What is the macroscopic cross section for natural uranium to thermal neutrons?

[Kirk Truax]

Hey all,

Does anyone happen to know the value of ν∑f for natural uranium? Here ν is the average number of neutron released from fission and ∑f is the macroscopic fission cross section of uranium.

Kirk

 

[jim hardy]

I'll wager there's a CANDU reactor engineer aboard who knows.
.

 

[Astronuc]

Hey all,

Does anyone happen to know the value of ν∑f for natural uranium? Here ν is the average number of neutron released from fission and ∑f is the macroscopic fission cross section of uranium.

Kirk

Developing a value for ∑_f depends on the atomic density, which depends on the form, e.g., elemental, alloy or ceramic. What form is one considering? The value of ν depends on neutron energy, and in a thermal spectrum, it will depend on U-235.

 

[jim hardy]

The value of ν depends on neutron energy,

Natural U being mostly this ,,
https://t2.lanl.gov/nis/data/endf/endfv-pdf/u238.pdf

 

[Astronuc]

Natural U being mostly this ,,
https://t2.lanl.gov/nis/data/endf/endfv-pdf/u238.pdf

Yeah, but that's for fast neutrons. Fast neutrons from fission have a peak distribution around 1 MeV and the energy distribution falls off rapidly up to 10 MeV. With d+t fusion, one gets up to 14.1 MeV neutrons. To go higher, one pretty much needs 20+ MeV protons and spallation reactions.

The OP did mention whether he flux was thermal, epithermal or fast.

 

[jim hardy]

The OP didn't mention whether he flux was thermal, epithermal or fast.

Fixed it for you

old jim

 

[Kirk Truax]

Yeah, but that's for fast neutrons. Fast neutrons from fission have a peak distribution around 1 MeV and the energy distribution falls off rapidly up to 10 MeV. With d+t fusion, one gets up to 14.1 MeV neutrons. To go higher, one pretty much needs 20+ MeV protons and spallation reactions.

The OP did mention whether he flux was thermal, epithermal or fast.

Hey guys,

You were right, I definitely did leave out that vital bit of information. I was simply looking for the macroscopic cross section for thermal neutrons. I was modeling a sub-critical pile with a large amount of graphite moderation. Turns out I was able to find a ν∑f for UO2 to thermal neutrons to be about 0.2274 cm^-1. This was from the good ole D&H tables.

Kirk