Atom or weight fraction in MOX fuel

[bkoz]

Hi.
I have a problem with some calculations. I have to find atom or weight fraction in MOX fuel. MOX fuel is a mixture of UO2 and PuO2. It can be mixed with a various enrichment of PuO2. The fraction of isotopes of uranium and plutonium are as here:
U234 234,041 0,00002
U235 235,044 0,002
U236 236,046 0,00001
U238 238,051 0,99797
Pu239 239,052 0,936
Pu 240 240,054 0,059
Pu 241 241,057 0,004
Pu 242 242,059 0,001
Do you have any ideas how to count this? It have to depend on a enrichment of PuO2. I have a problem with finding atom/weight fraction of oxygen in fuel.
Thank you in advance !

 

[Astronuc]

There is insufficient information to determine the enrichment. Basically one has two isotopic vectors for the U and Pu, but not how much Pu vs U.

The U is depleted, and 0.99797 U-238. The Pu is 0.939 Pu-239 and 0.049 Pu-240, and traces of Pu-240 and Pu-241.

One would need to fraction of U,Pu that is Pu. I would be 0.06 Pu, 0.94 U for a commercial reactor, and one could assume a stoichiometric oxide, (U,Pu)O₂. A higher enrichment in Pu would be used in a fast reactor.