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

Hartl

et al. 2019

Heliyon

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.

Section: Introductionmentioning

confidence: 99%

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

Hartl

et al. 2019

Heliyon

“…Some O‐ring will operate in vacuum, so in absence of oxidative phenomena. A case study dedicated to the lifetime prediction of these O‐rings under mixed irradiation was published . In this study, the foreseen evolution of the O‐rings during the facility operation was based on data collected in CT at maximum power and was correlated to the total absorbed dose parameter only, under the unproved assumption that dose rate effects were negligible.…”

Section: Discussionmentioning

confidence: 99%

“…In order to gather information on the resistance of polymeric O‐rings in such extreme conditions, in a previous work, two rubbers, namely ethylene propylene diene monomer (EPDM) rubber and a fluoroelastomer (FPM), were irradiated in reactor mixed neutron and gamma fields to investigate the effect of the adsorbed dose on their tensile properties and compression set values . EPDM O‐rings were then studied to assess their sealing performance both during the facility service time and the postservice storage phase . FPM is often used in high‐temperature applications due to its excellent heat resistance and oxidative stability, whereas EPDM is employed when low temperature leak tightness is required.…”

Section: Introductionmentioning

confidence: 99%

Degradation of EPDM and FPM elastomers irradiated at very high dose rates in mixed gamma and neutron fields

Pandini

Polymer Engineering & Sci

et al. 2019

Elastomers are widely used in radioactive environments, where ionizing radiations induce a deterioration of their properties due to degradative phenomena occurring in the polymer structure. Their radiation resistance is usually assessed using γ‐rays and relatively low dose rates, but in actual applications, they are often exposed to mixed radiation fields and higher dose rates. Ethylene propylene diene monomer (EPDM) is known for its excellent resistance to γ‐rays but absorbs a larger dose by neutron interactions than fluoroelastomer (FPM). In this work, EPDM and FPM were irradiated in mixed neutron and gamma fields, using high dose rates (from 22 to 700 kGy h−1) and total absorbed doses between 0.2 and 3.5 MGy. The effects of irradiation were assessed by swelling tests, differential scanning calorimetry analysis and dynamic mechanical thermal analysis, and tensile tests. The results show that, even if irradiations were carried out in air, degradation took place under nonoxidative conditions owing to the high dose rates employed. Under such conditions, crosslinking is the dominant radiation‐induced reaction in both elastomers. Moreover, material degradation seems to be influenced mostly by the total absorbed dose and not by the type of radiation. Contrary to what observed at the lower dose rates employed with γ‐rays, major dose rate effects are not observed. POLYM. ENG. SCI., 59:2522–2532, 2019. © 2019 Society of Plastics Engineers

“…For these reasons, experimental radiation resistance tests of candidate products for use in high-power environment where neutron radiation dominates are necessary. Irradiation and testing methodologies have been developed in the last years, dedicated to the selection of elastomeric O-rings to be used in the SPES project [4,5]. The objective of this study is to examine nine commercial greases for selection for applying to use in ESS and SPES facilities [6].…”

Section: Introductionmentioning

confidence: 99%

Radiation Effects in Greases for Use in Facilities Producing Intense Neutron Fields

Proceedings of the 14th International Workshop on Spallation Materials Technology

Lee

et al. 2020

Polymeric components are used in accelerator and target environments where intense neutron and gamma fields are present. Nine commercially available greases were selected to study their radiation-induced functional degradation for use in spallation neutron sources and in facilities producing radioactive ion beams. Grease samples were irradiated in the mixed neutron and gamma field of a nuclear research reactor up to several MGy of total absorbed dose. Methodologies for the irradiation and post-irradiation examination of grease samples are developed. The different degree of radiation tolerance of the tested samples was compared. Some of the greases showed dramatic radiation-induced changes of their physical properties, while others remain stable up to the highest values of delivered absorbed dose.