[ RadSafe ] Fukishima Pu-239

sfisher373 at aol.com sfisher373 at aol.com
Fri Jun 6 19:15:22 CDT 2014

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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