Cable technology |
Ageing well – designing nuclear cables to survive 60 years
Lynxeo has recently won an order from EDF to supply 15 000 km of specialised cables for various new nuclear projects, including the six EPR2 reactors to be built in France, as well as for its operational fleet. What are the challenges to be addressed in designing and testing cables to survive 60 years in the hostile environment of the nuclear island?
Olivier Dervout Nuclear Global Market Director, Lynxeo
Within the hostile environment of the pressurised water reactor nuclear island – which includes reactor vessel, steam generators, and safety systems – electrical equipment must be able to function reliably and safely under elevated temperatures, high humidity, and substantial levels of radiation. Most importantly, this equipment must remain operational during and after severe accidents, such as a loss of coolant accident (LOCA) or a steam line break accident (SLBA), where sudden environmental changes occur within the containment. Cables specifically designed and qualified for use in the nuclear island environment are classified under very stringent standards. These low voltage (LV) and medium voltage (MV) cables must meet rigorous criteria for thermal and radiological ageing resistance, as well as accident
scenarios within the containment zone: ● K1 cables are qualified for the most demanding conditions, including exposure to gamma radiation and proven performance in LOCA scenarios. They are installed in areas where both high radiation and accident conditions are possible.
● K2 cables are designed to be gamma radiation resistant, for use in areas where significant radiation exposure is anticipated, but not necessarily under LOCA conditions.
● K3 cables are intended for use in the conventional island, also known as the non-nuclear or turbine island. This includes systems such as turbines, generators, condensers, feedwater systems, and auxiliary
power supplies. They are exposed to normal industrial conditions rather than radiation. In addition, all nuclear safety cables must demonstrate proven performance in accordance with IEC 60216. This guarantees reliable operation over a service life of 60 years under continuous exposure to an ambient temperature of 90°C.
By adhering to these protocols and standards, and by carefully selecting the cable types appropriate to their installation environment, nuclear facilities ensure the long- term safety, reliability, and compliance of their electrical infrastructure. A single EDF EPR third generation PWR might require around 5000 km of various types of cable.
Accelerated ageing Lynxeo cable. Image: Lynxeo
The main concern for nuclear power plant operators is of course safety. They must be able to achieve a controlled shutdown of the reactor under all projected scenarios and prevent any release of radioactive material. All equipment must be qualified to operate in these conditions, even in the event of the most severe accidents. Cables must continue to serve numerous systems, such as pumps, valves, generators and all kinds of essential monitoring equipment for pressure, temperature, radiation, etc. Special cable qualification procedures are applied to confirm ability to survive severe irradiation and hot steam/ water at high pressure. In addition to qualification procedures prior to installation, cables undergo mandatory condition monitoring on site to ensure sustained performance over time. It is extremely important for cables to be resistant to degradation over time, to be able to fulfil their expected safety function over the full lifetime of the power station. If cables don’t last long enough, they are very difficult to replace because they are often installed in inaccessible or sealed areas. That means cable replacement would result in very long outage times. That is why Lynxeo ENERGEN® cables are designed to meet the industry expected lifetime of 60 years. To reduce susceptibility to ageing, we expose cables to artificial ageing procedures that reproduce the actual damage that occurs over time. For cables outside the reactor core, the biggest concern is degradation of polymers by
36 | April 2026 |
www.modernpowersystems.com
oxidation. Since oxidation is caused by ambient air, and accelerated by heat, the ageing tests are conducted by exposing the cables to very high temperatures. Additionally, cables have to resist high levels of radiation.
Thermal ageing
Ageing refers to a loss of certain properties over time. Oxygen reacts with the polymer chains, making them hard and brittle. This process is strongly correlated with temperature and can be described by the Arrhenius model. This provides a basis to extrapolate the expected lifetime at low temperature from experimental data obtained at high temperature in a relatively short period. According to this model, the logarithm of the lifetime is a linear function of the inverse absolute temperature (1/Kelvin). Arrhenius test results are used to define specific accelerated ageing test conditions for the whole cable, representing the expected lifetime. For non LOCA cables, the evaluation stops there. For LOCA cables, further tests are required. To ensure good ageing resistance, our R&D laboratories have developed, tested and applied special polymer formulations.
Radiation ageing and accident radiation
Radiation can cause and accelerate the same degradation mechanisms as thermal ageing, especially when the cables are exposed to air. Depending on three main parameters, dose rate, integrated dose, and temperature, polymers can become hard and brittle. The dose absorbed by the cable varies depending on its location within the reactor building. It is low under normal operating conditions. To confirm a cable’s resistance during an accident, much higher doses are applied during the qualification process. In case of an accident, cables must resist strong radiation with both high dose rate and high integrated dose. The resistance of a cable to both ageing and radiation is tested with a single cumulative dose of up to 2 000 kGy, depending on reactor design. This dose is very high compared to a lethal dose for humans of about 0.005 kGy.
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