Company: Henan Lubao Special Cable Co., Ltd.
Contact: Manager Su
Address: No. 13 Workshop B, Tiantan Venture Park, Huling Industrial Gathering District, Jiyuan City, Henan Province
Nuclear-grade cables come in many varieties and quantities. It is estimated that a million-kilowatt nuclear power unit requires more than 100 types of cables, with a total length of nearly 2 million meters and a value of about 100 million yuan. According to the purpose, there are five categories: power cables , control cables , measurement cables, communication cables, and fire-resistant cables (silicon-insulated cables). They should not only have the general characteristics of ordinary cables, but also have low smoke, halogen-free, flame retardant and other characteristics, and have specific environmental resistance (such as radiation resistance, LOCA resistance). At present, although there are cable companies specializing in the development and production of nuclear-grade cables in China, there are still few companies that can really produce excellent nuclear-grade cables.
The special performance requirements of nuclear-grade cables make the biggest difference between nuclear-grade cables and general industrial cables in the performance requirements of cable materials for nuclear power plants. Low-smoke and halogen-free flame retardant ordinary low-voltage flame-retardant cables are generally made of chlorine such as PVC Polymer for insulation and sheathing.
The insulation and sheath materials of nuclear-grade cables must use low-smoke, non-toxic, non-corrosive halogen-free flame-retardant cable materials, such as thermoplastic flame-retardant halogen-free or cross-linked flame-retardant halogen-free materials, to meet special requirements. Nuclear safety requirements. When a halogen-free cable is fired, the amount of smoke emitted by the combustion is very low, non-toxic and corrosive, and its flame retardant component can effectively play a flame retardant role, and will not make the cable a channel for flame spread.
Halogen-free cables use halogen-free polymers as the base material, and do not generate acid gases during combustion, so their toxicity and corrosivity are much lower than ordinary PVC cables.
Flame retardant mechanism of flame retardant halogen-free flame retardant cable
Adding a large amount of fillers such as aluminum hydroxide or magnesium hydroxide to halogen-free polymers, they release crystal water when the cable burns and absorbs a large amount of heat, thereby inhibiting the polymer temperature from rising, delaying thermal decomposition, and reducing the burning rate . In addition, the water vapor generated by dehydration can dilute the flammable gas and produce a flame retardant effect. The flame retardancy of polymers is usually evaluated by the oxygen index method, which indicates the minimum oxygen content required for the sample to burn in a mixture of oxygen and nitrogen. The larger the index, the smaller the flammability and the more flame retardancy. it is good. Generally, the oxygen index (OI) is at least 28 to have non-combustible properties.
When people demand that the cable line can continue to play a role in the event of a fire, and when the cable is set up on a line in a high-risk area due to its use, the cable must have fire resistance. Once a fire alarm is encountered, this fire-resistant cable can continue to operate safely for a certain period of time, providing electrical energy for personnel and equipment rescue. The fire resistance of nuclear cables varies according to the requirements of use, and is divided into general fire resistance requirements and special fire resistance requirements. The special fire resistance requirements are: 1000%, 5min combustion test under the impact condition of the cable, and the impact is continued for 5min after the flame is extinguished. At the same time, the cable is flushed with high pressure water at the specified pressure, and the cable must be kept energized throughout the test.
After the United States formulated the IEEE 383 cable standard in 1974, nuclear power plant cables caught fire and burned each year, prompting people to pay attention to the strictness of the flame resistance test standards. For the finished products of nuclear island cables, halogen-free, low-smoke, and flame-retardant are achieved, that is, the finished cables are required to pass the IEC332-3 bundled combustion test, the combustion smoke concentration meets the technical requirements of IEC1034-2, and the burning corrosive gases reach IEC754-2 As required by the specified recommended values, the insulated cores have passed the single vertical flame test specified by IPCEAS-19-81.
The materials for nuclear-grade cables must have the environmental resistance required by the inherent working environment of nuclear power plants, that is, heat resistance, radiation resistance, and LOCA resistance.
Because nuclear-grade cables often work in high-temperature environments, they are required to have long-term heat resistance. Polymers that meet the requirements for heat resistance must be selected, and the cables can have a service life of more than 40 years.
Mitigation of the environment, severe environment When nuclear cables are exposed to a large amount of radiation, the insulation and sheath materials will become brittle and the mechanical properties will be poor. Therefore, as the insulation and sheath material for nuclear power station cables, it must have excellent radiation resistance.
Different polymers have different radiation resistance. People usually add anti-radiation agents to polymers to improve their radiation resistance. With regard to the resistance of the cable to L0CA, different nuclear power plants have different requirements.
In summary, in addition to the performance of ordinary cables, nuclear-grade cables must also have halogen-free, low-smoke, and flame-retardant properties, and meet the safety functions required for normal and accident environments in the laying area. The necessary performance requirements are also to meet the requirements of earthquake resistance, normal and accident conditions-radiation exposure, environment resistant to LOCA / HELB accident conditions, and the service life of the power station design life at operating temperature.
In addition, the service life of nuclear-grade cables, the original design index is more than 40 years, Henan Wire and Cable next-generation nuclear power plant required to reach 60 years, so whether the original design can meet the requirements of use, remains to be further experimental verification. How to extend the service life of cables has become an important research topic.
Low-smoke halogen-free flame-retardant nuclear cable is a special cable with high performance level and difficult manufacturing. Even imported products have exposed many problems in the application process, and some are even serious problems. How to deal with these problems can not be avoided. Whether it is possible to consider the use of low-smoke and low-halogen flame-retardant materials to produce special cables for nuclear power plants is an idea that cable industry workers can explore. This will reduce the difficulty of formula design of cable materials, make the production process easier to implement, product quality will be more reliable, and it will be safer in practical applications.
Nuclear-grade cable is a kind of cable with high performance level and difficult manufacturing technology. At present, the production technology is not fully mature and needs to be further studied.