Uniform mesh check modification (terrapower#472)

* Fix applyInputParams bug when values are zero
* Only check against user-provided power when the current node power is available

No new capability is added. The check of the power on the uniform mesh against the
user-provided power for the cycle is only changed so that it no longer occurs on
the BOC time node of each cycle, when the power data on the blocks is stale.

armi/reactor/converters/uniformMesh.py

@@ -339,20 +339,23 @@ def _checkConversion(self):
         sourcePow = self._sourceReactor.core.getTotalBlockParam("power")
         convPow = self.convReactor.core.getTotalBlockParam("power")
         if sourcePow > 0.0 and convPow > 0.0:
-            expectedPow = (
-                self._sourceReactor.core.p.power
-                / self._sourceReactor.core.powerMultiplier
-            )
             if abs(sourcePow - convPow) / sourcePow > 1e-5:
                 runLog.info(
                     f"Source reactor power ({sourcePow}) is too different from "
                     f"converted power ({convPow})."
                 )
-            if sourcePow and abs(sourcePow - expectedPow) / sourcePow > 1e-5:
-                raise ValueError(
-                    f"Source reactor power ({sourcePow}) is too different from "
-                    f"user-input power ({expectedPow})."
+
+            if self._sourceReactor.p.timeNode != 0:
+                # only check on nodes other than BOC
+                expectedPow = (
+                    self._sourceReactor.core.p.power
+                    / self._sourceReactor.core.powerMultiplier
                 )
+                if sourcePow and abs(sourcePow - expectedPow) / sourcePow > 1e-5:
+                    raise ValueError(
+                        f"Source reactor power ({sourcePow}) is too different from "
+                        f"user-input power ({expectedPow})."
+                    )
 
     def _setParamsToUpdate(self):
         """Activate conversion of various neutronics paramters."""