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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

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- Thread starter Kirk Truax
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- #1

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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

- #2

jim hardy

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

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Astronuc

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Developing a value for ∑

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

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jim hardy

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The value of ν depends on neutron energy,

Natural U being mostly this ,,

https://t2.lanl.gov/nis/data/endf/endfv-pdf/u238.pdf

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Astronuc

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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.Natural U being mostly this ,,

https://t2.lanl.gov/nis/data/endf/endfv-pdf/u238.pdf

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

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jim hardy

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

Fixed it for ya

old jim

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Hey guys,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.

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

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