Mechanical and physico-chemical properties of EPDM type cable polymers after thermal and radiochemical ageing
(2019)
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- Instrumentation, control and power cables are related to the funda- mental safety systems of Nuclear Power Plants. Their safe operation must be ensured in order to secure current and possibly extended NPP operation, under normal and accident conditions. Operating environ- ment of these cables implies harsh ageing factors, including increased temperatures and radiation. Degradation with ageing might jeopardize cable functionality and cable integrity has to be regularly monitored. Cable structural integrity is often monitored by studying mechanical and electrical properties of cable insulation, which is mainly made out of polymers. This study aims to contribute to the plant life extension validation and plant life management improvement through a better understanding of physico-chemical processes responsible for the cable insulation ageing, in parallel with development of cable life time prediction model. In order to do so, accelerated ageing with a broad ageing condition matrix was applied to the industrial and non-industrial (neat) polymer samples. The non-aged and aged samples were investigated using mechanical, microstructural and physico-chemical investigation techniques. Attempt was made to correlate the properties on macroscopic and microscopic scale with respect to the ageing processes and ageing mechanisms. Issues related to the necessity and the limitations with respect to the usage of accelerated ageing, with the emphasis on the diffusion limited oxidation effect were discussed and the results are incorporated into the life time predicting model. Regarding the mechanical properties, elongation at break is generally used as a benchmark criterion for cable insulation ageing assessment. However this is a destructive technique and attempts are being taken to develop an alternative non-destructive, rapid, and on-site monitoring technique. The indenter measurement test conforms to the above re- quirements and this technique is proposed to be implemented to assess the condition of cables installed in a nuclear plant. The present thesis aims at the analysis of the elongation at break and indenter modulus data for polymer insulation materials, with the chal- lenging goal of establishing correlations between the two techniques. The setting up correlations will provide the capability of assessing the condition of cable materials by use of an in-situ, non-destructive technique. In order to establish such a correlation, a modelling based on a phenomenological approach of the polymer ageing, as well as an experimental characterization of polymer degradation is required. Empirical modelling, supported by a phenomenological background is further used for predicting the evolution of elongation at break under long-term operating conditions, in order to estimate the time for reaching a given end - of - life criteria.
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Sarac, T. (2019). Mechanical and physico-chemical properties of EPDM type cable polymers after thermal and radiochemical ageing. https://hdl.handle.net/2078.5/96831