"""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
STEAM_LATENT_HEAT = 2_200_000.0  # J/kg approximate latent heat of vaporization
CORE_MELTDOWN_TEMPERATURE = 2_873.0  # K (approx 2600C) threshold for irreversible meltdown
MAX_CORE_TEMPERATURE = CORE_MELTDOWN_TEMPERATURE  # Allow simulation to approach meltdown temperature
MAX_PRESSURE = 15.0  # MPa typical PWR primary loop limit
CONTROL_ROD_SPEED = 0.03  # fraction insertion per second
CONTROL_ROD_WORTH = 0.042  # delta rho contribution when fully withdrawn
CONTROL_ROD_BANK_WEIGHTS = (0.4, 0.35, 0.25)
ROD_MANUAL_STEP = 0.025
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
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
BASE_AUX_LOAD_MW = 5.0  # control, instrumentation, misc.
NORMAL_CORE_POWER_MW = 3_000.0
TEST_MAX_POWER_MW = 4_000.0
PRIMARY_OUTLET_TARGET_K = 580.0
SECONDARY_OUTLET_TARGET_K = 520.0
PRIMARY_NOMINAL_PRESSURE = 7.0  # MPa typical RBMK channel header pressure
SECONDARY_NOMINAL_PRESSURE = 7.0  # MPa steam drum/steam line pressure surrogate
STEAM_GENERATOR_UA_MW_PER_K = 25.0  # overall UA for steam generator (MW/K)
# Loop volume / inventory assumptions
PRIMARY_LOOP_VOLUME_M3 = 350.0
SECONDARY_LOOP_VOLUME_M3 = 320.0
PRIMARY_PRESSURIZER_SETPOINT_MPA = 7.0
PRIMARY_PRESSURIZER_DEADBAND_MPA = 0.15
PRIMARY_PRESSURIZER_HEAT_RATE_MPA_PER_S = 0.08
PRIMARY_PRESSURIZER_SPRAY_RATE_MPA_PER_S = 0.12
PRIMARY_PRESSURIZER_LEVEL_DRAW_PER_S = 0.002
PRIMARY_PRESSURIZER_LEVEL_FILL_PER_S = 0.001
LOOP_INVENTORY_CORRECTION_RATE = 0.08  # fraction of nominal mass restored per second toward target
PRIMARY_INVENTORY_TARGET = 0.95
SECONDARY_INVENTORY_TARGET = 0.9
SECONDARY_STEAM_LOSS_FRACTION = 0.02  # fraction of steam mass that leaves the loop each second
NPSH_REQUIRED_MPA = 0.25
LOW_LEVEL_FLOW_FLOOR = 0.05
# 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
}