From bc1ab31746518ab420f01695ab91da4390134cd4 Mon Sep 17 00:00:00 2001
From: Paul Romano <paul.k.romano@gmail.com>
Date: Fri, 3 Jun 2022 09:09:52 -0500
Subject: [PATCH] Raise exception if timestep in [MWd/kg] is given with zero
 power

---
 openmc/deplete/abc.py        | 3 +++
 openmc/deplete/stepresult.py | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/openmc/deplete/abc.py b/openmc/deplete/abc.py
index df30579e57..457c51a8ae 100644
--- a/openmc/deplete/abc.py
+++ b/openmc/deplete/abc.py
@@ -719,6 +719,9 @@ class Integrator(ABC):
             elif unit.lower() == 'mwd/kg':
                 watt_days_per_kg = 1e6*timestep
                 kilograms = 1e-3*operator.heavy_metal
+                if rate == 0.0:
+                    raise ValueError("Cannot specify a timestep in [MWd/kg] when"
+                                     " the power is zero.")
                 days = watt_days_per_kg * kilograms / rate
                 seconds.append(days*_SECONDS_PER_DAY)
             else:
diff --git a/openmc/deplete/stepresult.py b/openmc/deplete/stepresult.py
index bfd1654816..6f30e934d9 100644
--- a/openmc/deplete/stepresult.py
+++ b/openmc/deplete/stepresult.py
@@ -20,7 +20,7 @@ __all__ = ["StepResult"]
 
 
 class StepResult:
-    """Output of a depletion run
+    """Result of a single depletion timestep
 
     Attributes
     ----------