Neutron Flux Sample Data

[mbaron]

Dear fispact developers and users,

I startet using the FISPACT-II code for some activation calculations. I am interested in typical neutron flux spectra.
In the FISPACT-II User Manual, serveral typical spectral profiles of neutron fluxes are plotted. I would like to download the fluxes input files for these spectra as offered in the manual. Unfortunately I cannot find them on the website. Could you please provide a download link?
Thanks a lot in advance!
Best regards,
Martin

[Michael Fleming]

Dear Martin,

Thank you for contacting us through the forum.

I have added a few reference spectra to the wiki at http://fispact.ukaea.uk/wiki/Reference_input_spectra.

These include the spectra in the manual and QA cases that come with the standard distribution. Please note that the files are in the arb_flux format with the input group provided in the file name. To simluate with FISPACT-II, the spectra must be converted to match one of the multi-groups of FISPACT-II - for example the 709 group for neutron data. There is a getting_started example provided in the distributions from version 3-00 and the wiki has an example page: http://fispact.ukaea.uk/wiki/Spectra_conversion.

I hope this helps.

Best regards,
Michael

[Michał Piotrowski]

Dear developers,
I would like to know how to add my own neutron spectra from research reactor in which I work? It is not included in the example spectras which you provided.
Thank you in advance.

Michał Piotrowski
National Centre for Nuclear Research, Otwock, Poland

[Michael Fleming]

Hello Michał,

Thanks for contacting us through the forum. The FISPACT-II wiki has a page on spectra conversion:

https://fispact.ukaea.uk/wiki/Spectra_conversion

The general process is to provide one file with a list of the energies that bound your group structure (descending order), followed by the flux values for each of the groups.

Note that there should be N+1 energies for N flux values.

Use the GRPCONVERT keyword, and potentially LIMGRP, to cut energies consistently.

There is also an example on the system tests for Release 4.0:

http://www.ccfe.ac.uk/FISPACT-II/Releas ... ts.tar.bz2

The Tst_conv test suite provides full examples.

Best regards,
Michael

[Michał Piotrowski]

Thank you for your answer!
I did my best to find a mistake in my arb_flux file, but console still return me a fatal error after typing command "fispact convert files.convert".
I used convert.i file and files.convert file the same as provided in getting_started. And how to ensure a correct group for my spectra (175, 407 etc.)?
I would like to give my arb_flux file to check.
Best regards,
Michał Piotrowski

[Michael Fleming]

Hi Michał,

This isn't a minimum working example, as is, but I think there are at least two issues:

1. You list 130 energies in the first set, which corresponds with a 129 group structure. This is followed by 131 values for your spectrum. Your convert.i should have two numbers, the first should be 129 and the second the group you want out. You should also clear up the 129 vs 131 issue.

2. The values for incident energy are in eV and in descending order. Your first energies are 1.0E+04. I suspect this is not correct, and all the numbers need to be adjusted.

Let me know how it goes.

Best,
Michael

[Michał Piotrowski]

Good day,
You were right, the values were in MeV so I made a correction. Output "fluxes" gives me only 0 in all lines after "fispact convert files.convert". I tried with two numbers: 129 and 131 - in two cases the same problem was appeared. Index of nuclides is ENDFdata/decay/decay_2012_index_2012?
Thank you!
Regards,
Michał Piotrowski

[Michael Fleming]

Just to confirm, your arb_flux input is not valid.

You must have n+1 energies (in eV) followed by n flux values. Then you run with GRPCONVERT n 709.

Please try to fix the arb_flux and try again. If it does not work, provide a full set of inputs so that I can determine where the error is.

Best regards,
Michael

[Michał Piotrowski]

I followed all the instructions, but the problem is still the same. Because of the invalid file extensions, I sent you files by an email.

Regards,
Michał Piotrowski

[Michael Fleming]

Hello Michał,

The example you sent had a couple of issues:

1. The number of energy groups is equal to the number of energies minus 1.
2. Please use full stops instead of commas in numbers - ie 1.00E+00 rather than 1,00E+00
3. You must have a 'wall loading value' after the flux values, typically use 1.0 if you don't need this
4. Optionally include a comment line as a description

You can find this in the documentation - see, for example, https://fispact.ukaea.uk/wiki/Keyword:GRPCONVERT

You should also consider the spectrum provided. The last group, <1.0E-03 eV, has a non-zero value. This will produce exceptionally large cross sections for non-threshold reactions if allowed to continue into arbitrarily low energies (say, 1.0E-05). If you have the lowest energy at zero, it will lump all of the data in the highest bin below the lowest non-zero input energy. See the example fluxes outputs for details. The calculations may need to be redone to better understand the low-energy spectrum.

Best regards,
Michael