From e74dc5037ebfc575a72ed963c2ab148fc374b5ee Mon Sep 17 00:00:00 2001
From: John Vincent Cauilan <64677361+johvincau@users.noreply.github.com>
Date: Mon, 8 Jul 2024 16:29:49 -0500
Subject: [PATCH] Enforce non-negative percents for material.add_nuclide to
 prevent unintended ao/wo flipping (#3075)

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

diff --git a/openmc/material.py b/openmc/material.py
index 6edc372161c..4b871b77d60 100644
--- a/openmc/material.py
+++ b/openmc/material.py
@@ -519,6 +519,7 @@ def add_nuclide(self, nuclide: str, percent: float, percent_type: str = 'ao'):
         cv.check_type('nuclide', nuclide, str)
         cv.check_type('percent', percent, Real)
         cv.check_value('percent type', percent_type, {'ao', 'wo'})
+        cv.check_greater_than('percent', percent, 0, equality=True)
 
         if self._macroscopic is not None:
             msg = 'Unable to add a Nuclide to Material ID="{}" as a ' \
@@ -727,6 +728,7 @@ def add_element(self, element: str, percent: float, percent_type: str = 'ao',
 
         cv.check_type('nuclide', element, str)
         cv.check_type('percent', percent, Real)
+        cv.check_greater_than('percent', percent, 0, equality=True)
         cv.check_value('percent type', percent_type, {'ao', 'wo'})
 
         # Make sure element name is just that