Symbol	Description	Units
A_ms	Surface area in contact between secondary water and metal tubes	m²
A_pm	Surface area in contact between and metal tubes and primary coolant	m²
C_p	specific heat of subcooled water	J/(kg˚C)
h_f	saturated water specific enthalpy	kJ/kg
h_fg	H_f − h_g	kJ/kg
h_g	saturated vapor specific enthalpy	kJ/kg
h_s	average enthalpy of secondary water	kJ/kg
L_b	height of boiling column	m
M_d	Mass of water in annular tank	kg
M_dw	mass of drum water	kg
M_p	Mass of half of the primary water	kg
M_s	mass of secondary coolant	kg
${\dot{Q}}_{m s 1}$	upward metal tube to secondary coolant heat transfer rate	J/s
${\dot{Q}}_{m s 2}$	downward metal tube to secondary coolant heat transfer rate	J/s
T_s	Average bulk mean temperature in the secondary lump	˚C
T_sat	saturation temperature	˚C
U_ms	Coefficient of heat transfer between the secondary coolant and metal tubes	J/(s m²˚C)
U_pm	Coefficient of heat transfer between the primary coolant and metal tubes	J/(s m²˚C)
W₁	mass flow rate of fluid from the downcomer to the riser	Kg/s
W₂	Mass flow rate of outlet secondary water	Kg/s
W₃	mass flow rate of secondary coolant leaving separator	kg/s
W_fi	Flow rate of feed water	kg/s
W_so	Flow rate of saturated steam	kg/s
ρ_f	saturated liquid density	kg/m³
ρ_g	saturated vapor density	kg/m³
υ_f	saturated liquid specific volume	m³/kg
υ_fg	υ_f − v_g	m³/kg
v_g	saturated vapor specific volume	m³/kg