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Radiochemical ageing of highly filled EPDM seals as revealed by accelerated ageing and ageing in-service for 21 years
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. (polymeric materials)ORCID iD: 0000-0003-3049-7225
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials. (polymeric materials)
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
2017 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 144, p. 473-484Article in journal (Refereed) Published
Abstract [en]

Highly filled EPDM rubber used in cable transit seals in nuclear power plants were exposed to gamma radiation at a high dose rate at 23 degrees C in media with different oxygen partial pressures (1-21.2 kPa). The motivation of this study was threefold: highly filled polymers are replacing halogen-containing polymers and these materials have rendered less attention in the literature; there is a need to find efficient tools to make possible condition monitoring and extrapolation. Several profiling methods were used: IR microscopy, micro-indentation, micro-sample extraction/gravimetry and non-invasive NMR spectroscopy, and three different deterioration processes were identified: polymer oxidation, migration of low molar mass species, and anaerobic changes in the polymer network. IR microscopy, micro-indentation profiling and the portable NMR method confirmed diffusion-limited oxidation in samples irradiated in air. The inner non-oxidized part of the blocks showed a pronounced change in the indenter modulus by migration of primarily glyceryl tristearate migration was accelerated by the presence of oxygen in the surface layer and anaerobic changes in the polymer network. For extrapolation or for condition monitoring, it is best to use the data obtained by indenter modulus profiling and to use the correlation between indenter modulus and strain-at-break to quantify the sample status. Non-invasive NMR profiling provided useful data but was less precise than the indenter modulus data to predict the strain-at-break.

Place, publisher, year, edition, pages
Elsevier, 2017. Vol. 144, p. 473-484
Keywords [en]
Ethylene propylene diene monomer rubber, Gamma radiation, Indenter modulus profiling, IR microscopy, Portable NMR spectroscopy
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-213008DOI: 10.1016/j.polymdegradstab.2017.09.008ISI: 000414111700048Scopus ID: 2-s2.0-85029583501OAI: oai:DiVA.org:kth-213008DiVA, id: diva2:1136325
Projects
Long-term performance of polymeric materials in nuclear power plants
Note

QC 20181205

Available from: 2017-08-27 Created: 2017-08-27 Last updated: 2018-12-05Bibliographically approved
In thesis
1. Long-term performance of polymeric materials in nuclear power plants.
Open this publication in new window or tab >>Long-term performance of polymeric materials in nuclear power plants.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Access to energy is crucial for modern societies to function sustainably. In addition, nuclear power has for a long time been considered a reliable source of energy. However, the majority of nuclear power plants are reaching the end of their service lifetimes, and it is crucial to verify that every component can withstand the added service time. With the ability to monitor the condition of components and perform lifetime predictions, suitable maintenance and safe operations can be achieved.

The specific focus of this study was on ethylene-propylene diene (EPDM) rubber sealants with high filler content, which are replacing halogen-containing polymers. Two types of EPDM seals were studied: Lycron (Brattbergare), which is used in cable transit seal systems in reactor containment, and a carbon black-filled EPDM rubber sealant installed in a transportation valve for transporting old/spent nuclear fuel situated underwater in a reactor basin.

The changes that occur in EPDM cable transit seals during thermal ageing and the causes of these changes were investigated. Samples were tested at different temperatures between 110 °C and 170 °C and evaluated with respect to the distance from the surface via modulus profiling, infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The results showed the existence of three different deterioration mechanisms during ageing. By combining the different profile parameters, it was possible to quantify the contributing mechanism and to obtain information about the kinetics of the different processes. The effects of γ-irradiation on the EPDM cable transit seals in media with different oxygen partial pressures (1 – 21.2 kPa) were studied. By employing different profiling methods, it was possible to separate the mechanisms: polymer oxidation, migration of molar mass species and anaerobic changes in the polymer network. Additionally, the migration process during γ-irradiation was found to be accelerated for higher oxygen partial pressures. The effects of radiation on carbon black-filled EPDM seals in air and water were studied via irradiating samples at high dose rates (7 kGy/h) up to 3.5 MGy. This is the first study on the cross-sectional profiles of highly filled EPDM materials exposed to radiation in water, and it shows great differences in the chemical and physical properties of the material after irradiation in air and water. Of particular interest in this study were the use of a non-invasive portable NMR sensor (NMR-MOUSE) to acquire spatially resolved information from samples and the investigation of this promising method for onsite condition monitoring tests. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. p. 93
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2017:31
Series
TRITA-CHE REPORT, ISSN 1654-1081 ; 2017:31
Keywords
EPDM, thermal ageing, radiation ageing, portable NMR spectroscopy, modulus profiling, condition monitoring, plasticizer migration
National Category
Polymer Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-213361 (URN)978-91-7729-460-3 (ISBN)
Public defence
2017-09-22, Q2, osquldas väg 10, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
Long-term performance of polymeric materials in nuclear power plants
Funder
Swedish Radiation Safety AuthorityVattenfall AB
Note

QC 20180829

Available from: 2017-08-29 Created: 2017-08-29 Last updated: 2017-08-29Bibliographically approved

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