Help debugging a geometry-related error in my MCNP input deck

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Discussion Overview

The discussion revolves around troubleshooting a geometry-related error in an MCNP input deck, specifically related to surface overlaps in a complex lattice structure. Participants explore the modeling of a TRISO fuel compact using a body-centered cubic (BCC) lattice and discuss the implications of geometry on computational results.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant seeks help with a geometry error in their MCNP input deck, suspecting surface overlaps.
  • Another participant notes that the input file is incomplete and suggests that the lattice should be explicitly defined to facilitate troubleshooting.
  • A participant describes their modeling approach, focusing on a TRISO fuel compact with a pseudo-BCC structure, highlighting challenges with void corners in the geometry.
  • Concerns are raised about the feasibility of achieving criticality with the described geometry, particularly given the small size of the spheres and the overall structure.
  • One participant suggests homogenizing the material to simplify the model and reduce computational time, questioning the relevant parameters needed for the problem.
  • A later post indicates that the original poster has decided to pursue a different method, effectively closing the thread.

Areas of Agreement / Disagreement

Participants express differing views on the modeling approach and the feasibility of the original geometry. The discussion remains unresolved as the original poster has chosen to abandon the current method.

Contextual Notes

Limitations include the incompleteness of the input file and the potential impact of the small scale of the spheres on the modeling results. There is also uncertainty regarding the parameters necessary for achieving criticality in the described setup.

Who May Find This Useful

Individuals interested in computational modeling of nuclear systems, particularly those working with MCNP and lattice geometries, may find this discussion relevant.

MadGander
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TL;DR
MCNP geometry error
I'm looking for someone to help troubleshoot my MCNP input deck. I'm getting a geometry related error most likely due to some sort of surface overlap. Haven't been able to identify the issue myself, so I'd appreciate a secondary check. Thanks!
 

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The input file is incomplete and is crashing for me. It seems to be a big lattice full of spheres. It's very verbose, with a lot of copy transpose.

I would suggest writing the lattice as a lattice. If you describe it I should be able to help.
 
Alex A said:
The input file is incomplete and is crashing for me. It seems to be a big lattice full of spheres. It's very verbose, with a lot of copy transpose.

I would suggest writing the lattice as a lattice. If you describe it I should be able to help.
Im trying to model a TRISO fuel compact using BCC lattice cells. I'm focusing specifically on the x-y plane to produce a cylindrical geometry. Depending on exact location, the periphery cells have some sort of pseudo-BCC structure to form the outer edge of the compact. Because of this, the periphery cells have certain void corners where no 1/8th particle slice exists. Appreciate the assistance.
 
If this is, for example, a 17x17 lattice then we can model this. The spheres are tiny though, under 1mm and I can't imagine this amount and geometry reaching criticality. If this is a set problem and you have to solve it this way we can do it. If what you want is the answer from MCNP on a running reactor with this material as fuel I would suggest you homogenise. If you have a structure that is 10cm across, neutrons will not care much about the fine structure, only the quantities. Working out quantities of elements in bigger units and building the reactor from the big units is easier to model and needs less computer time.

So what are all the relevant parameters of the problem, what answers do you need and how do you want to solve it?
 
Thread can be closed. I ended up ditching this route and am pursuing a different method.
 
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If it's something you can share, please do consider sharing it. All the best with the new method!
 

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