Coaxial Cable for Nuclear Power Generation

Abstract

The present invention relates to a coaxial cable for nuclear power plants. More specifically, it includes an inner conductor disposed at the very center of the cable, an insulating layer formed of a foamed material that is arranged to surround the outer circumference of the inner conductor and forms a plurality of porous cells, and a sheath layer arranged to surround the outer circumference of the insulating layer. The coaxial cable for nuclear power plants is characterized in that the activation energy of the insulating layer is in the range of 2.06 eV to 2.84 eV. Thereby, it is possible to provide a coaxial cable for nuclear power plants that can maintain a certain level of performance even after a defined lifespan has passed.

Description

Technical Field

[0001] The present invention relates to a coaxial cable for nuclear power plants, and more particularly to a coaxial cable for nuclear power plants that can maintain a certain level of performance for application to nuclear power plants.

Background Art

[0002] Among various types of cables, cables for nuclear power plants are used for the purpose of being laid in various facilities in a nuclear power plant to transmit electric power, various control signals, and the like.

[0003] Due to the usage environment where cables for nuclear power plants are continuously exposed to gamma rays, which have high penetration and destructive power among radiation, physical and chemical properties different from those of general cables are required.

[0004] Normally, reliability tests are carried out for cables for nuclear power generation with the idea of long-term operation for decades or more. The containment vessel in which the nuclear reactor operates always maintains a high-temperature atmosphere, and the continuous use temperature reaches 90°C, creating a much harsher temperature atmosphere compared to the atmosphere where general polymer material cables are used.

[0005] Furthermore, the nuclear reactor must be simulated in advance for the loss-of-coolant accident, which is the worst accident. In this regard, when the coolant of the nuclear reactor flows out, it is temporarily exposed to a large amount of radiation, and instantaneously, it is not only exposed to an ultra-high temperature and high-pressure atmosphere, but also must be able to withstand a virtual test in which a large amount of chemical agents are sprayed.

[0006] The important reason for this process is that if the cables connecting various control devices are damaged and cannot withstand a virtual accident, the nuclear reactor will be damaged without being able to proceed with the process of minimizing the accident damage of the nuclear power plant itself, and the worst accident of radioactive leakage to the neighboring area may occur.

[0007] As a result, for cables used in nuclear power plants, radiation resistance, heat resistance, chemical resistance, and long-term reliability are important product design criteria, so the development of cables suitable for nuclear power plants is required.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] In order to solve the above-mentioned problems, the technical problem that the present invention aims to solve is to provide a coaxial cable for nuclear power plants that can maintain communication characteristics and the like even after a specified lifespan by applying an insulator having an activation energy of a certain level or higher to the cable.

[0010] The problems to be solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

Means for Solving the Problems

[0011] As means for solving the above-mentioned technical problems, The present invention provides a coaxial cable for nuclear power plants, which includes an inner conductor disposed at the center of the cable, an insulating layer formed of a foamed material that is disposed to surround the outer periphery of the inner conductor and forms a plurality of porous cells, and a sheath layer disposed to surround the outer periphery of the insulating layer, wherein the activation energy of the insulating layer is in the range of 2.06 eV to 2.84 eV.

[0012] In addition, the present invention provides a coaxial cable for nuclear power plants, characterized in that the foaming degree of the insulating layer is 79% to 93%.

[0013] The present invention also provides a coaxial cable for nuclear power generation, characterized in that the relative permittivity of the insulating layer is in the range of 1.1 to 1.29.

[0014] The present invention also provides a coaxial cable for nuclear power generation, characterized in that the signal propagation speed of the cable is in the range of 88% to 96% compared to the signal propagation speed in air.

[0015] The present invention also provides a coaxial cable for nuclear power generation, further comprising an inner skin layer interposed between the inner conductor and the insulating layer, an outer conductor formed to surround the outer periphery of the insulating layer, and an outer skin layer interposed between the insulating layer and the outer conductor.

[0016] The present invention also provides a coaxial cable for nuclear power generation, characterized in that the insulating layer is any one of high-density polyethylene (HDPE), low-density polyethylene (LDPE), and a mixture of the high-density polyethylene and the low-density polyethylene.

[0017] The present invention also provides a coaxial cable for nuclear power generation, characterized in that the mixing ratio of the mixture of the high-density polyethylene (HDPE) and the low-density polyethylene (LDPE) is in the range of 6:4 to 8:2.

[0018] The present invention also provides a coaxial cable for nuclear power generation, characterized in that the relative permittivity of the high-density polyethylene (HDPE) is 1.99 to 2.69, the melt flow index at 190°C is 6.8 g / 10 min to 9.2 g / 10 min, the relative permittivity of the low-density polyethylene (LDPE) is 1.93 to 2.61, and the melt flow index at 190°C is 5.1 g / 10 min to 6.9 g / 10 min.

[0019] The present invention also provides a coaxial cable for nuclear power generation, characterized in that after the cable has undergone 70 Mrad of radiation aging, the insulation resistance of the cable is 1 MΩ or more.

[0020] The present invention also provides a coaxial cable for nuclear power plants, characterized in that the insulation resistance after accelerating heat aging corresponding to at least 20 years in the cable is 1 MΩ or more.

[0021] The present invention also provides a coaxial cable for nuclear power plants, characterized in that the insulation resistance after conducting a bending test of bending the cable to less than 20 times its diameter and then expanding it again is 1 MΩ or more.

[0022] The present invention also provides a coaxial cable for nuclear power plants, characterized in that the insulation resistance after immersing the cable in water for 1 hour and then applying a voltage of 2.5 kVdc for 5 minutes is 1 MΩ or more.

[0023] The present invention also provides a coaxial cable for nuclear power plants, characterized in that the relative permittivity of the cable maintains a change rate of ±10% compared to a non-aged cable, and the signal propagation speed maintains a change rate of ±10% compared to the non-aged cable.

Advantages of the Invention

[0024] According to the present invention, by applying an insulator having an activation energy above a certain level to the cable, there is an effect of providing a coaxial cable for nuclear power plants that can maintain communication characteristics and the like even after a defined lifespan.

[0025] Also, by forming the insulating layer of the cable with a foamed material, there is an effect of providing a coaxial cable for nuclear power plants that can reduce the permittivity of the insulating layer and improve the propagation speed of the signal transmitted through the cable.

[0026] The effects of the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

Brief Description of the Drawings

[0027] The attached drawings are for explaining the content of the present invention in more detail to those of ordinary skill in the art, and the technical idea of the present invention is not limited thereto.

Figure 1

Figure 2

Figure 3a

Figure 3b

Mode for Carrying Out the Invention

[0028] The above objects, other objects, features, and advantages of the present invention will be easily understood through the following desirable embodiments and the like related to the attached drawings. However, the present invention is not limited to the embodiments described herein and can also be embodied in other forms. Instead, the embodiments introduced herein are provided so that the disclosed content can be thorough and complete, and so that the idea of the present invention can be sufficiently conveyed to those skilled in the art.

[0029] In this specification, when it is mentioned that a certain component is on another component, it means that it can be directly formed on the other component or a third component can be interposed between them. Also, in the drawings and the like, the thickness of components and the like is exaggerated for the effective explanation of the technical content.

[0030] When an element, component, device, or system is referred to as including a component consisting of a program or software, even without an explicit mention, it should be understood that the element, component, device, or system includes the hardware (e.g., memory, CPU, etc.) and other programs or software (e.g., operating system, drivers necessary to drive the hardware, etc.) necessary for the program or software to execute or operate.

[0031] Also, if there is no special mention in the realization of an element (or component), it should be understood that the element (or component) can be realized in any form of software, hardware, or software and hardware.

[0032] Also, the terms used in this specification are for explaining embodiments and the like, and are not intended to limit the present invention. In this specification, the singular form includes the plural form unless otherwise specifically mentioned in the text. The components referred to as "comprises" and / or "comprising" used in the specification do not exclude the presence or addition of one or more other components.

[0033] FIG. 1 is a cross-sectional view of a coaxial cable for nuclear power plants according to a preferred embodiment of the present invention.

[0034] Referring to FIG. 1, a coaxial cable for nuclear power plants according to a preferred embodiment of the present invention will be described. As shown in the figure, the coaxial cable for nuclear power plants includes an inner conductor 10, an insulating layer 20, and a sheath layer 30.

[0035] The inner conductor 10 is located at the very center of the cable and is the part where signals are transmitted. For this purpose, a conductor made of a metal material that facilitates the transmission of high-frequency signals is applied to the inner conductor 10.

[0036] For example, a conductor made of a metal material can be composed of any one of copper, aluminum, iron, and nickel as a single metal, or can be composed of two or more metal alloys. Further, in some cases, it can be in a form in which another metal is plated on one metal, and in the case of an alloy, it is preferably a copper alloy plated with copper or another metal.

[0037] Hypothetically, when the metal material is copper, it is preferable to use an oxygen-free copper wire without an oxygen content. When using an oxygen-free copper wire, there is an advantage that the electrical transmission rate can be improved.

[0038] Further, when the metal material is a copper alloy plated with a different metal, it is preferable to use a tin-plated oxygen-free copper wire or a silver-plated oxygen-free copper wire in which a tin plating layer or a silver plating layer is formed on the outer peripheral surface of the aforementioned oxygen-free copper wire. When forming a tin plating layer or a silver plating layer on the oxygen-free copper wire, oxidation of the conductor can be suppressed and discoloration of the conductor can be prevented.

[0039] On the other hand, the inner conductor 10 can be formed in a hollow shape to improve the flexibility of the cable, and can be formed in various sizes.

[0040] The insulating layer 20 is formed in a form that covers the inner conductor 10 on the outer periphery of the inner conductor 10, and is an element composed of a polymer insulating material. The insulating layer 20 can use any one of low-density polyethylene (LDPE), high-density polyethylene (HDPE), and a mixture of the low-density polyethylene and the high-density polyethylene. Here, the mixing ratio of the high-density polyethylene and the low-density polyethylene (HDPE:LDPE) can be blended in the range of 6:4 to 8:2. Further, the relative permittivity of the high-density polyethylene (HDPE) can be 1.99 to 2.69, the melt flow index at 190°C can be 6.8 g / 10 min to 9.2 g / 10 min, the relative permittivity of the low-density polyethylene (LDPE) can be 1.93 to 2.61, and the melt flow index at 190°C can be 5.1 g / 10 min to 6.9 g / 10 min.

[0041] More specifically, the insulating layer 20 is formed of a foamed material that forms a plurality of porous cells. The smaller the dielectric constant of the insulating layer 20, the higher the propagation speed of the signal transmitted to the cable. At this time, if we want to improve the propagation speed of the signal transmitted through the cable, we must reduce the dielectric constant of the insulating layer 20. By increasing the degree of foaming of the foam and decreasing the foam density, the dielectric constant of the insulating layer 20 can be decreased. Here, the degree of foaming means the ratio of air occupied per unit volume in the foam.

[0042] When the degree of foaming of the insulating layer 20 is high, the relative dielectric constant becomes low and the propagation speed increases. As a result, in a sample with a high relative dielectric constant, the propagation speed of the cable shows a tendency to decrease compared to the propagation speed in air. Also, when the degree of foaming of the insulating layer 20 is too high, the relative dielectric constant becomes low, but then it shows vulnerable characteristics in the accelerated heat aging test and the bending test. That is, when the degree of foaming is too high, the physical stability of the insulating layer 20 decreases and the insulation resistance can be reduced. Therefore, it is necessary to maintain an appropriate degree of foaming. The insulating layer 20 of the coaxial cable for nuclear power plants according to the present invention can be formed in the range of 79% to 93% in terms of its degree of foaming. If the degree of foaming of the insulating layer 20 increases, the relative dielectric constant decreases and the propagation speed increases. However, in this embodiment, the relative dielectric constant of the insulating layer 20 can be in the range of 1.1 to 1.29.

[0043] The sheath layer 30 is formed on the outermost shell of the coaxial cable for nuclear power plants of the present invention and is arranged in a form surrounding the outer circumference of the insulating layer 20. The sheath layer 30 can be formed of various materials according to the situation. For example, it can be formed from a composition containing a polyethylene-based resin or a polyolefin-based resin as a base resin.

[0044] Figure 2 is a cross-sectional view of a coaxial cable for nuclear power plants according to another desirable embodiment of the present invention.

[0045] In FIG. 1, a cross-section of a coaxial cable for nuclear power plants with a simple structure in which an inner conductor 10, an insulating layer 20, and a sheath layer 30 are laminated is illustrated. However, in the present embodiment, a cross-section of a coaxial cable for nuclear power plants further provided with an inner skin layer 40, an outer skin layer 50, and an outer conductor 60 in addition to the inner conductor 10, the insulating layer 20, and the sheath layer 30 is illustrated. Since the inner conductor 10, the insulating layer 20, and the sheath layer 30 are the same as those in the previous embodiment, the description thereof will be omitted.

[0046] The inner skin layer 40 is interposed between the inner conductor 10 and the insulating layer 20 and is a thin film coating layer that increases the interfacial adhesion force. Preferably, the inner skin layer 40 can contain a polymer resin of a material similar to that of the insulating layer 20.

[0047] The inner skin layer 40 can adopt a polymer resin that minimizes the influence of the dielectric properties of the insulating layer 20 and can provide interfacial properties even without self-adhesive properties. When the material of the insulating layer 20 is a polyethylene-based resin, it is preferable to adopt a polyolefin-based resin with excellent compatibility as the polymer resin applied to the inner skin layer 40.

[0048] Here, the polyethylene-based resin can be one single substance selected from high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), and linear low-density polyethylene, or a polymer blend of two or more thereof. The polyolefin-based resin is a polymer blend containing polyethylene, polypropylene, and polyisobutylene.

[0049] The outer skin layer 50 is interposed between the insulating layer 20 and the sheath layer 30 and corresponds to an overfoaming suppression layer that suppresses overfoaming of the insulating layer 20 or cracking characteristics of the foam cells provided in the insulating layer 20.

[0050] When the material of the insulating layer 20 is a polyethylene-based resin, polyethylene, polypropylene, polyethylene terephthalate, or a mixture thereof can be selectively adopted for the outer skin layer 50.

[0051] An external conductor 60 is formed on the outer periphery of the outer skin layer 50. The external conductor 60 serves to prevent the signal flowing through the internal conductor 10 from leaking outside the cable and to shield interference such as electromagnetic waves from the outside. It can be formed of various metal materials. In particular, it can be formed of copper or an alloy containing copper, which is excellent in conductivity and corrosion resistance. Preferably, the external conductor 60 can be formed in a corrugated tube shape having a certain pitch in order to ensure the flexibility of the cable, and can be formed in a cylindrical tube spaced at equal intervals from the internal conductor 10.

[0052] With such a structure, the insulating layer 20 comes to be located between the internal conductor 10 and the external conductor 60, serving to insulate between the internal conductor 10 and the external conductor 60 and to maintain the gap between the internal conductor 10 and the external conductor 60. Also, the characteristic impedance between the internal conductor 10 and the external conductor 60 is formed by the dielectric constant of the insulating layer 20, and the propagation speed of the signal transmitted through the cable can be determined by this characteristic impedance.

[0053] Figures 3a and 3b are graphs for explaining the activation energy of the coaxial cable for nuclear power plants according to a preferred embodiment of the present invention.

[0054] Activation energy refers to the minimum energy required for a chemical reaction to proceed. The smaller the activation energy, the faster the reaction rate, and the higher the activation energy, the slower the reaction rate.

[0055] The activation energy of the coaxial cable for nuclear power plants according to the present invention can be calculated according to the standard of ASTM E1641-07, and either one of the Flynn-wall-ozawa technique and the Kissinger technique can be used. Although the activation energies calculated by the Flynn-wall-ozawa technique and the Kissinger technique are different in their interpretation methods, there is no significant difference in the results, so either one of the two techniques can be used without special restrictions.

[0056] In one example, when calculating the activation energy using the Flynn-wall-ozawa technique, assuming the initial mass is 100 and the final mass is 0, the activation energy is calculated based on the temperature at which the reference change rate is reached. At this time, it is assumed that the decomposition is carried out by first-order kinetics, and the activation energy is calculated based on the initial reaction regardless of the reaction order.

[0057] In still another example, when calculating the activation energy using the Kissinger technique, the activation energy is calculated based on the temperature at the point where the slope is the steepest in the graph where the material is decomposed by heating and the mass decreases. Here, when reactions of various orders occur, it is determined based on the reaction with the highest reaction rate.

[0058] Figure 3a is a graph showing the test results obtained after performing the thermal decomposition progress operation using TGA. When performing the thermal decomposition progress using TGA, the heating rate is changed within the range of 1 °C / min to 10 °C / min. Although the heating rate is changed at least 4 times, in this embodiment, the heating rates are changed to 1 °C / min, 2 °C / min, 5 °C / min, and 10 °C / min.

[0059] In the illustrated graph, the x-axis is temperature and the y-axis is mass loss. This graph shows that the material is decomposed by heating and the mass decreases.

[0060] When calculating the activation energy for the coaxial cable used in this nuclear power plant with reference to such a graph, if the Kissinger technique is applied, the activation energy can be calculated based on the temperature at the point with the steepest slope on the graph. If reactions of various orders occur, it is determined based on the reaction with the highest reaction rate.

[0061] Figure 3b is for calculating the activation energy by applying the Flynn-wall-ozawa technique. In the graph, the x-axis is the temperature and the y-axis is the rate of change (Log Heating Rate) with respect to the heating rate. The activation energy is calculated based on the slope of the graph illustrated in this embodiment.

[0062] The activation energy of the coaxial cable used in this nuclear power plant can be calculated in the manner mentioned above, and the insulating layer 20 of the coaxial cable used in this nuclear power plant is made such that its activation energy is in the range of 2.06 eV to 2.84 eV.

[0063] When the activation energy is low, less than 2.06 eV, the cable characteristics after accelerated aging tend to change more significantly compared to the non-aged cable. That is, after accelerated aging, the relative permittivity and the rate of change of the signal propagation speed may be high, and the original communication characteristics may not be maintained. On the other hand, when the activation energy is high, exceeding 2.84 eV, the foaming degree may be low. This is because a higher activation energy requires more energy during the foaming process. Therefore, to increase the foaming degree, it is necessary to lower the linear velocity or work at a higher temperature, which reduces the work efficiency. Due to the low foaming degree, there are problems such as a high relative permittivity and a low cable propagation speed compared to the propagation speed in air.

[0064] The activation energy can be changed depending on the type, mixing ratio, physical properties, etc. of the composition forming the insulating layer 20. According to an embodiment of the present invention, for the insulating layer 20, the mixing ratio of high-density polyethylene and low-density polyethylene (HDPE:LDPE) can be blended in the range of 6:4 to 8:2. The relative permittivity of the high-density polyethylene (HDPE) can be 1.99 to 2.69, the melt flow index at 190°C can be 6.8 g / 10 min to 9.2 g / 10 min, the relative permittivity of the low-density polyethylene (LDPE) can be 1.93 to 2.61, and the melt flow index at 190°C can be 5.1 g / 10 min to 6.9 g / 10 min.

[0065] In order to evaluate the characteristics of the coaxial cable for nuclear power generation according to the present invention, the mixing ratio of low-density polyethylene and high-density polyethylene of the insulating layer 20 constituting the cable and the range of their respective molecular weights were fabricated to be different from each other, and the cable characteristics were measured through non-aged cable characteristic tests and aged cable characteristic tests, and these are shown in Table 1 below.

[0066]

Table 1

[0067] The items listed in the characteristic test column in Table 1 above are as follows. A is the HDPE:LDPE ratio, B is the foaming degree, C is the activation energy (eV) of the insulating layer, D is the relative permittivity, E is the signal propagation speed ratio of the cable with respect to air, F is the insulation resistance (500 Vdc, 1 minute standard), G is the radiation aging test (70 Mrad standard), H is the insulation resistance (500 Vdc, 1 minute standard), I is the accelerated thermal aging test (20-year life, 70°C standard), J is the insulation resistance (500 Vdc, 1 minute standard), K is the bending test (20D standard), L is the insulation resistance (500 Vdc, 1 minute standard), M is the immersion withstand voltage test (immersed for 1 hour or more, 2.5 kVdc, and 5 minute standard), N is the relative permittivity change rate with respect to the non-aged cable, and O corresponds to the signal propagation speed change rate with respect to the non-aged cable.

[0068] As shown in Table 1 above, the applicant measured the non-aged cable characteristics and aged cable characteristics for eight samples, namely #1 to #8, with different mixing ratios of HDPE and LDPE and different molecular weight ranges for each of HDPE and LDPE. The foaming degree of the insulating layer 20 is to be included within the range of 79% to 93%.

[0069] The aged cable characteristics were measured for the same cable samples as those during the non-aged cable characteristics test. For the same samples as those for the characteristic test, a radiation aging test was primarily conducted, then an accelerated thermal aging test was conducted secondarily, and finally, the results of a bending test were measured data.

[0070] More specifically, after conducting a radiation aging test on samples #1 to #8, the insulation resistance was measured. After conducting an accelerated thermal aging test on the samples that had undergone the radiation aging test, the insulation resistance was measured. After conducting a bending test on the samples that had undergone the radiation aging test and the accelerated thermal aging test, the insulation resistance, the withstand voltage test under water immersion, the change rate of relative permittivity, and the change rate of signal propagation speed were measured.

[0071] The HDPE within the insulating layer 20 serves as the structure of the foamed insulation. Also, the higher the LDPE content within the insulating layer 20, the higher the tendency of the foaming degree to be. When the foaming degree is high, the relative permittivity becomes low and the propagation speed increases. As a result, in samples with a high relative permittivity, the propagation speed of the cable shows a tendency to decrease compared to the propagation speed in air.

[0072] However, when the foaming degree is too high, the relative permittivity becomes low, but it may become vulnerable in subsequent accelerated thermal aging tests and bending tests. That is, when the foaming degree is too high, the physical stability decreases. Consequently, when the foaming degree is too high, the insulation resistance relatively decreases.

[0073] When the activation energy is high (2.06 eV or higher), the changes in relative permittivity and communication characteristics, which are the characteristics after aging, tend to be low. Therefore, Samples #4 to #8 having an activation energy of 2.06 eV or higher show a low change rate in communication characteristics after accelerated aging. On the other hand, Samples #1 to #3 with a low activation energy of less than 2.06 eV show a high change in characteristics after aging.

[0074] In the case of Sample #2 with an activation energy of 2.11 eV, which is a level higher than 2.06 eV, conversely, the communication characteristics after aging decrease. This is because due to the high degree of foaming, the structure of the foam was damaged during the bending test process after accelerated thermal aging.

[0075] Comparing Samples #5 and #6, although the ratio of HDPE to LDPE is the same for both, Sample #6 with a high activation energy shows a phenomenon of low foaming degree. This is because the activation energy of the insulating layer 20 is high and more energy is required during the foaming process. To increase the foaming degree, it is necessary to lower the linear velocity or work at a higher temperature.

[0076] When the activation energy is extremely high, exceeding 2.83 eV as in Samples #6 to #8, the foaming degree is low. To increase the foaming degree, more energy is required, and it is necessary to lower the linear velocity or work at a higher temperature. This leads to a decrease in work efficiency, and due to the low foaming degree, there are problems such as a high relative permittivity and a low cable propagation speed compared to the propagation speed in air.

[0077] The results that satisfy all the tests were confirmed to be Samples #4 and #5. The activation energy of Sample #4 is 2.06 eV, and the activation energy of Sample #5 is 2.83 eV. Based on the experimental results of other samples, it was confirmed that when outside the activation energy ranges of Samples #4 and #5, the final results are unsatisfactory.

[0078] As a result, even after undergoing 70 Mrad of radiation aging, the cable has an insulation resistance of 1 MΩ or more. Also, even after undergoing accelerated thermal aging equivalent to at least 20 years, the insulation resistance remains 1 MΩ or more. Further, even after conducting a bending test where the cable is bent to less than 20 times its diameter and then expanded again, no abnormality occurs in the appearance. Additionally, even when the cable is immersed in tap water at room temperature for 1 hour and then a voltage of 2.5 kVdc is applied for 5 minutes, the insulation is not destroyed, and the subsequent insulation resistance appears as 1 MΩ or more. Moreover, it was confirmed that the relative permittivity of the aged cable maintains a change rate of ±10% compared to the non-aged cable without aging progress, and the signal propagation speed also maintains a change rate of ±10% compared to the non-aged cable.

[0079] In this way, through various tests, it was proven that the coaxial cable for nuclear power plants according to the present invention can maintain a certain level of performance even after passing the defined lifespan.

[0080] Those skilled in the art within the technical field to which the present invention pertains will be able to understand that the present invention can be implemented in other specific forms without changing its technical idea and essential features. Therefore, it must be understood that the embodiments described above are exemplary in all aspects and not restrictive. The scope of the present invention is represented by the claims described later rather than the above detailed description, and it should be interpreted that any changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts are included in the scope of the present invention.

Explanation of Reference Numerals

[0081] 10 Inner Conductor 20 Insulation Layer 30 Sheath Layer 40 Inner Skin Layer 50 Outer Skin Layer 60 Outer Conductor

Claims

1. An inner conductor disposed at the very center of the cable, an insulating layer formed of a foamed material that is disposed to surround the outer periphery of the inner conductor and forms a plurality of porous cells, a sheath layer disposed to surround the outer periphery of the insulating layer, comprising: A coaxial cable for nuclear power plants, wherein the activation energy of the insulating layer is in the range of 2.06 eV to 2.84 eV.

2. The coaxial cable for nuclear power plants according to claim 1, wherein the degree of foaming of the insulating layer is 79% to 93%.

3. The coaxial cable for nuclear power plants according to claim 1, wherein the relative permittivity of the insulating layer is in the range of 1.1 to 1.

29.

4. The coaxial cable for nuclear power plants according to claim 1, wherein the signal propagation speed of the cable is in the range of 88% to 96% compared to the signal propagation speed in air.

5. An inner skin layer interposed between the inner conductor and the insulating layer, an outer conductor formed to surround the outer periphery of the insulating layer, an outer skin layer interposed between the insulating layer and the outer conductor, The coaxial cable for nuclear power plants according to claim 1, further comprising:

6. The coaxial cable for nuclear power plants according to claim 1, wherein the insulating layer is any one of high-density polyethylene (HDPE), low-density polyethylene (LDPE), and a mixture of the high-density polyethylene and the low-density polyethylene.

7. The coaxial cable for nuclear power plants according to claim 6, wherein the mixing ratio of the mixture of the high-density polyethylene (HDPE) and the low-density polyethylene (LDPE) is in the range of 6:4 to 8:

2.

8. The relative permittivity of the high-density polyethylene (HDPE) is 1.99 to 2.69, and the melt flow index at 190 ° C is 6.8 g / 10 min to 9.2 g / 10 min. The coaxial cable for nuclear power plants according to claim 7, wherein the relative permittivity of the low-density polyethylene (LDPE) is 1.93 to 2.61, and the melt flow index at 190 ° C is 5.1 g / 10 min to 6.9 g / 10 min.

9. The coaxial cable for nuclear power plants according to claim 1, wherein after the cable has undergone 70 Mrad of radiation aging, the insulation resistance of the cable is 1 MΩ or more.

10. The coaxial cable for nuclear power plants according to claim 9, characterized in that the insulation resistance after accelerating heat aging corresponding to at least 20 years in the cable is 1 MΩ or more.

11. The coaxial cable for nuclear power plants according to claim 10, characterized in that the insulation resistance after conducting a bending test in which the cable is bent to less than 20 times its diameter and then expanded again is 1 MΩ or more.

12. The coaxial cable for nuclear power plants according to claim 11, characterized in that the insulation resistance after immersing the cable in water for 1 hour and then applying a voltage of 2.5 kVdc for 5 minutes is 1 MΩ or more.

13. The coaxial cable for nuclear power plants according to claim 12, characterized in that the relative permittivity of the cable maintains a change rate of ±10% compared to a non-aged cable, and the signal propagation speed maintains a change rate of ±10% compared to the non-aged cable.

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