Analysis of thermal conductivity degradation in irradiated molybdenum for the safety and design of megawatt-class heat pipe reactors

Reliable and transportable power for remote, defense, space, and deep-sea missions is driving the development of megawatt-class microreactors. Heat-pipe-cooled designs offer inherent safety, but scaling to the megawatt level imposes stringent requirements on core structural materials, such as molybdenum, for which irradiation-dependent thermal conductivity data remain scarce. This work establishes a multiscale framework to quantify the evolution of molybdenum’s total thermal conductivity from the pristine state to the saturated irradiation-damage condition at a maximum damage level of 1.5 cdpa over a wide temperature range from 300 K to 2800 K. Primary knock-on atom spectra are obtained from SRIM, and irradiation-induced defect structures are generated using the Creation-Relaxation Algorithm (CRA) combined with PARCAS cascade simulations and molecular dynamics simulations. Athermal atom statistics are incorporated into an excess thermal resistivity model for electron transport. The total thermal conductivity is determined using a Matthiessen-type formulation that combines electron-related scattering with the phonon thermal conductivity from equilibrium molecular dynamics. The results show pronounced degradation at low temperatures, even at low levels of irradiation damage. At 300 K, the conductivity decreases from about 140 W m −1 K −1 in the nearly undamaged state to about 20 W m −1 K −1 at the highest damage level, corresponding to a reduction of nearly 85 percent. In contrast, at 2800 K, the conductivity decreases only from about 87 W m −1 K −1 to 73 W m −1 K −1 . A substantial fraction of the total degradation already occurs at 0.1 cdpa or lower. The resulting temperature- and damage-dependent database provides reactor-grade thermophysical input for multiphysics coupled simulations of megawatt-class heat pipe reactors and supports subsequent studies of the thermal behavior of irradiated molybdenum-based core structures. • A multiscale framework is developed to quantify irradiation-induced thermal conductivity degradation in Mo. • Temperature- and dose-dependent total thermal conductivity of Mo is evaluated up to 1.5 cdpa and 2800 K. • Strong low-temperature conductivity degradation is revealed even at low irradiation doses. • The resulting database supports multiphysics simulations of megawatt-class heat pipe reactors.