Nuclear power plant cables refer to the raw materials used for insulation and sheathing in nuclear power plant cables, including various types such as plastics and rubbers. The type of cable is determined by the type of cable itself. 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, which should also have a lifespan of over 40 years. The IE-class nuclear power plant cables are further divided into K1, K2, and K3, each representing a different safety grade. 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. From Table 1, it can be seen that nuclear power plant cables mainly use the following types.

Selection of cable components for nuclear power plants:

Cross-linked polyethylene

Cross-linked PolyethyleneInked polyethylene, or XLPE, is a high polymer formed by treating linear polyethylene with appropriate methods, resulting in a network or skeletal structure. It boasts excellent heat resistance (softening point of 200%), electrical insulation, low-temperature resistance, and chemical resistance. It also has good radiation resistance and is used 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 significant amount of flame retardant to achieve flame retardancy.

Silicone rubber

Silicone rubber or silicone compounds are elastomers with a saturated silicon and oxygen backbone structure, boasting high chemical stability, excellent resistance to heat 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 (with some employing double insulation, such as inner EPR and outer EVA), and cross-linked EVA rubber for sheathing. The reason lies in the fact that rubber materials are less prone to deformation under high-temperature and high-pressure tests, ensuring the cable's normal structure and offering greater safety compared to plastic materials. For nuclear-grade cables used within containment shells, the insulation and sheathing are mainly 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 polyolefins for sheathing. Some also use EPR for insulation and cross-linked EVA for sheathing.

Cable Characteristics

Low smoke performance

Insulation and sheathing materials for nuclear power plant cables must be flame-retardant cables without halogens, low smoke, non-toxic, and non-corrosive, such as thermosetting flame-retardant halogen-free or cross-linked flame-retardant halogen-free materials, to meet the special nuclear safety requirements. Halogen-free cables emit very low smoke when on fire, are non-toxic and non-corrosive, and their flame-retardant components can effectively inhibit combustion, preventing the cable from becoming a pathway for火焰 spread. The main technical characteristics of halogen-free flame-retardant cables include: (1) the total smoke accumulation of the cable for nuclear power plants Dm < 150; (2) non-toxicity and non-corrosiveness, meaning the cable does not release HCI and CO upon combustion; (3) flame retardancy, which is usually evaluated by the oxygen index (OI), generally OI ≥ 28.

Environmental resistance

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

(1) Heat Resistance: Due to the fact that 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 and be made from polymers that meet these requirements, allowing the cables to have a lifespan of over 40 years.

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

(3) In nuclear power plants with LOCA resistance, Loss of Cooling Accident (LOCA) and High Energy Line Break (HELB) are commonly referred to as LOCA. During a LOCA/HELB event, cables are subjected to the impact and corrosion from high-temperature, high-pressure steam and corrosive chemicals, and they must withstand higher doses of radiation than normal operating conditions. Therefore, nuclear power plant cables should have LOCA resistance.