[ RadSafe ] Graphite SWAG Answer - Helium on tubine? - thori um cycle

John Andrews andrewsjp at chartertn.net
Tue Nov 15 21:54:37 CST 2005

Joe and All,

As I recall, the thorium for the General Atomic HTGRs used selected 
thorium from  low uranium content ore to keep the amount of Th-230 low 
in the separated thorium.  If there is significant Th-230 in the thorium 
used in the reactor, then it breeds U-232 which has the same daughters 
as thorium in the decay chain because U-232 decays to Th-228, but has a 
much shorter parent in the 74 year U-232.  Since the U-232 cannot be 
separated from the U-233, the resultant uranium becomes very radioactive 
with high energy gamma rays rather quickly after separation from the 
daughters.  This means that any weapons production (or fuel, for that 
matter) must be done within a month or two of the separation process and 
massive shielding is necessary for storage and handling of the U-233 
containing trace amounts of U-232.  This may be acceptable for fuel 
production, but would really inhibit the use of U-233 for weapons.

John Andrews, Knoxville, Tennessee

Nardi, A. Joseph wrote:

>It is not accurate to assume that the Th-232/U-233 fuel cycle is nuclear
>proliferation resistant.  Here are a couple of points for consideration:
>1) I have never seen an analysis of the potential to make a weapon from
>U-233 but it would seem to be similar to high enriched uranium.  U-233 is
>fissile and most probably could be used to make a weapon but has not been
>available and has higher associated dose rates.  In the Th-232/U-233 fuel
>cycle it would be possible to chemically separate the Th and U and therefore
>have U-233 in a pure form.  This would be similar to extracting Pu from a
>low enriched uranium fuel cycle.  You could not count on a "once through"
>fuel cycle because that loses the entire point of Th-232/U-233 fuel cycle.  
>2) It is not possible to startup the Th-232/U-233 fuel cycle without a
>fissile component such as high enriched uranium or Pu.  Th-232 can not be
>made to go critical as you can do with natural uranium.  So the first core
>would have to be fueled with Th-232/U-235 or Th-232/Pu to start the
>generation of U-233.
>3) Most Th-232/U-233 fuel cycles are "burners" rather than "breeders" so you
>would have to continue to feed fissile material such as high enriched
>uranium or Pu to make up for net consumption of fissile material in the fuel
>cycle.  There have been some attempts at developing thermal breeder reactors
>for the Th-232/U-233 fuel cycle but I understand the breeding ratio is very
>low so it would take a long time to breed enough U-233 to start the next
>A. Joseph Nardi
>Westinghouse Electric Company
>P.O. Box 355
>Pittsburgh, PA 15230
>Phone - 412-374-4652
>FAX - 412-374-3832
>email - nardiaj at westinghouse.com
>From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On Behalf
>Of JGinniver at aol.com
>Sent: Saturday, November 12, 2005 2:23 PM
>To: hflong at pacbell.net
>Cc: radsafe at radlab.nl
>Subject: Re: [ RadSafe ] Graphite SWAG Answer - Helium on tubine?
>  As  far 
>as I know the best hope for a fuel cycle that can't be used to produce  
>nuclear weapons is the Thorium to Uranium-233 fuel cycle.  I believe that
>it was 
>only India that has worked on this option in recent years.
>    Julian
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