Canadian Coalition for Nuclear Responsibility http://www.ccnr.org/

Gordon Edwards is the President of the Canadian Coalition for Nuclear Responsibility http://www.ccnr.org/

Gordon Edwards on thorium reactors: 

Background:

Uranium and thorium are "primordial radionuclides" with very
long half-lives that can be found in various minable ore deposits
around the world. There is roughly 3 times more thorium than 
there is uranium in the Earth's crust.

Present-day reactors are fuelled with uranium -- and
the uranium in the reactor fuel cannot be used for bombs.
That's because there is too much uranium-238 (U-238) in
comparison with uranium-235 (U-235).  For a bomb,
you need to achieve a high percentage of U-235 -- such
material is called "highly enriched uranium" (HEU).

Future reactors may be fuelled with plutonium -- a man-made
element created whenever U-238 atoms absorb neutrons and are
changed into plutonium atoms.  This happens automatically inside 
every reactor that is fuelled with uranium.  But the plutonium can 
only be extracted from the irradiated nuclear fuel by a dangerous 
and difficult operation called "reprocessing".

Once extracted from irradiated nuclear fuel, plutonium can be used 
to fabricate fuel for nuclear reactors or it can be used directly 
for bombs without any need for enrichment. Thus plutonium-based 
fuels pose a much greater proliferation risk than currently used 
uranium-based fuels -- which, as stated earlier, are not weapons-
usable because the uranium is not highly enriched .

Now, the article below refers to "thorium fuel" for nuclear reactors.
Strictly speaking, "thorium fuel" does not exist, since thorium is 
not fissile.  It cannot sustain a nuclear chain reaction and therefore
cannot be used as fuel in a nuclear reactor.  Not can it be used
to make atomic bombs. 

But thorium-232 is "fertile".  When thorium-232 is blended with a fissile 
material such as plutonium, that blend (called MOX fuel) can be used
to run a nuclear reactor.  It's the plutonium that keeps the chain
reaction going.  And while that is happening, the thorium-232 atoms 
absorb neutrons and are changed into uranium-233 (U-233) atoms.  

Now U-233 is a man-made isotope of uranium; it does not exist in nature. 
And U-233 is fissile, like U-235 -- it can sustain a nuclear chain reaction.
 
So thorium-232 "breeds" the man-made fissile material U-233, in much
the same way that U-238 "breeds" the man-made fissile material plutonium.

Uranium-233 is a severe proliferation hazard because 

  (1) it is an immediately weapons-usable material with a smaller 
     critical mass than pure U-235, 

  (2) it is 100% enriched when produced in a thorium matrix and 
     therefore immediately weapons-usable.

The United States first tested U-233 as part of a bomb core in 

Operation Teapot in 1955.

The idea behind "thorium fuel" is to reprocess the irradiated thorium-
plutonium blend to extract the uranium-233, then made a new blend of
thorium-and-uranium-233, run it through the reactor, thereby producing
even more U-233, reprocess that spent fuel again, and continue in this
way as long as possible.

The idea of using thorium for reactors is an old one.  It has not been
adopted before now because it poses very serious proliferation problems.  
It presupposes reprocessing of irradiated fuel -- first to get the plutonium
needed to start the process going, then to get the uranium-233 which
allows the process to continue.

Without reprocessing, and the handling of immediately weapons-usable
materials such as plutonium and uranium-233, thorium "fuel" is not possible.  

AECL tried to get this elaborate process going in Canada back in 1977. 
The nuclear scientists involved had in fact been dreaming about it since the 
early 1940s (back in the days of the WWII "Montreal Laboratory").

See my 1978 discussion of the AECL effort by clicking here:
http://www.ccnr.org/AECL_plute.html

Where thorium fits into the decay chain, and the byproducts that follow

http://www.ccnr.org/decay_U238.html