Materials and components used in the presence of intense neutron fields are expected to absorb high dose levels inducing substantial modifications of their physical and mechanical properties, possibly causing loss of their function. Protocols for irradiation and testing of radiation-sensitive non-metallic materials in reactor mixed neutron and gamma fields have been developed. Elastomeric O-ring and lubricating grease and oil samples are irradiated using the Central Thimble in-core facility of the TRIGA Mark II reactor of the LENA Laboratory of the University of Pavia (Italy). Post-irradiation tests measure the evolution of the main mechanical and physical properties as a function of the absorbed dose. Particular care is devoted to dosimetry calculations, since absorbed dose in high-energy neutron fields is highly dependent on the material composition and, in particular, on the hydrogen content.
Four elastomeric compounds, one FPM and three EPDM based, have been selected from the market, irradiated up to about 2 MGy absorbed dose and submitted to standard tensile and compression set tests. A dramatic increase of stiffness and brittleness is reported for the FPM material, that features the largest property variations. One EPDM shows rapid changes in mechanical properties, whereas the others feature more stable behaviors. Seven lubricating greases and one lubricating oil have been selected and irradiated up to about 5 MGy of absorbed dose. Grease consistency and oil viscosity are measured according to standard testing procedures. Outstanding out-of-scale softening is reported for some greases, while others show a stable behavior. The tested lubricating oil shows an intriguing increase in viscosity as a function of the absorbed dose.
Some tested products are rated as radiation resistant in pure gamma radiation fields, but they display much more severe degradation in the in-core nuclear reactor irradiation conditions, given the same amount of total dose. The results represent an original set of data achieved in mixed neutron and gamma radiation fields, generally lacking in the literature. They provide information about radiation damage of organic materials in irradiation conditions different from the ones usually employed, evidencing remarkable differences. Apart from the scientific interest, the results represent a reference for nuclear projects using non-metallic components in intense neutron fields, as radioisotope production facilities and nuclear spallation sources. The predictive capability of the performed tests as well as the applicable concept of radiation damage threshold are discussed in view of the use of the examined products in the SPES facility, under construction at the Legnaro National Laboratories (LNL) of the Italian Istituto Nazionale di Fisica Nucleare (INFN), and in the European Spallation Source (ESS), under construction in Lund.
ATS Seminars Organisers: H. Burkhardt (BE), M. Modena (ATS), T. Stora (EN)
Coffee / tea will be served after the seminar in room 30/7-012 next to the Auditorium