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5. Irradiation resistance
Increase knowledge of nuclear grade cable knowledge
There are many types and quantities of nuclear grade cables . If divided by purpose: 1. Power cable 2. Control cable 3. Measurement cable 4. Communication cable 5. Fireproof cable (silicon insulated cable) and other five categories. Not only should have the general characteristics of ordinary cables, but also have low-smoke, halogen-free, flame-retardant and other characteristics, and must have a specific environmental resistance (such as radiation resistance, LOCA resistance). Although there are currently domestic cable companies that specialize in R&D and production of nuclear grade cables, there are still a few companies that can truly produce excellent nuclear grade cables.
The requirements of nuclear grade cable performance make the nuclear grade cable the most different from general industrial cable. The biggest difference lies in the performance requirements of the cable material for nuclear power plants. Low smoke, halogen-free flame retardant, common low-voltage flame retardant cables are generally made of PVC and other chlorine-containing polymers. Insulation and sheathing.
The insulation and sheathing material of nuclear grade cable must use low smoke, non-toxic and non-corrosive halogen-free flame retardant cable material, such as thermoplastic flame retardant halogen-free or cross-linked flame retardant halogen-free material, to meet special requirements. Nuclear safety requirements. In the event of a fire, halogen-free cables emit low amounts of fumes without toxicity and corrosiveness. The flame-retardant components of the halogen-free cables can effectively function as flame-retardant materials, and will not make the cable a flame propagation path.
Halogen-free cables use halogen-free polymers as the base material and do not generate acid gases when they are burned. Therefore, their toxicity and corrosivity are much lower than ordinary PVC cables.
1. Fire-retardant mechanism of halogen-free flame retardant cable
Adding a large amount of fillers such as aluminum hydroxide or magnesium hydroxide in halogen-free polymers, they release crystalline water when the cable burns, absorbing a lot of heat, thereby inhibiting polymer temperature rise, delaying thermal decomposition, and reducing the burning rate. . In addition, water vapor generated by dehydration can dilute flammable gases and produce flame retardant effects. The flame retardancy of polymers is usually assessed by the oxygen index method. It means the minimum oxygen content required when the sample is burned in a mixture of oxygen and nitrogen. The larger the index, the lower the flammability and the greater the flame retardancy. it is good. A general oxygen index (OI) of at least 28 has non-flammable characteristics.
2. Fire resistance
When people demand that the cable line continue to function in the event of a fire, and when the cable is placed on a line in a high-risk area due to its use, the cable must be fire-resistant. In the event of a fire, such fire-resistant cables can continue to operate safely for a certain period of time, providing electrical energy for the rescue of personnel and equipment. The fire resistance of nuclear cables is different according to the requirements of use. It is divided into general fire resistance requirements and special fire resistance requirements. The special fire resistance requirements are as follows: 1000%, 5min combustion test under the cable impact condition. After the flame is extinguished, it will continue to impact for 5min. At the same time, the high pressure water rushed cable with the specified pressure shall be required to maintain the power continuity of the cable throughout the test.
3. Environment resistance
The material for nuclear grade cables must have the environmental resistance required by the inherent working environment of the nuclear power plant, namely, heat resistance, radiation resistance, and LOCA resistance.
4. Heat resistance
Since nuclear grade cables often work in high temperature environments, they are required to have long-term heat-resistant serviceability. Polymers that meet the requirements of heat resistance are selected, and the cables can have a service life of more than 40 years.
Mitigating the environment and harsh environment When nuclear-grade cables are exposed to a large amount of radiation, the insulating and sheathing materials become brittle and the mechanical properties deteriorate. Therefore, as the insulating and sheathing material for a nuclear power plant cable, it must have excellent radiation resistance.
In summary, the nuclear grade cable must have the characteristics of halogen-free, low-smoke, and flame-retardant, in addition to the performance of the ordinary cable, and satisfy the safety function according to its normal and accidental environment in the laying area. The necessary performance requirements, that is, to meet the needs of earthquake-resistant, normal and accident conditions - radiation, LOCA / HELB accident conditions, the working temperature of the plant with the service life of the life of the design life.
Kexun cable tells everyone about nuclear-level cable knowledge, we now know it!