[ExI] Could Thorium solve our energy problem?

[Brent Neal]

On 8 Jul, 2010, at 20:36, samantha wrote:

> John Clark wrote:
>> I've been reading about Thorium reactors, in particular Liquid Fluoride Thorium Reactors (LFTR) and I'm very impressed, I don't believe nearly enough is being done in this area. With all respect to Keith Henson I think this is much more likely to provide our energy needs than space based solar. I think this is what fusion wanted to be, certainly it's better than conventional nuclear fission. Consider the advantages:
> 
> Thanks for sharing what you found.  This was on my list of things to look into in more detail.  If you have some useful links then please share them.  
> I agree that this is a much more immediate energy solution than space based solar, at least SBSP of any design I am familiar with.  The first problem with SBSP is the huge mass all the mirrors and collectors represent and the high cost of launch.   The second is that you have no way to do all the assembly and maintenance required at GEO.  Doing it with astronauts is a non-starter.  We would need a lot better space robotics than we have.   Of course you could mine near earth asteroids first for much of the needed material and volatiles without hauling so much mass up the gravity well.  Which we should do anyway including for rare earths and precious metals.  But that is a different topic.
>> 
>> *Thorium is much more common than Uranium, almost twice as common as Tin in fact. And Thorium is easier to extract from its ore than Uranium.
>> 
> Yes.  I have heard we have 10.000 years at current energy needs of the stuff.
>> *A Thorium reactor burns up all the Thorium in it so at current usage that element could supply our energy needs for many thousands, perhaps millions of years; A conventional light water reactor only burns .7% of the Uranium in it.
>> 
> Not millions but thousands.
>> 

Actually, less than a thousand.

I base this on a calculation I did for a presentation on sustainable energy for the layperson that I recently gave.

The relevant data are:
4.3 Mton world thorium reserves (source: OECD)
Energy density: 80TJ / ton thorium (estimate based on conversion to U233 via slow neutrons)
World energy consumption (2006): 498 EJ (source: EIA, IAEA, OECD)
World energy annual growth rate (computed from 1980-2006): 1.8%

The calculation of when the cumulative energy usage exceeds the energy available in the world's reserves of thorium is left as an exercise to the reader. Please note that you have to include the efficiency of a Carnot engine in the calculation for full marks. :)

B



--
Brent Neal, Ph.D.
http://brentn.freeshell.org
<brentn at freeshell.org>