Questions about Fuel Temperature Coefficient

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1

Hi there,
I am using openmc 13.1 (conda version) to calculate the fuel Doppler coefficient for a solid state heat pipe space reactor (U235 enrichment above 90%). I am using the ENDF/B-VII.1 library. But the results obtained by simply considering the fuel temperature changes seam like incorrect (maybe it’s right when in the range of -0.1 to -0.3 pcm/K). I tested several different fuel temp, but could not explain the results.

I used the following fuel, its temperature and the settings.

    un_original = openmc.Material(material_id=1, name='UN')
    un_original.add_element('U', 1.0, enrichment=90.3)
    un_original.add_element('N',1.0)
    un_original.set_density('g/cm3',10.815)
    un_original.temperature = 1524 # k  

    heatpipe_gd = openmc.Material(material_id=3, name='Gd')
    heatpipe_gd.add_element('Gd',1.0,'ao')
    heatpipe_gd.set_density('g/cm3',7.90)

    poison_content = 0.01
    un = openmc.Material.mix_materials([un_original, heatpipe_gd], [1-poison_content, poison_content], 'wo', name='UN_poison')
    un.temperature = 1524 # k

    settings = openmc.Settings()
    settings.batches = 300
    settings.inactive = 50
    settings.particles = 300000
    settings.source = openmc.Source(space=openmc.stats.Point((1.2, 0., 16.)))
    settings.temperature =  {'multipole': True, 'method': 'interpolation', 'range': [293.15, 2500]}
    settings.export_to_xml()

The results obtained were as follows.

result
result752×208 37.4 KB

2

Hello,
I have extensive experience with this. Your settings.temperature specification looks good. Double check that that your cross section environment variable is pointing to the correct data that includes wmp files.

The next thing to try is to specify the temperature on the cells, rather than the materials. I’m not completely sure why, but temperature changes need to be made on the cells, whereas density changes need to be made on the materials.