Setting depletion power equal 0 to perform decay calculations stopped working

User Support
1

Hello.

In the past, I used OpenMC 0.12 to perform some decay calculations as mentioned here, by setting power to 0. It calculated k-eff values for each decay step.

Now, I have tried to repeat the same calculation using OpenMC 0.13.3 and it does perform any calculation. In the depletion_results file, k-eff is exactly 0 for all time steps. For it to work, I had to set power to a value like 0.0000000001. This way the code performs k-eff calculations along decay.

Is that an intended change? It is a bit confusing. Thank you

EDIT: Attached a test case for a pincel based on OpenMC documentation. Variable power can be modified to see this issue.

import openmc
import math

fuel = openmc.Material(name="uo2")
fuel.add_element("U", 1, percent_type="ao", enrichment=4.25)
fuel.add_element("O", 2)
fuel.set_density("g/cc", 10.4)

clad = openmc.Material(name="clad")
clad.add_element("Zr", 1)
clad.set_density("g/cc", 6)

water = openmc.Material(name="water")
water.add_element("O", 1)
water.add_element("H", 2)
water.set_density("g/cc", 1.0)
water.add_s_alpha_beta("c_H_in_H2O")
materials = openmc.Materials([fuel, clad, water])

radii = [0.42, 0.45]

pin_surfaces = [openmc.ZCylinder(r=r) for r in radii]
pin_univ = openmc.model.pin(pin_surfaces, materials)

bound_box = openmc.rectangular_prism(1.24, 1.24, boundary_type="reflective")
root_cell = openmc.Cell(fill=pin_univ, region=bound_box)
geometry = openmc.Geometry([root_cell])

settings = openmc.Settings()
settings.particles = 1000
settings.inactive = 10
settings.batches = 50

fuel.volume = math.pi * radii[0] ** 2

import openmc.deplete

chain = openmc.deplete.Chain.from_xml("/opt/openmc_data/chain_endfb71_pwr.xml")

model = openmc.Model(geometry=geometry, settings=settings)
operator = openmc.deplete.CoupledOperator(model, "/opt/openmc_data/chain_endfb71_pwr.xml")

#The following power Works:
#power = 0.00000001
#The following power does not work, but used to work as of version 0.12:
power = 0

time_steps = [3] * 4

integrator = openmc.deplete.PredictorIntegrator(operator, time_steps, power, timestep_units='d')
integrator.integrate()
2

Well, I found the reason here:

One major caveat is that in version 0.12, performing a decay-only timestep still results in a transport calculation (even though we know the reaction rates will be all zero). This has been fixed in the developmental version of OpenMC so that no transport solve takes place when the power is zero and will be part of the next release.

Is there a way to force transport calcluations during decay to study criticality of spent fuel along decay? I am doing it by setting a very low power for the moment.

3

but does the new version decay materials as it should?

4

Yes, it decays materials as it should