diff --git a/src/reactor_sim/control.py b/src/reactor_sim/control.py
index c68586c..271a98e 100644
--- a/src/reactor_sim/control.py
+++ b/src/reactor_sim/control.py
@@ -59,12 +59,26 @@ class ControlSystem:
             self.manual_control = manual
             LOGGER.info("Rod control %s", "manual" if manual else "automatic")
 
-    def coolant_demand(self, primary: CoolantLoopState) -> float:
-        desired_temp = 580.0
+    def coolant_demand(self, primary: CoolantLoopState, core_power_mw: float | None = None) -> float:
+        desired_temp = constants.PRIMARY_OUTLET_TARGET_K
         # Increase demand when outlet is hotter than desired, reduce when cooler.
-        error = (primary.temperature_out - desired_temp) / 100.0
-        demand = clamp(0.8 + error, 0.0, 1.0)
-        LOGGER.debug("Coolant demand %.2f for outlet %.1fK", demand, primary.temperature_out)
+        temp_error = (primary.temperature_out - desired_temp) / 100.0
+        demand = 0.8 + temp_error
+        # Keep pumps spinning proportionally to reactor power so we do not idle them at full load.
+        power_floor = 0.0
+        if core_power_mw is not None:
+            power_fraction = clamp(core_power_mw / constants.NORMAL_CORE_POWER_MW, 0.0, 1.5)
+            power_floor = 0.1 + 0.7 * power_fraction
+        demand = max(demand, power_floor)
+        demand = clamp(demand, 0.0, 1.0)
+        LOGGER.debug(
+            "Coolant demand %.2f (temp_error=%.2f, power_floor=%.2f) for outlet %.1fK power %.1f MW",
+            demand,
+            temp_error,
+            power_floor,
+            primary.temperature_out,
+            core_power_mw or 0.0,
+        )
         return demand
 
     def save_state(
diff --git a/src/reactor_sim/reactor.py b/src/reactor_sim/reactor.py
index ca1d6f1..a3882d4 100644
--- a/src/reactor_sim/reactor.py
+++ b/src/reactor_sim/reactor.py
@@ -197,7 +197,9 @@ class Reactor:
         state.core.add_emitted_particles(particles)
         self._check_poison_alerts(state)
 
-        pump_demand = overrides.get("coolant_demand", self.control.coolant_demand(state.primary_loop))
+        pump_demand = overrides.get(
+            "coolant_demand", self.control.coolant_demand(state.primary_loop, state.core.power_output_mw)
+        )
         self.primary_pump_active = self.primary_pump_active and any(self.primary_pump_units)
         self.secondary_pump_active = self.secondary_pump_active and any(self.secondary_pump_units)
         primary_units_active = [