[ RadSafe ] RE: [cdn-nucl-l] Rise & Fall of the IFR

[George Stanford]

Marek:

         Yes, it's the rising temperature of the fuel.
The core configuration in an IFR is such that only
a moderate rise in temperature is needed to
increase the neutron leakage enough to bring the
reactor subcritical without control-rod movement.

         The IFR fuel, being metallic, is a good heat
conductor, which means that the temperature
profile through the fuel pin is very much flatter
than is the case with an oxide (or other ceramic)
fuel pin, and therefore there is little stored
heat to be dissipated if coolant pumping power is
lost.   Consequently, cooling by convective flow
of the sodium keeps the temperature of the fuel
well below its melting point.

         Does this help?

                 George

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At 10:01 PM 6/20/2007, mzigin wrote:
Great article, very interesting piece of history. Thanks George!

I'm having trouble understanding one thing. Article mentions that during
the accident conditions (such as lost of heat sink), reactor shutdowns
itself, and my understanding is that without safety system available. It
also mentions that negative reactivity feedback of the system is very
small. Therefore, I would assume that shutdown of the reactor due to
negative reactivity feedback is relatively slow, and without the heat
sink, the core should overheat quite quickly. Am I missing something? I
thought that sodium is only a coolant with minimal influence to neutron
economy, so what does shutdown the reactor? Is it the rising temperature
of the fuel? For example, in case of LWR it is quite easy, lost of
moderator means no slow neutrons, thus reaction cannot continue. But in
this case, if sodium is only a coolant and system operates on fast
neutrons only, how the loss of coolant impacts neutron economy and shuts
the reactor down?

Thanks,
Marek

-----Original Message-----
From: cdn-nucl-l-admin at mailman1.cis.McMaster.CA
[mailto:cdn-nucl-l-admin at mailman1.cis.McMaster.CA] On Behalf Of George
Stanford
Sent: Saturday, June 16, 2007 2:05 PM
To: cdn-nucl-l at mailman1.cis.McMaster.CA; radsafe at radlab.nl
Subject: [cdn-nucl-l] Rise & Fall of the IFR


For an eloquent inside account of the rise
and fall of the IFR (Integral Fast Reactor), see
the PDF file at <http://tinyurl.com/2gnctw>.

George Stanford
Reactor physicist, retired

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