Independent thesis Advanced level (professional degree), 20 credits / 30 HE credits
To be able to operate, the nuclear power plants use a large amount of cables to connect everything from regulators and monitors to lights. Maintenance and change of its degrading cables is of outmost importance as short-circuits could lead to error in control values etc. Therefore to be able to operate the plant safely it is important to evaluate the life-time expectancy of its cables.
In this study, the polymeric components of the cables are examined and the degradation variation with colour. The used cable insulation material is poly(vinyl-chloride) (PVC), a extensively used material in cables for its cheep cost and ability to be tailored after need.
Cabling can be subjected to a variety of heat and stress related factors that cause aging and consequently its degradation. To evaluate the conditions of the cables, samples that had undergone accelerated aging by heat were studied, and analyzed using different analytical methods; tensile testing, thermo gravimetric analysis, differential scanning calorimetry and high performance liquid chromatography.
The sample material was provided by Forsmarks Kraftgrupp, Sweden, where it had been used in an electrical cabinet. The accelerated thermal ageing was done in the oven in dry air at different temperatures (90, 100 and 110 degrees Celsius) and at different aging times. Then they were tested and analyzed, to determine the degradation mechanisms.
The data from mechanical testing showed that colour pigmentation affected the rate of degradation of the material. Also results showed a non linearity in the Arrhenius equation for activation energies, due to the material being subjected to more than one degradation effect. Also that at higher temperatures degradation due to dehydrochlorination dominated. It also showed that the large fluctuation in mechanical properties of brown could not be due to degradation effects but already inherent flaws created during production.
In this study the degrading/modifying effect of gamma radiation on Ethylene-propylene-diene-monomer (EPDM) was also analyzed.
The results showing little correlation to radiation degree, confirming that the major degradation on the EPDM is due to thermal aging, as proposed in the previous study by Milena Valentini.
2012. , 41 p.