Add cell_wise MGXS generation method#3987
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Add method="cell_wise" to Model.convert_to_multigroup: like material_wise, but gives each cell its own multigroup cross sections. The material in every material-filled cell is cloned (each clone gets a unique id), then the standard per-material generation runs, so per material becomes per cell. This captures the intra-material spatial-spectrum variation that material_wise averages away when one material spans a strong gradient. The implementation reuses the material_wise path entirely; the only new code is the per-cell cloning step in convert_to_multigroup plus the dispatch entry. Adds unit tests (CSG and DAGMC: two cells sharing a material get distinct macroscopics) and a user guide entry in the MGXS methods table. Builds on the name+id library keying from openmc-dev#3984 (now in develop). Co-authored-by: jon-proxima <jon@proximafusion.com>
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Add a
cell_wiseMGXS generation methodLike
material_wise, but gives each cell its own multigroup cross sections, so itcaptures the intra-material spatial variation that
material_wiseaverages away(for example a steel material reused in several cells).
Implementation
Full reuse of the
material_wisepath. Before generation, the material in everymaterial-filled cell is cloned (each clone gets a unique id via
Material.clone()). The standard per-material generation then produces and assignsone cross section set per cell. The only new code is the per-cell cloning step in
convert_to_multigroupplus the dispatch entry (about 20 lines).material_wisebehavior is unchanged.
Works for both CSG and DAGMC.
convert_to_multigroupalready synchronizes DAGMCcells before generation, so the per-cell clones become standard DAGMC per-cell
material overrides with no special handling.
Contents
openmc/model/model.py: the per-cell cloning step and dispatch entry.tests/unit_tests/test_model.py: CSG unit test (two cells sharing a material getdistinct macroscopics).
tests/unit_tests/dagmc/test_convert_to_multigroup.py: DAGMC unit test (a modelwith two fuel volumes sharing one material yields three distinct per-cell
macroscopics).
docs/source/usersguide/random_ray.rst: addscell_wiseto the methodlist and to the "Comparison of Automatic MGXS Generation Methods" table.
Verification
section sets, while
material_wiseon the same model produces one (regressionintact).
dagmc.h5mmodel (two fuel volumes sharing one material,plus water) yields three distinct per-cell macroscopics; void volumes are
skipped.
Status
develop(the name+id library keying from Preserve user material names in convert_to_multigroup and avoid overwriting material with same name bug fix #3984 is merged).distribcell(per-instance) granularity. This PR doesper-cell-definition (one cross section set per cell, shared across lattice
instances).