Handle heat-sink loss and update turbine controls

AGENTS.md

@@ -12,7 +12,7 @@ All source code lives under `src/reactor_sim`. Submodules map to plant systems:
 - A git remote for `origin` is configured; push changes to `origin/main` once work is complete so dashboards stay in sync.
 
 ## Operations & Control Hooks
-Manual commands live in `reactor_sim.commands.ReactorCommand`. Pass a `command_provider` callable to `ReactorSimulation` to adjust rods, pumps, turbine, coolant demand, or the attached `ElectricalConsumer`. Use `ReactorCommand.scram_all()` for full shutdown, `ReactorCommand(consumer_online=True, consumer_demand=600)` to hook the grid, or toggle pumps (`primary_pump_on=False`) to simulate faults. Control helpers in `control.py` expose `set_rods`, `increment_rods`, and `scram`, and you can switch `set_manual_mode(True)` to pause the automatic rod controller. For hands-on runs, launch the curses dashboard (`FISSION_DASHBOARD=1 FISSION_REALTIME=1 python run_simulation.py`) and use the on-screen shortcuts (q quit/save, space SCRAM, p/o pumps, t turbine, 1/2/3 toggle individual turbines, r reset/clear saved state, +/- rods in 0.05 steps, [/ ] consumer demand, s/d setpoint, `a` toggles auto/manual rods). Recommended startup: enable manual rods (`a`), withdraw to ~0.3 before ramping the turbine/consumer, then re-enable auto control when you want closed-loop operation.
+Manual commands live in `reactor_sim.commands.ReactorCommand`. Pass a `command_provider` callable to `ReactorSimulation` to adjust rods, pumps, turbine, coolant demand, or the attached `ElectricalConsumer`. Use `ReactorCommand.scram_all()` for full shutdown, `ReactorCommand(consumer_online=True, consumer_demand=600)` to hook the grid, or toggle pumps (`primary_pump_on=False`) to simulate faults. Control helpers in `control.py` expose `set_rods`, `increment_rods`, and `scram`, and you can switch `set_manual_mode(True)` to pause the automatic rod controller. For hands-on runs, launch the curses dashboard (`FISSION_DASHBOARD=1 FISSION_REALTIME=1 python run_simulation.py`) and use the on-screen shortcuts (q quit/save, space SCRAM, p/o pumps, t turbine, 1/2 toggle individual turbines, y/u turbine maintenance, m/n pump maintenance, k core maintenance, c consumer, r reset/clear saved state, +/- rods in 0.05 steps, [/ ] consumer demand, s/d setpoint, `a` toggles auto/manual rods). Recommended startup: enable manual rods (`a`), withdraw to ~0.3 before ramping the turbine/consumer, then re-enable auto control when you want closed-loop operation.
 The plant now boots cold (ambient core temperature, idle pumps); scripts must sequence startup: enable pumps, gradually withdraw rods, connect the consumer after turbine spin-up, and use `ControlSystem.set_power_setpoint` to chase desired output. Set `FISSION_REALTIME=1` to run continuously with real-time pacing; optionally set `FISSION_SIM_DURATION=infinite` for indefinite runs and send SIGINT/Ctrl+C to stop. Use `FISSION_SIM_DURATION=600` (default) for bounded offline batches.
 
 ## Coding Style & Naming Conventions

src/reactor_sim/dashboard.py

@@ -52,8 +52,8 @@ class ReactorDashboard:
             DashboardKey("p", "Toggle primary pump"),
             DashboardKey("o", "Toggle secondary pump"),
             DashboardKey("t", "Toggle turbine"),
-            DashboardKey("1/2/3", "Toggle turbine units 1-3"),
+            DashboardKey("1/2", "Toggle turbine units 1-2"),
-            DashboardKey("y/u/i", "Maintain turbine 1/2/3"),
+            DashboardKey("y/u", "Maintain turbine 1/2"),
             DashboardKey("c", "Toggle consumer"),
             DashboardKey("r", "Reset & clear state"),
             DashboardKey("m", "Maintain primary pump"),
@@ -162,8 +162,6 @@ class ReactorDashboard:
                 self._queue_command(ReactorCommand.maintain("turbine_1"))
             elif ch in (ord("u"), ord("U")):
                 self._queue_command(ReactorCommand.maintain("turbine_2"))
-            elif ch in (ord("i"), ord("I")):
-                self._queue_command(ReactorCommand.maintain("turbine_3"))
 
     def _queue_command(self, command: ReactorCommand) -> None:
         if self.pending_command is None:
@@ -302,12 +300,12 @@ class ReactorDashboard:
             y,
             "Turbine / Grid",
             [
-                ("Turbines", " ".join(self._turbine_status_lines())),
+            ("Turbines", " ".join(self._turbine_status_lines())),
-                ("Electrical", f"{state.total_electrical_output():7.1f} MW"),
+            ("Electrical", f"{state.total_electrical_output():7.1f} MW"),
-                ("Load", f"{self._total_load_supplied(state):7.1f}/{self._total_load_demand(state):7.1f} MW"),
+            ("Load", f"{self._total_load_supplied(state):7.1f}/{self._total_load_demand(state):7.1f} MW"),
-                ("Consumer", f"{consumer_status}"),
+            ("Consumer", f"{consumer_status}"),
-                ("Demand", f"{consumer_demand:7.1f} MW"),
+            ("Demand", f"{consumer_demand:7.1f} MW"),
-            ],
+        ],
         )
         self._draw_health_bar(win, y + 1)
 
@@ -323,8 +321,8 @@ class ReactorDashboard:
         tips = [
             "Start pumps before withdrawing rods.",
             "Bring turbine and consumer online after thermal stabilization.",
-            "Toggle turbine units (1/2/3) for staggered maintenance.",
+            "Toggle turbine units (1/2) for staggered maintenance.",
-            "Use m/n/k/y/u/i to request maintenance (stop equipment first).",
+            "Use m/n/k/y/u to request maintenance (stop equipment first).",
             "Press 'r' to reset/clear state if you want a cold start.",
             "Watch component health to avoid automatic trips.",
         ]

src/reactor_sim/failures.py

@@ -56,7 +56,7 @@ class HealthMonitor:
             "primary_pump": ComponentHealth("primary_pump"),
             "secondary_pump": ComponentHealth("secondary_pump"),
         }
-        for idx in range(3):
+        for idx in range(2):
             name = f"turbine_{idx + 1}"
             self.components[name] = ComponentHealth(name)
         self.failure_log: list[str] = []

src/reactor_sim/reactor.py

@@ -59,7 +59,7 @@ class Reactor:
             secondary_pump=Pump(nominal_flow=16_000.0, efficiency=0.85),
             thermal=ThermalSolver(),
             steam_generator=SteamGenerator(),
-            turbines=[Turbine() for _ in range(3)],
+            turbines=[Turbine() for _ in range(2)],
             atomic_model=atomic_model,
             consumer=ElectricalConsumer(name="Grid", demand_mw=800.0, online=False),
             health_monitor=HealthMonitor(),
@@ -150,11 +150,17 @@ class Reactor:
             state.secondary_loop.pressure = 0.5
 
         self.thermal.step_core(state.core, state.primary_loop, total_power, dt)
-        transferred = heat_transfer(state.primary_loop, state.secondary_loop, total_power)
+        if not self.secondary_pump_active or state.secondary_loop.mass_flow_rate <= 1.0:
+            transferred = 0.0
+        else:
+            transferred = heat_transfer(state.primary_loop, state.secondary_loop, total_power)
         self.thermal.step_secondary(state.secondary_loop, transferred)
 
         self._step_turbine_bank(state, transferred)
 
+        if (not self.secondary_pump_active or state.secondary_loop.mass_flow_rate <= 1.0) and total_power > 50.0:
+            self._handle_heat_sink_loss(state)
+
         failures = self.health_monitor.evaluate(
             state,
             self.primary_pump_active,
@@ -388,6 +394,16 @@ class Reactor:
                 )
         return plant
 
+    def _handle_heat_sink_loss(self, state: PlantState) -> None:
+        if not self.shutdown:
+            LOGGER.critical("Loss of secondary heat sink detected. Initiating SCRAM.")
+            self.shutdown = True
+            self.control.scram()
+            self._set_turbine_state(False)
+        # Clear turbine output and demands to reflect lost steam.
+        for turbine_state in state.turbines:
+            self._reset_turbine_state(turbine_state)
+
     def _check_poison_alerts(self, state: PlantState) -> None:
         inventory = state.core.fission_product_inventory or {}
         for symbol, threshold in constants.KEY_POISON_THRESHOLDS.items():

src/reactor_sim/thermal.py

@@ -15,6 +15,8 @@ LOGGER = logging.getLogger(__name__)
 
 def heat_transfer(primary: CoolantLoopState, secondary: CoolantLoopState, core_power_mw: float) -> float:
     """Return MW transferred to the secondary loop."""
+    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
     efficiency = 1.0 - math.exp(-conductance * delta_t)

tests/test_simulation.py

@@ -37,7 +37,7 @@ def test_health_monitor_flags_core_failure():
     reactor = Reactor.default()
     state = reactor.initial_state()
     state.core.fuel_temperature = constants.MAX_CORE_TEMPERATURE
-    failures = reactor.health_monitor.evaluate(state, True, True, [True, True, True], dt=200.0)
+    failures = reactor.health_monitor.evaluate(state, True, True, [True, True], dt=200.0)
     assert "core" in failures
     reactor._handle_failure("core")
     assert reactor.shutdown is True
@@ -52,3 +52,16 @@ def test_maintenance_recovers_component_health():
     assert restored is True
     assert pump.integrity == pytest.approx(0.8)
     assert pump.failed is False
+
+
+def test_secondary_pump_loss_triggers_scram_and_no_steam():
+    reactor = Reactor.default()
+    state = reactor.initial_state()
+    # Make sure some power is present to trigger heat-sink logic.
+    state.core.power_output_mw = 500.0
+    reactor.secondary_pump_active = False
+    reactor.control.manual_control = True
+    reactor.control.rod_fraction = 0.1
+    reactor.step(state, dt=1.0)
+    assert reactor.shutdown is True
+    assert all(t.electrical_output_mw == 0.0 for t in state.turbines)