Re: Questions on uranium reserves

dezakin@xxxxxxx wrote:

G. R. L. Cowan wrote:
phosphaenus@xxxxxxxx included:

Question 3: I've seen estimates of the "energy threshold" for uranium
ores (i.e. the grade below which you need more energy for U extraction
than you can gain by current technologies) as high as 0.02% and as low
as 0.002%. Any comments?

Oil sands mining gets two-thirds net energy from sand that is
six percent oil; this is thermally equivalent to 0.0004 percent uranium.

Electrical rock crushers would just break even, the power plant
powering them would take all the uranium they would free from the rock,
at 0.00005 percent.

Which would lead me to conclude that high temperature molten salt
breeders would get an energy payback of 600 from average crust, given
that you can make high temperature molten salt reactors at least 50%
more thermodynamically efficient, they use all the uranium instead of
just the .7% U235, and thorium is also present and fertile and three
times as abundant. Even rock crushers have their day it seems.

At http://tinyurl.com/aduug University of Melbourne physicists
find a high net energy fraction for U extracted from 0.001 percent ore.
Seawater is different: no crushing, lifting or heating is required

But it is rate limited. Theres only so much you can get out of the
oceans at once.

for the extraction whose trials are reported at
http://npc.sarov.ru/english/digest/132004/appendix8.html and
http://npc.sarov.ru/english/digest/132004/appendix8p1.html
and accordingly the net energy fraction there seems very close
to 100 percent, even though the ore grade is 0.0000003 percent.



[In fact, I wonder whether the energy
threshold is very relevant... perhaps before you get this low you hit
an "environmental threshold", i.e. a grade below which the
environmental impact of the mining operation becomes socially
unacceptable?]

Most unlikely.

I suspect our robot overlords will have more pressing matters
concerning the conquest of the andromeda galaxy by the time we have to
worry about it.

It's already coming at us. Events are unfolding more quickly
than I had anticipated ...

What U fraction are you putting for average crust? It's definitely
not 0.00005 percent.


--- G. R. L. Cowan, former hydrogen fan
Boron: internal combustion, nuclear cachet --
http://www.eagle.ca/~gcowan/Paper_for_11th_CHC.html
.

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