Updated Oct 2, 2011
Plutonium detected outside N-plant site (Daily Yomiuri, Oct.2)
Plutonium believed to have been released from the crippled Fukushima No. 1 nuclear power plant after the March 11 earthquake has been detected outside the power plant site for the first time, it has been learned.
One of the spots found contaminated with the hazardous substance is 45 kilometers from the plant.
A map released by the Education, Culture, Sports, Science and Technology Ministry on Friday shows plutonium was found in soil samples taken from a total of six locations in Futabamachi, Namiemachi and Iitatemura, Fukushima Prefecture.
The map is based on a survey conducted by the ministry to determine how much soil around the power plant contains plutonium and strontium, which is also a hazardous radioactive substance.
However, a ministry official said because amounts of both substances were very small, decontamination efforts should focus on radioactive cesium.
The survey was conducted in June and July by sampling soil at 100 locations around the plant. The ministry compared the data obtained from the survey with data obtained in surveys conducted from fiscal 1999 to fiscal 2008 to measure the residual effects of radioactive fallout on Japan from nuclear atmospheric tests conducted during the Cold War.
The six spots where plutonium was detected are all in the no-entry zone, within a 20-kilometer radius of the plant, or in the expanded evacuation zone outside the no-entry zone, which may be exposed to more than 20 millisieverts of radioactive substances within a year from the accident.
Four becquerels per square meter of plutonium-238 was detected at one site in Namiemachi in the latest survey. This is about half of the maximum quantity of 8 becquerels detected in the 1999-2008 surveys.
A preliminary ministry calculation shows that the level of plutonium contamination in Namiemachi will remain at 0.027 millisieverts for about 50 years. The other five spots were contaminated with 0.55 to 2.3 becquerels of plutonium.
The farthest spot from the plant where plutonium was detected was in Iitatemura, about 45 kilometers from the plant.
Meanwhile, strontium-89 and strontium-90, both believed to have been released from the power plant, were detected at 45 spots.
The maximum quantity of strontium-90, whose half-life of about 29 years is much longer than the approximately 50-day half-life of strontium-89, was 5,700 becquerels per square meter detected in Futabamachi. This is six times that of the maximum quantity of 950 becquerels found before the Fukushima plant accident.
Plutonium detected 45 kilometers from nuke plant
Small amounts of plutonium have been detected in samples of soil taken at locations including a spot 45 kilometers away from the troubled Fukushima Daiichi nuclear plant. This is the first time that the government has detected plutonium outside the nuclear plant since the accident.
The science ministry announced on Friday that the plutonium was detected in samples taken from 6 locations in the towns of Futaba and Namie, and Iitate Village in Fukushima Prefecture — all located northwest of the nuclear plant. The radioactive substance is believed to have been released by the nuclear plant after the disaster.
The ministry says the samples taken from a location in Iitate, farthest among the 6, contained 0.82 becquerels per square meter of plutonium-238 and a total of 2.5 becquerels of plutonium-239 and -240.
The ministry had collected soil samples at 100 locations within an 80-kilometer radius of the plant in June and July.
Experts say that if plutonium is inhaled or ingested, it remains in the body for a long time and can cause cancer.
But ministry officials say that possible exposure to the detected plutonium is believed to be very low.
In June, university researchers detected smaller amounts of plutonium in soil outside the plant after they collected samples during filming by NHK.
Friday, September 30, 2011
Plutonium has been detected at six locations in Fukushima Prefecture, including Iitate village around 45 km northwest of the Fukushima No. 1 nuclear plant, which suffered three reactor meltdowns after the March 11 earthquake and tsunami, science ministry officials said.
It is the first time the government has confirmed the spread of plutonium outside Tokyo Electric Power Co.’s stricken plant. The plutonium turned up in soil samples.
The detected amounts of plutonium were small and posed no danger to health, the officials said.
Plutonium has an extremely long half-life and is associated with a high risk of cancer if it enters the human body via breathing or other means.
“Because the fuels (in the reactors) melted down, plutonium may have been emitted with steam or other small particles and sent airborne,” a Tepco official said. “(Judging by the amount of plutonium) it is believed to be from the accident.”
The science ministry has also looked into radioactive strontium and detected the isotope at several dozen observation sites out of 100 it inspected, including a location about 80 km from the Fukushima plant
See also Plutonium detected in soil outside Fukushima nuclear plant (Japantoday.com, Oct. 01, 2011) |
Cesium fallout map illustrates Kanto levels
The science ministry’s latest aerial monitoring over Chiba and Saitama prefectures in September confirmed that radioactive cesium released from the Fukushima No. 1 power plant has contaminated parts of the Kanto region.
A ministry report released Thursday revealed that contamination was found in northern Chiba, including the cities of Kashiwa, Matsudo and Abiko, and in the mountainous areas of Chichibu in Saitama Prefecture’s west and Misato in the prefecture’s east.
The highest contaminated areas contained between 60,000 to 100,000 becquerels of cesium-134 and -137 per square meter, it showed. Cesium-134 has a half-life of two years and the one for -137 is 30 years.
Radiation levels in the area were between 0.2 to 0.5 microsieverts per hour, the report said.
Simply calculated, if a person is exposed to 0.5 microsieverts per hour for 365 days, the total dose would be 4.38 millisieverts. Exposure to a cumulative radiation dose of 100 millisieverts increases one’s cancer risk by 0.5 percent, scientists say.
Kyodo News reported that radioactive materials spewed from the plant are estimated to have spread in a northwest direction to the mountain areas near the city of Fukushima before winds shifted southwest, sending the materials into the western part of Gunma Prefecture.
Radioactive materials detected in Ibaraki Prefecture are believed to have also been carried by the wind into the northern part of the prefecture before some were blown into the Pacific Ocean, Kyodo reported. However, it is estimated that the wind carrying radioactive isotopes again changed direction, this time contaminating northwestern parts of Chiba Prefecture.
The aerial monitoring was conducted in the two prefectures between Sept. 8 and 12 as part of the science ministry’s effort to draft a contamination map of 22 prefectures, from Aomori Prefecture in the north to Aichi Prefecture in the west. In cooperation with local governments, the ministry had completed maps of eight prefectures in the Tohoku and Kanto regions as of Thursday.
The ministry plans to release results of aerial monitoring it has conducted over Tokyo and Kanagawa by the end of October.
A city office in Fukushima Prefecture has launched a section dedicated exclusively to monitoring and removing radiation discharged from the disaster-stricken nuclear plant.
Nihonmatsu City launched the 6-member section on Friday.
The city is about 50 kilometers from the Fukushima Daiichi nuclear plant. Relatively high levels of radiation have been detected in parts of the city.
One township recently found radioactive cesium in pre-harvest rice at levels as high as the government’s safety limit.
The new section is to measure levels of radioactive substances in soil, well water and crops, and draw up a decontamination plan for the city.
NHK Friday, September 30, 2011
Radiation spread reaches Chiba and Saitama (Asahi, Oct 1)
Fairly high levels of accumulated radioactive cesium in Chiba and Saitama prefectures were shown in a new contamination map released by the science ministry on Sept. 29.
The two prefectures, neighboring the municipal areas of Tokyo, are located about 200 kilometers from the disabled Fukushima No. 1 nuclear power plant. The measurements for Chiba and Saitama prefectures were taken from Sept. 8 to Sept. 12 using helicopters.
In Chiba Prefecture, the highest levels of cesium-137, between 30,000 and 60,000 becquerels per square meter, were detected in northern areas, such as Kashiwa, Matsudo, Abiko and Nagareyama. Cesium-137 has a half-life of 30 years.
In Saitama Prefecture, some mountainous areas of Chichibu, located 250 km from the plant, recorded 30,000 to 60,000 becquerels per square meter.
In the 1986 Chernobyl nuclear accident, areas with 37,000 becquerels or more of radioactivity per square meter were designated contaminated zones, while levels of 555,000 becquerels or more required forcible relocation.
In Chiba and Saitama prefectures, the highest radiation levels were 0.2 to 0.5 microsievert per hour. In most other areas, the radiation levels were 0.1 microsievert or less.
Government planners investigated the risk of terrorists attacking a nuclear power plant in Japan but concluded there was little risk of a release of radioactive substances, according to a secret government report obtained by The Asahi Shimbun.
The officials concluded that the safety of nuclear power plants was ensured by multiple layers of security, according to the document presented to lawmakers by officials at the Science and Technology Agency and the Ministry of International Trade and Industry in 1997. No action has since been taken on the issue.
The report said that intruders might try to steal nuclear fuel from a plant or release radioactive substances by damaging piping or changing the operation of the reactor.
But its authors concluded that it would be difficult for outsiders to enter the containment vessels that house pipes carrying nuclear materials because of their solid construction. In any case, the report said, nuclear substances would not immediately leak outside of the building if piping was severed.
It said reactors could be suspended by remote control even if intruders did manage to take over the central control room.
The document was distributed at a meeting of lawmakers organized by the Security Council of Japan at the Prime Minister’s Official Residence in September 1997 and was collected again after the meeting. Prime Minister Ryutaro Hashimoto was present.
At the meeting, Fumio Kyuma, director-general of the Defense Agency, said it was necessary to mobilize the Self-Defense Forces more promptly.
Nuclear power plants are generally guarded by security companies, which inform police when they detect suspicious individuals. SDF personnel are mobilized only when police cannot deal with the case.
Seiroku Kajiyama, the chief Cabinet secretary at the time, told a news conference that extremely strong safeguards were taken at nuclear power plants against attacks by outsiders.
Police introducing radiation-proof vehicles (NHK, Friday, September 30, 2011)
Japan’s National Police Agency will introduce radiation-proof vehicles as part of stepped-up counter-terrorism measures at nuclear power plants.
The agency says the new vehicles will be installed at 9 police headquarters in the country. The vehicles are shielded with lead, which blocks radiation.
The vehicles will enable police officers to protect themselves from radiation when apprehending terrorists and rescuing the injured in cases of terror attacks or accidents at nuclear plants.
In the wake of the September 11th attacks in the United States in 2001, Japanese police have been guarding some of the country’s nuclear plants and related facilities. Armed officers and bullet-proof vehicles are on duty around the clock.
Agency officials say they are stepping up counter-terrorism measures in the belief that the accident at the Fukushima Daiichi plant has increased the likelihood of nuclear facilities being targeted.
Asahi, Aug 1
The Foreign Ministry had simulated a possible attack on nuclear plants in 1984 that included a scenario in which all power sources were lost–as occurred at the Fukushima No. 1 nuclear plant–but chose to keep the results confidential, The Asahi Shimbun learned.
If the ministry report had been shared with many officials in the government, it could have helped to raise attention to the need to prepare for a possible nuclear power station blackout.
The ongoing nuclear crisis was triggered by a complete loss of the electricity grid, emergency diesel generators and depletion of backup batteries in the March 11 Great East Japan Earthquake and tsunami. Pumps for cooling water were also broken down in the disaster.
The report on the study of possible attacks on nuclear facilities and projected damages, compiled in February 1984, was obtained by The Asahi Shimbun.
It is the first of its kind known to have been compiled by the government. The report’s first scenario anticipated that a complete loss of power sources would lead to a situation where damaged fuel rods would fall to the bottom of the containment vessel, breaching the vessel. That would result in the leakage of radioactive materials into the atmosphere. The report also projected that a hydrogen explosion would likely be triggered.
This is precisely what occurred in the No. 1 and No. 3 reactors at the Fukushima No. 1 nuclear plant.
The station blackout scenario came to be discussed in the 1990s and later in Japan. But no adequate measures were taken to address the possibility.
Tetsuya Endo, who was involved in the compilation of the report as an official at the ministry’s division handling affairs related to the United Nations, said the report was designed to be just a reference for the ministry.
“No measures were taken for nuclear facilities” to improve safeguards, Endo said.
The report projected up to 18,000 deaths from acute radiation exposure in an attack on a nuclear reactor that damages the containment vessel and the cooling system, resulting in a meltdown and immediate release of radioactive materials into the air.
But the ministry decided not to disclose results of the study, even to the prime minister’s office, fearing it could inflame the anti-nuclear power movement.
The United States and European countries carry out contingency drills based on studies simulating terror attacks on nuclear power plants.
The ministry commissioned the study to the Japan Institute of International Studies, a private organization, after the global community was shaken by Israel’s bombing of a research nuclear facility in Iraq in 1981.
The attack did not lead to a leak of radioactive materials because the nuclear reactor was under construction at the time. More here