Influence of Gamma Radiation on the Mechanical Behavior of Seismic Protective Devices

Some advanced reactor designs are considering seismic isolation and damping devices to both protect nuclear safety-critical assets from extreme earthquake shaking and to enable standardization. If these devices are installed near a reactor vessel, without shielding, they will be exposed to gamma radiation, which may affect their mechanical properties. The United States Department of Energy, as part of the Nuclear Energy University Program, funded a study, beginning in late 2022, to characterize the effect of incremented gamma dose on the mechanical properties of isolators, damping devices, and fluids. This paper is the first publication to describe the objectives of the project, the types of seismic protective devices and fluids being investigated, some details on pre-irradiation testing, and results of the first sequence of tests. The irradiation of these devices is the being performed at the Idaho National Laboratory. Pre- and post-irradiation mechanical tests are being executed at the University at Buffalo. The paper presents pre- and post-irradiation results for six viscous fluids, which are characterized here using dynamic viscosity. Results demonstrate that the viscosity of these fluids increases with incremented gamma dose, with three of six fluids solidifying. Monte Carlo N-Particle analysis of the protective devices is being performed to estimate absorbed dose in the different heterogeneous seismic protective devices as a function of exposure in the Foss irradiator, to support the next round of experiments.