Just off the NHK news broadcast, Chiba prefecture is conducting tests on kyushoku samples (1 week’s worth of kyushoku meals) to check on food safety, the results will be posted to the Chiba Prefecture HP about 1 month later. …
Radiation hotspot in Chiba linked to Fukushima (Japan Today, Nov 29)
TOKYO — Radiation levels as high as those in the evacuation zone around the Fukushima Daiichi nuclear power plant, that were detected in Kashiwa, Chiba Prefecture, last month, were likely caused by the disaster, Environment Ministry officials said Tuesday.
The hotspot, a small area of about one meter radius, was found in a vacant lot in Kashiwa. Radiation levels of 4.11 microsieverts per hour were detected one meter above the surface of the soil, equivalent to some areas in the evacuation zone around the crippled nuclear power plant. Up to 450,000 becquerels per kilogram of radioactive substances were detected in the soil below the surface, an Environment Ministry official said, Fuji TV reported.
The area is located some 195 kilometers from the accident site.
Inspectors believe the hotspot was created after radioactive cesium carried by rainwater became concentrated in a small area because of a broken gutter.
A Kashiwa city official said the area had been covered with sand and plastic sheets, which so far have lowered the radiation levels in the air, Fuji reported.
Variable winds, weather and topography result in an uneven spread of contamination from the nuclear plant, experts say, and radioactive elements tend to concentrate in places where dust and rain water accumulate such as drains and ditches.
As researchers carry out tests to map how far contamination has spread from the plant, radiation fears are a daily fact of life in many parts of Japan following the earthquake and tsunami-sparked meltdowns at the plant, with reported cases of contaminated water, beef, vegetables, tea and seafood.
Cesium find makes Date rice off-limits (Japan Times, Nov 29)
The government on Tuesday ordered a ban on the shipment of rice harvested in two more districts in Fukushima Prefecture, after tests detected dangerously high levels of radioactive cesium.
Chief Cabinet Secreatary Osamu Fujimura said the central government has instructed Fukushima Gov. Yuhei Sato to impose the ban on about 1,900 kg harvested in the Oguni district and 1,500 kg in the Tsukidate district, both in the city of Date.
On Monday, the Fukushima Prefectural Government announced that a combined 3,400 kg of unmilled rice harvested by two farms in the Oguni district and by one farm in the Tsukidate district contained between 580 and 1,050 becquerels per kilogram of radioactive cesium. The government’s limit is 500 becquerels.
One of the farms in the Oguni district already has sold 9 kg of the tainted rice, the prefectural government said, adding it has yet to establish the identity of the buyer. The remainder of the Oguni rice has not reached the market, it said.
None of the rice harvested by the farm in Tsukidate has been distributed, and all 1,500 kg are currently being stored by the Japan Agricultural Cooperatives.
It is the second ban on rice grown in Fukushima Prefecture in the last two weeks. On Nov. 17, the government banned rice in the Onami district of the city of Fukushima after excessively high levels of cesium were detected.
The prefectural government also decided Tuesday to inspect rice harvested by about 2,300 farms in certain districts of the cities of Nihonmatsu and Motomiya where high radiation levels have been recorded.
Date is located next to the city of Fukushima, and parts of it have been designated as radiation hot spots where the annual exposure could exceed the maximum 20-millisievert limit.
“While we carried out the best inspection process we could think of, we must take the fact (that contaminated rice has been found) seriously,” agriculture minister Michihiko Kano said after a Cabinet meeting, hinting it may be necessary to devise new processes for inspecting rice.
The government will do its best to identify the buyer of the contaminated Oguni rice, he said.
The tainted rice was detected in new tests the Fukushima Prefectural Government started conducting on rice harvested by about 1,500 farms in the cities of Fukushima and Date after the central government banned rice from the Onami district.
As of Monday, the tests had confirmed that rice from 10 farms in Onami contained excessive levels of cesium.
In October, Gov. Sato officially announced that test results for rice at 1,174 spots in the prefecture, including Date, confirmed that Fukushima’s rice was not contaminated by radioactive materials and was safe to consume.
The initial inspections showed that 82 percent of the rice tested showed no traces of contamination, and the remaining samples contained radioactive cesium below the government-set limit.
TEPCO says no explosion occurred at No.2 reactor (November 29, 2011)
The operator of the damaged Fukushima Daiichi nuclear power plant says there was no explosion at the No. 2 reactor, denying an earlier report that there was. But the company says it is still unable to determine how and why radioactive substances were released from the reactor.
NHK has obtained Tokyo Electric Power Company’s interim report on the nuclear accident that was triggered by the earthquake and tsunami on March 11th.
The report includes findings from a study that the utility launched in June to analyze how the accident occurred and how workers responded to it.
The report says that almost all electricity sources for the reactors were lost at once following the tsunami.
As a result, multiple safety functions were also lost, causing meltdowns from the No. 1 to the No. 3 reactors.
TEPCO analyzed seismographic data recorded within the plant in the early morning of March 15th, 4 days after the disaster, when a large blast was reportedly heard near the containment vessel of the No. 2 reactor.
The company concluded in the report that there was no explosion at the No. 2 reactor, and that a blast at the No. 4 reactor was mistakenly believed to have occurred at the No. 2.
Later that day, pressure inside the No. 2 reactor vessel dropped sharply, and radiation levels near the plant’s main gate rose above 10 millisieverts per hour, then the highest level so far.
The interim report fails to specify how the leakage occurred at the containment vessel, just saying that gas in the vessel was somehow released into the air.
Expert urges probe of No.2 reactor leak (NHK, Nov 2)
The spike in radiation levels following unspecified trouble at the No.2 reactor on March 15th was much more prominent than on March 12th or 14th, when explosions hit the No.1 and No.3 reactors.
Shinichiro Kado, an associate professor at the University of Tokyo, calls the reactor containment vessel “a final fortress” for keeping radioactive substances trapped, and a “cornerstone” for the integrity of a nuclear plant.
Kado says a breach of the vessel is extremely grave.
He says TEPCO needs to clarify how radioactive substances were released, by cross-referencing data on reactor conditions and patterns of radioactive dispersion in the atmosphere.
Grad student publishes comics about quake survivors(Asahi, Nov 29) | Ginza displays illustrations from kids in disaster areas(Asahi, Nov 29)
Scientists have produced maps showing how much fallout was found in the environment in the weeks after the magnitude 9 earthquake and resulting tsunami crippled Japan’s Fukushima Daiichi nuclear-power plant and spewed radioactive material for hundreds of miles. (Los Angeles Times)
LOS ANGELES — Eight months after a magnitude 9 earthquake and resulting tsunami crippled Japan’s Fukushima Daiichi nuclear-power plant and spewed radioactive material for hundreds of miles, scientists have produced maps showing how much fallout was found in the environment in the weeks after the disaster.
In two studies published last week in the journal Proceedings of the National Academy of Sciences, researchers identified “hot spots” where the radioactivity levels were highest as well as the areas that were most safe.
The maps could help the government decide what to do with different tracts of land: whether to abandon them, return them to farming or remove contaminated topsoil first. They also should help scientists build better models to predict how radioactive particles are carried by wind and rain and channeled by mountains after such disasters.
In one study, researchers examined levels of the radioactive isotope cesium-137 in soil collected in and around the Fukushima plant. With a half-life of 30.1 years, cesium-137 poses a much longer-term risk than other isotopes released by the damaged plant; iodine-131, for instance, has a half-life of eight days.
The international team of scientists started with a particle-dispersion model and plugged in weather data based on actual events since the March 11 quake and tsunami. Weather and geography directly affect where radioactive material lands: Wind carries it to other areas, and mountain ranges block its path. Rain washes it out of the air and into the ground, which becomes its final resting place.
The scientists found that parts of western and northwestern Japan largely were sheltered from contamination by mountains that run like a spine up the main island of Honshu.
But in the eastern part of Fukushima prefecture, close to the epicenter of the quake offshore, soil levels of cesium-137 exceeded 2,500 becquerels per kilogram, which would leave food production in the area “severely impaired,” according to the study. Farming would be “partially impacted” in the nearby prefectures of Iwate, Miyagi, Yamagata, Niigata, Tochigi, Ibaraki and Chiba, where radioactivity levels exceeded 250 becquerels per kilogram of soil.
“But one of the main products of the Fukushima area is rice, and so far the levels of rice contamination are lower than I personally expected,” said study co-author Ryugo Hayano, a nuclear physicist at the University of Tokyo. “Most of the rice-growing areas are now declared to be OK: not completely free of contamination, but edible.”
Another study published by the journal measured the gamma radiation emitted by soil samples collected from east-central Japan. The readings helped researchers determine the degree to which the samples were contaminated by isotopes of cesium, iodine and tellurium. Then they matched that with observed weather patterns.
The researchers found that two major downpours washed significant amounts of radiation into the soil — on March 15-16 in Fukushima and on March 21-23 in Tochigi, Ibaraki, Saitama and Chiba prefectures.
In an area north of the Fukushima nuclear plant, cesium-137 rates were 200 times normal, said study leader Norikazu Kinoshita, a nuclear physicist at the University of Tsukuba. In eastern Fukushima and parts of neighboring prefectures, cesium-137 levels were about 0.5 microsieverts per hour, or about 10 times the normal rate of 0.05 microsieverts per hour, he said.
“It’s not huge amounts of radiation,” said Gerry Thomas, a molecular pathologist at Imperial College London and director of the Chernobyl Tissue Bank, an international coalition that collects and stores tissue samples from people who were exposed to radioactive iodine as children by the Chernobyl nuclear disaster in 1986.
A third study, which appeared last week in the journal PLoS ONE, surveyed more than 5,000 people over a three-month period after the disaster and found that radiation levels in people were lower than had been predicted. Only 10 people had exceptionally high doses of radiation in their systems.
“The Japanese took proper precautions,” said Thomas, who was not involved in any of the studies. “An awful lot of (the radiation) went into the ocean rather than the atmosphere. … The levels they’re talking about are not going to damage people’s health at all. But it’s sensible to be precautionary.”