Experimental study of consistency degradation of different greases in mixed neutron and gamma radiation

Matteo Ferrari; Aldo Zenoni; Monika Hartl; Yongjoong Lee; Alberto Andrighetto; Alberto Monetti; Andrea Salvini; Fabio Zelaschi

doi:10.1016/j.heliyon.2019.e02489

Experimental study of consistency degradation of different greases in mixed neutron and gamma radiation

Heliyon. 2019 Sep 25;5(9):e02489. doi: 10.1016/j.heliyon.2019.e02489. eCollection 2019 Sep.

Authors

Matteo Ferrari^{1

2}, Aldo Zenoni^{1

2}, Monika Hartl³, Yongjoong Lee³, Alberto Andrighetto⁴, Alberto Monetti⁴, Andrea Salvini⁵, Fabio Zelaschi⁵

Affiliations

¹ Dipartimento di Ingegneria Meccanica e Industriale, Università degli Studi di Brescia, Via Branze 38, I-25123 Brescia, Italy.
² Istituto Nazionale di Fisica Nucleare, Via Bassi 6, I-27100 Pavia, Italy.
³ European Spallation Source, Odarslövsvägen 113 SE-22484 Lund, Sweden.
⁴ Laboratori Nazionali di Legnaro dell'INFN, Viale dell'Università 2, I-35020 Legnaro (PD), Italy.
⁵ Laboratorio Energia Nucleare Applicata LENA, Università degli Studi di Pavia, Via Aselli 41, I-27100 Pavia, Italy.

Abstract

Many of the moving components in accelerator and target environments require lubrication. Lubricants in such environments are exposed to high fluxes of secondary radiation, which originates from beam interactions with the target and from beam losses. The secondary radiation is a mix of components, which can include significant fractions of neutrons. Lubricants are radiation-sensitive polymeric materials. The radiation-induced modifications of their structure reduce their service lifetime and impose additional facility maintenance, which is complicated by the environmental radioactivity. The study of the lubricants radiation resistance is therefore necessary for the construction of new generation accelerators and target systems. Nevertheless, data collected in mixed radiation fields are scarce. Nine commercial greases were irradiated at a TRIGA Mark II Research Reactor to serve for the construction of new accelerator projects like the European Spallation Source (ESS) at Lund (Sweden) and Selective Production of Exotic Species (SPES) at Legnaro, (Italy). Mixed neutron and gamma doses ranging from 0.1 MGy to 9.0 MGy were delivered to the greases. For an experimental quantification of their degradation, consistency was measured. Two of the greases remained stable, while the others became fluid. Post-irradiation examinations evidence the cleavage of the polymeric structure as the dominant radiation effect. Dose and fluence limits for the use of each product are presented. Apart from the scientific significance, the results represent an original and useful reference in selecting radiation resistant greases for accelerator and target applications.

Keywords: Aerospace engineering; Industrial engineering; Lubricating grease; Materials chemistry; Materials science; Mechanical engineering; Mixed radiation field; Neutron damage; Nuclear engineering; Nuclear reactor irradiation; Polymer degradation; Radiation effect.