Repair welding method of metal cask

Abstract

To provide a repair welding method of a metal cask for repair welding a member made of carbon steel or low-alloy steel, without applying preheating treatment.SOLUTION: In a method for repair welding, for example, a secondary lid 5 and a body 2, as members made of carbon steel or low-alloy steel constituting a sealed container 1 of a metal cask, preheating treatment is not applied, and welding metal of austenite stainless steel is used to perform the repair welding.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for repair welding of carbon steel or low alloy steel members constituting a sealed container of a metal cask for storing spent nuclear fuel. [Background technology]

[0002] Metal cask structural standards (see, for example, Non-Patent Document 1) stipulate that carbon steel or low alloy steel is used as the material for the members constituting the sealed container of the metal cask. In a method for welding carbon steel or low alloy steel members, it is generally assumed that the deposited metal is of the same type (i.e., carbon steel or low alloy steel), and a preheating treatment is performed to prevent low temperature cracking according to the chemical composition of the material and the dimensions of the member (see, for example, Non-Patent Documents 2 to 5). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Japan Society of Mechanical Engineers, JSME S FA1-2007 "Standards for Spent Fuel Storage Facilities Metal Cask Construction Standards (2007 Edition)" [Non-Patent Document 2] JIS B8265:2017 "Construction of pressure vessels - General matters" [Non-Patent Document 3] JIS B8266:2003 "Construction of pressure vessels - Specific standards" [Non-Patent Document 4] JIS B8267:2022 "Design of Pressure Vessels" [Non-Patent Document 5] JIS Z3183:2012 "Quality classification of submerged arc weld metals for carbon steel and low alloy steel" [Non-Patent Document 6] "Joining and Welding Technology Q&A 1000" Editorial Committee, "Joining and Welding Technology Q&A 1000", 1999, serial number Q10-1-2 Summary of the Invention [Problem to be solved by the invention]

[0004] In the operation of metal casks, if damage occurs to carbon steel or low alloy steel components due to some reason such as an abnormality or disaster, it is necessary to take action as quickly as possible to ensure the strength and soundness of the components. One of the measures to take is repair welding. However, depending on the circumstances of an abnormality or disaster, there may be cases where there is no equipment for preheating or it is not possible to prepare it, or the space is too narrow to perform preheating.

[0005] Here, it has been reported that if a deposited metal of stainless steel called 29-9 (29Cr-9Ni) is used, carbon steel or low alloy steel materials can be welded without preheating (see, for example, Non-Patent Document 6). However, this report has limitations, such as the need to take an appropriate groove, perform buttering on the groove surface, and perform peening to reduce internal stress in the weld.

[0006] The present invention has been made in consideration of the above circumstances, and one of its objects is to repair welding of carbon steel or low alloy steel members without carrying out preheat treatment. [Means for solving the problem]

[0007] In order to solve the above problems, the configurations described in the claims are applied. The present invention includes a plurality of means for solving the above problems, and an example thereof is a method for repair welding of carbon steel or low alloy steel members constituting a sealed container of a metal cask for storing spent nuclear fuel, in which the members are repair welded using austenitic stainless steel weld metal or nickel or nickel-based alloy weld metal without preheating. Effect of the Invention

[0008] According to the present invention, it is possible to repair weld carbon steel or low alloy steel components without carrying out a preheat treatment.

[0009] Problems, configurations and effects other than those described above will become apparent from the following description. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view showing repair welding of a sealed vessel of a metal cask in the first embodiment of the present invention. [Diagram 2] 2 is a partially enlarged cross-sectional view of a portion II in FIG. 1. [Diagram 3] FIG. 4 is a cross-sectional view showing repair welding of a sealed vessel of a metal cask in a second embodiment of the present invention. [Figure 4] FIG. 4 is a partially enlarged cross-sectional view of a portion IV in FIG. [Diagram 5] FIG. 11 is a partial cross-sectional view showing repair welding of a sealed vessel of a metal cask in a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] First, the metal cask to which the present invention is applied will be described.

[0012] A metal cask is a container for storing or transporting spent nuclear fuel. When in a transport state, the metal cask includes a cylindrical sealed container 1 for storing spent nuclear fuel, and a plurality of buffers (not shown) attached to the outside of the sealed container 1. When in a transport state, the sealed container 1 of the metal cask includes a bottomed cylindrical body 2, a disk-shaped primary lid 4 arranged at the opening of the body 2 and fixed with a plurality of fastening bolts 3A, a disk-shaped secondary lid 5 arranged at the opening of the body 2 and outside the primary lid 4 and fixed with a plurality of fastening bolts 3B, and a disk-shaped tertiary lid 6 arranged at the opening of the body 2 and outside the secondary lid 5 and fixed with a plurality of fastening bolts 3C (see Figs. 3 to 6 described later). When the metal cask is in a transition from a transport state to a storage state, the buffers are removed, and further the tertiary lid 6 is removed (see Figs. 1 and 2 described later).

[0013] The members constituting the sealed container 1 of the metal cask (specifically, the shell 2, the primary lid 4, the secondary lid 5, or the tertiary lid 6) are made of carbon steel or low alloy steel. To explain in detail, the carbon steel members are the same type of material as the carbon steel plate for intermediate and normal temperature pressure vessels specified in JIS G3118:2010 (specifically, any one of SGV410, SGV450, and SGV480) or the low temperature carbon steel forgings specified in JSME S NJ1-2012 (specifically, any one of GLF1 and GLF2). The low alloy steel members are the same type of material as the low temperature alloy steel forgings specified in JSME S NJ1-2012 (specifically, GLF3).

[0014] In the above-mentioned method for welding carbon steel or low alloy steel members, if the deposited metal is of the same type (i.e., carbon steel or low alloy steel), a preheating treatment is required to prevent cold cracking. However, if austenitic stainless steel deposited metal is used, preheating is not necessary. Furthermore, the inventors of the present application have found through their tests that if a groove preparation method and a welding method are selected that take into account on-site welding, cold cracking will not occur and sufficient strength can be ensured even without peening. The metal cask repair method of the present invention is based on the above-mentioned findings, and an embodiment thereof will be described.

[0015] A first embodiment of the present invention will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a cross-sectional view showing repair welding of a sealed vessel of a metal cask in this embodiment. Fig. 2 is a partially enlarged cross-sectional view of part II in Fig. 1.

[0016] In this embodiment, assuming that a metal cask from which the buffer body and the tertiary lid 6 have been removed is damaged for some reason, such as an abnormality or disaster, the carbon steel or low alloy steel members constituting the sealed container 1 of the metal cask are repaired by welding. In detail, repair welding is performed to join the secondary lid 5 and the shell 2 at a weld 10.

[0017] In the repair welding method of this embodiment, first, a suitable groove 11 is machined on the outer periphery of the secondary cover 5 using a disk grinder or air arc gouging. If there is a possibility of interference with the fastening bolts 3B, the groove 11 is machined only in the area between the fastening bolts 3B. When a disk grinder is used, no significant thermal deformation occurs, but when air arc gouging is used, a large amount of heat is generated. Therefore, when air arc gouging is used, it is desirable to use it intermittently to suppress thermal deformation.

[0018] Next, without preheating, repair welding is performed by joining the secondary lid 5 and the body 2 at the welded portion 10 using austenitic stainless steel weld metal. At this time, one or more passes of the first layer 12 are performed by TIG welding or laser welding, which have excellent weldability, and the remaining layer 13 is performed by covered metal arc welding, carbon dioxide gas arc welding, MIG welding, MAG welding, submerged arc welding or self-shielded arc welding, which have a large amount of deposition per pass. To explain in detail, a covered metal arc welding rod that corresponds to F-8A in the category specified in JIS Z3040-1995 and can obtain austenitic stainless steel weld metal, or a weld material (including wire) that corresponds to Y-8 in the category specified in JIS Z3040-1995 and can obtain austenitic stainless steel weld metal, is used. Furthermore, a flux that corresponds to G-21 or G-22 in the category specified in JIS Z3040-1995 may be used.

[0019] If repair welding is performed to join the secondary cover 5 and the body 2 at the welded portion 10 because the tightening bolt 3B is damaged, the mechanical strength of the welded portion 10 shall be equal to or greater than the load to fix the secondary cover 5 obtained by the tightening bolt 3B before the damage. The mechanical strength of the welded portion 10 is determined from the area of ​​the groove 11, which is the product of the depth d and width of the groove 11 (more specifically, the circumferential length perpendicular to the depth direction of the groove 11; if the groove 11 is discontinuous in the circumferential direction, this is the integrated length), and the material strength of the weld metal.

[0020] According to the above-described embodiment, the secondary cover 5 and the shell 2 made of carbon steel or low alloy steel can be repair-welded without preheating. Furthermore, no low-temperature cracking occurs and sufficient strength can be ensured without peening. Furthermore, the welding time can be significantly reduced compared to when all layers are TIG welded or laser welded. Therefore, repair welding can be performed as quickly as possible.

[0021] A second embodiment of the present invention will be described with reference to Fig. 3 and Fig. 4. Fig. 3 is a cross-sectional view showing repair welding of a sealed vessel of a metal cask in this embodiment. Fig. 4 is a partially enlarged cross-sectional view of part IV in Fig. 3. Note that descriptions of parts equivalent to those of the first embodiment will be omitted as appropriate.

[0022] In this embodiment, assuming that a metal cask from which the buffer body has been removed is damaged for some reason such as an abnormality or disaster, the carbon steel or low alloy steel members constituting the sealed container of the metal cask are repaired by welding. In detail, the repair welding is performed to join the tertiary lid 6 and the shell 2 at the welded portion 10.

[0023] In this embodiment, first, a disk grinder or air arc gouging is used to machine an appropriate groove 11 in the tertiary cover 6 and the body 2. If there is a possibility of interference with the tightening bolts 3C, the groove 11 is machined only in the area between the tightening bolts 3C.

[0024] Next, without performing preheating, repair welding is performed using austenitic stainless steel weld metal to join the tertiary lid 6 and the body 2 at the weld 10. At this time, one or more passes of the first layer 12 are performed by TIG welding or laser welding, and the remaining layer 13 is performed by shielded metal arc welding, carbon dioxide gas arc welding, MIG welding, MAG welding, submerged arc welding or self-shielded arc welding.

[0025] In addition, if repair welding is performed to join the tertiary lid 6 and the body 2 at the welded joint 10 due to damage to the fastening bolt 3C, the mechanical strength of the welded joint 10 must be greater than or equal to the load for fixing the tertiary lid 6 obtained by the fastening bolt 3C before it was damaged.

[0026] According to the above-described embodiment, the tertiary cover 6 and the shell 2 made of carbon steel or low alloy steel can be repair-welded without preheating. Furthermore, even without peening, low-temperature cracking does not occur and sufficient strength can be ensured. Furthermore, the welding time can be significantly reduced compared to when all layers are TIG welded or laser welded. Therefore, repair welding can be performed as quickly as possible.

[0027] A third embodiment of the present invention will be described with reference to Fig. 5. Fig. 5 is a cross-sectional view showing repair welding of a sealed vessel of a metal cask in this embodiment. Note that descriptions of parts equivalent to those of the first and second embodiments will be omitted as appropriate.

[0028] In this embodiment, it is assumed that a metal cask from which the buffer body has been removed is damaged for some reason, such as an abnormality or a disaster, and the members constituting the sealed container 1 of the metal cask are repaired by welding. In detail, it is assumed that a damaged portion 7 occurs on the outside of the body 2, and repair welding is performed to join the body 2 and a backing plate 8 at a welded portion 10.

[0029] In the repair welding method of this embodiment, first, if a coating is present around the damaged portion 7 of the body 2, the coating is removed using a disk grinder or the like. Next, a backing plate 8 made of, for example, austenitic stainless steel is placed so as to cover the damaged portion 7 of the body 2. Next, repair welding is performed in which the body 2 and the backing plate 8 are joined at a weld 10 using a deposited metal of austenitic stainless steel without performing a preheat treatment.

[0030] According to the present embodiment described above, the shell 2 made of carbon steel or low alloy steel can be repair welded without carrying out preheat treatment.

[0031] In the first to third embodiments, the case where the weld metal of austenitic stainless steel is used is described as an example, but the present invention is not limited thereto. The inventors of the present invention have found through their tests that the object of the present invention can be achieved by using a weld metal with a small weld crack susceptibility composition (Pcm). Therefore, instead of the weld metal of austenitic stainless steel, a weld metal of nickel or a nickel-based alloy may be used. To explain in detail, a covered electrode that is specified in JIS Z3224:2010 and that can obtain a weld metal of nickel or a nickel-based alloy, or a fusible material (specifically, a fusible rod, wire, or strip) that is specified in JIS Z3334:2017 or JIS Z3335:2014 and that can obtain a weld metal of nickel or a nickel-based alloy may be used. In the third embodiment, if a weld metal of nickel or a nickel-based alloy is used, it is preferable to use a backing plate 8 of the same type (i.e., made of nickel or a nickel-based alloy).

[0032] In addition, in the first to third embodiments, an example has been described in which repair welding is performed on any of the body 2, secondary lid 5, and tertiary lid 6 as carbon steel or low alloy steel components that constitute the sealed container 1 of the metal cask, but this is not limited to this and other components may also be repair welded.

[0033] Considering the possibility that abnormalities or disasters may occur at multiple locations simultaneously, it is extremely important to have materials and equipment for the repair welding method in one or more locations different from the location where the repair welding method described above is performed. It is also important to have a database in which information on personnel with the ability to perform repair welding is registered. By setting up an organization or department to manage materials and equipment and personnel in advance, it is possible to respond quickly when abnormalities or disasters occur. [Explanation of symbols]

[0034] 1. Sealed metal cask container 2. Torso 3A, 3B, 3C Fastening bolts 4 Primary lid 5 Secondary lid 6 Tertiary lid 10 Welding 11 Bevel 12 First layer 13 Residual layer

Claims

1. A method for repair welding of carbon steel or low alloy steel members constituting a sealed container of a metal cask for storing spent nuclear fuel, comprising the steps of:

1. A method for repair welding of a metal cask, comprising the steps of repair welding the member without preheating, using a weld metal of an austenitic stainless steel or a weld metal of nickel or a nickel-base alloy.

2. The repair welding method for a metal cask according to claim 1, A repair welding method for a metal cask, characterized in that one or more passes of a first layer are performed by TIG welding or laser welding, and the remaining layers are performed by shielded metal arc welding, carbon dioxide gas arc welding, MIG welding, MAG welding, submerged arc welding, or self-shielded arc welding.

3. The repair welding method for a metal cask according to claim 2, A repair welding method for a metal cask, comprising the steps of: preparing a groove in at least one of the components, the lid and the body, using a disc grinder or air arc gouging; and performing repair welding to join the lid and the body.

4. The repair welding method for a metal cask according to claim 3, A repair welding method for a metal cask, characterized in that the mechanical strength of the weld joining the lid and the body is equal to or greater than the load securing the lid obtained by the tightening bolt before the damage, due to damage to the tightening bolt securing the lid to the body.

5. The repair welding method for a metal cask according to claim 4, providing equipment and materials for the repair welding method at one or more locations different from a location where the repair welding method is performed; A method for repairing and welding a metal cask, comprising the step of providing a database in which information on personnel capable of performing the repair welding is registered.

6. The repair welding method for a metal cask according to claim 1, The method for repairing and welding a metal cask, wherein the carbon steel member is made of the same material as the carbon steel plate for medium and normal temperature pressure vessels specified in JIS G3118:2010 or the carbon steel forgings for low temperature use specified in JSME S NJ1-2012.

7. The repair welding method for a metal cask according to claim 1, The method for repairing and welding a metal cask is characterized in that the low alloy steel member is the same type of material as the low-temperature alloy steel forgings specified in JSME S NJ1-2012.

8. The repair welding method for a metal cask according to claim 2, A repair welding method for a metal cask, comprising using a covered metal arc welding rod which corresponds to the F-8A category specified in JIS Z3040-1995 and from which a deposited metal of the austenitic stainless steel can be obtained, or using a fusible material which corresponds to the Y-8 category specified in JIS Z3040-1995 and from which a deposited metal of the austenitic stainless steel can be obtained.

9. The repair welding method for a metal cask according to claim 7, A method for repair welding of a metal cask, comprising using a flux classified as G-21 or G-22 according to JIS Z3040-1995.

10. The repair welding method for a metal cask according to claim 2, A method for repair welding of a metal cask, comprising using a covered electrode for arc welding that is specified in JIS Z3224:2010 and that can obtain a weld metal of the nickel or nickel-base alloy, or using a fusible material that is specified in JIS Z3334:2017 or JIS Z3335:2014 and that can obtain a weld metal of the nickel or nickel-base alloy.

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