Random Ray Linear Source Stability Improvement (#3322)

2026-07-27 13:45:36 -04:00 · 2025-02-24 17:25:11 -06:00 · 2025-02-24 17:25:11 -06:00 · cba132c4b4
commit cba132c4b4
parent c794065d46
9 changed files with 132 additions and 126 deletions
--- a/src/random_ray/linear_source_domain.cpp
+++ b/src/random_ray/linear_source_domain.cpp
@ -78,13 +78,19 @@ void LinearSourceDomain::update_neutron_source(double k_eff)
      source_regions_.source(sr, g_out) =
        (scatter_flat + fission_flat * inverse_k_eff) / sigma_t;

-      // Compute the linear source terms
-      // In the first 10 iterations when the centroids and spatial moments
-      // are not well known, we will leave the source gradients as zero
-      // so as to avoid causing any numerical instability.
-      if (simulation::current_batch > 10) {
+      // Compute the linear source terms. In the first 10 iterations when the
+      // centroids and spatial moments are not well known, we will leave the
+      // source gradients as zero so as to avoid causing any numerical
+      // instability. If a negative source is encountered, this region must be
+      // very small/noisy or have poorly developed spatial moments, so we zero
+      // the source gradients (effectively making this a flat source region
+      // temporarily), so as to improve stability.
+      if (simulation::current_batch > 10 &&
+          source_regions_.source(sr, g_out) >= 0.0) {
        source_regions_.source_gradients(sr, g_out) =
          invM * ((scatter_linear + fission_linear * inverse_k_eff) / sigma_t);
+      } else {
+        source_regions_.source_gradients(sr, g_out) = {0.0, 0.0, 0.0};
      }
    }
  }
--- a/tests/regression_tests/random_ray_fixed_source_linear/linear/results_true.dat
+++ b/tests/regression_tests/random_ray_fixed_source_linear/linear/results_true.dat
@ -1,9 +1,9 @@
 tally 1:
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 tally 2:
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 tally 3:
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--- a/tests/regression_tests/random_ray_fixed_source_linear/linear_xy/results_true.dat
+++ b/tests/regression_tests/random_ray_fixed_source_linear/linear_xy/results_true.dat
@ -1,9 +1,9 @@
 tally 1:
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 tally 2:
-1.081600E-01
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 tally 3:
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--- a/tests/regression_tests/random_ray_fixed_source_subcritical/linear_xy/results_true.dat
+++ b/tests/regression_tests/random_ray_fixed_source_subcritical/linear_xy/results_true.dat
@ -1,168 +1,168 @@
 tally 1:
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--- a/tests/regression_tests/random_ray_fixed_source_subcritical/test.py
+++ b/tests/regression_tests/random_ray_fixed_source_subcritical/test.py
@ -17,7 +17,7 @@ class MGXSTestHarness(TolerantPyAPITestHarness):


@pytest.mark.parametrize("shape", ["flat", "linear_xy"])
-def test_random_ray_source(shape):
+def test_random_ray_fixed_source_subcritical(shape):
    with change_directory(shape):
        openmc.reset_auto_ids()

--- a/tests/regression_tests/random_ray_void/linear/results_true.dat
+++ b/tests/regression_tests/random_ray_void/linear/results_true.dat
@ -1,9 +1,9 @@
 tally 1:
-2.356821E+00
-2.782548E-01
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+2.782542E-01
 tally 2:
-1.082935E-01
-6.029854E-04
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 tally 3:
-7.301975E-03
-2.717553E-06
+7.302705E-03
+2.718076E-06
--- a/tests/regression_tests/random_ray_volume_estimator_linear/hybrid/results_true.dat
+++ b/tests/regression_tests/random_ray_volume_estimator_linear/hybrid/results_true.dat
@ -1,9 +1,9 @@
 tally 1:
-2.339084E+00
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 tally 2:
-1.090051E-01
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 tally 3:
-7.300117E-03
-2.715425E-06
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--- a/tests/regression_tests/random_ray_volume_estimator_linear/naive/results_true.dat
+++ b/tests/regression_tests/random_ray_volume_estimator_linear/naive/results_true.dat
@ -1,9 +1,9 @@
 tally 1:
-2.339575E+00
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 tally 2:
-1.086360E-01
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 tally 3:
-7.298937E-03
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--- a/tests/regression_tests/random_ray_volume_estimator_linear/simulation_averaged/results_true.dat
+++ b/tests/regression_tests/random_ray_volume_estimator_linear/simulation_averaged/results_true.dat
@ -1,9 +1,9 @@
 tally 1:
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 tally 2:
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 tally 3:
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