www.ditl.org

Coalition wrote:

sunnyside wrote:I'm no expert on pebble bed reactors. But just because you stop the nuclear reaction doesn't mean you're in the clear. Decay heat from the nuclear products is, in other reactors anyway, enough to melt the core, which is than capable of melting through at least the initial layers of containment if not the main concrete structure. And it's tricky to reliably contain all of the released steam. Bleeding pressue off to maintain containment or the pipping leaving main containment may be neccessary, which means some degree of environmental contamination.

Most pebble bed reactors are designed to already be at near-overload state as part of normal operations. This means that the reaction can barely get any hotter, even if the coolant gets turned off. So it literally cannot melt down.

Check it out:
http://en.wikipedia.org/wiki/Pebble_bed_reactor

Again I'm not an expert, but I'm not entirely unfamiliar. The key factor in there is that the plant operated fine by using natural circulation. I.e. heat is still being removed from the system. I believe most if not all current generation nuclear power plants can actually do the same, ditto for naval reactors.

Where problems show up is when you have break or clog in the system such that you no longer have natural circulation removing heat.

I think the advantage of a pebble bed reactor may be that such a situation is less likely and if the gas coolant escapes I'd think you'd just start sucking in air which I would presume would sitll serve to cool the decay heat, though that would raise fire and environmental contamination issues.

Still, like many proposed new generation reactors, I bet it's very safe.