## Uncertainty methodology

Discussion on physics, models and calculation methods
tim wyant
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### Uncertainty methodology

My PHYSOR paper using SERPENT has been accepted for publication pending slight revision. One request is giving some background in the uncertainty methodology SERPENT uses. I'm looking at uncertainty in k-eff, pin power, and number density of certain isotopes. I know that SERPENt doesn't produce uncertainty for ND, so any background into the methodology for how k-eff and pin power uncertainties are calculated would be useful. Has the methodology been discussed in any published work, or does SERPENT use a standard Monte Carlo uncertainty routine? If you could point me in the right direction it would be greatly appreciated.

Thanks, as always!

Jaakko Leppänen
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### Re: Uncertainty methodology

The uncertainty (statistical error) is calculated similarly for every output parameter. For every source cycle the code calculates an estimate from the collisions and other events that occur during that cycle. At the end of the calculation, these cycle-wise estimates are combined to calculate the statistical mean and the associated standard deviation or relative statistical error.
- Jaakko

Antti Rintala
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### Re: Uncertainty methodology

We've been discussing the meaning of your words "the associated standard deviation or relative statistical error" in the previous post in this topic. If I have a result, say, FLUX = [9.33622E+14 0.00050], is the 0.00050 the percentage standard deviation or some other statistical term called "relative statistical error"? If I multiply the error and the value (9.33622E+14 * 0.00050), do I get the standard deviation or something else?

Jaakko Leppänen
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### Re: Uncertainty methodology

All statistical errors in the _res.m output file are relative statistical errors, i.e. standard deviation divided by the mean. So multiplying the two values gives you standard deviation. K-eff printed in the run-time output is accompanied by the standard deviation.
- Jaakko

ishitatrivedi
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### Re: Uncertainty methodology

Hi Jaakko,

From what I understand from your last response - all statistical errors are accompanied by rel statistical error (=stddev/mean).
And, keff is accompanied by std dev (not the statistical error?).

So, in this value:

Code: Select all

``````ANA_KEFF                  (idx, [1:   6]) = [  1.19742E+00 0.00016  2.97563E-01 0.00016  1.79044E-03 0.00269 ];
IMP_KEFF                  (idx, [1:   2]) = [  1.19738E+00 3.7E-05 ];``````
the stdev for ana_keff = .00016 and for implicit is 3.75E-5? Also, if the values following the mean is either stdev (as in case of keff) or statistical error - how can i tell which one is which?

Sorry I am a little bit confused here. Thank you in advance for your help.

-Ishi

Jaakko Leppänen
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### Re: Uncertainty methodology

What I mean by run-time output is what Serpent prints out in the console when the code is run. All values in _res.m are stddev/mean, including the *_KEFF variables.
- Jaakko

ishitatrivedi
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### Re: Uncertainty methodology

Thank you for the clarification!