Add turbine throttle mapping and back-pressure penalty

FEATURES.md

@@ -5,6 +5,6 @@
 - **Coolant & hydraulics**: primary/secondary pumps with head/flow curves, power draw scaling, wear tracking; pressure floors tied to saturation; auxiliary power model with generator auto-start.
 - **Heat transfer**: steam-generator UA·ΔT_lm model with a pinch cap to keep the primary outlet hotter than the secondary, coolant heating uses total fission power with fuel heating decoupled from exchanger draw, and the secondary thermal solver includes passive cool-down when flow is low.
 - **Pressurizer & inventory**: primary pressurizer trims toward 7 MPa with level tracking, loop inventories/levels steer flow availability, secondary steam boil-off draws down level with auto makeup, and pumps reduce flow/status to `CAV` when NPSH is insufficient.
-- **Steam cycle**: three turbines with spool dynamics, load dispatch to consumer, steam quality gating for output, generator states with batteries/spool.
+- **Steam cycle**: three turbines with spool dynamics, throttle mapping, condenser back-pressure penalty, load dispatch to consumer, steam quality gating for output, generator states with batteries/spool.
 - **Protections & failures**: health monitor degrading components under stress, automatic SCRAM on core or heat-sink loss, relief valves per loop, maintenance actions to restore integrity.
 - **Persistence & ops**: snapshots auto-save/load to `artifacts/last_state.json`; dashboard with live metrics, protections/warnings, heat-exchanger telemetry, component health, and control shortcuts.

src/reactor_sim/constants.py

@@ -24,6 +24,14 @@ PUMP_SPOOL_TIME = 5.0  # seconds to reach commanded flow
 PRIMARY_PUMP_SHUTOFF_HEAD_MPA = 8.0  # approximate shutoff head for primary pumps
 SECONDARY_PUMP_SHUTOFF_HEAD_MPA = 7.0
 TURBINE_SPOOL_TIME = 12.0  # seconds to reach steady output
+
+# Turbine/condenser parameters
+TURBINE_THROTTLE_MIN = 0.1
+TURBINE_THROTTLE_MAX = 1.0
+TURBINE_THROTTLE_EFFICIENCY_DROP = 0.15  # efficiency loss when at minimum throttle
+CONDENSER_BASE_PRESSURE_MPA = 0.01
+CONDENSER_MAX_PRESSURE_MPA = 0.3
+CONDENSER_BACKPRESSURE_PENALTY = 0.35  # fractional power loss at max back-pressure
 GENERATOR_SPOOL_TIME = 10.0  # seconds to reach full output
 # Auxiliary power assumptions
 PUMP_POWER_MW = 12.0  # MW draw per pump unit

src/reactor_sim/dashboard.py

@@ -435,6 +435,7 @@ class ReactorDashboard:
                     "Unit3 Elec",
                     f"{state.turbines[2].electrical_output_mw:7.1f} MW" if len(state.turbines) > 2 else "n/a",
                 ),
+                ("Throttle", f"{self.reactor.turbines[0].throttle:5.2f}" if self.reactor.turbines else "n/a"),
                 ("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"),
                 ("Consumer", f"{consumer_status}"),

src/reactor_sim/reactor.py

@@ -461,6 +461,10 @@ class Reactor:
                 break
             turbine_state = state.turbines[idx]
             if idx in active_indices:
+                # Simple throttle map: reduce throttle when electrical demand is low, open as demand rises.
+                demand = turbine_state.load_demand_mw
+                throttle = 0.4 if demand <= 0 else min(1.0, 0.4 + demand / max(1e-6, turbine.rated_output_mw))
+                turbine.throttle = throttle
                 turbine.step(state.secondary_loop, turbine_state, steam_power_mw=power_per_unit, dt=dt)
                 if power_per_unit <= 0.0 and turbine_state.electrical_output_mw < 0.1:
                     turbine_state.status = "OFF"

src/reactor_sim/turbine.py

@@ -27,6 +27,7 @@ class Turbine:
     mechanical_efficiency: float = constants.STEAM_TURBINE_EFFICIENCY
     rated_output_mw: float = 400.0  # cap per unit electrical output
     spool_time: float = constants.TURBINE_SPOOL_TIME
+    throttle: float = 1.0  # 0-1 valve position
 
     def step(
         self,
@@ -46,11 +47,15 @@ class Turbine:
             state.condenser_temperature = max(305.0, loop.temperature_in - 20.0)
             return
 
+        throttle = min(constants.TURBINE_THROTTLE_MAX, max(constants.TURBINE_THROTTLE_MIN, self.throttle))
+        throttle_eff = 1.0 - constants.TURBINE_THROTTLE_EFFICIENCY_DROP * (constants.TURBINE_THROTTLE_MAX - throttle)
+
         enthalpy = 2_700.0 + loop.steam_quality * 600.0
-        mass_flow = effective_mass_flow * 0.6
+        mass_flow = effective_mass_flow * 0.6 * throttle
         computed_power = (enthalpy * mass_flow / 1_000.0) / 1_000.0
         available_power = steam_power_mw if steam_power_mw > 0 else computed_power
-        shaft_power_mw = available_power * self.mechanical_efficiency
+        backpressure_loss = 1.0 - _backpressure_penalty(loop)
+        shaft_power_mw = available_power * self.mechanical_efficiency * throttle_eff * backpressure_loss
         electrical = shaft_power_mw * self.generator_efficiency
         if electrical > self.rated_output_mw:
             electrical = self.rated_output_mw
@@ -71,5 +76,15 @@ class Turbine:
 def _ramp(current: float, target: float, dt: float, time_constant: float) -> float:
     if time_constant <= 0.0:
         return target
-    alpha = min(1.0, max(0.0, dt / time_constant))
+    alpha = min(1.0, max(0.0, dt / max(1e-6, time_constant)))
     return current + (target - current) * alpha
+
+
+def _backpressure_penalty(loop: CoolantLoopState) -> float:
+    base = constants.CONDENSER_BASE_PRESSURE_MPA
+    max_p = constants.CONDENSER_MAX_PRESSURE_MPA
+    pressure = max(base, min(max_p, loop.pressure))
+    if pressure <= base:
+        return 0.0
+    frac = (pressure - base) / max(1e-6, max_p - base)
+    return min(constants.CONDENSER_BACKPRESSURE_PENALTY, frac * constants.CONDENSER_BACKPRESSURE_PENALTY)

tests/test_turbine.py

@@ -6,10 +6,11 @@ from reactor_sim.turbine import Turbine
 
 def test_turbine_spools_toward_target_output():
     turbine = Turbine()
+    turbine.throttle = 1.0
     loop = CoolantLoopState(
         temperature_in=600.0,
         temperature_out=650.0,
-        pressure=6.0,
+        pressure=0.02,
         mass_flow_rate=20_000.0,
         steam_quality=0.9,
     )
@@ -20,14 +21,15 @@ def test_turbine_spools_toward_target_output():
         condenser_temperature=300.0,
     )
     target_electric = min(
-        turbine.rated_output_mw, 300.0 * turbine.mechanical_efficiency * turbine.generator_efficiency
+        turbine.rated_output_mw,
+        300.0 * turbine.mechanical_efficiency * turbine.generator_efficiency,
     )
 
-    dt = 5.0
+    dt = 1.0
     turbine.step(loop, state, steam_power_mw=300.0, dt=dt)
     assert 0.0 < state.electrical_output_mw < target_electric
 
-    for _ in range(5):
+    for _ in range(60):
         turbine.step(loop, state, steam_power_mw=300.0, dt=dt)
 
     assert state.electrical_output_mw == pytest.approx(target_electric, rel=0.05)