Tunable eos material model in the simulation of pulsed mercury spallation target vessel

A pulsed spallation target is subjected to very short (∼1μs) but intense loads from repeated proton pulses. The effect of this pulsed loading on the stainless-steel target module that contains flowing mercury target material is difficult to predict. Different simulation approaches and material models for the mercury have been tried. To date the best matching simulation to the experimental data was obtained by an equation of state (EOS) material model with a specified tensile cutoff pressure, which simulates the cavitation threshold [1]. The inclusion of a threshold to represent cavitation was a key parameter in achieving successful predictions of stress waves triggered by the high energy pulse striking the mercury and vessel. However, recent measurements of strain responses of target modules showed that significant discrepancy between the measured strain and simulated value with the EOS mercury model still exists. These differences grow to irreconcilable values when noncondensable helium gas is intentionally injected into the flowing mercury. A novel EOS mercury model embedded into ABAQUS VUMAT has been investigated in this project, which introduces the concept of proportional, integral, and derivative (PID) control into the mercury EOS model. By tuning the new introduced PID parameters (Kp, Ki and Kd), we replace the specified cutoff pressure with an adjustable spring-damper-like material behavior which may better match the complex dynamics of the mercury and helium mixture. This approach is expected to reduce the gap between measured and simulated vessel strain responses. Primitive application of this tunable EOS mercury model on prototypic shape experimental target has demonstrated its capability and potential of improving mechanical behavior of EOS mercury with cutoff pressure considered.