Fallout forensics hike radiation toll
Global data on Fukushima challenge Japanese estimates.
The disaster at the Fukushima Daiichi nuclear plant in March released far more radiation than the Japanese government has claimed. So concludes a study1that combines radioactivity data from across the globe to estimate the scale and fate of emissions from the shattered plant.
The study also suggests that, contrary to government claims, pools used to store spent nuclear fuel played a significant part in the release of the long-lived environmental contaminant caesium-137, which could have been prevented by prompt action. The analysis has been posted online for open peer review by the journal Atmospheric Chemistry and Physics.
Andreas Stohl, an atmospheric scientist with the Norwegian Institute for Air Research in Kjeller, who led the research, believes that the analysis is the most comprehensive effort yet to understand how much radiation was released from Fukushima Daiichi. “It’s a very valuable contribution,” says Lars-Erik De Geer, an atmospheric modeller with the Swedish Defense Research Agency in Stockholm, who was not involved with the study.
The reconstruction relies on data from dozens of radiation monitoring stations in Japan and around the world. Many are part of a global network to watch for tests of nuclear weapons that is run by the Comprehensive Nuclear-Test-Ban Treaty Organization in Vienna. The scientists added data from independent stations in Canada, Japan and Europe, and then combined those with large European and American caches of global meteorological data.
Stohl cautions that the resulting model is far from perfect. Measurements were scarce in the immediate aftermath of the Fukushima accident, and some monitoring posts were too contaminated by radioactivity to provide reliable data. More importantly, exactly what happened inside the reactors — a crucial part of understanding what they emitted — remains a mystery that may never be solved. “If you look at the estimates for Chernobyl, you still have a large uncertainty 25 years later,” says Stohl.
Nevertheless, the study provides a sweeping view of the accident. “They really took a global view and used all the data available,” says De Geer.
Japanese investigators had already developed a detailed timeline of events following the 11 March earthquake that precipitated the disaster. Hours after the quake rocked the six reactors at Fukushima Daiichi, the tsunami arrived, knocking out crucial diesel back-up generators designed to cool the reactors in an emergency. Within days, the three reactors operating at the time of the accident overheated and released hydrogen gas, leading to massive explosions. Radioactive fuel recently removed from a fourth reactor was being held in a storage pool at the time of the quake, and on 14 March the pool overheated, possibly sparking fires in the building over the next few days.
But accounting for the radiation that came from the plants has proved much harder than reconstructing this chain of events. The latest report from the Japanese government, published in June, says that the plant released 1.5 × 1016 bequerels of caesium-137, an isotope with a 30-year half-life that is responsible for most of the long-term contamination from the plant2. A far larger amount of xenon-133, 1.1 × 1019 Bq, was released, according to official government estimates.
The new study challenges those numbers. On the basis of its reconstructions, the team claims that the accident released around 1.7 × 1019 Bq of xenon-133, greater than the estimated total radioactive release of 1.4 × 1019 Bq from Chernobyl. The fact that three reactors exploded in the Fukushima accident accounts for the huge xenon tally, says De Geer.
Xenon-133 does not pose serious health risks because it is not absorbed by the body or the environment. Caesium-137 fallout, however, is a much greater concern because it will linger in the environment for decades. The new model shows that Fukushima released 3.5 × 1016 Bq caesium-137, roughly twice the official government figure, and half the release from Chernobyl. The higher number is obviously worrying, says De Geer, although ongoing ground surveys are the only way to truly establish the public-health risk.
Stohl believes that the discrepancy between the team’s results and those of the Japanese government can be partly explained by the larger data set used. Japanese estimates rely primarily on data from monitoring posts inside Japan3, which never recorded the large quantities of radioactivity that blew out over the Pacific Ocean, and eventually reached North America and Europe. “Taking account of the radiation that has drifted out to the Pacific is essential for getting a real picture of the size and character of the accident,” says Tomoya Yamauchi, a radiation physicist at Kobe University who has been measuring radioisotope contamination in soil around Fukushima.
Stohl adds that he is sympathetic to the Japanese teams responsible for the official estimate. “They wanted to get something out quickly,” he says. The differences between the two studies may seem large, notes Yukio Hayakawa, a volcanologist at Gunma University who has also modelled the accident, but uncertainties in the models mean that the estimates are actually quite similar.
The new analysis also claims that the spent fuel being stored in the unit 4 pool emitted copious quantities of caesium-137. Japanese officials have maintained that virtually no radioactivity leaked from the pool. Yet Stohl’s model clearly shows that dousing the pool with water caused the plant’s caesium-137 emissions to drop markedly (see‘Radiation crisis’). The finding implies that much of the fallout could have been prevented by flooding the pool earlier.
The Japanese authorities continue to maintain that the spent fuel was not a significant source of contamination, because the pool itself did not seem to suffer major damage. “I think the release from unit 4 is not important,” says Masamichi Chino, a scientist with the Japanese Atomic Energy Authority in Ibaraki, who helped to develop the Japanese official estimate. But De Geer says the new analysis implicating the fuel pool “looks convincing”.
The latest analysis also presents evidence that xenon-133 began to vent from Fukushima Daiichi immediately after the quake, and before the tsunami swamped the area. This implies that even without the devastating flood, the earthquake alone was sufficient to cause damage at the plant.
The Japanese government’s report has already acknowledged that the shaking at Fukushima Daiichi exceeded the plant’s design specifications. Anti-nuclear activists have long been concerned that the government has failed to adequately address geological hazards when licensing nuclear plants (see Nature 448, 392–393; 2007), and the whiff of xenon could prompt a major rethink of reactor safety assessments, says Yamauchi.
The model also shows that the accident could easily have had a much more devastating impact on the people of Tokyo. In the first days after the accident the wind was blowing out to sea, but on the afternoon of 14 March it turned back towards shore, bringing clouds of radioactive caesium-137 over a huge swathe of the country (see‘Radioisotope reconstruction’). Where precipitation fell, along the country’s central mountain ranges and to the northwest of the plant, higher levels of radioactivity were later recorded in the soil; thankfully, the capital and other densely populated areas had dry weather. “There was a period when quite a high concentration went over Tokyo, but it didn’t rain,” says Stohl. “It could have been much worse.”
Additional reporting by David Cyranoski and Rina Nozawa.
- Stohl, A. et al. Atmos. Chem. Phys. Discuss. 11, 28319-28394 (2011).
- Chino, M. et al. J. Nucl. Sci. Technol. 48, 1129-1134 (2011).
High levels of radiation detected at 2 schools in Chiba Prefecture
ABIKO, Chiba — High levels of radiation have been detected on the premises of two elementary schools here, local education authorities have revealed.
According to the Abiko Municipal Board of Education, 11.3 microsieverts of radiation per hour was detected just above the surface of the ground near a ditch in the compounds of the Abiko Municipal Daiichi Elementary School on Sept. 15. The amount was 1.7 microsieverts in the air 50 centimeters above the ground.
Soil had piled up in the ditch, which had been damaged by growing tree roots, a situation similar to a residential area of the Chiba Prefecture city of Kashiwa where 57.5 microsieverts per hour was detected.
Radioactive cesium amounting to 60,768 becquerels per 1 kilogram of soil was found in the ditch.
The amount of radiation 50 centimeters above the ground had declined to 0.6 microsieverts per hour by Oct. 7 after the soil was removed.
The Education, Culture, Sports, Science and Technology Ministry pointed to the possibility that rain water contaminated with radioactive cesium overflowed from the ditch, soaked the nearby soil and accumulated in it.
At the Abiko Municipal Namiki Elementary School, 10.1 microsieverts per hour of radiation was detected near the surface of the ground where sludge removed from its swimming pool had been buried.
The school covered the area with a waterproof tarp and piled up dirt on the tarp to decrease the radiation emissions, after which 0.6 microsieverts per hour was detected 50 centimeters above the ground.
The two schools have sealed off the areas where high levels of radiation were detected.
(Mainichi Japan) October 26, 2011
Food safety fair features radiation monitors
An annual food safety exhibition has opened in Tokyo with devices for measuring radiation on display for the first time.
Machines that use a conveyor belt to run food past a radiation sensor proved very popular on Wednesday. They can check an item’s radiation level in 12 seconds, which means a number of foods can be tested in a short time.
The devices are in high demand from farmers’ cooperatives, beef processors and restaurant chains, despite a minimum price tag of 56,000 dollars.
Also on display are small devices that check foods placed in a beaker for radioactive substances.
They are intended for companies and even housewives. The most inexpensive types cost about 9,000 dollars.
An official at a confectioner said the company wants to learn how to take steps to alleviate consumers’ fears on its own.
An official from a manufacturer of radiation monitoring devices said the company wants to help farmers dispel rumors that their products may be contaminated.
The exhibition runs through Friday.
Wednesday, October 26, 2011 15:54 +0900 (JST)
Volunteers lend an ear to brighten lives of earthquake victims
MORIOKA — A volunteer organization here is helping earthquake and tsunami victims recover from their devastating experience by simply being there for them to listen to their stories.
Seven months after the March 11 earthquake and tsunami, the emotional damage caused by the freighting experience is still haunting many. It is even stronger among the elderly who live at temporary housing units alone, away from their homes and previous surroundings.
An organization based in Morioka in Iwate Prefecture has addressed the problem of elderly people’s loneliness by dispatching volunteers to share time with them and listen to their stories.
Whether through recollections of the earthquake day itself, or simple random talk, the conversations provide a chance for the victims to escape — even if temporarily — from their anxieties and isolation.
As of present, over 330 volunteers have visited evacuation shelters and temporary housing units in some of the prefecture’s most heavily damaged towns, including Rikuzentakata, Otsuchi and Yamada.
“I feel a bit relieved now having done something different. It was fun,” says a 79-year-old man, who lives alone at a temporary housing unit in Otsuchi, after spending about an hour talking with a volunteer.
“Their gloomy facial expressions change into a bright smile after talking for some time,” said Kazutaka Fujiwara, 58, a volunteer with the organization. “What we do is fulfilling.”
(Mainichi Japan) October 26, 2011
Municipalities divided over nuke plants restart
Japanese municipalities hosting nuclear power plants are divided over whether reactors that are currently offline should resume operations.
An association of host cities and towns held a meeting in Tokyo on Tuesday. Mayors and officials from 15 communities attended.
The main issue discussed was resuming power generation at reactors which have been idle since the March accident at Fukushima Daiichi.
44 of 54 nuclear reactors in Japan are currently offline. They have no prospects of being restarted soon after data errors were found in safety stress tests required before bringing them back online.
Complicating the issue is the manipulation of public opinion on nuclear power at explanatory meetings for local residents that came to light in summer.
Some municipalities demanded the restart of reactors to benefit their economies after their safety is confirmed.
But others remained cautious, preventing the association from reaching a conclusion.
One representative noted the cause of the Fukushima accident has not been confirmed. Another said neither the central government nor power utilities have clarified their policies on the future of nuclear power in Japan.
Wednesday, October 26, 2011 10:41 +0900 (JST)
Tokai No. 2 plant reports radioactive water leakage
TOKYO, Oct. 26, Kyodo
Water containing radioactive substances has leaked from a reactor pressure vessel at the Tokai No. 2 power plant in Ibaraki Prefecture, although there was no release of toxic substances into the outside environment, the government’s nuclear safety agency said Wednesday.
Some 64 tons of water may have escaped from the pressure vessel to the outer primary container of the plant’s boiling water reactor, which is undergoing regular checkups, the agency said. The incident has not affected the cooling process of the nuclear fuel, it said.
According to plant operator Japan Atomic Power Co., workers erroneously loosened a screw located at the bottom part of the pressure vessel, resulting in the leakage of water. Water splashed onto four workers, but they were not exposed to radiation.
By ENENEWS Staff
“Just the tip of the iceberg”: Van emitting 110 uSv/hr — Ended up 370 miles from Fukushima in Kobe — “Dangerously radioactive” vehicles must be resold within Japan
Though barred from export, used car dealers have resorted to re-registering vehicles to disguise the origin, and selling them to customers “who have no idea of the risk to which they are being exposed”.
One van was so radioactive that “sitting inside it for two hours a day will expose the occupant to more than the government’s recommended maximum dose over the course of a year”. It “emitted radiation at a level of 110 microsieverts an hour,” according to a reporter for the Asahi Shimbun.
A car dealer told Asahi, “It is just the tip of the iceberg. If high radiation is detected, decontamination is too difficult. This is why such vehicles are auctioned within Japan.”
The van’s owner said, “I decontaminated repeatedly after the test, and retested the filter of the air conditioner, the wipers and tyres, replacing them thoroughly, but the radiation level dropped only to 30 microsieverts per hour. I decided to sell the vehicle in Japan because I couldn’t afford to lose the money.”
“The vehicle eventually sold at auction in Kobe, 370 miles from Fukushima,” according to The Times.
Reporter hot on the trail of a radioactive vehicle
BY AKIHIRO YAMADA STAFF WRITER
Vehicles for export are lined up on a pier at Sakai-Senboku Port in Izumi-Otsu, Osaka Prefecture, where a radioactive used vehicle was brought. (Ryo Ikeda)
It’s not the stuff of legends, but a rumor has been circulating among used car dealers about a used vehicle with a high radioactive level that has been popping up for sale in various locations in Japan.