diff --git a/src/reactor_sim/constants.py b/src/reactor_sim/constants.py
index e540c29..b223904 100644
--- a/src/reactor_sim/constants.py
+++ b/src/reactor_sim/constants.py
@@ -29,6 +29,8 @@ NORMAL_CORE_POWER_MW = 3_000.0
 TEST_MAX_POWER_MW = 4_000.0
 PRIMARY_OUTLET_TARGET_K = 580.0
 SECONDARY_OUTLET_TARGET_K = 520.0
+PRIMARY_NOMINAL_PRESSURE = 7.0  # MPa typical RBMK channel header pressure
+SECONDARY_NOMINAL_PRESSURE = 7.0  # MPa steam drum/steam line pressure surrogate
 # Threshold inventories (event counts) for flagging common poisons in diagnostics.
 KEY_POISON_THRESHOLDS = {
     "Xe": 1e20,  # xenon
diff --git a/src/reactor_sim/reactor.py b/src/reactor_sim/reactor.py
index 0749e54..941dc7a 100644
--- a/src/reactor_sim/reactor.py
+++ b/src/reactor_sim/reactor.py
@@ -230,7 +230,9 @@ class Reactor:
 
         if self.primary_pump_active:
             total_flow = 0.0
-            target_pressure = (12.0 * pump_demand + 2.0) * power_ratio
+            target_pressure = (
+                0.5 + (constants.PRIMARY_NOMINAL_PRESSURE - 0.5) * pump_demand
+            ) * power_ratio
             loop_pressure = 0.5
             target_flow = self.primary_pump.flow_rate(pump_demand) * power_ratio
             for idx, pump_state in enumerate(state.primary_pumps):
@@ -280,7 +282,9 @@ class Reactor:
                 pump_state.status = "STOPPING" if pump_state.flow_rate > 1.0 else "OFF"
         if self.secondary_pump_active:
             total_flow = 0.0
-            target_pressure = 12.0 * 0.75 + 2.0
+            target_pressure = (
+                0.5 + (constants.SECONDARY_NOMINAL_PRESSURE - 0.5) * 0.75
+            ) * power_ratio
             loop_pressure = 0.5
             target_flow = self.secondary_pump.flow_rate(0.75) * power_ratio
             for idx, pump_state in enumerate(state.secondary_pumps):