Transient Gap Conductance in Nuclear Fuel Rods

A new expression is derived for estimating transient thermal conductance across two surfaces of nuclear materials bounding a gas. It considers two-surface thermal resistances in series with a parallel combination of two bulk thermal resistances arising from molecular and acoustic modes of heat pulse propagation in the interstitial gas. The resulting estimates offer the first technical explanation for the excess gap conductance observed during heat pulse propagation between UO₂ and Zircaloy surfaces through heavier inert gases like argon.