Improve persistence and reactor dynamics

AGENTS.md

@@ -4,12 +4,15 @@
 All source code lives under `src/reactor_sim`. Submodules map to plant systems: `fuel.py` and `neutronics.py` govern fission power, `thermal.py` and `coolant.py` cover heat transfer and pumps, `turbine.py` drives the steam cycle, and `consumer.py` represents external electrical loads. High-level coordination happens in `reactor.py` and `simulation.py`. The convenience runner `run_simulation.py` executes the default scenario; add notebooks or scenario scripts under `experiments/` (create as needed). Keep assets such as plots or exported telemetry inside `artifacts/`.
 
 ## Build, Test, and Development Commands
-- `python -m reactor_sim.simulation` — run the default 10-minute transient and print JSON snapshots.
+- `.venv/bin/python -m reactor_sim.simulation` — run the default 10-minute transient and print JSON snapshots using the checked-in virtualenv.
-- `python run_simulation.py` — same as above, handy for IDE launch configs.
+- `.venv/bin/python run_simulation.py` — same as above, handy for IDE launch configs.
-- `python -m pip install -e .[dev]` — install editable package with optional tooling when dev dependencies are defined.
+- `.venv/bin/python -m pip install -e .[dev]` — install editable package with optional tooling when dev dependencies are defined.
+- When running pytest or ad-hoc scripts, prefer `.venv/bin/python -m pytest` so everyone uses the shared interpreter and dependency set that ships with the repo.
+- State snapshots now auto-save/load from `artifacts/last_state.json`; override the path via `FISSION_STATE_PATH` (or continue to use `FISSION_SAVE_STATE`/`FISSION_LOAD_STATE` for explicit overrides).
+- 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, +/- 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, 1/2/3 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.
 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
@@ -25,4 +28,4 @@ Write commits in imperative mood (`Add turbine moisture separator model`). Squas
 Sim parameters live in constructors; never hard-code environment-specific paths. When adding new physics, guard unstable calculations with clamps and highlight operating limits in comments. Sensitive experiments (e.g., beyond design basis) should default to disabled flags so scripted studies remain safe by default.
 
 ## Reliability & Persistence
-Component wear is tracked via `failures.py`; stress from overheating, pump starvation, or turbine imbalance will degrade integrity and eventually disable the affected subsystem with automatic SCRAM for core damage. Persist plant snapshots with `ControlSystem.save_state()`/`load_state()` (used by `Reactor.save_state`/`load_state`) so long-running studies can resume; `FISSION_LOAD_STATE`/`FISSION_SAVE_STATE` env vars wire this into the CLI.
+Component wear is tracked via `failures.py`; stress from overheating, pump starvation, or turbine imbalance will degrade integrity and eventually disable the affected subsystem with automatic SCRAM for core damage. Plant state now persists between runs to `artifacts/last_state.json` by default (override via `FISSION_STATE_PATH` or the explicit save/load env vars). In the dashboard, press `r` to clear the saved snapshot and reboot the reactor to a cold, green-field state whenever you need a clean slate.

src/reactor_sim/commands.py

@@ -20,8 +20,15 @@ class ReactorCommand:
     consumer_online: bool | None = None
     consumer_demand: float | None = None
     rod_manual: bool | None = None
+    turbine_units: dict[int, bool] | None = None
+    maintenance_components: tuple[str, ...] = tuple()
 
     @classmethod
     def scram_all(cls) -> "ReactorCommand":
         """Convenience constructor for an emergency shutdown."""
         return cls(scram=True, turbine_on=False, primary_pump_on=True, secondary_pump_on=True)
+
+    @classmethod
+    def maintain(cls, *components: str) -> "ReactorCommand":
+        """Request maintenance for the provided component names."""
+        return cls(maintenance_components=tuple(components))

src/reactor_sim/dashboard.py

@@ -6,6 +6,7 @@ import curses
 import logging
 from collections import deque
 from dataclasses import dataclass
+from pathlib import Path
 from typing import Optional
 
 from .commands import ReactorCommand
@@ -37,6 +38,7 @@ class ReactorDashboard:
         self.pending_command: Optional[ReactorCommand] = None
         self.sim: Optional[ReactorSimulation] = None
         self.quit_requested = False
+        self.reset_requested = False
         self.log_buffer: deque[str] = deque(maxlen=4)
         self._log_handler: Optional[logging.Handler] = None
         self._previous_handlers: list[logging.Handler] = []
@@ -47,7 +49,9 @@ 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("c", "Toggle consumer"),
+            DashboardKey("r", "Reset & clear state"),
             DashboardKey("+/-", "Withdraw/insert rods"),
             DashboardKey("[/]", "Adjust consumer demand −/+50 MW"),
             DashboardKey("s", "Setpoint −250 MW"),
@@ -68,24 +72,34 @@ class ReactorDashboard:
         curses.init_pair(4, curses.COLOR_RED, -1)
         stdscr.nodelay(True)
         self._install_log_capture()
-        self.sim = ReactorSimulation(
-            self.reactor,
-            timestep=self.timestep,
-            duration=None,
-            realtime=True,
-            command_provider=self._next_command,
-        )
-        self.sim.start_state = self.start_state
         try:
-            for state in self.sim.run():
+            while True:
-                self._draw(stdscr, state)
+                self.sim = ReactorSimulation(
-                self._handle_input(stdscr)
+                    self.reactor,
+                    timestep=self.timestep,
+                    duration=None,
+                    realtime=True,
+                    command_provider=self._next_command,
+                )
+                self.sim.start_state = self.start_state
+                try:
+                    for state in self.sim.run():
+                        self._draw(stdscr, state)
+                        self._handle_input(stdscr)
+                        if self.quit_requested or self.reset_requested:
+                            self.sim.stop()
+                            break
+                finally:
+                    if self.save_path and self.sim and self.sim.last_state and not self.reset_requested:
+                        self.reactor.save_state(self.save_path, self.sim.last_state)
                 if self.quit_requested:
-                    self.sim.stop()
                     break
+                if self.reset_requested:
+                    self._clear_saved_state()
+                    self._reset_to_greenfield()
+                    continue
+                break
         finally:
-            if self.save_path and self.sim and self.sim.last_state:
-                self.reactor.save_state(self.save_path, self.sim.last_state)
             self._restore_logging()
 
     def _handle_input(self, stdscr: "curses._CursesWindow") -> None:
@@ -104,6 +118,9 @@ class ReactorDashboard:
                 self._queue_command(ReactorCommand(secondary_pump_on=not self.reactor.secondary_pump_active))
             elif ch in (ord("t"), ord("T")):
                 self._queue_command(ReactorCommand(turbine_on=not self.reactor.turbine_active))
+            elif ord("1") <= ch <= ord("9"):
+                idx = ch - ord("1")
+                self._toggle_turbine_unit(idx)
             elif ch in (ord("+"), ord("=")):
                 self._queue_command(ReactorCommand(rod_position=self._clamped_rod(-0.05)))
             elif ch == ord("-"):
@@ -117,6 +134,8 @@ class ReactorDashboard:
             elif ch in (ord("c"), ord("C")):
                 online = not (self.reactor.consumer.online if self.reactor.consumer else False)
                 self._queue_command(ReactorCommand(consumer_online=online))
+            elif ch in (ord("r"), ord("R")):
+                self._request_reset()
             elif ch in (ord("s"), ord("S")):
                 self._queue_command(ReactorCommand(power_setpoint=self.reactor.control.setpoint_mw - 250.0))
             elif ch in (ord("d"), ord("D")):
@@ -143,6 +162,35 @@ class ReactorDashboard:
         if self.pending_command.rod_position is not None and self.pending_command.rod_manual is None:
             self.pending_command.rod_manual = True
 
+    def _toggle_turbine_unit(self, index: int) -> None:
+        if index < 0 or index >= len(self.reactor.turbine_unit_active):
+            return
+        current = self.reactor.turbine_unit_active[index]
+        self._queue_command(ReactorCommand(turbine_units={index + 1: not current}))
+
+    def _request_reset(self) -> None:
+        self.reset_requested = True
+        if self.sim:
+            self.sim.stop()
+
+    def _clear_saved_state(self) -> None:
+        if not self.save_path:
+            return
+        path = Path(self.save_path)
+        try:
+            path.unlink()
+            LOGGER.info("Cleared saved state at %s", path)
+        except FileNotFoundError:
+            LOGGER.info("No saved state to clear at %s", path)
+
+    def _reset_to_greenfield(self) -> None:
+        LOGGER.info("Resetting reactor to initial state")
+        self.reactor = Reactor.default()
+        self.start_state = None
+        self.pending_command = None
+        self.reset_requested = False
+        self.log_buffer.clear()
+
 
     def _next_command(self, _: float, __: PlantState) -> Optional[ReactorCommand]:
         cmd = self.pending_command
@@ -230,9 +278,9 @@ class ReactorDashboard:
             y,
             "Turbine / Grid",
             [
-                ("Turbine", "ON" if self.reactor.turbine_active else "OFF"),
+                ("Turbines", " ".join(self._turbine_status_lines())),
-                ("Electrical", f"{state.turbine.electrical_output_mw:7.1f} MW"),
+                ("Electrical", f"{state.total_electrical_output():7.1f} MW"),
-                ("Load", f"{state.turbine.load_supplied_mw:7.1f}/{state.turbine.load_demand_mw:7.1f} MW"),
+                ("Load", f"{self._total_load_supplied(state):7.1f}/{self._total_load_demand(state):7.1f} MW"),
                 ("Consumer", f"{consumer_status}"),
                 ("Demand", f"{consumer_demand:7.1f} MW"),
             ],
@@ -251,6 +299,8 @@ 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.",
+            "Press 'r' to reset/clear state if you want a cold start.",
             "Watch component health to avoid automatic trips.",
         ]
         for idx, tip in enumerate(tips, start=y + 2):
@@ -259,11 +309,12 @@ class ReactorDashboard:
     def _draw_status_panel(self, win: "curses._CursesWindow", state: PlantState) -> None:
         win.erase()
         win.hline(0, 0, curses.ACS_HLINE, win.getmaxyx()[1])
+        turbine_text = " ".join(self._turbine_status_lines())
         msg = (
             f"Time {state.time_elapsed:7.1f}s | Rods {self.reactor.control.rod_fraction:.3f} | "
             f"Primary {'ON' if self.reactor.primary_pump_active else 'OFF'} | "
             f"Secondary {'ON' if self.reactor.secondary_pump_active else 'OFF'} | "
-            f"Turbine {'ON' if self.reactor.turbine_active else 'OFF'}"
+            f"Turbines {turbine_text}"
         )
         win.addstr(1, 1, msg, curses.color_pair(3))
         if self.reactor.health_monitor.failure_log:
@@ -306,6 +357,19 @@ class ReactorDashboard:
             row += 1
         return row + 1
 
+    def _turbine_status_lines(self) -> list[str]:
+        if not self.reactor.turbine_unit_active:
+            return ["n/a"]
+        return [
+            f"{idx + 1}:{'ON' if active else 'OFF'}" for idx, active in enumerate(self.reactor.turbine_unit_active)
+        ]
+
+    def _total_load_supplied(self, state: PlantState) -> float:
+        return sum(t.load_supplied_mw for t in state.turbines)
+
+    def _total_load_demand(self, state: PlantState) -> float:
+        return sum(t.load_demand_mw for t in state.turbines)
+
     def _draw_health_bar(self, win: "curses._CursesWindow", start_y: int) -> None:
         height, width = win.getmaxyx()
         if start_y >= height - 2:

src/reactor_sim/failures.py

@@ -30,6 +30,15 @@ class ComponentHealth:
             self.failed = True
             LOGGER.error("Component %s has failed", self.name)
 
+    def restore(self, amount: float) -> None:
+        if amount <= 0.0:
+            return
+        previous = self.integrity
+        self.integrity = min(1.0, self.integrity + amount)
+        if self.integrity > 0.05:
+            self.failed = False
+        LOGGER.info("Maintenance on %s: %.3f -> %.3f", self.name, previous, self.integrity)
+
     def snapshot(self) -> dict:
         return asdict(self)
 
@@ -46,8 +55,10 @@ class HealthMonitor:
             "core": ComponentHealth("core"),
             "primary_pump": ComponentHealth("primary_pump"),
             "secondary_pump": ComponentHealth("secondary_pump"),
-            "turbine": ComponentHealth("turbine"),
         }
+        for idx in range(3):
+            name = f"turbine_{idx + 1}"
+            self.components[name] = ComponentHealth(name)
         self.failure_log: list[str] = []
 
     def component(self, name: str) -> ComponentHealth:
@@ -58,10 +69,11 @@ class HealthMonitor:
         state: PlantState,
         primary_active: bool,
         secondary_active: bool,
-        turbine_active: bool,
+        turbine_active: Iterable[bool],
         dt: float,
     ) -> List[str]:
         events: list[str] = []
+        turbine_flags = list(turbine_active)
         core = self.component("core")
         core_temp = state.core.fuel_temperature
         temp_stress = max(0.0, (core_temp - 900.0) / (constants.MAX_CORE_TEMPERATURE - 900.0))
@@ -82,17 +94,23 @@ class HealthMonitor:
         else:
             self.component("secondary_pump").degrade(0.0005 * dt)
 
-        if turbine_active:
+        turbines = state.turbines if hasattr(state, "turbines") else []
-            electrical = state.turbine.electrical_output_mw
+        for idx, active in enumerate(turbine_flags):
-            load_ratio = (
+            name = f"turbine_{idx + 1}"
-                0.0
+            component = self.component(name)
-                if state.turbine.load_demand_mw <= 0
+            if active and idx < len(turbines):
-                else min(1.0, electrical / max(1e-6, state.turbine.load_demand_mw))
+                turbine_state = turbines[idx]
-            )
+                demand = turbine_state.load_demand_mw
-            stress = 0.0002 + abs(1 - load_ratio) * 0.003
+                supplied = turbine_state.load_supplied_mw
-            self.component("turbine").degrade(stress * dt)
+                if demand <= 0:
-        else:
+                    load_ratio = 0.0
-            self.component("turbine").degrade(0.0001 * dt)
+                else:
+                    load_ratio = min(1.0, supplied / max(1e-6, demand))
+                mismatch = abs(1 - load_ratio)
+                stress = 0.00005 + mismatch * 0.0006
+            else:
+                stress = 0.00002
+            component.degrade(stress * dt)
 
         for name, component in self.components.items():
             if component.failed and name not in self.failure_log:
@@ -105,6 +123,14 @@ class HealthMonitor:
 
     def load_snapshot(self, data: dict) -> None:
         for name, comp_data in data.items():
-            if name in self.components:
+            mapped = "turbine_1" if name == "turbine" else name
-                self.components[name] = ComponentHealth.from_snapshot(comp_data)
+            if mapped in self.components:
+                self.components[mapped] = ComponentHealth.from_snapshot(comp_data)
 
+    def maintain(self, component: str, amount: float = 0.05) -> bool:
+        comp = self.components.get(component)
+        if not comp:
+            LOGGER.warning("Maintenance requested for unknown component %s", component)
+            return False
+        comp.restore(amount)
+        return True

src/reactor_sim/neutronics.py

@@ -15,12 +15,12 @@ LOGGER = logging.getLogger(__name__)
 def temperature_feedback(temp: float) -> float:
     """Negative coefficient: higher temperature lowers reactivity."""
     reference = 900.0
-    coefficient = -5e-5
+    coefficient = -2.5e-5
     return coefficient * (temp - reference)
 
 
 def xenon_poisoning(flux: float) -> float:
-    return min(0.05, 1e-8 * flux)
+    return min(0.015, 2e-9 * flux)
 
 
 @dataclass

src/reactor_sim/reactor.py

@@ -30,15 +30,23 @@ class Reactor:
     secondary_pump: Pump
     thermal: ThermalSolver
     steam_generator: SteamGenerator
-    turbine: Turbine
+    turbines: list[Turbine]
     atomic_model: AtomicPhysics
     consumer: ElectricalConsumer | None = None
     health_monitor: HealthMonitor = field(default_factory=HealthMonitor)
     primary_pump_active: bool = True
     secondary_pump_active: bool = True
     turbine_active: bool = True
+    turbine_unit_active: list[bool] = field(default_factory=lambda: [True, True, True])
     shutdown: bool = False
 
+    def __post_init__(self) -> None:
+        if not self.turbines:
+            self.turbines = [Turbine()]
+        if not self.turbine_unit_active or len(self.turbine_unit_active) != len(self.turbines):
+            self.turbine_unit_active = [True] * len(self.turbines)
+        self.turbine_active = any(self.turbine_unit_active)
+
     @classmethod
     def default(cls) -> "Reactor":
         atomic_model = AtomicPhysics()
@@ -50,7 +58,7 @@ class Reactor:
             secondary_pump=Pump(nominal_flow=16_000.0, efficiency=0.85),
             thermal=ThermalSolver(),
             steam_generator=SteamGenerator(),
-            turbine=Turbine(),
+            turbines=[Turbine() for _ in range(3)],
             atomic_model=atomic_model,
             consumer=ElectricalConsumer(name="Grid", demand_mw=800.0, online=False),
             health_monitor=HealthMonitor(),
@@ -79,15 +87,18 @@ class Reactor:
             mass_flow_rate=0.0,
             steam_quality=0.0,
         )
-        turbine = TurbineState(
+        turbine_states = [
-            steam_enthalpy=2_000.0,
+            TurbineState(
-            shaft_power_mw=0.0,
+                steam_enthalpy=2_000.0,
-            electrical_output_mw=0.0,
+                shaft_power_mw=0.0,
-            condenser_temperature=ambient,
+                electrical_output_mw=0.0,
-            load_demand_mw=0.0,
+                condenser_temperature=ambient,
-            load_supplied_mw=0.0,
+                load_demand_mw=0.0,
-        )
+                load_supplied_mw=0.0,
-        return PlantState(core=core, primary_loop=primary, secondary_loop=secondary, turbine=turbine)
+            )
+            for _ in self.turbines
+        ]
+        return PlantState(core=core, primary_loop=primary, secondary_loop=secondary, turbines=turbine_states)
 
     def step(self, state: PlantState, dt: float, command: ReactorCommand | None = None) -> None:
         if self.shutdown:
@@ -126,19 +137,13 @@ class Reactor:
         transferred = heat_transfer(state.primary_loop, state.secondary_loop, total_power)
         self.thermal.step_secondary(state.secondary_loop, transferred)
 
-        if self.turbine_active:
+        self._step_turbine_bank(state, transferred)
-            self.turbine.step(state.secondary_loop, state.turbine, self.consumer, steam_power_mw=transferred)
-        else:
-            state.turbine.shaft_power_mw = 0.0
-            state.turbine.electrical_output_mw = 0.0
-            if self.consumer:
-                self.consumer.update_power_received(0.0)
 
         failures = self.health_monitor.evaluate(
             state,
             self.primary_pump_active,
             self.secondary_pump_active,
-            self.turbine_active,
+            self.turbine_unit_active,
             dt,
         )
         for failure in failures:
@@ -157,11 +162,54 @@ class Reactor:
             prompt_power,
             fission_rate,
             state.primary_loop.temperature_out,
-            state.turbine.electrical_output_mw,
+            state.total_electrical_output(),
-            state.turbine.load_supplied_mw,
+            sum(t.load_supplied_mw for t in state.turbines),
-            state.turbine.load_demand_mw,
+            sum(t.load_demand_mw for t in state.turbines),
         )
 
+    def _step_turbine_bank(self, state: PlantState, steam_power_mw: float) -> None:
+        if not state.turbines:
+            return
+        active_indices = [
+            idx for idx, active in enumerate(self.turbine_unit_active) if active and idx < len(state.turbines)
+        ]
+        power_per_unit = steam_power_mw / len(active_indices) if active_indices else 0.0
+        for idx, turbine in enumerate(self.turbines):
+            if idx >= len(state.turbines):
+                break
+            turbine_state = state.turbines[idx]
+            if idx in active_indices:
+                turbine.step(state.secondary_loop, turbine_state, steam_power_mw=power_per_unit)
+            else:
+                self._reset_turbine_state(turbine_state)
+        self._dispatch_consumer_load(state, active_indices)
+
+    def _reset_turbine_state(self, turbine_state: TurbineState) -> None:
+        turbine_state.shaft_power_mw = 0.0
+        turbine_state.electrical_output_mw = 0.0
+        turbine_state.load_demand_mw = 0.0
+        turbine_state.load_supplied_mw = 0.0
+
+    def _dispatch_consumer_load(self, state: PlantState, active_indices: list[int]) -> None:
+        total_electrical = sum(state.turbines[idx].electrical_output_mw for idx in active_indices)
+        if self.consumer:
+            demand = self.consumer.request_power()
+            supplied = min(total_electrical, demand)
+            self.consumer.update_power_received(supplied)
+        else:
+            demand = 0.0
+            supplied = 0.0
+        demand_per_unit = demand / len(active_indices) if active_indices else 0.0
+        total_for_share = total_electrical if total_electrical > 0 else 1.0
+        for idx, turbine_state in enumerate(state.turbines):
+            if idx not in active_indices:
+                turbine_state.load_demand_mw = 0.0
+                turbine_state.load_supplied_mw = 0.0
+                continue
+            share = 0.0 if total_electrical <= 0 else supplied * (turbine_state.electrical_output_mw / total_for_share)
+            turbine_state.load_demand_mw = demand_per_unit
+            turbine_state.load_supplied_mw = share if demand_per_unit <= 0 else min(share, demand_per_unit)
+
     def _handle_failure(self, component: str) -> None:
         if component == "core":
             LOGGER.critical("Core failure detected. Initiating SCRAM.")
@@ -171,8 +219,9 @@ class Reactor:
             self._set_primary_pump(False)
         elif component == "secondary_pump":
             self._set_secondary_pump(False)
-        elif component == "turbine":
+        elif component.startswith("turbine"):
-            self._set_turbine_state(False)
+            idx = self._component_index(component)
+            self._set_turbine_state(False, index=idx)
 
     def _apply_command(self, command: ReactorCommand, state: PlantState) -> dict[str, float]:
         overrides: dict[str, float] = {}
@@ -196,12 +245,18 @@ class Reactor:
             self._set_secondary_pump(command.secondary_pump_on)
         if command.turbine_on is not None:
             self._set_turbine_state(command.turbine_on)
+        if command.turbine_units:
+            for key, state_flag in command.turbine_units.items():
+                idx = key - 1
+                self._set_turbine_state(state_flag, index=idx)
         if command.consumer_online is not None and self.consumer:
             self.consumer.set_online(command.consumer_online)
         if command.consumer_demand is not None and self.consumer:
             self.consumer.set_demand(command.consumer_demand)
         if command.coolant_demand is not None:
             overrides["coolant_demand"] = max(0.0, min(1.0, command.coolant_demand))
+        for component in command.maintenance_components:
+            self._perform_maintenance(component)
         return overrides
 
     def _set_primary_pump(self, active: bool) -> None:
@@ -214,10 +269,46 @@ class Reactor:
             self.secondary_pump_active = active
             LOGGER.info("Secondary pump %s", "enabled" if active else "stopped")
 
-    def _set_turbine_state(self, active: bool) -> None:
+    def _set_turbine_state(self, active: bool, index: int | None = None) -> None:
-        if self.turbine_active != active:
+        if index is None:
-            self.turbine_active = active
+            for idx in range(len(self.turbine_unit_active)):
-            LOGGER.info("Turbine %s", "started" if active else "stopped")
+                self._set_turbine_state(active, index=idx)
+            return
+        if index < 0 or index >= len(self.turbine_unit_active):
+            LOGGER.warning("Ignoring turbine index %s", index)
+            return
+        if self.turbine_unit_active[index] != active:
+            self.turbine_unit_active[index] = active
+            LOGGER.info("Turbine %d %s", index + 1, "started" if active else "stopped")
+        self.turbine_active = any(self.turbine_unit_active)
+
+    def _component_index(self, name: str) -> int:
+        if name == "turbine":
+            return 0
+        try:
+            return int(name.split("_")[1]) - 1
+        except (IndexError, ValueError):
+            return -1
+
+    def _perform_maintenance(self, component: str) -> None:
+        if component == "core" and not self.shutdown:
+            LOGGER.warning("Cannot maintain core while reactor is running")
+            return
+        if component == "primary_pump" and self.primary_pump_active:
+            LOGGER.warning("Stop primary pump before maintenance")
+            return
+        if component == "secondary_pump" and self.secondary_pump_active:
+            LOGGER.warning("Stop secondary pump before maintenance")
+            return
+        if component.startswith("turbine"):
+            idx = self._component_index(component)
+            if idx < 0 or idx >= len(self.turbine_unit_active):
+                LOGGER.warning("Unknown turbine maintenance target %s", component)
+                return
+            if self.turbine_unit_active[idx]:
+                LOGGER.warning("Stop turbine %d before maintenance", idx + 1)
+                return
+        self.health_monitor.maintain(component)
 
     def attach_consumer(self, consumer: ElectricalConsumer) -> None:
         self.consumer = consumer
@@ -233,6 +324,7 @@ class Reactor:
             "primary_pump_active": self.primary_pump_active,
             "secondary_pump_active": self.secondary_pump_active,
             "turbine_active": self.turbine_active,
+            "turbine_units": self.turbine_unit_active,
             "shutdown": self.shutdown,
             "consumer": {
                 "online": self.consumer.online if self.consumer else False,
@@ -246,7 +338,10 @@ class Reactor:
         plant, metadata, health = self.control.load_state(filepath)
         self.primary_pump_active = metadata.get("primary_pump_active", self.primary_pump_active)
         self.secondary_pump_active = metadata.get("secondary_pump_active", self.secondary_pump_active)
-        self.turbine_active = metadata.get("turbine_active", self.turbine_active)
+        unit_states = metadata.get("turbine_units")
+        if unit_states:
+            self.turbine_unit_active = list(unit_states)
+        self.turbine_active = metadata.get("turbine_active", any(self.turbine_unit_active))
         self.shutdown = metadata.get("shutdown", self.shutdown)
         consumer_cfg = metadata.get("consumer")
         if consumer_cfg:
@@ -262,4 +357,17 @@ class Reactor:
         if health:
             self.health_monitor.load_snapshot(health)
         LOGGER.info("Reactor state restored from %s", filepath)
+        if len(plant.turbines) < len(self.turbines):
+            ambient = constants.ENVIRONMENT_TEMPERATURE
+            while len(plant.turbines) < len(self.turbines):
+                plant.turbines.append(
+                    TurbineState(
+                        steam_enthalpy=2_000.0,
+                        shaft_power_mw=0.0,
+                        electrical_output_mw=0.0,
+                        condenser_temperature=ambient,
+                        load_demand_mw=0.0,
+                        load_supplied_mw=0.0,
+                    )
+                )
         return plant

src/reactor_sim/simulation.py

@@ -7,6 +7,7 @@ import json
 import logging
 import os
 from dataclasses import dataclass, field
+from pathlib import Path
 from threading import Event
 import time
 from typing import Callable, Iterable, Optional
@@ -21,6 +22,11 @@ LOGGER = logging.getLogger(__name__)
 CommandProvider = Callable[[float, PlantState], Optional[ReactorCommand]]
 
 
+def _default_state_path() -> Path:
+    custom = os.getenv("FISSION_STATE_PATH")
+    return Path(custom) if custom else Path("artifacts/last_state.json")
+
+
 @dataclass
 class ReactorSimulation:
     reactor: Reactor
@@ -80,8 +86,11 @@ def main() -> None:
         timestep = 1.0 if dashboard_mode or realtime else 5.0
 
     sim = ReactorSimulation(reactor, timestep=timestep, duration=duration, realtime=realtime)
+    state_path = _default_state_path()
     load_path = os.getenv("FISSION_LOAD_STATE")
-    save_path = os.getenv("FISSION_SAVE_STATE")
+    if not load_path and state_path.exists():
+        load_path = str(state_path)
+    save_path = os.getenv("FISSION_SAVE_STATE") or str(state_path)
     if load_path:
         sim.start_state = reactor.load_state(load_path)
     if dashboard_mode:

src/reactor_sim/state.py

@@ -49,7 +49,7 @@ class PlantState:
     core: CoreState
     primary_loop: CoolantLoopState
     secondary_loop: CoolantLoopState
-    turbine: TurbineState
+    turbines: list[TurbineState]
     time_elapsed: float = field(default=0.0)
 
     def snapshot(self) -> dict[str, float]:
@@ -60,18 +60,27 @@ class PlantState:
             "neutron_flux": self.core.neutron_flux,
             "primary_outlet_temp": self.primary_loop.temperature_out,
             "secondary_pressure": self.secondary_loop.pressure,
-            "turbine_electric": self.turbine.electrical_output_mw,
+            "turbine_electric": self.total_electrical_output(),
         }
 
+    def total_electrical_output(self) -> float:
+        return sum(t.electrical_output_mw for t in self.turbines)
+
     def to_dict(self) -> dict:
         return asdict(self)
 
     @classmethod
     def from_dict(cls, data: dict) -> "PlantState":
+        turbines_blob = data.get("turbines")
+        if turbines_blob is None:
+            # Compatibility with previous single-turbine snapshots.
+            old_turbine = data.get("turbine")
+            turbines_blob = [old_turbine] if old_turbine else []
+        turbines = [TurbineState(**t) for t in turbines_blob]
         return cls(
             core=CoreState(**data["core"]),
             primary_loop=CoolantLoopState(**data["primary_loop"]),
             secondary_loop=CoolantLoopState(**data["secondary_loop"]),
-            turbine=TurbineState(**data["turbine"]),
+            turbines=turbines,
             time_elapsed=data.get("time_elapsed", 0.0),
         )

src/reactor_sim/turbine.py

@@ -6,10 +6,7 @@ from dataclasses import dataclass
 import logging
 
 from . import constants
-from typing import Optional
-
 from .state import CoolantLoopState, TurbineState
-from .consumer import ElectricalConsumer
 
 LOGGER = logging.getLogger(__name__)
 
@@ -33,7 +30,6 @@ class Turbine:
         self,
         loop: CoolantLoopState,
         state: TurbineState,
-        consumer: Optional[ElectricalConsumer] = None,
         steam_power_mw: float = 0.0,
     ) -> None:
         enthalpy = 2_700.0 + loop.steam_quality * 600.0
@@ -41,31 +37,14 @@ class Turbine:
         available_power = max(steam_power_mw, (enthalpy * mass_flow / 1_000.0) / 1_000.0)
         shaft_power_mw = available_power * self.mechanical_efficiency
         electrical = shaft_power_mw * self.generator_efficiency
-        if consumer:
-            load_demand = consumer.request_power()
-            supplied = min(electrical, load_demand)
-            consumer.update_power_received(supplied)
-            LOGGER.debug(
-                "Consumer %s demand %.1f -> supplied %.1f MW",
-                consumer.name,
-                load_demand,
-                supplied,
-            )
-        else:
-            load_demand = 0.0
-            supplied = 0.0
         condenser_temp = max(305.0, loop.temperature_in - 20.0)
         state.steam_enthalpy = enthalpy
         state.shaft_power_mw = shaft_power_mw
         state.electrical_output_mw = electrical
         state.condenser_temperature = condenser_temp
-        state.load_demand_mw = load_demand
-        state.load_supplied_mw = supplied
         LOGGER.debug(
-            "Turbine output: shaft=%.1fMW electrical=%.1fMW condenser=%.1fK load %.1f/%.1f",
+            "Turbine output: shaft=%.1fMW electrical=%.1fMW condenser=%.1fK",
             shaft_power_mw,
             electrical,
             condenser_temp,
-            supplied,
-            load_demand,
         )

tests/test_neutronics.py

@@ -0,0 +1,26 @@
+from reactor_sim.neutronics import NeutronDynamics
+from reactor_sim.state import CoreState
+
+
+def _core_state(
+    temperature: float = 950.0,
+    flux: float = 2e7,
+    burnup: float = 0.01,
+    power: float = 500.0,
+) -> CoreState:
+    return CoreState(
+        fuel_temperature=temperature,
+        neutron_flux=flux,
+        reactivity_margin=0.0,
+        power_output_mw=power,
+        burnup=burnup,
+    )
+
+
+def test_reactivity_increases_with_rod_withdrawal():
+    dynamics = NeutronDynamics()
+    state = _core_state()
+    rho_full_out = dynamics.reactivity(state, control_fraction=0.0)
+    rho_half = dynamics.reactivity(state, control_fraction=0.5)
+    assert rho_full_out > 0.0
+    assert rho_full_out > rho_half

tests/test_simulation.py

@@ -4,6 +4,7 @@ from pathlib import Path
 import pytest
 
 from reactor_sim import constants
+from reactor_sim.failures import HealthMonitor
 from reactor_sim.reactor import Reactor
 from reactor_sim.simulation import ReactorSimulation
 
@@ -13,7 +14,7 @@ def test_reactor_initial_state_is_cold():
     state = reactor.initial_state()
     assert state.core.fuel_temperature == constants.ENVIRONMENT_TEMPERATURE
     assert state.primary_loop.mass_flow_rate == 0.0
-    assert state.turbine.electrical_output_mw == 0.0
+    assert state.total_electrical_output() == 0.0
 
 
 def test_state_save_and_load_roundtrip(tmp_path: Path):
@@ -36,7 +37,18 @@ 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, dt=200.0)
+    failures = reactor.health_monitor.evaluate(state, True, True, [True, True, True], dt=200.0)
     assert "core" in failures
     reactor._handle_failure("core")
     assert reactor.shutdown is True
+
+
+def test_maintenance_recovers_component_health():
+    monitor = HealthMonitor()
+    pump = monitor.component("secondary_pump")
+    pump.integrity = 0.3
+    pump.fail()
+    restored = monitor.maintain("secondary_pump", amount=0.5)
+    assert restored is True
+    assert pump.integrity == pytest.approx(0.8)
+    assert pump.failed is False