geoff wrote:
In message o.uk, Dave
Liquorice writes
On Sun, 15 Apr 2012 07:51:09 +0100, Dave N wrote:

Er I assumed that the idea of this conversion was to produce a
liquid
fuel that would then be burnt. How does that "dispose" of the
orginal
C02? The carbon is still fossil in orgin.

Obviously it doesn't but wouldn't burning recycled carbon be preferable
to mining and extracting new sources of carbon?

Provided that the energy required for this caputure didn't require
any more fossil (would TNP prefer "ancient"?) carbon to be released.
There is so much spin and distorion of the facts in this area that
one has to be very careful in the choice of words used. "Dipose"
carries implications that the problem has been safely solved, it
hasn't by any measure.

Re-use of stored energy is arguably better than burning more and more
new sources of carbon energy, which would add to the total of free
carbon dioxide?

Depends on where that carbon energy is sourced from. Fossil/ancient
sources releases carbon that has been stored for millions of years.
Biomass releases carbon that was taken from the atmosphere in the
last few tens of years or even shorter. The latter has the potential
to become a carbon cycle, like the water cycle.

So, how much realistically easily extractable uranium do we have
How many years of economically viable extraction?

Very hard to say. At last 50 possibly 1500 years.Its very common, but
just not in large quantities.

The sea for example, contains a **** of a lot of it, but the sea is a
big place...

Also we hardly sue any of what we DO mine. Most ofa fuel rod is
depeleted uranium (U238) and is not used. Of the U-1235 most of that is
not used either - it gets poisoned by plutonium and that's what
reprocessing does - removes the plutonium and other by products and
puts in some fresh uranium.

We have a waste problem in part because this costs MORE than refining
raw uranium.

we can use fast breeders to make lots of plutonium from U238 (I think)
but we dont yet need to.

We can use U238 and thorium in different reactors giving 100 - 1000
times more fuels .

So its a terribly variable bit of string.

The greenies talk of 50 years, by which they mean 'all known sources of
fresh uranium economic at current rates, depleted'

But as we know, the per unit electricity contributions is about 0.1p -
it could go 10x times as expensive and still only add a penny to the
electricity cost. At which point plutonium, and MOX fuels are definitely
on the cards as are fast breeders. And huge deposits of uranium no one
is even bothered to stick a pick into yet becomee viable..


(Today over half te oil reveres we have are opt profitable below $75 a
barrel..25 years ago the oil price was well under that.)


And given enough neutron flux, you can make even more exotic unstable
elements.

Remember what a reactor does is not 'burn uranium' it 'destroys mass
itself' The 50 tonnes of fuel rods that go in lose a kg of mass after
they have been fizzing for a year. we only need to find ways of
destroying a few unpleasant elements and turning them into pleasant ones
and we have the waste burner to end all waste burners.



What's the carbon footprint of extraction?


very low.

Simply because you don't need very much of it.

There is a good respurce here

http://www.world-nuclear.org/how/mining.html

and that site should answer nearly all the questions you have.




--
To people who know nothing, anything is possible.
To people who know too much, it is a sad fact
that they know how little is really possible -
and how hard it is to achieve it.