Tag Archives: Tokyo

10/25/2011 Fallout forensics hike radiation toll: Global data on Fukushima challenge Japanese estimates

The Fukushima accident led to mass evacuations from nearby towns such as Minamisoma. AP Photo/S. Ponomarev: 10/25/2011 Fallout forensics hike radiation toll Published online: 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 study that combines radioactivity data from across the globe to estimate the scale and fate of emissions from the shattered plant.

The disaster at the Fukushima Daiichi nuclear plant in March released far more radiation than the Japanese government has claimed. So concludes a study1 that 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.

Challenging numbers

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.

10/14/2011 NY Times ASIA PACIFIC: Citizens’ Testing Finds 20 Hot Spots Around Tokyo

Toshiyuki Hattori, who runs a sewage plant in Tokyo, surrounded by sacks of radioactive sludge. By HIROKO TABUCHI 10/14/2011 New York Times: Citizens’ Testing Finds 20 Hot Spots Around Tokyo: TOKYO — Takeo Hayashida signed on with a citizens’ group to test for radiation near his son’s baseball field in Tokyo after government officials told him they had no plans to check for fallout from the devastated Fukushima Daiichi nuclear plant. Like Japan’s central government, local officials said there was nothing to fear in the capital, 160 miles from the disaster zone.

Then came the test result: the level of radioactive cesium in a patch of dirt just yards from where his 11-year-old son, Koshiro, played baseball was equal to those in some contaminated areas around Chernobyl.

The patch of ground was one of more than 20 spots in and around the nation’s capital that the citizens’ group, and the respected nuclear research center they worked with, found were contaminated with potentially harmful levels of radioactive cesium.

It has been clear since the early days of the nuclear accident, the world’s second worst after Chernobyl, that that the vagaries of wind and rain had scattered worrisome amounts of radioactive materials in unexpected patterns far outside the evacuation zone 12 miles around the stricken plant. But reports that substantial amounts of cesium had accumulated as far away as Tokyo have raised new concerns about how far the contamination had spread, possibly settling in areas where the government has not even considered looking.

The government’s failure to act quickly, a growing chorus of scientists say, may be exposing many more people than originally believed to potentially harmful radiation. It is also part of a pattern: Japan’s leaders have continually insisted that the fallout from Fukushima will not spread far, or pose a health threat to residents, or contaminate the food chain. And officials have repeatedly been proved wrong by independent experts and citizens’ groups that conduct testing on their own.

“Radioactive substances are entering people’s bodies from the air, from the food. It’s everywhere,” said Kiyoshi Toda, a radiation expert at Nagasaki University’s faculty of environmental studies and a medical doctor. “But the government doesn’t even try to inform the public how much radiation they’re exposed to.”

The reports of hot spots do not indicate how widespread contamination is in the capital; more sampling would be needed to determine that. But they raise the prospect that people living near concentrated amounts of cesium are being exposed to levels of radiation above accepted international standards meant to protect people from cancer and other illnesses.

Japanese nuclear experts and activists have begun agitating for more comprehensive testing in Tokyo and elsewhere, and a cleanup if necessary. Robert Alvarez, a nuclear expert and a former special assistant to the United States secretary of energy, echoed those calls, saying the citizens’ groups’ measurements “raise major and unprecedented concerns about the aftermath of the Fukushima nuclear disaster.”

The government has not ignored citizens’ pleas entirely; it recently completed aerial testing in eastern Japan, including Tokyo. But several experts and activists say the tests are unlikely to be sensitive enough to be useful in finding micro hot spots such as those found by the citizens’ group.

Kaoru Noguchi, head of Tokyo’s health and safety section, however, argues that the testing already done is sufficient. Because Tokyo is so developed, she says, radioactive material was much more likely to have fallen on concrete, then washed away. She also said exposure was likely to be limited.

“Nobody stands in one spot all day,” she said. “And nobody eats dirt.”

Tokyo residents knew soon after the March 11 accident, when a tsunami knocked out the crucial cooling systems at the Fukushima plant, that they were being exposed to radioactive materials. Researchers detected a spike in radiation levels on March 15. Then as rain drizzled down on the evening of March 21, radioactive material again fell on the city.

In the following week, however, radioactivity in the air and water dropped rapidly. Most in the city put aside their jitters, some openly scornful of those — mostly foreigners — who had fled Tokyo in the early days of the disaster.

But not everyone was convinced. Some Tokyo residents bought dosimeters. The Tokyo citizens’ group, the Radiation Defense Project, which grew out of a Facebook discussion page, decided to be more proactive. In consultation with the Yokohama-based Isotope Research Institute, members collected soil samples from near their own homes and submitted them for testing.

Some of the results were shocking: the sample that Mr. Hayashida collected under shrubs near his neighborhood baseball field in the Edogawa ward measured nearly 138,000 becquerels per square meter of radioactive cesium 137, which can damage cells and lead to an increased risk of cancer.

Of the 132 areas tested, 22 were above 37,000 becquerels per square meter, the level at which zones were considered contaminated at Chernobyl.

Edwin Lyman, a physicist at the Union of Concerned Scientists in Washington, said most residents near Chernobyl were undoubtedly much worse off, surrounded by widespread contamination rather than isolated hot spots. But he said the 37,000 figure remained a good reference point for mandatory cleanup because regular exposure to such contamination could result in a dosage of more than one millisievert per year, the maximum recommended for the public by the International Commission on Radiological Protection.

The most contaminated spot in the Radiation Defense survey, near a church, was well above the level of the 1.5 million becquerels per square meter that required mandatory resettlement at Chernobyl. The level is so much higher than other results in the study that it raises the possibility of testing error, but micro hot spots are not unheard of after nuclear disasters.

Japan’s relatively tame mainstream media, which is more likely to report on government pronouncements than grass-roots movements, mainly ignored the citizens’ group’s findings.

“Everybody just wants to believe that this is Fukushima’s problem,” said Kota Kinoshita, one of the group’s leaders and a former television journalist. “But if the government is not serious about finding out, how can we trust them?”

Hideo Yamazaki, an expert in environmental analysis at Kinki University in western Japan, did his own survey of the city and said he, too, discovered high levels in the area where the baseball field is located.

“These results are highly localized, so there is no cause for panic,” he said. “Still, there are steps the government could be taking, like decontaminating the highest spots.”

Since then, there have been other suggestions that hot spots were more widespread than originally imagined.

Last month, a local government in a Tokyo ward found a pile of composted leaves at a school that measured 849 becquerels per kilogram of cesium 137, over two times Japan’s legally permissible level for compost.

And on Wednesday, civilians who tested the roof of an apartment building in the nearby city of Yokohama — farther from Fukushima than Tokyo — found high quantities of radioactive strontium. (There was also one false alarm this week when sky-high readings were reported in the Setagaya ward in Tokyo; the government later said they were probably caused by bottles of radium, once widely used to make paint.)

The government’s own aerial testing showed that although almost all of Tokyo had relatively little contamination, two areas showed elevated readings. One was in a mountainous area at the western edge of the Tokyo metropolitan region, and the other was over three wards of the city — including the one where the baseball field is situated.

The metropolitan government said it had started preparations to begin monitoring food products from the nearby mountains, but acknowledged that food had been shipped from that area for months.

Mr. Hayashida, who discovered the high level at the baseball field, said that he was not waiting any longer for government assurances. He moved his family to Okayama, about 370 miles to the southwest.

“Perhaps we could have stayed in Tokyo with no problems,” he said. “But I choose a future with no radiation fears.”

Matthew L. Wald contributed reporting from Washington, and Kantaro Suzuki from Tokyo.

10/8/2011 The Economist: Radiation in Japan Hot spots and blind spots – The mounting human costs of Japan’s nuclear disaster

10/8/2011 The Economist: Radiation in Japan Hot spots and blind spots – The mounting human costs of Japan’s nuclear disaster: CREST the hill into the village of Iitate, and the reading on a radiation dosimeter surges eightfold—even with the car windows shut. “Don’t worry, I’ve been coming here for months and I’m still alive,” chuckles Chohei Sato, chief of the village council, as he rolls down the window and inhales cheerfully. He pulls off the road, gets out of the car and buries the dosimeter in the grass. The reading doubles again.

Iitate is located 45km (28 miles) from the Fukushima Dai-ichi nuclear power plant hit by a tsunami on March 11th this year. In the mountains above the town, the forests are turning the colour of autumn. But their beauty is deceptive. Every time a gust of wind blows, Mr Sato says it shakes invisible particles of radioactive caesium off the trees and showers them over the village. Radiation levels in the hills are so high that villagers dare not go near them. Mr Sato cannot bury his father’s bones, which he keeps in an urn in his abandoned farmhouse, because of the dangers of going up the hill to the graveyard.

Iitate had the misfortune to be caught by a wind that carried radioactive particles (including plutonium) much farther than anybody initially expected after the nuclear disaster. Almost all the 6,000 residents have been evacuated, albeit belatedly, because it took the government months to decide that some villages outside a 30km radius of the plant warranted special attention. Now it offers an extreme example of how difficult it will be to recover from the disaster.

That is mainly because of the enormous spread of radiation. Recently the government said it needed to clear about 2,419 square kilometres of contaminated soil—an area larger than greater Tokyo—that received an annual radiation dose of at least five millisieverts, or over 0.5 microsieverts an hour. That covered an area far beyond the official 30km restriction zone (see map). Besides pressure- hosing urban areas, this would involve removing about 5cm of topsoil from local farms as well as all the dead leaves in caesium-laden forests.

However, Iitate’s experience suggests the government may be underestimating the task. Villagers have removed 5cm of topsoil from one patch of land, but because radioactive particles continue to blow from the surrounding trees, the level of radiation remains high—about one microsievert an hour—even if lower than in nearby areas. Without cutting down the forests, Mr Sato reckons there will be a permanent risk of contamination. So far, nobody has any idea where any contaminated soil will be dumped.

The second problem is children’s health. On September 30th the government lifted an evacuation advisory warning to communities within a 20-30km radius of the plant. The aim was partly to show that the authorities were steadily bringing the crippled reactors under control.

But these areas are still riddled with radiation hot spots, including schools and public parks, which will need to be cleaned before public confidence is restored. Parents say they are particularly concerned about bringing their children back because the health effects of radiation on the young are so unclear. What is more, caesium particles tend to lurk in the grass, which means radiation is more of a risk at toddler height than for adults. In Iitate, Mihori Takahashi, a mother of two, “believes only half of what the doctors say” and says she never wants to bring her children back. That, in itself, may be a curse. “The revival of this town depends on the children returning,” says Mr Sato.

And even if people return, Mr Sato worries how they will make a living. These are farming villages, but it will take years to remove the stigma attached to food grown in Fukushima, he reckons. He is furious with Tokyo Electric Power, operator of the plant, for failing to acknowledge the long-term impacts of the disaster. He says it is a way of scrimping on compensation payouts.

One way to help overcome these problems would be to persuade people to accept relaxed safety standards. A government panel is due to propose lifting the advisory dose limit above one millisievert per year. This week in Tokyo, Wade Allison, a physics professor at Oxford University, argued that Japan’s dose limit could safely be raised to 100 millisieverts, based on current health statistics. Outside Mr Sato’s house, however, a reading of the equivalent of 150 millisieverts a year left your correspondent strangely reluctant to inhale.