increase in mass during burnup and decay calculations

[Margarita Tzivaki]

Hi all,

I am calculating fuel burnup with origami and subsequent decay with origen. When looking at the origen outputs I noticed an increase in concentration (in grams and gramatoms) in the first couple of timesteps. This is not noticable in the printed totals rounded to 4 digits, but only when summing all the table entries. My initial hypothesis was, that this has something to do with the fuel library that I have generated. But I could reproduce this effect also with one of the pregenerated libraries (s18x18), however less pronounced than in the ones I am using.

I rarely look at the mass tables, so this had not ocurred to me before, but looking back to older calculations I keep noticing small increases in grams in the first couple timesteps.

I am wondering if I have made an input mistake or if this is a known artefact of rounding and how this happens.

Any help would be great! Many thanks,

Margarita

[Willem van Rooijen]

Your question is impossible to answer.

In order to get proper support:

- send (part of) an output file which shows the problem. Otherwise, perhaps an output from OPUS, PlotOPUS.

- send an MWE (*) so that others can reproduce your calculation to see whether or not they can confirm the issue, and perhaps give solutions.

- implicitly, you mention that you are using non-SCALE libraries ("But I could reproduce this effect also with one of the pregenerated libraries (s18x18), however less pronounced than in the ones I am using"). It is possible that your "depletion matrix" is (slightly) non-conservative. That is to say: in the depletion matrix, the diagonal elements determine the rate at which an isotope disappears. However, "mass" is conserved, so that means that if one nucleus disappears, something else must appear. In the case of fission, two fission products, in the case of radioactive decay, the daughter nucleus. It is possible that your matrix elements are slightly non-conservative. If I remember correctly there is a way of checking the matrix for such properties, but I don't remember how from the top of my head.

Let us know.

Namizono

(*) MWE : Minimal Working Example, an example of a simple input file which shows the problem.

2024年11月12日火曜日 19:00:20 UTC+9 Margarita Tzivaki:

[Margarita Tzivaki]

Hi all,

My apologies for not following up on this after I solved the issue. I am attaching a plot of my results to demonstrate the problem (gold is SCALE that I was comparing with another code in green). It seems that this effect was produced by a decay calculation over long timescales in combination with the standard cutoff in SCALE. My calculations ran over 100.000 years and it seems that any nuclide falling under the mass cutoff over the cumulative time is not printed in the output. The issue disappears if I run the same burnup and decay for only 40 years.

Cheers,

Margarita