Concept & Approach
The design of nuclear cables can vary depending on the voltage (low voltage or medium voltage) or on the generic type of cable (control, power or instrumentation). However, the most sensitive parts of a cable in terms of ageing are the polymeric ones, i.e. the insulation (dielectric) and the jacket.
Illustration to the right: Cross section of a cable showing its components.
Choice of materials
TeaM Cables will focus its research on the insulation materials as the insulation of the cable is essential for ensuring the electrical function (whereas the jacket is necessary for mechanical protection or in some cases it serves as a protection layer against water/humidity ingress) and current end-of-life criteria of nuclear cables is based on elongation at break of insulation materials. Considering that each cable will be aged in different forms, at different conditions and that many characterisation methods will be used to make an in-depth multiscale study,
TeaM Cables has chosen to limit the number of cable materials to be studied in the project to two types of insulation polymer families:
- Cross-linked Polyethylene (XLPE), the most used low voltage cable in Gen III reactors, and
- Ethylene propylene diene terpolymer (EVA-EPDM), a medium voltage cable, commonly used for systems important to safety.
For the study of XLPE, three types of materials will be considered:
- Model component materials with growing formulation complexity: cross-linked matrix alone, cross-linked matrix + antioxidant(s), crosslinked matrix + antioxidants + fillers;
- « Real » component materials taken from cables;
- Whole cables.
Conditions and scenarios
The study of polymers with growing formulation complexity will allow the role of each ingredient during the polymer ageing to be identified. The study will cover both normal conditions, i.e. soft accelerated ageing representative of normal conditions inside a reactor building, and abnormal conditions, i.e. exposure to design basis event and/or severe accidents. Two accidents scenarios will be studied with simultaneous loads applied: thermodynamic conditions and irradiation. One additional accidental test will be studied, following a thermodynamic standard profile, without simultaneous irradiation. On one hand, experimental characterisations will be carried out at different scales to bring out ageing mechanisms and consequences. On the other hand, models will be developed to relate the scales by using experimental data as input for modelling or to validate the models.
Overal approach and workflow
The illustration below shows the TeaM Cables overall approach and workflow. The results from experiments will be integrated into a database for statistical analysis in order to help in the identification of ageing markers but also in order to define the uncertainties and reproducibility of the different measurement techniques. A Round-robin test will be carried out on new materials at the beginning of the project. This will also lead to guidelines to refine the standard test specifications.
Based on the experiments, generic multiscale and kinetic models will be elaborated and implemented in the Virtual Polymer software. The implemented models enable the prediction of the evolution of the macroscopic properties with an unprecedented inclusion of the elementary ageing mechanisms. Data obtained from in situ (non-destructive) tests will be used for the optimisation and adjustment of the implemented kinetic models.
EDF’s polymer modelling tool “Virtual Polymer” will integrate new models and will be interfaced with Framatome’s cable ageing management tool, “COMSY Cables” which will be the entry point to access the new “TeaM Cables tool”. On this interface, NPP operators will enter power plant and cable type specific data. All calculated and obtained data on each specific piece of cable in the plant will be stored in COMSY Cables.
Through the setup of an end-user group, the TeaM Cables novel modelling approach and associated tool will be assessed by different end-users during the second phase of the project to confirm its accuracy, reliability and transposability to data obtained in other international research projects. The TeaM Cables tool will thus start at a TRL of 2 (technology concept formulated) and will by the end of the project reach TRL 5 (technology validated in relevant environment).