Gamma radiation effects on fluids for seismic damping devices in nuclear energy facilities

The U.S. DOE funded a research project that integrated irradiation experiments, MCNP simulations, and dynamic testing to characterize the effects of gamma radiation on the mechanical properties of seismic isolation and damping devices: information needed to support their deployment close to advanced nuclear reactors. This paper addresses the effects of gamma radiation on the mechanical properties of silicone fluids suitable for use in 1D fluid viscous dampers (FVDs) and/or 3D viscoelastic fluid dampers (VEDs) and provides a pathway for predicting changes in damper response. The fluids were categorized as either low -viscosity (for use in FVDs) or high -viscosity (for use in VEDs). For the low -viscosity fluids, results are presented as changes in viscosity as a function of absorbed gamma dose. For the high -viscosity fluids, results are presented as changes in storage and loss moduli as a function of frequency. Nine silicone fluids, with kinematic viscosities ranging from 50 cSt to 1,000,000 cSt, were irradiated to a maximum absorbed gamma dose of 2800 kGy using a cobalt-60 irradiator at Idaho National Laboratory. The gamma dose absorbed by each fluid sample was computed using a validated MCNP model of the irradiator and the test articles. The viscosity of all nine fluids increased with absorbed gamma dose, with six fluids eventually solidifying. The effect of absorbed dose rate on change in viscosity was negligible, noting that the gamma dose delivered by the irradiator was much higher than that anticipated for applications of the dampers in nuclear energy facilities. The storage and loss moduli of the high -viscosity fluids increased with absorbed gamma dose.