Two-Bullet Roulette

In Russian roulette, the players--all resigned to the possibility of death--put a single bullet into one of the six chambers of a revolver, spin the cylinder and take turns putting the gun to their heads. It starts as a one-in-six chance of disaster.

Those odds, however, are tame compared to those favored by our government's nuclear power regulators. They've recently been told by top scientists of a potential problem: floating paint chips and other debris can get past a poorly designed strainer and clog a key pump. If uncorrected, the scientists reported, this problem represents a one-in-three chance of disaster at an American nuclear power plant by 2007. The regulators' response? The problem ought to be fixed by, oh, say, 2008. That's the equivalent of chambering two bullets before spinning the cylinder and pulling the trigger.

"I don't see any issue out there that's more safety significant than this one," says David Lochbaum, a nuclear safety expert with the Union of Concerned Scientists. "This problem creates a one-in-three chance of a reactor accident by January 2007. The problem can be fixed in less than one year. The NRC's current plans call for it to be solved [before the first day of 2008]."

Choking on Paint

A nuclear power reactor needs a steady flow of cooling water. Otherwise it overheats and damages itself, and, in the worst-case, melts down. So if a pipe carrying coolant into or out of the reactor vessel should leak, water spills onto the floor, the level of available coolant drops and the reactor gets hotter. At that point, backup systems kick in. One such system is elegantly simple: The water leaking onto the floor drains into a collecting pool--which has a pump at the bottom that sucks it back into the system.

But some loss-of-coolant accidents are violent affairs, which flay insulation and paint off adjacent pipes and equipment. This and other debris gets washed down into the collecting pool--and, it turns out, it can choke the pump.

Is that disastrous? Not necessarily. There's a backup supply of coolant water that can be tapped for the short term. But outside water pumped into a leaking system means more water pouring out onto the floor. So the inside of the containment building floods, and rising water eventually submerges and destroys critical electrical equipment. Eventually, the weight of all that water may even break apart the containment building itself. And in any case, the backup water supply quickly runs out, since it's not being repleinshed.

Pretty scary. But c'mon: Floating paint chips bringing down a nuclear reactor? This sounds like something any neighborhood auto mechanic could fix. Why not just put a better debris-catching grate over the collecting pool? Or install a pump with a larger mouth that doesn't clog so easily?

Government regulators are considering such options. In fact, if you check out the references page the NRC has put together on problems with "PWR Sump Performance"--the technical label for the collecting pool-pump issue--you'll see they've been grappling with this for nearly twenty years.

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