[geeks] Global warming, was Mr Bill?

[wa2egp at att.net]

> isotopic separation is not easy...  weight difference between
> elemental 235 and 238 is less than 1.3%, and they can't be chemically
> distinguished.

No kidding.  That's why one technique uses a centrifuge to amplify the mass difference.  Not easy at all.

> from the 56th crc: natural uranium is 99.283% u-238, 0.711% u-235, and
> 0.0054% u-234.  it is 'slightly' enriched [amount unspecified] for
> power plant use, 'spent' [depleted] when u-235 falls to 0.2%.
> 
> if we have 'plenty' of u-235, we are positively swimming in ~140x as
> much u-238.

Obviously from your figures.  I didn't look in the CRC Handbook to see the percentages but the raw uranium doesn't work so well in out present reactors. :)  No surprise the ratio in fuel rods is not so reddily available.

> i believe power plant fuel rods are still over - perhaps well over -
> 95% u-238 ['slightly' above could well mean 'up to 1%', and i've heard
> numbers like 1-3% for fuel rod fissionable consumption].  yes, it's
> -relatively- safe to handle [suggested by the above enrichment levels
> - though i'd rather not] and the way to use it is to breed it, usually
> to pu-239.  the safe way would be to breed the pu only as fast as it
> fissions, a 'slow breeder' reactor, for which there are several
> proposed designs.  my favorite is the liquid-fueled slow breeder,
> which constantly reprocesses the fuel load, removing lead and adding
> fissionables as needed.

As I've said before, because we have so much 235 the US has not been investing in breeder reactors.  The big problem is not the 238 but the breakdown products from the 235 which are more intensely radioactive.

> nb. india is working on thorium slow breeders, as it's more abundant
> than uranium and they're sitting on half the world's known th
> reserves.  they'd work by breeding th-232 to u-233, and iirc need a
> uranium 'ignition charge' to start.

Interesting.


Bob