F1-NPP) of Tokyo Electric Power Company (TEPCO), the measurement of the soil samples collected both before and after the day of the accident from the same sampling locations is necessary. However, very few reports have investigated the background contaminant data before the accident even though several studies have been conducted to investigate the effects of the F1-NPP accident. To address the lack of the passed 90Sr information and reestablished baseline, this study focuses on the stored topsoil samples that are collected from the same sampling locations from the Fukushima Prefecture before and after the F1-NPP accident, which are analyzed for obtaining the 90Sr concentrations. The results of our investigation exhibited that the 90Sr concentrations in the Fukushima Prefecture soils ranged from 0.2 to 20.4 Bq/kg in the samples that were collected before the accident and from 1.37 to 80.8 Bq/kg in the samples that were collected after the accident from identical sampling locations. Further, the soil samples that were collected from 30 out of 56 locations displayed significant differences in terms of concentrations before and after the accident. In addition, the relations between the 90Sr concentrations and the soil properties of the samples (organic content, pH, water content, and composition) were investigated, and it was found that the organic content and water content had a positive correlation with 90Sr concentrations and, in contrast, the sandiness was shown to have a negative correlation with 90Sr concentrations. The depth characteristics were also investigated. The aforementioned results indicate that this tendency would be observed even in the future.
 
Introduction
 
A large amount of radioactive materials was scattered throughout the environment (ocean, atmosphere, land, and so on) because of the accident that occurred on March 11, 2011 at the Fukushima Daiichi Nuclear Power Plant (F1-NPP) that was owned by Tokyo Electric Power Company Holdings, Inc. (TEPCO).(1−3) Seven years have passed by since the accident, and research institutes around the world have been monitoring the influence of the environmental dynamics of radionuclides that have been released.(4−13) More specifically, there have been several environmental monitoring reports regarding β-ray-emitting nuclides, such as radioiodine and radiocesium, because multiple samples can be analyzed in a relatively short time using certain types of instruments such as a germanium semiconductor detector, a sodium iodide scintillator detector, and a lantern bromide scintillator detector.(14−19) Meanwhile, radiostrontium (90Sr) (half-life: 28.79 y(20)) is a pure β-ray-emitting nuclide that does not emit γ-rays, which makes it necessary to chemically isolate it for measuring β-rays because the β-ray spectra overlap. In particular, it is imperative to monitor 90Sr over a long period because it will require several decades to decommission F1-NPP. In Japan, instead of a few literature concerning the development of a rapid analytical means,(21−25) radiochemical analysis using milking-low background gas-flow counter (milking-LBC) is adopted as the official analysis method for analyzing 90Sr because of good sensitivity and/or high-precision analysis in low concentration levels in the environment.(26) This method requires considerable amount of time and effort to pretreat the analysis as compared to those required by the γ-ray measurement method. Although various studies have been vigorously conducted,(27−33) the study related to the scattering of 90Sr is not as advanced as compared to that related to the γ-ray-emitting nuclides such as radiocesium.
To precisely understand the status of scattered 90Sr after an incident of nuclear accident, the samples collected both before and after the day of the accident should be measured, thereby distinguishing from the fallout of atmospheric nuclear tests (20th century’s) that have been conducted in the past. So far, the survival ratios of nuclides with short half-lives in samples have been employed in several studies.(34) However, this technique cannot track the long-term process because it becomes difficult to evaluate the nuclides that exhibit a short decrease in half-lives. The optimal method for addressing these issues is to measure the radioactive concentrations of 90Sr in soil that is collected at identical locations before and after the accident. However, few examples exhibited the presence of 90Sr in soil before the F1-NPP accident, which was completely unexpected. Fortunately, we already possessed analytical data related to the 90Sr concentrations in soil samples that were collected before the accident with precise sampling locations throughout the Fukushima Prefecture (not published). Therefore, in this study, we succeeded in estimating the exact amount of 90Sr deposition before and after the F1-NPP accident. When performing the long-term observation, understanding the background level of 90Sr before the accident was observed to be considerably important for understanding the environmental radioactivity and the environmental dynamics or the usage of 90Sr as a tracer.
In this study, we measured the radioactivity concentrations of 90Sr in the topsoil at the same locations in the Fukushima Prefecture before and after the accident and obtained the background levels of 90Sr before the F1-NPP accident. Thus, we revealed the deposition status of 90Sr before and after the accident. We also investigated the correlation between the soil properties and 90Sr to determine the status of deposition of 90Sr on the topsoil in Fukushima prefecture (Figure 1).
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