Experimental testing and numerical simulations for life prediction of gate valve O-rings exposed to mixed neutron and gamma fields

Abstract EPDM O-ringsof gate valvesemployed for the construction of a second-generation accelerator for the production of neutron-rich Radioactive Ion Beams were studied in order to assess their sealing performance both during the facility service time and the post-service storage phase. Several O-ringspecimens were at first exposed to different dose levels of mixed neutron and gamma radiations. Correspondent modifications of physical and mechanical properties of the material were investigated by means of uniaxial tensile tests, dynamic mechanical analyses, aging, compression setand vacuum leak tests. A hyperelastic strain energy function was adopted to fit the mechanical response of the material as a function of the absorbed dose. The minimum squeeze degree that guarantees O-ringsealing efficiency at different irradiation levels was determined by varying the interference between O-ringsand grooves. A finite element model of the vacuum leak test was then set up to assess the contact pressure level required to ensure sealing. Numerical simulations of the gate valvemain O-ringwere subsequently carried out. By comparison of the predicted contact pressure and strain levels with experimental results, a life prediction map, as function of the service time, the storage time and the O-ringsqueeze degree, was proposed.