"""Physical constants and engineering limits for the simulation."""

from __future__ import annotations

SECONDS_PER_MINUTE = 60.0
MEGAWATT = 1_000_000.0
NEUTRON_LIFETIME = 0.1  # seconds, prompt neutron lifetime surrogate
FUEL_ENERGY_DENSITY = 200.0 * MEGAWATT  # J/kg released as heat
COOLANT_HEAT_CAPACITY = 4_200.0  # J/(kg*K) for water/steam
COOLANT_DENSITY = 700.0  # kg/m^3 averaged between phases
MAX_CORE_TEMPERATURE = 1_800.0  # K
MAX_PRESSURE = 15.0  # MPa typical PWR primary loop limit
CONTROL_ROD_SPEED = 0.03  # fraction insertion per second
STEAM_TURBINE_EFFICIENCY = 0.34
GENERATOR_EFFICIENCY = 0.96
ENVIRONMENT_TEMPERATURE = 295.0  # K
AMU_TO_KG = 1.660_539_066_60e-27
MEV_TO_J = 1.602_176_634e-13
ELECTRON_FISSION_CROSS_SECTION = 5e-16  # cm^2, tuned for simulation scale
PUMP_SPOOL_TIME = 5.0  # seconds to reach commanded flow
TURBINE_SPOOL_TIME = 12.0  # seconds to reach steady output
# Threshold inventories (event counts) for flagging common poisons in diagnostics.
KEY_POISON_THRESHOLDS = {
    "Xe": 1e20,  # xenon
    "I": 1e20,  # iodine precursor to xenon
    "Sm": 5e19,  # samarium
}