feat: add reactor control persistence and tests

src/reactor_sim/thermal.py

@@ -0,0 +1,55 @@
+"""Thermal hydraulics approximations."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+import logging
+
+from . import constants
+from .state import CoolantLoopState, CoreState
+
+LOGGER = logging.getLogger(__name__)
+
+
+def heat_transfer(primary: CoolantLoopState, secondary: CoolantLoopState, core_power_mw: float) -> float:
+    """Return MW transferred to the secondary loop."""
+    delta_t = max(0.0, primary.temperature_out - secondary.temperature_in)
+    conductance = 0.05  # steam generator effectiveness
+    transferred = min(core_power_mw, conductance * delta_t)
+    LOGGER.debug("Heat transfer %.2f MW with ΔT=%.1fK", transferred, delta_t)
+    return transferred
+
+
+def temperature_rise(power_mw: float, mass_flow: float) -> float:
+    if mass_flow <= 0:
+        return 0.0
+    return (power_mw * constants.MEGAWATT) / (mass_flow * constants.COOLANT_HEAT_CAPACITY)
+
+
+@dataclass
+class ThermalSolver:
+    primary_volume_m3: float = 300.0
+
+    def step_core(self, core: CoreState, primary: CoolantLoopState, power_mw: float, dt: float) -> None:
+        temp_rise = temperature_rise(power_mw, primary.mass_flow_rate)
+        primary.temperature_out = primary.temperature_in + temp_rise
+        core.fuel_temperature += 0.1 * (power_mw - temp_rise) * dt
+        core.fuel_temperature = min(core.fuel_temperature, constants.MAX_CORE_TEMPERATURE)
+        LOGGER.debug(
+            "Primary loop: flow=%.0f kg/s temp_out=%.1fK core_temp=%.1fK",
+            primary.mass_flow_rate,
+            primary.temperature_out,
+            core.fuel_temperature,
+        )
+
+    def step_secondary(self, secondary: CoolantLoopState, transferred_mw: float) -> None:
+        delta_t = temperature_rise(transferred_mw, secondary.mass_flow_rate)
+        secondary.temperature_out = secondary.temperature_in + delta_t
+        secondary.steam_quality = min(1.0, max(0.0, delta_t / 100.0))
+        secondary.pressure = min(constants.MAX_PRESSURE, 6.0 + delta_t * 0.01)
+        LOGGER.debug(
+            "Secondary loop: transferred=%.1fMW temp_out=%.1fK quality=%.2f",
+            transferred_mw,
+            secondary.temperature_out,
+            secondary.steam_quality,
+        )