Fukushima Daiichi crisis: Fallout
Public exposure in Japan15 August 2011
The earthquake and tsunami that hit Japan on 11 March has affected the entire country. Multiple agencies have been monitoring radiation release from the six 1970s BWRs at the Fukushima Daiichi site since then, both at the site and beyond, although predicting the long-term effects of the radiation remains premature. By Penny Hitchin
Units 4, 5 and 6 were undergoing planned maintenance outages when disaster struck. Units 1, 2, and 3 shut down automatically in response to the earthquake. The subsequent tsunami disabled the emergency diesel generators required to cool the reactors. A loss of cooling water to the reactors and to the spent fuel cooling ponds led to hydrogen explosions, fires, leaks and core meltdown. Over the following weeks the utility TEPCO (Tokyo Electric Power Company) battled to contain the damaged reactors, a situation, which a month later, continues to pose highly complex challenges.
The International Atomic Energy Association (IAEA)’s Convention on Early Notification of a Nuclear Accident requires civil nuclear nations to provide data about the accident’s time, location and radiation releases when trans-boundary radiation release is feared. This treaty, introduced following the 1986 Chernobyl nuclear accident, requires countries to have specific reporting mechanisms, giving internationally recognized figures for releases of radiation.
The utility which owns and operates Fukushima Daiichi, TEPCO has been releasing daily bulletins about the state of the reactors at Fukushima Daiichi and the results of its own radiation monitoring. Radiation monitoring across the whole country has been carried out by Japanese authorities, which have been releasing data regularly, some available in English. Two IAEA monitoring teams were dispatched to Japan following the accident.
The US Department of Energy carried out aerial monitoring in Japan and a team from the US National Nuclear Security Administration (NNSA) collected and analyzed data gathered from more than 40 hours of flights and thousands of ground monitoring points. In addition IAEA has been giving daily press releases, interpreting and clarifying the news from Japan. Greenpeace started monitoring outside the evacuation zones at the end of March.
As the stricken reactor sites continued to release radioactive liquid into the sea, TEPCO was authorised by the Japanese regulators to discharge 10,000 tons of low level contaminated water into the sea (to make capacity to store highly contaminated water), and monitoring of the marine environment was stepped up.
NHK, the Japanese Broadcasting Service reported April 4 that the Japanese government withheld the release of projections indicating high levels of radioactivity more than 30 km from FD1 following explosions at the plant. The estimates used the Education, Culture, Sports, Science and Technology Ministry (MEXT) System for Prediction of Environmental Emergency Dose Information (SPEEDi) for dispersal forecasts. The projections used available data and were based on the assumption that radioactive substances had been released for 24 hours from midnight on March 14th (Figure 1). The SPEEDi estimate showed that in some areas more than 30 km from FD1, radiation would exceed 100 milliSieverts (mSv) in people who remained outdoors for 24 hours between March 12th and 24th. This is 100 times higher than the 1 mSv-per-year reference level for humans recommended by the International Commission on Radiological Protection (ICRP). The figures, prepared on March 16 but not released until a week later, showed higher levels of radioactive substances to areas to the northwest and southwest of the plant. Japan’s Nuclear Safety Commission says it did not release the projections because the location or the amount of radioactive leakage was not specified at the time.
Separately, on April 4 the government said it had ordered the Japan Meteorological Agency to promptly disclose its data on the projected spread of radioactive materials from Fukushima Daiichi. Chief Cabinet Secretary Yukio Edano said in a news conference on April 4 that he had told the agency “should have made the data public along with an adequate explanation.” The projection formed part of reference materials compiled in response to a request from the International Atomic Energy Agency.
Graphs of radiation trends as of 4 April collected by local prefectures, and collected and plotted by the Japan Atomic Industrial Forum (Figures 2-5) show that radiation has generally fallen since mid-March, although there are large disparities between some sampling locations.
Environmental scientist Steve Jones told NEI magazine (on April 1) that the releases at Fukushima Daiichi are significant. Over the area 50 to 60 km from the site, the contamination levels are greater than were found over the same distance from the source after the UK Windscale Pile fire in 1957 (rated INES 5). However it is too early to make an assessment of the long-term effects on the health of the population. He says that after Chernobyl (INES 7), it took 5-10 years before information about the extent of early effects (particularly thyroid cancers in children) started to emerge.
Jones said that the major concern in Japan is the food chain: “The critical factor is how successful Japan will be in keeping contaminated foodstuffs out of the human food chain.” Terrestrial readings in Fukushima and neighbouring Prefectures are showing elevated levels of iodine-131 and caesium-137, with high localized contamination.
Jones says that the main area of potential concern is the terrestrial route. If radioactivity is released to the atmosphere it can be carried as vapour (iodine) or airborne particulate (iodine and caesium) before being deposited on the ground or on vegetation. Direct deposition onto foliage leads to high concentrations immediately after an accidental release, hence the prevalence of leafy vegetables in the lists of restricted foods. Grazing animals can consume the contamination. In the case of dairy cows grazing on contaminated vegetation, the effect will show up in the milk within a few days.
Much of the initial deposit will be removed from vegetation by weathering within a few weeks, with the radioactivity being transferred to the soil. Radioactive material in the soil can be taken up by plant roots and transferred back into the plant, although this will result in lower concentrations than were caused by the initial deposit onto vegetation.
Radioecologist Nick Beresford of the Centre for Ecology and Hydrology, Lancaster Environment Centre, has been looking at the implications of the release of radioactive material for the food chain. He told NEI that the farm animal management system in the affected prefectures involves keeping animals indoors most of the year. “A lot of the animal feed is imported, which will minimize the transfer through the food chain.”
Radioactive caesium will remain in the soil for a long time, but the rate at which it will transfer back to the plant depends on the soil type. Jones says, “The experience from Chernobyl is that caesium uptake by plants is highest when soil has low mineral content. Lowland pasture soils with higher mineral content bind the caesium and reduce the transfer back to plants.”
How long will food restrictions be necessary? Jones says that deposition levels to the northwest of the plant are very high and that while I-131 will disappear within a few months, caesium deposition will mean that areas with peaty or sandy soils may be under restriction for a long time. Restrictions were imposed on sale or movement of sheep from upland farms in the UK which received fallout from Chernobyl in 1986 and some are still in place 25 years later. Beresford says, “It looks as though restrictions and counter- measures will be in place for some time. From the current data it is difficult to tell the extent of the area which will be affected.”
The marine food chain is complicated: fish can take up of contamination through their gills as they respire, while filter feeders can pick up sediment. Contamination can be transferred up the food chain from phytoplankton through grazing and predatory organisms. Very high levels of contamination have been reported in seawater close to the Fukushima Daiichi site. As a fraction of the caesium becomes bound to sediment and can stay in place, Jones believes there are likely to be long term problems within a few kilometres of the site even if the leaks are stopped quickly.
By March 21 the Ministry of Health, Labour and Welfare had bans in place on distribution and consumption of fresh foods, including raw milk and leafy vegetables such as broccoli, cabbage, cauliflower, kakina, komatsuna and spinach, and turnips from Fukushima. The adjoining prefectures of Ibaraki (8), Gunma (10) and Tochigi (9) also had restrictions placed on spinach and kakina. But the next day Prime Minister Naoto Kan placed an indefinite ban on spinach and another local vegetable produced by Fukushima and neighbouring prefectures after samples were found to be abnormally radioactive. He also suspended Fukushima milk.
Standards hastily drafted by Japan’s Health, Labour and Welfare Ministry (HLWM) state milk or other dairy products containing more than 300 becquerels of radioactive iodine or 200 becquerels of radioactive caesium per kg cannot be shipped. The figure for vegetables is 2000 becquerels and 500 becquerels respectively.
HLWM published new food contamination data at the beginning of April. The analysis covered a total of 134 samples taken on 15 March (2 samples), 29-31 March (77 samples) and 1-2 April (55 samples). Analytical results for 133 of the 134 samples cover various vegetables, spinach and other leafy vegetables, mushrooms, strawberries, beef and pork, seafood and unprocessed raw milk in Chiba (12), Fukushima (7), Gunma (10), Ibaraki (8), Kanagawa (14), Kyoto (26), Niigata (15), Saitama (11), Shizuoka (22), Tochigi (9) and Tokyo (13). IAEA says that the analysis indicated that I-131, Cs-134 and/or Cs-137 were either not detected or were below the regulation values set by the Japanese authorities. Only one sample of shiitake mushrooms taken on 1 April in Fukushima prefecture was above the regulation values set by the Japanese authorities for I-131, Cs-134 and Cs-137.
On 4 April HLWM reported analytical results for a total of 24 samples taken on 31 March (4 samples) and 1st, 3rd and 4th April (20 samples). Analytical results for all of the 24 samples for various vegetables, strawberry and seafood in Gunma (10), Ibaraki (8), Niigata (15), Saitama (11) and Tochigi (9) indicated that I-131, Cs-134 and/or Cs-137 were either not detected or were below the regulation values set by the Japanese authorities. In neither report were the actual readings made available.
Monitoring of the marine environment is being stepped up as contaminated water continues to escape into the sea. The levels of Cs-37 and I-131 in the immediate vicinity of the plant are very high. On the coast of Fukushima (7), fishing and related activities have been halted. Japan’s Fisheries Agency believes that if radioactive materials are released into the sea, the concentration level will remain low, due to the huge volume of the seawater and the current of the sea. However, according to various east Asian news reports, exports and sales of Japanese seafood have been badly affected, as many foreign buyers put safety first and shun the products.
The Japanese Broadcasting Company NHK reported on April 5 that small fish caught in waters off the coast of Ibaraki Prefecture have been found to contain radioactive caesium above the legal limit. Ibaraki Prefecture (8) says 526 becquerels of radioactive caesium was detected in one kilogram of sand lances. The acceptable limit is 500 becquerels. It was the first time that higher-than-permitted levels of radioactive caesium in fish have been reported.
Fukushima Prefecture (7) relies on large-scale agricultural and fishery industries, supplying food to the 30 million people of Tokyo as well as further afield. The annual catch, of shore and ocean fish, is about 235,000 tons. The prefecture is Japan’s fourth largest farmland area; the Fukushima Basin is noted for its rice fields and orchards, while further inland the Aizu Basin produces high-quality rice, which is used by the local sake-brewing industry. Livestock is also important, although the Ministry of Agriculture, Forestry and Fisheries of Japan say that, because of winter conditions, most cattle, pigs and chickens are still indoors, and are being primarily fed on stored dried grass, silage and grain that has not been contaminated by the releases from Fukushima Daiichi.
Japan is self-sufficient in rice, a staple of the local diet. Fukushima produced 439,100 tons of rice last year, accounting for 5.3 percent of the nation’s total output, while neighbouring Ibaraki (8) prefecture, south of Fukushima, was Japan’s fifth-biggest rice producer with 392,800 tons. Miyagi prefecture (4), north of Fukushima, was ranked sixth with 391,300 tons.
Planting for the 2011 rice crop should have started in mid-April, but local news sources say that farmers are unlikely to go ahead unless they receive assurance from the government that their crops will be saleable. Japan’s Ministry of Agriculture, Forestry and Fisheries (MAFF) is reported to have started collecting data for each crop on acceptable levels of radioactivity in the soil. MAFF says it hopes to complete testing of 150 samples by mid-April.
Iodine tablet recommended for evacuees
On March 16 the Japanese Nuclear Safety Commission recommended that evacuees leaving the 20-kilometre area around Fukushima Daiichi should take a single dose of stable iodine, from 12.5mg-76mg, depending on age. Iodine is a trace mineral required by the body for the synthesis of the thyroid hormones which are essential for metabolism. Under normal circumstances people have approximately 20 to 30 mg of iodine in their bodies, most of which is stored in the thyroid gland. Ingesting stable iodine (usually in the form of potassium iodide, KI) is a precaution against the uptake of radioactive I-131 which can cause cancer by damaging cell DNA. This is especially serious if the cells are multiplying quickly – hence the importance of iodine tablets for infants, children and pregnant women. Further afield, notably in the USA, sales of potassium iodide tablets are reported to be soaring, despite the fact that local levels of I-131 detected are tiny.
Cs-137 has a half life of 30 years, but its biological half-life in humans is between one and four months. It behaves like potassium in the environment and in the body and can cause different kinds of cancer. If ingested, the half-life can be shortened by ingesting Prussian Blue, which acts as a solid ion exchanger absorbing the caesium while releasing potassium ions.
Undoubtedly there will be long term effects, political, operational and radiological, from the disastrous sequence of events at Fukushima Daiichi, but at this stage, with the site yet to stabilised, it is too early to predict how serious they will be, and how far they will extend.