Simplified Analysis of Coolant Flow and Outlet Temperature in Gas-Cooled Nuclear Reactor Cores

If the coolant mass flow were constant across the core, the coolant temperature rise would be proportional to the channel power. But, without orificing, the coolant mass flow in the hot channel is smaller than the average flow while the outlet temperature is hotter than the mixed mean temperature. The approximate radial distributions of coolant mass flow (M/M₀) and temperature rise (ΔT/ΔT₀) are shown to depend only upon the (arbitrary) radial flux distribution (H/H₀) and upon a single lumped core parameter (δ), proportional to the product of the pressure by the pressure drop. For simple radial flux distributions and when δ goes from zero to infinity, (M₀/M_av) increases approximately from (H_av/H₀) to one, while (ΔT₀/ΔT_av) decreases approximately from (H₀/H_av)² to (H₀/H_av). The relationships between hot channel parameters, maximum clad or fuel temperatures, and thermal power are derived in the Appendix for a “chopped cosine” axial flux distribution.