#japan #earthquake #fukushima*

Конкретни данни за радиацията в Европа

http://www.dw-world.de/dw/article/0,,14942725,00.html

How Much Fuel Is at Risk at Fukushima?
by Eliot Marshall and Sara Reardon on 17 March 2011, 5:39 PM
The maximum hazard from a crippled nuclear power plant depends on how much radioactive fuel is on site, both in the reactors and in the storage pools. And the Daiichi complex in Fukushima, Japan, damaged by the 11 March earthquake and tsunami contains more fuel than was at risk at Three Mile Island.
The Daiichi complex had a total of 1760 metric tons of fresh and used nuclear fuel on site last year, according to a presentation by its owners, the Tokyo Electric Power Company (Tepco). The most damaged Daiichi reactor, number 3, contains about 90 tons of fuel, and the storage pool above reactor 4, which the Nuclear Regulatory Commission's (NRC's) Gregory Jaczko reported yesterday had lost its cooling water, contains 135 tons of spent fuel. The amount of fuel lost in the core melt at Three Mile Island in 1979 was about 30 tons; the Chernobyl reactors had about 180 tons when the accident occurred in 1986.
When the 9.0 earthquake struck, three of the six nuclear reactors at the Daiichi complex were running and were immediately shut down. The other three were already down for inspection, and their fuel had been unloaded.
The three machines in service—only one of which appears to have been seriously damaged in the quake—contain partly burned fuel that could harm the environment and endanger public health. Storage ponds that contain used fuel also pose a risk—as Jaczko, the NRC chair, emphasized in dramatic testimony yesterday to the U.S. Congress. Citing the deterioration of Daiichi's cooling systems, he recommended that people evacuate the area around the plant within a 50-mile radius.
Some saw Jaczko's comments as an overreaction. But it raised the question of what a worst-case scenario would look like.
The answer must take into account fuel rods held in standby in the reactors plus used fuel in the seven storage pools—one co-located with each reactor and a central holding facility. Although cooling and fuel containment systems have done their jobs as designed in most cases, one reactor appears to be leaking from its containment structure. And one holding pool—according to Jaczko, but not Tepco—may have run out of water. The temperature of some other pools is elevated.
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Trackers Seek More Data on the Release of Radioactive Material
by John Bohannon and Daniel Clery on 17 March 2011, 5:31 PM
As teams of Japanese engineers scramble to prevent a disastrous release of radioactive material from the Fukushima nuclear plant, scientists are already preparing for a challenge that may unfold over several years: Tracking the spread of radioactive material beyond the reactors and monitoring the radiation it emits in the environment.
"The good news," says Tony Roulstone, a nuclear engineer at the University of Cambridge in the United Kingdom, is that radiation "is simple to measure, and to measure at levels vastly below that significant to human health." But that still leaves the question of where to look for it. The answer requires modeling the release and spread of radioactive material through the environment.
Those models are "adequate," says Raúl Periáñez, a nuclear physicist at the University of Seville in Spain. "The problem is the lack of data to feed the models," He says. For example, if a fire or explosion sends material into the air, "it may be released as an aerosol and/or attached to particles." The size of those particles can make a huge difference in the range of spread.
So far, researchers have little data from the Fukushima disaster to work with.
Gerhard Proehl is scientific secretary of a program at the International Atomic Energy Agency (IAEA) in Vienna that creates these computer models. The physicist says that his research group has offered its expertise to colleagues in Japan but has received only a trickle of data. Most of it is radiation measurements taken at monitoring stations positioned around the nuclear plant. "Using these numbers with our models is very difficult," he says, because they do not distinguish between air and ground radiation. "What we really need are separate measurements," he says.
Beyond the radiation monitoring, Proehl says that scientists will need to map the distribution of different radioactive species in the environment. The worst of these is the plutonium in the reactor cores. But absent a massive explosion or an intense fire, he says, the plutonium "will not go far." The more immediate worry is the release of more volatile species such as cesium-137 (with a 30-year half-life), cesium-134 (with a 2-year half-life), and iodine-131 (with an 8-day half-life).
Another group monitoring the spread of radioactive materials is the Comprehensive Nuclear-Test-Ban Treaty Organization. The CTBTO has built up a worldwide network of sensors to pick up the signals of clandestine nuclear tests, including seismic detectors, acoustic sensors in the air and oceans, and radionuclide stations as part of its mission to ensure that no countries carry out nuclear tests. Among the 60 radionuclide stations currently operating, CTBTO has ones scattered across the Pacific and around the Pacific Rim. Each station contains an air filter that collects specks of dust from air. The filters are checked once daily with a gamma-ray detector.
Once a radionuclide station detects something that may have come from a nuclear test, researchers use sophisticated atmospheric models to wind back the clock and so finger the possible nuclear cheat. Those models can run forward equally well and estimate where debris from Fukushima might end up. CTBTO is making those calculations, but its results may go only to the governments that have signed up to the treaty. Hence none of its predictions has been made public, although The New York Times says it has seen a CTBTO report from Tuesday.
It is too soon to say how far the radioactive material has spread beyond the Fukushima plant, says Proehl. "There have been a series of plumes released at different times, with different weather conditions," he says. "It's extremely complex." A small IAEA team will visit Japan tomorrow.