Retune reactivity for withdrawn and partially inserted rods

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)