Hi there,
I am modeling depletion of VVER-440 fuel assembly using CoupledOperator and CECMIntegrator and want to compare the results of the OpenMC simulation with a similar SCALE6.2.4 t-6 depl sequence results. However, there is a noticeable discrepancy in the k_{eff} - Burnup depth results:
It looks like the OpenMC graph is squeezed horizontally by a factor of 10 compared to the SCALE’s one. I also fond a peak typical for that fuel composition and assembly profile between 10 and 20 MWd/kgU and the similar peak on OpenMC graph is about 1 and 2 MWd/kgU.
Could you please check the chunk of OpenMC code and hint me what am I doing wrong?
# settings
settings = openmc.Settings()
settings.batches = 100
settings.inactive = 20
settings.particles = 10_000
settings.temperature['method'] = 'interpolation'
settings.temperature['multipole'] = True
# source
min_extents = (-assembly_case_in_edge, -assembly_case_in_apothem, -124.)
max_extents = (assembly_case_in_edge, assembly_case_in_apothem, 124.)
source_dist = openmc.stats.Box(lower_left=min_extents, upper_right=max_extents)
settings.source = openmc.IndependentSource(space=source_dist, constraints={'domains': [uo2_type1, uo2_type2, uo2_type3, uo2_type4],
'fissionable': True})
settings.export_to_xml()
# depletion
import openmc.deplete
chain_path = '/home/imelnyk/openmc-nuclear-data/endfb-vii.1-hdf5/chain_endfb71_pwr.xml'
# set volumes .....
# .................
# .................
model = openmc.Model(geometry=geom, settings=settings)
depletion_operator = openmc.deplete.CoupledOperator(model, chain_path, normalization_mode='energy_deposition')
power_mass_density = 35. # W/gU
time_steps = [1., 2., 3., 4., 5., 6., 7.571428571] + 60 * [28.57142857]
integrator = openmc.deplete.CECMIntegrator(depletion_operator, timesteps=time_steps, power_density=power_mass_density, timestep_units='d')
integrator.integrate()
Probably, there might be an error in timesteps(?).
P.S. Some fuel pins contain Gd.
Cheers,
Ihor
I believe, it may have to do with OpenMC’s timesteps being relative to the previous given timestep point, so your current time steps
[1., 2., 3., 4., 5., 6., 7.571428571]
aren’t seen as constantly increasing by 1, that series is interpreted as [1,3,6,10,15,21,28.571428571].
I’m just getting started with OpenMC myself, so I am not incredibly familiar with the burnup capabilities, but I did learn about this a few days ago.
Hi imelnyk,
Since you use the burnup MWD/kg as x axis, I think there must be something in the composition. If you have made sure the geometry, power density, timestep and accumulation time was identic berween each code, you might want to compare the fuel and burnable poison BP composition calculated by each code during depletion. You can use time as x axis when comparing both results.
Also, you might want to check that the depleteable parameter on the material was set as True, either for the fuel or BP, and each should have a proper volume so that the initial isotope mass between each code was the same. The power density will be multiplied by the heavy metal mass, so you could also do a sensitivity analysis by directly supplying the fuel assembly power to the openmc.
Hi @doriangaboo,
Thanks for your answer! However, I’m not sure that the time steps are supposed to be cumulative, since the opposite is literally specified in the lecture on depletion:
Hi @wahidluthfi,
Thanks for your advises! I double check the material and couldn’t find anything suspicious for the moment. I set the material for fuel pins with BA mixing UO2 and Gd materials. I thought that I any material contain Uranium it should be implicitly treated as a depletable, but probably it does not work for Gd. So, I set the Gd mat. to be depletable explicitly and start the calculations. I will see the results later …
Okay, you can also compare the decrease in fissile and BP isotope materials vs time or burnup between each code to find some clue, because I think the decrease in reactivity should have come from those isotopes; either your fissile atomic density decreases faster in openmc, or the BP is not depleted, suppressing the reactivity without even burning it.
Reading back what I said I definitely wrote that poorly, my apologies. I was trying to communicate what they state there, how a burn up calculations with 6 time steps of 30 days, would be defined like [30,30,30,30,30,30] instead of [30, 60, 90, 120, 150, 180]
Unfortunately I can’t speak to whether that could be the cause, I’m not familiar enough with burnup mechanics, but hopefully you get it! Best of luck
