Quantification and evaluation of strain reduction from small-bubble gas injection in Spallation Neutron Source target vessels

• Strain measurement data of SNS targets were used to evaluate the effect of small-bubble gas injection on the strain responses to proton pulses. • Significant strain reductions with gas injections were quantified, about 20 %–80 % for targets operated with gas injections. • The strain reductions due to various gas injection rates and different bubbler types as well as the effect of gas injection on baseline strain shift were studied and discussed. • SNS targets were simulated to numerically evaluate the gas injection effect on the strain reductions. • The fatigue lifetimes of the target vessel with gas injection operations were estimated using fe-safe based on the FEA simulations of stress and strain. Small-bubble gas injection has been routinely utilized in the operation of Spallation Neutron Source (SNS) mercury targets since 2017 to mitigate cavitation-induced erosion damage to target vessels. Strain measurements of target vessels collected in-situ during initial operation with gas injection were used to study the gas injection effect on the structural response of targets to proton pulses. A significant strain reduction owing to gas injection was found by comparing the strain measurement data during operation with and without gas injection. The research presented here focuses on quantifying strain reductions in SNS targets and evaluating the effect of small-bubble gas injection by comparing different bubbler types and target designs. The strain measurement results show the gas injection significantly reduced strain in SNS target vessels; strain values decreased by 30% to 80% for targets operating with gas injection. Stress and strain responses of SNS targets were simulated to numerically evaluate the gas injection effect. Based on the predicted stresses with and without gas injection, the fatigue lifetimes of SNS jet-flow design target were estimated using fe-safe fatigue analysis software. The simulations show these reductions should improve the fatigue life of target vessels and allow SNS targets to meet their fatigue design goal.