Monday, November 26, 2012

Pebble bed - it lives again

Catalyst: Next Generation Nuclear Power - ABC TV Science

I used to comment on pebble bed reactors as a new nuclear design with impressive sounding passive safety.   But the South African plans to build one ran out of money, and was deemed to be too ambitious in design, and we don't hear much about them any more.  (Apart from the fact that China had built at least one; I'm not sure that it has ever been more than a research reactor, though.)

So, I was surprised to see on Catalyst a few weeks ago as story about continuing research into them in California.

This one is to use molten salts as a coolant (instead of helium as per the defunct South African plan.)  The advantages:
 Dr Graham Phillips
This reactor doesn't use water to flow through the fuel elements and extract the heat - it uses melted salt. Now not table salt, sodium chloride, but the related substances lithium and beryllium fluoride. Heat these guys to about 450 degrees Celsius and they turn into a clear liquid.

Mike Laufer
One of the big advantages of the salt is that it's very effective in moving heat around, but it's at low pressure.

NARRATION
Low pressure means a less accident-prone reactor. Today's generation IIIs run at a staggering 70 times atmospheric pressure.

Prof Per Peterson
If we switch to liquid coolants, like these fluoride salts that we're using, then we can build much more compact, high power density systems that operate at atmospheric pressure, and that gives us a system which is intrinsically safe, because there's no source of pressure to disperse radioactive material.
 Sounds good to me.

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