Index: Ringtoets/Piping/src/Ringtoets.Piping.Data/PipingCalculationScenario.cs
===================================================================
diff -u -rc5f90c4f9b42d985f16f99ad8732576b9217267a -r23a37b025a5d0358c1f30fb31de41a2c284519a5
--- Ringtoets/Piping/src/Ringtoets.Piping.Data/PipingCalculationScenario.cs	(.../PipingCalculationScenario.cs)	(revision c5f90c4f9b42d985f16f99ad8732576b9217267a)
+++ Ringtoets/Piping/src/Ringtoets.Piping.Data/PipingCalculationScenario.cs	(.../PipingCalculationScenario.cs)	(revision 23a37b025a5d0358c1f30fb31de41a2c284519a5)
@@ -50,12 +50,30 @@
 
         public RoundedDouble Contribution { get; set; }
 
-        public RoundedDouble? Probability
+        public RoundedDouble Probability
         {
             get
             {
-                return SemiProbabilisticOutput != null ? SemiProbabilisticOutput.PipingProbability : (RoundedDouble?) null;
+                if (CalculationScenarioStatus != CalculationScenarioStatus.Done)
+                {
+                    throw new InvalidOperationException("The probability can only be accessed when the status is done.");
+                }
+
+                return SemiProbabilisticOutput.PipingProbability;
             }
         }
+
+        public CalculationScenarioStatus CalculationScenarioStatus 
+        {
+            get
+            {
+                if (SemiProbabilisticOutput == null)
+                {
+                    return CalculationScenarioStatus.NotCalculated;
+                }
+
+                return double.IsNaN(SemiProbabilisticOutput.PipingProbability) ? CalculationScenarioStatus.Failed : CalculationScenarioStatus.Done;
+            }
+        }
     }
 }
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