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Long-term performance of polymeric materials in nuclear power plants.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.ORCID iD: 0000-0003-3049-7225
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 [en]
EPDM, thermal ageing, radiation ageing, portable NMR spectroscopy, modulus profiling, condition monitoring, plasticizer migration
National Category
Polymer Chemistry
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-213361ISBN: 978-91-7729-460-3 (print)OAI: oai:DiVA.org:kth-213361DiVA, id: diva2:1136870
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
List of papers
1. Profiling of thermally aged EPDM seals using portable NMR, indenter measurements and IR spectroscopy facilitating separation of different deterioration mechanisms
Open this publication in new window or tab >>Profiling of thermally aged EPDM seals using portable NMR, indenter measurements and IR spectroscopy facilitating separation of different deterioration mechanisms
Show others...
2016 (English)In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 53, p. 77-84Article in journal (Refereed) Published
Abstract [en]

The changes occurring in EPDM cable transit seals during thermal ageing and the causes of these changes were investigated. Samples were aged at a temperature of 170 °C, and subsequently evaluated with respect to the distance from the surface with modulus profiling, infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy, based on the extractable mass fraction profiles for initial and aged materials. The ageing resulted in an increase in the modulus and in the degree of oxidation and in a decrease in the NMR transverse relaxation time, T2. The NMR data were obtained in a non-invasive manner by ex situ experiments performed with a portable low-field spectrometer (NMR MOUSE). The results showed deterioration processes that can be attributed to different mechanisms i.e. oxidation, anaerobic crosslinking and migration of oil extender. The unique combination of parameter profiles made it possible to resolve and quantify these three contributing mechanisms. The NMR results highlight the potential of this method for on-site testing.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Ethylene propylene rubber; Thermal ageing; Portable NMR spectroscopy; Modulus profiling; Condition monitoring
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-191377 (URN)10.1016/j.polymertesting.2016.05.015 (DOI)000380628800011 ()2-s2.0-84969945017 (Scopus ID)
Note

QC 20160907

Available from: 2016-09-07 Created: 2016-08-30 Last updated: 2017-11-21Bibliographically approved
2. Deterioration of highly filled EPDM rubber exposed to thermal ageing in air: kinetics and non-destructive monitoring
Open this publication in new window or tab >>Deterioration of highly filled EPDM rubber exposed to thermal ageing in air: kinetics and non-destructive monitoring
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The effects of thermal ageing on EPDM cable transit seals were investigated. Samples were aged in air at 110, 120, 150 and 170 °C, and evaluated with tensile testing, indenter modulus profiling, oxidation profiling (using IR spectroscopy), nuclear magnetic resonance (NMR) spectroscopy profiling. The ageing resulted in an increase in the indenter modulus, the degree of oxidation and in a decrease in the NMR transverse relaxation time, T2. Diffusion-limited oxidation (DLO) occurred with a large oxidation gradient close to the sample surface. The portable NMR MOUSE (non-invasive method) was used to obtain detailed degradation profiles, up to a depth of 5 mm of the aged samples. The results indicated a deterioration process that was attributed to several mechanisms, i.e. oxidation, anaerobic crosslinking and migration of oil extender. By combining the data acquired from the profiling, separation and quantification of these three contributing mechanisms was determined. Additionally, it was shown that the portable NMR data correlated well with the strain at break data, highlighting the potential use of the portable NMR for condition monitoring.

Keywords
Ethylene propylene rubber, Thermal ageing, Portable NMR spectroscopy, Modulus profiling, Condition monitoring
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-213010 (URN)
Projects
Long-term performance of polymeric materials in nuclear power plants
Note

QC 20170829

Available from: 2017-08-27 Created: 2017-08-27 Last updated: 2017-08-29Bibliographically approved
3. Radiochemical ageing of highly filled EPDM seals as revealed by accelerated ageing and ageing in-service for 21 years
Open this publication in new window or tab >>Radiochemical ageing of highly filled EPDM seals as revealed by accelerated ageing and ageing in-service for 21 years
2017 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321Article in journal (Refereed) Submitted
Abstract [en]

Highly filled EPDM rubber used in cable transit seals in nuclear power plants were

exposed to γ radiation at a high dose rate at 23 °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.

Keywords
Ethylene propylene diene monomer rubber, Gamma radiation, Indenter modulus profiling, IR microscopy, Portable NMR spectroscopy
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-213008 (URN)
Projects
Long-term performance of polymeric materials in nuclear power plants
Note

QCR 20170828

Available from: 2017-08-27 Created: 2017-08-27 Last updated: 2017-08-29Bibliographically approved
4. Effect of radiation on carbon-black-filled EPDM seals in water and air
Open this publication in new window or tab >>Effect of radiation on carbon-black-filled EPDM seals in water and air
Show others...
2017 (English)Manuscript (preprint) (Other academic)
Abstract [en]

The effects of γ-radiation in air and water on a highly filled carbon-black-containing EPDM seal, used in transportation valves for old-fuel rods, were investigated. Samples were irradiated at a dose rate of 7 kGy/h until total doses of 0.35, 1.4, 2.1 and 3.5 MGy were reached. The doses were chosen to correspond to 1, 4, 6 and 10 years in service. Infrared spectroscopy, mechanical indenter and NMR relaxation time (T2) measurements indicated an oxidative crosslinking of the seal, which increased monotonically with the dose. The effects were larger in air than in water, and in air, diffusion-limited oxidation was observed. The compression set increased with increasing doses of radiation and was the highest for seals irradiated in air. The water uptake into the rubber, which was always lower than 1 wt%, increased with the dose, showing the effects of increased polarity/oxidation of the rubber.

Keywords
EPDM, gamma radiation, water, air, carbon black, high dose-rate.
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-213009 (URN)
Projects
Long-term performance of polymeric materials in nuclear power plants
Note

QCR 20170828

Available from: 2017-08-27 Created: 2017-08-27 Last updated: 2017-11-09Bibliographically approved

Open Access in DiVA

The full text will be freely available from 2018-09-22 13:40
Available from 2018-09-22 13:40

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