CAD-to-Neutronics Workflows
Converting engineering CAD geometry into transport-code models is a distinct workflow, since neutronics codes need watertight, analyzable representations.
A geometry gap
Engineers design components in CAD, but Monte-Carlo transport codes historically require geometry described by mathematical surfaces or clean meshes. Bridging this gap, turning a detailed CAD assembly into a model a neutronics code can trace particles through, is a specialized and error-prone workflow that dedicated tools address.
Two paths
- Conversion to constructive solid geometry: translate CAD solids into surface-based cells
- Direct-accelerated CAD tracking: trace particles on the CAD tessellation itself
- Unstructured-mesh models: mesh the CAD for both transport and coupling to thermal or structural codes
The watertight requirement
Transport tracking fails if there are gaps or overlaps between regions, since a particle can become lost or double-counted. CAD models built for manufacturing often contain small imperfections that must be cleaned or repaired. Ensuring a watertight, consistent geometry is the hardest and most time-consuming part of the workflow.
Fidelity versus tractability
Full engineering CAD is far too detailed to trace efficiently, so the model is simplified: tiny features are removed, and complex assemblies are grouped. Choosing what to keep requires judgment, because an over-simplified model can miss streaming paths through gaps that dominate shielding, while an over-detailed one will not run.
Why it belongs in the code discussion
The neutronics answer depends as much on the geometry model as on the physics, so the CAD-to-neutronics step is part of the analysis, not mere preparation. Documenting the simplifications made is part of the provenance of a breeding or shielding result.
Producing a defensible neutronics model of a real machine geometry is a recognized effort in its own right, and Kronos treats the geometry-preparation choices as part of the recorded method.