Located just a few miles from the epicenter of yesterday's nearly unprecedented 5.8 magnitude earthquake in Virginia is the North Anna Nuclear Generating Station and its two aging reactors.

The plant lost power and automatically halted operations after the quake. While a Dominion spokesman reported no "major" damage to the facility, three diesel generators were required to kick in and keep the reactors' radioactive cores cool. A fourth diesel unit failed.

Fortunately, central Virginia is even less prone to tsunamis than it is to earthquakes, and so the backup generators survived long enough for power to be restored this morning. Disaster averted (that is, assuming we can trust a spokesman from a nuclear power company). On the one hand, the backup system apparently worked the way it was supposed to. Yay. On the other hand...

"Nuclear power plants lose a significant margin of safety when they're forced to rely on these emergency back-up systems," said Paul Gunter, director of reactor oversight at Beyond Nuclear, an anti-nuclear lobby group.

Just something to keep in mind as we debate a major expansion of nuclear power in the United States.