From 230db28d39ae1e3011e3ad85cb8b5090693fe862 Mon Sep 17 00:00:00 2001
From: John Tramm <john.tramm@gmail.com>
Date: Tue, 28 Oct 2025 03:22:37 -0500
Subject: [PATCH] FW-CADIS Disregard Max Realizations Setting (#3616)

---
 docs/source/usersguide/variance_reduction.rst |  3 +--
 src/simulation.cpp                            |  7 ++-----
 src/weight_windows.cpp                        | 15 +++++++++++----
 3 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/docs/source/usersguide/variance_reduction.rst b/docs/source/usersguide/variance_reduction.rst
index 369e33e2d..5c2485158 100644
--- a/docs/source/usersguide/variance_reduction.rst
+++ b/docs/source/usersguide/variance_reduction.rst
@@ -133,8 +133,7 @@ random ray mode can be found in the :ref:`Random Ray User Guide <random_ray>`.
        # we used for source region decomposition
        wwg = openmc.WeightWindowGenerator(
            method='fw_cadis',
-           mesh=mesh,
-           max_realizations=settings.batches
+           mesh=mesh
        )
 
        # Add generator to openmc.settings object
diff --git a/src/simulation.cpp b/src/simulation.cpp
index f55546c4c..05d554526 100644
--- a/src/simulation.cpp
+++ b/src/simulation.cpp
@@ -400,11 +400,8 @@ void finalize_batch()
   simulation::time_tallies.stop();
 
   // update weight windows if needed
-  if (settings::solver_type != SolverType::RANDOM_RAY ||
-      simulation::current_batch == settings::n_batches) {
-    for (const auto& wwg : variance_reduction::weight_windows_generators) {
-      wwg->update();
-    }
+  for (const auto& wwg : variance_reduction::weight_windows_generators) {
+    wwg->update();
   }
 
   // Reset global tally results
diff --git a/src/weight_windows.cpp b/src/weight_windows.cpp
index 0d648d333..674fae49c 100644
--- a/src/weight_windows.cpp
+++ b/src/weight_windows.cpp
@@ -26,6 +26,7 @@
 #include "openmc/random_ray/flat_source_domain.h"
 #include "openmc/search.h"
 #include "openmc/settings.h"
+#include "openmc/simulation.h"
 #include "openmc/tallies/filter_energy.h"
 #include "openmc/tallies/filter_mesh.h"
 #include "openmc/tallies/filter_particle.h"
@@ -966,11 +967,17 @@ void WeightWindowsGenerator::update() const
 
   Tally* tally = model::tallies[tally_idx_].get();
 
-  // if we're beyond the number of max realizations or not at the corrrect
-  // update interval, skip the update
-  if (max_realizations_ < tally->n_realizations_ ||
-      tally->n_realizations_ % update_interval_ != 0)
+  // If in random ray mode, only update on the last batch
+  if (settings::solver_type == SolverType::RANDOM_RAY) {
+    if (simulation::current_batch != settings::n_batches) {
+      return;
+    }
+    // If in Monte Carlo mode and beyond the number of max realizations or
+    // not at the correct update interval, skip the update
+  } else if (max_realizations_ < tally->n_realizations_ ||
+             tally->n_realizations_ % update_interval_ != 0) {
     return;
+  }
 
   wws->update_weights(tally, tally_value_, threshold_, ratio_, method_);