TOKYO (Kyodo) — The Japanese government has instructed the education boards of 17 prefectures in eastern and northeastern Japan to set the upper limit on radioactive substance exposure for food and drink served in school meals at 40 becquerels per kilogram, officials said Thursday.
The directive on meals offered at elementary and junior high schools is the first issued by the central government since the Fukushima nuclear crisis was triggered by the March 11 earthquake and tsunami.
The threshold is one-fifth of the current provisional limit on radioactive cesium for items of general consumption — 200 becquerels per kilogram for drinking water, milk and dairy products.
The maximum allowable amount for rice, vegetables, meat and fish is set at 500 becquerels per kilogram.
The officials of the Ministry of Education, Culture, Sports, Science and Technology said they newly set the criteria for school meals as the government plans to lower the upper limit of annual internal exposure to radioactive cesium through food and drink consumption to 1 millisievert from the current provisional threshold of 5 millisieverts.
The 17 prefectures include Fukushima, Iwate, Miyagi, Ibaraki, Tokyo, Niigata, Yamanashi, Nagano and Shizuoka.
The ministry has earmarked about 100 million yen in the third extra budget for the current fiscal year to cover part of the cost to purchase dosimeters to detect radiation amounts in meals at schools in the 17 prefectures, according to the officials.
Under the directive, municipal governments are requested to buy equipment that can detect radiation levels in food and drink below 40 becquerels and to stop serving items with radioactive substances that exceed the upper limit, the officials said.
First radiation limit set for school meals (Japan Times, Dec 2)
The government instructs the boards of education of 17 eastern and northeastern prefectures to set the upper limit on radioactive substance exposure for food and drink served in school meals at 40 becquerels per kilogram.
TEPCO injects nitrogen into pressure vessels (NHK, December 02, 2011)
The operator of the Fukushima Daiichi nuclear power plant has started injecting nitrogen, an inert gas, into the pressure vessels of the crippled reactors to prevent another hydrogen explosion.
In late October, Tokyo Electric Power Company began extracting gases from the containment vessel of the No.2 reactor to remove radioactive substances. During the work, TEPCO found hydrogen accumulating in parts of the reactor at a density of up to 2.9 percent.
TEPCO started pumping nitrogen into the pressure vessels of the No.1, 2, 3 reactors on Thursday to lessen the concentration of hydrogen.
The density of hydrogen accumulating in the containment and pressure vessels is thought to be below 4 percent, the level where an explosion could occur.
TEPCO says the nitrogen injection will push out hydrogen and reduce its concentration.
Keeping hydrogen density low is an indispensible condition in the second step of the process decided upon by the government and TEPCO to resolve the nuclear accident. They are aiming to achieve a state of cold shutdown for the reactors by the end of the year.
The Nuclear and Industrial Safety Agency plans to assess how well TEPCO can manage hydrogen levels.
Almost all the nuclear fuel inside the No. 1 reactor of the crippled Fukushima No. 1 nuclear power plant has melted, damaging the pressure vessel and eroding the concrete bottom of the containment vessel by up to 65 centimeters, the plant’s operator has found.
Tokyo Electric Power Co. released its latest analysis Wednesday on the cores of the plant’s Nos. 1 to 3 reactors, based on temperature, water levels and other data. TEPCO said the fuel inside the reactors has melted to various degrees following the March 11 earthquake and tsunami.
The No. 2 reactor’s fuel is up to 57 percent melted, while that of the No. 3 reactor is up to 63 percent melted, TEPCO’s analysis has shown.
TEPCO has made the latest analysis to judge to what degree the fuel has cooled, as well as to ascertain if it can achieve its year-end target of a cold shutdown of the reactors, as stipulated in the timetable the utility company and the government have compiled to bring the nuclear crisis under control.
Following the March 11 earthquake and tsunami, water injection at the No. 1 reactor was suspended for about 14 hours, resulting in damage more serious than in the Nos. 2 and 3 reactors, which had water injection suspended for six to seven hours, according to TEPCO.
The nuclear fuel at the No. 1 reactor melted as its temperature reached nearly 3,000 C at one time, TEPCO estimated. In the No. 1 reactor, TEPCO believes, almost all of the about 68 tons of fuel melted. This has not only seriously damaged the bottom of the steel pressure vessel enough to create holes, but the fuel has also fallen to the concrete bottom of the containment vessel, eroding it by up to 65 centimeters.
Only 37 centimeters of concrete remains between the fuel and the vessel’s outermost steel wall in the most damaged area, TEPCO said.
Without water, the No. 1 reactor’s fuel temperature was more than high enough to have melted everything inside the pressure vessel, not only the fuel itself but also the fuel control rods, the utility said.
TEPCO currently maintains a steady supply of water to the three reactors, enabling the No. 1 reactor to always have about 40 centimeters of cool water at the bottom of the containment vessel, enough to cover the melted fuel, according to the utility.
Both the government and the utility said the three reactors are experiencing no problems in maintaining cooling functions.
However, the melted fuel likely will be a major hurdle in removing fuel from the troubled reactors in the decommissioning process, which is expected to take more than 30 years.
Study Shows Worse Picture of Meltdown in Japan (NY Times, Nov 30) Excerpted below:
“The simulation suggested that the meltdown may have been more severe than had previously been thought. …
In the No. 1 reactor, the overheated fuel may have eroded the primary containment vessel’s thick concrete floor, and it may have gotten almost within a foot of a crucial steel barrier, the utility said the new simulation suggested. Beneath that steel layer is a concrete basement, which is the last barrier before the fuel would have begun to penetrate the earth.
Some nuclear experts have warned that water from a makeshift cooling system now in place at the plant may not be able to properly cool any nuclear fuel that may have seeped into the concrete. The new simulation may call into question the efforts to cool and stabilize the reactor, but the Tokyo Electric Power Company, or Tepco, says it is not worried more than eight months after the accident.
The findings are the latest in a series of increasingly grave scenarios presented by Tepco about the state of the reactors. The company initially insisted that there was no breach at any of the three most-damaged reactors; it later said that there might have been a breach, but that most of the nuclear fuel had remained within the containment vessels.
“This is still an overly optimistic simulation,” said Hiroaki Koide, an assistant professor of physics at the Kyoto University Research Reactor Institute, who has been a vocal critic of Tepco’s lack of disclosure of details of the disaster. Tepco would very much like to say that the outermost containment is not completely compromised and that the meltdown stopped before the outer steel barrier, he said, “but even by their own simulation, it’s very borderline.”
“I have always argued that the containment is broken, and that there is the danger of a wider radiation leak,” Mr. Koide said. “In reality, it’s impossible to look inside the reactor, and most measurement instruments have been knocked out. So nobody really knows how bad it is.”
Still, a spokesman for Tepco, Junichi Matsumoto, said Wednesday that the nuclear fuel was no longer eating into the concrete, and that the new simulation would not affect efforts to bring the reactors to a stable state known as a “cold shutdown” by the end of the year.
“The containment vessel as a whole is being cooled, so there is no change to our outlook,” Mr. Matsumoto said at a news conference. “… Read more here.
While disputing the details, nuclear experts basically concurred Thursday with the findings of a computer simulation run by Tokyo Electric Power Co. that concluded nuclear fuel in reactors at the Fukushima No. 1 plant had melted into but not breached their containment vessels.
The announcement by Tepco Wednesday was the latest indication that three overheated cores at the plant had not penetrated their concrete and steel containers and melted deep into the earth — a worst-case scenario China syndrome.
However, there is reason to dispute Tepco’s claim that the nuclear fuel in reactor 1 came within 37 cm of melting through surrounding concrete and reaching the containment vessel’s steel shell, said Kenji Sumita, a professor emeritus of nuclear engineering and a former deputy chief of the Nuclear Safety Commission.
“There are many computer simulation methods. I want to see simulations conducted by organizations other than Tepco,” Sumita said.
Commenting on the unknown margin of error in Tepco’s simulation, “I don’t believe the fuel got as close as 2 or 3 cm to the steel shell, but I am not sure how credible their details are,” he said.
However, Sumita claimed it was certain nuclear fuel had not escaped the containment vessels because no radioactive substances have leaked into the groundwater near the reactors.
Toshihiro Yamamoto, a specialist in reactor safety management at Kyoto University Research Reactor Institute, pointed out the difficulty of collecting data to base the computer simulation on.
“You cannot have experimental meltdowns. Thus the simulation will have to rely on many assumptions,” he said.
Meanwhile, Hiromi Ogawa, a former engineer at Toshiba Corp. who managed its nuclear power generation project, effectively guaranteed the credibility of the simulation.
“The simulation referred to lots of data collected from many experiments, and thus I think the results are very precise,” he said. “Still, the situation will have to be confirmed visually.”
According to Tepco’s simulation, the nuclear fuel in reactor 1 probably penetrated through as much as 65 cm of the containment vessel’s concrete floor, reaching as close as 37 cm to the vessel’s outer steel shell, the last line of defense.
Reactor 1 suffered the worst damage in the accident triggered by the March 11 earthquake and tsunami.
The findings also suggest that the nuclear fuel in reactor 2 melted through 12 cm of the vessel’s concrete floor, while fuel from reactor 3 burned through 20 cm.
A study by Tokyo Electric Power Co., operator of the crippled Fukushima Daiichi nuclear power plant, has shown that water in the No. 4 unit’s spent fuel pool temporarily dropped to a level close to exposing the stored nuclear fuel, sources close to the matter said Thursday.
After the No. 4 unit lost its key cooling functions along with the plant’s other reactors in the wake of the March 11 earthquake and tsunami, the water level in the No. 4 spent fuel pool fell at one point to only 1.5 meters above the top of the fuel assemblies, as heat from the fuel had caused the coolant to evaporate. The water level is usually around 7 meters above the assemblies.
The water level remained low for over a month until at least April 20. Workers injected around 930 tons of water into the spent fuel pool between April 22 and 27, filling up the pool, but a graph compiled by Tokyo Electric shows that the fuel would have been exposed in early May if water had not been injected.
Fukushima Pref. to ask TEPCO to shut N-reactors (Yomiuri, Dec.2) | TEPCO pulls plug on N-plant / Utility unable to secure funds due to huge compensation payouts (Yomiuri, Dec.2)
High levels of cesium found in port soil at Fukushima Daiichi plant (Kyodo, Dec. 1, 2011) Click here to see ENFORMABLE map chart showing with cesium figures at various locations of the port facility.
Earlier news: The Watchers – Radioactive farmlands around Fukushima mapped (The Watchers, Nov 16, 2011)
“A study released on Monday in the Proceedings of the National Academy of Sciences (PNAS) modeled the spread of cesium-137, a radionuclide that can persist in soils for 30 years, across much of the country. The new map defines the highest risk areas beyond Fukushima and neighboring prefectures, which were already known from soil samples to far exceed contamination limits set by Japanese law. Nuclear fallout in farmland in eastern Japan is even worse than expected.
Until now, officials have had to rely almost exclusively on sporadic soil samples to make decisions such as banning shipments of beef that consumed radioactive hay from the area. Areas hardest hit (red in the map below) are nearest the Fukushima Daiichi Nuclear Power Plant, which experienced reactor meltdowns following the March 11, 2011, earthquake and tsunami.
Cesium-137 is bound to dust and water particles in the air so it travels with the weather. The new model, which infused actual cesium-137 measurements from observatories across the country into meteorological data for the month following the accident, reveals that the areas of highest concern are northern and eastern Japan (green and blue, above). Mountain ranges kept air masses confined in the east until most of the radiation washed out, largely shielding western parts of the country.
Two major rainstorms in the week following the disaster accounted for most of the radionuclide deposition, according to a second study in Monday’s issue of PNAS. Rain on March 15 affected Fukushima prefecture, while a March 21 storm accounts for much of the fallout recorded in Ibaraki, Tochigi, Saitama, and Chiba prefectures and in Tokyo. …
The team found that the area of eastern Fukushima had levels of the radioactive element that exceeded official government limits for arable land. Under Japanese Food Sanitation Law, 5,000 becquerel per kg (Bq/kg) of caesium is considered the safe limit in soil (caesium-137 makes up about half of total radioactive caesium, and therefore its safe limit is 2,500 Bq/kg). The researchers estimate that caesium-137 levels close to the nuclear plant were eight times the safety limit, while neighbouring regions were just under this limit.
The study showed that most of Japan was well below (average about 25 Bq/kg) the safety limit. Relatively low contamination levels in western Japan could be explained by mountain ranges sheltering those regions from the dispersal of radioactive material, the authors said…
” Read more here.
Some useful collated data for giving us an overview of the post-disaster situation at Wikipedia page “Radiation effects from the Fukushima Daiichi Nuclear Disaster” including links to the following:
Combined based and aerial monitoring results (Source: National Nuclear Security Administration (NNSA) US Department of Energy)
A bar graph of the levels of different radioisotopes in soil 500 meters from the damaged reactors at Fukuashima compared with the release at Chernboyl (OECD report). Source: TEPCO data obtained from the Japan Chemical Anaylsis Centre
Source: Wikimedia Commons
“There is no allowable limit for internal exposure that can conclusively be said not to pose any problems,”
Greenpeace said in a petition submitted to Prime Minister Naoto Kan on Tuesday,
noting the need to keep consumption of the food containing elevated levels of radioactive materials to a minimum.