JP2018054515A - Concrete cask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a concrete cask capable of preventing occurrence of stress corrosion crack (SCC) even when a cooling period of spent fuel becomes an extended period.SOLUTION: A concrete cask 10 comprises: a metallic canister 2 in which spent fuel is stored inside thereof in a sealed state; a concrete container body 1 in which the canister 2 is held inside; and a cooling passage 3 arranged between an inner peripheral surface of the container body 1 and an outer peripheral surface of the canister 2 in which air cooling the canister 2 is passed therethrough. An induction heating coil 11 heating surface of the canister 2 by energization to suppress stress corrosion crack is arranged at at least one of the cooling passage 3, an upper cooling space 6 or a lower cooling space 7 connected to the cooling passage 3, and the container body 1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a concrete cask.

  A dedicated container for storing or transporting spent nuclear fuel taken out of the nuclear reactor (hereinafter referred to as spent fuel) is called a cask. As the type of this cask, the spent fuel is contained in a very thick metal cylinder in a sealed state, so-called metal cask, and the spent fuel is placed in a metal container called a canister that is thinner than the metal cylinder. There is a so-called concrete cask which is housed in a sealed state and the canister is housed in a thick cylindrical concrete container body. As a material for the metal cylinder of the metal cask or the canister of the concrete cask, a rust-resistant metal such as stainless steel is used.

  In the concrete cask, since the canister is housed in a concrete container body, the metal thickness of the canister can be made much thinner than the metal thickness of the metal cask, and the amount of metal used can be greatly reduced. Therefore, it is possible to reduce the manufacturing cost of the entire concrete cask including the container body made of concrete and the canister as compared with the metal cask. Concrete casks are disclosed in, for example, Patent Documents 1 and 2.

  Since spent fuel generates decay heat, in a concrete cask, in order to suppress an excessive temperature rise due to decay heat, the inner peripheral surface of the container body 101 and the canister 102 are simplified as shown in FIGS. An air introduction path 104 leading to the lower end portion of the cooling passage 103 and an air exhaust path 105 leading to the upper end portion of the cooling passage 103 are arranged in a state having a gap formed by a substantially cylindrical cooling passage 103 between the outer peripheral surface. However, the container body 101 is provided so as to penetrate in the radial direction. Then, after the cooling air is introduced into the lower end portion of the cooling passage 103 through the air introduction passage 104, it is heated upward by decay heat released from the canister 102 (that is, while absorbing this decay heat) upward. It naturally circulates and is discharged from an air discharge path 105 connected to the upper end of the cooling passage 103.

  15 and 16, the air introduction path 104 and the air discharge path 105 are provided with a bent portion or the like in the middle, and radiation is transmitted through the air introduction path 104 and the air discharge path 105. It is configured not to leak (or to be difficult to leak). 15 and 16, 104 a is an air inlet, 105 a is an air outlet, and 101 a is a lid of the container body 101.

  FIG. 17 shows the relationship between the storage period of spent fuel (fuel rods) and the calorific value. Specifically, per fuel per cooling period (year) after the reactor is shut down. The calorific value (kW / body) is shown. As shown in FIG. 17, when the cooling period is extremely short, the amount of heat generated from the spent fuel is large, but thereafter, the amount of heat generated from the spent fuel is rapidly reduced.

JP 2001-141883 A JP 2007-108052 A

  By the way, when the concrete cask is stored in a seawater atmosphere in the coastal area and the vicinity thereof, air containing salty seawater is introduced into the cooling passage 103 of the concrete cask. In an environment where the air introduced into the cooling passage 103 contains salt and is dew-condensed on the surface of the canister 102 and the humidity is high, the salt is dissolved in the moisture of the moisture and dissolved chloride ions. As a result, rust and corrosion may occur in the canister 102 and stress corrosion cracking (SCC) may occur.

  That is, as shown in FIG. 17, when the spent fuel cooling period is still short and is several years (for example, within 5 years), the calorific value of the spent fuel is large, and the surface temperature of the canister 102 is Since it is high and dry, chloride ions are not generated and, therefore, stress corrosion cracking does not occur. However, when the spent fuel cooling period becomes relatively long, for example, when nearly 10 years have passed, the amount of heat generated from the spent fuel becomes small, so that the surface temperature of the canister 102 becomes low and condensation occurs. Humidity increases and chloride ions are generated on the surface of the canister 102, which may cause stress corrosion cracking (SCC).

  An object of the present invention is to provide a concrete cask capable of suppressing the occurrence of stress corrosion cracking (SCC) even when the spent fuel is cooled for a long period of time.

  In order to solve the above-described problems, the present invention provides a metal canister in which spent fuel is accommodated, a concrete container body that accommodates the canister, an inner peripheral surface of the container body, and an outer periphery of the canister. An induction heating coil for suppressing stress corrosion cracking by heating the surface of the canister by being energized. The cooling passage, the cooling space (upper cooling space or lower cooling space) connected to the cooling passage, and the container main body are provided at least in part.

  With this configuration, since the induction heating coil is provided in at least a part of the cooling passage, the cooling space connected to the cooling passage, and the container body, the induction heating coil is used when the calorific value of the spent fuel is reduced. By supplying current to the canister, it is possible to prevent the surface temperature of the canister from lowering and the air in the space between the container body and the canister from condensing or becoming humid in this area. Even when the air contains salt, it is possible to suppress the occurrence of stress corrosion cracking due to the generation of chloride ions on the surface of the canister.

  The induction heating coil is preferably provided in the cooling passage or the inner periphery of the container body. According to this configuration, by energizing the induction heating coil, the outer peripheral surface of the canister facing the cooling passage is heated, and it is possible to prevent the air from condensing or becoming humid in this location, As a result, even when the air introduced into the container body contains salt, it is possible to suppress the occurrence of stress corrosion cracking due to the generation of chloride ions on the outer peripheral surface of the canister.

  Moreover, you may provide an induction heating coil in the upper cooling space between the upper surface part of a canister, and the cover part inner side of a container main body, or the cover part of a container main body. According to this configuration, by energizing the induction heating coil, it is possible to prevent the upper surface of the canister from being heated, thereby preventing air from condensing or humid in this location, and thus the container body. Even when the air introduced into the inside contains salt, it is possible to suppress the occurrence of stress corrosion cracking due to the generation of chloride ions on the upper surface of the canister.

  Moreover, you may provide an induction heating coil in the lower cooling space between the bottom face part of a canister and the bottom face part inside a container main body, or the bottom face part of a container main body. According to this configuration, by energizing the induction heating coil, it is possible to prevent the bottom surface of the canister from being heated and air from condensing or becoming humid at this location, and thus the container body. Even when the air introduced into the inside contains salt, it is possible to suppress the occurrence of stress corrosion cracking due to the generation of chloride ions on the bottom surface of the canister.

  Further, the induction heating coil may be embedded in the container body. In this case, the induction heating coil is protected by the container body, and it is possible to prevent the salty air from being exposed to the induction heating coil in contact with the induction heating coil, and without inhibiting the flow of cooling air by the induction heating coil. Thus, the cooling performance can be maintained well. Further, there is no need to provide a mounting member for fixing or supporting the induction heating coil at a predetermined position.

  In addition, a temperature detection sensor that detects the temperature of the surface portion of the canister and a control unit to which the temperature detection sensor is connected are provided, and the control unit causes the temperature of the surface portion of the canister to cause stress corrosion cracking. In this case, it is preferable that the induction heating coil is energized. According to this configuration, the induction heating coil is not energized when the temperature is not lowered to a temperature at which stress corrosion cracking occurs on the surface of the canister. Therefore, when the decay heat is relatively large, it is introduced into the container body. The generated air is not indirectly heated by the induction heating coil, and the decay heat emitted from the canister can be satisfactorily absorbed by the air introduced into the container body. On the other hand, when the temperature at which the stress corrosion crack is likely to occur in the surface portion of the canister is reached, the induction heating coil is energized to suppress the stress corrosion cracking.

  According to the present invention, the induction heating coil that suppresses stress corrosion cracking by heating the surface of the canister by energization is provided in at least a part of the cooling passage, the cooling space connected to the cooling passage, and the container body. Even when the calorific value of the spent fuel is reduced, it is possible to prevent the humidity of the canister from increasing due to low surface temperature of the canister and condensation of the cooling air, and chloride ions are generated on the surface of the canister. As a result, the occurrence of stress corrosion cracking can be suppressed, and as a result, the reliability of the concrete cask can be improved. Further, according to the present invention, Joule heat is generated by the eddy current inside the surface portion of the canister and heat is generated from the inside, so that heating can be performed more efficiently and quickly than when heat is generated by the resistance of the conductive wire.

  In addition, an induction heating coil is provided in the cooling passage or in the inner peripheral portion of the container body, and by energizing the induction heating coil, the outer peripheral surface of the canister can be heated, and chloride ions are generated on the outer peripheral surface of the canister. It is possible to suppress the occurrence of stress corrosion cracking.

  In addition, an induction heating coil is provided in the upper cooling space between the upper surface of the canister and the inside of the lid of the container body or the lid of the container body, and by energizing the induction heating coil, the surface of the upper surface of the canister is It can heat and can suppress that a chloride ion generate | occur | produces on the upper-surface part surface of a canister, and produces a stress corrosion crack.

  In addition, an induction heating coil is provided in the lower cooling space between the bottom surface of the canister and the inside of the bottom surface of the container body or the bottom surface of the container body, and by energizing the induction heating coil, the surface of the bottom surface of the canister is It can heat and can suppress that a chloride ion generate | occur | produces on the surface of the bottom face part of a canister, and produces a stress corrosion crack.

  Moreover, since the induction heating coil is covered with a concrete container body by embedding the induction heating coil in the container body, it is possible to prevent the air containing salt from seawater from being exposed to direct contact with the induction heating coil. Damage to the induction heating coil due to salinity can be minimized. Furthermore, the cooling performance can be maintained well without hindering the flow of the cooling air in the cooling passage by the induction heating coil. Further, it is not necessary to provide a mounting member for fixing or supporting the induction heating coil at a predetermined position, and it is not necessary to consider deterioration of the mounting member. Further, for example, even when the canister is taken out from the container main body for inspection or the like, the canister or the like can be prevented from coming into contact with the induction heating coil and damaged, and as a result, the reliability of the concrete cask can be improved.

  In addition, a temperature detection sensor that detects the temperature of the surface portion of the canister and a control unit are provided, and the induction heating coil is energized when the control unit reaches a temperature at which stress corrosion cracking may occur in the surface portion of the canister. By configuring as described above, when the temperature does not drop to a temperature at which stress corrosion cracking occurs in the surface portion of the canister, the induction heating coil is not energized, so the decay heat from the canister is introduced into the container body. It can be absorbed well by air. On the other hand, when the temperature at which the stress corrosion crack is likely to occur in the surface portion of the canister is reached, the induction heating coil is energized to suppress the stress corrosion cracking.

It is front sectional drawing of the concrete cask which concerns on embodiment of this invention. It is a partial notch perspective view of the concrete cask. It is a plane sectional view of the concrete cask. It is a plane sectional view (modification 1) of the concrete cask. It is a plane sectional view (modification 2) of the concrete cask. It is a plane sectional view (modification 3) of the concrete cask. It is a plane sectional view (modification 4) of the concrete cask. It is a plane sectional view (modification 5) of the concrete cask. It is principal part front sectional drawing of the concrete cask which concerns on other embodiment of this invention. It is principal part plane sectional drawing of the concrete cask. It is principal part front sectional drawing (modification 6) of the concrete cask. It is principal part front sectional drawing of the concrete cask which concerns on other embodiment of this invention. It is principal part plane sectional drawing of the concrete cask. It is principal part front sectional drawing (modification 7) of the concrete cask. It is a partial notch perspective view of the conventional concrete cask. It is front sectional drawing of the conventional concrete cask. It is a figure which shows the emitted-heat amount (kW / body) per fuel with respect to the cooling period after the furnace stop of a concrete cask.

Hereinafter, a concrete cask according to an embodiment of the present invention will be described with reference to the drawings.
1 and 2 denotes a concrete cask according to the embodiment (first embodiment) of the present invention. The concrete cask 10 includes a metal cylindrical canister 2 in which spent fuel (spent nuclear fuel) is housed in a sealed state, and a concrete cylindrical container body 1 in which the canister 2 is housed. A cooling passage 3 to be described later. As the metal material of the canister 2, a rust-resistant metal material such as stainless steel is used.

  Since the spent fuel stored in the canister 2 in a sealed state generates decay heat, the concrete cask 10 has an inner circumference surface of the container body 1 and an outer circumference of the canister 2 in order to suppress an excessive temperature rise due to the decay heat. A substantially cylindrical cooling passage 3 is provided between the surface and the surface. Also, a plurality of air introduction passages 4 leading to the lower end portion of the cooling passage 3 and air discharge passages 5 leading to the upper end portion of the cooling passage 3 are provided through the container body 1 in the radial direction (radial direction). The cooling air introduced into the lower end portion of the cooling passage 3 through the air introduction passage 4 is warmed by the decay heat from the canister 2 (that is, the decay heat from the canister 2 is absorbed to cool the canister 2). While being naturally circulated upward and discharged from the air discharge passage 5 connected to the upper end of the cooling passage 3 to the outside of the concrete cask 10 or the like.

  In the canister 2, spent fuel (spent nuclear fuel) is accommodated in a main body 2 a having a bottomed cylindrical shape and an upper surface opened, and thereafter, the lid 2 b is fixed to the main body 2 a by welding or the like. The inside is hermetically sealed. For example, the main body 2a is manufactured by bending a rectangular sheet metal, welding the curved ends to form a cylindrical peripheral surface, and welding and joining the bottom surface to the cylindrical portion. The lid 2b is often composed of an outer ring-shaped part and a central disk part, and the outer ring-shaped part and the central disk part are often fixed together by welding or the like, but is not limited thereto. 2 and 2c in FIG. 1 and FIG. 2 are the outer periphery welding parts provided in the outer peripheral surface of the canister 2 so that it may extend substantially linearly along the up-down direction, 2d joins the main-body part 2a and the cover part 2b of the canister 2 It is an upper surface welded part.

  In addition, as shown in FIG. 1, the air introduction path 4 and the air discharge path 5 are provided with bent portions or the like in the middle, and the radiation from the canister 2 leaks through the air introduction path 4 and the air discharge path 5. It is configured not to be (or difficult to leak). Moreover, in FIG. 1, 1a is the cover part of the container main body 1, 4a is an air inlet, 5a is an air discharge port. Further, 6 is an upper cooling space provided between the upper surface portion of the canister 2 and the inside of the lid portion of the container body 1 and connected to the upper end portion of the cooling passage 3, and 7 is a bottom surface portion of the canister 2 and a bottom surface portion of the container body 1. A lower cooling space 8 provided between the inside and the lower end of the cooling passage 3 is placed on the bottom surface of the container main body 1 to support the canister 2 from below. In addition, it is good also as a structure which supports the canister 2 directly from the lower part in the bottom face part of the container main body 1, without providing the canister support body 8. FIG.

  The concrete cask 10 is provided with an induction heating coil 11 that energizes the surface of the canister 2 to suppress stress corrosion cracking. In the concrete cask 10 shown in FIG. 1, the induction heating coil 11 is wound around the outer periphery of the canister 2 (but is not in direct contact with the outer peripheral surface of the canister 2). Arranged in the area.

  The induction heating coil 11 is connected to a power source (AC power source) 13 via a control unit 12 provided outside, and the control unit 12 has a temperature detection composed of a thermocouple for detecting the temperature of the surface portion of the canister 2. A sensor 14 is also connected. Then, the control unit 12 has a temperature at which stress corrosion cracking (SCC) may occur in the surface portion of the canister 2 (for example, moisture in the air becomes water droplets (liquid) in the surface portion of the canister 2. When the temperature reaches a temperature (100 ° C. or less), the induction heating coil 11 is energized. The temperature detection sensor 14 is preferably attached to the lower part (such as the vicinity of the lower end part) or the bottom part of the canister 2 where the air introduced into the concrete cask 10 first comes into contact and is likely to be at the lowest temperature. Instead, the temperature of the air circulating in the cooling passage 3 (for example, the lower part or the lower end of the cooling passage 3) is detected, and this temperature is equal to or lower than the temperature at which stress corrosion cracking occurs in the surface portion of the canister 2. Then, the induction heating coil 11 may be energized (so-called feedback control).

  For example, as shown in FIG. 3, the induction heating coil 11 is wound around a mounting member 15 that is hard to be magnetized, and the induction heating coil 11 is disposed in the region of the cooling passage 3. The member 15 may be attached to the inner peripheral surface of the container body 1 (or the outer peripheral surface of the canister 2 as shown in FIG. 4). Alternatively, as shown in FIG. 5 and FIG. 6, for example, it functions as a spacer and is magnetized between the outer peripheral surface of the canister 2 and the inner peripheral surface of the container body 1 (that is, the cooling passage 3). The induction heating coil 11 may be assembled to the difficult mounting member 16 (16A, 16B), and the mounting member 16 may be disposed in the cooling passage 3. As shown in FIG. 5, the mounting member 16 has a substantially U-shaped cross section in plan view (a so-called eco-hat shape in which adjacent portions open alternately on the inner peripheral side and the outer peripheral side). The member 16A may be used, or the mounting member 16B having a so-called I-shaped cross section as shown in FIG. 6 may be used, but is not limited thereto.

  Further, instead of providing the induction heating coil 11 in the region of the cooling passage 3, the induction heating coil 11 may be embedded in the inner peripheral portion of the container body 1. In this case, as shown in FIG. 7, it is more preferable that the induction heating coil 11 (specifically, the coiled portion of the induction heating coil 11) is embedded so as not to be exposed from the inner peripheral surface of the container body 1. However, the present invention is not limited to this, and the induction heating coil 11 may be embedded in a state where a part (for example, the inner peripheral side portion) is exposed.

  In the above configuration, when the temperature of the surface portion of the canister 2 detected by the temperature detection sensor 14 is higher than the temperature at which stress corrosion cracking may occur in the surface portion of the canister 2 (for example, 100 ° C.), induction The heating coil 11 is not energized. That is, when the spent fuel cooling period is still short and several years, etc., when the calorific value of the spent fuel is still large and the surface temperature of the canister 2 is high and higher than the temperature at which stress corrosion cracking occurs. The induction heating coil 11 is not energized, and therefore the canister 2 is not heated. Thus, in a state where the decay heat is relatively large, the air in the canister 2 and the cooling passage 3 is not heated, and the decay heat emitted from the canister 2 can be favorably absorbed by the cooling air in the cooling passage 3.

  In addition, when the temperature of the surface portion of the canister 2 detected by the temperature detection sensor 14 is equal to or lower than a temperature at which stress corrosion cracking may occur, the induction heating coil 11 is energized. As a result, a magnetic field (indicated by a thick dotted line in FIG. 1) that passes vertically inside the induction heating coil 11 is generated and an eddy current is generated in the surface portion of the canister 2 to be heated, and the surface of the canister 2 is heated. In the part, it is prevented that the humidity becomes high due to adhesion of water droplets or the like.

  Here, stress corrosion cracking (SCC) tends to occur at locations where tensile stress is applied in addition to the conditions of temperature, humidity, and salinity as described above. The canister 2 having a cylindrical shape bends a rectangular sheet metal and welds the curved ends to form a cylindrical peripheral surface. After the spent fuel is stored in the portion 2c or the bottomed cylindrical main body 2a, the upper surface welded portion 2d that closes the upper surface of the main body of the canister 2 may cause stress corrosion cracking (SCC). May increase. However, according to the above configuration, when the temperature of the surface portion of the canister 2 reaches a temperature at which stress corrosion cracking may occur, the induction heating coil 11 is energized and includes the side surface welding portion 2c and the top surface welding portion 2c. Water droplets and the like are prevented from adhering to the surface portion of the canister 2 and being in a high humidity state. Therefore, even when the cooling air contains salt, it is possible to suppress the occurrence of chloride ions on the surface of the canister 2 to cause stress corrosion cracking (SCC), thereby improving the reliability of the concrete cask 10. Can do.

  Further, according to this configuration, Joule heat is generated by the eddy current inside the surface of the canister 2 and heat is generated from the inside, so that heating can be performed with higher efficiency and quicker than when heat is generated by the resistance of the conductive wire. . It is also possible to control (control) how deep the surface is heated by changing the frequency. When the frequency is increased, eddy currents concentrate on the surface of the canister 2 due to the skin effect, and only the surface is heated. It becomes possible to do. For example, it is preferable to energize at a frequency of several hundred hertz (for example, two hundred hertz) or more, but the present invention is not limited to this. In addition, as a method for energizing the induction heating coil 11 and performing induction heating, the induction heating coil 11 may be heated by any method of electromagnetic induction heating or high frequency induction heating.

  In addition, when the induction heating coil 11 is embedded in the container body 1, it is not necessary to provide a mounting member for fixing or supporting the induction heating coil 11 in a predetermined position, thereby reducing the manufacturing cost. Is possible. Further, the induction heating coil 11 is covered with the concrete container body 1 so that the air containing the salt content of seawater becomes difficult to contact (that is, difficult to be exposed to) the induction heating coil 11, and the salt-induced induction heating coil 11. Damage can be minimized and reliability can be improved. Further, the cooling air flow in the cooling passage 3 is not obstructed by the induction heating coil 11 or the like, and the cooling performance can be maintained satisfactorily. Further, for example, even when the canister 2 is taken out from the container body 1 for inspection or the like, the canister 2 or the like can be prevented from coming into contact with the induction heating coil 11 to be damaged, and as a result, the reliability of the concrete cask 10 can be improved. There is also an advantage that can be. It is particularly preferable to embed the entire induction heating portion (coiled portion) of the induction heating coil 11 in the container body 1, and in this case, the induction heating coil 11 is not exposed to air containing salty seawater. However, the present invention is not limited to this, and when a part of the induction heating portion (coiled portion) of the induction heating coil 11 is embedded in the container body 1, the embedded portion is made of seawater. There is an advantage that it is not exposed to salty air.

  Moreover, in the said embodiment, although the case where there was no thing which has magnetism, such as a reinforcing bar, in the container main body 1 was shown, there is a possibility that the container main body 1 may be heated with magnetism such as the reinforcing bar 18 8, a magnetic shield 17 that shields magnetism is applied to the inner peripheral surface of the container main body 1 as shown in FIG. 8, and the induction heating coil 11 is arranged on the inner peripheral side of the cooling shield 3 with respect to the magnetic shield 17. May be provided. Further, the magnetic shield 17 may be provided (provided) on the inside of the lid of the container body 1 facing the upper surface of the canister 2 or on the inside of the bottom surface of the container body 1 facing the bottom of the canister 2. The magnetic shield 17 may be made of a highly permeable material, an electromagnetic steel plate, a magnetic sheet, or the like, but is not limited thereto.

  As described above, when there is a thing in the container main body 1 that may be heated with magnetism such as the rebar 18, by providing the magnetic shield 17 on the inner surface of the container main body 1, induction heating is performed. The magnetic force generated when the coil 11 is energized is prevented from heating a magnetic material such as a reinforcing bar in the container body 1, thereby improving the reliability of the concrete cask 10.

  Even if there is no magnet such as the reinforcing bar 18 in the container main body 1 that may be heated by magnetism, the magnetic force generated when the induction heating coil 11 is energized from the container main body 1 to the outside. In order to prevent leakage, a magnetic shield 17 may be provided on the container body 1 (inner side area, outer surface side area, intermediate part, etc.).

  9 and 10 are a front sectional view and a sectional plan view of the main part of a concrete cask 20 according to another embodiment of the present invention. As shown in FIGS. 9 and 10, in the concrete cask 20, the induction heating coil 21 is provided in the upper cooling space 6 between the upper surface portion of the canister 2 and the inside of the lid portion 1 a of the container body 1. . For example, the induction heating coil 21 may be provided in the upper cooling space 6 by being attached to the inside of the lid portion 1a of the container body 1 or the upper surface portion of the canister 2 via the attachment member 22, but is not limited thereto. Absent. Further, as the induction heating coil 21, as shown in FIG. 10, it is preferable to use a spiral coil, but it is not limited to this. Similarly to the case shown in FIG. 8, if there is a possibility that the container main body 1 is heated with magnetism such as the reinforcing bar 18, the bottom surface of the lid portion 1 a of the container main body 1 is magnetized. You may give the magnetic shield 17 which shields (not shown).

  Instead of providing the induction heating coil 21 in the upper cooling space 6, as shown in FIG. 11, the induction heating coil 21 may be embedded in the lid portion 1 a of the container body 1. In this case, as shown in FIG. 11, it is preferable that the induction heating coil 21 (specifically, the coiled portion of the induction heating coil 21) is embedded so as not to be exposed from the lower surface of the lid portion 1 a of the container body 1. However, the present invention is not limited to this, and a part (for example, the lower part) of the induction heating coil 21 may be embedded in a state of being exposed from the lower surface of the lid portion 1 a of the container body 1.

  Note that the induction heating coil 11 as described in the above embodiment is not provided in the cooling passage 3 or the inner peripheral portion of the container body 1, and only the induction heating coil 21 is covered with the upper cooling space 6 or the container body 1. However, the present invention is not limited to this, and the induction heating coil 11 as described in the above embodiment is provided on the cooling passage 3 or the inner peripheral portion of the container body 1 and induction heating is performed. The coil 21 may be provided in the upper cooling space 6 or the lid 1 a of the container body 1.

  Although not shown in FIGS. 9 to 11, in this embodiment as well, the induction heating coil 21 is connected to the power source via the controller 12 provided outside as in the above embodiment. (AC power source) 13 is connected to the control unit 12, a temperature detection sensor (not shown) including a thermocouple for detecting the temperature of the surface of the canister 2 (for example, the surface of the upper surface of the canister 2). The temperature detection sensor 14 shown in FIG. 1 may be shared). Then, the control unit 12 energizes the induction heating coil 21 at a temperature at which stress corrosion cracking may occur in the surface portion of the canister 2.

  In the canister 2, spent fuel (spent nuclear fuel) is accommodated in a main body 2 a having a bottomed cylindrical shape and an upper surface opened, and thereafter, the lid 2 b is fixed to the main body 2 a by welding or the like. The inside is sealed. The lid 2b is often composed of an outer ring-shaped part and a central disk part, and the outer ring-shaped part and the central disk part are often fixed together by welding (upper surface welded part 2d). It is not limited to. When the lid 2b and the main body 2a (and the outer ring-shaped part and the central disk part) are fixed (that is, welded) by welding, a tensile stress acts on the upper surface weld 2d. There is an area. Therefore, if the air introduced into the upper cooling space 6 through the cooling passage 3 contains salt and the environment is high due to dew condensation on the surface of the canister 2, the salt is dissolved in the moisture of the moisture. In addition, the dissolved chloride ions may cause rust and corrosion in the canister 2 to cause stress corrosion cracking (SCC).

  However, according to the above configuration, when the temperature of the surface portion of the canister 2 becomes equal to or lower than the dew condensation temperature, the induction heating coil 21 is energized, so a magnetic field passing through the induction heating coil 11 is generated and the surface portion of the canister 2 ( In this embodiment, an eddy current is generated and heated in the upper surface portion of the canister 2 and the humidity is prevented from becoming high due to condensation of the cooling air. Therefore, even when the cooling air contains salt, it is possible to better suppress the occurrence of stress corrosion cracking (SCC) due to the generation of chloride ions on the upper surface portion of the canister 2 including the upper surface welded portion 2d. As a result, the reliability of the concrete cask 20 can be improved.

  Further, when the induction heating coil 21 is embedded in the lid portion 1a of the container body 1, there is no need to provide a mounting member or the like for fixing or supporting the induction heating coil 11 at a predetermined position. Can be reduced. In addition, since the induction heating coil 21 is covered with the concrete container body 1, it becomes difficult for air containing salt content of seawater to contact the induction heating coil 21, and damage to the induction heating coil 21 due to salt content is minimized. The reliability can be improved. Moreover, the air flow in the upper cooling space 6 is not obstructed by the induction heating coil 21 or the like, and the cooling performance can be maintained satisfactorily. Furthermore, for example, even when the canister 2 is taken out from the container main body 1 for inspection or the like, it is possible to prevent the canister 2 or the like from coming into contact with the induction heating coil 11 and damage it, thereby improving the reliability of the concrete cask 20. There is also an advantage that can be.

  12 and 13 are a front sectional view and a plan sectional view of a principal part of a concrete cask 30 according to another embodiment of the present invention. As shown in FIGS. 12 and 13, in the concrete cask 30, the induction heating coil 31 is provided in the lower cooling space 7 between the bottom portion of the canister 2 and the inside of the bottom portion of the container body 1. For example, the induction heating coil 31 may be provided in the lower cooling space 7 by being attached to the inside (upper surface portion) of the bottom of the container body 1 or the bottom surface of the canister 2 via the attachment member 32, but is not limited thereto. It is not a thing. Similarly to the case shown in FIG. 8, when there is a possibility that the container main body 1 is heated with magnetism such as the reinforcing bar 18, the magnetism is shielded on the upper surface of the bottom surface of the container main body 1 or the like. A magnetic shield 17 may be provided (not shown).

  Further, instead of providing the induction heating coil 31 in the lower cooling space 7, the induction heating coil 31 may be embedded in the bottom surface of the container body 1 as shown in FIG. 13. In this case, as shown in FIG. 13, it is preferable that the induction heating coil 31 (specifically, the coiled portion of the induction heating coil 31) is embedded so as not to be exposed from the upper surface of the bottom surface of the container body 1. However, the present invention is not limited to this, and a part (for example, the upper part) of the induction heating coil 31 may be embedded so as to be exposed from the upper surface of the bottom surface of the container body 1.

  Note that the induction heating coil 11 as described in the above embodiment is not provided in the cooling passage 3 or the inner peripheral portion of the container body 1, and only the induction heating coil 31 is provided in the lower cooling space 7 or the bottom surface of the container body 1. However, the present invention is not limited to this, and the induction heating coil 11 as described in the above embodiment is provided in the cooling passage 3 or the inner peripheral portion of the container body 1 and the induction heating coil. The 31 induction heating coil 21 may be provided in the lower cooling space 7 or the bottom surface of the container body 1. Further, the induction heating coil 21 may be provided in the upper cooling space 6 or the lid portion 1a of the container body 1.

  Although not shown in FIGS. 12, 13 and the like, in this embodiment as well, the induction heating coil 31 is connected to the outside via the control unit 12 provided outside as in the above embodiment. A temperature detection sensor (not shown) is connected to a power source (AC power source) 13 and includes a thermocouple that detects the temperature of the surface of the canister 2 (for example, the bottom surface of the canister 2). The temperature detection sensor 14 shown in FIG. 1 may be shared). Then, the control unit 12 energizes the induction heating coil 31 at a temperature at which stress corrosion cracking occurs at the surface portion of the canister 2.

  According to the above configuration, the induction heating coil 31 is energized when the temperature of the surface portion (bottom surface portion, etc.) of the canister 2 reaches a temperature at which stress corrosion cracking may occur. Is generated, and an eddy current is generated and heated on the surface portion of the canister 2 (the bottom surface portion of the canister 2 in this embodiment), thereby preventing condensation of the cooling air. Therefore, even when the cooling air contains salt, it is possible to suppress the occurrence of stress corrosion cracking (SCC) due to the generation of chloride ions at the bottom surface of the canister 2, thereby improving the reliability of the concrete cask 10. be able to. In particular, in this case, there is an advantage that the bottom surface portion of the canister 2 and the lower cooling space 7 can be satisfactorily heated, which tends to be low temperature when the induction heating coil 31 is not energized.

  In the above embodiment, the case where the temperature detection sensor 14 including a thermocouple for detecting the temperature of the surface portion (bottom surface portion, etc.) of the canister 2 is described, but the present invention is not limited to this, and a temperature sensor is provided. Instead, a test or the like may be performed in advance to examine the period for reaching the dew condensation temperature, and when this period is reached, the induction heating coils 11, 21, 31 may be energized.

  Moreover, in the said embodiment, even if the area | region where the tensile stress is acting in the side surface weld part 2c and the upper surface weld part 2d of the canister 2 remains, by heating with the induction heating coils 11, 21, and 31, The case where rust and corrosion are generated in the canister 2 due to dissolved chloride ions to prevent stress corrosion cracking (SCC) has been described. However, the present invention is not limited to this, and in order to prevent stress corrosion cracking more reliably, in the welded portion such as the side surface welded portion 2c or the upper surface welded portion 2d of the canister 2, no region where tensile stress is applied remains. Needless to say, it may be processed or a structure that does not remain may be added.

DESCRIPTION OF SYMBOLS 1 Container body 2 Canister 3 Cooling passage 4 Air introduction path 5 Air discharge path 6 Upper cooling space 7 Lower cooling space 8 Canister support 10, 20, 30 Concrete cask 11, 21, 31 Induction heating coil 12 Control part 13 Power supply (AC Power supply)
14 Temperature detection sensor 15, 16, 16A, 16B, 22, 32 Mounting member 17 Magnetic shield 18 Rebar

Claims (6)

A metal canister that contains spent fuel, a concrete container body that houses the canister, and an inner peripheral surface of the container body and an outer peripheral surface of the canister to cool the canister A concrete cask having a cooling passage through which air is passed,
An induction heating coil that suppresses stress corrosion cracking by energizing the surface of the canister is provided in at least a part of the cooling passage, the cooling space connected to the cooling passage, and the container body. Concrete cask.   The concrete cask according to claim 1, wherein the induction heating coil is provided in an inner peripheral portion of the cooling passage or the container main body.   The concrete cask according to claim 1, wherein the induction heating coil is provided in an upper cooling space between the upper surface portion of the canister and the inside of the lid portion of the container body or in the lid portion of the container body.   The concrete cask according to claim 1, wherein the induction heating coil is provided in a lower cooling space between the bottom surface portion of the canister and the inside of the bottom surface portion of the container body or the bottom surface portion of the container body.   The concrete cask according to any one of claims 1 to 4, wherein the induction heating coil is embedded in the container body.   A temperature detection sensor that detects the temperature of the surface portion of the canister and a control unit to which the temperature detection sensor is connected are provided, and when the control unit reaches a temperature at which stress corrosion cracking may occur in the surface portion of the canister The concrete cask according to any one of claims 1 to 5, wherein the induction heating coil is energized.

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