Enable "hybrid" tallies in get_microxs_and_flux (#3831)

tests/regression_tests/microxs/test.py

@@ -34,6 +34,7 @@ def model():
     [
         ("materials", "direct"),
         ("materials", "flux"),
+        ("materials", "hybrid"),
         ("mesh", "direct"),
         ("mesh", "flux"),
     ]
@@ -49,12 +50,21 @@ def test_from_model(model, domain_type, rr_mode):
         domains = mesh
     nuclides = ['U235', 'O16', 'Xe135']
     kwargs = {
-        'reaction_rate_mode': rr_mode,
         'chain_file': CHAIN_FILE,
         'path_statepoint': 'neutron_transport.h5',
     }
     if rr_mode == 'flux':
+        kwargs['reaction_rate_mode'] = 'flux'
         kwargs['energies'] = 'CASMO-40'
+    elif rr_mode == 'hybrid':
+        kwargs['reaction_rate_mode'] = 'flux'
+        kwargs['energies'] = 'CASMO-40'
+        kwargs['reaction_rate_opts'] = {
+            'nuclides': ['U235'],
+            'reactions': ['fission'],
+        }
+    else:
+        kwargs['reaction_rate_mode'] = rr_mode
     _, test_xs = get_microxs_and_flux(model, domains, nuclides, **kwargs)
     if config['update']:
         test_xs[0].to_csv(f'test_reference_{domain_type}_{rr_mode}.csv')

tests/regression_tests/microxs/test_reference_materials_hybrid.csv

@@ -0,0 +1,7 @@
+nuclides,reactions,groups,xs
+U235,"(n,gamma)",1,0.1500301670375847
+U235,fission,1,1.2578145727734291
+O16,"(n,gamma)",1,0.00012069778439640312
+O16,fission,1,0.0
+Xe135,"(n,gamma)",1,0.014820264774863558
+Xe135,fission,1,0.0

tests/unit_tests/test_deplete_microxs.py

@@ -6,12 +6,15 @@ to a custom file with new depletion_chain node
 
 from os import remove
 from pathlib import Path
+from unittest.mock import patch
 
 import pytest
-from openmc.deplete import MicroXS
+import openmc
+from openmc.deplete import MicroXS, get_microxs_and_flux
 import numpy as np
 
 ONE_GROUP_XS = Path(__file__).parents[1] / "micro_xs_simple.csv"
+CHAIN_FILE = Path(__file__).parents[1] / "chain_simple.xml"
 
 
 def test_from_array():
@@ -124,3 +127,127 @@ def test_microxs_zero_flux():
 
     # All microscopic cross sections should be zero
     assert np.all(microxs.data == 0.0)
+
+
+def test_hybrid_tally_setup():
+    """In hybrid mode a 1-group RR tally is added alongside the flux tally."""
+    # Create a simple model with one material and a few nuclides for testing
+    model = openmc.Model()
+    mat = openmc.Material(components={'U235': 1.0, 'O16': 2.0})
+    sphere = openmc.Sphere(r=10.0, boundary_type='vacuum')
+    cell = openmc.Cell(region=-sphere, fill=mat)
+    model.geometry = openmc.Geometry([cell])
+    model.settings.batches = 2
+    model.settings.particles = 10
+
+    # Define 2-group energy structure for the test
+    energies = [0., 0.625, 2.0e7]
+
+    # Function to replace Model.run and capture the tallies that were created
+    captured = {}
+    def capture_run(**kwargs):
+        captured['tallies'] = list(model.tallies)
+        raise StopIteration
+
+    # Call get_microxs_and_flux but replace Model.run with a function that
+    # captures the tallies and raises StopIteration to exit early
+    with patch.object(model, 'run', side_effect=capture_run):
+        with pytest.raises(StopIteration):
+            get_microxs_and_flux(
+                model, [mat],
+                nuclides=['U235', 'O16'],
+                reactions=['fission', '(n,gamma)'],
+                energies=energies,
+                reaction_rate_mode='flux',
+                reaction_rate_opts={'nuclides': ['U235'], 'reactions': ['fission']},
+                chain_file=CHAIN_FILE,
+            )
+
+    # Check that both tallies were created with the expected properties
+    tally_names = [t.name for t in captured['tallies']]
+    assert 'MicroXS flux' in tally_names
+    assert 'MicroXS RR' in tally_names
+
+    # Check that the RR tally has the expected nuclides and reactions
+    rr = next(t for t in captured['tallies'] if t.name == 'MicroXS RR')
+    assert rr.nuclides == ['U235']
+    assert rr.scores == ['fission']
+
+    # RR tally must use a 1-group energy filter spanning the full energy range
+    ef = next(f for f in rr.filters if isinstance(f, openmc.EnergyFilter))
+    assert len(ef.values) == 2
+    assert ef.values[0] == pytest.approx(energies[0])
+    assert ef.values[-1] == pytest.approx(energies[-1])
+
+# ---------------------------------------------------------------------------
+# Tests for MicroXS.merge()
+# ---------------------------------------------------------------------------
+
+def _make_microxs(nuclides, reactions, values, groups=1):
+    """Helper: build a MicroXS from a flat list of values (nuclide-major order)."""
+    data = np.array(values, dtype=float).reshape(
+        len(nuclides), len(reactions), groups)
+    return MicroXS(data, nuclides, reactions)
+
+
+def test_merge_disjoint():
+    """Merging two MicroXS with no overlapping nuclides or reactions."""
+    m1 = _make_microxs(['U235', 'U238'], ['fission', '(n,gamma)'],
+                        [1., 2., 3., 4.])
+    m2 = _make_microxs(['Pu239'], ['(n,2n)'], [5.])
+
+    merged = m1.merge(m2)
+
+    assert merged.nuclides == ['U235', 'U238', 'Pu239']
+    assert merged.reactions == ['fission', '(n,gamma)', '(n,2n)']
+    assert merged.data.shape == (3, 3, 1)
+
+    # Self data preserved
+    assert merged['U235', 'fission'] == pytest.approx([1.])
+    assert merged['U238', '(n,gamma)'] == pytest.approx([4.])
+    # New data from other
+    assert merged['Pu239', '(n,2n)'] == pytest.approx([5.])
+    # Cross-terms that had no data should be zero
+    assert merged['U235', '(n,2n)'] == pytest.approx([0.])
+    assert merged['Pu239', 'fission'] == pytest.approx([0.])
+
+
+def test_merge_prefer_other():
+    """prefer='other': other overwrites shared entries, adds new ones."""
+    # m1: U235 and U238, reactions fission and (n,gamma)
+    m1 = _make_microxs(['U235', 'U238'], ['fission', '(n,gamma)'],
+                        [1., 2., 3., 4.])
+    # m2: only U235, reactions fission (overlap) and (n,2n) (new)
+    m2 = _make_microxs(['U235'], ['fission', '(n,2n)'], [9., 5.])
+
+    merged = m1.merge(m2)
+
+    # Nuclide/reaction sets
+    assert set(merged.nuclides) == {'U235', 'U238'}
+    assert set(merged.reactions) == {'fission', '(n,gamma)', '(n,2n)'}
+
+    # U235/fission overwritten by m2
+    assert merged['U235', 'fission'] == pytest.approx([9.])
+    # U235/(n,gamma) untouched
+    assert merged['U235', '(n,gamma)'] == pytest.approx([2.])
+    # New reaction added from m2
+    assert merged['U235', '(n,2n)'] == pytest.approx([5.])
+    # U238 data preserved
+    assert merged['U238', 'fission'] == pytest.approx([3.])
+    assert merged['U238', '(n,gamma)'] == pytest.approx([4.])
+    # U238/(n,2n) not in either → zero
+    assert merged['U238', '(n,2n)'] == pytest.approx([0.])
+
+
+def test_merge_prefer_self():
+    """prefer='self': shared pairs keep self's value; new entries use other's value."""
+    m1 = _make_microxs(['U235', 'U238'], ['fission', '(n,gamma)'],
+                        [1., 2., 3., 4.])
+    m2 = _make_microxs(['U235'], ['fission', '(n,2n)'], [9., 5.])
+
+    merged = m1.merge(m2, prefer='self')
+
+    # U235/fission: self wins
+    assert merged['U235', 'fission'] == pytest.approx([1.])
+    # U235/(n,2n): other used
+    assert merged['U235', '(n,2n)'] == pytest.approx([5.])