Handle multi-particle importance syntax

src/openmc_mcnp_adapter/parse.py

@@ -12,7 +12,7 @@
 # Regular expressions for cell parameters
 _KEYWORDS = [
     r'\*?trcl', r'\*?fill', 'tmp', 'u', 'lat',
-    'imp:.', 'vol', 'pwt', 'ext:.', 'fcl', 'wwn', 'dxc', 'nonu', 'pd',
+    'imp:(?:.(?:,.)*)', 'vol', 'pwt', 'ext:.', 'fcl', 'wwn', 'dxc', 'nonu', 'pd',
     'elpt', 'cosy', 'bflcl', 'unc', 'mat', 'rho',
     'pmt'  # D1SUNED-specific
 ]

tests/test_multiparticle_importance.py

@@ -0,0 +1,66 @@
+# SPDX-FileCopyrightText: 2025 UChicago Argonne, LLC and contributors
+# SPDX-License-Identifier: MIT
+
+from textwrap import dedent
+
+from openmc_mcnp_adapter import mcnp_str_to_model, parse_cell
+
+
+def test_multiparticle_importance():
+    """Test that multi-particle importance keywords (e.g., imp:n,p) are parsed correctly."""
+    mcnp_str = dedent("""
+    title
+    1   1 -1.0  -1  imp:n,p=1
+    2   0        1  imp:n,p=0
+
+    1   so 1.0
+
+    m1   1001.80c  1.0
+    mode n p
+    """)
+    model = mcnp_str_to_model(mcnp_str)
+
+    # Get cells
+    cells = model.geometry.get_all_cells()
+    cell1 = cells[1]
+    cell2 = cells[2]
+
+    # Check that cells exist and have correct IDs
+    assert cell1.id == 1
+    assert cell2.id == 2
+
+    # Test parse_cell directly
+    line1 = "1   1 -1.0  -1  imp:n,p=1"
+    cell_dict1 = parse_cell(line1)
+    assert 'imp:n,p' in cell_dict1['parameters']
+    assert cell_dict1['parameters']['imp:n,p'] == '1'
+
+    line2 = "2   0       1  imp:n,p=0"
+    cell_dict2 = parse_cell(line2)
+    assert 'imp:n,p' in cell_dict2['parameters']
+    assert cell_dict2['parameters']['imp:n,p'] == '0'
+
+
+def test_multiparticle_importance_three_particles():
+    line = "1   1 -1.0  -1  imp:n,|,e=1"
+    cell_dict = parse_cell(line)
+    assert 'imp:n,|,e' in cell_dict['parameters']
+    assert cell_dict['parameters']['imp:n,|,e'] == '1'
+
+
+def test_multiparticle_importance_with_other_params():
+    """Test that multi-particle importance works with other cell parameters."""
+    line = "1   1 -1.0  -1  imp:n,p=1 vol=5.0 u=2"
+    cell_dict = parse_cell(line)
+    assert 'imp:n,p' in cell_dict['parameters']
+    assert cell_dict['parameters']['imp:n,p'] == '1'
+    assert cell_dict['parameters']['vol'] == '5.0'
+    assert cell_dict['parameters']['u'] == '2'
+
+
+def test_single_particle_importance_still_works():
+    """Ensure single-particle importance still works correctly."""
+    line = "1   1 -1.0  -1  imp:n=1"
+    cell_dict = parse_cell(line)
+    assert 'imp:n' in cell_dict['parameters']
+    assert cell_dict['parameters']['imp:n'] == '1'