From 2db8bbe060867f1a0194ec4e5f0b2edea0055faf Mon Sep 17 00:00:00 2001
From: Will Boyd <wbinventor@gmail.com>
Date: Wed, 29 Jul 2015 23:55:17 -0700
Subject: [PATCH] Now initialize mean and std_dev to None in Tally.slice(...)

---
 openmc/tallies.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/openmc/tallies.py b/openmc/tallies.py
index 3695885b0c..afdc19048b 100644
--- a/openmc/tallies.py
+++ b/openmc/tallies.py
@@ -2082,6 +2082,8 @@ class Tally(object):
                                      nuclides, 'sum_sq')
         new_tally.sum = new_sum
         new_tally.sum_sq = new_sum_sq
+        new_tally._mean = None
+        new_tally._std_dev = None
 
         ############################     FILTERS      ##########################
         if filters: