[extropy-chat] Nuke 'em

Damien Sullivan phoenix at ugcs.caltech.edu
Sun Oct 23 17:22:56 UTC 2005

On Sun, Oct 23, 2005 at 09:36:46AM -0700, Robert J. Bradbury wrote:
> On Sun, 23 Oct 2005, Damien Sullivan wrote:

> > My model had been 20 kW toward electricity and the rest to make synthetic
> > hydrocarbons from CO2 (at 11% efficiency, a bit higher than plants,
> > *cough*) but if one assumes 10% overall that gives 5 kW of usable power,

> I'd like to see how you are getting CO2 to synthetic hydrocarbons at 11%
> efficiency!  Just for general education -- plants generally are harvesting

With vigorous handwaving!

I'd assumed electricity generation at 33% efficiency, and then electricity to
liquid fuel at 33% efficiency, on the grounds of converting energy forms often
being about 30%.  I did know 8% was the highest I'd ever heard for
photosynthesis, but for my original purpose (seeing if 10 billion people could
be sustained at US levels) I hoped it was close enough and maybe some less
fuel could be used.  Or maybe being able to liquefy air would make CO2
extraction more efficient?  I also don't know if we even have industrial tech
for CO2->fuel, and am struck that no one ever talks about it even as a
research possibility.  It's oil from coal, or hydrogen from water, never oil
from air.

> solar energy at 1-2%.  Sugar cane under ideal conditions (Brazil presumably)
> can push 3-4%.  A photobioreactor which has light sources surrounding a
> vessel containing photosynthetic bacteria/algae can push 8%.  Anything

"Clearly plants are really inefficient and we can do better!"  But I suspect
the limiting factor is the low concentration of CO2; dealing with a 300 ppm
input can't be pretty.  But unavoidable, if we're using carbon as an energy
store and burning it.  No wonder hydrogen looks attractive.  Realistically I'd
guess we'd be hard put to even approach plants at what they're doing.

What's the efficiency for solar ponds with bacterial methanogenesis?  Are
there ways of turning the methane into liquid fuel, and at what rates?

> > Waste takes a lot less volume and lasts less if you don't bury the U-238
> > and actinide products along with the fission fragments.
> As I said in a previous message -- just transmute the radioactive materials

Sounds good; I don't know if it's something we can count on.  Alternately,
just the fission products don't take up much volume, and supposedly they dim
out in 500 to 1000 years, with plutonium being the main "hundreds of thousands
of years!" culprit, but also being fuel we shouldn't be burying.

> into non-radioactive materials.  One might also want to consider breeder
> reactors so one can produce more fuel over time.  This works well if one

At global scales there's no 'might' about it.

-xx- Damien X-) 

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