20111101-Tepco work on submersilble cable 317 110810_5.jpg
work on submerslble cable
In April 2011, Tokyo Electric Power Co. (TEPCO), the operator of the crippled Fukushima plant, has said the cores of the Nos. 1 to 3 reactors have been damaged by 25 percent to 70 percent. But the agency at that stage emphasized that the figures were only estimates. “The disaster damaged some reactors' pressure and containment vessels, causing leaks of radioactive water that were detected in turbine building basements and maintenance tunnels outside the area restricted due to radiation. The contaminated water posed a major hindrance to efforts to restore electricity to the reactors.:[Source: Yomiuri Shimbun, April 2011]

The Yomiuri Shimbun reported: “The pressure vessel of the No. 1 reactor at the Fukushima No. 1 nuclear power plant is believed to have been damaged five hours after the March 11 earthquake, according to an analysis by the Nuclear and Industrial Safety Agency. The finding differs with a provisional analysis earlier released by plant operator Tokyo Electric Power Co., which stated the the pressure vessel was believed to have been damaged 15 hours after the March 11 Great East Japan Earthquake. [Source: Yomiuri Shimbun, June 8, 2011]

“NISA, a nuclear watchdog body run by the Economy, Trade and Industry Ministry, disclosed the results of a detailed analysis regarding damage at the Nos. 1 to 3 nuclear reactors at the Fukushima facility. NISA estimates that the No. 2 reactor's pressure vessel was damaged 80 hours after the disaster. TEPCO's analysis contends the No. 2 reactor's pressure vessel was damaged 109 hours after the quake.” [Ibid]

According to NISA's analysis, the No.1 reactor's core began suffering damage three hours after the earthquake. The No. 1 reactor's pressure vessel was damaged at 8 p.m. on March 11, five hours after the earthquake. The No. 2 reactor's pressure vessel suffered damage at 10:50 p.m. on March 14, while the No. 3 reactor's pressure vessel suffered damage at 10:10 p.m. on March 14. NISA data showed the pressure vessels at the Nos. 1 and 2 reactors were damaged earlier than TEPCO's analysis showed.

On the other hand, the No. 3 reactor's pressure vessel was found to have been damaged 13 hours later than TEPCO's data showed. NISA presumed the vessels failed when there was almost no water in the reactor cores of the Nos. 2 and 3 reactors.


Damage to Containment Vessels at the Fukushima Reactors

20110413-TEPCO water pumping 110322_1f_kirin_1.jpg
water pumping
In May 2011, TEPCO said that not only the pressure vessels, but the containment vessels of the Nos. 1 to 3 reactors at the Fukushima No. 1 nuclear power plant were probably damaged within 24 hours of the March 11 earthquake and tsunami. The finding, released as a report to Japanese government nuclear agency, was based on the analysis and minute calculations on internal pressure and other measurements in the nuclear reactors after the earthquake. [Source: Yomiuri Shimbun, May 26, 2011]

According to the Yomiuri Shimbun: TEPCO said it found that an isolation condenser, a type of emergency cooling device, did not work properly at the No. 1 reactor. This caused the core meltdown to progress until it damaged the bottom of the pressure vessel about 15 hours after the earthquake. Along with the meltdown, the temperature inside the steel containment vessel, which contains the pressure vessel, rose until it reached 300 C in 18 hours after the quake, much higher than 138 C the vessel was designed for. It is believed the internal temperature continued to rise after that.

Containment vessels are designed for a much lower temperature and pressure than pressure vessels, which can be exposed to temperatures close to 300 C and pressure reaching 70 bars when a reactor is in operation. Rubber and metal parts used to seal pipes and other devices in the containment vessel apparently deteriorated quickly under temperatures exceeding 300 C. This may have caused steam containing radioactive materials to leak, the report said.

The pressure inside the containment vessel reached 8.4 bars 12 hours after the quake, which is nearly two times the pressure it was designed for. Damage to the containment vessel might have progressed faster than the analysis, TEPCO said. On the basis of fluctuations in pressure measurements inside the containment vessel of the No. 2 reactor, it is assumed a 10-centimeter-diameter hole appeared in the side of the vessel, causing steam to leak 21 hours after the quake. If there was no leakage, the rise of internal pressure would have been much sharper. This makes it difficult to explain the actual pressure measurements. Damage in a pressure control chamber has already been acknowledged, but damage to the containment vessel itself has not been confirmed.

Pumping Seawater on the Reactors

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spraying purified water
Workers used the process of “feed and bleed”---feeding cool water around the reactors’ fuel rods to bleed away excess heat. “Pumping water into nuclear reactors and storage pools for spent fuel rods at the Fukushima No. 1 power plant was an indispensable move. If the reactors were not kept cool and the pools full, an even worse disaster could have occurred at the stricken nuclear facility.”

According to data released by TEPCO on May 16, injection of seawater into the No. 1 reactor began at 7:04 p.m. on March 12. TEPCO decided to use seawater because its freshwater supply was running short. According to the sources, TEPCO informed Kan in advance about the plan to switch from freshwater to seawater. Kan asked Haruki Madarame, chairman of the Cabinet Office's Nuclear Safety Commission whether injecting seawater would pose a risk of re-criticality, and Madarame said it was possible. Therefore at 6 p.m. March 12, Kan instructed the commission and the Nuclear and Industrial Safety Agency of the Economy, Trade and Industry Ministry to examine the possibility that injecting seawater would lead to re-criticality. Later Madarame said he said no such thing, adding “I’m insulted by the claim.” [Source: Yomiuri Shimbun, May 22, 2011]

Because the prime minister expressed concern, TEPCO stopped injecting seawater at 7:25 p.m., about 20 minutes after it had begun. At 7:40 p.m., the commission reported to Kan that injecting seawater would not trigger re-criticality. At 7:55 p.m., Kan ordered Economy, Trade and Industry Minister Banri Kaieda to instruct TEPCO to resume injecting seawater. TEPCO did so at 8:20 p.m. It was originally that injection of seawater was stopped for about 55 minutes but it turned out that plant chief Masao Yoshida disobeyed the order and kept injecting seawater even though he was todl not to. Kan denied claims that he instructed TEPCO to stop injecting seawater into the No. 1 reactor.

Prof. Hisashi Ninokata of Tokyo Institute of Technology, an expert in nuclear reactor engineering, said: "It's certain the nuclear fuel rods inside the No. 1 reactor were damaged. It's highly likely that suspending the injection of seawater made the situation worse." "As it was the second day of the crisis, there was almost no information about conditions inside the reactor, and thus it was necessary to cool the fuel at any cost," Ninokata said. "Even if the seawater caused re-criticality, it wouldn't discharge extremely high levels of energy. If the prime minister was more afraid of re-criticality [than of the nuclear fuel continuing to overheat], he was completely wrong."

Between March 12---the day after the plant was damaged by a massive earthquake and tsunami---and April 12 about 30,000 tons of water have been sprayed into the reactors by Self-Defense Forces, police and other workers.” [Source: Yomiuri Shimbun, April 2011]

But the action was not without consequences. Water inside the building of the second reactor became so contaminated that a worker would only be able to be exposed to it for no more than fifteen minutes each year. Ironically, the water that was so essential to cool the reactors turned out to be the biggest obstacle to repairing them, a development no one in the government anticipated. TEPCO officials thought they could end the water pouring operations if the cooling system could be repaired. The most important thing, they felt, was cooling the reactor cores. Pouring water on the reactors was therefore only a stopgap measure and they never considered what would happen if the water used became highly radioactive and leaked to other parts of the plant.” [Source: Yomiuri Shimbun, April 2011]

Pools of contaminated water have been found in the Nos. 1, 2 and 4 reactors. The most problematic was water in the No. 2 reactor building that measured more than 1,000 millisieverts per hour. "I can barely stand to look at that figure," Hidehiko Nishiyama, spokesman of the Nuclear and Industrial Safety Agency, said at a news conference.

When TEPCO official Teruaki Kobayashi was asked what would happen to the water being sprayed by fire engines and helicopters he said it would "stay in the reactor building because it's designed to prevent leaks." His colleague Hikaru Kuroda told reporters, "The water being poured into the reactors will evaporate in due course."

Decision to Pump Seawater on the Reactors

Norimitsu Onishi and Martin Fackler wrote in the New York Times, “On the evening of March 12, the Fukushima Daiichi nuclear plant’s oldest reactor had suffered a hydrogen explosion and risked a complete meltdown. Prime Minister Naoto Kan asked aides to weigh the risks of injecting seawater into the reactor to cool it down. At this crucial moment, it became clear that a prime minister who had built his career on suspicion of the collusive ties between Japan’s industry and bureaucracy was acting nearly in the dark. He had received a confusing risk analysis from the chief nuclear regulator, a fervently pro-nuclear academic whom aides said Mr. Kan did not trust. He was also wary of the company that operated the plant, given its history of trying to cover up troubles.” [Source: Norimitsu Onishi and Martin Fackler, New York Times, June 12, 2011]

“Mr. Kan did not know that the plant manager had already begun using seawater. Based on a guess of the mood at the prime minister’s office, the company ordered the plant manager to stop. But the manager did something unthinkable in corporate Japan: he disobeyed the order and secretly continued using seawater, a decision that experts say almost certainly prevented a more serious meltdown and has made him an unlikely hero.” [Ibid]

In testimony in Parliament in late May, Mr. Kan said that he asked advisers to weigh the risks that the seawater injection could cause “recriticality,” a phenomenon in which nuclear fission resumes in melted nuclear fuel lying on the floor of a storage pool or reactor core. Mr. Kan’s aides said they grew worried after Haruki Madarame, the chairman of the Nuclear Safety Commission, a nuclear regulator in the prime minister’s office, warned that the chances of this happening were “not zero.” [Ibid]

On March 12, about 28 hours after the tsunami struck, Tepco executives had ordered workers to start injecting seawater into Reactor No. 1. But 21 minutes later, they ordered the plant’s manager, Masao Yoshida, to suspend the operation. They were relying on an account by the Tepco liaison to the prime minister, who reported back that he seemed to be against it. “Well, he said that was the atmosphere or the mood,” Sakae Muto, Tepco’s executive vice president, explained at a news conference. Atsuyuki Sassa, the former head of the Cabinet Security Affairs Office, said: “Mood? Is this a joke? Making decisions based on mood?” [Ibid]

“But Mr. Yoshida chose to ignore the order,” Onishi and Martin Fackler wrote. “The injections were the only way left to cool the reactor, and halting them would mean possibly causing an even more severe meltdown and release of radiation, experts said. Mr. Yoshida had the authority as the plant manager to make the decision, said Junichi Matsumoto, a senior official at Tepco. And indeed, guidelines from the International Atomic Energy Agency specify that technical decisions should be left to plant managers because a timely response is critical, said Sung Key-yong, a nuclear accident expert who participated in the agency’s recent fact-finding mission to Japan.” [Ibid]

“After revealing in May that he had ignored the order, Mr. Yoshida explained himself to a television reporter by saying that “suspending the seawater could have meant death” for those at the plant. Mr. Yoshida, 56, according to friends, is a square-jawed, hard-drinking and sometimes rough-talking man who is a straight shooter. A practitioner of kendo in his youth, he also quotes from Raymond Chandler and enjoys cooking Italian food. “In class, if a teacher didn’t explain something properly, he’d push for an explanation that satisfied him,” said Masanori Baba, a childhood friend.”

“His candor impressed Mr. Kan, who met him the day after the tsunami when he took a trip on a military helicopter to the plant. They shared a willingness to buck the system, as Mr. Kan had when he uncovered the tainted blood scandal. And, in a country where alumni ties are extremely important, they found they had attended the same college, the Tokyo Institute of Technology.”

Using Helicopters and Water Canons to Battle the Crisis at the Fukushima Nuclear Plant

On events of March 17, about a week after the earthquake and tsunami, the New York Times reported: “Japanese engineers battled to cool spent fuel rods and restore electric power to pumps at the stricken Fukushima Daiichi Nuclear Power Station as new challenges seemed to accumulate by the hour, with steam billowing from one reactor and damage at another apparently making it difficult to lower temperatures... The Japanese decision to focus their efforts on the No. 3 reactor appeared to suggest that officials believe it is a greater threat, since it is the only one at the site loaded with mox fuel. [Source: New York Times]

“Authorities reached for ever more desperate and unconventional methods to cool stricken reactors, deploying helicopters and water cannons in a race to prevent perilous overheating, but were hampered by high radiation levels. Japan’s Self-Defense Forces dumped seawater from a helicopter on Reactor No. 3, using a 7.5-ton red bucket suspended several meters below the helicopter. making four passes and dropping a total of about 32,000 liters over it as a plume of white smoke billowed. [Ibid]

Britain’s ITN reported: “Two Ground Self-Defense Force choppers dropped seawater in a 7,500-liter bag four times each in the morning on the No. 3 reactor, an operation about which Defense Minister Toshimi Kitazawa said in Tokyo, “We decided to do this because we thought that today is the time limit.” The 12-minute operation was followed in the evening by the shooting of high-pressure streams of water by six SDF fire trucks. A water cannon truck dispatched by the Metropolitan Police Department also began spraying water, but suspended the work later, the National Police Agency said.” [Source: ITN]

“Kitazawa said that he believes the water from the copters reached the reactor, but plant operator Tokyo Electric Power Co. said that the radiation level remained unchanged at the nuclear plant afterward. .. Concerns are growing that the level of the water filling the spent fuel pool of the No. 4 unit is also becoming low, but Tokyo Electric officials said that the GSDF decided to first spray water on the No. 3 unit, which has vented smoke from Wednesday. The smoke is likely to be steam coming from water boiling in the pool.” [Ibid]

“But a GSDF chopper found earlier in the day that water is left in the pond at the No. 4 unit, according Tokyo Electric. The pools of both the No. 3 and No. 4 units are situated near the roof of the buildings housing the reactors, but are no longer covered with roofs that would reduce any possible radiation leaks since they were blown off by apparent hydrogen blasts.” [Ibid]

Cooling the Reactors at Fukushima Power Plant with Water

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recirculation pump
About 500 tons of water was poured on to the No.1, No. 2 and No. 3 reactors everyday to keep them from overheating. Radiation at reactor No. 1 peaked at 162 sieverts per hour on March 14. Radiation at reactor No. 2 peaked at 138 sieverts per hour on March 15. These readings were recorded after the reactors loss significant amounts of cooling water, leaving large parts of them exposed to the air. The same happened to reactor No. 3 The injection of water caused radiation levels to drop to between 20 and 31 sieverts, 11 to 22 percent of their peaks, by early April.

Initially seawater was used. One of the problems with the salt is that it corrodes water pipes water pipes, increasing the likelihood of leaks. An effort was made to switch over to fresh water as soon as possible. This was largely achieved by late March with the help of a water-carrying barge provided by the U.S. Navy. Some of the operation involved pumping water into the reactor. It also involved spraying water from fire trucks on containment vessel that hold the reactor.

The emergency cooling process of the fuel in the stricken reactors and spent fuel ponds is a process that may continue for a year or more even after fission has stopped. Japanese reactor operators have little choice but to periodically release radioactive steam and water as they accumulate during the cooling process. Until the damaged cooling apparatus was up and running again TEPCO plant's operator must constantly try to flood the reactors with seawater, then release the resulting radioactive steam and water, to keep the reactor cores from melting down, [Source: David E. Sanger and Matt Wald, New York Times, March 14, 2011]

This suggests that the tens of thousands of people who have been evacuated may not be able to return to their homes for a considerable period, and that shifts in the wind could blow radioactive materials toward Japanese cities rather than out to sea. Re-establishing the normal cooling system first required restoring electric power--- which was cut in the earthquake and tsunami--- and that took weeks and required plant technicians to work in areas that had become highly contaminated with radioactivity. After that more time was needed to make repairs to pumps and other machines necessary to get the cooling system online. [Ibid]

David E. Sanger and Matt Wald wrote in the New York Times: “The essential problem is the definition of ''off'' in a nuclear reactor. When the nuclear chain reaction is stopped and the reactor shuts down, the fuel is still producing about 6 percent as much heat as it did when it was running, caused by continuing radioactivity, the release of subatomic particles and of gamma rays. Usually when a reactor is first shut down, an electric pump pulls heated water from the vessel to a heat exchanger, and cool water from a river or ocean is brought in to draw off that heat.” [Ibid]

“But at the Japanese reactors, after losing electric power, that system could not be used. Instead the operators are dumping seawater into the vessel and letting it cool the fuel by boiling. But as it boils, pressure rises too high to pump in more water, so they have to vent the vessel to the atmosphere, and feed in more water, a procedure known as ''feed and bleed.'' When the fuel was intact, the steam they were releasing had only modest amounts of radioactive material, in a nontroublesome form. With damaged fuel, that steam is getting dirtier.” [Ibid]

Radioactive Water Leaks at the Fukushima Nuclear Plants

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radiation water leak
As progress was made keeping fuel rods cool and bringing some degree of control to the crisis, attention shifted to radiation leaks as workers at the Fukushima plant began piling up sandbags and readied emergency storage tanks to stop leaks of highly contaminated water from reaching the ocean.

“On the morning of April 2 when a TEPCO employee who was installing a camera to monitor contaminated water near the No. 2 reactor's water intake saw liquid gushing out from a crack in the side of a concrete shaft into the sea. The worker attempted to measure the radiation level of the water but his dosimeter maxed out. It was over 1,000 millisieverts per hour...It was estimated that 60,000 tons of contaminated water had accumulated in the reactors, an amount that was considered too huge to be dealt with by simply moving it to storage.”[Source: Yomiuri Shimbun, April 2011]

The New York Times reported: “A deluge of contaminated water, plutonium traces in the soil and an increasingly hazardous environment for workers at the plant have forced government officials to confront the reality that the emergency measures they have taken to keep nuclear fuel cool are producing increasingly dangerous side effects. And the prospect of restoring automatic cooling systems anytime soon is fading.”

Readings taken in the sea near the plant in late March showed that levels of radioactive iodine 131 had risen to 4,385 times the statutory limit. The rise seemed to indicate that contaminants from the plant were continuously leaking into the sea.. The day before the water tested at 3,355 times the safety standard for the isotope, up from 1,150 times the maximum level four days before. The same isotope was detected at levels 10,000 the safety limit at Reactor No. 1, according to a TEPCO report. Most of the radioactive water seemed be leaking into the sea from a 20-centimeter crack in a pit used to inspect power cables at No.2 reactor.

On April 7, workers using liquid glass were finally able to stop a leak of highly radioactive water from reactor No.1 into the Pacific. The water entered the sea through a crack near the No.2 reactor’s intake The liquid glass was injected at nine locations near the pit of a tunnel containing radioactive water. The liquid glass was deployed after an attempt too plug the leak with an polymeric absorbent powder used in diapers didn’t work. Before pictures showed a steady stream of water gushing from the crack. After photos showed no leakages.

Discharging Radioactive Water Into the Sea

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water retaining fence
Some of this water leaked out and accumulated in pools under the plant facility. By early April about 80,000 tons of radioactive water had built up in storage facilities and tunnels under the turbine buildings. Some caches of water was more than others. The most radioactive water---containing 2 million times more radioactivity than the low-level radioactive water---was in the basement of the No. 2 reactor

“The government and TEPCO were eventually forced to release water contaminated with low-level radiation into the sea from the plant's waste disposal facilities. On April 4 and 5---in an action that is believed to have never been taken before on Earth---radioactive water was released from a tank into the sea to make space available to store water contaminated with higher levels of radioactivity.” The previous day, a Democratic Party of Japan lawmaker close to Prime Minister Naoto Kan reportedly told TEPCO officials to "deal with the crises in order of priority." The lawmaker asked the utility to consider releasing the mildly radioactive water into the sea.[Source: Yomiuri Shimbun, April 2011]

About 11,500 tons of low-level radioactive water (the equivalent of about 10 Olympic-size swimming pool) was released into the sea in part to make room for more highly contaminated water. This was done because floating storage facilities and a vessel that decontaminates water that been ordered but would not be delivered until May and drastic action was need to make room for the more highly radioactive water under reactor No. 2 .This caused a big brouhaha---especially among fishermen in the area---as high levels of radioactivity were detected in sea water and some radioactivity was found in caught fish. The head of TEPCO apologized to fishermen as they presented him a formal complaint. Other nations also complained about the releases of radiation into the sea.

The radiation water leaked into the sea from the water leaks was 20,000 times the annual limit. The 520 tons of water that leaked into the sea contained 5,000 terabecquerels, including 4,700 terabecquerels of iodine-131, cesium 134 and cesium 137. This was 30,000 times more than the radioactive substances contained in the 10,000 tons of relatively low-level radioactive water purposely discharged by TEPCO.

A total of 250 tons of highly contaminated radioactive water leaked into the sea in early May from the No. 3 reactor at the Fukushima Daiichi nuclear power plant, TEPCO said. The water, leaked from a pit near a seawater intake of the reactor, contained an estimated 20 terabecquerels of radioactive substances, TEPCO was quoted by Kyodo News as saying. The leak is estimated to have lasted for 41 hours from 2 a.m. on May 10 through 7 p.m. on the following day. The estimated amount of radioactive substances was about 100 times the annual allowable limit for release outside the plant, said TEPCO, but was far less radioactive that the water rleased from Reactor No. 2 in April.

By late April the radioactive material released from Fukushima nuclear power plant was one percent of what it was and the concentrations of iodine-131 in seawater near the plant were below government-set danger limits.

Researchers at the Meteorological Research Institute and the Central Research Institute of Electric Power Industry estimated that the amount of radioactive cesium-137 that was directly released into the sea came to 3,500 terabecquerels from March to the end of May, while estimating that roughly 10,000 terabecquerels fell into the ocean after it was released into the air.

In October 2011, the French government's nuclear research institute, IRSN, said the amount of radioactive cesium that has leaked from Fukushima Daiichi nuclear power plant into the ocean is 20 times larger than TEPCO estimated. Their report calculated that 27.1 thousand terabecquerels of radioactive cesium 137 had leaked into the ocean as of the middle of July. The largest amount was released by early April from a pit at the Number 2 reactor and other plant facilities, about 20 times the estimate made by TEPCO. The report says the nuclear accident caused significant water contamination, but radioactive substances will be dispersed by ocean currents. [Source: October 30, 2011]

In October 2011, NHK reported, high concentrations of radioactive cesium have been found in plankton from the sea near the Fukushima Daiichi Nuclear Power Plant. Researchers from Tokyo University of Marine Science and Technology collected plankton in waters up to 60 kilometers from the coast of Iwaki City in July. They found 669 becquerels per kilogram of radioactive cesium in animal plankton from waters 3 kilometers offshore. They say a wide range of fish feed on animal plankton and that the contamination could accumulate in the food chain and have a more serious impact when its gets into relatively large fish. The research group's leader, Professor Takashi Ishimaru, says the plankton were so heavily contaminated because sea currents continuously carried contaminated water southward from the nuclear plant. He says detailed studies are needed to determine how long the effect on fish will continue. [Source:, NHK, October 15, 2011]

Storing Radioactive Water

Getting rid of the water in the tunnels under the turbine is a critical step in getting the reactor cooling system operating again so the reactors can be stabilized. Releasing highly radioactive water into the sea is not an option, A megafloat capable of holding 10,000 tons and 400 makeshift storage tanks capable of holding 20,000 tons are supposed to arrive at the plant in mid April. In the meantime TEPCO was studying the possibility of distilling the radioactive water to reduce its volume so less storage space would be needed.

In mid April work began on removing highly radioactive water---particularly in the basements of reactors No. 1 and No.3 reactors and the trenches that connect them “which had prevented restarting the reactor’s cooling system and stabilizing the plant. The goal was to transfer 60,000 tons of water to nearby tanks and other storage facilities. The workers began by pumping water near the No.2 reactor which was rising apparently because of action to stop leaks of radioactive water into the sea.

Workers Battle Radiation Leaks at the Fukushima Nuclear Plants

David Jolly and Matthew L. Wald wrote in the New York Times, “Workers have been dousing reactors and spent-fuel pools at the plant with water to prevent full meltdowns while they frantically try to restore power and restart the cooling systems, but the resulting floods of dangerously contaminated water have complicated their efforts. On Thursday workers prepared more tanks for transferring the water from turbine buildings at Reactors 1, 2 and 3 in a quest to keep the radioactive water from flooding into the ocean.[David Jolly and Matthew L. Wald, New York Times, March 31, 2011]

20110413-TEPCO megafloat 110407_MegaFloat_1.jpg
megafloat storage vessel

One of the most dangerous jobs was pumping contaminated water from the pools in the turbine buildings. NHK reported that because many of the plant’s radiation detectors were destroyed in the earthquake workers have had to share the devices in small groups. Under normal circumstances each worker would have a device since it is not possible to accurately measure individual radiation exposure without them. Some workers have become enraged and walked off the job as a result, NHK reported. Enough devices eventually arrived, the Daily News reported, so there was now enough for everyone. But safety standards have repeatedly been relaxed to ensure work can continue without violations.

TEPCO said 18 employees and three contractors were exposed to 100 millisieverts of radiation. The average dose for a nuclear plant worker is 50 millisieverts over five years. Two workers in Reactor 3 were admitted to hospital after their feet were exposed to 170-180 millisiverts---levels close to what emergency workers are allowed to be exposed to in a year--- according to the International Atomic Energy Agency. The radiation radioactivity was in water that seeped in through the top of their boots. The workers were trying to reconnect a power cable under reactor No. 3; they continued with their work even though their radiation dosimeters warned them of high levels of nuclear reactor in the area. In the early days of the crisis one workers

During the crisis at the Fukushima plant the Japanese government raised the legal limit of radiation workers could be exposed to from 100 to 250 millisieverts,” Chris Hogg of the BBC wrote. “That is more than 12 times the legal dose for workers dealing with radiation under British law. But you would need to be exposed to a dose probably twice that maximum before you would expect to see the so-called “early effects” people associated with radiation sickness, like a lowering of white blood cells. You would need a level of exposure in the region of 1,000 millisieverts before you might feel nauseous or feel ill. The "late effects" of exposure to radiation may not occur for many years. It can increase the likelihood you will develop cancer, but this is only an increased possibility, not a certainty.” [Source: Chris Hogg BBC News, March 17, 2011]

In mid April, workers began installing enclosures in the sea just outside the Fukushima nuclear power plant to prevent radioactive water from spreading into the Pacific. Around the same time TEPCO began using a small unmanned helicopter---the Honeywell-produced T-hawk---to survey the plant and get a look inside the No. 1 to No. 4 reactor---something workers had been unable to do because of worries about radiation. Designed for military use, the 7.7-kilogram T-Hawk has two video cameras and can be operated from than 10 kilometers away. GPS technology allows it a hoover at precise locations.

Restoring Power and Injecting Nitrogen Into the Reactor Containment Vessels

20110413-TEPCO cables k6002.jpg
power cables
On events of March 17, about a week after the earthquake and tsunami, the New York Times reported: “Japanese engineers battled to cool spent fuel rods and restore electric power to pumps at the stricken Fukushima Daiichi Nuclear Power Station as new challenges seemed to accumulate by the hour, with steam billowing from one reactor and damage at another apparently making it difficult to lower temperatures... The Japanese decision to focus their efforts on the No. 3 reactor appeared to suggest that officials believe it is a greater threat, since it is the only one at the site loaded with mox fuel.

“Workers at the crippled nuclear power plant tried to bring its command centers back online and restore electricity to vital cooling systems but an overheating spent fuel pool hampered efforts and raised the threat of further radiation leaks.... Efforts to stabilize the hobbled nuclear power plant in Fukushima hit a snag when engineers found that crucial machinery at one reactor requires repair, a process that will take two to three days, government officials said. Another team of workers trying to repair another reactor was evacuated in the afternoon after gray smoke rose from Reactor No. 3.

An important milestone was achieved March 20 when a power cable was connected at reactor No. 2 providing electricity to activate the central control room and providing hope that maybe electricity could be restored to cooling system that could stabilize the reactor. Of the four damaged reactors reactor No. 2 suffered the least damage to its pumps and electrical equipment and had the best chance of gets its cooling system up and running. Electricity was sent from the No.2 reactor to the other reactors, an operation that was difficult by debris, radioactive water and high radiation, and getting the cooling system going proved to be an arduous task as back-up water systems motors and power-supply units needed to be repairs or replaced.

About two weeks after the March 11 quake workers were finally able to connect power cables to all six reactors at the plant. Another major milestone was on March 24 when control power was restored. With that objective achieved workers immediately began work on reactivating the pumps and deliver more fresh water to the reactors. By mid-April, an emergency makeshift power supply source was moved to higher ground and a firefighting vehicle was deployed as part of anti-tsunami measures. Backup cooling systems had also been installed.

In early April workers began injecting nitrogen into the reactor containment vessels to deter any new hydrogen explosions. Nitrogen can prevent highly combustible hydrogen from exploding---as it did three times at the compound in the early days of the crisis. Nuclear officials said there was no immediate threat of more explosions, but the nitrogen plans were an indication that such an explosion---within the reactor containment vessel itself not the reactor buildings as was the earlier hydrogen explosions---was a possibility and a sign that many serious challenges still lie ahead.

Videos of the Fukushima Nuclear Power Plant Crisis

Video of Tsunami Hitting Fukushima Nuclear Power Plant

Tsunami Hits Fukushima Power Plant

Fukushima Plant After Tsunami

Video of Explosions at Fukushima Nuclear Power Plant

Fukushima Explosion

Explosion at Reactor No. 1

Fukushima Explosions at Reactor 3 and 4

Video of Damage to Fukushima Nuclear Power Plant After Explosions

Helicopter Video of Smoking Fukushima Plant

Smoke 10 Days After Tsunami

Video of Brave Workers at Fukushima Nuclear Power Plant After Explosions

Video, Slides of Fukushima Plant and Workers

Fukushima Fifty

Hospitalized Fukushima Workers

Brave Fukushima Workers

Video of Fears About Radiation from Fukushima Nuclear Power Plant

Fears Over Japanese Food

Worried About Radiation in Tokyo

Image Sources: TEPCO

Text Sources: New York Times, Yomiuri Shimbun, Daily Yomiuri, Washington Post, Los Angeles Times, Kyodo News, National Geographic, The Guardian. Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, and various books and other publications.

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© 2008 Jeffrey Hays

Last updated October 2011

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