Cable for nuclear power plant

Abstract

To provide a nuclear power plant cable capable of retaining insulation performance even when SA occurred.SOLUTION: A nuclear power plant cable used as wiring connected to equipment that can operate even when a severe accident occurs, comprising a conductor formed in a long shape with electrical conductivity, and an insulation formed using a cross-linked copolymer made of tetrafluoroethylene and polypropylene that surrounds the conductor. The insulation has an insulation resistance value of 1×106 Ω or higher in a steam exposure test, in which it is first exposed to an environment of 235°C for 10 minutes and then exposed to an environment of 200°C for 168 hours.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electric wire for a nuclear power plant and a cable for a nuclear power plant. [Background technology]

[0002] Radiation-resistant cables and the like have been proposed as electric wires and cables (hereinafter also referred to as "cables, etc.") to be used in nuclear power plants, nuclear fuel reprocessing facilities, and the like (hereinafter also referred to as "nuclear power plants, etc.") (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 4-325701 Summary of the Invention [Problem to be solved by the invention]

[0004] Cables used in nuclear power plants and other facilities are required to have insulation performance in addition to the radiation resistance mentioned above. Cables used in nuclear power plants are required to maintain the desired insulation performance even in the event of an accident during the nuclear power plant's commercial operation. Specifically, they are required to meet the safety standards set by the government.

[0005] In serious accidents that far exceed the scale anticipated at the time of the design of a nuclear power plant, such as the one that occurred at the Fukushima Daiichi Nuclear Power Plant during the Great East Japan Earthquake in 2011, where reactor fuel was severely damaged, severe conditions arose that exceeded the safety standards previously set by the government (hereinafter referred to as the old safety standards).

[0006] Therefore, the Nuclear Regulation Authority and other organizations have established new safety standards (hereinafter referred to as the new safety standards) that stipulate that cables and other items will maintain the desired insulation performance even in the event of a serious accident like the one that occurred at the Fukushima Daiichi Nuclear Power Plant or a similar serious accident (hereinafter referred to as a severe accident or SA).

[0007] The new safety standards require that cables, etc., maintain the insulation resistance value specified in the standards after environmental testing (described below) and withstand a desired voltage withstand test. An example of the environmental testing is a steam exposure test (in the case of a boiling water reactor) in which cables, etc., are exposed to a 235°C atmosphere for 10 minutes and then to a 200°C atmosphere for 168 hours (7 days). Examples of the desired voltage withstand test include tests specified by the Japanese Industrial Standards (hereinafter also referred to as JIS), the Electrical Appliance and Material Safety Act, the Institute of Electrical and Electronics Engineers (IEEE), and other standards.

[0008] Nuclear power plants that are operating or being restarted use equipment (e.g., water level gauges, resistance temperature detectors, thermocouples, radiation monitors, etc.) that can operate in the accident atmosphere inside the reactor containment vessel even in the event of a severe accident and are necessary to respond to such an accident. Cables and other wiring materials that are connected to such equipment and have the functions of supplying power to the equipment and transmitting signals for monitoring and controlling the equipment are required to meet the insulation performance specified in the new safety standards. However, there was a problem in that conventional cables and other wiring materials for nuclear power plants, even if they met the insulation performance specified in the old safety standards, did not meet the insulation performance specified in the new safety standards.

[0009] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an electric wire for a nuclear power plant that can maintain its insulating performance even when SA occurs. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides the following means. An electric wire for a nuclear power plant according to a first aspect of the present invention is an electric wire for a nuclear power plant used as wiring material connected to equipment that can operate even in the event of a severe accident, the electric wire comprising: a conductive conductor formed in a long shape; and an insulator that covers the conductor and is formed using a cross-linked copolymer made of tetrafluoroethylene and polypropylene, wherein the insulator has an insulation resistance of 1×10 Ω or more during a steam exposure test in which the insulator is exposed to an atmosphere at 235°C for 10 minutes and then to an atmosphere at 200°C for 168 hours.

[0011] A cable for use in a nuclear power plant according to a second aspect of the present invention is a cable used as wiring material connected to equipment that can operate even in the event of a severe accident, and is provided with a plurality of electric wires each composed of a long, electrically conductive conductor and an insulator that is formed using a polymer containing tetrafluoroethylene as a component and that covers the conductor, and a sheath that covers the plurality of electric wires.

[0012] According to the electric wire for nuclear power plant according to the first aspect of the present invention and the cable for nuclear power plant according to the second aspect, by using an insulator formed of a polymer containing tetrafluoroethylene as a component, the electric wire or cable can have an insulation resistance value of 1×10 as specified by the standard during and after an exposure test whose conditions are determined based on SA. 6 Ω and can withstand the desired withstand voltage test. [Effects of the Invention]

[0013] The electric wire for use in a nuclear power plant of the present invention has an effect of being able to maintain its insulating performance even when SA occurs, by using an insulator formed from a polymer containing tetrafluoroethylene as a component. [Brief explanation of the drawings]

[0014] [Figure 1]1 is a cross-sectional view of a configuration of an electric wire according to an embodiment of the present invention. [Figure 2] 1 is a cross-sectional view of a cable configuration according to an embodiment of the present invention; [Figure 3] FIG. 10 is a cross-sectional view of a cable configuration according to another embodiment of the present invention. [Figure 4] 1 is a cross-sectional view of a conventional cable configuration. [Figure 5] FIG. 1 is a cross-sectional view of another configuration of a conventional cable. [Figure 6] 3 is a table illustrating evaluation results for the cable 100 of FIG. 2. [Figure 7] 4 is a table illustrating the evaluation results of the cable 100. [Figure 8] 5 is a table illustrating the evaluation results of the cable 100. DETAILED DESCRIPTION OF THE INVENTION

[0015] An electric wire 10 for a nuclear power plant (hereinafter also simply referred to as "electric wire 10") and a cable for a nuclear power plant (hereinafter also simply referred to as "cable 100") according to one embodiment of the present invention will be described with reference to Figs. 1 to 8. The electric wire 10 and the cable 100 of this embodiment are intended for use in a radiation environment, particularly in a nuclear power plant. Note that the electric wire 10 and the cable 100 may also be used in other radiation environments, such as in a fast breeder reactor, a nuclear fuel reprocessing facility, and a particle acceleration facility.

[0016] Fig. 1 is a cross-sectional view illustrating the configuration of an electric wire 10 according to one embodiment of the present invention. As shown in Fig. 1, the electric wire 10 includes a conductor 11, a separator 12, and an insulator 13.

[0017] The conductor 11 is a long, electrically conductive member. In this embodiment, the conductor 11 is formed using a tin-plated annealed copper wire. The conductor 11 may be formed from a known electrically conductive material such as a pure copper wire. The conductor 11 may also be formed by twisting a plurality of wires (for example, tin-plated annealed copper wires) together by concentric twisting or bunch twisting.

[0018] The separator 12 is a layered member provided between the conductor 11 and the insulator 13. The separator 12 is a member formed from a known material used in electric wires. In this embodiment, an example in which the separator 12 is provided on the electric wire 10 will be described. Note that the separator 12 does not have to be provided depending on the cross-sectional area of ​​the conductor 11. In that case, the electric wire 10 has a structure in which the conductor 11 and the insulator 13 are in contact with each other.

[0019] The insulator 13 is an insulating member that covers the periphery of the conductor 11. The insulator 13 is made of a polymer containing tetrafluoroethylene as a component. More specifically, the insulator 13 is made of a cross-linked copolymer of tetrafluoroethylene and polyolefin, as shown in the following chemical formula: X in the following chemical formula is polyolefin. Examples of polyolefins include polyethylene and polypropylene. An example of a cross-linked copolymer in which X is polypropylene is Flonlex (registered trademark: Hitachi Metals, Ltd.). In this embodiment, the insulator 13 is described as being formed using a cross-linked copolymer as shown in the following chemical formula, in which the polyolefin is polypropylene.

[0020] [ka]

[0021] In this embodiment, the insulator 13 is formed as a single layer. However, the insulator 13 may have a multi-layer structure.

[0022] 2 is a cross-sectional view illustrating the configuration of a cable 100 according to one embodiment of the present invention. As shown in FIG. 2, the cable 100 includes a stranded wire 101, a tape member 103, and a sheath 105.

[0023] The stranded wire 101 is a two-core stranded wire in which two electric wires 10, each having a conductor 11, a separator 12, and an insulator 13, are twisted together with an insert 102. A string made of rubber or the like can be used as the insert 102. The number of electric wires 10 included in the stranded wire may be two, three, or more. Furthermore, when the conductor 11 is formed by twisting together a plurality of wires, the twisting direction of the stranded wire 101 is preferably the same as the twisting direction of the plurality of wires that make up the conductor 11. In this case, the twisting pitch of the stranded wire 101 is preferably larger than the twisting pitch of the plurality of wires.

[0024] The tape member 103 is a member that is disposed around the stranded wire 101 and is wound around the outer circumferential surface of the stranded wire 101. A member made of a known material can be used as the tape member 103. In addition, it is preferable that the tape member 103 is wound in the same twisting direction as the twisting direction of the stranded wire 101.

[0025] The sheath 105 is a component disposed around the tape member 103 and covers the stranded wires 101 and the tape member 103. In this embodiment, the sheath 105 is formed using a chloroprene rubber composition containing an antioxidant and chloroprene rubber. The antioxidant contained in the chloroprene rubber composition is one that is resistant to water absorption during a steam exposure test and does not cause the insulation resistance measured in the steam exposure test to fall below the judgment threshold due to the water absorption.

[0026] In this embodiment, the sheath 105 is formed of a single layer. However, the sheath 105 may have a multi-layer structure.

[0027] Fig. 3 is a cross-sectional view of the configuration of a cable 100A according to another embodiment of the present invention. The cable 100A shown in Fig. 3 differs from the cable 100 shown in Fig. 2 in that the sheath 105A is formed using a cross-linked copolymer of tetrafluoroethylene and polyolefin, as shown in the chemical formula below. The other components of the cable 100A are the same as those of the cable 100 shown in Fig. 2. In this embodiment, the sheath 105A is formed using a copolymer of the cross-linked copolymer of tetrafluoroethylene and polyolefin, as shown in the chemical formula below, in which the polyolefin is polypropylene.

[0028] [ka]

[0029] In the above chemical formula, X is a polyolefin, such as polyethylene and polypropylene.

[0030] In cable 100A, sheath 105A is made of a polymer containing tetrafluoroethylene as a component (i.e., a cross-linked copolymer represented by the above chemical formula), which reduces the amount of gas (e.g., chlorine gas) generated from the sheath when the cable burns, compared to sheath 105 made of a chloroprene rubber composition. Reducing gases such as chlorine gas can prevent corrosion of metals constituting devices connected to cable 100A.

[0031] Next, a description will be given of the evaluation results for the cable 100 having the above configuration. For comparison of the evaluation results, the configurations of a cable 100X having a conventional configuration and a cable 100Y are shown in Figures 4 and 5, respectively.

[0032] As shown in FIG. 4, the cable 100X includes a stranded wire 101X, a tape member 103, and a sheath 105X. The stranded wire 101X is a two-core stranded wire in which two electric wires 10X, each having a conductor 11 and an insulator 13X, are twisted together with an interposer 102.

[0033] The insulator 13X is an insulating member that covers the periphery of the conductor 11. In this embodiment, the insulator 13X is formed using a composition containing a flame retardant and ethylene propylene rubber. The filler 102 may be a string made of rubber or the like.

[0034] The sheath 105X is a member disposed around the tape member 103, and is a member that covers the stranded wires 101X and the tape member 103. In this embodiment, the description will be given by applying it to an example in which the sheath 105X is formed using chloroprene rubber.

[0035] As shown in FIG. 5, the cable 100Y includes a stranded wire 101Y, a tape member 103, and a sheath 105. The stranded wire 101Y is a two-core stranded wire in which two electric wires 10Y, each having a conductor 11 and an insulator 13Y, are twisted together with an interposer 102.

[0036] The insulator 13Y is an insulating member that covers the periphery of the conductor 11. In this embodiment, the insulator 13Y is formed using an ethylene propylene rubber composition containing an antioxidant, a flame retardant, and ethylene propylene rubber. The antioxidant contained in the ethylene propylene rubber composition is one that is resistant to water absorption during a steam exposure test and does not cause the insulation resistance measured in the steam exposure test to fall below the judgment threshold due to the water absorption. The filler 102 can be a string made of rubber or the like.

[0037] In the evaluation of the environmental resistance test, first, the cables 100, 100X, and 100Y (hereinafter also referred to as "cables, etc.") are subjected to aging degradation and radiation degradation.

[0038] In this embodiment, a 5m long cable 100 was subjected to heat of 100°C and gamma rays of 100 Gy / h simultaneously, and an accelerated test was performed based on the Arrhenius equation (Arrhenius law) at a normal operating temperature of 66°C, resulting in a product equivalent to 40 years of deterioration that had been subjected to aging and radiation deterioration equivalent to 40 years of deterioration.

[0039] In addition, for the comparative cables 100X and 100Y, which were 5 m long, accelerated tests were conducted under the same conditions as for cable 100, and products equivalent to 40 years of deterioration were obtained by subjecting them to aging and radiation deterioration equivalent to 40 years of deterioration.

[0040] After aging and radiation degradation, the cables are exposed to a 235°C atmosphere for 10 minutes, and then to a 200°C atmosphere for 168 hours (7 days) in a steam exposure test (for boiling water reactors). The insulation resistance of the cables is measured during and after the steam exposure test. A voltage withstand test is also conducted after the steam exposure test.

[0041] If all insulation resistance measurements and voltage withstand test results are good or pass, the cable is deemed capable of carrying 600V, 3A. In other words, it is deemed to meet the new safety standards even in the event of a severe accident. If even one test is defective or fails, the cable is deemed unable to carry 600V, 3A.

[0042] Here, we use 1×10 as an index to evaluate whether the new safety standards are met. 6 Ω (1MΩ) was used as the judgment threshold for the insulation resistance measurement value. The withstand voltage test used conditions specified in JIS C3621, IEEE-383, and the Electrical Appliance and Material Safety Act (hereinafter referred to as "Den-an Act").

[0043] Regarding the insulation resistance judgment threshold, in this evaluation, when the length of the cable laid inside the reactor containment vessel is 100m, based on the insulation resistance (0.1MΩ) of the cable that is considered to enable the equipment connected to the cable to operate when an SA occurs, if the insulation resistance when the cable is 5m long is at least 1MΩ, it is evaluated that the equipment connected to a 50m long cable can be considered to be able to operate even when an SA occurs.

[0044] Additionally, the following voltage withstand tests were conducted to evaluate compliance with the new safety standards. In the voltage withstand test based on JIS C3621, the voltage is quickly increased to a test voltage of 1500V and an evaluation is made to see if it can withstand for one minute. In the voltage withstand test based on IEEE-383, the voltage is quickly increased to a test voltage of 2560V or 3000V and an evaluation is made to see if it can withstand for five minutes. In the test voltage based on the DEN-AN Act, the voltage was quickly increased to 3000V for Cable 100 and an evaluation is made to see if it can withstand for one minute.

[0045] 6 is a table illustrating the evaluation results of the cable 100 having the above-described configuration. The cable 100, even in a product equivalent to 40 years of deterioration, had an insulation resistance measurement value of 1×10 6 It was judged to be good (passed) as it maintained a resistance of Ω (1MΩ) or more.

[0046] Furthermore, the withstand voltage test was judged to be good (passed) in both the tests based on the Safety Act and the IEEE standards. The test voltage for cable 100 is 3000V in both the tests based on the Safety Act and the IEEE standards. Based on the above, it was judged that cable 100 was capable of carrying 600V, 3A during and after the steam exposure test, even if it was equivalent to 40 years of deterioration.

[0047] Cable 100A is obtained by replacing sheath 105 of cable 100 with sheath 105A. Cable 100A is considered to have higher resistance than cable 100 because sheath 105A has higher heat resistance and radiation resistance than sheath 105, and it is determined that cable 100A is capable of carrying a current of 600 V and 3 A during and after the steam exposure test, even if it is equivalent to 40 years of deterioration.

[0048] The 40-year deterioration equivalent product (without sheath) in Figure 6 is the cable 100 without the sheath 105. Since there is no sheath 105, it is considered to be equivalent to the electric wire 10. This 40-year deterioration equivalent product (without sheath) was subjected to accelerated testing under the same conditions as the cable 100, and was given aging and radiation degradation equivalent to 40 years of deterioration, making it a 40-year deterioration equivalent product.

[0049] For wire 10, the insulation resistance measured during and after the steam exposure test was 1 x 10 6 It is considered to be good (passed) as it maintains a resistance of Ω or more. Furthermore, in the withstand voltage test, it is considered to be good in both tests based on the Denan Law and IEEE standards.

[0050] From the above, it is considered that the electric wire 10 is capable of carrying a current of 600 V and 3 A during and after the steam exposure test, even when the electric wire 10 is equivalent to 40 years of deterioration.

[0051] Fig. 7 is a table illustrating the evaluation results for the cable 100X having the above configuration. Fig. 8 is a table illustrating the evaluation results for the cable 100Y having the above configuration.

[0052] As shown in Figure 7, Cable 100X, equivalent to a 40-year aging product, had an insulation resistance value of 0.25 MΩ (less than the judgment threshold) during the steam exposure test. It was also judged as failing (failed) in the JIS-based voltage withstand test. The test voltage used for Cable 100X in the JIS-based voltage withstand test is 1500 V. In the IEEE-based voltage withstand test shown in Figure 7, the test voltage is 2560 V. However, because the JIS-based voltage withstand test resulted in a fail when a test voltage of 1500 V was applied, the IEEE-based voltage withstand test was not conducted. Therefore, the word "not conducted" is shown in Figure 7.

[0053] Based on the above, it was determined that Cable 100X was unable to carry a current of 600V and 3A during and after the steam exposure test, even if it had deteriorated for 40 years.

[0054] As shown in Figure 8, the insulation resistance value of Cable 100Y during the steam exposure test was 0.25 MΩ (less than the judgment threshold) for a product equivalent to 40 years of aging. It was also judged to be good in the withstand voltage tests based on JIS and IEEE. The test voltage for Cable 100X was 1500 V for the withstand voltage test based on JIS, and 2660 V for the withstand voltage test based on IEEE.

[0055] From the above, it was determined that cable 100Y was unable to carry a current of 600V and 3A during and after the steam exposure test, even if it was equivalent to 40 years of deterioration.

[0056] According to the electric wire 10, cable 100, and cable 100A having the above configuration, by using the insulator 13 formed of a polymer containing tetrafluoroethylene as a component (particularly, a cross-linked copolymer represented by the above chemical formula, in which the polyolefin is made of polypropylene), the electric wire 10, cable 100, and cable 100A can maintain the insulation resistance value specified by the standard after an exposure test and can withstand the desired voltage resistance test.

[0057] By forming sheath 105A of cable 100A from a polymer containing tetrafluoroethylene as a component (particularly, a cross-linked copolymer represented by the above chemical formula in which the polyolefin is polypropylene), cable 100A becomes more likely to retain the insulation resistance value specified by the standard after exposure testing, and is more likely to withstand the desired voltage resistance test. [Explanation of symbols]

[0058] 10...Nuclear power plant electric wire, 11...Conductor, 13...Insulator, 100,100A...Nuclear power plant cable, 105,105A...Sheath

Claims

[Claim 1] An electric wire for a nuclear power plant used as a wiring material connected to equipment that can operate even when a severe accident occurs, a conductive conductor formed in an elongated shape; an insulator formed using a cross-linked copolymer composed of tetrafluoroethylene and polypropylene and covering the conductor; is established, The insulator had an insulation resistance of 1×10 or less during a steam exposure test in which it was exposed to an atmosphere at 235° C. for 10 minutes and then to an atmosphere at 200° C. for 168 hours. ６ is greater than or equal to Ω, Electric wires for nuclear power plants.

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