Retune reactivity for withdrawn and partially inserted rods

src/reactor_sim/constants.py

@@ -11,7 +11,7 @@ COOLANT_DENSITY = 700.0  # kg/m^3 averaged between phases
 MAX_CORE_TEMPERATURE = 1_800.0  # K
 MAX_PRESSURE = 15.0  # MPa typical PWR primary loop limit
 CONTROL_ROD_SPEED = 0.03  # fraction insertion per second
-CONTROL_ROD_WORTH = 0.03  # delta rho contribution when fully withdrawn
+CONTROL_ROD_WORTH = 0.042  # delta rho contribution when fully withdrawn
 STEAM_TURBINE_EFFICIENCY = 0.34
 GENERATOR_EFFICIENCY = 0.96
 ENVIRONMENT_TEMPERATURE = 295.0  # K

src/reactor_sim/neutronics.py

@@ -15,7 +15,7 @@ LOGGER = logging.getLogger(__name__)
 def temperature_feedback(temp: float) -> float:
     """Negative coefficient: higher temperature lowers reactivity."""
     reference = 900.0
-    coefficient = -1.5e-5
+    coefficient = -1.7e-5
     return coefficient * (temp - reference)
 
 
@@ -28,7 +28,7 @@ class NeutronDynamics:
     beta_effective: float = 0.0065
     delayed_neutron_fraction: float = 0.0008
     external_source_coupling: float = 1e-6
-    shutdown_bias: float = -0.02
+    shutdown_bias: float = -0.014
 
     def reactivity(self, state: CoreState, control_fraction: float) -> float:
         rho = (
@@ -50,6 +50,7 @@ class NeutronDynamics:
 
     def step(self, state: CoreState, control_fraction: float, dt: float, external_source_rate: float = 0.0) -> None:
         rho = self.reactivity(state, control_fraction)
+        rho = min(rho, 0.02)
         shutdown = control_fraction >= 0.95
         if shutdown:
             rho = min(rho, -0.04)

tests/test_simulation.py

@@ -155,8 +155,26 @@ def test_full_rod_withdrawal_reaches_gigawatt_power():
     reactor.primary_pump_active = True
     reactor.secondary_pump_active = True
 
-    for _ in range(60):
+    early_power = 0.0
+    for step in range(60):
+        reactor.step(state, dt=1.0)
+        if step == 10:
+            early_power = state.core.power_output_mw
+    assert state.core.power_output_mw > max(2_000.0, early_power * 2)
+    assert state.core.fuel_temperature > 600.0
+
+
+def test_partially_inserted_rods_hold_near_three_gw():
+    reactor = Reactor.default()
+    state = reactor.initial_state()
+    reactor.shutdown = False
+    reactor.control.manual_control = True
+    reactor.control.rod_fraction = 0.4
+    reactor.primary_pump_active = True
+    reactor.secondary_pump_active = True
+
+    for _ in range(120):
         reactor.step(state, dt=1.0)
 
-    assert state.core.power_output_mw > 2_000.0
-    assert state.core.fuel_temperature > 400.0
+    assert 2_000.0 < state.core.power_output_mw < 4_000.0
+    assert 500.0 < state.core.fuel_temperature < 800.0