http://www.project-syndicate.org/commen ... n1/English
The Fukushima Daiichi nuclear crisis in Japan has underscored the dangers of storing highly radioactive spent fuel in pools of water that are susceptible to breaches from natural disasters and hydrogen explosions from accidents. The crisis should serve as a wake-up call for governments and industry to take action to reduce the risks of spent-fuel storage.
Unfortunately, spent-fuel storage has been “an afterthought,” as Ernest Moniz, Director of the Energy Initiative at MIT, puts it. In dozens of countries, tens of thousands of tons of highly radioactive material has been kept in buildings that provide little of the usually rigorous protection surrounding radioactive material in reactors’ cores.
Pools have become overcrowded in many countries, owing to the lack of permanent repositories for nuclear waste. No country has opened such a repository, although Sweden has made significant progress in doing so.
The hazards of pools for spent nuclear fuel have been known for many years, but little action has been taken to alleviate the risks. One notable exception has been Germany. About 25 years ago, the German government began requiring spent fuel to be well protected. The older spent fuel that has cooled for about five years is placed in hardened, dry storage casks, and the younger, more radioactive, and hotter spent fuel is cooled in pools of water surrounded by strong containment structures.
These measures cost more money, but they afford much greater protection against accidents, disasters, and terrorist attacks. Is it worth it? A 2003 study, led by Robert Alvarez, a former official at the United States Department of Energy, estimated that a worse-case terrorist attack could drain cooling pools, resulting in spent fuel rods heating up and possibly combusting. That, in turn, would cause substantial amounts of radioactive material to be released if containment structures are breached, potentially resulting in an area of contamination greater than that caused by the Chernobyl accident in 1986.
Despite this alarming conclusion, the study did not prompt the US Nuclear Regulatory Commission to order utilities to remove spent fuel from overcrowded pools at more than 100 US commercial reactors. It did, however, spur the preparation of a US National Academy of Sciences’ report, which concluded that “successful terrorist attacks on spent fuel pools, though difficult, are possible.”
While the report did not recommend placement of older spent fuel into dry storage casks, it did advise the less expensive method of rearranging spent fuel in the pools so that hotter, newly discharged fuel would be surrounded by cooler, older spent fuel. Doing so would likely prevent a fire. The report also called for water-spray systems to fill up draining pools, but made this conditional on a cost-benefit analysis conducted by each plant.
Is reprocessing spent fuel the answer? While China, France, India, Japan, and Russia have favored reprocessing in order to recycle plutonium for new fuel, this has not solved the waste problem, because the resulting spent fuel is usually not further recycled. Instead, it is stored in spent-fuel pools.
Recycling proponents want ultimately to build a fleet of fast neutron reactors that could consume the plutonium and other fissionable material. But these reactors have experienced safety problems and are more expensive to operate than current reactors. Use of plutonium fuels also increases the risk of nuclear-weapons proliferation.
Several decades from now, reprocessing might offer a safe means of spent-fuel disposal. In the interim, the most promising method is to use dry storage casks, which, according to technical studies, provide up to 100 years of safe and secure storage.
But industry has expressed concern that each storage cask costs more than $1 million, and that a typical plant’s total costs thus could be tens of millions of dollars. The Alvarez study estimated a cost of $3-5 billion for the entire US reactor fleet, which is the largest in the world.
This would be the major one-time cost. After that, the costs would be a few hundred million dollars annually. For comparison, nuclear power in the US generates annual revenues exceeding $30 billion, whereas the cost of a severe accident can easily soar to billions of dollars, as the world is witnessing at Fukushima Daiichi.
Industry has also been concerned about minimizing workers’ exposure to radiation when they transfer spent fuel to casks. Moreover, there is a risk of further radiation exposure during the transfer of spent fuel from the casks to permanent storage.
To minimize this risk, casks should be developed that can easily be transferred to a secure interim storage facility while permanent repositories receive approval. We should not wait for the next Fukushima Daiichi to act on reducing the risks of spent fuel.
Charles D. Ferguson, a physicist and nuclear engineer, is the president of the Federation of American Scientists and the author of the forthcoming book Nuclear Energy: What Everyone Needs to Know.
Are larger earthquakes a sign of the times? Seismologists debate whether the recent spate of megaquakes is a statistical fluke or something more.
http://www.nature.com/news/2011/110414/ ... 1.241.html
Beginning in late 2004, a flurry of massive, tsunami-spawning earthquakes have rocked the world, first slamming Indonesia, then Chile and most recently Japan. Temblors that size are rare indeed: only 7 quakes as large or larger than 8.8 — the magnitude of last February's Chilean event — have occurred since 1900.
So what does it mean that three of those seven shocks have happened almost within the span of six years? While some scientists argue that these 'megaquakes' could be the vanguard of an extended outburst of strong seismic events, many others suggest that the apparent cluster of recent temblors is nothing more than a statistical fluke.
The recent spate of far-flung quakes is remarkably similar to a cluster that occurred in the middle of the last century, says Charles Bufe, a seismologist retired from the US Geological Survey (USGS) in Denver, Colorado. The seismic events in that supposed grouping, consisting of 3 magnitude 9 or higher temblors, struck Kamchatka, then Chile and then Alaska within a 12-year interval. The odds of quakes that large occurring randomly within such a short time span is only four per cent, Bufe noted today at the annual meeting of the Seismological Society of America in Memphis, Tennessee.
In an update to an analysis first published in June 2005, Bufe and colleague David Perkins, a USGS geophysicist also in Denver, argue that the most recent round of large temblors may mark the beginning of a new global outbreak of megaquakes. According to their model, Bufe says, the probability of another quake of magnitude 9 or larger striking in the next 6 years is about 63 per cent. "There's now an increased hazard situation for these very large earthquakes," he notes.
It's an ominous warning considering what scientists are now reporting about the monumental forces behind the 9.0 Tohoku quake, which wreaked devastation on Japan on 11 March. At the meeting, researchers revealed that the main shock ruptured a previously locked seismic interface more than 250 kilometres long and 175 kilometres wide. Although most of the quake's energy was released in the first 2 minutes, several aftershocks — many of them magnitude 6.4 or larger — occurred in the 20 minutes or so that followed. Altogether, that temblor and its aftershocks ruptured areas that had previously slipped in five separate quakes, the researchers say. As a result, the entire northern portion of Honshu, Japan's largest island, moved about 1 meter toward the east, with one site near the temblor's epicentre sliding 5.4 meters horizontally and sinking 1.1 meters — a sudden subsidence that aggravated the damage from the tsunami that slammed the shore minutes later.
Yet the apparent clustering of such megaquakes, including the recent Indonesian, Chilean and Japanese events can be accounted for without a direct link, several scientists say. "When you run statistical tests, you can often get numbers that sound interesting," says Richard Aster, a geophysicist at the New Mexico Institute of Mining and Technology in Socorro. In this case, he suggests, the clumping could come down to the statistics of small sample sizes. Since 1900, there have been only 14 quakes larger than magnitude 8.5. And whereas modern seismology goes back only a little more than a century, the tectonic processes that generate major earthquakes unfold over hundreds or thousands of years, he adds.
Looking for patterns
In a separate analysis, Andrew Michael, a seismologist with USGS in Menlo Park, California, scrutinized databases of major quakes for evidence of clustering. Rather than use a single threshold for earthquake magnitude, he ran several statistical analyses using different magnitude thresholds, looking for patterns in quakes over various intervals ranging in length from months to years — and found nothing. "I've run a large number of tests and can't find any reason to reject the idea that clustering is random," he says.
That's not to say that major quakes don't stimulate further seismic activity. Barely 4 months after the December 2004 quake struck Indonesia, a magnitude 8.6 temblor occurred just down the coast — the result, scientists say, of the first quake's redistribution of stress in Earth's crust. Usually, the extent of such stress shifts are limited to the immediate region, says Aster. Although there is evidence that the ground motions induced by major temblors trigger small quakes thousands of kilometres away, there's no sign that such triggering occurs for large quakes, he adds.
Research published online 27 March in Nature Geoscience bolsters those notions. Tom Parsons, a seismologist also with the USGS in Menlo Park, and colleague Aaron Velasco, of the University of Texas at El Paso, analyzed the USGS earthquake database to see if temblors of magnitude 7 and higher might have triggered midsized quakes elsewhere in the world. Between 1979 and 2009, seismometers recorded 205 quakes with magnitudes above 7, Parsons notes. Although many of those quakes triggered local aftershocks in the day or so after the initial event, Parsons and Velasco found no corresponding increase in the frequency of distant quakes with magnitudes ranging between 5 and 7.
The team's analysis also suggests that stress redistribution to nearby faults after a major quake is limited to distances from the epicentre no more than two or three times the length ruptured by the original quake. That, says Parsons, means that even megaquakes shouldn't trigger large quakes more than a couple of thousand kilometres away.
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- lower number estimated is less than 100, BTW by some} 
