Over on Hot Air, Steven Den Beste claims that thorium reactors are a huge proliferation risk.

Unfortunately, he

1. oversimplifies and gets it wrong, and
2. is going to be taken as gospel by lots of people anyway

Here's the real dope, in a nutshell:

• Thorium (Th-232) can be bred to fissile uranium 233 (U-233) by hitting it with a neutron, allowing the Th-233 to decay to protactinium (Pa-233) and then to uranium.
• Separation of pure U-233 requires not just a liquid-fuel reactor, but either something called a "two-fluid reactor", or chemical separation of Pa-233.  Pa-233 is a strong neutron absorber and will go to Pa-234, which decays to U-234 which is not fissile (it takes yet another neutron to make U-235, which is the natural fissile isotope).
• The likelihood of Pa-233 grabbing a neutron before it beta-decays to U-233 is proportional to the neutron flux, so reactors with low power density don't need separation of the breeding and power sections.  They can do it all with one uniform fluid.
• In a one-fluid reactor, U-233 sometimes gets hit with a neutron and, instead of fissioning, loses another neutron.  This is the (n, 2n) reaction and it makes another isotope of uranium, U-232.
• U-232 is not fissionable, but another neutron turns it back to U-233.
• U-232 has a decay path which creates thallium 208 (Tl-208).  Tl-208 is a very powerful gamma emitter, which will degrade explosives and fry electronics unless they are behind heavy shields.
• Because U-232 cannot be separated from U-233 by chemical means, any uranium removed from a one-fluid thorium reactor will soon have a growing amount of Tl-208 frying anything nearby and shining like a beacon saying "Here I am!".  You can remove the thallium chemically, but as long as there's still U-232 you'll have more as soon as you stop.
• A bomb built to fit on a missile can't have heavy shielding, and a "stealth bomb" to be sneaked into an enemy city isn't going to work if its core can be detected though a foot of lead.
• If that's not good enough, there's a scheme called a "denatured molten-salt reactor" (DMSR) which has a mix of stuff that's even more useless for bombs and doesn't even breed to breakeven.  You have to add small amounts of enriched fuel to keep it going (but you can run 20 years or so without removing anything, making it cheap and trouble-free).
• This isn't a problem with solid fuels.  The thorium-uranium rods being developed by Lightbridge are even more of a headache for proliferators than straight uranium.

That's why nobody's ever tried to base a weapons program on thorium; if it was so easy, Kim Il Sung, A.Q. Khan and Saddam Hussein would have gone that way.  Even the USA realized that neither a weapons program nor a plutonium economy could come from thorium reactors (which we now know is a good thing).  Nobody did because they know more about nuclear technology than Steven Den Beste.

For more information, start with this lecture by Dr. David LeBlanc and the supporting materials.

¶ 8/31/2010 11:42:00 PM 7 comments

Using a multi-cyclic Hubbard analysis, researcher Tad Patzek has concluded that the world will experience "peak coal" as soon as next year (h/t GCC).

Several things are obvious:

1. This is going to be one heck of a shock to the system.
2. Efficiency will become much more important.
3. Alternative means of exploiting coal which is otherwise not recoverable, such as underground coal gasification (UCG), will become much more attractive—and perhaps shortcomings such as groundwater contamination will be overlooked.

The study does contain a caveat:  "new cycles could occur if a technological breakthrough allowed mining of coal from very thin seams or at much greater depths, or if non-producing coal districts become important producers."

I believe UCG is one of the wildcards.  Massive deposits of deep, thin or undersea coal are not recoverable by conventional mining, but these could potentially be pyrolized in place and extracted as gas.  With an estimated 3000 billion tons of coal off Norway and strong interest in Britain, coal could return as supplies of Russian natural gas taper off.

This does make it doubtful that carbon emissions would fall very far before rebounding.  Nuclear is looking better and better every day.

Labels: CO2, coal, energy, energy substitution, peak coal, resources

¶ 8/02/2010 11:55:00 PM 4 comments

GCC has a post on biomass-to-naptha schemes, upgrading pyrolysis oil to hydrocarbons.  The projected cost is $2.11-$3.09 per gallon.  My analysis follows.

2000 dry tons/day = 730,000 tons/year.  The yield is 48 gallons/ton for the hydrogen production scenario and 79 gallons/ton for the merchant hydrogen scenario.  (I calculate the carbon fraction captured in the product to be about 26% and 47%, respectively.  This is not a very efficient scheme.)

If we take the figure of the 446 million dry tons of crop residues as a given, the potential output from this process is 21 billion gallons/year in the hydrogen-production scenario and 35 billion gallons/year in the purchased hydrogen scenario.  (The question of the provenance of purchased hydrogen is significant.)

Even if the biomass supply can be doubled (or tripled), this scheme still falls short of providing BAU supplies of motor fuel.  It can supply the liquid fuel needs of the PHEV component of an electrified fleet.

Labels: analysis, BAU, biofuels, PHEV

¶ 8/01/2010 02:55:00 PM 0 comments