Radiation Effects on Thermal Properties of Advanced Nuclear Materials

Abstract

Understanding the effects of irradiation on critical thermophysical properties is fundamental for the advancement of next-generation nuclear systems operating in high-flux neutron and gamma environments. Zirconium hydride (ZrH) and yttrium hydride (YH) have emerged as promising neutron moderating materials due to their exceptional hydrogen density leading to superior moderating power. Yet, the radiation-induced microstructural evolution and its correlation to macroscopic thermal transport phenomena remain insufficiently characterized.

In this work, ZrH and YH specimens were characterized pre- and post-irradiation via laser flash analysis, high-resolution dilatometry, and differential scanning calorimetry. Comparative analysis revealed that even low-fluence neutron irradiation induced complex defect clusters that degraded thermal diffusivity, while the crystallographic lattice parameters, vibrational energy states (inferred from thermal expansion measurements), and heat capacity exhibited an inconclusive response to radiation damage.

To address limitations in current characterization methods for large-scale, anisotropic composite nuclear materials, we developed an advanced thermal transport measurement facility using infrared photothermal excitation. This platform enables spatially-resolved thermal diffusivity mapping of silicon carbide (SiC) composites—materials with complex three-dimensional fiber arrangements being evaluated for accident-tolerant fuel cladding applications. Complementary Thermal Conductivity Microscopy (TCM) measurements conducted at Idaho National Laboratory provided microscale resolution of constituent thermal properties, establishing a multi-scale characterization approach that bridges microscopic thermal transport mechanisms with bulk composite performance. These findings advance the qualification of advanced nuclear materials, enabling more accurate thermomechanical modeling and performance prediction under the extreme conditions of next-generation reactors.