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Photo Gallery: Learning to Think in Millisievert

Foto: YURIKO NAKAO/ REUTERS

Fukushima Fallout How Dangerous Is Japan's Creeping Nuclear Disaster?

The destroyed reactors at Fukushima have been releasing radiation for weeks. According to model calculations, the stricken nuclear plant could already have released one-tenth of the amount of radiation unleashed in the Chernobyl disaster. How serious a risk does the disaster pose to humans?

The technicians had tried for days to restore electricity to the remains of the Fukushima nuclear power plant. But then it was ordinary rubber boots, of all things, that would come to symbolize their desperation, helplessness and defeat.

On Thursday, the three men had made their way into the basement of the turbine building for reactor No. 3 to examine the situation there. When they returned later, they came fully equipped with tools and protective gear that included helmets, masks, rubber gloves and raincoats on top of their radiation suits.

The one thing the men were not prepared for was that suddenly they would be wading through more than a few inches of water. Two of the workers were only wearing ankle-high boots, which allowed the water to seep in. With wet feet, the men spent three-quarters of an hour working on the cables, despite the fact that their dosimeters were beeping for a long time.

The workers are now under observation at the National Institute of Radiological Sciences. The water at Fukushima was so contaminated that radioactive beta radiation burned their skin. In less than an hour, they were exposed to about 180 millisievert of radiation, or nine times as much as one nuclear power plant employee is exposed to in an entire year. "These kinds of burns will be causing problems for the men for a long time to come," says Peter Jacob, director of the Institute for Radiation Protection at the Helmholtz Center in Munich, Germany. Commenting on the exposure, a coworker of the three men said laconically: "We do pay attention. But now we have to be even more careful as we work."

The incident revealed, once again, how little experts know about the dangers that still lurk on the grounds of the ill-fated plant. No one had expected the radiation level in the water in the basement to be as high as it was. The levels of radiation in water in the basement of reactors No. 1, No. 2 and No. 3 reached record highs, with water at No. 2 measuring 1,000 millisieverts per hour. This was due to a partial core melt. Also, the containment vessel for the third reactor was apparently damaged, representatives of the Japanese nuclear regulatory agency concluded. Could this mean that there is a crack in the barrier between the highly radioactive core and the surrounding environment?

The beginning of last week offered grounds for cautious optimism. Power had been restored to the damaged reactor No. 1, a German concrete mixer was pumping water into the dangerously empty pool containing spent fuel rods in Unit 4, and there had been no explosions in the plant for an entire week. Two weeks after the disaster in Fukushima  began, all of this sounded like good news.

'An Ongoing, Massive Release of Radioactivity'

Meanwhile, however, the engineers have been forced to realize that they have made almost no headway in restoring the cooling system. By Friday night, pumps were still not working in any of the damaged reactors. Up to 45 tons of sea salt have apparently accumulated in the containment vessels, complicating the cooling effort. The salt is crystallizing in warm spots and creating an unwanted layer of insulation. The engineers planned to start flushing fresh water into the reactors on Friday afternoon. But the reactors are only one problem. There's also the issue of the 3,450 spent fuel rods, which are red-hot, presumably severely damaged and exposed to the air in half-empty pools.

"We are experiencing an ongoing, massive release of radioactivity," says Wolfram König, head of Germany's Federal Office for Radiation Protection. "And everyone should know by now that this isn't over by a long shot." Nuclear expert Helmut Hirsch says: "All I hear is that people are wondering whether this will turn into a meltdown. But the thing is, it already is a partial meltdown." The difference, in this case, is that Fukushima is a creeping disaster.

To make matters worse, the wind changed on Friday. Radioactive particles over the Pacific were now drifting westward across Japan. High levels of radiation were detected in vegetables, water and soil near the Fukushima plant.

The Japanese authorities have so far only evacuated a zone within 20 kilometers (12.4 miles) of Fukushima. But the risks posed by radiation are also growing for people outside this zone. "It is high time Japanese authorities extend the 20- kilometer (12.4-mile) evacuation zone around the crippled nuclear-power plant at Fukushima ... Pregnant women and small children should immediately be evacuated from a progressively increasing area," writes nuclear critic Mycle Schneider, lead author of the World Nuclear Industry Status Reports. Embryos, fetuses and infants are at the highest risk, because radiation targets cells that divide quickly.

There are currently 77,000 people living in emergency shelters set up in places like gymnasiums. Another 62,000 people live within the 30-kilometer zone. The head of the United States Nuclear Regulatory Agency (NRC) recommends expanding the evacuation zone to 80 kilometers, in which case 2 million people would have to be relocated -- in addition to the hundreds of thousands of earthquake and tsunami victims. Japanese authorities are now asking people to leave the area voluntarily.

The beleaguered Japanese are also being peppered with concerned advice, demands and speculation from the United States, Russia, Finland and Germany. Even France's nuclear safety agency IRSN, not exactly known for its cautionary approach to nuclear risks, published a disturbing model calculation last week. According to the report, by last Tuesday the Fukushima plant had already released into the environment one-tenth of the amount of radioactive material that was released at Chernobyl  in 1986.

The International Atomic Energy Agency (IAEA), however, believes that this estimate is highly exaggerated. According to its calculations, which are based on readings taken by measuring equipment at the site, the amount of radiation released to date is only a fraction of the French estimate.

Contaminated Food and Water

The French physicists and engineers based their assumptions on their knowledge of the amount of fissile material in the reactors, their own research on the condition of hot fuel rods and readings taken in the vicinity of Fukushima. German nuclear expert Helmut Hirsch, who has performed model calculations for Greenpeace, says: "This is not an exaggeration." There are more than 2,500 tons of uranium and plutonium in Fukushima, a "gigantic radioactive inventory, at least 20 times as much as there was at Chernobyl," says nuclear critic Schneider.

In fact, things could get even worse, much worse, than the French calculation suggests. The French scientists assume that most of the radioactive particles currently being measured come from reactor vessels 1, 2 and 3. The active fuel rods, which have hardly cooled at all, had caused temperatures in the containment vessels to rise so significantly than the plant engineers were forced to release radioactively contaminated air through valves in the interior of the reactors. In reactors in Germany and the United States, these emergency valves contain filters to capture radioactive particles. There were no such filters at the Fukushima plant.

Nevertheless, the best scenario, under the current circumstances, would have been to allow the radiation to reach the environment in this fashion. Indeed, the engineers at Fukushima have not had to release any more of this radioactive steam for more than a week now. If the French assumptions are correct, the worst emissions of radioactivity could already be over.

'We Don't Have the Slightest Idea of What Conditions Are Like'

Other experts support a different theory. Bill Borchardt of the NRC, for example, blames the high radiation values near Fukushima primarily on the spent fuel rods in the holding pools.

This would be a much more difficult problem to contain. The spent fuel rods, normally kept underwater and protected by the roof of the reactor building, are now emitting radiation to the open air. Only cooling water prevents the rods from igniting, and yet the cooling water is constantly turning into radioactive steam. Even more worrisome is the question of how it will be possible to ever refill the holding pools, which may have been damaged in the earthquake.

How much radioactivity is released also depends on the condition of the fuel element. A fuel element consists of about 100 four-meter-long fuel rods, each about as thick as a human thumb. The rods themselves are made of a zirconium alloy, which is filled with rounded tablets of uranium oxide, not unlike pills in a tube. Experts fear, however, that the metal shells could have become oxidized and have partially melted. If that is the case, larger amounts of fissile products are escaping from the rods.

Instruments in a helicopter flying over the plant measured 80 millisievert of radiation at an altitude of 40 meters (131 feet) above the roof of the plant, with levels dropping to only 4 millisievert 200 meters higher up. This suggests that the radiation is coming directly from the holding pools.

Could this assessment prove to be completely wrong? "I think we don't have the slightest idea of what conditions are like in the reactor buildings," says the NRC's Borchardt.

Radiation Detected in Vegetables

As an American, Borchardt is familiar with the problem. After the reactor accident at Three Mile Island near Harrisburg, Pennsylvania in 1979, it took six years before engineers could open the reactor core. Only then were they able to see how far the meltdown had progressed. A monitoring system for such accidents is now required in the United States. It measures how much radioactivity is released, as well as the condition of the fuel rods. Japan has no such systems.

Instead Tepco, the plant's operator, has published photos taken during the power outage. They show workers with flashlights and clipboards groping their way through the pitch-dark control room of reactor Units 1 and 2 to check measuring equipment.

Otherwise, the only alternative has been to read the smoke signals. Experts believe that dark smoke comes from burning cables and debris, while white smoke signifies water evaporating over the hot fuel elements.

Meanwhile, Tepco measured 500 millisievert per hour near the No. 2 reactor. Anyone who remains within this zone for 12 hours will die of radiation sickness. The radiation levels in proximity to the three exposed electricians were almost as high.

The eerie radiation has long since spread beyond the grounds of the nuclear plant. Food safety monitors measured 82,000 bequerel per kilogram in cabbage grown in a region 40 kilometers northwest of Fukushima. The maximum allowed value is 500. The highest readings measured in spinach were 54,000 bequerel per kilogram.

Experiences from Chernobyl show, once again, how long radioactivity can persist in the food chain. Some 25 years after the reactor accident, the meat from one in five wild boars hunters shoot in certain parts of Bavaria has to be thrown away , because it contains more than 1,000 bequerel per kilogram.

Japanese authorities have also found radioactive iodine in drinking water, although levels remain relatively low. Nevertheless, when the government recommended against using tap water to make infant formula, Tokyo supermarkets quickly sold out of bottled water. "There isn't a single bottle left on the shelf," reports Philip White of the Citizens Nuclear Information Center, the center of Japan's cautious anti-nuclear movement.

Panic buying in Tokyo is already making it more difficult to provide drinking water to people in the areas hit by the tsunami, where many water lines were destroyed. But what happens if radiation in the drinking water reaches truly worrisome levels?

Just How Reliable Are the Radiation Measurements?

The Japanese will have to learn to think in terms of millisievert. For example, the highest reported hourly dose at the edge of the evacuation zone was 0.16 millisievert. A person who spends 25 days constantly exposed to such levels would receive the maximum permissible annual dose for workers at nuclear power plants.

There is also an underlying sense of uncertainty over just how reliable the radiation measurements actually are. And critics wonder why the highest radiation readings near Fukushima are usually taken by police personnel and not Tepco or the Japanese nuclear regulatory agency.

But even if suspicions are unfounded, the insidious aspect of radiation is that it is so unpredictable. "We will see a patchwork of areas of higher and lower radiation levels," says Peter Küppers of the Eco-Institute Darmstadt in southwestern Germany. The radiation level depends on wind direction, rain and where water collects. The differences were extreme after Chernobyl. "There were parts of northeast Bavaria and at Konigssee Lake in Germany that were more contaminated than some spots within the 30-kilometer exclusion zone directly surrounding Chernobyl," says Küppers.

Dispersal over such a large area can be practically ruled out in Japan. This only occurred at Chernobyl because the reactor burned for days, propelling radioactive material into extremely high air layers.

But where the fallout descends also depends largely on the wind in Japan. "At first Japan was very lucky, as far as the weather was concerned," says König of Germany's Federal Office for Radiation Protection. The sinister plumes initially drifted out to sea. But the weather gods will not always remain as merciful.

A Sense of Foreboding and Uncertainty

There is already a sense of foreboding among the residents of Fukushima. Yoshihiro Amano owned a small grocery store six kilometers from the nuclear power plant. Now he is waiting in line for a bowl of noodle soup in an evacuation center, trying to make the best of the situation. "There's no point in getting angry," he says. "But we are afraid. We don't know if it will take days, months or decades before we can go home again."

The Japanese will have to live with this uncertainty from now on, because our knowledge of the health effects of radioactive radiation is so appallingly slim.

Studies involving the survivors of Hiroshima and Nagasaki concluded that if 100 people received a dose of 100 millisievert, one of these people would eventually die of cancer as a result of the exposure.

This can certainly be seen as a comforting piece of news. On the one hand, it indicates that if about 40 of 100 Japanese would normally die of cancer at some point in their lives, that number would only rise to 41 among 100 people exposed to 100 millisievert of radiation. On the other hand, 100 millisievert is an enormous dose. To date, only a handful of workers in Japan have been exposed to such a bombardment of radioactivity.

But what about those who were exposed to lower levels of radiation? What if each of the 35 million residents of Tokyo is exposed to a few millisievert of radiation? There are few questions in science that are being discussed more heatedly, and yet there are no reliable answers.

'Any Amount Is Harmful'

One thing is clear: Even in the region surrounding Chernobyl, there has been no statistically significant evidence of elevated levels of leukemia and cancer following the accident. The one exception is thyroid cancer in children, for which there is clear evidence of a connection with the accident. On the other hand, there is no official lower limit at which radiation becomes harmless. "Any amount is harmful," says Edmund Lengfelder, director of the Otto Hug Radiation Institute in Munich. "And the younger the person, the more harmful it is."

Radiation poses the greatest danger to embryos in the womb during their earliest stages of development. Radiation can cause Down's syndrome, spina bifida, cleft palate and other birth defects. Genetic changes can also be passed on to the next generation, as DNA testing of healthy children of the workers involved in the Chernobyl cleanup has shown.

According to the results of a disturbing simulation just released by the Japanese nuclear safety commission, young children outside the 30-kilometer radius surrounding the damaged nuclear power plant may have already absorbed a dose of 100 millisievert in their thyroid glands, as a result of the radioactive iodine leaked from the plant. In two-year-olds, this increases the risk of developing thyroid cancer by the age of 15 by a factor of five.

In the long term, the radioactive isotope cesium 137 is even more dangerous than radioactive iodine. It has a 30-year half-life and accumulates in the soil and in animals. "Cesium 137 becomes distributed throughout the body and can therefore promote cancer development in various places," says Wolfgang-Ulrich Muller, a radiobiologist in the western German city of Essen.

It can take years or even decades until that happens. Nevertheless, Wolfram König, head of Germany's Federal Office for Radiation Protection, is convinced that the radiation from the Fukushima nuclear power plant has already claimed its first victims -- because of the fear of radiation and not the radiation itself. "It's possible that many of the people who died in the rubble lost their lives because no one dared to help them," says König.

Translated from the German by Christopher Sultan
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