Simple, analytic expressions for temperatures and axial fuel expansions in an exponentially heated, heterogeneous reactor are derived. Constant thermal resistances, equal to the steady-state values, are assumed, and the effects of using this assumption are discussed. Multiregion fuel elements are treated, both with and without coolant flow. The effect of mechanical inertia upon axial expansion of fuel rods with one fixed end is taken into account. Numerical examples which pertain to EBR-II are presented.