A magnitude 9 earthquake struck Japan on 11 March 2011, triggering a powerful tsunami and severely damaging the Fukushima Daiichi nuclear power station. This is the story of the struggle to regain control of the failing station, and to deal with the released radioactivity. It had been compiled from the continuing and excellent reporting by the Nature News team.
Created by edyong209 on Apr 1, 2011
Last updated: 02/28/12 at 06:01 AM
Tags: fukushima nuclear japan earthquake tsunami
Today the Japanese government announced that three reactors that suffered meltdowns in early March had officially reached “cold shutdown”. Perhaps inevitably, many in the press are reporting the announcement as a “major milestone” in the Fukushima saga. But in truth, cold shutdown will mean very little in any practical sense for what goes on at the plant. Nor is it likely to change the fate of the thousands of evacuees who were forced to leave their homes after the Fukushima crisis.
http://www.nature.com/news/fukushima-reaches-cold-shutdown-1.9674
Two Japanese members of parliament, writing in Nature, call for the stricken nuclear plant to be nationalized so scientists can find out exactly what happened.
http://www.nature.com/nature/journal/v480/n7377/full/480313a.html
The nuclear accident at the Fukushima power plant in Japan has prompted the World Association of Nuclear Operators (WANO), the industry's self-regulating body, to broaden its remit from accident prevention to regulating and verifying how well plants are prepared to cope with a serious nuclear accident and mitigate its consequences. But WANO seems likely to stop short of publicly identifying plants that have failed to address safety and other issues.
http://www.nature.com/news/nuclear-industry-safety-body-takes-on-lessons-of-fukushima-1.9401
The distribution of fallout from the crippled Fukushima Daiichi nuclear power plant has now been mapped by two independent teams. The charts reduce the uncertainty surrounding the amount of contamination across Japan, and help to show which areas should be safe to return to farming.
http://www.nature.com/news/fukushima-maps-identify-radiation-hot-spots-1.9355
The distribution of fallout from the crippled Fukushima Daiichi nuclear power plant has now been mapped by two independent teams. The charts reduce the uncertainty surrounding the amount of contamination across Japan, and help to show which areas should be safe to return to farming.
http://www.nature.com/news/fukushima-maps-identify-radiation-hot-spots-1.9355
With the Fukushima nuclear reactors seemingly under control, the Japanese government is now facing the daunting task of cleaning up the highly contaminated areas around the reactors so that residents can move back. But it is estimated that more than 100 million cubic metres of soil and debris will need to be removed. Where does one get started?
http://www.nature.com/news/japan-funds-projects-to-clean-up-fukushima-1.9351
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.
http://www.nature.com/news/2011/111025/full/478435a.html
The discovery of 'hot spots' of radioactive material is spreading fear far beyond the damaged Japanese nuclear power plant at Fukushima. But experts say that there is no threat from the small spots of increased radioactivity now being discovered in large-scale surveys.
http://www.nature.com/news/2011/111014/full/news.2011.593.html
Japan has launched a long-term project to monitor children near the Fukushima nuclear plant for thyroid problems.
On 9 October health workers tested the first 100 of a planned 360,000 children who were under 18 when the crisis began in March. They will be tested again every two years until they turn 20, then every five years thereafter.
http://blogs.nature.com/news/2011/10/japan_begins_thyroid_screening.html
Some of the most recent data from Fukushima allow the best comparison yet with Chernobyl. Click the link below to see our Google Earth graphic that compares the radioactive fallout from each meltdown.
http://blogs.nature.com/news/2011/09/directly_comparing_fukushima_t.html
Six months after the disaster that caused three meltdowns, efforts to stabilize the Japanese nuclear power plant continue. And the work will not be completed for decades to come.
http://www.nature.com/news/2011/012345/full/news.2011.525.html
It appears that the Japanese government is close to announcing what many of us have suspected since the nuclear crisis at Fukushima Daiichi began: some people won't be going home.
The potential exclusion zone around the Fukushima plant. It will mainly include villages less than 19 kilometers from the plant, but look closer and the situation is much more complicated than that.
http://blogs.nature.com/news/2011/08/does_japans_new_fukushima_excl.html
On 11 March, the Japan Meteorological Agency (JMA) warned that a 3-metre-plus tsunami would hit northeastern Japan. In fact, the wave that came ashore stood more than 10 metres high — reaching 50 metres in some places.
In the future, the agency will no longer forecast a tsunami wave's height for earthquakes of magnitude eight or above, warning instead of "the possibility of a huge tsunami".
http://www.nature.com/news/2011/110811/full/news.2011.477.html
After the Fukushima nuclear disaster spewed radiation across northern Japan, some feared that farming there would be shut down for years. But early studies of how the radiation has accumulated in plants and the soil now suggest that farmers in much of the region can go back to work. But the most contaminated soils need urgent clean-up.
http://www.nature.com/news/2011/110712/full/475154a.html
Japanese broadcaster NHK reports 110,000 tons of radioactive water are stagnating in Fukushima’s reactor basements and turbine halls. At Unit 2, temperatures inside the reactor building and turbine hall are around 30 degrees C and humidity levels around 99.9%, effectively making it Japan's most radioactive sauna. TEPCO’s plans to decontaminate the water have been delayed by leaks in the reprocessing equipment, further hindering any clean-up operations.
http://blogs.nature.com/news/2011/06/fukushima_still_wet_n_wild_1.html
Scientists working with the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) are calling for the public release of data about radiation levels around Fukushima. Since the accident, the CTBTO’s global network of 63 monitoring stations has been collecting data about radiation levels. These have been shared with governments around the world but not academics or the public.
Now, the CTBTO’s own scientists want the data released to the wider scientific community, so unanswered questions about the network’s performance and the spread of radiation can be addressed.
http://www.nature.com/news/2011/110613/full/news.2011.366.html
Radioactive water has become the biggest obstacle to cleaning up the Fukushima site. More than 100,000 tonnes of water are swilling around various parts of the site, and work has slowed to a crawl. Storage tanks are rapidly reaching capacity and, if the trend continues, drainage trenches will start overflowing as early as 20 June, according to a TEPCO report.
The failed proposal to install a closed-loop cooling system left TEPCO with few good options. It plans to install a decontamination system to remove radio¬isotopes from the water so that it can be reused to cool the reactors, which will need cooling for many months to come. The system is expected to be up and running on 15 June but it will still generate large amounts of radioactive waste. And experts fear that the salt content of the water will make the decontamination process less efficient.
TEPCO estimates that it will need to decontaminate some 250,000 tonnes of water by mid-January 2012, when it hopes the reactors will finally be cool enough to shut down permanently.
http://www.nature.com/news/2011/110607/full/474135a.html
In a preliminary assessment, French scientists estimate that in the first 30 days after 11 March, trees, birds and forest-dwelling mammals were exposed to daily radiation doses up to 100 times greater than are generally considered safe. However, land species may get off lightly because the accident happened early in the flowering season.
Aquatic organisms, like fish, molluscs, crustaceans and seaweed, were hit even harder, by doses so large that they are likely to markedly increase mortality.
Meanwhile, the Japanese government is preparing an environmental monitoring programme that involves around 300 experts from across the country. The accident could help scientists to gain a better understanding of the effects of nuclear radiation on wildlife and the environment. Fukushima could become the natural observatory site that Chernobyl never did because of political circumstances.
http://www.nature.com/news/2011/110527/full/news.2011.326.html
Radioactive water from the cores of three damaged reactors appears to be leaking. TEPCO initially hoped that the leaks were largely coming from pipes that could be repaired, but they now concede that both the reactors' pressure vessels and primary containment vessels, which are designed to contain an accident, are probably leaking water.
TEPCO had also hoped to pump any water used to cool the cores into storage tanks, to prevent it from flowing into the basements of buildings and the Pacific Ocean. But it seems that the storage tanks are also leaking.
The leaks will probably force TEPCO to abandon its plans to set up a recirculation system that can cool the reactor cores without dumping water straight into them. That's a serious blow to efforts to bring the reactors to a safe temperature within months. In a new plan, TEPCO will instead try to recirculate water from the basements of the damaged buildings into the reactor cores.
http://blogs.nature.com/news/2011/05/fukushima_nuclear_plant_is_lea_1.html
A preliminary analysis suggests that a fire inside the unit 4 reactor building at the Fukushima Daiichi nuclear power plant may have been sparked by hydrogen gas from unit 3.
The new findings contradict previous reports of serious fuel damage at the unit 4 reactor and may mean that clean up of its fuel will be less difficult than previously feared.
A common ventilation system shared by the two reactors could have allowed explosive hydrogen gas to seep from unit 3 to unit 4, a new analysis from the Tokyo Electric Power Company (TEPCO) concludes. The work is preliminary and could still turn out to be wrong, the company emphasized. But it could explain why fuel inside unit 4 appears mostly intact, contrary to early reports of heavy damage.
http://blogs.nature.com/news/2011/05/exclusive_fire_in_fukushima_un.html
The unit 1 reactor at Japan's Fukushima Daiichi nuclear plant melted down entirely after a massive earthquake and tsunami struck on 11 March, according to analysis from the plant's owners, the Tokyo Electric Power Company.
Data provided by recalibrated equipment inside the reactor indicates that the fuel rods had lost their surrounding coolant four and a half hours after the tsunami arrived. Most of the fuel had probably already fallen to the bottom of the vessel by the time it was flooded with sea water. The full meltdown will complicate future clean-up efforts.
http://blogs.nature.com/news/2011/05/understanding_the_complete_mel.html
The Tokyo Electric Power Company has released some video of what could arguably be the least glamorous job on Earth right now: going inside the damaged Fukushima Daiichi power station to set up ventilation equipment. The video is about a minute long and shows what appears to be filtration equipment in place inside the reactor's turbine hall. The company also released some video of the spent fuel pools at the unit 3 and unit 4 reactor.
Workers entered the buildings that house the damaged unit 1 reactor at Fukushima nuclear power plant. They didn't hang around for long, since robot scouts had shown dangerously high levels inside the building.
But their presence was necessary. TEPCO, the plant's operators, want to get cooling water re-circulating - rather than continually pumping in water which becomes highly radioactive and must be disposed of.
To do that, workers have to install blowers to filter out some of the radioactive isotopes from the air, and new instruments to monitor the reactor water level.
http://blogs.nature.com/news/2011/05/why_workers_must_risk_entering_1.html
A new analysis posted to the popular physics preprint server ArXiv.org suggests that the damaged reactors at Fukushima Daiichi have not restarted their nuclear processes since 11 March. The work is not peer-reviewed, and like all speculation about Fukushima, it is based on sketchy and sometimes incorrect readings from the plant.
By examining two much-discussed (and much recorded) isotopes from the accident: Iodine-131 and Caesium-137, Tetsuo Matsui, a physicist at the University of Tokyo, concludes that the reactors likely shut down successfully and did not restart. But he suspects something may have happened at the fuel pool at unit 4—perhaps contamination or a brief burn of some of the fuel in the pool.
http://blogs.nature.com/news/thegreatbeyond/2011/05/analysis_suggests_fukushima_re_1.html#more
The Japanese government has started to enforce its 20-kilometre exclusion zone around the Fukushima nuclear plant, to stop people from returning to irradiated land. Roughly 27,000 households are included in the zone. From 21 April, unauthorized entry was declared illegal; checkpoints block the routes in. At the Fukushima plant itself, robots continued surveying the reactor cores while workers of the Tokyo Electric Power Company injected cooling water into the reactors and to pump radioactive water out into storage buildings.
http://blogs.nature.com/news/thegreatbeyond/2011/04/evacuations_are_now_mandatory.html
One month after the earthquake and partial meltdown of fuel at the Fukushima nuclear plant, Nature Video provides a brief summary of events so far, and what lies ahead for the damaged reactors.
http://blogs.nature.com/news/thegreatbeyond/2011/04/video_the_fukushima_nuclear_cr_1.html
Ever since a massive earthquake and tsunami struck the Fukushima Daiichi nuclear power plant on 11 March, activities at the site have been hasty, improvised, and often uncoordinated.
But that all changed today, when plant owners TEPCO put forward a plan, complete with flowchart, to stabilize the plant within six to nine months.
According to the strategy, workers will continue to douse damaged reactors and spent fuel pools with cooling water, while in parallel developing techniques to store and decontaminate used water on the site. The company also plans to cover the damaged reactors with temporary structures, in order to limit the release of radioactivity.
http://blogs.nature.com/news/thegreatbeyond/2011/04/fukushima_crisis_gets_a_flowch.html
Over the weekend, remote-controlled robots entered the Fukushima Daiichi nuclear power plant. The robots took the first photos inside the units 1 and 3 reactors and assessed radiation levels.
The Tokyo Electric Power Company (TEPCO) sent Packbots, from the American company iRobot. Packbots are used for explosive ordinance disposal in Iraq and Afghanistan, but in the wake of the nuclear accident iRobot sent two to Fukushima, along with two larger Warrior bots. The robots are equipped with cameras and radiation detector equipment, and are even capable of opening doors (if they're not locked).
The robots detected peak radiation levels of around 50 millisieverts per hour inside units 1 and 3 - meaning that rates in some places at least were far too high for human workers to enter the plant.
http://blogs.nature.com/news/thegreatbeyond/2011/04/robots_enter_fukushima.html
Days of work to shift radioactive water made little impact on amounts of the water leaking from the damaged Fukushima plant.
TEPCO estimated some 50,000 tons of highly radioactive water on site, and fresh water (for cooling) was being pumped into the reactors at around 6/7 tons per hour.
Short-term efforts to contain the radioactive water included using zeolite sandbags, or waste tanks on land.
And a report from the Atomic Energy Society of Japan said that it would take a minimum of 2-3 months to stabilize the reactors. It corroborated the opinions of others that the unit 1, 2 and 3 reactors at the plant suffered a partial meltdown.
http://blogs.nature.com/news/thegreatbeyond/2011/04/fukushima_stable_but_radioacti.html
The Japanese government officially upgraded Fukushima on the International Nuclear Events Scale to a 7, or "Major accident".
The new rating was the highest possible on the scale, and had only previously been used to describe the Chernobyl disaster in 1986.
The assessment was changed after the Japanese Nuclear and Industrial Safety Agency re-evaluated the amount of radiation released, which it said was one-tenth of that from Chernobyl.
http://blogs.nature.com/news/thegreatbeyond/2011/04/how_fukushima_is_and_isnt_like_1.html
Another powerful earthquake, this one magnitude 6.6, struck less than 600 kilometres to the southeast of Fukushima, disrupting operations for about an hour.
Meanwhile, the Japanese government said it would expand the evacuation zone around the plant to some regions beyond an existing 20-kilometre radius. Those regions were seeing radiation exposure rates above 20 millisieverts a year.
The new evacuation zones showed an increasing level of sophistication from Japanese authorities, who until now had concentrated mainly on setting up circular exclusion zones - even though weather conditions could carry radiation further.
Many citizens, though, were not happy with the situtation. On 10 April, thousands marched in Tokyo to protest nuclear energy. Meanwhile, Fukushima's governor refused to meet with executives from the Tokyo Electric Power Company which runs the plant. Bottom line: authorities were getting a handle on the nuclear fallout from the plant, but the political fallout was just beginning.
http://blogs.nature.com/news/thegreatbeyond/2011/04/new_evacuations_announced_as_e.html
As the immediate threat from Fukushima Daiichi's damaged nuclear reactors recedes, engineers and scientists were facing up to a clean-up process that could last for many decades, or even a century.
Radiation around the plant is beginning to wane, but with massive aftershocks striking nearby, the threat of further releases has not yet passed.
The first priority will be to deal with the radioactive water around the site. It could be years before anyone can look inside the cores themselves, with robots and humans sharing the inspection work. Indeed, the effort required seems likely to be more akin to the clean-up strategy at Chernobyl in the Ukraine than that of Three Mile Island.
TEPCO almost certainly cannot afford a clean-up on this scale. "I think that, ultimately, the government is going to have to pay for it," says Robert Alvarez at the Institute for Policy Studies in Washington DC, who oversaw clean-up of former US nuclear weapons plants during the administration of President Bill Clinton.
Given the complexity of the task ahead, some thought it might be better to abandon Fukushima entirely — at least for the time being. But with the threat of earthquakes, tsunamis and typhoons in the future - is that a wise strategy?
http://www.nature.com/news/2011/110411/full/472146a.html
Trying to stop another massive explosion, TEPCO began bleeding nitrogen gas into the heavily damaged reactor 1 at Fukushima Daiichi. The inert nitrogen would, in theory, keep volatile hydrogen and oxygen from mixing inside the containment vessel and reactor. The injection would continue over the next week.
http://blogs.nature.com/news/thegreatbeyond/2011/04/fukushima_update_nitrogen_begi_1.html
North-eastern Japan had been buffeted by a constant stream of 4 and 5 magnitude aftershocks ever since the 11 March 9.0 quake.
But at nearly midnight local time on 7 April, a powerful 7.1 magnitude hit the disaster region, marking the largest aftershock yet. It occurred at 13.1 kilometres depth 330 kilometres northeast of Tokyo, according to the US Geological Survey.
At Fukushima, workers were temporarily evacuated - a reminder of the fragility of the situation.
http://blogs.nature.com/news/thegreatbeyond/2011/04/new_quake_rocks_japan.html
Good news: TEPCO announced it had staunched the flow of extremely radioactive water into the sea from the Fukushima plant, by injecting 5,000 litres of 'coagulant'.
Bad news: New evidence suggested the situation inside the reactors themselves could be far grimmer than the Japanese had admitted. The New York Times cited a leaked 26 March document from the US Nuclear Regulatory Commission, suggesting the reactors were in terrible shape. Fuel inside the cores might be so melted down that cooling water couldn't circulate properly, the report said. And old fuel (from the reactors' spent-fuel pools) might have scattered a mile after hydrogen explosions rocked the reactors - making cleanup all the more difficult.
http://blogs.nature.com/news/thegreatbeyond/2011/04/water_stops_at_fukushima_but_b.html
Academic researchers worldwide pored over releases of data on population exposure rates to radioactive fallout from the Fukushima nuclear disaster. But they found it hard to make any sense of the data.
Data was strewn across many webpages from various agencies and ministries, often in different units and with no clear details of sampling techniques used.
In a joint statement to Nature (see go.nature.com/cckfoe), the RERF's vice-chairman and chief of research Roy Shore, and Kotaro Ozasa, its head of epidemiology, said it was vital to gather baseline data — such as the exact locations of people exposed to fallout — as soon as possible.
"The problem is that it is very difficult to get a real picture of the exposure of the population," said Elisabeth Cardis, a radiation epidemiologist at the Centre for Research in Environmental Epidemiology in Barcelona, Spain.
Still, first measurements showed minimal radioiodine doses in the thyroids of children in the most contaminated areas around the Fukushima plant.
http://www.nature.com/news/2011/110405/full/472013a.html
The operator of the Fukushima power plant, TEPCO, began deliberately discharging thousands of tons of radioactive water into the sea. The company needed to make room in storage tanks for highly radioactive water that was flooding the basement of the turbine buildings of reactor 2.
Separately, nuclear engineers continued to debate the extent of damage to Fukushima's reactor units. US Energy secretary, Steven Chu, reckoned 70% of the core of reactor 1 might be damaged.
http://blogs.nature.com/news/thegreatbeyond/2011/04/fukushima_update_tepco_forced.html
Japan's chief cabinet secretary, Yukio Edano, told a news conference that it could be several months before radioactive particles stop being released from the Fukushima nuclear plant.
http://blogs.nature.com/news/thegreatbeyond/2011/04/fukushima_update_tepco_forced.html
Japan’s Nuclear and Industrial Safety Agency claimed that TEPCO had released incorrect data on groundwater contamination, although the agency did not dispute that groundwater had been contaminated. TEPCO also came under fire for not providing its workers with radiation monitoring badges, although the company claimed that many of its supplies had been destroyed in the quake and tsunami.
Water is still being pumped into the reactors to cool their fuel rods, while more pumping trunks are on the way. TEPCO plans to spray a water-soluble resin over debris around the plant to damp down radioactive dust that could be blown into the air.
TEPCO confirmed that its four damaged nuclear reactors will have to be scrapped, at a cost of billions of dollars.
http://blogs.nature.com/news/thegreatbeyond/2011/04/fukushima_update_more_radiatio.html
The US Department of Energy revealed that ground radioactivity around the plant had continued to fall since 17-19 Mar, with no significant extra dumps of radioactive material. The survey flights picked up higher-than-background levels more than 40km away from the plant, but not enough to warrant evacuation.
However, the International Atomic Energy Agency (IAEA) confirmed that people should be urgently evacuated from localised hotspots northwest of the plant. These hotspots contained levels of radioactivity one or two orders of magnitude above the evacuation threshold – 25 megaBecquerels per square metre of iodine-131 and 3.7 megaBq/m2 of caesium-137.
http://blogs.nature.com/news/thegreatbeyond/2011/03/fukushima_update_against_the_o_1.html
Reports from the International Atomic Energy Agency (IAEA) indicated that the plant’s discharge pipes were continuing to feed high levels of radioactive material into the surrounding seawater, with no decrease in sight. Readings of 130 000 Bq/l of iodine-131, 32 000 Bq/l of caesium-137 and 31 000 Bq/l of caesium-134 were reported near Units 1 – 4, far higher than the recommended maximum coastal discharges of 4,000 Bq/l or lower.
http://blogs.nature.com/news/thegreatbeyond/2011/03/fukushima_update_local_contami_1.html
Extremely radioactive floodwater in the basements of Units 1-3 continued to hamper attempts to get the reactors under control. The areas need to be pumped and cleaned to get to the cables connecting the control rooms and coolant systems. Workers had also started trying to pump contaminated water out of the piping trenches outside the reactors building.
http://blogs.nature.com/news/thegreatbeyond/2011/03/fukushima_update_against_the_o_1.html
The radioactive water in the basement of Unit 2 seemed to be seeping into piping trenches outside the main reactor buildings, less than 70m away from the seashore. The seepage raised the spectre of serious contamination of sea and groundwater.
http://www.nature.com/news/2011/110329/full/471555a.html
NHK reported that floodwater in the basement of Unit 2 contained radioactivity levels 10 million times higher than normal. The reported dose of 1,000 milliSieverts per hour would be lethal within a few hours of exposure, and workers were evacuated. However, TEPCO later said that the readings must have been a mistake..
http://blogs.nature.com/news/thegreatbeyond/2011/03/breaking_news_fukushima_radioa.html
After a week of growing optimism, new reports stimulated fresh concerns about the Fukushima plant. Japan's Nuclear and Industrial Safety Agency today said that the core of Unit 3 had probably been breached, resulting in highly contaminated water. Radioactive elements in the water included non-volatiles like cobalt-60, which must have come from broken fuel rods in the water. Unit 3 was also the only reactor in the plant to use plutonium, increasing the hazards of a leak. Pools of contaminated water were also found in Units 1, 2 and 4.
TEPCO started using freshwater provided by two US Navy barges to cool the reactors, in place of seawater. Salt crusts formed by the seawater were threatening to heat the fuel rods up more quickly, leading to the release of more radioactive material.
Evacuation zones were extended by a further 10km around the plant. The government encouraged people in those areas to leave voluntarily. Meanwhile, monitoring stations detected fallout from Fukushima as far away as Western Europe, albeit at dilute and negligible levels.
http://blogs.nature.com/news/thegreatbeyond/2011/03/fukushima_crisis_new_setbacks_1.html
Japan’s science ministry detected radioactive isotopes in surface seawater near Fukushima. At a site 30km off-shore, they measured abnormally high levels of iodine-131 (24.9 to 76.8 Becquerel per litre) and caesium-137 (11.2 to 24.1 Bq/l).
Later, the International Atomic Energy Agency reported that radioactivity levels near the plant's discharge pipes were increasing, with 74,000 Bq l−1 of iodine-131 and 12,000 Bq l−1 of caesium-134 and caesium-137 combined. Recommended maximum coastal discharges from nuclear power plants are typically lower than 4,000 Bq l−1. Japan has banned all fishing within 20 km of the Fukushima plant.
http://blogs.nature.com/news/thegreatbeyond/2011/03/fukushima_crisis_new_setbacks_1.html
The Japanese science ministry, MEXT, released radioactivity readings for soil and pond samples near Fukushima. On 19 Mar, upland soil at a site 40km northwest of the plant contained 28,100 Becquerels per kilogram of Cs-137 and 300,000 Bq/kg of I-131. One day later, these same figures were 163,000 Bq/kg of Cs-137 and 1,170,000 Bq/kg of I-131.
Radioactivity levels exceeding safety levels for infants had been found at water purification plants serving several cities. One plant detected 298 Bq/kg of I-131, almost three times the safe limit for infants, and bordering the 300 Bq/kg limit for adults. On Mar 23, officials advised against giving tap water to young infants after high levels of I-131 were found at a Tokyo plant, but lifted that advice on the 24th as levels fell later on in the day.
http://blogs.nature.com/news/thegreatbeyond/2011/03/fukushima_nuclear_data_prolife.html
In Unit 3, three workers were sent to hospital after highly radioactive floodwater seeped through their clothes, exposing the skin below their ankles to an estimated 2-6 Sieverts.
Austria’s Central Institute for Meteorology and Geodynamics estimated that Fukushima was emitting radioactive caesium-137 and iodine-131 at levels approaching that of Chernobyl. However, there was little or no release of other less volatile isotopes, leading to far lower total radiation levels. Prevailing winds had pushed much of the radioactive caesium out over the Pacific Ocean, and rain has quickly washed out any inland material.
http://blogs.nature.com/news/thegreatbeyond/2011/03/fukushima_nuclear_data_prolife.html
Over the weekend, the plant starts to regain power. Power was reconnected to Unit 2, a new line was laid to Unit 4, and cooling systems on Units 5 and 6 started working again under the influence of repaired diesel generators. The pools of spent fuels in these units returned to their normal temperatures. Fears that the reactor in Unit 3 would need to be vented again proved unfounded. Two plumes of smoke were seen coming out of Units 2 and 3. The International Atomic Energy Agency (IAEA) reported that 16 of Japan's 47 prefectures showed daily deposition rates on the ground of less than 860 becquerels per square metre (Bq m−2) for iodine-131, and 100 Bq m−2 for caesium-137.
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