## Reaction rate vs Burnup.

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Osama
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### Reaction rate vs Burnup.

Dear all,

1. When using

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det Totalflux dm Am
should I divide the result on the volume of Am material to get the total neutron flux in Am material integrated over space and energy (from 0 to infinity)?

2. To calculate the total microscopic reaction rate of Am-241 in the Am material I set the following detector setup:

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mat Am241 1.0 95241.09c 1.0
det TotalRR dm Am dr 1  Am241

Here also should I divide the result on the volume of Am material? Is the result multiplied by the Am-241 atomic density? If yes, why the reaction rate of Am-241 is increasing with burnup? please see the Figs. below.

3. I use

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det TotalXS dm Am dr 1  Am241 dt 3 Totalflux
to calculate the total microscopic cross sections of Am-241 in the Am material. Is this the best way to do that? and the unit will be in [barn]?

Last edited by Osama on Sat Sep 05, 2020 7:32 pm, edited 1 time in total.

Osama
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### Re: Reaction rate vs Burnup.

i
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Jaakko Leppänen
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### Re: Reaction rate vs Burnup.

All cell flux detectors are integrated over volume, so the flux detector gives you the integral flux, reaction rate detector the integral reaction rate. So if you want your flux to be in units n/cm²s, you need to divide by volume, etc. For the calculation of microscopic cross sections this is not necessary, because you are calculating the ratio of two integral terms.

Also note that microscopic reaction rate is sometimes expressed in terms of reactions per atom, in which case you need to change the divider.
- Jaakko

Osama
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### Re: Reaction rate vs Burnup.

Dear Jaakko Leppänen,

Why we set the density to unity here?

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mat Am241 1.0 95241.09c 1.0
Is the response function

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dr 1
means σ total [barn] * rho [atom/barn.cm]?
Also note that microscopic reaction rate is sometimes expressed in terms of reactions per atom, in which case you need to change the divider.
Did you mean reaction per sec, if yes, what will be the divider in this case?

Thanks

Ana Jambrina
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### Re: Reaction rate vs Burnup.

The ENDF reaction MT numbers are universal and related to isotopic cross sections. These reactions may not be used with materials consisting of more than one nuclide. The result is multiplied by the material atomic density and microscopic reaction rates can be calculated by setting the density to unity. (For further details: http://montecarlo.vtt.fi/download/Serpent_manual.pdf, section 7.1).

Check Serpent standard units for clarification: http://serpent.vtt.fi/mediawiki/index.p ... _constants.
- Ana

Jaakko Leppänen
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### Re: Reaction rate vs Burnup.

To be precise, material density is used as a multiplier only for macroscopic reaction rates (negative response numbers). For microscopic rates the density in the material card plays no role.
- Jaakko

Osama
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### Re: Reaction rate vs Burnup.

Does anyone can explain this:

The input is

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det Totalflux dm Am
mat Am241 1.0 95241.09c 1.0
det TotalRR dm Am dr 1  Am241
det TotalXS dm Am dr 1  Am241 dt 3 Totalflux
the output is

DETTotalflux = [
1 1 1 1 1 1 1 1 1 1 1.09991E+17 0.02933
];
DETTotalRR = [
1 1 1 1 1 1 1 1 1 1 2.37857E+18 0.02049
];
DETTotalXS = [
1 1 1 1 1 1 1 1 1 1 2.88750E+02 0.03870
];

Why DETTotalRR/DETTotalflux NOT equal the DETTotalXS ??
The volume of the Am material (cylinder) is 83.333 cm3.

Jaakko Leppänen
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### Re: Reaction rate vs Burnup.

Can you post the full input or send it o me by email?
- Jaakko

Jaakko Leppänen