Micro / macro group structure effects

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david.holler
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Micro / macro group structure effects

Post by david.holler » Wed Mar 17, 2021 3:27 pm

Hello all,

Has anyone observed unexpected group structure dependence in high-temperature reactor modeling? My macro group constants are showing dependency on higher energy group boundaries, but I haven't determined the exact cause yet. My guess is either materials or homogenization, or a combination of both, but I could be wrong. Thanks for reading and please let me know if my question needs clarification.

David H.

Ana Jambrina
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Re: Micro / macro group structure effects

Post by Ana Jambrina » Wed Mar 17, 2021 6:28 pm

What do you mean by unexpected? There might be a remarkable interdependence between spectral zone and energy group structure - but that does not have anything of unexpected.
- Ana

david.holler
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Re: Micro / macro group structure effects

Post by david.holler » Wed Mar 17, 2021 9:57 pm

The dependence on group structure was unexpected since I was modeling 2D & 3D single fuel assemblies with all reflective BCs.
I should be more clear - the group structure dependence only occurs when I use Serpent-generated group constants in a nodal code. For this type of problem, though, a nodal code should be able to reproduce the Serpent eigenvalue without much trouble.

Antti Rintala
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Re: Micro / macro group structure effects

Post by Antti Rintala » Thu Mar 18, 2021 8:44 am

What did you exactly calculate with Serpent and how, and what did you calculate with the nodal program? And what was the problem with the results?

AudreyWilkins
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Re: Micro / macro group structure effects

Post by AudreyWilkins » Thu Mar 18, 2021 6:13 pm

Hi, I read this with excitement. What materials do you use? It could be because of them!
Last edited by AudreyWilkins on Sat Mar 20, 2021 7:52 pm, edited 3 times in total.

david.holler
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Re: Micro / macro group structure effects

Post by david.holler » Thu Mar 18, 2021 11:29 pm

I can't provide detail on materials, but I am looking into them as well as what my Serpent model is doing. I will try other intermediate group structures and see if there are any sensitivities present.

I'm just using Serpent 2 group constants for k-eigenvalue calculations in a nodal diffusion code. There isn't a problem with Serpent results, just the process of replicating them with a diffusion code.

Antti Rintala
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Re: Micro / macro group structure effects

Post by Antti Rintala » Fri Mar 19, 2021 8:53 am

Replicating the Serpent results with a nodal program depends a lot (for example) on what kind of model you are trying to model and how, and what results of the Serpent group constant output you are using. Without any details, there is not much to say on this matter.

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