diff --git a/nucon/rl.py b/nucon/rl.py
index a44f4f4..3485e89 100644
--- a/nucon/rl.py
+++ b/nucon/rl.py
@@ -5,6 +5,10 @@ import time
 from typing import Dict, Any
 from enum import Enum
 from nucon import Nucon, BreakerStatus, PumpStatus, PumpDryStatus, PumpOverloadStatus
+try:
+    from nucon.sim import HighUncertaintyError
+except ImportError:
+    HighUncertaintyError = None
 
 Objectives = {
     "null": lambda obs: 0,
@@ -127,7 +131,13 @@ class NuconEnv(gym.Env):
 
         self._total_steps += 1
         if self.simulator:
-            self.simulator.update(self.seconds_per_step)
+            try:
+                self.simulator.update(self.seconds_per_step)
+            except Exception as e:
+                if HighUncertaintyError and isinstance(e, HighUncertaintyError):
+                    truncated = True
+                else:
+                    raise
         else:
             # Sleep to let the game advance seconds_per_step game-seconds,
             # accounting for the game's simulation speed multiplier.
@@ -350,7 +360,13 @@ class NuconGoalEnv(gym.Env):
 
         self._total_steps += 1
         if self.simulator:
-            self.simulator.update(self.seconds_per_step)
+            try:
+                self.simulator.update(self.seconds_per_step)
+            except Exception as e:
+                if HighUncertaintyError and isinstance(e, HighUncertaintyError):
+                    truncated = True
+                else:
+                    raise
         else:
             sim_speed = self.nucon.GAME_SIM_SPEED.value or 1.0
             time.sleep(self.seconds_per_step / sim_speed)
diff --git a/nucon/sim.py b/nucon/sim.py
index 784b94b..1fcc8cf 100644
--- a/nucon/sim.py
+++ b/nucon/sim.py
@@ -8,6 +8,18 @@ import torch
 from nucon.model import ReactorDynamicsModel, ReactorKNNModel
 import pickle
 
+class HighUncertaintyError(Exception):
+    """Raised by NuconSimulator when the dynamics model uncertainty exceeds the threshold.
+
+    Caught by NuconEnv/NuconGoalEnv and returned as truncated=True so the RL
+    algorithm bootstraps the value rather than treating it as a terminal state.
+    """
+    def __init__(self, uncertainty: float, threshold: float):
+        self.uncertainty = uncertainty
+        self.threshold = threshold
+        super().__init__(f"Model uncertainty {uncertainty:.3f} exceeded threshold {threshold:.3f}")
+
+
 class OperatingState(Enum):
     # Tuple indicates a range of values, while list indicates a set of possible values
     OFFLINE = {
@@ -163,13 +175,14 @@ class NuconSimulator:
             for param_name in nucon.get_all_readable():
                 setattr(self, param_name, None)
 
-    def __init__(self, host: str = 'localhost', port: int = 8786):
+    def __init__(self, host: str = 'localhost', port: int = 8786, uncertainty_threshold: float = None):
         self._nucon = Nucon()
         self.parameters = self.Parameters(self._nucon)
         self.host = host
         self.port = port
         self.time = 0.0
         self.allow_all_writes = False
+        self.uncertainty_threshold = uncertainty_threshold
         self.set_state(OperatingState.OFFLINE)
         self.model = None
         self.readable_params = list(self._nucon.get_all_readable().keys())
@@ -268,7 +281,12 @@ class NuconSimulator:
             with torch.no_grad():
                 next_state = self.model.forward(state, time_step)
         else:
-            next_state = self.model.forward(state, time_step)
+            if self.uncertainty_threshold is not None:
+                next_state, uncertainty = self.model.forward_with_uncertainty(state, time_step)
+                if uncertainty > self.uncertainty_threshold:
+                    raise HighUncertaintyError(uncertainty, self.uncertainty_threshold)
+            else:
+                next_state = self.model.forward(state, time_step)
 
         # Update only the output params the model predicts
         for param_id, value in next_state.items():