Prevent turbine output without steam

src/reactor_sim/turbine.py

@@ -35,6 +35,16 @@ class Turbine:
         steam_power_mw: float = 0.0,
         dt: float = 1.0,
     ) -> None:
+        if steam_power_mw <= 0.0 and loop.steam_quality <= 0.01:
+            # No steam available; turbine should idle.
+            state.shaft_power_mw = 0.0
+            state.electrical_output_mw = 0.0
+            state.load_demand_mw = 0.0
+            state.load_supplied_mw = 0.0
+            state.steam_enthalpy = 0.0
+            state.condenser_temperature = max(305.0, loop.temperature_in - 20.0)
+            return
+
         enthalpy = 2_700.0 + loop.steam_quality * 600.0
         mass_flow = loop.mass_flow_rate * 0.6
         available_power = max(steam_power_mw, (enthalpy * mass_flow / 1_000.0) / 1_000.0)

tests/test_turbine.py

@@ -31,3 +31,25 @@ def test_turbine_spools_toward_target_output():
         turbine.step(loop, state, steam_power_mw=300.0, dt=dt)
 
     assert state.electrical_output_mw == pytest.approx(target_electric, rel=0.05)
+
+
+def test_turbine_produces_no_power_without_steam():
+    turbine = Turbine()
+    loop = CoolantLoopState(
+        temperature_in=295.0,
+        temperature_out=295.0,
+        pressure=6.0,
+        mass_flow_rate=20_000.0,
+        steam_quality=0.0,
+    )
+    state = TurbineState(
+        steam_enthalpy=0.0,
+        shaft_power_mw=0.0,
+        electrical_output_mw=0.0,
+        condenser_temperature=300.0,
+    )
+
+    turbine.step(loop, state, steam_power_mw=0.0, dt=1.0)
+
+    assert state.electrical_output_mw == 0.0
+    assert state.shaft_power_mw == 0.0