80-year-life irradiation crosslinking type halogen-free low-smoke flame-retardant polyolefin sheath material and preparation method thereof

Abstract

The invention provides an 80-year-life irradiation crosslinking type halogen-free low-smoke flame-retardant polyolefin sheath material and a preparation method thereof, and belongs to the technical field of sheath materials. Through base material selection, processing modification, interface compatibilization, radiation-resistant agent compounding and antioxidant / light stabilizer compounding design, long-acting reliability of the material under extreme conditions of high temperature, radiation, mineral oil infiltration and the like is achieved, and a matched sheath material meeting the requirement for the 80-year service life of the fourth-generation nuclear power station is developed. The modified polyether-ether-ketone is adopted as a main base material, the material can tolerate the peak temperature of 300 DEG C for a short time, stable operation is achieved under the accident working condition of 260 DEG C, and the mineral oil resistance is effectively improved. According to the double-compatibilization system disclosed by the invention, the polyolefin elastomer and the ethylene-vinyl acetate are bridged by the maleic anhydride, so that the problem of compatibility between a non-polar polyolefin chain and polar vinyl acetate is solved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sheath materials, and particularly provides an 80-year service life irradiation crosslinking type halogen-free low-smoke flame-retardant polyolefin sheath material and a preparation method thereof. BACKGROUND

[0002] The design life of early nuclear power plants (first / second generation reactor type) is generally 30-40 years. With the continuous progress of technology, the design life of newly built nuclear power plants is generally 60 years, that is, the third generation of nuclear power plants. Compared with the first and second generation nuclear power plants, the third generation nuclear power plants have significant improvements in safety, economy, service life and the like. In the development of the fourth generation of nuclear power technology, some countries and organizations are also continuously exploring to improve the performance indicators such as safety, economy and service life of nuclear power plants, and in this process, the demand for the design life of nuclear power plants reaching 80 years has gradually formed. As a key part of the nuclear power plant, the nuclear grade cable needs to achieve maintenance-free throughout the life cycle, and the service life needs to match the overall design life of the nuclear power plant, so as to avoid affecting the normal operation of the nuclear power plant due to the aging failure of the cable, and to reduce the huge cost and safety risk caused by replacing the cable during the operation of the nuclear power plant. This requires that the supporting polyolefin cable material achieve a generational breakthrough in core indicators such as heat-resistant life and radiation resistance.

[0003] There are a large number of mechanical equipment in the nuclear power plant, and various types of oil are used in the operation process to ensure normal operation. Once the oil leaks, it is easy to contact the surrounding cables. If the cable does not have good oil resistance, it will be eroded by oil, causing the cable material to swell, soften or become brittle, and thus seriously affecting the safe operation of the nuclear power plant. In the patent with the publication number CN116855008A, a thermosetting sheath material for nuclear power plants with a service life of 80 years is reported. The basic formula of the material includes two substrates: 7320M with a vinyl acetate (VA) content of 9wt% and a combination of 5110J with a vinyl acetate content of 17.6-20.4wt%. On the one hand, the polarity of the two substrates is low, and the performance of mineral oil ASTM 902# is poor, and the melting point is lower than 100℃, which is difficult to meet the oil resistance requirements of the cable in the nuclear power plant at 100℃ or 121℃. On the other hand, the amount of antioxidant is 6-8 parts, and the amount of light stabilizer is 1-2 parts in examples 1-3. In the low-polarity base system, the "blooming" phenomenon occurs, that is, the white problem caused by the precipitation of additives on the surface of the sheath. In addition, the grafting material uses maleic anhydride grafted poly-4-methyl-1-pentene, wherein the melting point of poly-4-methyl-1-pentene is 240℃, and its chemical structure and physical properties are significantly different from those of EVA, and the compatibility between the two is poor, thereby affecting the mechanical properties of the material.

[0004] In the patent with publication number CN 115353744 A, a halogen-free low-smoke flame-retardant polyolefin insulation material for nuclear-grade cables is reported. As shown by the test data in Examples 2 and 5, the thermal extension is 23% and 25%, but in the examples, it is introduced that in Example 2, the antioxidant is 12 parts, the anti-radiation agent is 10 parts, in Example 5, the antioxidant is 8 parts, and the anti-radiation agent is 5 parts. Only TAIC or TMPTMA, a crosslinking agent, is not added. Under the condition of a large amount of antioxidant and a large amount of anti-radiation additives, it is difficult to produce crosslinking, and the radiation dose is only 80-200 kgy. From the perspective of those skilled in the art, it can be judged that the thermal extension of the insulation material provided by the patent will exceed 100%, not 23% and 25% as described in the patent. As introduced in Example 5, the halogen-free flame retardant is a mixture of aluminum hydroxide and aluminum diethyl phosphinate. The decomposition of aluminum diethyl phosphinate during combustion produces diethyl phosphinic acid (DEP), which hydrolyzes to form acidic substances (such as phosphoric acid), affecting the pH value of the material. High-entropy rare earth zirconate modified polyimide-siloxane block copolymer is used in the entire example, and the weight fraction is relatively large. The main products of polyimide combustion and decomposition include carbon monoxide, carbon dioxide, hydrogen cyanide, nitrogen oxide, and a small amount of nitrogen-containing heterocyclic compounds. The products tested in GB / T 19666 include carbon monoxide, carbon dioxide, sulfur dioxide, nitrogen oxide, and hydrogen cyanide. The combustion and decomposition products of polyimide basically contain these substances, which have a large impact on the toxicity index. Therefore, the actual measured value of the toxicity index of Examples 2 and 5 exceeds the standard limit value of ≤3.

[0005] In the patent with publication number CN 112143086 A, a 1E-grade heat-shrinkable sleeve for nuclear power plants and its preparation method are disclosed. The 1E-grade heat-shrinkable sleeve for nuclear power plants is prepared using a formula comprising vinyl copolymer, hydrogenated styrene-butadiene-styrene block copolymer, modified polyether ether ketone, compatibilizer, flame retardant, and anti-aging agent. As shown in the test examples, the longest thermal life calculated from the 90℃ heat aging experiment is 66 years, which cannot meet the requirement of 80 years of thermal life. In addition, the anti-aging agent is added in an amount of 15-25 parts, which is far beyond the saturation limit of the base resin (the saturation limit of the base resin is 10 parts), and the anti-aging agent may "spray frost", affecting the use.

[0006] Therefore, it can be seen that the supporting materials for the fourth-generation nuclear power plants with a design life of 80 years are still being developed and optimized, and breakthroughs need to be made to seek halogen-free low-smoke flame-retardant sheath materials that can be used in nuclear power plant environments for a long time, have long-term aging resistance, radiation resistance, and oil resistance, have good flame retardance, and have good mechanical properties. SUMMARY

[0007] TECHNICAL PROBLEM The application aims to provide a sheath material with a service life of up to 80 years and a preparation method thereof, so as to ensure that the sheath material can meet the 80-year service life requirement, and at the same time, meet the requirements of halogen-free, low smoke, flame retardation and low toxicity, and have good oil resistance, aging resistance and radiation resistance.

[0008] Technical scheme In view of the defects of the prior art, the application is solved by the following technical scheme: The first object of the application is to provide a sheath material with a service life of up to 80 years, which comprises the following components by weight fraction: Resin matrix 100 parts, flame retardant 130-160 parts, radiation resistant agent 10-15 parts, antioxidant / light stabilizer mixture 4-6 parts, crosslinking agent 2-3 parts; wherein the resin matrix comprises modified polyether ether ketone 40-60 parts, EVM 30-50 parts, and a dual compatibilization system 10-15 parts.

[0009] In an embodiment of the application, the modified polyether ether ketone is obtained by blending modification of polyether ether ketone (PEEK) as a matrix, addition of hyperbranched polyester (HBP), maleic anhydride grafted polyolefin elastomer (POE-g-MAH) and nano nucleating agent.

[0010] In an embodiment of the application, the nano nucleating agent comprises nano titanium dioxide TiO2 or carbon nanotube CNTs.

[0011] In an embodiment of the application, the dual compatibilization system comprises maleic anhydride grafted polyolefin elastomer (POE-g-MAH) and maleic anhydride grafted ethylene-vinyl acetate copolymer (EVM-g-MAH).

[0012] In an embodiment of the application, the maleic anhydride grafted ethylene-vinyl acetate copolymer is prepared from raw materials comprising the following components by weight fraction: EVM 100 parts, maleic anhydride (MAH) 2-3 parts, dicumyl peroxide (DCP) 0.2-0.3 parts, antioxidant 0.1-0.2 parts, lubricant 0.2-0.3 parts, and styrene 1-2 parts.

[0013] In an embodiment of the application, the antioxidant is 1010; and the lubricant is polyethylene wax and stearic acid.

[0014] In an embodiment of the application, the grafting rate of the maleic anhydride grafted ethylene-vinyl acetate copolymer is 0.5-1.5%.

[0015] In an embodiment of the application, the flame retardant comprises magnesium hydroxide.

[0016] In one embodiment of the present application, the radiation resistant agent is cerium oxide and / or boron oxide.

[0017] In one embodiment of the present application, the radiation resistant agent is cerium oxide and boron oxide.

[0018] In one embodiment of the present application, the mass ratio of the cerium oxide and boron oxide is 1: (1~2).

[0019] In one embodiment of the present application, the antioxidant is one or more of ST-10, ST-9228, ST-300, 412S or ST-626.

[0020] In one embodiment of the present application, the antioxidant is a mixture of ST-10, ST-9228, 412S and ST-626 or a mixture of ST-10, ST-9228, ST-300 and ST-626.

[0021] In one embodiment of the present application, the mass ratio of the mixture is (1~2):(1~2):(1~2):1.

[0022] In one embodiment of the present application, the light stabilizer is UV-944 and / or ST-3529.

[0023] In one embodiment of the present application, the light stabilizer is UV-944 and ST-3529.

[0024] In one embodiment of the present application, the mass ratio of the UV-944 and ST-3529 is 1:1.

[0025] In one embodiment of the present application, the crosslinking agent is triallyl isocyanurate (TAIC), triallyl cyanurate (TAC) or trimethylolpropane triacrylate / trimethacrylate (TMPTA / TMPTMA).

[0026] A second object of the present application is to provide a cable comprising the jacketing material.

[0027] In one embodiment of the present application, the jacketing material is radiation crosslinked and / or the cable is radiation crosslinked.

[0028] In one embodiment of the present application, the radiation crosslinking is performed after the cable is finished with extrusion coating.

[0029] In one embodiment of the present application, the crosslinking is performed with 400~600 kGy of radiation.

[0030] A third object of the present application is to provide a method for preparing the jacketing material, the method comprising the steps of: (a) Premixing of the additives: the radiation resistance agent, the antioxidant and the light stabilizer are premixed to form a uniform additive mixture; (b) Preparation of the carrier: the additive mixture and part of the EVM are granulated by twin-screw extrusion to produce additive masterbatch (B material); (c) Main mixing: the modified PEEK, the flame retardant, the functionalized elastomer, the remaining EVM and the B material are mixed and discharged after reaching the preset phase transition temperature; (d) Post-processing: the main mixing product is subjected to twin-screw shearing dispersion and single-screw extrusion granulation in sequence to obtain the finished product.

[0031] Optionally, in order to detect the performance of the finished product, the finished product is subjected to irradiation crosslinking, and the product for sale is the finished product without irradiation crosslinking, which is subjected to irradiation crosslinking after the cable is completed extrusion coating.

[0032] Optionally, the finished product is subjected to high-energy radiation of 400-600 kGy.

[0033] Preferably, the finished product is subjected to high-energy radiation of 506 kGy.

[0034] In an embodiment of the present application, in step (b), the amount of the EVM is 20%-30% of the total mass fraction of the EVM.

[0035] In an embodiment of the present application, in step (b), the temperature gradient of the twin-screw extrusion granulation is: 110-120℃ for the feeding section, 130-140℃ for the melting section, 140-150℃ for the shearing section, and 130-140℃ for the homogenization section to the die head.

[0036] In an embodiment of the present application, in step (c), the functionalized elastomer includes maleic anhydride grafted polyolefin elastomer (POE-g-MAH) and maleic anhydride grafted ethylene-vinyl acetate copolymer (EVM-g-MAH).

[0037] In an embodiment of the present application, the preset phase transition temperature is 160-170℃.

[0038] In an embodiment of the present application, in step (d), the temperature gradient of the twin-screw shearing is: 120-130℃ for the feeding section, 110-120℃ for the melting section, 90-100℃ for the shearing section, and 80-90℃ for the homogenization section.

[0039] In an embodiment of the present application, the temperature gradient of the single-screw extrusion is: 120-130℃ for the body and 130-140℃ for the die head.

[0040] In one embodiment of the present application, in step (a), the premixing is carried out in a vertical ribbon mixer, and the premixing time is 5-10 min.

[0041] A fourth object of the present application is to provide the use of said sheath material in nuclear facility cables or in cables for high radiation environments.

[0042] Advantages 1. The present application innovatively uses modified polyether ether ketone as the core base material, achieving (1) short-term overload tolerance: solving the problem that ordinary base materials cannot withstand short-term 260℃ high-temperature operation under accident conditions, with a short-term peak tolerance temperature of 300℃; (2) radiation stability: after more than 2500 kgy of radiation dose, the mechanical property retention rate is ≥60%, improving the ability of polyolefin materials to resist nuclear radiation; (3) chemical corrosion resistance: the tensile strength change rate is ≤16% after 100℃ mineral oil immersion for 24h, and the tensile strength change rate is ≤25% after 121℃ mineral oil immersion for 18h, solving the problem of oil failure resistance of nuclear power plant cables.

[0043] 2. The present application effectively reduces the processing temperature of polyether ether ketone by blending modification, introduces hyperbranched polyester / maleic anhydride grafted elastomer / nano nucleating agent, enhances the bonding force of the PEEK and elastomer two-phase interface, and induces low-temperature crystallization of polyether ether ketone, finally reducing the processing temperature of modified polyether ether ketone to 200℃, solving the decomposition problem of ethylene-vinyl acetate / polyolefin elastomer resin under high-temperature processing conditions.

[0044] 3. The present application innovatively selects a dual compatibilization system, reacts maleic anhydride groups (MAH) with polyolefin elastomer (POE) and EVM respectively, and forms a "POE-MAH-EVM" bridging structure, solving the problem of poor compatibility between non-polar polyolefin chains in modified polyether ether ketone and polar vinyl acetate units in EVM.

[0045] 4. The present application selects cerium oxide / boron oxide as a radiation-resistant agent, which can effectively absorb and convert radiation energy in a nuclear radiation environment. In addition, boron oxide can act as a binder to repair carbon layer cracks under high-temperature combustion conditions.

[0046] 5. The present application selects an antioxidant / light stabilizer binary compound synergistic system, which has the functions of high-temperature thermal oxidation resistance, medium and low-temperature thermal oxidation resistance, light aging resistance and radiation aging resistance, ensuring that the service life of the material reaches 80 years in an environment of 90℃. DETAILED DESCRIPTION

[0047] The application will be further described in detail in connection with specific examples, but the application is not limited to these examples. In the application, unless otherwise specified, "phr" refers to parts by weight per hundred parts of a mixture composed of modified PEEK, EVM, POE-g-MAH and EVM-g-MAH.

[0048] 1. Base formula: modified PEEK 40-60 parts, EVM 30-50 parts, POE-g-MAH / EVM-g-MAH 10-15 parts, magnesium hydroxide 130-160 parts, radiation-resistant agent 10-15 parts, antioxidant / light stabilizer mixture 4-6 parts, crosslinking agent 2-3 parts.

[0049] 2. The production process of modified PEEK is as follows: (1) Pretreatment: PEEK particles are crushed and ground into powders with a particle size of ≤20 μm; (2) Drying: the PEEK powder in step (1) is dried at a temperature of 150°C for 5h to ensure that the water content is ≤0.01%; (3) Compounding: the dried PEEK powder in step (2) is uniformly premixed with HBP liquid at a mass ratio of 100:(5-10), and the mixture is blended and granulated with POE-g-MAH at a mass ratio of 100:(8-20), high-speed shearing (rotation speed 200-250 rpm) is performed by using a double-screw extruder, the temperature is set to be 195-205°C in the melting section, 185-195°C in the shearing section and 175-185°C in the homogenizing section, an ultrasonic vibrator (frequency 20 kHz) is embedded in the melting section, and 0.5% of nano nucleating agent TiO2 is added in the homogenizing section; (4) Finished product: die cutting and liquid nitrogen spraying treatment (cooling rate ≥50°C / s) are performed to rapidly cool to below 80°C. Finally, modified PEEK with a processing temperature below 200°C is obtained.

[0050] 3. The production process of EVM-g-MAH is as follows, based on the weight of EVM: (1) A three-in-one dehumidifying dryer is used to dry EVM (500HV) at a temperature of 50°C for 2-3h.

[0051] (2) EVM, MAH, DCP, antioxidant, lubricant and styrene are weighed according to the mass ratio, and are premixed in a high-speed mixer for 5-8 minutes.

[0052] (3) Maleic anhydride grafting reaction is carried out by using double screw (length-diameter ratio 40:1) extrusion process, and the product particles are obtained by using a draw bar, water cooling and granulation, and then through boiling bed drying. A vacuum pump is connected to the reaction section to remove the reaction by-products. Temperature parameters: feeding section 120-140°C, melting section 160-180°C, reaction section 180-200°C, homogenization section 170-190°C, and head 150-160°C.

[0053] Example 1 Preparation of a sheath material with a service life of 80 years According to the components and mass proportions in Table 1, the components are weighed and then used to prepare the sheath material: (1) Premixing of additives: The radiation-resistant agent, antioxidant and light stabilizer are weighed according to the mass proportions, and then put into a vertical ribbon mixer for premixing, with a premixing time of 5 min.

[0054] (2) Preparation of B material: The premixed additives and (5-8) phr EVM are mixed and granulated by using a double screw (length-diameter ratio 36:1) mixing and extruding granulator to prepare the B material. Double screw temperature parameters: feeding section 110-120°C, melting section 130-140°C, shear section 140-150°C, homogenization section 130-140°C, and head 130-140°C.

[0055] (3) Preparation of finished product: The modified PEEK, POE-g-MAH, EVM-g-MAH, magnesium hydroxide and the remaining EVM in Table 1 are weighed and mixed with the B material in an internal mixer, and the mixture is discharged when the material temperature reaches 160-170°C. Then, the mixture is subjected to double screw shearing and finally single screw extrusion granulation to obtain the finished product. Double screw (length-diameter ratio 32:1) temperature parameters: feeding section 120-130°C, melting section 110-120°C, shear section 90-100°C, and homogenization section 80-90°C. Single screw temperature parameters: body 120-130°C and head 130-140°C.

[0056] (4) Irradiation treatment: The finished product prepared in step (3) is molded into a sample sheet of a certain thickness by a flat vulcanizing instrument (hot pressing for 15 min and cold pressing for 5 min), and then the sample sheet is subjected to high-energy radiation of 506 kGy by an electron accelerator irradiation device for detection.

[0057] Table 1 Example 2 Preparation of a sheath material with a service life of 80 years According to the components and mass proportions in Table 2, the components are weighed and then used to prepare the sheath material according to the process of Example 1.

[0058] Table 2 Preparation of a sheathing material with a service life of 80 years The components and mass proportions in Table 3 were weighed, and after weighing, the sheathing material was prepared according to the process of Example 1.

[0059] Table 3 Preparation of a sheathing material with a service life of 80 years The components and mass proportions in Table 4 were weighed, and after weighing, the sheathing material was prepared according to the process of Example 1.

[0060] Table 4 Preparation of a sheathing material with a service life of 80 years The components and mass proportions in Table 5 were weighed, and after weighing, the sheathing material was prepared according to the process of Example 1.

[0061] Table 5 Preparation of a sheathing material with a service life of 80 years The components and mass proportions in Table 6 were weighed, and after weighing, the sheathing material was prepared according to the process of Example 1.

[0062] Table 6 Preparation of a sheathing material with a service life of 80 years The components and mass proportions in Table 7 were weighed, and after weighing, the sheathing material was prepared according to the process of Example 1.

[0063] Table 7 Preparation of a sheathing material with a service life of 80 years The components and mass proportions in Table 8 were weighed, and after weighing, the sheathing material was prepared according to the process of Example 1.

[0064] Table 8 Preparation of a sheathing material with a service life of 80 years The components and mass proportions in Table 9 were weighed, and after weighing, the sheathing material was prepared according to the process of Example 1.

[0065] Table 9 Preparation of a sheathing material with a service life of 80 years The components and mass proportions in Table 10 were weighed according to the process of Example 1 to prepare the sheath material.

[0066] Table 10 Preparation of sheath material of Comparative Example 4 The components and mass proportions in Table 11 were weighed according to the process of Example 1 to prepare the sheath material.

[0067] Table 11 Preparation of sheath material of Comparative Example 5 The components and mass proportions in Table 12 were weighed according to the process of Example 1 to prepare the sheath material.

[0068] Table 12 Performance determination of sheath material of Examples 1-7 and Comparative Examples The results are shown in Tables 13 and 14. It can be seen from the test data of Example 1 and Comparative Examples 1 and 5 that, after removing the modified PEEK, the original tensile strength, oil resistance and radiation resistance performance decreased significantly, but the flame retardant performance improved significantly; and after removing the EVM 500HV, the original elongation at break decreased significantly, but the oil resistance and radiation resistance performance improved greatly, which indicates that the modified PEEK can improve the radiation resistance and oil resistance of the material to a certain extent, and it takes advantage of the high-temperature resistance and radiation resistance of the rigid chain of the modified PEEK; and the filling coefficient of EVM 500HV is large, which can accommodate more inorganic filler materials and improve the elongation at break. In addition, the vinyl acetate units in 500HV will decompose to produce carboxylic acid and olefin at high temperature, and these products can further dehydrate and crosslink to form aromatic carbon structure, which provides a stable carbon layer skeleton for combustion and improves the flame retardant performance. Therefore, the use of modified PEEK and EVM in combination has better effect.

[0069] It can be seen from the test data of Example 2 and Comparative Example 2 that, after removing the EVM-g-MAH, the performance of the material has a downward trend, which may be because the modified PEEK non-polar polyolefin chain has poor compatibility with the polar vinyl acetate units in EVM, and after removing the EVM-g-MAH, there are defects between the two-phase interfaces, which leads to the performance decline. Therefore, the use of a dual compatibilization system POE-g-MAH / EVM-g-MAH can obtain better comprehensive performance.

[0070] From the test data of Example 3 and Comparative Example 3, it can be seen that after reducing the radiation resistant agent, the flame retardant performance and radiation resistance of the material are significantly reduced, which may be because the cerium oxide / boron oxide plays a role in nuclear radiation resistance, and in addition, the boron oxide as a binder plays a role in repairing the cracks of the carbon layer during combustion, improving the flame retardant performance.

[0071] From the test data of Example 4, Example 5 and Comparative Example 4, it can be seen that after increasing the filling amount of the flame retardant, the performance of the material has a downward trend except the flame retardant performance, which may be because the large amount of flame retardant makes the interaction force between the polymer chains small, resulting in a decrease in physical properties, and the thermal life evaluation is also inversely affected, reducing the service life; after removing the light stabilizer, the crosslinking degree of the material is improved, but the radiation resistance is reduced, which may be because the light stabilizer can inhibit the crosslinking reaction to a certain extent, and at the same time, it plays a role in inhibiting the secondary crosslinking reaction of nuclear radiation.

[0072] From the thermal life evaluation data of Example 2, Example 6 and Example 7, it can be seen that different amounts of antioxidants have a greater impact on the 90℃ life, and the thermal aging termination time at different temperature points is reduced to varying degrees when the amount of light stabilizer is reduced, and the amount of long-acting high-temperature antioxidant 412S is increased, and the 90℃ thermal life is improved.

[0073] Table 13 Table 14 The above only describes the embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent transformation or direct or indirect application in related technical fields using the content of the present application is also included in the patent protection scope of the present application.

Claims

1. A sheath material with a service life of up to 80 years, characterized in that, The sheath material comprises the following components in parts by weight: 100 parts resin matrix, 130-160 parts flame retardant, 10-15 parts radiation resistant agent, 4-6 parts antioxidant / light stabilizer mixture, and 2-3 parts crosslinking agent; the resin matrix comprises 40-60 parts modified polyetheretherketone, 30-50 parts EVM, and 10-15 parts dual compatibilization system. The modified polyetheretherketone is obtained by blending and modifying polyetheretherketone with hyperbranched polyester, maleic anhydride-grafted polyolefin elastomer and nano-nucleating agent; the dual compatibilization system includes maleic anhydride-grafted polyolefin elastomer and maleic anhydride-grafted ethylene-vinyl acetate copolymer.

2. The sheath material according to claim 1, characterized in that, The grafting rate of the maleic anhydride-grafted ethylene-vinyl acetate copolymer is 0.5-1.5%.

3. The sheath material according to claim 1, characterized in that, The flame retardant includes magnesium hydroxide.

4. The sheath material according to claim 1, characterized in that, The radiation-resistant agent is cerium oxide and / or boron oxide; further, the radiation-resistant agent is cerium oxide and boron oxide in a mass ratio of 1:(1~2).

5. The sheath material according to claim 1, characterized in that, The antioxidant is any one or more of ST-10, ST-9228, ST-300, 412S or ST-626; further, the antioxidant is a mixture of ST-10, ST-9228, 412S and ST-626 or a mixture of ST-10, ST-9228, ST-300 and ST-626 in a mass ratio of (1~2):(1~2):(1~2):

1.

6. The sheath material according to claim 1, characterized in that, The light stabilizer is UV-944 and / or ST-3529.

7. The sheath material according to claim 1, characterized in that, The crosslinking agent is triallyl isocyanurate, triallyl cyanurate, or trimethylolpropane triacrylate / trimethacrylate.

8. A cable for a nuclear power plant, characterized in that, The cable comprises the sheath material described in any one of claims 1 to 7.

9. A method for preparing the sheath material according to any one of claims 1 to 7, characterized in that, The method includes the following steps: (a) Additive premixing stage: Radiation resistant agent, antioxidant and light stabilizer are premixed to form a homogeneous additive mixture; (b) Carrier preparation stage: The additive mixture and a portion of EVM are granulated by twin-screw extrusion to obtain additive masterbatch; (c) Main mixing stage: The modified polyether ether ketone, flame retardant, functionalized elastomer, remaining EVM and the aforementioned additive masterbatch are mixed to the preset phase change temperature and then discharged. (d) Post-processing stage: The main compound product is subjected to twin-screw shear dispersion and single-screw extrusion granulation in sequence.

10. The use of the sheath material according to any one of claims 1 to 7 in the manufacture of cables for nuclear facilities or cables for high-radiation environments.

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