[ RadSafe ] Fukishima Pu-239

Jaro Franta jaro_10kbq at videotron.ca
Fri Jun 6 20:31:54 CDT 2014

Actually, enriched fuel like Fukishima produces MORE Pu than a heavy water
reactor using unenriched fuel, for the simple reason that the irradiation of
enriched fuel is about five times greater.


-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of sfisher373 at aol.com
Sent: June-06-14 8:15 PM
To: radsafe at health.phys.iit.edu
Subject: [ RadSafe ] Fukishima Pu-239

Pu-239 comes from the U-238 in the fuel.  So enriched fuel like Fukishima
produces less Pu than a heavy water reactor using unenriched fuel.  

The neutrons are thermalized in the fuel and cause the U-235 to fission.
The ideal place for fissioning is on the outside of the fuel bundle.  Deeper
in the neutrons have lost energy and are resonantly absorbed by the U-238.
The U-239 fissions easier than the U-235 so any U-239 formed on the outside
will fission.  However, burnup also depends on where in the reactor the fuel
bundle is. So the statement that there is more Pu on the outside of the
bundle rather than deeper in does not make much sense.  

In Candu reactors about half the energy comes from the Pu-239 fissions.  One
of the reasons why nuclear non proliferation groups do not like the CANDU
reactor, along with on line refueling so it is theoretically easier to steal
a bundle.  

However, separating the isotopes from a spent fuel bundle requires more
expertise than just enriching fuel.  

Spencer M Fisher

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