diff --git a/include/openmc/simulation.h b/include/openmc/simulation.h
index 38b0ad314..564516e60 100644
--- a/include/openmc/simulation.h
+++ b/include/openmc/simulation.h
@@ -26,12 +26,13 @@ extern "C" double k_abs_tra;     //!< sum over batches of k_absorption * k_track
 extern "C" double log_spacing;   //!< lethargy spacing for energy grid searches
 extern "C" int n_lost_particles; //!< cumulative number of lost particles
 extern "C" bool need_depletion_rx; //!< need to calculate depletion rx?
-extern "C" bool restart_batch;   //!< batch at which a restart job resumed
+extern "C" int restart_batch;   //!< batch at which a restart job resumed
 extern "C" bool satisfy_triggers; //!< have tally triggers been satisfied?
 extern "C" bool simulation_initialized; //!< has simulation been initialized?
 extern "C" int total_gen;        //!< total number of generations simulated
 extern "C" int64_t work;         //!< number of particles per process
 
+extern std::vector<double> k_generation;
 extern std::vector<int64_t> work_index;
 
 // Threadprivate variables
@@ -52,6 +53,9 @@ extern "C" int thread_id;  //!< ID of a given thread
 //! Initialize simulation
 extern "C" void openmc_simulation_init_c();
 
+//! Determine overall generation number
+extern "C" int overall_generation();
+
 //! Determine number of particles to transport per process
 void calculate_work();
 
diff --git a/src/simulation.cpp b/src/simulation.cpp
index 5c2a13678..98c3d3677 100644
--- a/src/simulation.cpp
+++ b/src/simulation.cpp
@@ -29,8 +29,33 @@ namespace openmc {
 
 namespace simulation {
 
+int current_batch;
+int current_gen;
+int64_t current_work;
+double keff {1.0};
+double keff_std;
+double k_col_abs {0.0};
+double k_col_tra {0.0};
+double k_abs_tra {0.0};
+double log_spacing;
+int n_lost_particles {0};
+bool need_depletion_rx {false};
+int restart_batch;
+bool satisfy_triggers {false};
+bool simulation_initialized {false};
+int total_gen {0};
+int64_t work;
+
+std::vector<double> k_generation;
 std::vector<int64_t> work_index;
 
+// Threadprivate variables
+bool trace;     //!< flag to show debug information
+#ifdef _OPENMP
+int n_threads {-1};  //!< number of OpenMP threads
+int thread_id;  //!< ID of a given thread
+#endif
+
 } // namespace simulation
 
 //==============================================================================
@@ -43,6 +68,12 @@ void openmc_simulation_init_c()
   calculate_work();
 }
 
+int overall_generation()
+{
+  using namespace simulation;
+  return settings::gen_per_batch*(current_batch - 1) + current_gen;
+}
+
 void calculate_work()
 {
   // Determine minimum amount of particles to simulate on each processor
diff --git a/src/simulation_header.F90 b/src/simulation_header.F90
index 8328b13b1..29ee34ccf 100644
--- a/src/simulation_header.F90
+++ b/src/simulation_header.F90
@@ -13,7 +13,7 @@ module simulation_header
   ! GEOMETRY-RELATED VARIABLES
 
   ! Number of lost particles
-  integer(C_INT), bind(C) :: n_lost_particles = 0
+  integer(C_INT), bind(C) :: n_lost_particles
 
   real(C_DOUBLE), bind(C) :: log_spacing ! spacing on logarithmic grid
 
@@ -22,14 +22,14 @@ module simulation_header
 
   integer(C_INT), bind(C) :: current_batch     ! current batch
   integer(C_INT), bind(C) :: current_gen       ! current generation within a batch
-  integer(C_INT), bind(C) :: total_gen     = 0 ! total number of generations simulated
-  logical(C_BOOL), bind(C) :: simulation_initialized = .false.
+  integer(C_INT), bind(C) :: total_gen         ! total number of generations simulated
+  logical(C_BOOL), bind(C) :: simulation_initialized
   logical(C_BOOL), bind(C) :: need_depletion_rx ! need to calculate depletion reaction rx?
 
   ! ============================================================================
   ! TALLY PRECISION TRIGGER VARIABLES
 
-  logical(C_BOOL), bind(C) :: satisfy_triggers = .false.       ! whether triggers are satisfied
+  logical(C_BOOL), bind(C) :: satisfy_triggers  ! whether triggers are satisfied
 
   integer(C_INT64_T), bind(C) :: work         ! number of particles per processor
   integer(C_INT64_T), allocatable :: work_index(:) ! starting index in source bank for each process
@@ -40,18 +40,18 @@ module simulation_header
 
   ! Temporary k-effective values
   type(VectorReal) :: k_generation ! single-generation estimates of k
-  real(C_DOUBLE), bind(C) :: keff = ONE  ! average k over active batches
-  real(C_DOUBLE), bind(C) :: keff_std    ! standard deviation of average k
-  real(C_DOUBLE), bind(C) :: k_col_abs = ZERO ! sum over batches of k_collision * k_absorption
-  real(C_DOUBLE), bind(C) :: k_col_tra = ZERO ! sum over batches of k_collision * k_tracklength
-  real(C_DOUBLE), bind(C) :: k_abs_tra = ZERO ! sum over batches of k_absorption * k_tracklength
+  real(C_DOUBLE), bind(C) :: keff      ! average k over active batches
+  real(C_DOUBLE), bind(C) :: keff_std  ! standard deviation of average k
+  real(C_DOUBLE), bind(C) :: k_col_abs ! sum over batches of k_collision * k_absorption
+  real(C_DOUBLE), bind(C) :: k_col_tra ! sum over batches of k_collision * k_tracklength
+  real(C_DOUBLE), bind(C) :: k_abs_tra ! sum over batches of k_absorption * k_tracklength
 
   ! ============================================================================
   ! PARALLEL PROCESSING VARIABLES
 
 #ifdef _OPENMP
-  integer(C_INT), bind(C) :: n_threads = NONE      ! number of OpenMP threads
-  integer(C_INT), bind(C) :: thread_id             ! ID of a given thread
+  integer(C_INT), bind(C) :: n_threads      ! number of OpenMP threads
+  integer(C_INT), bind(C) :: thread_id      ! ID of a given thread
 #endif
 
   ! ============================================================================
@@ -66,20 +66,15 @@ module simulation_header
   interface
     subroutine entropy_clear() bind(C)
     end subroutine
+
+    pure function overall_generation() result(gen) bind(C)
+      import C_INT
+      integer(C_INT) :: gen
+    end function overall_generation
   end interface
 
-
 contains
 
-!===============================================================================
-! OVERALL_GENERATION determines the overall generation number
-!===============================================================================
-
-  pure function overall_generation() result(gen) bind(C)
-    integer(C_INT) :: gen
-    gen = gen_per_batch*(current_batch - 1) + current_gen
-  end function overall_generation
-
 !===============================================================================
 ! FREE_MEMORY_SIMULATION deallocates global arrays defined in this module
 !===============================================================================