Irradiation cross-linked polyolefin insulating material for 80-year-life nuclear safety grade cable and preparation method of radiation cross-linked polyolefin insulating material

Abstract

The invention discloses an irradiation crosslinking polyolefin insulating material for a 80-year-life nuclear safety grade cable and a preparation method thereof, and belongs to the field of insulating materials. The low-density polyethylene, the ethylene-vinyl acetate and the ethylene propylene diene monomer are combined according to a specific proportion, and under the synergistic effect of an antioxidant system, a copper damage resistant system and a radiation resistant system, the radiation cross-linked polyolefin insulating material has excellent electrical properties and also has excellent aging resistance, radiation resistance, copper damage resistance and other properties, and the service life of the radiation cross-linked polyolefin insulating material is prolonged. Particularly, the hot service life at 90 DEG C reaches more than 80 years. The irradiation cross-linked polyolefin insulating material provided by the invention is highly adaptive to a fourth-generation nuclear power station, and provides powerful support for stable operation of the nuclear power station.

Description

Technical Field

[0001] The present invention relates to the field of insulating materials, and in particular provides a radiation-crosslinked polyolefin insulating material for 80-year life nuclear safety-grade cables and a preparation method thereof. Background Art

[0002] Nuclear power plants require enormous construction investments and long operating cycles, typically with a design lifespan of 60 years or even longer. To ensure safe and stable power supply throughout the plant's entire operational lifespan, the cables within them must also have a correspondingly long lifespan to reduce the safety risks and economic costs associated with cable aging and replacement. Furthermore, nuclear cables must operate stably and reliably under both normal operation and extreme operating conditions, with a near-zero failure tolerance. To ensure nuclear power plant safety, these cables are required to have a service life of 60-80 years. With continuous advances in materials science and manufacturing processes, the design lifespan of nuclear cables is showing signs of further improvement, and 80-year lifespan nuclear cables are currently in the development stage.

[0003] First, irradiation-crosslinked polyolefin insulation used in nuclear safety-grade cables with an 80-year lifespan must demonstrate an 80-year thermal lifespan at 90°C, verified using the Arrhenius model. Currently, few polyolefin materials meet this requirement, and only a few mainstream irradiation-crosslinked polyolefin insulation materials meet the 60-year requirement. Second, the radiation resistance of nuclear cable materials is a key indicator for safe operation in the extreme environments of nuclear power plants. Ionizing radiation in nuclear power plants accelerates oxidative degradation of materials, shortening the service life of nuclear cables. Currently, in a gamma-ray environment with a cumulative dose of ≥2500 kGy (equivalent to 40 years of radiation exposure within the nuclear island), the material's elongation at break must be retained at >70%. Conventional polyolefins experience brittle fracture at 1000 kGy. In direct contact with metal conductors, metal ions catalyze oxidative degradation, shortening the insulation's service life. Conventional antioxidants are susceptible to ineffectiveness under high-temperature irradiation. Therefore, a nuclear-grade cable that meets the 80-year thermal lifespan requirement at 90°C must simultaneously demonstrate radiation resistance, metal resistance, and aging resistance. Summary of the Invention

[0004]

Technical Issues

[0005]

Technical solution

[0006] In one embodiment of the present invention, the resin matrix is ​​composed of low-density polyethylene (LDPE), ethylene vinyl acetate (EVA) and ethylene propylene diene monomer (EPDM).

[0007] In one embodiment of the present invention, the mass ratio of LDPE, EVA and EPDM is (30-50): (30-50): (10-20).

[0008] In one embodiment of the present invention, the melt index of the LDPE is 2-3 g / 10 min.

[0009] In one embodiment of the present invention, the melt index of the EVA is 1.8-2.8 g / 10min.

[0010] In one embodiment of the present invention, the EPDM rubber has a Mooney viscosity of 20-30 MU and an ethylene content of 50-70%.

[0011] In one embodiment of the present invention, the antioxidant is selected from one or more of hindered polyphenol antioxidants, thioester antioxidants and phosphite antioxidants.

[0012] In one embodiment of the present invention, the antioxidant is prepared by compounding a hindered polyphenol antioxidant, a thioester antioxidant and a phosphite antioxidant.

[0013] In one embodiment of the present invention, the weight ratio of the hindered polyphenol antioxidant, the thioester antioxidant and the phosphite antioxidant is 2:2:1.

[0014] In one embodiment of the present invention, the hindered polyphenol antioxidant is selected from antioxidant 330, antioxidant 3125 or antioxidant 3224.

[0015] In one embodiment of the present invention, the thioester antioxidant includes antioxidant 412S, antioxidant DLTP or antioxidant 300.

[0016] In one embodiment of the present invention, the phosphite antioxidant includes antioxidant 626 or antioxidant 636.

[0017] In one embodiment of the present invention, the anti-copper agent is a compound of MDA-5 and a benzotriazole rust remover.

[0018] In one embodiment of the present invention, the weight ratio of the MDA-5 to the benzotriazole rust remover is (1-5):1.

[0019] In one embodiment of the present invention, the benzotriazole rust remover is benzotriazole.

[0020] In one embodiment of the present invention, the cross-linking sensitizer is triallyl isocyanurate (TAIC).

[0021] A second object of the present invention is to provide a cable comprising the radiation-crosslinked polyolefin insulation material.

[0022] The third object of the present invention is to provide a method for preparing the radiation cross-linked polyolefin insulation material, which comprises the following steps: weighing the raw materials in sequence, stirring them uniformly, and then preparing the radiation cross-linked polyolefin insulation material through mixing, filtering and pelletizing steps.

[0023] In one embodiment of the present invention, the mixing is performed by a reciprocating extruder, the filtration is performed through a 100-200 mesh filter, and the pelletizing is performed underwater.

[0024] In one embodiment of the present invention, pelletizing is followed by a drying step.

[0025] In one embodiment of the present invention, the temperature sections of the mixing are: feeding section 90-100°C, melting and plasticizing section 160-180°C, homogenizing section and exhaust section 150-170°C, filter 150-170°C, and die head 140-160°C.

[0026] A fourth object of the present invention is to provide use of the radiation-crosslinked polyolefin insulation material in the manufacture of cables for nuclear facilities or cables for radiation environments.

[0027] Resin: The resin should be made of polyethylene with good mechanical properties, excellent electrical insulation properties and easy extrusion processing as the main base material. Low-density polyethylene (LDPE) with high degradation activation energy is preferred, which can easily increase the thermal life of the material; adding some ethylene vinyl acetate (EVA), ethylene butyl acrylate (EBA), ethylene propylene diene monomer (EPDM) and other materials containing polar groups can improve the compatibility between the resin and additives, increase the addition amount of antioxidants, anti-copper agents and other additives without precipitation, and on the other hand, increase the activation energy of the material and extend the material life.

[0028] Antioxidant system: Hindered polyphenol antioxidants with little effect on radiation cross-linking efficiency are selected as the main antioxidants, and thioester antioxidants and phosphite antioxidants are compounded as auxiliary antioxidants. Phosphites are preferably antioxidants with anti-copper effects such as 626 and 636. The ratio of main antioxidant: thioester antioxidant: phosphite antioxidant is 2:2:1. The material has high activation energy, and the aging termination time at various temperature points (180℃, 165℃, 150℃, 1350℃) meets the requirements.

[0029] Radiation-resistant system: Select the highly efficient light stabilizer 2020. Light stabilizer 2020 has the dual functions of antioxidant and light stabilizer, and has excellent synergistic effect with antioxidants to improve the termination time of thermal oxidative aging of materials.

[0030] Anti-copper damage system: A combination of the hindered phenol anti-copper agent MDA-5 and a benzotriazole rust remover is used in a ratio of (1-5):1; preferably, a ratio of 3:1. MDA-5 has both antioxidant and copper resistance properties. The hindered phenol structure captures free radicals and decomposes hydroperoxides, improving the material's antioxidant properties. The hydrazide structure chelates metal ions, preventing or slowing their catalytic degradation, particularly copper ions. The benzotriazole rust remover forms an isolation film on the surface of metal conductors, preventing metal ions from entering the insulating material.

[0031] Crosslinking sensitization system: Select a sensitizer and add an appropriate proportion of TAIC. The number of sensitizer functional groups and the amount of sensitizer added directly affect the material's radiation crosslinking efficiency. A large amount of sensitizer increases efficiency, but residual sensitizer easily precipitates and affects the material's electrical insulation and mechanical properties. Too little addition results in low efficiency and, consequently, low radiation crosslinking efficiency.

[0032] Beneficial effects 1. The present invention uses LDPE, EVA and EPDM as resin matrices to prepare radiation cross-linked polyolefin insulation materials. The resin matrices are combined in a specific ratio, and under the synergistic effect of the antioxidant system, the copper damage resistance system and the radiation resistance system, the radiation cross-linked polyolefin insulation materials of the present invention can have excellent electrical properties, with a resistivity of 5*10 14 The dielectric strength reaches above 33MV / m, and the insulation performance is good. At the same time, it has excellent aging resistance, radiation resistance, metal ion resistance and other properties. The thermal life at 90℃ can reach more than 80 years.

[0033] 2. The present invention compounds the antioxidant system, the copper damage resistance system and the radiation resistance system, further explores the addition ratio, synergistically improves the efficiency of the additives, and increases the thermal life of the material at 90°C. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the present invention is not limited to these embodiments.

[0035] The implementation conditions used in the examples can be further adjusted according to specific requirements. The implementation conditions not specified are usually those used in routine experiments.

[0036] Unless otherwise specified in the following examples, all raw materials were purchased from commercial sources or prepared by conventional methods in the art.

[0037] Formula composition: 30-50 parts of LDPE, 30-50 parts of EVA, 10-20 parts of EPDM; 2-3 parts of antioxidant, including main antioxidant: thioester antioxidant: phosphite antioxidant = 2:2:1, 1-2 parts of anti-copper agent, including MDA-5: benzotriazole rust remover = 3:1, 1-2 parts of radiation resistance additive, and 0.5-1 part of cross-linking sensitizer.

[0038] Example 1 In this embodiment, a radiation-crosslinked polyolefin insulation material for a nuclear safety-grade cable with an 80-year service life is provided. The raw materials for preparing the insulation material include the following components in parts by weight: Table 1 The preparation process of polyolefin insulation material is as follows: 1. First, accurately weigh the base resin according to the proportion and stir it evenly with an automatic mixer for use; weigh the antioxidant according to the proportion and stir it evenly with a mixer to make a composite antioxidant; weigh the anti-copper agent according to the proportion and stir it evenly with a mixer to make a composite anti-copper agent.

[0039] 2. The base resin, composite antioxidant, composite anti-copper agent, radiation-resistant additive (light stabilizer), and crosslinking agent are accurately weighed using a loss-in-weight scale and then injected into a reciprocating extruder for mixing. The mixture is filtered, pelletized underwater, and air-dried to produce an 80-year lifespan radiation-crosslinked polyolefin insulation material for nuclear safety-grade cables. The temperature sections of the reciprocating extruder are: feeding section 100°C, melt-plasticizing section 170°C, homogenizing section and exhaust section 160°C, filter 160°C, and die head 150°C.

[0040] The insulation material in Example 1 was subjected to a performance test, and the performance values ​​are shown in Table 11.

[0041] Example 2 In this embodiment, an 80-year lifespan radiation-crosslinked polyolefin insulation material for nuclear safety-grade cables is provided. The raw materials for its preparation include the following components in parts by weight. Compared with Example 1, the addition ratio of various resins is adjusted: Table 2 The preparation method is the same as that of Example 1.

[0042] The insulation material in Example 2 was subjected to a performance test, and the performance values ​​are shown in Table 11.

[0043] Example 3 In this embodiment, an 80-year lifespan radiation-crosslinked polyolefin insulation material for nuclear safety-grade cables is provided. The raw materials for its preparation include the following components in parts by weight. Compared with Example 1, the addition ratio of various resins is adjusted: Table 3 The preparation method is the same as that of Example 1.

[0044] The insulation material in Example 3 was subjected to performance testing, and the performance values ​​are shown in Table 11.

[0045] Comparative Example 1 In this embodiment, an insulating material is provided. The raw materials for preparing the insulating material include the following components in parts by weight. The difference from Example 1 is that the EVA in the resin is replaced with EVM 40L-03.

[0046] Table 4 The preparation method is the same as that of Example 1.

[0047] The insulation material in Comparative Example 1 was subjected to performance testing, and the performance values ​​are shown in Table 11.

[0048] Comparative Example 2 In this embodiment, an insulating material is provided. The raw materials for preparing the insulating material include the following components in parts by weight. The difference from Example 1 is that the main antioxidant is replaced with 1076, and the auxiliary antioxidant is replaced with DLTP and 168.

[0049] Table 5 The preparation method is the same as that of Example 1.

[0050] The insulation material in Comparative Example 2 was subjected to performance testing, and the performance values ​​are shown in Table 11.

[0051] Comparative Example 3 In this embodiment, an insulating material is provided. The raw materials for preparing the insulating material include the following components in parts by weight. The difference from Example 1 is that the light stabilizer 2020 is not added, and the added part is replaced by an antioxidant.

[0052] Table 6 The preparation method is the same as that of Example 1.

[0053] The insulation material in Comparative Example 3 was subjected to performance testing, and the performance values ​​are shown in Table 11.

[0054] Comparative Example 4 In this embodiment, an insulating material is provided. The raw materials for preparing the insulating material include the following components in parts by weight. The difference from Example 1 is that no anti-copper agent is added, and the added part is replaced by an antioxidant.

[0055] Table 7 The preparation method is the same as that of Example 1.

[0056] The insulation material in Comparative Example 4 was subjected to performance testing, and the performance values ​​are shown in Table 11.

[0057] Comparative Example 5 In this embodiment, an insulating material is provided. The raw materials for preparing the insulating material include the following components in parts by weight. The difference from the embodiment 1 is that only MDA-5 is added as the copper resist.

[0058] Table 8 The preparation method is the same as that of Example 1.

[0059] The insulation material in Comparative Example 5 was subjected to performance testing, and the performance values ​​are shown in Table 11.

[0060] Comparative Example 6 In this embodiment, an insulating material is provided. The raw materials for preparing the insulating material include the following components in parts by weight. The difference from the embodiment 1 is that only BTA is added as the copper-resistant agent.

[0061] Table 9 The preparation method is the same as that of Example 1.

[0062] The insulation material in Comparative Example 6 was subjected to performance testing, and the performance values ​​are shown in Table 11.

[0063] Comparative Example 7 In this embodiment, an insulating material is provided. The raw materials for preparing the insulating material include the following components in parts by weight. The difference from Example 1 is that the anti-copper agent is replaced by sodium tripolyphosphate (STPP) and MB.

[0064] Table 10 The preparation method is the same as that of Example 1.

[0065] The insulation material in Comparative Example 7 was subjected to performance testing, and the performance values ​​are shown in Table 11.

[0066] Test Case The volume resistivity of irradiated cross-linked polyolefin insulation for 80-year nuclear safety-grade cables was evaluated according to GB / T 31838.2-2019.

[0067] The dielectric strength of irradiated cross-linked polyolefin insulation for 80-year nuclear safety-grade cables was evaluated according to GB / T 1408.1-2016.

[0068] The thermal expansion of irradiated cross-linked polyolefin insulation materials for 80-year nuclear safety-grade cables was evaluated according to GB / T 2951.21-2008.

[0069] The thermal aging of irradiated cross-linked polyolefin insulation materials used in 80-year nuclear safety-grade cables was evaluated according to GB / T 1040.3 and GB / T 2951.12 standards.

[0070] The 90°C thermal life of irradiated cross-linked polyolefin insulation materials used in 80-year nuclear safety-grade cables was evaluated according to GB / T 11026.1.

[0071] The copper resistance of irradiated cross-linked polyolefin insulation for 80-year nuclear safety-grade cables was evaluated according to GB / T 12706.1.

[0072] The radiation resistance of irradiated cross-linked polyolefin insulation materials for 80-year nuclear safety-grade cables was evaluated according to GB / T 26168.2-2010.

[0073] The xenon lamp aging test of irradiated cross-linked polyolefin insulation for 80-year nuclear safety-grade cables was evaluated according to GB / T 12527-2008.

[0074] Evaluate the withstand voltage test of irradiated cross-linked polyolefin insulation for 80-year nuclear safety-grade cables according to GB / T 1408.1.

[0075] Evaluate the post-radiation withstand voltage test of irradiated cross-linked polyolefin insulation materials for 80-year nuclear safety-grade cables according to GB / T 22577.

[0076] The test results are shown in Table 11.

[0077] Table 11 As can be seen from Table 11, the insulating material prepared by the combined formula of the resin, composite antioxidant, composite anti-copper agent, radiation-resistant auxiliary agent (light stabilizer) and cross-linking agent provided by the present invention exhibits excellent performance in terms of aging resistance, metal ion resistance, and radiation resistance. If the anti-copper agent or light stabilizer is not added, the aging resistance and radiation resistance of the final insulating material will be significantly affected, thereby adversely affecting the 90°C thermal life. In the selection of anti-copper agents, if only MDA-5 or BTA is added, or if MDA-5 and BTA are replaced with STPP and MB, the tensile strength retention rate and elongation at break retention rate are significantly affected, and the maximum can only reach 58%, which is far lower than the 90% and 92% in Example 1. It can be seen that in the technical solution of the present invention, the antioxidant system, the anti-copper damage system and the radiation resistance system work together with each other, with significant synergy, providing strong support for the preparation of irradiated cross-linked polyolefin insulation materials for nuclear safety-grade cables with an 80-year lifespan.

[0078] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention specification, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A radiation cross-linked polyolefin insulation material, characterized in that: The invention is prepared from raw materials comprising the following components: in parts by weight, 100 parts of a resin matrix, 2-3 parts of an antioxidant, 1-2 parts of an anti-copper agent, 1-2 parts of a radiation-resistant additive, and 0.5-1 parts of a cross-linking sensitizer; wherein the resin matrix is ​​composed of low-density polyethylene, ethylene-vinyl acetate, and ethylene propylene diene monomer rubber in a mass ratio of (30-50): (30-50): (10-20).

2. The radiation cross-linked polyolefin insulation material according to claim 1, characterized in that: The antioxidant is selected from one or more of hindered polyphenol antioxidants, thioester antioxidants and phosphite antioxidants.

3. The radiation cross-linked polyolefin insulation material according to claim 2, characterized in that: The weight ratio of the hindered polyphenol antioxidant, the thioester antioxidant and the phosphite antioxidant is 2:2:

1.

4. The radiation cross-linked polyolefin insulation material according to claim 3 or 4, characterized in that: The hindered polyphenol antioxidant is selected from antioxidant 330, antioxidant 3125 or antioxidant 3224; the thioester antioxidant includes antioxidant 412S, antioxidant DLTP or antioxidant 300; and the phosphite antioxidant includes antioxidant 626 or antioxidant 636.

5. The radiation cross-linked polyolefin insulation material according to claim 1, characterized in that: The anti-copper agent comprises: MDA-5 and benzotriazole rust remover.

6. The radiation cross-linked polyolefin insulation material according to claim 5, characterized in that: The mass ratio of MDA-5 and benzotriazole rust remover is (1-5):

1.

7. The radiation cross-linked polyolefin insulation material according to claim 1, characterized in that: The cross-linking sensitizer is triallyl isocyanurate.

8. A cable, characterized in that: The cable comprises the radiation-crosslinked polyolefin insulation material according to any one of claims 1 to 7.

9. A method for preparing the radiation-crosslinked polyolefin insulation material according to any one of claims 1 to 7, characterized in that: The method comprises the steps of: (a) Weigh the raw materials according to the ratio; (b) stirring the raw materials separately and then mixing them; (c) kneading, filtering and pelletizing the mixed raw materials in sequence; (d) drying the pelletized product to obtain a radiation-crosslinked polyolefin insulation material.

10. Use of the radiation-crosslinked polyolefin insulation material according to any one of claims 1 to 7 in the manufacture of cables for nuclear facilities or cables for radiation environments.

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