AbstractAn energy balance, similar to the Hicks-Menzies concept but including a simple examination of the pressure versus temperature path to equilibrium, has been performed for mixtures of steel and mixed-oxide reactor fuel with ratios of mass of fuel to mass of steel ranging from 0.5 to 5.0 and with initial fuel temperatures from 3500 to 7500 K. The results yield fundamental collapse criteria for the response of such a mixture to compressive perturbations and act as bounding criteria for potential compressive-driven recriticality when other criticality conditions are met