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Hi all,
I have a question. In fast reactors, it is generally considered unsafe to have too high an amount of americium (mainly am-241) in the core, because it diminishes all the safety parameters of the core:
- it has too high an absorption cross section, so that it "shadows" the U-238 resonances which give the Doppler effect
- it has a much lower retarded neutron fraction, hence diminishing the safety margin to prompt criticality
- it has a rising fission cross section which overshadows that of U-238, hence increasing fission when the spectrum hardens, which is bad for the void factor.
At least, that's what I understand.
But now, my question is: when I look at the Pu-240 cross sections, they seem to have similar problems. So why isn't Pu-240 then such a problem ?
cheers,
Patrick.
I have a question. In fast reactors, it is generally considered unsafe to have too high an amount of americium (mainly am-241) in the core, because it diminishes all the safety parameters of the core:
- it has too high an absorption cross section, so that it "shadows" the U-238 resonances which give the Doppler effect
- it has a much lower retarded neutron fraction, hence diminishing the safety margin to prompt criticality
- it has a rising fission cross section which overshadows that of U-238, hence increasing fission when the spectrum hardens, which is bad for the void factor.
At least, that's what I understand.
But now, my question is: when I look at the Pu-240 cross sections, they seem to have similar problems. So why isn't Pu-240 then such a problem ?
cheers,
Patrick.