From 592efd4dda0e8811f16822aa4008b69ce1737270 Mon Sep 17 00:00:00 2001
From: GuySten <guyste@post.bgu.ac.il>
Date: Sun, 19 Jul 2026 17:08:35 +0300
Subject: [PATCH] control NJOY damage energy threshold

---
 openmc/data/njoy.py                   | 14 +++++++++++---
 tests/unit_tests/test_data_neutron.py |  8 ++++++++
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/openmc/data/njoy.py b/openmc/data/njoy.py
index ddc68cc378..3d0fcc1109 100644
--- a/openmc/data/njoy.py
+++ b/openmc/data/njoy.py
@@ -259,14 +259,14 @@ broadr / %%%%%%%%%%%%%%%%%%%%%%% Doppler broaden XS %%%%%%%%%%%%%%%%%%%%%%%%%%%%
 _TEMPLATE_HEATR = """
 heatr / %%%%%%%%%%%%%%%%%%%%%%%%% Add heating kerma %%%%%%%%%%%%%%%%%%%%%%%%%%%%
 {nendf} {nheatr_in} {nheatr} /
-{mat} 4 0 0 0 /
+{mat} 4 0 0 0 0 {damage_threshold}/
 302 318 402 444 /
 """
 
 _TEMPLATE_HEATR_LOCAL = """
 heatr / %%%%%%%%%%%%%%%%% Add heating kerma (local photons) %%%%%%%%%%%%%%%%%%%%
 {nendf} {nheatr_in} {nheatr_local} /
-{mat} 4 0 0 1 /
+{mat} 4 0 0 1 0 {damage_threshold}/
 302 318 402 444 /
 """
 
@@ -411,7 +411,7 @@ def make_pendf(filename, pendf='pendf', **kwargs):
 def make_ace(filename, temperatures=None, acer=True, xsdir=None,
              output_dir=None, pendf=False, error=0.001, broadr=True,
              heatr=True, gaspr=True, purr=True, evaluation=None,
-             smoothing=True, **kwargs):
+             smoothing=True, damage_threshold=None, **kwargs):
     """Generate incident neutron ACE file from an ENDF file
 
     File names can be passed to
@@ -463,6 +463,8 @@ def make_ace(filename, temperatures=None, acer=True, xsdir=None,
         indicates which evaluation should be used.
     smoothing : bool, optional
         If the smoothing option (ACER card 6) is on (True) or off (False).
+    damage_threshold : float, optional
+        Displacement damage threshold in eV. Used in heatr to calculate damage-energy cross section. When None use NJOY defaults.
     **kwargs
         Keyword arguments passed to :func:`openmc.data.njoy.run`
 
@@ -515,6 +517,12 @@ def make_ace(filename, temperatures=None, acer=True, xsdir=None,
 
     # heatr
     if heatr:
+        # prevent using NJOY default by setting to a small number
+        if damage_threshold == 0.0:
+            damage_threshold = 1e-5
+        # the NJOY default is 0
+        if damage_threshold is None:
+            damage_threshold = 0.0
         nheatr_in = nlast
         nheatr_local = nheatr_in + 1
         tapeout[nheatr_local] = (output_dir / "heatr_local") if heatr is True \
diff --git a/tests/unit_tests/test_data_neutron.py b/tests/unit_tests/test_data_neutron.py
index c767f01712..115541a06c 100644
--- a/tests/unit_tests/test_data_neutron.py
+++ b/tests/unit_tests/test_data_neutron.py
@@ -244,6 +244,14 @@ def test_kerma(run_in_tmpdir, am244, h2):
     assert 901 in read_in
     assert np.all(read_in[901].xs['300K'].y == h2[901].xs['300K'].y)
 
+@needs_njoy
+def test_damage_energy(tmpdir, endf_data):
+    endf_file = os.path.join(endf_data, 'neutrons', 'n-014_Si_030.endf')
+    si30 = openmc.data.IncidentNeutron.from_njoy(endf_file)
+
+    si30_copy = openmc.data.IncidentNeutron.from_njoy(endf_file, damage_threshold=100)
+    assert not np.allclose(si30[444].xs['294K'].y, si30_copy[444].xs['294K'](si30[444].xs['294K'].x))
+                            
 
 def test_urr(pu239):
     for T, ptable in pu239.urr.items():