Re: Russia: Iran May Seek More Reactors

[Bernard L Cohen <blc+@pitt.edu>]

On Tue, 18 Jan 2000, Michael McNaughton wrote:

> At 12:03 PM 1/17/00 -0600, you wrote:
> >I suppose because the RMBK can be easily
> >used to produce weapons grade plutonium 
> 
> In what way is the RMBK specially suited for this purpose? I thought that
> any source of thermal neutrons could be used to make Pu-239.

	--To make "bomb grade" plutonium, it is important for the fuel to
be left in the reactor for only about 30 days. If it is left in longer,
plutonium-239 conversion to plutonium-240 by neutron capture becomes
important. Plutonium-240 decays frequently by spontaneous fission,
which releases neutrons and thereby causes bombs to fizzle -- the chain
reaction starts before the highly supercritical mass is assembled. so the
explosive power is much reduced. 
	The RMBK is designed such that fuel can be changed, a fraction of
it every day, without shutting down the reactor, so leaving fuel in the
reactor 30 days is practical. In a light water reactor, a fuel change
requires shutting down the reactor for several weeks, so a monthly change
is not practical.
 > 
Bernard L. Cohen
Physics Dept.
University of Pittsburgh
Pittsburgh, PA 15260
Tel: (412)624-9245
Fax: (412)624-9163
e-mail: blc+@pitt.edu


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