imposing inward current in criticality mode

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imposing inward current in criticality mode

Post by nico » Sat Apr 24, 2021 1:10 pm

Dear Serpent Team,
I have a very basic question concerning the simulation of a set of fuel assemblies for a PWR. Is it possible to impose the incoming neutron current on the surfaces surrounding a set of fuel assemblies in criticality mode?
I would like to compute the homogenised two-group constants for some perturbed fuel assemblies located in a very decoupled core (the UAM benchmark). Since the full-core simulation is very long (even if I save the fission source distribution), I planned to do some cell-calculations, but the assemblies I am simulating are close to the reflector, so I would like to impose the incoming current in order to take into account the spectrum shift.
I know I can store the inward current spectrum of the reactor in a detector but I wonder how I can use that information in the following criticality cell-calculations with perturbations.

Thank you so much,

Ana Jambrina
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Re: imposing inward current in criticality mode

Post by Ana Jambrina » Sun Apr 25, 2021 10:02 pm

In general, the use of a surface (ds ‘surf’ -1) and file (df) detectors would provide a surface source distribution (saving all particles that go through the surface to the region of interest).

Therefore, in external source calculation where all neutrons are started from the given distribution, you could, e.g., by using such source for a region of interest (container) to model different scenarios (content).
On the other hand, in criticality source calculations, anything defined under the ‘src’ card is used as the initial guess for the k-eff power iteration.
- Ana

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Jaakko Leppänen
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Re: imposing inward current in criticality mode

Post by Jaakko Leppänen » Wed May 05, 2021 9:22 am

I think this issue is more related to the formulation of the criticality eigenvalue problem. The conventional definition (also used in Serpent) is that time dependence and external sources are dropped, and balance between source and loss terms is obtained by scaling the fission neutron production rate.

I think it would be possible to add a constant external source to the simulation, but the solution would then no longer correspond to the solution of the conventional k-eigenvalue problem.
- Jaakko

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