Proton-Pulse Induced Dynamic Strain Prediction, Measurement, and Simulation Validation of SNS Target With a Novel Gas Injector

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) produces neutrons for scientific research and industrial development. Helium gas injection into the flowing mercury has been used since 2017 to mitigate fatigue and cavitation-induced erosion damage to the stainless-steel target vessel. Gas injection into the bulk flow was generally effective at mitigating erosion damage, but the central zone of the target vessel at the proton beam entrance region has continued to show significant erosion. Recently, a nose injector system was developed and installed in the 2MW design target to inject gas at the center zone of the target nose and further improve damage mitigation near the beam’s center. Strain measurements of the target vessel’s response to proton pulses were collected during operation with gas injected into the bulk flow, through the new nose injector, and combinations of both gas injection systems. Responses of SNS target were simulated using a material model that accounts for the dynamic effects of the helium gas bubbles. This simulation technique was extended to include bubbles from both bulk-flow bubblers and the nose injector. The bubble size distribution (BSD), a critical parameter of the mercury bubble material model, for the nose injector was scaled from experimental measurements of the BSD produced by a nose injector in a 1:1 replica of the target with flowing water. In the present work, the strain simulation with gas injection from the bubblers and the nose injector is compared with the strain simulation with gas injection from the bulk-flow bubblers only, which was compared to data obtained from in-situ strain measurements of the vessel’s response. A good agreement between the simulation and measurement data indicates that the simulation technique works well to account for the strain reduction effect from operation with the nose gas injector system