Effect of radiation on lubrication performance and the consequences for mechanical equipment at CERN

Successful operation of the accelerator complex at CERN relies on Beam Intercepting Devices (BIDs) which are exposed to high doses of radiation and severely restricted maintenance access over their operating life. Instances of lubrication problems have been observed, such as high friction, overheating, corrosion and, in extreme cases, seizure. Understanding the root causes and the mechanisms controlling such failures is key to avoid downtime and improve maintenance schedules and processes. The paper reviews radiation degradation of lubricants and examines their tribological implications. Several examples of lubrication problems observed at CERN are investigated, and preliminary explanations are provided in the light of tests performed on irradiated samples. This highlights the need for better testing protocols and a thorough assessment of the time-varying performance of lubricants operating in the presence of radiation. • Lubricated components are exposed to high levels of radiation at CERN. • Lubricants properties are susceptible to radiation exposure. • Current knowledge on radiation effects on lubricants is reviewed. • Inspection of in-service components at CERN has shown evidence of grease degradation. • Degradation patterns observed include grease liquefaction, thickening and oxidation. • Lubricant damage can induce friction and corrosion, impairing mechanism performance. • Controlled grease irradiation has reproduced said degradation and failure behaviours.