Add chemistry-driven fouling and HX/condenser penalties

tests/test_simulation.py

@@ -268,6 +268,28 @@ def test_auto_control_resets_shutdown_and_moves_rods():
     assert reactor.control.rod_fraction < 0.95
 
 
+def test_chemistry_builds_fouling_and_backpressure():
+    reactor = Reactor.default()
+    state = reactor.initial_state()
+    # Push impurities high to accelerate fouling dynamics.
+    state.dissolved_oxygen_ppm = 200.0
+    state.sodium_ppm = 100.0
+    state.secondary_loop.mass_flow_rate = 20_000.0
+    state.secondary_loop.steam_quality = 0.3
+    state.secondary_loop.temperature_out = 600.0
+    state.secondary_loop.temperature_in = 560.0
+    base_hx = state.hx_fouling
+    base_foul = state.turbines[0].fouling_penalty if state.turbines else 0.0
+    base_pressure = state.turbines[0].condenser_pressure if state.turbines else constants.CONDENSER_BASE_PRESSURE_MPA
+
+    reactor._update_chemistry(state, dt=20.0)
+
+    assert state.hx_fouling > base_hx
+    if state.turbines:
+        assert state.turbines[0].fouling_penalty > base_foul
+        assert state.turbines[0].condenser_pressure >= base_pressure
+
+
 def test_full_power_reaches_steam_and_turbine_output():
     """Integration: ramp to full power with staged rod control and verify sustained steam/electric output."""
     reactor = Reactor.default()

tests/test_thermal.py

@@ -2,7 +2,7 @@ import pytest
 
 from reactor_sim import constants
 from reactor_sim.state import CoolantLoopState
-from reactor_sim.thermal import ThermalSolver, saturation_temperature
+from reactor_sim.thermal import ThermalSolver, heat_transfer, saturation_temperature
 
 
 def _secondary_loop(temp_in: float = 350.0, pressure: float = 0.5, flow: float = 200.0) -> CoolantLoopState:
@@ -36,3 +36,15 @@ def test_secondary_generates_steam_when_energy_exceeds_sensible_heat():
     assert loop.temperature_out == pytest.approx(sat_temp, rel=0.05)
     assert loop.steam_quality > 0.0
     assert loop.steam_quality < 1.0
+
+
+def test_heat_transfer_reduced_by_fouling():
+    primary = CoolantLoopState(
+        temperature_in=360.0, temperature_out=380.0, pressure=15.0, mass_flow_rate=50_000.0, steam_quality=0.0
+    )
+    secondary = CoolantLoopState(
+        temperature_in=320.0, temperature_out=330.0, pressure=6.5, mass_flow_rate=50_000.0, steam_quality=0.1
+    )
+    clean = heat_transfer(primary, secondary, core_power_mw=7_000.0, fouling_factor=0.0)
+    fouled = heat_transfer(primary, secondary, core_power_mw=7_000.0, fouling_factor=0.25)
+    assert fouled < clean