Nuclear power plant cables refer to the raw materials used for the insulation and sheath of nuclear power plant cables, including various types such as plastics and rubbers. The types of cables are determined by the cable type. There are two classification methods for nuclear power plant cables: one is by function, including measurement cables, communication cables, instrument cables, fire-resistant cables (silicone-insulated cables), etc.; the other is by safety level, with the safety level of cables used in nuclear power plants belonging to the IE class. They should also have a service life of over 40 years. The IE-class nuclear power plant cables are further divided into K1, K2, and K3, each with three safety levels. The development process of nuclear power plant cable products is essentially an update of materials. The selection of raw materials for cable types is shown in Table 1. As shown in Table 1, nuclear power plant cables mainly use the following types.

Selection of components for nuclear power plant cables

Cross-linked polyethylene

Cross-linked PolyethyleneInked polyethylene, also known as XLPE, is a high polymer produced by treating linear polyethylene with appropriate methods, forming a reticulated or three-dimensional structure. It boasts excellent heat resistance (softening point of 200%), electrical insulation properties, low-temperature resistance, and chemical resistance. It also has good radiation resistance, making it suitable as insulation material for cables.

EVA elastomer

Ethylene-vinyl acetate copolymer (EVA) is a copolymer of ethylene and vinyl acetate. It boasts excellent radiation resistance and chemical resistance properties, and is used as cable sheath. However, it requires the addition of a substantial amount of flame retardant to achieve flame retardancy.

Silicone rubber

Silicone rubber or silicone compounds are elastomers with a saturated silicon-oxygen backbone structure, offering chemical stability, excellent resistance to thermal aging, ozone, radiation, and high-pressure steam, as well as superior electrical insulation properties. They are suitable for use as insulating materials. Typically, nuclear-grade cables use ethylene propylene rubber (EPR) for insulation (some also employ double insulation, such as inner EPR and outer EVA), while cross-linked EVA rubber is used for sheathing. The reason is that rubber materials are less prone to deformation under high-temperature and high-pressure tests, ensuring the cable's normal structure and providing greater safety than plastic materials. For nuclear-grade cables used within containment shells, the insulation and sheathing are primarily made of thermoplastic flame-retardant halogen-free or cross-linked flame-retardant halogen-free materials, such as XLPE for insulation and low-smoke halogen-free thermoplastic polyolefins for sheathing. Some also use EPR for insulation and cross-linked EVA for sheathing.

Cable Characteristics

Low-smoke performance

Insulation and sheath materials for nuclear power plant cables must be halogen-free, low-smoke, non-toxic, and non-corrosive flame-retardant cables, such as thermoplastic flame-retardant halogen-free or cross-linked flame-retardant halogen-free materials, to meet the specific nuclear safety requirements. Halogen-free cables emit very little smoke when on fire, are non-toxic and non-corrosive, and their flame-retardant components effectively inhibit flame spread, preventing the cable from becoming a pathway for fire. The main technical characteristics of halogen-free flame-retardant cables include: (1) Total smoke accumulation of the cable used in nuclear power plants, Dm < 150; (2) Non-toxic and non-corrosive, meaning the cable does not emit HCI and CO upon combustion; (3) Flame retardant, with the flame retardancy of polymers typically evaluated by the Oxygen Index (OI), usually OI ≥ 28.

Environmental durability

Materials for nuclear power plant cables must possess environmental resistance, including heat resistance, radiation resistance, and LOCA resistance.

(1) Heat Resistance: As nuclear power plant cables often operate in high-temperature environments, they are classified as high-temperature cables. Consequently, they must possess long-term heat resistance properties. Suitable heat-resistant polymers should be selected to ensure the cables have a lifespan of over 40 years.

(2) Irradiation Resistance (Mild Environment, Severe Environment) When nuclear power plant cables are exposed to a large amount of radiation, the insulation and sheath materials become brittle and their mechanical properties degrade. Therefore, insulation and sheath materials used for nuclear power plant cables must possess excellent irradiation resistance. Different high polymers exhibit varying levels of irradiation resistance. Antiradiation agents are commonly added to high polymers to enhance their irradiation resistance.

(3) In nuclear power plants with LOCA-resistant designs, Loss of Cooling Accident (LOCA) and High Energy Line Break (HELB) incidents are often collectively referred to as LOCA. During a LOCA/HELB event, cables are subjected to the impact of high-temperature, high-pressure steam and the action of corrosive chemicals, as well as higher doses of radiation than during normal operation. Therefore, nuclear power plant cables should possess LOCA resistance.