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Nuclear Engineer Sees Evidence That Fuel Melted Through Reactor Pressure Vessel

Special Report: Fukushima and the Future of Nuclear Power

This is part of IEEE Spectrum's ongoing coverage of Japan's earthquake and nuclear emergency. For more details on how Fukushima Dai-1's nuclear reactors work and what has gone wrong so far, see our explainer and our timeline.

In an article in The Guardian on Tuesday, Richard T. Lahey, former chair of nuclear engineering at Rensselaer Polytechnic Institute, in Troy, N.Y., was quoted as saying that the evidence he had seen indicated that fuel melted through the pressure vessel of reactor No. 2 at some point after the crisis began. He told The Guardian:

"The indications we have, from the reactor to radiation readings and the materials they are seeing, suggest that the core has melted through the bottom of the pressure vessel in unit two, and at least some of it is down on the floor of the drywell."

This morning, Lahey elaborated on his analysis for IEEE Spectrum, which he said had been accurately reported by The Guardian, but misinterpreted by some. (A careless read of the article suggests a new meltdown at the plant, rather an analysis of what probably occurred early on in the crisis.)

Lahey says his analysis was based on the data sources seen by him and colleagues around the world, but that the information has been inconsistent and changes hourly. “It’s really hard to read the tea leaves,” Lahey says. “They keep blowing around… I may be wrong. I hope I’m wrong.”

However, his best take is that “all cores have melted, and it appears as though Unit 2 has melted through.”

His conclusion about reactor No. 2 comes largely from the amount of radiation in the water found there and the chemical contents of that water.

Flooding the building with sea water was the right move, he says. In a meltdown, where the fuel escapes through the bottom of the chamber, the mix of molten metal—called corium, a buzzword for steel, uranium, zircolite, and other molten goop from the reactor—will vaporize the concrete and create dangerous radioactive aerosols. “The water will scrub out the radioactive aerosols” besides cooling the molten mass.

How long it will take to cool the corium beneath the vessel will depend on exactly how it escaped. If it melted a single big hole through the bottom of the vessel, it would pile up as a blob on the concrete. The blob’s low surface-area-to-volume ratio will make it hard to cool.

However, Lahey thinks there’s a chance that the corium escaped through narrow channels formed by the control rods, which in this type of reactor go all the way to the bottom of the vessel. In that case, the corium could have been extruded through the channels, forming something with more surface area.

Lahey explained the different scenarios with this analogy: imagine trying to cool food with a fan, while it is being cooked at the same time by microwaves. The energy from the microwaves is akin to the decay heat the fuel generates. The fan is like the injected seawater. If the corium is a blob, it’s like trying to cool a potato. If the corium has escaped through the control rod channels it’s more like trying to cool french fries.

No matter what has happened, cooling will have to be maintained at Fukushima for a long time. As an example, Lahey says it takes five years of immersion in water before the decay heat from a fuel rod freshly removed from a reactor is low enough for air cooling. “It’s not an event that goes all that fast,” he says.

We’ll check in with Lahey later as the situation develops.

Our correspondent, John Boyd, questioned experts in Japan about Lahey’s claim, but they were doubtful. Hidehiko Nishiyama, the deputy director general of the Nuclear Industry and Safety Agency (NISA), did not see evidence of a big breach of the pressure vessel, but acknowledged that its not completely contained. “When we look at the release of radioactive material up to now, while we do not believe there is any major breach either to the pressure vessel or the containment vessel, we are pretty sure there is some leakage,” he told Boyd.

Windows Get Smart

We’re used to displays doing windows—but what would we do if every window on a building were also a display?

That’s not a farfetched idea, insists Frank Shiu, deputy division director of Taiwan’s Industrial Technology Research Institute’s (ITRI) Display Technology Center. Shiu is working with using electrowetting displays as window glass. This technology relies on transparent honeycombs of glass or plastic that contain droplets of colored liquid in each compartment. Electronics on the edges of the display control the behavior of the droplets, contracting them down so they are nearly invisible, or expanding them to cover their compartment with color; researchers around the world are working on the technology with an eye on the e-book market.

Shiu and his team have a ways to go before electrowetting technology starts replacing ordinary window glass. In particular, they’ve got to figure out how to make it cheaper, right now, adding the necessary electrodes and pigment to window glass costs about US$10 for 39 cm2 inches; that means glass for an average window would cost around $200. And that doesn't include the cost of the control electronics or the solar cells that would power the systems.

ITRI estimates that the price can come down to $60 for 1 m2 as the manufacturing process improves, for the materials involved aren’t particularly expensive. Shiu envisions these windows replacing shades and blinds, with early versions custom made to match room décor, and later versions able to display images, for example, details about products in store windows.

A Forest Of Sound

You’d think the main thing people would come to see at a flower show would be, well, flowers. That’s not necessarily true at the Taipei International Flora Exposition, running through 25 April. Instead, the most popular attraction at this international exhibition is the only one that houses no real flowers, just virtual ones.

This Pavilion of Dreams is billed as an interactive showcase of advanced technology themed around the life cycles of flowers and butterflies. Mainly created by technologists from Taiwan’s Industrial Technology Research Institute (ITRI), it’s one hot ticket; visitors stand in long lines simply to get a reservation to get in the line that eventually goes into the exhibit.

To me, the story line seemed a little hokey—visitors first pick a category of dreams, like family or career, and make a wish in that category while standing in front of what seems a lot like a vending machine with some 3-D bells and whistles. The machine assigns a personal flower to you, displays it in a video image, and releases an RFID bracelet. The bracelet identifies your flower and category of dreams, and, as you move through the exhibit, your personal flower sometimes appears in front of you; your presence also triggers trees growing and other effects. The walk through the exhibit takes about an hour; the experience ends when you toss your virtual flower into a virtual river to send it flowing off to carry your wishes into some magical place.

While the story line may have been a bit clunky, the integration of ITRI’s technology into the experience, however, was impressively lovely. Some 150 of ITRI’s FleXpeakers (photo, left), thin loudspeakers less than 1 mm thick, made mostly out of paper, hang in a silver  forest, blending in stunningly with hundreds of other abstract leaves  that fill the entry hall. Or, as the brochure puts it more poetically, “hundreds of speakers as thin as leaves serenade visitors with the sounds of the Earth”

And ITRI's flexible display technology powers rows of curved displays that show dreamlike images of fields and flowers (photo, below right). This is FlexUPD, a breakthrough technology introduced last year that solved a key manufacturing problem for plastic displays, that is, it’s hard to lay circuitry down accurately on something that’s very thin and very flexible. ITRI’s solution was to develop what it calls a de-bonding layer, that is, a material that allows the plastic to stick to a glass substrate during manufacture but easily peel off that substrate later. Spectrum described that development here last fall.

Also making an appearance at the Flower Expo—glasses-free 3D displays (photo, below left). Big ones, not the little handheld gizmos now coming onto the market. Going glasses-free on a large scale is tricky, because the sweet spot, that is, where you have to stand to see the 3D effect at its best, is small and can be hard to find (handheld displays assume a standard distance from eyes to hands, and you naturally make adjustments in how you hold it if something is a little off). But, in the Pavilion of Dreams, this isn’t much of a problem; by the time visitors arrive at these displays, they’ve already been trained to stand in marked spots on the floors, because some of these spots trigger animations. So when they hit the 3D gallery, visitors look at the floor first, find their spot, then look up and see perfect glasses-free 3D.

This version of glasses free technology is a twist on the typical lenticular lens approach, in which the two images for the right and left eyes interlace horizontally and a rippled sheet of plastic on the surface of the display sends the different views in the right directions. ITRI’s lenticular displays interlace the images vertically, necessary because the flowers and trees being displayed are typically vertical images.

The Pavilion of Dreams also incorporated a wireless sensing technology that purportedly detected breathing patterns and pulse rates. I couldn’t tell whether or not this worked or not; it was integrated into the exhibit in a section where visitors were instructed to stand in front of a display and breathe calmly because somehow their breathing would cause the image of a seedling to grow into a beautiful tree. The crowd followed instructions and all the virtual trees grew at basically the same pace, proving, I guess, that all of the visitors, at least, were alive and not virtual.

TEPCO Balances Cooling and Contamination Concerns at Japanese Nuclear Station

Special Report: Fukushima and the Future of Nuclear Power

Editor's Note: John Boyd is an IEEE Spectrum contributor reporting from Kawasaki, Japan. This is part of IEEE Spectrum's ongoing coverage of Japan's earthquake and nuclear emergency. For more details on how Fukushima Dai-1's nuclear reactors work and what has gone wrong so far, see our explainer and our timeline.

More concerns about radioactive contamination from the damaged nuclear plant in Fukushima emerged Monday night when Tokyo Electric Power Co. (TEPCO) said results from soil samples taken near the plant showed the presence of plutonium, though in very small amounts. Meanwhile, the power company is facing a fine balancing act of keeping the three troubled reactors from overheating by injecting water into them, while at the same time trying to prevent leaking contaminated water from flowing into the ground or the Pacific Ocean.

Late Monday night, TEPCO reported that it had taken soil samples in five areas around the plant a week ago and the results showed plutonium contamination in two of the samples taken some 500 meters from the reactor buildings. The amounts measured 0.54 becquerels per kilogram. Plutonium is a by-product of nuclear reactors employing uranium. (For reference, a banana produces 15 Bq per gram.)

Sakae Muto, vice president of TEPCO, told journalists that the amounts of plutonium detected were “extremely small,” and did not pose a problem for human health.  But he added that further monitoring would be conducted.

According to the World Nuclear Association, there “are several tons of plutonium in our biosphere, a legacy of atmospheric weapons testing the 1950s and 1960s.” Chief Cabinet Secretary Yukio Edano, in a morning update for journalists, alluded to this when he said that the amount of plutonium detected was comparable to what is already present in the environment, but the “composition is different” from the plutonium in fallout from nuclear testing, suggesting that it originated at the Fukushima reactor. This finding and the earlier discovery of the pooling radioactive water in the turbine basements and trenches strengthen the belief that fuel rods have melted.

In a morning press conference, Hidehiko Nishiyama, deputy director general of Japan’s Nuclear and Industrial Safety Agency (NISA) said TEPCO was now using three pumps to move radioactive water that had pooled in the basement of No. 1 turbine building into the condenser tank located there. In a later report, NHK, Japan’s national broadcaster, said that though some water had been pumped out, TEPCO could not say how much, or when the process might be completed.

The situation at the No. 1 and No. 2 turbine buildings is more complex than at the No. 3 reactor because both their condenser tanks are full, as are storage tanks outside the buildings that are used when the condenser tanks need to be emptied. Nishiyama said that preparations where being made to pump water from the outside storage tanks to the reactor surge tanks. Surge tanks are normally used to remove water from the suppression pool, or torus, of the reactor—a doughnut-shaped chamber below the reactor where steam is vented to relieve pressure. Surge tanks are connected to the torus, but are some distance from its. . A later report said this process had begun at the No. 3 turbine building at 5:30 p.m. Once the outside tanks are emptied, then water from the condenser tanks can be transferred into them, freeing them up to take up the pooling water on the turbine floors.

Radioactive water was discovered in 16-meter-deep concrete tunnels called trenches Monday. Nishiyama said that they were being checked each day and there was no evidence that there had been overflows from them. He added that TEPCO had stacked sandbags and concrete panels around the shaft entrance of the No. 1 trench to protect the surroundings should it overflow, given that the water level was a mere 10 centimeters from the rim. He added that this safety precaution hadn’t been necessary with No. 2 and No. 3 trenches because the water levels were lower and were not rising.

In a later press conference Edano added that cooling the reactor vessels and the spent fuel storage tanks through water injection has to be given top priority to prevent them heating up. But he noted they also wanted to drain the leaked contaminated water as soon as possible. “So we need to look at both situations and maintain a balance,” he said.

By evening it appeared that little progress had been made in removing the leaked water and there was no word about where the leak or leaks might be coming from. But one piece of good news came when TEPCO said it had restored lighting to the control room of the No. 4 reactor. Now lighting has been restored to all six reactor control rooms.

PHOTO: Reuters

The Continuing Evolution of Nuclear Power

Editor's Note: This is part of our ongoing coverage of Japan's earthquake and nuclear emergency.This column expresses the opinion of the author and not the position of the IEEE.

The nearly simultaneous earthquake, tsunami, and nuclear incidents in Japan have forced us to think long and hard about the use of nuclear power. Is nuclear power safe? Is it environmentally sound? Is it even necessary? These questions are valid, but they’re the same questions we always ask when new technologies cause harm. Rather than give up on nuclear power, we must continue to make it safer.

As a child in the 1950s, I remember when my favorite uncle died in an airliner collision. It was a full 50 years after the new technology of flight had gained a foothold. Flight struggled through decades of poor safety after the “new technology” of flying was born. I remember many, many people questioning commercial aviation in the mid-20th century. Today, planes are incredibly safe, but they could have never evolved to be so if we had given up.

I have raced sports cars semiprofessionally for almost 50 years (semiprofessionally means it costs me more than I earn). In the 1960s and 1970s I lost several friends and many acquaintances in race car crashes. In 2010, I walked away with no physical effects from a crash that was much more severe. Why? Because the “new technology” of vehicle and passenger safety dynamics was still in its infancy 50 years ago, and it has matured.

The evolution of all new technologies is a process, and that evolution comes from identifying and solving problems as they arise. We just don’t understand everything when we begin with a new technology. In the case of aircraft, we have learned to design using design margins well over requirements. So, for example, a passenger airplane will be designed with a failure wing loading of perhaps 1.5 times the maximum anticipated or specified wing loading. We have also learned to make the air traffic control system more robust and user friendly. This evolutionary process of flight continues today and will forever.

In fact, design margins have helped limit the damage in Japan. The Fukushima facility survived intact after the magnitude 9.0 earthquake, though that was a far higher than what it was designed to withstand--the designers thought the largest foreseeable earthquake would have a magnitude around 8.0, and earthquake magnitudes are not a linear scale. The design of the facility performed beyond expectations. The problem we are now facing is that the design did not, apparently, consider a tsunami of the size that resulted from the earthquake.

So what should we learn from this? The events of the last couple of years all around the world seems to indicate that Mother Nature is becoming a bit more violent than we have experienced in the past, so perhaps we need to design to more severe requirements than the common 100-year worst-case natural event; perhaps we need to design for 200-year or 500-year worst-case events. We obviously need to consider how a nuclear facility built on a coastline will survive a tsunami much larger than we have considered in the past. We also must take a step back and reassess the design and construction of our current reactor facilities in light of today’s learning, and retrofit them as necessary for tsunami survival and construction design margin.

The cry against current or new nuclear power ignores the real issues of electrical power generation now and in the future. I know few people who would willingly give up their current use of electrical energy, and the increasing use of plug-in hybrid vehicles will increase the need for electrical generation. Our world of rapidly increasing population and industrial development will increase the need for electrical energy simply with population growth, in spite of any increases in the efficiency of use of energy. So the question we must answer is, how do we cope with our current and increasing electrical needs?

Today, almost 50% of electricity in the United States comes from coal, almost 20% from natural gas, almost 20% from nuclear and 7% from hydroelectric. That adds up to over 95% of the United States electrical energy generation capability. Everything else, including solar and wind, today contributes less than 5% of U.S. electrical needs. Other countries have different mixes, as France gets over 80% of its electricity from nuclear, but coal, fossil fuel, and nuclear power are, and will be well into the future, responsible for generating most of our world's electricity.

Realistically and practically, sustainable technologies like wind and solar are not going to be large contributors to the needed generation of electrical energy for decades, even if you ignore their need for energy storage in times of calm or darkness. These technologies need large amounts of land for relatively small generating capacities. Fusion electrical generation will not be able to contribute significantly to our need for electrical power for the best part of 100 years.

Our decisions on energy technologies are often based on politics, or are reached by comparing dollars spent versus dollars paid back, using inflated future dollars. Dollars, however, are not the real issue. The real issue for the world is the “energy spent” versus the “energy paid back”. The “energy spent” includes the energy needed to grow or find the resources (like ore or vegetation), mine or harvest the resources, refine the resources, transport the resources, build the energy sources, maintain the energy sources (like windmills or solar facilities), and refurbish or remove the sources after their nominal life. It seems to be a well-discussed fact that the production of ethanol from vegetation and its distribution use more energy in fossil fuels and electricity than we derive from the ethanol itself--so why do we still use it? Political considerations, I think. I wonder why we haven’t also seen energy-in versus energy-out calculations from solar and wind generation, and why we don’t demand this calculation for all new technologies.

For at least the next couple of generations, we're stuck using coal, fossil fuels, and nuclear power to provide the vast majority of our electrical needs. We may not like any of these choices, but they simply are our available choices given today’s technology and fiscal resources. Shouldn’t we increasingly focus on making them better and safer today and in the near future? Let’s learn to build safer nuclear reactors and cleaner fossil fuel facilities today while we fund the R&D that will be necessary for the breakthrough technologies that will replace these older energy generation technologies.

About the Author

Harold L. Flescher, a nuclear physicist, was general chairman of IEEE’s Nuclear and Space Radiation Effects Conference in 1980, was president of IEEE’s Nuclear and Plasma Sciences Society in the early 1990s, and was recently Vice-President of the IEEE Technical Activities Board and has been TA Treasurer twice. He is today the Treasurer of IEEE and a member of the IEEE Board of Directors.

Apple Rejects Application that Measures Cellphone Radiation

If I made an iPhone app, I'd probably be pretty bummed if Steve Jobs took a moment out of his day to personally reject it. It's unlikely that I'd post an announcement about it on my website. But then, I'm not a startup with a product that measures cellphone radiation levels, harboring a publicity-ready response from Jobs:

jobs_email

Tawkon, the creator of said app, first requested approval from Apple about a year ago, receiving essentially the same (albeit wordier) response, which cited the confusion that the application might cause iPhone owners from a usability standpoint. The company now seems to have given up on the App Store route. In the above mentioned blog announcement, it says that the app, already available on Android and Blackberry, will now be available to iPhone users via Cydia. Cydia apps require a jailbroken iPhone.

Given that the scientific consensus seems to find no long-term health effects of cellphone radiation the purpose of the app is potentially controversial. According to Tawkon, its radiation-measuring technology works by leveraging existing components in cellphones, and detecting a range of environmental factors. From there, its ‘complex algorithms’ ensure that the application works accurately and helps users reduce radiation exposure.

The company’s website states that the iPhone rarely gets close to its maximum SAR level, which is a metric regulated by the FCC. But when it does get close to the max, the app will suggest ways to bring it down: "'go back' to previous location, 'activate speakerphone', 'hold your phone vertically' or activate headset while traveling fast, among other actions."

Based on this pitch, quantitative questions arise. If a device's maximum SAR level is already deemed safe for users by the FCC, then the above actions might only prevent imaginary cancer. Even if the Interphone Study's more alarming findings (which suggest potential harm from long-term, moderate cellphone exposure) are eventually proven, would Tawkon's radiation-reducing actions make a significant difference in one's overall deleterious exposure to electromagnetic radiation? This isn't necessarily the company’s claim, but it'd be a logical motivation for users.

To date, even the most comprehensive and well-funded studies have struggled to map the behavioral and demographic complexities of cellphone usage to health problems. Worse, data on how a lifetime of regular cellphone use affect users’ health doesn't yet exist. But people will still worry about cellphone radiation, so shouldn’t iPhone users they be able to access the same information that Android and Blackberry owners can?

Jobs' decision to reject an application (on whatever grounds) can be viewed as either defensible or imperious. Tawkon's display of this e-mail exchange in tandem with its Cydia announcement can be viewed as either liberated or sensationalist. Until the dangers of cellphone radiation are more satisfactorily disputed, it’ll be hard to see as a technological quarrel, hidden, as it is, by the shadows of the outsized personalities at hand.

Contaminated Water Discovered in Tunnels at Fukushima Plant

Special Report: Fukushima and the Future of Nuclear Power

Editor's Note: John Boyd is an IEEE Spectrum contributor reporting from Kawasaki, Japan. This is part of IEEE Spectrum's ongoing coverage of Japan's earthquake and nuclear emergency. For more details on how Fukushima Dai-1's nuclear reactors work and what has gone wrong so far, see our explainer and our timeline.

During the past few days, workers at the damaged nuclear power plant in Fukushima Japan contended with high radiation levels, unexpected pools of water contaminated with radioactive material, and narrowing options for what to do with that water as they continued to try to bring the plant completely under control.

Tokyo Electric Power Co. (TEPO) raised already heightened concerns when over the weekend it reported a huge spike in radiation levels at the damaged Fukushima Dai-1 Nuclear Power Plant Saturday. But the company later had to apologize for giving incorrect figures.

TEPCO initially reported it had detected 2.9 billion becquerels of iodine-134 per cubic centimeter in water pooled on the floor of the No. 2 reactor turbine building on Saturday night. The news was relayed by the Nuclear and Industrial Safety Agency (NISA) on Sunday morning when it said that the radioactivity level was “10 million times higher” than water found in a typical reactor.

But only hours later TEPCO said it had been mistaken and revised its figures downward to 100 000 times higher than normal—still very high. The radiation level at the surface of the pooled water was measured at more than 1000 millisieverts per hour on Monday.

TEPCO’s announcement followed the discovery that three workers had stepped in radioactive water in the turbine basement building of the No. 3 reactor last Thursday and had been exposed to between 173 to 180 millisieverts of radiation. TEPCO has raised the maximum level of radiation a worker may be exposed to in one year from a relatively low 50 millisieverts to 250 millisieverts so as to be able to cope with the emergency.

One of the doctors in the hospital where the three workers had been taken for examination said Monday that the workers had left the hospital at noon, having been found to be in good health. He said they would be examined again in several days, but any symptoms that might later develop were not expected to be serious.

Finding a place to put the contaminated water is proving to be a problem. Hidehiko Nishiyama, deputy director general of NISA, told reporters Monday morning that TEPCO planned to pump radioactive water in the No. 2 turbine room into the condenser tank located in the same building. The condenser tank is used to take steam from the reactor used to turn the turbines, and turn it back into water to complete the cycle. But the procedure had been delayed when TEPCO found the tank itself was already almost full of water. The company then decided to transfer the condenser water to nearby outside storage tanks, only to discover that these too were full. Nishiyama says TEPCO must now empty these outside tanks before it can begin draining the No. 2 turbine room.

A similar situation exists for the No. 3 turbine room, condenser tank, and outside storage tanks, says Nishiyama.

Yukio Edano, the Chief Cabinet Secretary, said in a press conference at 11:30 Monday morning that based on preliminary analysis it seemed the contaminated water in the No. 3 turbine basement had come into contact with “possibly melted fuel elements, and had leaked out” of the reactor. He added that it was essential the water should not be allowed to seep into the ground or the sea.

But that dangerous scenario looked likely to happen when TEPCO later told reporters that radiated water had been found in an area called “the trench” outside the No. 2 turbine building the day before. NISA’s Nishiyama later described the trench to reporters as a deep concrete tunnel used to carry electric cables and pipes for the turbine room. Originally he said the cables and pipes had been laid on the ground, but to prevent accidents they were housed inside this tunnel. At one end of the trench there is 16-meter shaft with an inspection manhole and when the manhole was removed, water was found to have leaked into the trench and risen “to a height of 14.9 meters and is increasing,” Nishiyama said. Radiation readings were taken and found to be more than 1000 millisieverts per hour on the surface—similar to the radiation found pooling in the turbine room, from where it has presumably leaked.

Nishiyama said the trenches of the No. 1 and No. 3 turbine buildings were also inspected and similar amounts of water were found in these tunnels too. However, the radiation level for the water filling the trench outside the No. 1 turbine building measured only 0.4 millisieverts per hour. Debris surrounding the manhole for the No. 3 turbine room prevented workers from taking a reading there.

Nishiyama added that the trenches were roughly 55 to 60 meters from the ocean and it was thought the contaminated water had not entered the sea. Nishiyama said TEPCO was making every effort to prevent this from happening.
 

Workers Step in Radioactive Water at Japan's Nuclear Plant

Special Report: Fukushima and the Future of Nuclear Power

Editor's Note: John Boyd is an IEEE Spectrum contributor reporting from Kawasaki, Japan. This is part of IEEE Spectrum's ongoing coverage of Japan's earthquake and nuclear emergency. For more details on how Fukushima Dai-1's nuclear reactors work and what has gone wrong so far, see our explainer and our timeline.

Two weeks after the March 11 earthquake and tsunami struck Japan, the damaged Fukushima Dai-1 nuclear power plant remains a dangerous and volatile place. High radiation levels continue to hamper the progress of the firefighter crews spraying water into spent fuel storage pools, and of the repair crews attempting to restart pumps and cooling systems in the explosion-wrecked reactor buildings. In the wake of an accident that exposed three workers to radiation, Japan's Nuclear and Industrial Safety Agency told reporters that radioactive materials may be leaking from the reactor in building No. 3.

The accident was a serious setback after a week that began with gradual progress, as Tokyo Electric Power Company (TEPCO) made headway in reconnecting the plant's six reactor buildings to the electricity grid.

On Thursday three workers were rushed to hospital after being exposed to high radiation levels at the plant. The three TEPCO subcontractors were laying electrical cables in the basement of the turbine room behind the No. 3 reactor building when they stepped into water contaminated with radiation, and received doses of between 173 and 180 millisieverts. The upper limit of exposure for nuclear plant operators dealing with an emergency is usually a cumulative dose of 100 millisieverts per year, but Japan has raised its threshold to 250 millisieverts per year for workers coping with the crisis at Fukushima Dai-1.

The workers were taken to a hospital for radiation monitoring--the image above shows Japan Self-Defense Force members in protective clothing preparing to transfer the injured workers to the hospital. Two of the men are being treated for severe radiation exposure to their feet; they may have suffered skin burns from beta particles. The third worker was wearing boots and apparently wasn't seriously injured.

Early Friday morning, a Nuclear and Industrial Safety Agency (NISA) official told reporters that the a dosage meter used by the workers warned of high radiation levels but the workers continued with their task. The official added that NISA had "doubts about radiation management measures" and the safety of the workers and these doubts had made known to TEPCO. Additional media reports said the subcontractors had been working in water as deep as 30 centimeters with high levels of radiation, while NHK reported that high levels of radioactive cerium-144 and iodeine-131 had been measured in the water, substances generated during nuclear fission.

Kyodo News reported that the two hospitalized men were not wearing rubber boots at the time of the accident. When the radiation alarm went off, the workers apparently thought it was due to a dose meter malfunction. Kyodo also said there was no-one present to specifically monitor radiation.

In a press conference on Friday morning, Hidehiko Nishiyama, deputy director general of NISA, explained the incident's implications. "The water had 10,000 times the radiation as is found in water circulating in standard operating reactor," Nishiyama said. He added that the high radiation level indicated that fuel inside the reactor may be damaged in some way, and suggested that the No. 3 reactor vessel may be leaking. TEPCO officials have been particularly concerned about the No. 3 reactor because it's the only one of the plant's six reactors that uses a mix of uranium and plutonium fuel.

However, not everyone believes that the No. 3 reactor vessel has been breached. A nuclear expert from Osaka University told NHK viewers that because the pressure in the No. 3 reactor was reported to be stable, it was more likely that a pipe or a valve in the reactor's water circulating system could be cracked. It's also possible that the spent fuel storage pool in the No. 3 building is the source of the radiation leak, but that's considered less likely.

Japan's Chief Cabinet Secretary held a press conference later on Friday to advise residents living between 20 and 30 kilometers from Fukushima Dai-1 to consider voluntary evacuation (people living within 20 kilometers of the plant have already been evacuated). He said it was possible the government will extend the mandatory evacuation zone to 30 kilometers if radiation levels increase.

In another turn of events, Minister of Defense Toshimi Kitazawa told reporters that the U.S. Navy is shipping fresh water from its base in Yokosuka (just south of Tokyo) to the stricken nuclear plant. He said the United States had expressed concern that Japan's use of seawater "could cause equipment to seize up and corrode. And as a result they are urging us to use fresh water," Kitazawa said.

Separately, NISA's Nishiyama said TEPCO was now making preparations to switch its pumps from seawater to fresh water for both its reactor cooling efforts and also in its attempts to refill the spent fuel storage pools.

TEPCO is continuing its efforts to bring power and lighting back to the central control rooms and pumping systems of all six reactor buildings.

PHOTO: Kyodo/Reuters

Radiation Monitoring in Japan Goes DIY

Special Report: Fukushima and the Future of Nuclear Power

Editor's Note: This is part of IEEE Spectrum's ongoing coverage of Japan's earthquake and nuclear emergency.

A group of device hackers are digitizing Geiger counter readings to monitor radiation levels in real time across Japan.

The data is being aggregated by the platform Pachube (pronounced “patch-bay”), which allows users to upload and share sensor data. 

So far, the crowd-sourced effort has produced a range of maps that show radiation levels across Japan. Ed Borden, who manages developer relations at Pachube, told me he foresees more applications for the radiation data, including cell phone programs that could inform the holder of nearby radiation levels. “These visualizations are kind of the first step," he says.

Japan’s Ministry of Education, Culture, Sports, Science & Technology issues periodic updates, indexed here, on radiation levels throughout the country by prefecture.

Pachube’s data is available in real-time, but it is likely not as precise. NPR notes that contamination, poor calibration, and varying levels of background radiation can make it difficult to interpret Geiger counter readings.

Borden says that aggregating radiation data from a number of sensors will allow people to cross-check readings for accuracy and may also inspire a healthy dose of skepticism when it comes to the numbers.

On the face of it, open access to critical environmental information seems like a good thing. The Atlantic's Alexis Madrigal says the crowd-sourced effort could inspire more confidence in official measurements.

I would argue that distributing unofficial radiation readings, particularly uncalibrated ones, may be counterproductive in an emergency. Evacuation planners must grapple with complicating issues, such as voluntary “shadow evacuations” of residents who live outside official evacuation zones. False or hard-to-interpret radiation measurements could encourage that behavior.

With just a few hundred Geiger counter feeds, Pachube’s data is too spotty to paint a clear picture of the radiation environment around the country.

But it will be interesting to see what real-time data the project collects going forward, particularly if the sensor network gets denser. The radiation environment around Fukushima is still changing. On Friday, Japan’s Chief Cabinet Secretary announced a voluntary evacuation for residents living between 20 and 30 kilometers from Fukushima Dai-1 (people living within 20 kilometers of the plant have already been evacuated).

For those interested in digitizing data from decades-old Geiger counters, one Pachube user has posted a tutorial detailing a way to convert analog chirps into data that can be uploaded to the web.

The Lights Are Going on at Japan's Stricken Nuclear Plant

Reactor No. 4

Special Report: Fukushima and the Future of Nuclear Power

Editor's Note: John Boyd is an IEEE Spectrum contributor reporting from Kawasaki, Japan. This is part of IEEE Spectrum's ongoing coverage of Japan's earthquake and nuclear emergency. For more details on how Fukushima Dai-1's nuclear reactors work and what has gone wrong so far, see our explainer and our timeline.

Lights were switched on in the central control room for the No. 3 reactor of the earthquake-hit Fukushima Dai-1 nuclear power plant on Tuesday night, and some instruments were in operation. With the No. 3 building successfully reconnected to the electricity grid, operators will now work on getting the building's cooling system back in action. Tokyo Electric Power Company (TEPCO) is working to reconnect the plant's other five buildings to the grid as well, which would be a major step towards stabilizing the plant and ending the immediate crisis.

But the good news was dampened with the announcement that Japan’s death toll from the earthquake and tsunami that struck on March 11 had passed 9,000, with 14,000 people still unaccounted for. Also, two British newspapers have reported that Japanese authorities knew about major safety problems at Fukushima Dai-1 for some time before the earthquake and tsunami.

Tokyo Electric Power Company (TEPCO) told reporters that it had lights back on in the central control room for the No. 3 reactors at 10:43 on Tuesday night. An official added that temperature gauges for reactors No. 1 and No. 3 indicated surface temperatures were considerably higher than normal: The temperature of the No. 1 reactor on Tuesday was 394 degrees Celsius. The official said workers had doubled the amount of seawater they were using to cool the reactor. Hidehiko Nishiyama, deputy director general of Japan's Nuclear and Industrial Safety Agency, said the reactor was designed to withstand temperatures of up to 300 degrees Celsius. An later bulletin said the temperature was starting to come down.

In a press conference for the foreign press Tuesday evening in Tokyo, Nishiyama gave an update on the other nuclear power plants that were impacted by the earthquake and tsunami that hit northeast Japan. Four reactor units of the Fukushima Dai-2 nuclear plant, one unit of the Tokai Dai-2 nuclear plant, and one unit of the Onagawa nuclear plant were impacted, but none experienced severe problems.

“All of these units were shut down because of the earthquake,” said Nishiyama. “But they all have power supplied from outside and were shut down in a stable manner, what we call a cold shutdown.”

Nishiyama added that before they could be returned to service, the integrity of the equipment first had to be ascertained. If the soundness of the equipment was confirmed, it would then be necessary to consider how the reactors could be restarted taking into account that more large earthquakes could occur. “We would also have to gain the acceptance of the residents in the surrounding areas as well,” said Nishiyama. “So I’m not able to say when we can put these plants back into service.”

NHK, Japan’s national broadcaster, reported that TEPCO expects the ongoing rolling power cuts to end in early May as the weather warms up. But TEPCO said that when heavy use of air conditioners increases with the rise of summer temperatures, it will have to reintroduce the blackouts. TEPCO estimates that there will be a supply gap of around 10 megawatts during that time.

Work at the crippled Fukushima Dai-1 plant continues to be interrupted by worrisome emissions. In a preliminary press briefing at 4:30 p.m. on Wednesday (local time) a TEPCO official said “black steam” had been seen rising from the No. 3 reactor building at 4:20 p.m. He said the workers had been withdrawn as a safety precaution. He had no other details available at that time. Black smoke from the same reactor building was also seen pluming into the sky on Monday, which brought work crews to a halt, but that smoke later turned white and subsided. NHK said TEPCO announced at 5:30 on Wednesday (local time) that the smoke was subsiding and that no rise in radiation had been observed in and around the plant.

NHK also reported TEPCO saying that the tsunami that hit the plant was more than 14 meters high, twice as high as the plant was prepared for.

Meanwhile, the criticisms of Japan's nuclear industry continue to mount. A British newspaper, The Telegraph, published a story last week alleging Japan was putting costs before safety concerns and that an official from the International Atomic Agency (IAEA) had warned Japan in December 2008 that strong earthquakes would pose a “serious problem” because nuclear power plant safety rules were out of date. The paper said that the Japanese government promised to upgrade its plants, but it was not known how extensive its efforts were. The paper based its article on U.S. government cables obtained by the WikiLeaks website.

A second British newspaper, The Guardian, raised allegations yesterday that spent fuel storage pools in the Dai-1 plant were over-full, creating a dangerous situation. The paper wrote that the plant was storing “far more fuel rods than it was designed to store, while its technicians repeatedly failed to carry out mandatory safety checks.” The newspaper says the charges are based on TEPCO’s own documents and “a presentation TEPCO gave to the International Atomic Energy Agency and later posted on the company’s website.”

PHOTO: TEPCO/Reuters

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