From 62d1771e5f5d965e706792f6546c909223db0002 Mon Sep 17 00:00:00 2001
From: nuclearkevin <66632997+nuclearkevin@users.noreply.github.com>
Date: Fri, 23 Jan 2026 14:04:25 -0600
Subject: [PATCH 1/6] Move random ray run and reset functions to the C-API.

---
 include/openmc/capi.h                         |   2 +
 .../openmc/random_ray/random_ray_simulation.h |   2 -
 src/random_ray/random_ray_simulation.cpp      | 113 +++++++++---------
 3 files changed, 61 insertions(+), 56 deletions(-)

diff --git a/include/openmc/capi.h b/include/openmc/capi.h
index d8041ef4149..22c0fd8f6c6 100644
--- a/include/openmc/capi.h
+++ b/include/openmc/capi.h
@@ -140,6 +140,8 @@ int openmc_remove_tally(int32_t index);
 int openmc_reset();
 int openmc_reset_timers();
 int openmc_run();
+void openmc_run_random_ray();
+void openmc_reset_random_ray();
 int openmc_sample_external_source(size_t n, uint64_t* seed, void* sites);
 void openmc_set_seed(int64_t new_seed);
 void openmc_set_stride(uint64_t new_stride);
diff --git a/include/openmc/random_ray/random_ray_simulation.h b/include/openmc/random_ray/random_ray_simulation.h
index 3db6510697c..711ad37dbfe 100644
--- a/include/openmc/random_ray/random_ray_simulation.h
+++ b/include/openmc/random_ray/random_ray_simulation.h
@@ -66,9 +66,7 @@ class RandomRaySimulation {
 //! Non-member functions
 //============================================================================
 
-void openmc_run_random_ray();
 void validate_random_ray_inputs();
-void openmc_reset_random_ray();
 void print_adjoint_header();
 
 } // namespace openmc
diff --git a/src/random_ray/random_ray_simulation.cpp b/src/random_ray/random_ray_simulation.cpp
index 7bab3a9b1b6..863e012eb62 100644
--- a/src/random_ray/random_ray_simulation.cpp
+++ b/src/random_ray/random_ray_simulation.cpp
@@ -1,5 +1,6 @@
 #include "openmc/random_ray/random_ray_simulation.h"
 
+#include "openmc/capi.h"
 #include "openmc/eigenvalue.h"
 #include "openmc/geometry.h"
 #include "openmc/message_passing.h"
@@ -22,49 +23,6 @@ namespace openmc {
 // Non-member functions
 //==============================================================================
 
-void openmc_run_random_ray()
-{
-  //////////////////////////////////////////////////////////
-  // Run forward simulation
-  //////////////////////////////////////////////////////////
-
-  if (mpi::master) {
-    if (FlatSourceDomain::adjoint_) {
-      FlatSourceDomain::adjoint_ = false;
-      openmc::print_adjoint_header();
-      FlatSourceDomain::adjoint_ = true;
-    }
-  }
-
-  // Initialize OpenMC general data structures
-  openmc_simulation_init();
-
-  // Validate that inputs meet requirements for random ray mode
-  if (mpi::master)
-    validate_random_ray_inputs();
-
-  // Initialize Random Ray Simulation Object
-  RandomRaySimulation sim;
-
-  // Initialize fixed sources, if present
-  sim.apply_fixed_sources_and_mesh_domains();
-
-  // Run initial random ray simulation
-  sim.simulate();
-
-  //////////////////////////////////////////////////////////
-  // Run adjoint simulation (if enabled)
-  //////////////////////////////////////////////////////////
-
-  if (sim.adjoint_needed_) {
-    // Setup for adjoint simulation
-    sim.prepare_adjoint_simulation();
-
-    // Run adjoint simulation
-    sim.simulate();
-  }
-}
-
 // Enforces restrictions on inputs in random ray mode.  While there are
 // many features that don't make sense in random ray mode, and are therefore
 // unsupported, we limit our testing/enforcement operations only to inputs
@@ -283,17 +241,6 @@ void validate_random_ray_inputs()
   }
 }
 
-void openmc_reset_random_ray()
-{
-  FlatSourceDomain::volume_estimator_ = RandomRayVolumeEstimator::HYBRID;
-  FlatSourceDomain::volume_normalized_flux_tallies_ = false;
-  FlatSourceDomain::adjoint_ = false;
-  FlatSourceDomain::mesh_domain_map_.clear();
-  RandomRay::ray_source_.reset();
-  RandomRay::source_shape_ = RandomRaySourceShape::FLAT;
-  RandomRay::sample_method_ = RandomRaySampleMethod::PRNG;
-}
-
 void print_adjoint_header()
 {
   if (!FlatSourceDomain::adjoint_)
@@ -671,3 +618,61 @@ void RandomRaySimulation::print_results_random_ray(
 }
 
 } // namespace openmc
+
+//==============================================================================
+// C API functions
+//==============================================================================
+
+void openmc_run_random_ray()
+{
+  //////////////////////////////////////////////////////////
+  // Run forward simulation
+  //////////////////////////////////////////////////////////
+
+  if (openmc::mpi::master) {
+    if (openmc::FlatSourceDomain::adjoint_) {
+      openmc::FlatSourceDomain::adjoint_ = false;
+      openmc::print_adjoint_header();
+      openmc::FlatSourceDomain::adjoint_ = true;
+    }
+  }
+
+  // Initialize OpenMC general data structures
+  openmc_simulation_init();
+
+  // Validate that inputs meet requirements for random ray mode
+  if (openmc::mpi::master)
+    openmc::validate_random_ray_inputs();
+
+  // Initialize Random Ray Simulation Object
+  openmc::RandomRaySimulation sim;
+
+  // Initialize fixed sources, if present
+  sim.apply_fixed_sources_and_mesh_domains();
+
+  // Run initial random ray simulation
+  sim.simulate();
+
+  //////////////////////////////////////////////////////////
+  // Run adjoint simulation (if enabled)
+  //////////////////////////////////////////////////////////
+
+  if (sim.adjoint_needed_) {
+    // Setup for adjoint simulation
+    sim.prepare_adjoint_simulation();
+
+    // Run adjoint simulation
+    sim.simulate();
+  }
+}
+
+void openmc_reset_random_ray()
+{
+  openmc::FlatSourceDomain::volume_estimator_ = openmc::RandomRayVolumeEstimator::HYBRID;
+  openmc::FlatSourceDomain::volume_normalized_flux_tallies_ = false;
+  openmc::FlatSourceDomain::adjoint_ = false;
+  openmc::FlatSourceDomain::mesh_domain_map_.clear();
+  openmc::RandomRay::ray_source_.reset();
+  openmc::RandomRay::source_shape_ = openmc::RandomRaySourceShape::FLAT;
+  openmc::RandomRay::sample_method_ = openmc::RandomRaySampleMethod::PRNG;
+}

From 313b218ef8728d6f809d51c3cd460871f1372456 Mon Sep 17 00:00:00 2001
From: nuclearkevin <66632997+nuclearkevin@users.noreply.github.com>
Date: Fri, 23 Jan 2026 14:24:24 -0600
Subject: [PATCH 2/6] Python bindings and docs.

---
 docs/source/capi/index.rst     |  8 ++++++++
 docs/source/pythonapi/capi.rst |  1 +
 openmc/lib/core.py             | 21 +++++++++++++++++++++
 3 files changed, 30 insertions(+)

diff --git a/docs/source/capi/index.rst b/docs/source/capi/index.rst
index 2583d51dff2..efd3c11ddd9 100644
--- a/docs/source/capi/index.rst
+++ b/docs/source/capi/index.rst
@@ -587,6 +587,10 @@ Functions
    :return: Return status (negative if an error occurs)
    :rtype: int
 
+.. c:function:: void openmc_reset_random_ray()
+
+  Reset the random ray solver
+
 .. c:function:: int openmc_remove_tally(int32_t index);
 
    Given an index of a tally, remove it from the tallies array
@@ -601,6 +605,10 @@ Functions
    :return: Return status (negative if an error occurs)
    :rtype: int
 
+.. c:function:: void openmc_run_random_ray()
+
+   Run a random ray simulation
+
 .. c:function:: int openmc_set_n_batches(int32_t n_batches, bool set_max_batches, bool add_statepoint_batch)
 
    Set number of batches and number of max batches
diff --git a/docs/source/pythonapi/capi.rst b/docs/source/pythonapi/capi.rst
index 67eca009471..772523356e4 100644
--- a/docs/source/pythonapi/capi.rst
+++ b/docs/source/pythonapi/capi.rst
@@ -38,6 +38,7 @@ Functions
    property_map
    reset
    reset_timers
+   reset_random_ray
    run
    run_in_memory
    sample_external_source
diff --git a/openmc/lib/core.py b/openmc/lib/core.py
index 02c7784d1cc..c354e560ce2 100644
--- a/openmc/lib/core.py
+++ b/openmc/lib/core.py
@@ -82,8 +82,12 @@ class _SourceSite(Structure):
 _dll.openmc_properties_import.errcheck = _error_handler
 _dll.openmc_run.restype = c_int
 _dll.openmc_run.errcheck = _error_handler
+_dll.openmc_run_random_ray.restype = None
+_dll.openmc_run_random_ray.errcheck = _error_handler
 _dll.openmc_reset.restype = c_int
 _dll.openmc_reset.errcheck = _error_handler
+_dll.openmc_reset_random_ray.restype = None
+_dll.openmc_reset_random_ray.errcheck = _error_handler
 _dll.openmc_reset_timers.restype = c_int
 _dll.openmc_reset_timers.errcheck = _error_handler
 _run_linsolver_argtypes = [_array_1d_dble, _array_1d_dble, _array_1d_dble,
@@ -458,6 +462,11 @@ def reset():
     _dll.openmc_reset()
 
 
+def reset_random_ray():
+    """Reset the random ray solver"""
+    _dll.openmc_reset_random_ray()
+
+
 def reset_timers():
     """Reset timers."""
     _dll.openmc_reset_timers()
@@ -479,6 +488,18 @@ def run(output=True):
         _dll.openmc_run()
 
 
+def run_random_ray(output=True):
+    """Run a random ray simulation
+
+    Parameters
+    ----------
+    output : bool, optional
+        Whether or not to show output. Defaults to showing output
+    """
+
+    with quiet_dll(output):
+        _dll.openmc_run_random_ray()
+
 def sample_external_source(
         n_samples: int = 1000,
         prn_seed: int | None = None

From 225283da388dbd34325aca2d6398ab8e2073635c Mon Sep 17 00:00:00 2001
From: nuclearkevin <66632997+nuclearkevin@users.noreply.github.com>
Date: Fri, 23 Jan 2026 15:39:37 -0600
Subject: [PATCH 3/6] Style changes.

---
 src/random_ray/random_ray_simulation.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/random_ray/random_ray_simulation.cpp b/src/random_ray/random_ray_simulation.cpp
index 863e012eb62..4a2afdb9893 100644
--- a/src/random_ray/random_ray_simulation.cpp
+++ b/src/random_ray/random_ray_simulation.cpp
@@ -668,7 +668,8 @@ void openmc_run_random_ray()
 
 void openmc_reset_random_ray()
 {
-  openmc::FlatSourceDomain::volume_estimator_ = openmc::RandomRayVolumeEstimator::HYBRID;
+  openmc::FlatSourceDomain::volume_estimator_ =
+    openmc::RandomRayVolumeEstimator::HYBRID;
   openmc::FlatSourceDomain::volume_normalized_flux_tallies_ = false;
   openmc::FlatSourceDomain::adjoint_ = false;
   openmc::FlatSourceDomain::mesh_domain_map_.clear();

From cc88df6db8573f5ad02962088063ad59a43d5f62 Mon Sep 17 00:00:00 2001
From: nuclearkevin <66632997+nuclearkevin@users.noreply.github.com>
Date: Sat, 24 Jan 2026 12:17:01 -0600
Subject: [PATCH 4/6] Remove openmc_reset_random_ray from the C-API - This is
 handled in openmc_finalize - Also rename openmc_reset_random_ray to
 openmc_finalize_random_ray (more clear IMO)

---
 docs/source/capi/index.rst                    |  4 ----
 docs/source/pythonapi/capi.rst                |  2 +-
 include/openmc/capi.h                         |  1 -
 .../openmc/random_ray/random_ray_simulation.h |  1 +
 openmc/lib/core.py                            |  8 -------
 src/finalize.cpp                              |  2 +-
 src/random_ray/random_ray_simulation.cpp      | 23 +++++++++----------
 7 files changed, 14 insertions(+), 27 deletions(-)

diff --git a/docs/source/capi/index.rst b/docs/source/capi/index.rst
index efd3c11ddd9..0a1962f7722 100644
--- a/docs/source/capi/index.rst
+++ b/docs/source/capi/index.rst
@@ -587,10 +587,6 @@ Functions
    :return: Return status (negative if an error occurs)
    :rtype: int
 
-.. c:function:: void openmc_reset_random_ray()
-
-  Reset the random ray solver
-
 .. c:function:: int openmc_remove_tally(int32_t index);
 
    Given an index of a tally, remove it from the tallies array
diff --git a/docs/source/pythonapi/capi.rst b/docs/source/pythonapi/capi.rst
index 772523356e4..6f18db56f36 100644
--- a/docs/source/pythonapi/capi.rst
+++ b/docs/source/pythonapi/capi.rst
@@ -38,9 +38,9 @@ Functions
    property_map
    reset
    reset_timers
-   reset_random_ray
    run
    run_in_memory
+   run_random_ray
    sample_external_source
    simulation_finalize
    simulation_init
diff --git a/include/openmc/capi.h b/include/openmc/capi.h
index 22c0fd8f6c6..868cca8f491 100644
--- a/include/openmc/capi.h
+++ b/include/openmc/capi.h
@@ -141,7 +141,6 @@ int openmc_reset();
 int openmc_reset_timers();
 int openmc_run();
 void openmc_run_random_ray();
-void openmc_reset_random_ray();
 int openmc_sample_external_source(size_t n, uint64_t* seed, void* sites);
 void openmc_set_seed(int64_t new_seed);
 void openmc_set_stride(uint64_t new_stride);
diff --git a/include/openmc/random_ray/random_ray_simulation.h b/include/openmc/random_ray/random_ray_simulation.h
index 711ad37dbfe..68c7779edad 100644
--- a/include/openmc/random_ray/random_ray_simulation.h
+++ b/include/openmc/random_ray/random_ray_simulation.h
@@ -68,6 +68,7 @@ class RandomRaySimulation {
 
 void validate_random_ray_inputs();
 void print_adjoint_header();
+void openmc_finalize_random_ray();
 
 } // namespace openmc
 
diff --git a/openmc/lib/core.py b/openmc/lib/core.py
index c354e560ce2..9eba337b4a9 100644
--- a/openmc/lib/core.py
+++ b/openmc/lib/core.py
@@ -83,11 +83,8 @@ class _SourceSite(Structure):
 _dll.openmc_run.restype = c_int
 _dll.openmc_run.errcheck = _error_handler
 _dll.openmc_run_random_ray.restype = None
-_dll.openmc_run_random_ray.errcheck = _error_handler
 _dll.openmc_reset.restype = c_int
 _dll.openmc_reset.errcheck = _error_handler
-_dll.openmc_reset_random_ray.restype = None
-_dll.openmc_reset_random_ray.errcheck = _error_handler
 _dll.openmc_reset_timers.restype = c_int
 _dll.openmc_reset_timers.errcheck = _error_handler
 _run_linsolver_argtypes = [_array_1d_dble, _array_1d_dble, _array_1d_dble,
@@ -462,11 +459,6 @@ def reset():
     _dll.openmc_reset()
 
 
-def reset_random_ray():
-    """Reset the random ray solver"""
-    _dll.openmc_reset_random_ray()
-
-
 def reset_timers():
     """Reset timers."""
     _dll.openmc_reset_timers()
diff --git a/src/finalize.cpp b/src/finalize.cpp
index 344eaa1a0a7..8eb37bb8650 100644
--- a/src/finalize.cpp
+++ b/src/finalize.cpp
@@ -184,7 +184,7 @@ int openmc_finalize()
   }
 #endif
 
-  openmc_reset_random_ray();
+  openmc_finalize_random_ray();
 
   return 0;
 }
diff --git a/src/random_ray/random_ray_simulation.cpp b/src/random_ray/random_ray_simulation.cpp
index 4a2afdb9893..af3916e3f13 100644
--- a/src/random_ray/random_ray_simulation.cpp
+++ b/src/random_ray/random_ray_simulation.cpp
@@ -617,6 +617,17 @@ void RandomRaySimulation::print_results_random_ray(
   }
 }
 
+void openmc_finalize_random_ray()
+{
+  FlatSourceDomain::volume_estimator_ = RandomRayVolumeEstimator::HYBRID;
+  FlatSourceDomain::volume_normalized_flux_tallies_ = false;
+  FlatSourceDomain::adjoint_ = false;
+  FlatSourceDomain::mesh_domain_map_.clear();
+  RandomRay::ray_source_.reset();
+  RandomRay::source_shape_ = RandomRaySourceShape::FLAT;
+  RandomRay::sample_method_ = RandomRaySampleMethod::PRNG;
+}
+
 } // namespace openmc
 
 //==============================================================================
@@ -665,15 +676,3 @@ void openmc_run_random_ray()
     sim.simulate();
   }
 }
-
-void openmc_reset_random_ray()
-{
-  openmc::FlatSourceDomain::volume_estimator_ =
-    openmc::RandomRayVolumeEstimator::HYBRID;
-  openmc::FlatSourceDomain::volume_normalized_flux_tallies_ = false;
-  openmc::FlatSourceDomain::adjoint_ = false;
-  openmc::FlatSourceDomain::mesh_domain_map_.clear();
-  openmc::RandomRay::ray_source_.reset();
-  openmc::RandomRay::source_shape_ = openmc::RandomRaySourceShape::FLAT;
-  openmc::RandomRay::sample_method_ = openmc::RandomRaySampleMethod::PRNG;
-}

From 943f5c05108e515a367f5c28800296d70b46c79a Mon Sep 17 00:00:00 2001
From: nuclearkevin <66632997+nuclearkevin@users.noreply.github.com>
Date: Sat, 24 Jan 2026 13:07:30 -0600
Subject: [PATCH 5/6] Add a test for run_random_ray.

---
 tests/unit_tests/test_lib.py | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/tests/unit_tests/test_lib.py b/tests/unit_tests/test_lib.py
index e5a4d198e88..3ec2a9ae444 100644
--- a/tests/unit_tests/test_lib.py
+++ b/tests/unit_tests/test_lib.py
@@ -5,6 +5,7 @@
 import numpy as np
 import pytest
 import openmc
+from openmc.examples import random_ray_pin_cell
 import openmc.exceptions as exc
 import openmc.lib
 
@@ -83,6 +84,19 @@ def uo2_trigger_model():
         yield
 
 
+@pytest.fixture(scope='module')
+def random_ray_pincell_model():
+    """Set up a random ray model to test with and delete files when done"""
+    openmc.reset_auto_ids()
+    # Write XML and MGXS files in tmpdir
+    with cdtemp():
+        model = random_ray_pin_cell()
+        model.settings.batches = 200
+        model.settings.inactive = 50
+        model.settings.particles = 50
+        model.export_to_xml()
+        yield
+
 @pytest.fixture(scope='module')
 def lib_init(pincell_model, mpi_intracomm):
     openmc.lib.init(intracomm=mpi_intracomm)
@@ -1052,3 +1066,15 @@ def test_sample_external_source(run_in_tmpdir, mpi_intracomm):
     openmc.lib.init(["-c"])
     openmc.lib.sample_external_source(100)
     openmc.lib.finalize()
+
+
+def test_random_ray(random_ray_pincell_model, mpi_intracomm):
+    openmc.lib.finalize()
+    openmc.lib.init(intracomm=mpi_intracomm)
+    openmc.lib.simulation_init()
+    openmc.lib.run_random_ray()
+    keff = openmc.lib.keff()
+
+    assert keff[0]==pytest.approx(1.3236826574065745)
+
+    openmc.lib.finalize()

From 8cb47b957cbd3ee7a85931947bf1821eda56ccbc Mon Sep 17 00:00:00 2001
From: nuclearkevin <66632997+nuclearkevin@users.noreply.github.com>
Date: Sun, 25 Jan 2026 10:52:42 -0600
Subject: [PATCH 6/6] Reset the solver type to Monte Carlo.

---
 src/finalize.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/finalize.cpp b/src/finalize.cpp
index 8eb37bb8650..ff5d79cb0c3 100644
--- a/src/finalize.cpp
+++ b/src/finalize.cpp
@@ -122,6 +122,7 @@ int openmc_finalize()
   settings::restart_run = false;
   settings::run_CE = true;
   settings::run_mode = RunMode::UNSET;
+  settings::solver_type = SolverType::MONTE_CARLO;
   settings::source_latest = false;
   settings::source_rejection_fraction = 0.05;
   settings::source_separate = false;