Neutron flux impact on rate of expansion of quartz

Abstract

The radiation-induced expansion of concrete aggregate is a significant concern in the aging management of concrete biological shielding in nuclear power plants. Understanding the sensitivity of rock-forming minerals, particularly quartz, to neutron radiation is essential in this context. In this study, we investigated the neutron irradiation effects on different types of quartz, including synthetic quartz, metachert, sandstone, and granodiorite, under irradiation temperatures ranging from 45 to 62 ℃ and the displacement damage in quartz ranging from 0.01 to 0.23 dpa. The rate of irradiation-induced expansion was determined using X-ray diffraction/Rietveld analysis, revealing a neutron flux dependency. Our findings suggest that radiation-induced relaxation or healing processes occur within quartz. To explain the observed flux-dependent and temperature-dependent radiation-induced expansion of quartz, we propose a two-phase model that considers the pristine and expanded phases. This model, based on four key variables, i.e. neutron flux, the equivalent cross-sections for phase change, and healing parameter, successfully reproduces the radiation-induced expansion behaviors observed in quartz. The model further indicates that radiation-induced relaxation, potentially linked to the diffusion of silicon (Si) or oxygen (O) within the quartz grain, plays a healing role that mitigates radiation-induced volume expansion.