Use different stream for source sampling

This commit makes it easier for eigenvalue and fixed source runs to use the same seeds when sampling sources.

src/constants.F90

@@ -348,6 +348,14 @@ module constants
        K_TRACKLENGTH = 3, &
        LEAKAGE       = 4
 
+  ! ============================================================================
+  ! RANDOM NUMBER STREAM CONSTANTS
+
+  integer, parameter :: N_STREAMS = 3
+  integer, parameter :: STREAM_TRACKING = 1
+  integer, parameter :: STREAM_TALLIES  = 2
+  integer, parameter :: STREAM_SOURCE   = 3
+
   ! ============================================================================
   ! EXTERNAL SOURCE PARAMETERS
 

src/fixed_source.F90

@@ -11,8 +11,6 @@ module fixed_source
   use tally,           only: synchronize_tallies, setup_active_usertallies
   use tracking,        only: transport
 
-!$omp threadprivate(source_site)
-
 contains
 
   subroutine run_fixedsource()
@@ -68,11 +66,6 @@ contains
         ! grab source particle from bank
         call sample_source_particle(p)
 
-        ! Reset random number seed (it was changed during source sampling and
-        ! it should be set before transport is called to make it consistent
-        ! with eigenvalue and particle_restart).
-        call set_particle_seed(p % id)
-
         ! transport particle
         call transport(p)
 

src/global.F90

@@ -258,6 +258,8 @@ module global
 
   ! Fixed source particle bank
   type(Bank), pointer :: source_site => null()
+!$omp threadprivate(source_site)
+
 
   ! Restart run
   logical :: restart_run = .false.

src/particle_restart.F90

@@ -9,7 +9,7 @@ module particle_restart
   use output,           only: write_message, print_particle
   use output_interface, only: BinaryOutput
   use particle_header,  only: Particle
-  use random_lcg,       only: set_particle_seed, prn
+  use random_lcg,       only: set_particle_seed
   use tracking,         only: transport
 
   implicit none

src/random_lcg.F90

@@ -1,15 +1,12 @@
 module random_lcg
 
+  use constants
+
   implicit none
 
   private
   save
 
-  ! Random number streams
-  integer, parameter :: N_STREAMS = 2
-  integer, parameter :: STREAM_TRACKING = 1
-  integer, parameter :: STREAM_TALLIES  = 2
-
   integer(8) :: prn_seed0  ! original seed
   integer(8) :: prn_seed(N_STREAMS) ! current seed
   integer(8) :: prn_mult   ! multiplication factor, g

src/source.F90

@@ -10,7 +10,7 @@ module source
   use output,           only: write_message
   use output_interface, only: BinaryOutput
   use particle_header,  only: Particle
-  use random_lcg,       only: prn, set_particle_seed
+  use random_lcg,       only: prn, set_particle_seed, prn_set_stream
   use string,           only: to_str
 
 #ifdef MPI
@@ -101,6 +101,9 @@ contains
     ! Set weight to one by default
     site % wgt = ONE
 
+    ! Set the random number generator to the source stream.
+    call prn_set_stream(STREAM_SOURCE)
+
     ! Sample position
     select case (external_source % type_space)
     case (SRC_SPACE_BOX)
@@ -189,6 +192,9 @@ contains
       call fatal_error()
     end select
 
+    ! Set the random number generator back to the tracking stream.
+    call prn_set_stream(STREAM_TRACKING)
+
   end subroutine sample_external_source
 
 !===============================================================================