Comprehensive investigation of lattice dynamics of neutron multiplier beryllides: vibrational spectra and thermal performances

Abstract

In order to realize tritium self-sufficiency during the operation of fusion reactors, neutron multiplier materials are needed to multiply the number of neutrons. Beryllium (Be) and beryllides (Be12V, Be12Ti) are considered as candidates for neutron multiplier materials in the tritium breeding blanket. Thermal performances are essential data to evaluate the service performance of materials in future fusion reactors. Due to the toxicity of beryllium, the preparation and analysis of neutron multiplier materials are challenging. As a result, the performance data of neutron multiplier materials are limited. It is essential to adopt the theoretical method to get the basic parameters for the design of a tritium breeding blanket and optimization of neutron multiplier. In the present work, the electron structure, vibrational spectra, and thermal performances have been theoretically investigated to understand thermal expansion and thermal conductivity properties. Experimental data are also included to compare with the calculated results and detailed analysis is presented. Due to the reactivity with water, BeO will form on the surface of Be. Therefore, BeO was studied as well. The bulk modulus of Be is the smallest of the four materials, while BeO is the largest. Higher bulk modulus has a better ability to restrain the deformation due to pressure. The c-axis of the Be12V has the largest thermal expansion coefficient, while the c-axis of the Be12Ti is the smallest. It has been found that the larger the lattice constant of crystal axes, the smaller the linear thermal expansion coefficient in same material. Electrons play a major role in the heat transfer of Be12V and Be12Ti. At high temperatures, phonon and electron coupling must be considered. Isotopeenrichment and enlarging the grain size cannot significantly improve the phonon thermal conductivity when the temperature is higher than room temperature. The calculated values can be adopted to predict the materials’ performances and support future fusion reactors’ neutron multiplier material preparation.