Shanghai Hufei Cable Co., Ltd.

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, 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, with three safety levels. The development process of nuclear power plant cable products is essentially an update and replacement 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 primarily use the following types.

Selection of cable components for nuclear power plants:

Cross-linked polyethylene

Cross-linked PolyethyleneInked polyethylene, also known as XLPE, is a high polymer obtained by treating linear polyethylene with appropriate methods, creating a reticulated or macromolecular structure. It boasts excellent thermal resistance (softening point at 200%), electrical insulation properties,低温 resistance, and chemical resistance, along with good radiation resistance. It 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, commonly used as cable sheathing. It also requires the addition of significant amounts of flame retardants to achieve flame retardancy.

Silicone rubber

Silicone rubber or silicone compounds are elastomers with a saturated silicon-oxygen backbone structure, known for their 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 (with some employing double insulation, such as inner EPR and outer EVA), and cross-linked EVA rubber 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 offering greater safety compared to plastic materials. The insulation and sheathing for nuclear-grade cables within containment shells are primarily made of thermoplastic flame-retardant halogen-free or cross-linked flame-retardant halogen-free materials, such as using 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 jacket 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, and the smoke is non-toxic and non-corrosive. Their flame-retardant components can effectively prevent flame spread, and the cables will not act as a pathway for the flame. The main technical characteristics of halogen-free flame-retardant cables include: (1) The total smoke accumulation of the cables used in nuclear power plants, Dm < 150; (2) Non-toxic and non-corrosive, meaning the cables do not emit HCI and CO upon combustion; (3) Flame-retardant, with the flame-retardant properties of polymers typically evaluated by the oxygen index (OI) method, usually OI ≥ 28.

Environmental resistance

Material for nuclear power plant cables must be environmentally resistant, including heat resistance, radiation resistance, and LOCA resistance.

(1) Heat resistance: Since nuclear power plant cables often operate under high-temperature environments, they are known as high-temperature cables. Consequently, they must possess long-term heat resistance for use, requiring the selection of polymers that meet the heat resistance requirements, enabling 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 high amount of radiation, resulting in decreased mechanical properties. Therefore, insulation and sheath materials for nuclear power plant cables must possess excellent irradiation resistance. Different types of high polymers exhibit varying degrees of irradiation resistance. Antiradiation agents are commonly added to these polymers to enhance their irradiation resistance.

(3) In nuclear power plants with LOCA-resistant design, 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 of high-temperature, high-pressure steam and the action of corrosive chemicals, and they must withstand higher doses of radiation than during normal operation. Therefore, nuclear power plant cables should be LOCA-resistant.