“…where m f is the fuel mass, c p f is the specific heat of the fuel, f f is the generated power fraction, h is the coefficient of heat transfer, A is the effective area of heat transfer, m c is the mass of coolant, c pc is the coolant specific heat, and W c is the coolant mass flow rate. Other thermal models can be also considered; see (e.g., [16,17]). The total reactivity ρ includes reactivity due to fuel temperature deviations ∆T f , coolant temperature deviation ∆T c , and the external, induced by control rods, reactivity ρ ext .…”