From 03fe9d3200bd61965dc738911652b98df85fcb7d Mon Sep 17 00:00:00 2001
From: Paul Romano <paul.k.romano@gmail.com>
Date: Thu, 13 Jan 2022 18:32:17 -0600
Subject: [PATCH] Don't modify wgt_last in russian_roulette

---
 src/physics_common.cpp | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/src/physics_common.cpp b/src/physics_common.cpp
index f6820f81f..964678fbe 100644
--- a/src/physics_common.cpp
+++ b/src/physics_common.cpp
@@ -12,12 +12,10 @@ namespace openmc {
 void russian_roulette(Particle& p)
 {
   if (p.wgt() < settings::weight_cutoff) {
-    if (prn(p.current_seed()) < p.wgt() / settings::weight_survive) {
+    if (settings::weight_survive * prn(p.current_seed()) < p.wgt()) {
       p.wgt() = settings::weight_survive;
-      p.wgt_last() = p.wgt();
     } else {
       p.wgt() = 0.;
-      p.wgt_last() = 0.;
       p.alive() = false;
     }
   }