Device and method for estimating axial force of fixing bolt for radioactive substance container

Abstract

To simplify work for estimating fastening force of a fixing bolt in a device and a method for estimating axial force of the fixing bolt for a radioactive substance storage container.SOLUTION: An axial force estimation device of a fixing bolt for a radioactive substance storage container for estimating an axial force of a bolt used for fixing the radioactive substance storage container includes a deformation amount measurement part for measuring a deformation amount of the bolt, and an estimation part for estimating the axial force of the bolt based on the deformation amount of the bolt measured by the deformation amount measurement part.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to an apparatus and method for estimating the axial force of a fixing bolt for a radioactive material storage container. [Background technology]

[0002] At nuclear facilities, radioactive waste such as spent fuel generated in reactors and other facilities is stored in radioactive material storage containers (casks) and transported to storage facilities, reprocessing facilities, etc., for storage or reprocessing. A radioactive material storage container consists of a body with a bottom and an open top, and a lid that is fixed to the top of the body and closes the opening. The radioactive material storage container is supported upright on a pedestal at the storage facility or reprocessing facility. At this time, the radioactive material storage container is placed upright on the pedestal, and its lower end is fixed to the pedestal and supported by multiple fasteners.

[0003] A support structure for a radioactive material storage container is described, for example, in Patent Document 1. Furthermore, a technology for measuring the displacement of a bolt is described, for example, in Patent Document 2. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-116887 [Patent Document 2] Japanese Patent Application Publication No. 2019-197025 Summary of the Invention [Problem to be solved by the invention]

[0005] The radioactive material storage container is placed upright on a pedestal, and its lower end is fixed to the pedestal and supported by multiple fasteners. The multiple fasteners are fixed to the pedestal with multiple fixing bolts. The radioactive material storage container is installed on the pedestal for a predetermined period of time. During this time, the fixing bolts may loosen due to natural phenomena such as earthquakes or shrinkage caused by a decrease in the heat generation rate of the radioactive material storage container. This requires measuring the tightening force of the fixing bolts and retightening them. In this case, the heat generation rate of the spent fuel stored in each cask varies, so the timing for retightening varies. Furthermore, since the gradient of the heat generation rate of the spent fuel changes over time, the gradient of the cask's elongation also changes over time. Therefore, the timing for retightening is set shorter than the period actually required to satisfy even the most stringent conditions. Conventionally, the tightening force of the fixing bolts is measured and retightened using a torque wrench. However, using a torque wrench requires that the work be performed on all fixing bolts, which increases the work time and the burden on the worker. That is, with the method using a torque wrench, even when considering variations in friction that occur on the bolt seating surface, an excessive torque is set so that the actual axial force applied satisfies the design conditions, which places a burden on the worker. Furthermore, setting an excessive torque requires the use of high-strength bolts, which also causes the bolts to be larger in size due to space constraints, which also places a burden on the design.

[0006] The present disclosure is intended to solve the above-mentioned problems, and aims to provide an apparatus and method for estimating the axial force of a fixing bolt for a radioactive material storage container that simplifies the work of estimating the tightening force of the fixing bolt. [Means for solving the problem]

[0007] In order to achieve the above object, the axial force estimation device for fixing bolts for radioactive material storage containers of the present disclosure is an axial force estimation device for fixing bolts for radioactive material storage containers that estimates the axial force of a bolt used to fix a radioactive material storage container, and includes: a deformation amount measurement unit that measures the deformation amount of the bolt; and an estimation unit that estimates the axial force of the bolt based on the deformation amount of the bolt measured by the deformation amount measurement unit.

[0008] Furthermore, the disclosed method for estimating the axial force of a fixing bolt for a radioactive material storage container is a method for estimating the axial force of a fixing bolt for a radioactive material storage container, which estimates the axial force of a bolt used to fix the radioactive material storage container, and includes the steps of measuring the deformation amount of the bolt and estimating the axial force of the bolt based on the deformation amount of the bolt. [Effects of the Invention]

[0009] According to the device and method for estimating the axial force of a fixing bolt for a radioactive material storage container of the present disclosure, the task of estimating the tightening force of the fixing bolt can be simplified. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a partially cutaway perspective view of a radioactive material storage container supported on a stand. [Figure 2] FIG. 2 is a front view showing the support structure at the bottom of the radioactive material storage container. [Figure 3] FIG. 3 is a block diagram showing the configuration of the device for estimating the axial force of a fixing bolt for a radioactive material storage container according to this embodiment. [Figure 4] FIG. 4 is an explanatory diagram showing an example of a first method for measuring the deformation amount of a fixing bolt. [Figure 5] FIG. 5 is an explanatory diagram showing an example of a second method for measuring the deformation amount of a fixing bolt. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. Note that the present disclosure is not limited to these embodiments, and when there are multiple embodiments, the present disclosure also includes configurations that combine the embodiments. Furthermore, the components in the embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially identical, and those that are within the so-called equivalent range.

[0012] <Radioactive material storage container> FIG. 1 is a partially cutaway perspective view of a radioactive material storage container supported on a stand.

[0013] As shown in FIG. 1, a cask 11 serving as a radioactive material storage container includes a trunk portion 12 and a lid portion 13. The trunk portion 12 has a container body 21. The container body 21 is cylindrical (in this embodiment, cylindrical), has an opening 22 formed at its upper axial end, and is closed at its lower axial end. The container body 21 has an internal cavity 23, and a basket 24 is provided in the cavity 23. The basket 24 is provided with a plurality of cells 25 that can independently store radioactive material (e.g., spent fuel assemblies). The container body 21 is a forged product made of carbon steel that has a gamma ray shielding function, but stainless steel can also be used instead of carbon steel. The container body 21 can also be a cast product made of spheroidal graphite cast iron, carbon steel cast steel, or the like.

[0014] In the trunk 12, an outer cylinder 26 is disposed on the outer peripheral surface of the container body 21 with a predetermined gap therebetween. The container body 21 is provided with a plurality of copper heat transfer fins 27 in the circumferential direction, which perform heat conduction between the outer peripheral surface and the inner peripheral surface of the outer cylinder 26. In the space surrounded by the outer cylinder 26 and the heat transfer fins 27, the container body 21 is provided with a resin (neutron shielding body) 28, which is a polymer material containing a large amount of hydrogen and contains boron or a boron compound that has a neutron shielding function.

[0015] The body 12 is provided with a bottom 29 that protrudes below the closed lower end of the container body 21. The bottom 29 is formed to have dimensions smaller than the outer diameter of the container body 21. The bottom 29 has a space surrounded by the closed lower end of the container body 21, and a resin (neutron shielding body) is provided in the space.

[0016] The barrel 12 is provided with a trunnion 30 for lifting the cask 11 on the vessel body 21. The trunnion 30 is provided penetrating the outer cylinder 26 from the vessel body 21, and protrudes most outward from the cask 11.

[0017] The lid portion 13 is provided at the opening 22 of the vessel body 21, and closes the opening 22 to hermetically seal the vessel body 21 (torso portion 12). The lid portion 13 is composed of a primary lid 31 and a secondary lid 32. The primary lid 31 is formed in a disk shape from a material such as carbon steel or stainless steel that shields against gamma rays. The secondary lid 32 covers the primary lid 31 and appears on the outside of the cask 11, and like the primary lid 31, is also formed in a disk shape from a material such as carbon steel or stainless steel that shields against gamma rays. A resin (neutron shield) 28 may be provided between the primary lid 31 and the secondary lid 32. In addition, a tertiary lid may be provided on the lid portion.

[0018] The primary lid 31 is fixed to a first step 22a formed at the opening 22 of the container body 21 with bolts (not shown) made of carbon steel or stainless steel, and is attached to the container body 21. The secondary lid 32 is fixed to a second step 22b formed at the opening 22 of the container body 21 with bolts (not shown) made of carbon steel or stainless steel, and is attached to the container body 21. Although not shown, metal gaskets are provided between the primary lid 31 and the first step 22a and between the secondary lid 32 and the second step 22b. The metal gaskets ensure sealing between the primary lid 31 and the first step 22a and between the secondary lid 32 and the second step 22b.

[0019] The barrel 12 surrounds the secondary lid 32 at the opening 22 of the vessel body 21, and has a cylindrical upper edge 22c that appears on the outside of the cask 11. The upper surface of the upper edge 22c is located higher than the surface of the secondary lid 32, and surrounds the secondary lid 32. The upper surface of the upper edge 22c has a plurality of bolt holes 33 spaced apart in the circumferential direction for attaching a buffer body A, which will be described later.

[0020] <Support structure for radioactive material storage containers> FIG. 2 is a front view showing the support structure at the bottom of the radioactive material storage container.

[0021] 1, the cask 11 is mounted and supported in an upright position on a pedestal 51. That is, the cask 11 is supported on the pedestal 51 with its axial direction aligned vertically. The pedestal 51 has a pedestal body 52, a plurality of legs 53, and a plurality of fasteners 54.

[0022] The gantry body 52 has a rectangular flat plate shape with a predetermined thickness. The gantry body 52 has a square plate shape, and the length of one side is longer than the diameter of the cask 11. However, the shape of the gantry body 52 is not limited to a square plate shape. The gantry body 52 has a recess 61 in the shape of a circular groove in the center of the upper surface. It is not necessary to provide the recess 61 on the gantry body 52, and it may have a flat shape. Legs 53 are fixed to the lower surface of the gantry body 52.

[0023] The multiple fixtures 54 are arranged at intervals along the circumferential direction around the recess 61 of the gantry body 52. ​​In this embodiment, the number of the multiple fixtures 54 is four, but the number is not limited thereto. The multiple fixtures 54 support the multiple trunnions 30 provided at the bottom of the cask 11. Therefore, it is preferable that the number of fixtures 54 is the same as the number of trunnions 30.

[0024] 2, the fixing device 54 has a receiving member 62, a pressing member 63, a plurality of fixing bolts 64, and a plurality of pressing bolts 65. The receiving member 62 is placed on the upper surface of the gantry main body 52, and has a semicircular receiving surface 62a at its upper part and through holes 62b on both sides. The pressing member 63 is placed on the upper part of the receiving member 62, and has a semicircular pressing surface 63a at its lower part and through holes 63b on both sides.

[0025] The receiving member 62 is placed at a predetermined position on the upper surface of the gantry main body 52, and a fixing bolt 64 passes through the through hole 62b and screws into a threaded portion (not shown) of the gantry main body 52, thereby fixing the receiving member 62 to the gantry main body 52. ​​When the cask 11 is mounted on the gantry 51, the trunnion 30 is placed on the receiving surface 62a of the receiving member 62. In this state, the pressing trunnion 30 is placed on top of the pressing member 63. At this time, the pressing surface 63a of the pressing member 63 presses the trunnion 30. Then, a pressing bolt 65 passes through the through hole 63b and screws into a threaded portion (not shown) of the receiving member 62, thereby fixing the pressing member 63 to the receiving member 62.

[0026] 1, the cask 11 is supported in an upright position on the pedestal 51 by the four trunnions 30 at the bottom being supported by fixtures 54 fixed to the pedestal 51. The pedestal 51 is then fixed in place by a plurality of foundation bolts 55.

[0027] <Axial force estimation device> FIG. 3 is a block diagram showing the configuration of the device for estimating the axial force of a fixing bolt for a radioactive material storage container according to this embodiment.

[0028] 3, the axial force estimation device 101 estimates the axial force of the bolts used to secure the cask 11. Here, the bolts used to secure the cask 11 include, but are not limited to, fixing bolts 64 (see FIG. 2) for securing the receiving member 62 to the cradle body 52, press bolts 65 (see FIG. 2) for securing the press member 63 to the receiving member 62, and bolts (not shown) for securing the primary lid 31 and the secondary lid 32 to the vessel body 21.

[0029] The axial force estimation device 101 includes a deformation amount measurement unit 111, a temperature measurement unit 112, and an estimation unit 113. The axial force estimation device 101 is connected to a determination unit 102, and the determination unit 102 is connected to an output unit 103.

[0030] The deformation amount measuring unit 111 measures the amount of deformation of the bolt. A bolt generally has a head and a shank (threaded portion). The deformation amount measuring unit 111 measures the amount of deformation of the entire bolt, the amount of deformation of the head, and the amount of deformation of the shank (threaded portion). The temperature measuring unit 112 is, for example, a thermocouple and measures the temperature of the bolt. The deformation amount measuring unit 111 outputs the measured amount of deformation of the bolt to the estimation unit 113. The temperature measuring unit 112 outputs the measured temperature of the bolt to the estimation unit 113.

[0031] <First deformation measurement method> FIG. 4 is an explanatory diagram showing an example of a method for measuring the deformation amount of a fixing bolt.

[0032] 4, for example, receiving member 62 is disposed on the upper surface of gantry main body 52, and is fixed to gantry main body 52 by having fixing bolts 64 pass through and screw into gantry main body 52. ​​Deformation measurement unit 111A measures the deformation of the head of fixing bolt 64 using a digital image correlation method. Deformation measurement unit 111A has an imaging unit (for example, a camera) 121 and a processing unit 122. Note that imaging unit 121 may be disposed for all bolts at all times, or may be disposed only during measurement.

[0033] The cask 11 is placed on the pedestal 51, and the cask 11 is fixed to the pedestal 51 by the fixing device 54. At this time, the photographing unit (e.g., a camera) 121 photographs the head of the fixing bolt 64, and the processing unit 122 stores the initial image of the head of the fixing bolt 64 photographed by the photographing unit 121. After a predetermined period of time has passed, the photographing unit 121 similarly photographs the head of the fixing bolt 64, and the processing unit 122 stores the current image of the head of the fixing bolt 64 photographed by the photographing unit 121. The processing unit 122 then compares the initial image with the current image and calculates the amount of deformation of the head of the fixing bolt 64. It is preferable that the amount of deformation of the head of the fixing bolt 64 be calculated as the amount of deformation in three-dimensional directions, for example.

[0034] <Second deformation measurement method> FIG. 5 is an explanatory diagram showing an example of a method for measuring the deformation amount of a fixing bolt.

[0035] 5, for example, the receiving member 62 is disposed on the upper surface of the gantry main body 52, and is fixed to the gantry main body 52 by having a fixing bolt 64 pass through and screw into the gantry main body 52. ​​The deformation amount measuring unit 111B measures the deformation amount of the fixing bolt 64 using an ultrasonic measurement method. The deformation amount measuring unit 111B has an ultrasonic wave transmitting / receiving unit 123 and a processing unit 124. Note that the transmitting / receiving unit 123 may be disposed for all bolts at all times, or may be disposed only during measurement.

[0036] The cask 11 is placed on the pedestal 51, and the cask 11 is fixed to the pedestal 51 by the fasteners 54. At this time, the transmitter / receiver 123 transmits ultrasonic waves in the axial direction from the heads of the fixing bolts 64. The ultrasonic waves transmitted from the transmitter / receiver 123 are reflected by the tip surfaces of the shanks of the fixing bolts 64 and received by the transmitter / receiver 123. The processing unit 122 estimates the length of the fixing bolts 64 based on the transmission and reception times of the ultrasonic waves by the transmitter / receiver 123, and stores the initial length. After a predetermined period of time has elapsed, the transmitter / receiver 123 similarly transmits ultrasonic waves to the fixing bolts 64 and receives the ultrasonic waves reflected by the tip surfaces of the shanks of the fixing bolts 64. The processing unit 124 estimates the length of the fixing bolts 64 based on the transmission and reception times of the ultrasonic waves by the transmitter / receiver 123, and stores the current length. The processing unit 124 then compares the initial length with the current length to calculate the amount of deformation of the fixing bolts 64 in the axial direction.

[0037] <Axial force estimation method> Returning to FIG. 3, the estimation unit 113 estimates the axial force of the bolt based on the amount of bolt deformation measured by the deformation amount measurement unit 111 (111A, 111B). In this case, the Young's modulus (modulus of longitudinal elasticity) is known from the material of the bolt. Therefore, the estimation unit 113 calculates the axial force of the bolt by multiplying the amount of bolt deformation measured by the deformation amount measurement unit 111 by the Young's modulus according to the material. Here, the axial force of the bolt is the tightening force of the bolt.

[0038] When the estimation unit 113 calculates the axial force of the bolt, it is preferable to take the temperature of the bolt into consideration. That is, the estimation unit 113 estimates the axial force of the bolt based on the amount of deformation of the bolt measured by the deformation amount measurement unit 111 and the temperature of the bolt measured by the temperature measurement unit 112. That is, the Young's modulus changes more as the temperature decreases and changes less as the temperature increases. Therefore, when the estimation unit 113 multiplies the amount of deformation of the bolt by the Young's modulus, it corrects the Young's modulus based on the temperature of the bolt measured by the temperature measurement unit 112.

[0039] Furthermore, the speed of ultrasonic waves passing through the interior of the bolt varies depending on the temperature of the material. Therefore, as shown in Fig. 5, when the deformation amount measuring unit 111B measures the deformation amount of the fixing bolt 64 using the ultrasonic measurement method, the estimation unit 113 corrects the deformation amount based on the temperature of the bolt measured by the temperature measuring unit 112. In this case, the deformation amount may be corrected based on the temperature of the bolt measured by the deformation amount measuring unit 111B.

[0040] <Fixing bolt looseness determination> The determination unit 102 determines whether a bolt is loose based on the axial force of the bolt estimated by the axial force estimation device 101. That is, the determination unit 102 determines whether retightening of the bolt is necessary based on the axial force of the bolt estimated by the axial force estimation device 101. The determination unit 102 determines whether a bolt is loose, that is, whether retightening of the bolt is necessary, by comparing the axial force of the bolt with a preset determination value. When the axial force of the bolt is lower than the preset determination value, the determination unit 102 determines that the bolt is loose and that retightening of the bolt is necessary.

[0041] The output unit 103 outputs the determination result of the determination unit 102. The output unit 103 is, for example, a monitor, a printer, a speaker, etc. The worker performs the work of retightening the bolt based on the determination result output from the output unit 103.

[0042] The estimation unit 113 and the determination unit 102 are control devices, which are controllers, and are realized by, for example, a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) executing various programs stored in a memory unit using RAM as a working area.

[0043] [Effects of this embodiment] The axial force estimation device for a fixing bolt for a radioactive material storage container according to the first aspect includes a deformation amount measurement unit 111 that measures the deformation amount of the bolt, and an estimation unit that estimates the axial force of the bolt based on the deformation amount of the bolt measured by the deformation amount measurement unit 111.

[0044] According to the device for estimating the axial force of fixing bolts for a radioactive material storage container of the first aspect, the amount of deformation of the bolt is measured and the axial force of the bolt is estimated based on the measured amount of deformation of the bolt, so that the worker does not need to retighten all the bolts using a torque wrench or the like, but only the bolts that need to be retightened using a torque wrench or the like. This simplifies the work of estimating the tightening force of the fixing bolts.

[0045] The device for estimating axial force of a fixing bolt for a radioactive material storage container according to the second aspect is the device for estimating axial force of a fixing bolt for a radioactive material storage container according to the first aspect, further comprising a temperature measurement unit 112 that measures the temperature of the bolt, and an estimation unit 113 that estimates the axial force of the bolt based on the amount of deformation of the bolt measured by the deformation amount measurement unit 111 and the temperature of the bolt measured by the temperature measurement unit 112. This makes it possible to estimate the axial force of the bolt with high accuracy by correcting the amount of deformation of the bolt according to the temperature of the bolt.

[0046] The device for estimating axial force of a fixing bolt for a radioactive material storage container according to the third aspect is the device for estimating axial force of a fixing bolt for a radioactive material storage container according to the first or second aspect, and further, the deformation amount measuring unit 111 (111B) measures the amount of deformation of the bolt head using a digital image correlation method. Thereby, the deformation amount measuring unit 111 (111B) can easily measure the amount of deformation of the bolt by measuring the amount of deformation of the bolt head using the digital image correlation method.

[0047] The device for estimating axial force of a fixing bolt for a radioactive material storage container according to the fourth aspect is the device for estimating axial force of a fixing bolt for a radioactive material storage container according to the first or second aspect, and further, the deformation amount measuring unit 111 (111B) measures the deformation amount of the bolt using ultrasonic measurement. Thereby, by measuring the deformation amount of the bolt head using ultrasonic measurement, the deformation amount of the bolt can be easily measured.

[0048] A method for estimating the axial force of a fixing bolt for a radioactive material storage container according to a fifth aspect includes the steps of measuring the deformation of the bolt and estimating the axial force of the bolt based on the deformation of the bolt. This eliminates the need for a worker to retighten all of the bolts using a torque wrench or the like, and only tightens the bolts that require retightening using a torque wrench or the like. This simplifies the process of estimating the tightening force of the fixing bolts. [Explanation of symbols]

[0049] 11 Cask (container for storing radioactive materials) 12 Torso 13 Lid 21 Container body 29 Bottom 30 Trunnion 51 Mounting stand 52 Stand body 53 Legs 54 Fixtures 55 Foundation bolt 61 Recess 62 Receiving member 63 Pressing member 64 Fixing bolt 65 Presser bolt 101 Axial force estimation device 102 Judgment section 103 Output section 111, 111A, 111B Deformation measurement unit 112 Temperature measurement unit 113 Estimation Department

Claims

1. An axial force estimation device for fixing bolts for radioactive material storage containers, which estimates the axial force of bolts used to fix radioactive material storage containers, a deformation amount measuring unit that measures the deformation amount of the bolt; an estimation unit that estimates an axial force of the bolt based on the deformation amount of the bolt measured by the deformation amount measurement unit; An axial force estimation device for fixing bolts for a radioactive material storage container, comprising:

2. a temperature measuring unit that measures the temperature of the bolt, and an estimating unit that estimates the axial force of the bolt based on the deformation amount of the bolt measured by the deformation amount measuring unit and the temperature of the bolt measured by the temperature measuring unit; The device for estimating axial force of a fixing bolt for a radioactive material storage container according to claim 1.

3. The deformation amount measuring unit measures the deformation amount of the head of the bolt using a digital image correlation method. The device for estimating axial force of a fixing bolt for a radioactive material storage container according to claim 1 or 2.

4. The deformation amount measuring unit measures the deformation amount of the bolt using an ultrasonic measurement method. The device for estimating axial force of a fixing bolt for a radioactive material storage container according to claim 1 or 2.

5. A method for estimating the axial force of a fixing bolt for a radioactive material storage container, which estimates the axial force of a bolt used to fix a radioactive material storage container, comprising: measuring the deformation of the bolt; estimating an axial force of the bolt based on a deformation amount of the bolt; A method for estimating axial force of fixing bolts for radioactive material storage containers.

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