Reduce steam generator conductance to raise primary temperatures

src/reactor_sim/thermal.py

@@ -18,7 +18,8 @@ def heat_transfer(primary: CoolantLoopState, secondary: CoolantLoopState, core_p
     if secondary.mass_flow_rate <= 0.0:
         return 0.0
     delta_t = max(0.0, primary.temperature_out - secondary.temperature_in)
-    conductance = 0.15  # steam generator effectiveness
+    # Require a larger temperature difference to push full power across the steam generator.
+    conductance = 0.02
     efficiency = 1.0 - math.exp(-conductance * delta_t)
     transferred = min(core_power_mw, core_power_mw * efficiency)
     LOGGER.debug("Heat transfer %.2f MW with ΔT=%.1fK", transferred, delta_t)