Worker exposure to high levels of nuclera radiation and the distribution of radioactive materials about the landscape and in possibly unexpected places are the stories of the week at Fukushima. Also, officials are wondering, how have the potential effects of a tsunami at Fukushima (and, apparently, it is possible to have a tsunami here) changed given that the reactor is now a series of large pools of highly contaminated water?
The power being supplied to cooling pumps at Units 1,2 and 3 had been switched back to emergency generators because the connections established several days ago need to be reworked. Subsequently, the supply was switched back to the off-site grid. Mysterious white smoke has stopped coming out of Reactor Unit 4 (about five or six days ago) but the smoke continues to be emitted from units 2 and 3. Water is still being pumped into reactors, and nitrogen is still begin injected to avoid a hydrogen explosion. Pressure and temperature readings at the reactors are still not what they should be for a cold shutdown.
Few people know it, but Fukushima Daiichi Power Plant once starred in a movie about how to build a nuclear reactor:
(more details here)
And now, Ana's Feed:
Japan to scrap workers' annual radiation dose limit at normal times - Kyodo, April 28
-The health ministry plans to scrap the annual radiation dose limit for nuclear power plant workers at normal times for the meantime to secure enough workers for maintenance and checkups of nuclear power plants other than the crisis-hit Fukushima power station, sources close to the matter said Wednesday.
Govt to set up nuclear accident probe committee - NHK, April 28
-Prime Minister Naoto Kan says his government will set up an independent committee by mid-May to investigate the ongoing nuclear crisis.
-Kan said he hopes that thoroughly investigating the accident will help Japan share its experience with other countries through the International Atomic Energy Agency and other organizations.
-He added that he hopes the probe will contribute to improving the safety of nuclear power plants across the globe.
Radioactive level halved at reactor water intake - NHK, April 28
operator of the quake-damaged nuclear power plant in northeastern Japan says levels of radioactive iodine in seawater samples taken near one of the plant's crippled reactors are down by more than half from the previous day.
-The Tokyo Electric Power Company says the level of radioactive iodine-131 per cubic centimeter in samples collected near the water intake of the No. 2 reactor was 63 becquerels on Wednesday.
-The figure is 1,600 times the state limit, but marked the first decline in 3 days.
The Japan Atomic Industrial Forum has put together a Buyers Guide, if you're interested:
TEPCO continues test for water injection (Reactor Unit 1) - NHK, April 28
-The temperature at the top of the reactor was 107 degrees Celsius as of 11 AM on Thursday, down 25 degrees from before the water increase.
-The pressure inside the reactor has slightly fallen. The utility is watching the pressure carefully and injecting nitrogen to prevent a possible hydrogen explosion.
-The firm is monitoring the state of the containment vessel carefully to determine whether to maintain the current level of water injection.
Moves on int'l nuclear safety rules - NHK, April 29
-The head of the International Atomic Energy Agency and the president of France have agreed that compiling international safety standards for nuclear power plants should take place as soon as possible.
-Yukiya Amano met with Nicolas Sarkozy in Paris on Thursday to discuss the crisis at the Fukushima Daiichi nuclear power plant.
Radiation adviser to Kan to quit over gov't nuke crisis response - Kyodo, April 29
-An adviser to Prime Minister Naoto Kan on the nuclear crisis at the Fukushima Daiichi power plant told the prime minister's office Friday he will resign in protest over what he called the government's impromptu handling of the crisis.
NRC: Fukushima plant situation "improved" - NHK, April 29
-The US Nuclear Regulatory Commission says the situation at the Fukushima Daiichi nuclear plant in Japan has "definitely improved" but still requires close monitoring.
Weather chief draws flak over plea not to release radiation forecasts - Kyodo, April 29
chief of the Meteorological Society of Japan has drawn flak from within the academic society over a request for member specialists to refrain from releasing forecasts on the spread of radioactive substances from the troubled Fukushima Daiichi nuclear plant.
Germany holds open debate on nuclear power - NHK, April 29
-An open debate is underway in Germany about the use of nuclear power there.
-The debate is being held on Thursday by the government-sponsored ethics commission on nuclear power generation, formed in the wake of the crisis at the Fukushima Daiichi plant.
-The government of Chancellor Angela Merkel plans to outline its new energy policies by early June after holding detailed public discussions.
Fukushima Daiichi's shoreline to be sandbagged - NHK, April 29
-As aftershocks of the March 11th earthquake continue, the operator of the troubled Fukushima Daiichi nuclear power plant will sandbag its shoreline as a temporary measure against another possible tsunami.
-The utility firm decided to sandbag the shoreline at the planttoa height of several meters.
-The firm fears that if the facility is hit by another tsunami, highly contaminated water may run into the ocean and damage the reprocessing facility
Is it safer for pregnant women to leave northern Japan? - Reuters AlertNet, April 29
"HONG KONG - To be afraid or not to be afraid is the question that has haunted millions of people as radioactivity leaks from a Japanese nuclear plant battered by last month's earthquake and tsunami.
Officials say health risks are minimal outside evacuation areas, but in the absence of detailed advice, many in northern Japan have fled."
Radiation exposure level nears limit for 1 worker at Fukushima plant - Kyodo, April 30
-Tokyo Electric Power Co. said Saturday that the level of radiation exposure for one of its employees came close to the legal yearly limit of 250 millisieverts at the crisis-hit Fukushima Daiichi nuclear power plant.
Kan nuclear adviser fed up, quits - AP, April 30
-Tokyo professor calls response impromptu, says short-term thinking resulted in delays.
-It is extremely rare for an intellectual adviser appointed by the prime minister to resign in protest at measures the government has taken.
-Kosako told reporters at the Diet on Friday it is problematic for the government to have delayed the release of forecasts on the spread of radiation from the Fukushima plant, done by the Nuclear Safety Technology Center's computer system, called the System for Prediction of Environmental Emergency Dose Information (SPEEDI).
-He also blasted the government for hiking the upper limit for Emergency workers seeking to bring the crippled plant under control to 250 millisieverts from 100 millisieverts after the crisis broke out.
Kan comments on nuclear advisor's resignation - NHK, April 30
-Speaking at a Lower House committee meeting on Saturday, Kan said Professor Kosako resigned because of disagreements with other scientists.
-Kan said the government responded to the nuclear accident based on advice from the Nuclear Safety Commission and has never taken ad hoc measures.
-Kosako also criticized the education ministry for allowing students at primary schools in Fukushima Prefecture to perform outdoor activities if the level of radiation of the school ground does not exceed 20 millisieverts per year.
Edano: No compensation exemption for TEPCO - JAIF, April 30
-Japan's Chief Cabinet Secretary Yukio Edano emphasized that Tokyo Electric Power Company cannot be exempt from paying compensation for the accident at the Fukushima Daiichi nuclear plant.
-The country's Act on Compensation for Nuclear Damages would allow the responsibility for compensation to be dismissed if the accident is regarded as an exceptionally massive natural disaster. TEPCO has implied this act should be applied to what happened at Fukushima Daiichi.
-But Chief Cabinet Secretary Edano says while the earthquake and tsunami were very powerful, Japan's Diet had warned the nuclear plant would face problems if hit by an enormous tsunami.
-Edano points out TEPCO cannot be exempt from its responsibility because the company was not prepared for what had been flagged by the Diet, and therefore the damage is not unexpected.
TEPCO president pledges swift, fair compensation - JAIF, April 30
-The president of Tokyo Electric Power Company has promised to quickly and fairly pay compensation for losses caused by the accident at the Fukushima Daiichi nuclear plant.
-Masataka Shimizu testified Friday before a Lower House committee. He referred to the 1st guidelines released Thursday by a government panel. They named evacuees, farmers and fishermen subject to shipping restrictions as among those eligible for compensation.
-Shimizu said his company will follow the guidelines and study how to calculate damages and pay them out. He acknowledged the number of claimants will be vast. But he said TEPCO will act fairly and swiftly with the government's support, financial and otherwise.
-Prime Minister Naoto Kan addressed the same Lower House committee on Friday. He said he will ensure that adequate relief reaches all the victims of the March 11th disaster, which he pointed out is the government's responsibility.
Radiation exposure levels near limit for 2 Fukushima nuke workers - Kyodo, April 30
-As the nuclear crisis continues at the Fukushima Daiichi power plant, two workers, who were previously hospitalized for possible radiation burns, turned out Saturday to have been exposed to radiation levels close to the limit of 250 millisieverts while seven women in affected areas were found with slightly contaminated breast milk.
Japan files protest over French TV show on quake, nuke emergency - Kyodo, April 30
Japan protests French TV's description of quake - NHK, April 30
-The embassy says some inappropriate contents were included in Canal Plus's puppetry program that caricatures current affairs. The offending segments were aired from March 14th to 17th, a few days after the massive disaster in Japan.
-Canal Plus has not offered any apology, citing freedom of expression.
Minute amount of radioactive substances found in breast milk of 7 - Kyodo, April 30
minute amount of radioactive substances have been found in breast milk of seven women in a survey covering 23 women in Tokyo and four other prefectures, including Fukushima and its neighboring Ibaraki, the health ministry said Saturday.
TEPCO official: Fukushima is man-made disaster - NHK, May 1
-A vice president of Tokyo Electric Power Company says he believes the nuclear crisis at Fukushima nuclear power plant is a man-made disaster.
-TEPCO vice president Norio Tsuzumi visited Iitate village in Fukushima Prefecture on Saturday and apologized to about 1,000 villagers who gathered to hear him speak.
-He said that some say the nuclear accident in Fukushima was beyond any expectations but personally he thinks adequate precautions should have been in place.
Kan: safety measures insufficient - NHK, May 1
-Prime Minister Naoto Kan says the government and Tokyo Electric Power Company failed to fully address safety issues that had come to light before the March 11 disaster.
-Kan said measures were not taken despite previous accidents and warnings, and that he must admit that the utility and the government failed to fully deal with the situation.
Non-nuclear nations call for safer nuclear power - NHK, May 1
-Foreign ministers from 10 countries without nuclear weapons have agreed that international cooperation should be promoted to improve the safety of nuclear power plants.
-They held the second non-nuclear state conference in Berlin, Germany, on Saturday, followed the first last September in the US.
More workers to be sent to Fukushima - NHK, May 1
-About 1,000 workers of Tokyo Electric Power Company and its contract companies are currently working at the power plant to bring it under control.
-The power company considers it necessary to have more people on site to proceed with the operation while ensuring the safety of the workers.
Cesium found in sludge - NHK, May 1
-Relatively high levels of radioactive cesium have been detected in the sludge from a waste water treatment plant in Koriyama City, Fukushima Prefecture.
-The prefectural government is tracking some of the sludge that has been shipped out of the prefecture to be used in making cement.
-The prefecture's investigation found that the sludge contained 26,400 becquerels of radioactive cesium per kilogram.
TEPCO faces uphill battle in filling nuclear reactor containment vessel with water - Mainichi, May 2
"Officials said the water level inside the reactor's pressure vessel remained almost unchanged -- at about 1.6 meters above the top of the fuel rods -- when the amount of water was temporarily increased. With water pumped into the pressure vessel leaking out, workers estimate that the water level inside the containment vessel stands at about 6 meters, but they do not know the exact level."
Another female nuke worker exposed to radiation above limit - Kyodo, May 2
-Tokyo Electric Power Co. said Sunday that a second female radiation worker at the crisis-hit Fukushima Daiichi nuclear power plant had been exposed to radiation exceeding the legal limit in the days after the crisis erupted March 11, after news of the first was reported earlier this week.
U.S. medical group blasts Tokyo radiation policy on Fukushima children - Kyodo, May 2
-Physicians for Social Responsibility, a U.S. nonprofit organization of medical experts, has condemned as ''unconscionable'' the Japanese government's safety standards on radiation levels at elementary and middle schools in nuclear disaster-stricken Fukushima Prefecture.
-The PSR statement directly challenges the Japanese government stance that it is safe for schoolchildren to use playgrounds on school premises in the prefecture as long as the dose they are exposed to does not exceed 20 millisieverts over a year.
-The PSR view is also in line with that voiced by Toshiso Kosako, who said Friday he would step down as an adviser to Prime Minister Naoto Kan on the Fukushima nuclear crisis in protest. The University of Tokyo professor urged the government to toughen guidelines on upper limits on radiation levels the education ministry recently announced for primary school playgrounds in Fukushima.
Link to PSR statement from April 26:
"Physicians for Social Responsibility (PSR) today cited gross inadequacies in evacuation zones around nuclear reactors and underscored the ongoing health risks of nuclear energy to the public. The 25th anniversary of Chernobyl and the continuing crisis at Fukushima--both Level 7 nuclear disasters--are clear reminders that standard evacuation zones cannot protect the public from a nuclear accident. One-third of the population of the United States (over 111 million people) lives within 50 miles of a nuclear reactor. Given the consequences of the Chernobyl and Fukushima disasters, PSR is calling for a major reassessment of contingency plans for nuclear accidents, as well as a full and fair accounting of the data on the impact to public health and the environment."
Gov't relaxes standards for residents' temporary return to homes near nuclear plant - Mainichi, May 2
"The government's headquarters for local disaster countermeasures met with officials from nine local bodies on May 1 and announced that it would allow up to two people from each household to return to collect items, a shift from its earlier position of allowing only one person to return. ... During a rehearsal on May 3, workers will assemble in the village of Kawauchi wearing protective clothing, traveling in three buses. Officials will work to expose any problems that could occur when residents return. It is expected officials will start allowing residents to temporarily return to their homes as early as the second week of May."
Shareholders want nuclear plants closed - NHK, May 2
-A group of Tohoku Electric Power Company shareholders will submit a motion calling for the closure of the company's nuclear plants.
-220 individual stockholders decided on the move ahead of the company's annual shareholders' meeting at the end of next month.
-The investors are demanding that the utility state in its agreement with shareholders that it will close its nuclear power plants and end its investment in a reprocessing plant in Aomori Prefecture and similar projects.
Emergency safety measures for reprocessing units - NHK, May 2
-Japan's nuclear safety agency has told two reprocessing units for spent nuclear fuel to take emergency safety measures in preparation for a possible suspension of external power.
-The agency is asking the reprocessing facilities to present their safety measure plans as soon as possible. It says it will assess if their measures are appropriate by the end of May.
Level now 3300 times limit at No. 2 reactor intake - NHK, May 2
-Tokyo Electric Power Company says it detected 130 becquerels of radioactive iodine-131 per cubic centimeter in samples collected near the water intake for the Number 2 reactor on Saturday. The figure is 3,300 times the national limit and 30 percent higher than the level detected on Friday.
Work underway to filter air in reactor bldg - NHK, May 2
-Tokyo Electric Power Company, the operator of the plant, said on Monday that workers are preparing to install devices that will reduce the amount of radioactive materials inside the No.1 reactor building.
-The equipment is designed to filter out 95 percent of the radioactive substances in the air coming through the ducts, when operated for 24
3 part diary entry on evacuation conditions by Kitamura, a JAIF consultant:
Thanks once again for your coverage.
This might also be worthy of note:-
"Fukushima I Nuke Plant: Japan Nuclear Technology Institute Senior Advisor Says "Reactors 1, 2, 3 All Had Complete Meltdown""
Thank you. I was listening to some news commentary this weekend on how Fukushima and Libya and fallen off the news radar in favor of stuff like Obama's Birth Certificate. (and now with the death of Osama, it will be non-existent.
Of course if you wish to add to your list a very good lbl scientific/engineering discussion on the reactors, the disaster, and the application to other reactors: http://today.lbl.gov/2011/04/18/lab-experts-discuss-fukushima-crisis/
Thanks for that link.
I thank you for the link, too.
It's provides a science-based, non-hype perspective.
It is a shame that the Physicians For Social Responsibility have abdicated that perspective in their anti-nuclear power zeal.
In the U.S., average radiation doses have almost doubled in the last twenty years or so. The PSR have been silent on this.
The reason for this doubling?
More medical exposures (sometimes inappropriate).
Had the reason been nuclear power plant exposures, they would have issued plenty of "statements".
Healthphysicist, you are being rhetorical again. PSR has issued a number of statements on medical radiation (e.g. http://tinyurl.com/3fo54cr and http://tinyurl.com/3skerhd) I'm not sure why you would argue that there is some politically motivated number.
You seem to be suggesting that they need to have issued more statements about medical than disaster related radiation, but I don't understand what the criteria for that would be. Or, is this simply a case of asking people to not bring up things you would rather not be brought up?
Do you count billboards and write a letter to the editor of there are there are too many on one topic!?!?!?
(Well, to be fair, I do that, but whatever...)
Did you even check your links?
One is a radiation basics primer for clinicians and one goes nowhere.
You have proven my point.
The PSR does NOT care about radiation exposures.
They are anti-nuclear power.
The fact that I accidentally gave you a dead link does not prove your point, or if that is your criterion for making a point you should recalibrate! You or anyone else can google this as well as I can.
But as usual you've failed to address the question: Why is some fantasy that is only in your head about the ratio of US medical radiation vs. Japan Nuclear Disaster radiation items by this group meaningful in any way at all? You have explicitly stated that the group's concerns about Fukushima is invalid because they issued more statements about Fukushima than about Medical radiation of the last 20 years. If they had issues the same exact number, would that be OK?
And if so, why?
Are they anti nuclear power? If so, do they have reasons for this? Or, would you say rather that being anti-nuclear power (as a conclusion they may have come to) invalidates any possible reason to become anti-nuclear power?
Do you see, yet, why what you are saying is crazy-talk?
This isn't about PSR and Fukushima. It's about PSR and nuclear power.
PSR was anti-nuclear power prior to Fukushima in Japan.
Meanwhile, these physicians ignored the increased cancer risk from medical exposures over the last 20 years to Americans.
That's not crazy talk....that's crazy.
Where is my last comment?
The PSR was anti-nuclear power prior to Fukushima, while they totally ignored medical radiation exposure risks.
Not crazy talk.
PSR was anti-nuclear power prior to Fukushima in Japan.
I'm not disputing or supporting that statement. I'm simply noting that you seem to judge the credibility of a source on the basis of whether or not you agree with it.
Meanwhile, these physicians ignored the increased cancer risk from medical exposures over the last 20 years to Americans.
This is similar to the argument that since most of the Fukushima workers who don't die of old age will die of a car accident (or train accident or whatever kills you in Japan) means that the women who were over-exposed based on the prevailing standards have no right to worry. I'm pretty sure there are not independent criteria that you are in charge of that determines what an organization should do and not do.
Example: The National Center for Science Education does almost none of the things one might think an organization interested in science education does. Rather, it spends all of its time fighting creationists. All organizations have the potential of having a list of priorities and record of activities that don't match an outsider's preconceptions. That discordance does not invalidate their priorities and most importantly it does not affect the validity of what they are saying or doing.
Comment moderation seems almost random on this platform.
Imagine Burger King criticizing McDonalds for their contribution to childhood obesity. Or the Catholic Church condemning the Baptists for pedophilia.
That is analogous to PSR criticizing the nuclear power industry based on radiation safety.
Not really....the medical industry has ACTUALLY, on average, doubled the radiation dose Americans receive. It's not some hypothetical nuclear power accident.
Greg and Ana,
Can't say thanks enough, but I'll keep saying it anyway, since major news outlets have clearly forgotten there is a problem in Fukushima.
"Contamination from radioactive particles escaping from the plant grounds has been an ongoing concern. On Tuesday Kyodo News quoted TEPCO reports that samples taken from the sea floor near the coastal plant have shown radiation levels 100 to 1,000 times background levels. The samples, recorded Friday, were taken at a depth of 20 to 30 meters.
Radioactive contaminants also have been found at a nearby sewage treatment plant, according the Asahi Shimbun newspaper. On April 30, sludge and the remnants of incinerated sludge from the sewage treatment plant in Koriyama, Fukushima Prefecture, tested positive for cesium at levels of 334,000 becquerels. Japanese regulators plan to meet to discuss the handling of the radioactive sludge, which does not fall within any current safety guidelines.
Officials believe runoff from rain washed contaminants accumulated on the ground into sewers. Material from the incinerated sewage routinely is shipped to cement companies in Japan. Local authorities are tracking shipments of potentially radioactive material, and officials say sludge at the treatment plant is being stored safely."
This really underscores how many avenues there are for radioactive materials to disseminate from Daiichi. First, the incineration of the sludge raises concerns about how the exhaust is vented (not to mention who is looking after the workers at the incineration plants); next, cement work is a pretty dusty business-- don't think I want much cesium floating around construction sites throughout Japan; finally, as any resonable person might have expected, radioactive materials are acumulating on the seabed, rather than dispersing and diluting in seawater. Between biological uptake through the foodchain, and churning of the seabed during storms, we can predict ongoing 're-dosing' with longer lived radionuclides for a long, long time.
HP: OK, that makes some sense, now that you explain what you meant.
It is not just their hypocrisy which is problematic. It is their intentional spinning of the science. For example, from one of your links to them:
"The nuclear industryâs most common argument is that there is no significant health consequences associated with low doses of radiation. However, it is the consensus of the medical and scientific community, summarized in the National Research Councilâs BEIR VII report, that there is no safe level of radiation. Any exposure, including exposure to naturally occurring background radiation, creates an increased risk of cancer. The BEIR report concluded that every thousand man rems of radiation exposure will cause one cancer."
BEIR VII does not speak to "safe levels" of radiation, though reading that paragraph, one might think otherwise. Safety is a relative term. And there is medical and scientific community consensus on what levels of radiation are relatively safe, contrary to what PSR claims.
And there is medical and scientific community consensus on what levels of radiation are relatively safe, contrary to what PSR claims.
I thought it was more like what is acceptable, not what is safe. Some of the effects of radiation are not dose dependent at all, but merely stochastic. Therefore, there can not be a "safe level."
As I said previously, "safety" is a relative term. It's like "massive". A boulder is massive relative to a pebble, but not relative to a continent.
"Acceptable" levels are those levels which are relatively safe.
A relatively unsafe level would not be acceptable.
Zero risk is safe. But you can have risk and still be relatively safe, if the risk is small relative to other risks one will encounter.
And this is why people like me bring up food safety or driving safety, etc. when discussing nuclear safety. Those comparisons provide context (risk relativity) in a world that is not zero risk. And you denounced me for that in an earlier blog.
Note that the PSR, in the above quoted paragraph, intentionally omitted the risk relativity from what BEIR VII actually said. BEIR VII actually says that in a lifetime, approximately 42 of 100 people will be diagnosed with cancer. 1 additional cancer per 100 people could result from a single exposure to 10 rem.
But PSR reframed that. They multiplied 10 rem and 100 people to get 1,000 man-rem yields one cancer (not a certainty according to BEIR, though you wouldn't know it from the PSR statement). And they failed to mention that there are 420 other cancers in that group of 1,000 people, which have other causes.
How Angela Merkel became Germany's unlikely green energy champion.
"Clearly, Angela Merkel has reacted to the Fukushima disaster completely differently from Barack Obama and other world leaders. In the past, Merkel too has been pro-nuclear. She was convinced that nuclear power was safe and clean, and that the Chernobyl accident was a result of Soviet inefficiency, not of the technology itself. Only last year, she fought to extend the operation time of Germany's reactors by 12 years on average, against fierce opposition from the left and environmental groups.
In my view, the key to the chancellor's radical turnaround lies deep in her past. In the 1980s, well before she became a politician, Merkel worked in the former East Germany as a researcher in quantum chemistry, examining the probability of events in the subatomic domain. Her years of research instilled in her the conviction that she has a very good sense of how likely events are, not only in physics but also in politics. Opponents of nuclear energy were "bad at assessing risks," she told me in the 1990s.
Then came the March disaster at the Fukushima-Daiichi nuclear power plant, which made the chancellor realize that she had been terribly wrong about the probability of a nuclear catastrophe in a highly advanced nation. Merkel's scientific sense of probability and rationality was shaken to the core. If this was possible, she reasoned, something similar might happen in Germany â not a tsunami, of course, but something equally unexpected. In her view, the field trial of nuclear energy had failed. As a self-described rationalist, she felt compelled to act.
"It's over," she told one of her advisers immediately after watching on TV as the roof of a Fukushima reactor blew off. "Fukushima has forever changed the way we define risk in Germany."
Merkel's conservative environment minister, Norbert RÃ¶ttgen, recently echoed this line of thinking when he said that the Fukushima disaster "has swapped a mathematical definition of nuclear energy's residual risk with a terrible real-life experience." He added: "We can no longer put forward the argument of a tiny risk of ten to the power of minus seven, as we have seen that it can get real in a high-tech society like Japan."
In case some of us have become distracted:
"Japan's crippled Fukushima nuclear power plant is leaking water from the center of the reactor seen as the closest to stabilizing...
Workers at the Fukushima Daiichi nuclear plant have been pumping water into four of the six reactors on the site to bring their nuclear fuel rods to a "cold shutdown" state by January.
But after repairing a gauge in the No. 1 reactor earlier this week, Tokyo Electric Power Co discovered that the water level in the pressure vessel that contains its uranium fuel rods had dropped about 5 meters (16 ft) below the targeted level to cover the fuel under normal operating conditions.
"There must be a large leak," Junichi Matsumoto, a general manager at the utility also known as TEPCO, told a news conference.
"The fuel pellets likely melted and fell, and in the process may have damaged ... the pressure vessel itself and created a hole," he added.
Since the surface temperature of the pressure vessel has been holding steady between 100 and 120 degrees Celsius, Matsumoto said the effort to cool the melted uranium fuel by pumping in water was working and would continue.
Based on the amount of water that is remaining around the partially melted and collapsed fuel, Matsumoto estimated that the pressure vessel had developed a hole of several centimeters in diameter.
The finding makes it likely that at one point in the immediate wake of the disaster the 4-meter-high stack of uranium-rich rods at the core of the reactor had been entirely exposed to the air, he said. Boiling water reactors like those at Fukushima rely on water as both a coolant and a barrier to radiation.
Matsumoto said the utility would study whether to increase the amount of water it was injecting to overcome the leak and raise the level of water covering the fuel, at the risk of allowing more radioactive water to leak out of the facility.
Nearly 10,400 metric tons of water has been pumped into the reactor so far, but it is unclear where the leaked water has been going. The high radiation levels makes it difficult for workers to check the site, Matsumoto said."