| Cable technology


EPR. Key: A: reactor building B: safeguard buildings (4) C: fuel building D: nuclear auxiliary building E: radioactive waste processing building F: emergency diesel generator building G: turbine building H: power transmission platform I: operator building J: pumphouse building K: outfall structure L: conventional electrical building Image: EDF


Loss of coolant accident The safety of a PWR relies on the safe transfer of heat produced within the reactor vessel. PWRs use water as their cooling fluid and one of the most severe accident scenarios involves a leak in the primary cooling circuit.


In this scenario, large quantities of radioactive


water at high temperature are released within the reactor containment, resulting in high pressures, temperatures and radiation levels. Design-specific emergency cooling and shutdown systems then reduce temperature and pressure until they return to nominal levels. In the meantime, safety-related equipment must continue to operate.


Cables qualified to 1E LOCA ensure power is delivered to the equipment and instrument readings are fed back to the control room. The precise LOCA scenario depends on reactor type, location in the reactor and the actions/ reactions of the safety systems.


LOCA cable tests are carried out in specially equipped autoclaves that allow the application to the cable samples of conditions arising from prescribed scenarios. At Lynxeo we have our own autoclave. This enables us to carry out tests beyond the usual specified parameters to anticipate future customer needs (up to 250°C and 20 bar).


Fire reaction


Fire reaction is also a vital consideration for nuclear cables. For a fire to form and spread, three elements must be present: combustible material; oxygen; and a heat source. There are


two main phases in the development of a fire: ● The initial spreading phase, when the fire spreads slowly and can be kept under control.


● The combustion phase, when it can no longer be kept under control.


The transition between the two phases is called the “flash over point.”


Cables are classified according to:


● fire reaction, which refers to their role as passive elements during a fire, characterised by flammability, fire spread, heat release, smoke emission and toxicity.


● fire resistance, which reflects their role as active elements characterised by electrical continuity under fire conditions.


Fire resistance is a key consideration as circuit integrity must be maintained when cables are subjected to fire under specified conditions. This includes the standard procedure for checking continuity as well as evaluating test results for low voltage power cables and control cables with rated voltage. Depending on which section of the standard is referenced, two different temperatures are used for fire resistance assessment: 750°C (IEC 60331-11); or 830°C (IEC 60331-1 & -2). The cable must demonstrate electrical continuity – its ability to continue to operate in the designated manner whilst subjected to a specified flame source for a certain period (90 minutes of flame application is typical).


Smoke and gas emissions during fire


Also critical to fire safety are smoke and gas emissions. Smoke can be more dangerous than the fire that creates it, due to its opaque and toxic nature.


Cables are installed throughout the entire facility. Therefore, during a fire, they can increase emissions of dense, corrosive and toxic smoke. To greatly reduce the level of emissions, as well as their toxicity and corrosivity, materials which do not contain halogens, known as Halogen Free Fire Retardant (HFFR) or Low Smoke Zero Halogen (LSOH), are used for both cable insulation and sheathing.


Certified expertise


Nuclear safety is not limited to just the designers and manufacturers of power plant components such as cables. It involves all players in the value chain, from engineers to operators, subcontractors and suppliers. Each link plays an essential role in guaranteeing a safe environment. That is why we have implemented a comprehensive set of rigorous measures to ensure that all our employees and partners fully understand their responsibilities. Our goal is to ensure that everyone involved in our operations – regardless of their function – is thoroughly aware of, and trained in, the safety requirements unique to the nuclear industry.


The ISO 19443 certification of Lynxeo’s lead manufacturing factory in Mehun-sur-Yèvre, France, provides a reference framework that guarantees risk control and the continuous improvement of safety practices. The standard defines the requirements for quality management systems in the nuclear supply chain. It imposes rigorous risk management, full traceability throughout the product lifecycle, and a strengthened safety culture among suppliers. For major projects such as Hinkley Point C, Sizewell C, and the French EPRs, ISO 19443 guides audits and the qualification of subcontractors, enhancing transparency and accountability within the supply chain. It promotes continuous improvement of processes and helps reduce potential failures, thereby improving the overall reliability of civil nuclear stakeholders. For Lynxeo, ISO 19443 certification reflects a high level of commitment to quality and nuclear safety. It positions us as a reliable partner, capable of contributing to complex and highly regulated projects, while ensuring controlled risk management and a continuous improvement approach within the supply chain.


For more information, visit: lynxeogroup.com www.modernpowersystems.com | April 2026 | 37


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