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We're also lucky that this particular plant isn't as close to an urban centre as many others in the US. It's nearly 50 miles from Richmond, and about 100 miles from Washington, DC. But the plant that the NRC deemed most at risk was the Indian Point 3 reactor in Buchanan, New York – just 38 miles from New York City. This is the primary reason why New York Governor Andrew Cuomo has called for the plant to be shut down. After Fukushima, everyone within 50 miles of the plant had to be evacuated. Right now, our evacuation plans for all our nuclear sites only cover a 10-mile radius. If something really bad were to happen at Indian Point, it could create the need to evacuate 21 million people

The North Anna plant is located about 15 miles from the epicentre of the quake in Mineral, Virginia. It was designed to withstand a 6.2-magnitude quake, according to its owner, Dominion Resources. The Nuclear Regulatory Commission lists the plant as one of the 10 US plants most at risk of damage in a seismic event. So, it seems like we got lucky in this case.

Though a spokesman for the Nuclear Regulatory Commission told reporters that "as far as we know, everything is safe", the event revived fears about the safety of US nuclear plants. Most of the region's reactors were reportedly designed to withstand a 5.9 to 6.1 magnitude quake – which means Tuesday's quake was, for many, too close for comfort.

don't believe we're going to shut down our existing nuclear energy infrastructure entirely any time soon. But at the very least, the 23 August quake should be a reminder that our worst-case scenarios might not be bad enough. We should perhaps rethink just how ready we are for the worst.

The review, launched well before the East Coast quake and the Japan nuclear disaster in March, marks the first complete update to seismic risk in years for the nation's 104 existing reactors, despite research showing greater hazards

But emails obtained in a more than 11,000-page records request by The Associated Press show that NRC experts were worried privately this year that plants needed stronger safeguards to account for the higher risk assessments.

The nuclear industry says last week's quake proved reactors are robust. When the rumbling knocked out off-site power to the North Anna plant in Mineral, Va., the reactors shut down and cooled successfully, and the plant's four locomotive-sized diesel generators turned on. The quake also shifted about two dozen spent fuel containers, but Dominion Virginia Power said Thursday that all were intact.Still, based on the AP analysis of NRC data, the plant is 38 percent more likely to suffer core damage from a rare, massive earthquake than it appeared in an analysis 20 years ago.

His view changed after a magnitude-6.9 quake killed more than 5,500 people on Jan. 17, 1995, and toppled sections of elevated expressway.After a disaster that Japanese engineers had said couldn’t happen, the nuclear regulator didn’t immediately re-evaluate its construction standards. It said the plants were “safe from the ground up,” as the title of a 1995 Science Ministry pamphlet put it. Ishibashi decided to investigate.The result was an article on Hamaoka published in the October 1997 issue of Japan’s Science Journal that reads like a post-mortem of the Fukushima disaster: A major quake could knock out external power to the plant’s reactors and unleash a tsunami that could overrun its 6-meter defenses, swamping backup diesel generators and leading to loss of cooling and meltdowns.

Ishibashi a ‘Nobody’“In the field of nuclear engineering, Mr. Ishibashi is a nobody,” Madarame said in a 1997 letter to the Shizuoka Legislature. Madarame, then a professor at the University of Tokyo school of engineering, is now in charge of nuclear safety in the country.

"It's the things inside the buildings that may have been shaken more than the design called for," Burnell said, adding that the buildings themselves appear to have been less affected. He said the analysis is based on a seismograph reading taken about 30 miles away by the U.S. Geological Survey.

Whatever the final numbers on shaking or ground motion, the plant withstood the jolts, Burnell said, indicating there's a "great deal" of safety margin."That margin was certainly enough for North Anna this time," he said.

"Maybe you shouldn't rely on the margin," said Edwin Lyman at the Union of Concerned Scientists, an organization critical of nuclear energy. "The jury is still out," he said, on whether the plant was adequately designed.The two reactors at the North Anna plant, which began operation in 1978 and 1980, have remained closed since the Aug. 23 quake. They automatically shut down after losing off-site power. Backup diesel generators kept their cores cool until electricity was restored several hours later.

Dan Stoddard, Dominion's senior vice president of operations, said Friday that initial readings from the facility's scratch plates and other monitors indicate its shaking during the quake exceeded its design, but he declined to give numbers. Dominion officials plan to brief the NRC today on those findings.

That's small consolation to one prominent nuclear watchdog, who says it's not what's above ground that gives him the greatest concern. "Central to the issue is miles of buried pipe under the plant that carry radioactive water," says Paul Gunter, director of a nonprofit group called Beyond Nuclear.

unter cites recent problems with underground pipes at nuclear plants in Illinois and Vermont, where millions of gallons of water contaminated with the radioactive hydrogen isotope tritium seeped into groundwater, even as the power companies that owned the plants denied for years that it was happening.

The result of those leaks and their public concealment by the Exelon and Intergy power companies– at the Braidwood Station plant in Illionis and at the Vermont Yankee Nuclear Power Plant– was not additional government oversight as one might expect, says Gunter, but merely the creation of two voluntary programs that allow the power companies to inspect their own pipes and groundwater and then report the findings to the Commission.

Here's an industry that has hidden these leaks that is now self-reporting and overseeing itself to the NRC," says a disgusted Gunter.

at North Anna, newly arrived government inspectors won't be conducting their own tests of the miles of underground pipes. And the assumption that those pipes didn't sustain damage during the earthquake, which knocked two Louisa County schools out of commission and caused cracks in the Washington Monument some 90 miles away, might be laughable to Gunter if he weren't convinced of potentially grave public danger.

How can an uninspectable, inaccessible buried pipe have integrity?" Gunter asks. "When this Augmented Inspection Team walks onto the site, they'll be walking over the buried pipe that could be leaking." "We have a limited number of inspector resources," acknowledges Commission spokesperson Roger Hannah, who says when it comes to the pipes, inspectors will "make sure we see what [Dominion is] doing."

Hannah scoffs at the notion that tritium, already considered by the Commission a much lesser danger than uranium, could leak from damaged pipes into the groundwater and go unnoticed by inspectors. "If you had some issue, you'd see some leakage fairly quickly," says Hannah, noting that no tests have revealed radioactive leakage anywhere at the North Anna.

Dominion spokesperson Richard Zuercher also offers reassurance that all is well at North Anna, above and under-ground. "We do have ways to detect if there's any leakage in water," says Zuercher, who says the only damage at the facility was "cosmetic" and didn't affect nuclear function and who insists Dominion will "do whatever is necessary to verify that everything is intact." Gunter, however, says he believes Dominion's not going far enough to protect the public."Given the industry history and what's been done before, Dominion should be distributing bottled water to the town of Mineral and to the residents of Lake Anna," he says. "Indefinitely."

According to the USGS website, under the undated heading, “Can we cause earthquakes? Is there any way to prevent earthquakes?” the agency notes, “Earthquakes induced by human activity have been documented in a few locations in the United States, Japan, and Canada. The cause was injection of fluids into deep wells for waste disposal and secondary recovery of oil, and the use of reservoirs for water supplies. Most of these earthquakes were minor. The largest and most widely known resulted from fluid injection at the Rocky Mountain Arsenal near Denver, Colorado. In 1967, an earthquake of magnitude 5.5 followed a series of smaller earthquakes. Injection had been discontinued at the site in the previous year once the link between the fluid injection and the earlier series of earthquakes was established.” Note the phrase, “Once the link between the fluid injection and the earlier series of earthquakes was established.” So both the U.S Army and the U.S. Geological Survey over fifty years of research confirm on a federal level that that “fluid injection” introduces subterranean instability and is a contributory factor in inducing increased seismic activity.” How about “causing significant seismic events?”

Fast forward to the present. Overseas, last month Britain’s Cuadrilla Resources announced that it has discovered huge underground deposits of natural gas in Lancashire, up to 200 trillion cubic feet of gas in all. On 2 November a report commissioned by Cuadrilla Resources acknowledged that hydraulic fracturing was responsible for two tremors which hit Lancashire and possibly as many as fifty separate earth tremors overall. The British Geological Survey also linked smaller quakes in the Blackpool area to fracking. BGS Dr. Brian Baptie said, “It seems quite likely that they are related,” noting, “We had a couple of instruments close to the site and they show that both events occurred near the site and at a shallow depth.” But, back to Oklahoma. Austin Holland’s August 2011 report, “Examination of Possibly Induced Seismicity from Hydraulic Fracturing in the Eola Field, Garvin County, Oklahoma” Oklahoma Geological Survey OF1-2011, studied 43 earthquakes that occurred on 18 January, ranging in intensity from 1.0 to 2.8 Md (milliDarcies.) While the report’s conclusions are understandably cautious, it does state, “Our analysis showed that shortly after hydraulic fracturing began small earthquakes started occurring, and more than 50 were identified, of which 43 were large enough to be located.”

Sensitized to the issue, the oil and natural gas industry has been quick to dismiss the charges and deluge the public with a plethora of televisions advertisements about how natural gas from shale deposits is not only America’s future, but provides jobs and energy companies are responsible custodians of the environment. It seems likely that Washington will eventually be forced to address the issue, as the U.S. Army and the USGS have noted a causal link between the forced injection of liquids underground and increased seismic activity. While the Oklahoma quake caused a deal of property damage, had lives been lost, the policy would most certainly have come under increased scrutiny from the legal community. While polluting a local community’s water supply is a local tragedy barely heard inside the Beltway, an earthquake ranging from Oklahoma to Illinois, Kansas, Arkansas, Tennessee and Texas is an issue that might yet shake voters out of their torpor, and national elections are slightly less than a year away.

Challenging numbers Japanese investigators had already developed a detailed timeline of events following the 11 March earthquake that precipitated the disaster. Hours after the quake rocked the six reactors at Fukushima Daiichi, the tsunami arrived, knocking out crucial diesel back-up generators designed to cool the reactors in an emergency. Within days, the three reactors operating at the time of the accident overheated and released hydrogen gas, leading to massive explosions. Radioactive fuel recently removed from a fourth reactor was being held in a storage pool at the time of the quake, and on 14 March the pool overheated, possibly sparking fires in the building over the next few days.

But accounting for the radiation that came from the plants has proved much harder than reconstructing this chain of events. The latest report from the Japanese government, published in June, says that the plant released 1.5 × 1016 bequerels of caesium-137, an isotope with a 30-year half-life that is responsible for most of the long-term contamination from the plant2. A far larger amount of xenon-133, 1.1 × 1019 Bq, was released, according to official government estimates.

Stohl believes that the discrepancy between the team's results and those of the Japanese government can be partly explained by the larger data set used. Japanese estimates rely primarily on data from monitoring posts inside Japan3, which never recorded the large quantities of radioactivity that blew out over the Pacific Ocean, and eventually reached North America and Europe. "Taking account of the radiation that has drifted out to the Pacific is essential for getting a real picture of the size and character of the accident," says Tomoya Yamauchi, a radiation physicist at Kobe University who has been measuring radioisotope contamination in soil around Fukushima. Click for full imageStohl adds that he is sympathetic to the Japanese teams responsible for the official estimate. "They wanted to get something out quickly," he says. The differences between the two studies may seem large, notes Yukio Hayakawa, a volcanologist at Gunma University who has also modelled the accident, but uncertainties in the models mean that the estimates are actually quite similar.

The new study challenges those numbers. On the basis of its reconstructions, the team claims that the accident released around 1.7 × 1019 Bq of xenon-133, greater than the estimated total radioactive release of 1.4 × 1019 Bq from Chernobyl. The fact that three reactors exploded in the Fukushima accident accounts for the huge xenon tally, says De Geer. Xenon-133 does not pose serious health risks because it is not absorbed by the body or the environment. Caesium-137 fallout, however, is a much greater concern because it will linger in the environment for decades. The new model shows that Fukushima released 3.5 × 1016 Bq caesium-137, roughly twice the official government figure, and half the release from Chernobyl. The higher number is obviously worrying, says De Geer, although ongoing ground surveys are the only way to truly establish the public-health risk.

The new analysis also claims that the spent fuel being stored in the unit 4 pool emitted copious quantities of caesium-137. Japanese officials have maintained that virtually no radioactivity leaked from the pool. Yet Stohl's model clearly shows that dousing the pool with water caused the plant's caesium-137 emissions to drop markedly (see 'Radiation crisis'). The finding implies that much of the fallout could have been prevented by flooding the pool earlier. The Japanese authorities continue to maintain that the spent fuel was not a significant source of contamination, because the pool itself did not seem to suffer major damage. "I think the release from unit 4 is not important," says Masamichi Chino, a scientist with the Japanese Atomic Energy Authority in Ibaraki, who helped to develop the Japanese official estimate. But De Geer says the new analysis implicating the fuel pool "looks convincing".

The model also shows that the accident could easily have had a much more devastating impact on the people of Tokyo. In the first days after the accident the wind was blowing out to sea, but on the afternoon of 14 March it turned back towards shore, bringing clouds of radioactive caesium-137 over a huge swathe of the country (see 'Radioisotope reconstruction'). Where precipitation fell, along the country's central mountain ranges and to the northwest of the plant, higher levels of radioactivity were later recorded in the soil; thankfully, the capital and other densely populated areas had dry weather. "There was a period when quite a high concentration went over Tokyo, but it didn't rain," says Stohl. "It could have been much worse."