From 3e0c960648053eb8ab4ff202ba4a6bf59ca46306 Mon Sep 17 00:00:00 2001
From: Will Boyd <wbinventor@gmail.com>
Date: Fri, 2 Oct 2015 18:12:35 -0400
Subject: [PATCH] Fixed multi-group chi calculation

---
 openmc/mgxs/mgxs.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/openmc/mgxs/mgxs.py b/openmc/mgxs/mgxs.py
index bc9167dfd..fd696ff72 100644
--- a/openmc/mgxs/mgxs.py
+++ b/openmc/mgxs/mgxs.py
@@ -1738,9 +1738,11 @@ class Chi(MultiGroupXS):
         nu_fission_in.remove_filter(energy_filter)
 
         # Compute chi
+        self._xs_tally = nu_fission_out / nu_fission_in
+
+        # Add the coarse energy filter back to the nu-fission tally
         nu_fission_in.add_filter(energy_filter)
 
-        self._xs_tally = nu_fission_out / nu_fission_in
         super(Chi, self).compute_xs()
 
     def get_xs(self, groups='all', subdomains='all', nuclides='all',