If an Earthquake Hit U.S. Nuclear Plants: A Nightmare Scenario

YahooNews:  The 5.8 magnitude earthquake that rocked the East Coast Tuesday and sent two nuclear reactors in Virginia offline has refocused concerns about the safety of nuclear plants in the U.S. and prompted reviews of plants in at least six states. Interestingly, the federal government has run exercises of how a doomsday earthquake-nuclear disaster would play out, as Noah Shachtman at Wired notes. Are we prepared for the worst? Experts around the web are highlighting the strengths and vulnerabilities of America's nuclear plants.
Related: Radioactive Water Leaking from Fukushima Reactor

The nightmare scenario  In May, the federal government ran a simulation of an earthquake disaster called National Level Exercise 11, which involved a quake hitting the Midwest leaving 7 million people homeless and the death of 100,000 Midwesterners. Shachtman explains the details:

    National Level Exercise 11, or NLE 11, was, in essence, a replay of a disaster that happened 200 years earlier. On Dec. 16, 1811, a magnitude 7.7 earthquake hit the New Madrid fault line, which lies on the border region of Illinois, Indiana, Missouri, Arkansas, Kentucky, Tennessee and Mississippi.

In that seismic zone, there are 15 nuclear power plants. Paul Stockton, the Defense Department’s senior homeland security official, explains what could happen.  “Electric power would go out, not for days, but for weeks and months in the four state region,” he said. “Municipal water systems, they all run on electricity, don’t they? Well, people are gonna get thirsty. You need water for firefighting, don’t you? Second, all gasoline pumps run on electric power. Same with diesel fuel. So in terms of road mobility, of getting the relief forces in, and evacuating people out — no gasoline? The cascading failures go on and on.” Here's a video of how it would play out:
Related: The Oil Spill and Michael Bay's Flaming Alligators

Nuclear plants are vulnerable elsewhere too Reuters notes that the 5.8 magnitude earthquake that hit Virginia brought the East Coast's plants awfully close to breaking point.

    Dominion spokesman Jim Norvelle said the plant was designed to withstand an earthquake of up to 6.2 in magnitude. But some experts expressed concern about the narrow margin between the design metrics and the quake's size.

    "It was uncomfortably close to design basis," said Edwin Lyman of the Union of Concerned Scientists, which has pushed for stronger nuclear regulations. "If Fukushima wasn't a wake-up call, this really needs to be to get the NRC and industry moving to do seismic reviews of all the nuclear power plants in the country."

The U.S. is not that vulnerable.  Pushing back against some of the whistle blowers, Michael Lemonick at The Guardian says U.S. nuclear plants have strengths and weaknesses, and the weaknesses should not be overstated:

    During an earthquake, the ground shakes back and forth, and the damage is roughly proportional to the ground's maximum acceleration (or PGA).  The PGA risk is what is typically used to set building codes. Most nuclear power plants are designed to operate under 0.2g PGA, and automatically shut off if the PGA exceeds 0.2g. However, they can withstand a PGA many times larger than that...

    If one safety measure fails, there are several others in place to prevent a nuclear emergency. The bottom line is that a major earthquake would probably not result in a nuclear meltdown at the reactors on the above map, but it could present significant engineering challenges. Quantifying the risks, and minimizing them as much as possible, is a key task for everyone involved in the nuclear energy industry.

There are mixed views on this After laying out a nuclear nightmare scenario, Shachtman explains the differences of opinions on its likelihood:

    Will another 1811-style earthquake hit the midwest again? At the Aspen forum, Stockton insisted that “we’re overdue.” That’s overblown, if an independent panel (.pdf) convened by the National Earthquake Prediction Evaluation Council is to be believed. There’s a one-in-50 chance of a mega-quake every 50 years. Before 1811, the big ones happened in approximately the years 1450 and 900. Still, this is all a game of percentages. No one can say for sure when the next disaster will strike. And it’s worth noting that New Madrid is considered the most active earthquake region east of the Rockies.