[ RadSafe ] Thorium nuclear fuel cycle

George Stanford gstanford at aya.yale.edu
Thu Nov 12 19:42:54 CST 2009


      There are many variations on the thorium reactor theme.  One of 
the more promising ones seems to be the LFTR (liquid fluoride thorium 
reactor).  For a good, competent talk extolling its virtues, see 
Robert Hargraves' lecture on YouTube, at 

      Regarding proliferation resistance, some advocates (not 
including Hargraves, I believe), overstate the thorium case.  Here's 
the situation, in brief.

      The fissile material that keeps the thorium reactor running is 
U-233, which comes from absorption of a neutron in the fertile Th-232 
nucleus.  The resulting Th-233 promptly beta-decays into Pa-233, 
which decays into U-233 with a 27-day half-life.

      Isotopically pure U-233 is an A-1 bomb-material.  However, as 
thorium-reactor advocates like to point out, the U-233 in the reactor 
tends to become contaminated with U-232, and only a little U-232 
renders it so nastily radioactive that making a bomb with it.is 
impractical: isotopic separation of U-232 from U-233 is not realistic.

      But there are two kickers here.

      First, it is quite feasible to obtain good-quality U-233 by 
chemically separating Pa-233 from the fuel, and waiting for it to 
decay.  In fact, such a process is part of some proposed thorium fuel cycles.

      Second, any reactor can be used to generate bomb-grade Pu-239 
by irradiating special U-238 fuel elements for short periods before 
reprocessing.  The thorium reactor is no exception.

      Thus the bottom line is that a thorium reactor is not 
significantly different, proliferation wise, from any other reactor

      Arguably, as a long-term nuclear-energy option the 
thorium-fueled reactor has no obvious advantage over the 
uranium-fueled fast reactor (IFR or PRISM).  The latter is much 
closer to technological maturity, and it can breed fissile material 
at a significant rate, turning uranium into an inexhaustible energy 

      It's important to realize that mere possession of a reactor 
does not enable a country to make nuclear weapons. The way to assure 
that illegitimate bomb-making is not going on is by means of 
international oversight of the fuel cycle -- specifically, of 
facilities for enriching uranium and for processing fuel.

      I hope this helps.

      --  George S. Stanford
      Reactor physicist, retired from Argonne National Laboratory.


At 05:03 PM 11/12/2009, Otto G. Raabe wrote:
November 12, 2009

Can anyone provide some information about the thorium nuclear fuel 
cycle and the reason it is supposed to be a better 
proliferation-resistant nuclear fuel cycle.



Prof. Otto G. Raabe, Ph.D., CHP
Center for Health & the Environment
University of California
One Shields Avenue
Davis, CA 95616
E-Mail: ograabe at ucdavis.edu
Phone: (530) 752-7754   FAX: (530) 758-6140

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