JP2019152555A - Supporting structure for used nuclear fuel, method for manufacturing supporting structure, and used nuclear fuel container - Google Patents

Abstract

To simplify the assembling process, reduce the manufacturing cost, and increase the strength characteristics of the structure of a basket (supporting structure).SOLUTION: A supporting structure 2 of a used nuclear fuel 7 includes: a first grid plate group 30 made of a plurality of grid plates 21 arranged in parallel; a second grid plate group 30 made of a plurality of grid plates arranged in parallel to intersect with the first grid plate group; and a plate-like grid supporting plate 19 containing a plurality of holes 20 arranged in a matrix, the supporting structure including an alternate engagement of the first grid plate group, the grid supporting plate, and the second grid plate group.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a spent nuclear fuel support structure, a method of manufacturing the support structure, and a spent nuclear fuel container.

  Spent nuclear fuel used in a nuclear power plant is temporarily stored in a spent fuel pool after being taken out of the core in order to reduce heat generation due to decay heat. Here, the spent nuclear fuel cooled for a predetermined period is transported to a reprocessing plant, where it is reprocessed, uranium and plutonium are taken out as resources, and reused as new fuel.

  In recent years, the amount of spent nuclear fuel generated at nuclear power plants has been increasing, and even if the reprocessing plant is in operation, the spent nuclear fuel generated in the country will exceed the processing capacity of the reprocessing plant. During this period, spent nuclear fuel needs to be stored and managed appropriately.

  Methods for storing and managing spent nuclear fuel inside or outside the nuclear power plant include metal cask storage, vault storage, silo storage, concrete cask storage, and other dry storage methods, and water pool wet storage methods. There is a method. Among these, dry storage is attracting attention in consideration of cost and long-term stable storage.

  Japanese commercial reactors mainly include pressurized water light water reactors (PWR) and boiling water light water reactors (BWR). PWR fuel has a higher number of fuel rods per fuel assembly and larger dimensions of the fuel assembly than BWR fuel, and therefore has high reactivity and tends to be critical. For this reason, in a support structure (hereinafter also referred to as “basket”) for supporting and housing PWR fuel, a gap for filling a predetermined thickness of water between the fuel assemblies is secured in order to enhance the subcriticality maintenance function. There is a case.

An example of the configuration of a conventional basket for storing spent nuclear fuel in a pressurized water reactor will be described with reference to FIG.
The basket 2 is provided with an uneven portion on a hollow lattice plate 31, the lattice plates 31 are crossed and fitted to each other at the uneven portion, and stacked in a lattice shape in the axial direction to constitute a basket 2, which is used as spent nuclear fuel. A method of accommodating in a container (hereinafter also referred to as “cask”) has been proposed.

  The basket 2 has a strength performance capable of withstanding the load applied from the spent nuclear fuel, a heat removal performance that transmits decay heat generated from the spent nuclear fuel to the outside of the container, and a performance that absorbs neutrons emitted from the spent nuclear fuel. Therefore, subcritical performance is required to keep the shape of the basket and prevent the spent nuclear fuel from coming into close proximity more than necessary.

  Among these, strength performance is particularly important in maintaining the basket shape and preventing the spent nuclear fuel from becoming critical in the event of an accident such as a cask dropping. As such a basket structure, a basket having a structure that does not require special skills for assembly as described above is preferable.

JP 2014-16323 A

  In the conventional basket structure described above, an uneven portion is provided on the long side of the lattice plate 31, and the recesses are fitted to cross each other. Therefore, the plate width corresponding to the concave portion of the lattice plate 31, that is, the portion of the plate width ½ from the long side end of the lattice plate 31 is separated by the concave portion, so that the strength of the basket 2 is compensated accordingly. Is desirable.

  For this reason, in the conventional basket structure, through holes 32 are provided in the lattice plate 31 and the communication member 33 is inserted, so that the communication member 33 bears the load of the spent nuclear fuel, and the structure strength of the basket 2 is compensated. ing.

However, the communication members 33 are arranged by the number of the lattice plates 31 and the number of parts to be managed increases. Normally, each part of a cask (used nuclear fuel container) used in a nuclear power plant must be managed so that it can be traced to the material certificate of each material. There is a concern that an increase in the number of parts leads to an increase in costs for procurement and management of materials.
Furthermore, since the number of parts increases, the number of assembly steps increases and the process becomes complicated, resulting in an increase in work load and cost.

  The present embodiment has been made to solve the above-mentioned problem, and spent nuclear fuel that can improve the structural strength characteristics of the basket (support structure), simplify the assembly process, and reduce the manufacturing cost. It is an object of the present invention to provide a support structure, a manufacturing method of the support structure, and a spent nuclear fuel container.

In order to solve the above-described problems, a spent nuclear fuel support structure according to the present embodiment includes a first lattice plate group including a plurality of lattice plates arranged in parallel, and orthogonal to the first lattice plate group. And a second lattice plate group composed of a plurality of lattice plates arranged in parallel to each other, and a plate-like lattice support plate having a plurality of holes arranged in a lattice shape therein, to support spent nuclear fuel A structure,
The support structure is formed by alternately stacking the first lattice plate group, the lattice support plate, and the second lattice plate group.

In addition, the manufacturing method of the support structure according to the present embodiment is arranged in parallel so as to be orthogonal to the first grid plate group including a plurality of grid plates arranged in parallel. In addition, the present invention is characterized in that a second lattice plate group composed of a plurality of lattice plates and a plate-like lattice support plate having a plurality of holes arranged in a lattice shape inside are alternately laminated.
In addition, the spent nuclear fuel container according to the present embodiment has the support structure for the spent nuclear fuel according to the present embodiment inside.

  According to the present embodiment, the structural strength characteristics of the support structure can be improved, and the assembling process can be simplified and the manufacturing cost can be reduced.

(A) is the whole block diagram of the spent nuclear fuel container which concerns on this embodiment, (b) is the sectional drawing. (A) is a block diagram of a lattice plate, (b) is an exploded view. The block diagram of a lattice support plate. The block diagram of a grating | lattice support plate (base plate). The schematic diagram of a positioning member. The schematic diagram of the lattice board group of the 1st step | paragraph. (A), (b) is a schematic diagram at the time of assembling | attaching the 1st-stage grid board group to the 1st-stage grid support board (base plate). (A), (b) is a schematic diagram at the time of assembling | attaching the 2nd step | paragraph grid support plate to the 1st step | paragraph grid plate group. (A), (b) is a schematic diagram at the time of assembling the 2nd-stage lattice board group to the 2nd-stage grid support board. (A), (b) is a schematic diagram at the time of assembling | attaching the 3rd-stage grid | lattice support plate to the 2nd-stage grid | lattice board group. (A), (b) is a schematic diagram at the time of assembling the 3rd-stage grid board group to the 3rd-stage grid support board. The principal part enlarged view of the conventional support structure (basket). It is a block diagram of the support structure which concerns on this embodiment, and is the sectional view on the AA line of FIG.11 (b). The block diagram of the conventional basket.

  Embodiments of a spent nuclear fuel support structure, a support structure manufacturing method, and a spent nuclear fuel container according to the present invention will be described below with reference to the drawings.

(Configuration of spent nuclear fuel container)
As shown in FIGS. 1A and 1B, a spent nuclear fuel container (cask) 1 according to the present embodiment is disposed in the inner container 3 and the inner container 3, and contains a plurality of spent nuclear fuels. Support structure 2 (basket), a plurality of heat transfer fins 5 disposed on the outer periphery of the inner container 3, an outer container 6 provided so as to surround the heat transfer fins 5, and an upper portion of the spent nuclear fuel container 1 And a plurality of lids 8 to 10.

  The inner container 3 is a metal or alloy container having a function of shielding radiation such as gamma rays. In the present embodiment, a cylindrical container is used as the inner container 3, but the present invention is not limited to this, and a polygonal, rectangular, or elliptical container may be used.

  Further, the space between the inner container 3 and the outer container 6 is filled with a neutron shielding material 4 for shielding radiation such as neutrons emitted from the spent nuclear fuel. As the neutron shielding material 4, boron (boron) having high neutron absorption capability or a compound thereof is used.

  As shown in FIG. 1B, the basket 2 is composed of a plurality of lattice support plates 19 and a lattice plate group 30 arranged in the height direction, and a plurality of rectangular sections S for containing spent nuclear fuel 7. Is formed. Details thereof will be described later.

(Composition of basket)
The basket 2 includes a plurality of disk-like lattice support plates 19 and a lattice plate group 30 including a plurality of plate-like lattice plates 21 assembled to the lattice support plate 19.

  As shown in FIGS. 2A and 2B, the lattice plate 21 is formed of a rectangular plate-like member, and a concave portion 13 and a convex portion 14 having a predetermined width are formed at regular intervals on the upper side and the lower side in the longitudinal direction. Yes. The cut depth L1 of the recess 13 is set to be about 1/4 when the length in the short direction of the lattice plate 21 is L.

  However, as shown in FIG. 6, a lattice plate 21 a having a flat upper side or lower side is used at the upper and lower ends of the basket 2 among the lattice plates 21. The lattice plate 21a is obtained by halving the lattice plate 21 shown in FIG. 2 in the height direction. The upper half of the lattice plate 21 is used at the lower end of the basket 2 and the lower half is used at the upper end.

  As shown in FIG. 2B, the lattice plate 21 is composed of a neutron shielding plate 12a including a neutron absorbing material and two plate-like members 12b having the same dimensions arranged on both sides thereof. ing.

  The material of the plate-like member 12b is preferably a material excellent in strength and thermal conductivity, and carbon steel, stainless steel, aluminum alloy and the like are suitable. Further, the neutron shielding plate 12a is preferably made of a material having neutron absorption capability, and for example, stainless steel or aluminum alloy to which boron is added is suitable.

  As shown in FIG. 3, the grid support plate 19 used in the grid support plate 19 other than the upper and lower ends is formed with a plurality of rectangular holes 20 arranged in a grid. The widths G, H, J, and K between the holes 20 are set such that a water gap for preventing the spent nuclear fuel 7 from reaching criticality is formed.

On the other hand, the grid support plates 19a (also referred to as “base plates”) used at the upper and lower ends of the basket 2 are stepped portions 22 for fitting and fixing flat sides of the grid plates 21a as shown in FIG. Is provided.
As a material of the lattice support plates 19 and 19a, a material having high strength and high thermal conductivity is preferable. For example, carbon steel, stainless steel, aluminum alloy, or the like is preferable.

  Further, a positioning hole 24 through which a rod-shaped positioning member 23 (see FIG. 5) for positioning the grid support plates 19 and 19a stacked in the vertical direction in the horizontal direction is inserted in the outer periphery of the grid support plates 19 and 19a. A plurality are provided. The positioning member 23 may be a solid rod-shaped member, but may be hollow. In the case of a hollow shape, it can be used as a drain pipe of the cask 1.

Although the lattice support plates 19 and 19a and the lattice plates 21 and 21a described above are assembled in the inner container 3 alternately in the vertical direction, the basket 2 having a plurality of rectangular sections S is formed. It will be described later.
In the example shown in FIGS. 3 and 4, the lattice support plates 19 and 19 a are disk-shaped, but are not limited thereto, and may be any shape such as a polygonal shape or a rectangular shape.

(Assembly method of basket)
The assembly method of the spent nuclear fuel container 1 comprised as mentioned above is demonstrated using FIGS.
FIG. 6 is a diagram showing a first-stage (lowermost) lattice plate group 30-1 including a plurality of lattice plates 21a. Here, for convenience, a direction parallel to the arrangement direction of the lattice plates 21a is referred to as an X direction (first radial direction), and an orthogonal direction is referred to as a Y direction (second radial direction).

  In the present embodiment, the lattice plate group 30-1 includes ten lattice plates 21a arranged in parallel to each other, and in the longitudinal direction of the two outer lattice plates 21a, according to the shape of the lattice support plate 19b. The length is set to be shorter than the length of the inner six sheets in the longitudinal direction.

  In the first-stage lattice plate group 30-1, the recesses 13 having a predetermined depth L1 are provided at predetermined intervals on the upper side of each lattice plate 21a. On the other hand, the lower side is flat and is fitted and fixed to a step portion 22 (see FIG. 4) provided along the holes 20 of the lattice support plate 19a.

  When the basket 2 is assembled, first, the first-stage lattice plate group 30-1 including the plurality of lattice plates 21a is assembled to the lattice support plate 19a. FIGS. 7A and 7B are schematic views when the lattice plate group 30-1 is assembled to the first lattice support plate 19a, and the flat lower side of each lattice plate 21a is provided on the first lattice support plate 19a. The stepped portion 22 is fitted and fixed.

  Next, as shown in FIGS. 8A and 8B, the second-stage lattice support plate 19 is assembled to the first-stage lattice plate group 30-1 arranged in the Y direction. At that time, the projection 14 on the upper side of each grid plate 21a is attached so as to be fitted into the rectangular hole 20 of the grid support plate 19 at the second stage.

  At this time, the positioning holes 24 formed in the first-stage grid support plate 19a and the positioning holes 24 formed in the second-stage grid support plate 19 are positioned at positions where the rod-shaped positioning member 23 can penetrate vertically. .

  Next, as shown in FIGS. 9A and 9B, the X-direction is applied to the first-stage grid plate group 30-1 in which the second-stage grid support plate 19 is assembled and arranged in the Y direction. Assembling the second-stage lattice plate group 30-2 arranged along the line. At that time, each lattice plate 21 of the lattice plate group 30-2 is assembled so that the lower recess 13 of the second-stage grid plate 21 is inserted into the upper recess 13 of the first-stage grid plate 21a.

  At the same time, the lower convex portion 14 of the second-stage grid plate 21 is assembled so as to be fitted into the holes 20 of the second-stage grid support plate 19. As a result, the first-stage lattice plate group 30-1 and the second-stage lattice plate group 30-2 are combined in a lattice shape that intersects at right angles at the respective concave portions 13.

  Next, as shown in FIGS. 10A and 10B, the third-stage lattice support plate 19 is assembled to the second-stage lattice plate group 30-2 arranged in a plurality along the X direction. . At this time, the upper convex portion 14 of the second-stage grid plate 21 is attached so as to be fitted into the hole 20 of the third-stage grid support plate 19.

  At this time, the positioning holes 24 formed in the first and second grid support plates 19 and 19a and the positioning holes 24 formed in the third grid support plate 19a are positions where the positioning member 23 can penetrate vertically. Is positioned.

Next, as shown in FIGS. 11A and 11B, with respect to the second-stage grid plate group 30-2 in which the third-stage grid support plate 19 is assembled and arranged in the X direction, the Y direction A plurality of third-stage grid plate groups 30-3 arranged along the line are assembled. At that time, the recess 13 on the lower side of each third-stage grid plate 21 is assembled so as to be inserted into the recess 13 on the upper side of the second-stage grid plate 21.
At the same time, the convex portion 14 on the lower side of the third-stage grid plate 21 is assembled so as to be fitted into the holes 20 of the third-stage grid support plate 19.

  As a result, similarly to the relationship between the first-stage grid plate group 30-1 and the second-stage grid plate group 30-2, the second-stage grid plate group 30-2 and the third-stage grid plate group 30- 3 is combined in a lattice shape intersecting at a right angle at the concave portion 13.

  Thereafter, similarly, a plurality of lattice plate groups 30 arranged in the X direction, a lattice support plate 19, and a plurality of lattice plate groups 30 arranged in the Y direction are alternately fitted and laminated to form the X direction. And the basket 2 which extends in the Z direction orthogonal to the Y direction and has a plurality of rectangular sections S is formed.

  As a term referring to the lattice plate group, a lattice plate group arranged in one direction (for example, the X direction) is a first lattice plate group, and a lattice plate group is arranged in a direction orthogonal to the first lattice plate group (for example, the Y direction). May be referred to as a second lattice plate group.

  Note that the upper end portion of the basket 2 uses a lattice support plate 19a and a lattice plate 21a having a flat upper side, similarly to the lower end portion. Since the assembling method is the same as the assembling method of the lattice support plate 19a and the lattice plate group 30-1 at the lower end portion described above, description thereof is omitted.

(effect)
First, a plurality of lattice plate groups 30 arranged in the X direction and a plurality of lattice plate groups 30 arranged in the Y direction need to fix the crossing angle according to the cross-sectional shape of the spent nuclear fuel 7 to be stored. In the present embodiment, the intersection angle between the lattice plate group 30 in the X direction and the lattice plate group 30 in the Y direction can be obtained by simply fitting the convex portions 14 of the lattice plates 21 and 21a into the holes 20 of the lattice support plates 19 and 19a. Can be easily fixed.

  Further, since positioning members 23 are inserted over the entire length in the vertical direction of the basket 2 (Z direction) into the positioning holes 24 formed in the outer peripheral portions of the lattice support plates 19 and 19a, a plurality of positioning members 23 are installed in the Z direction. The horizontal displacement between the grid support plates 19 and 19a can be suppressed. As a result, it becomes easy to manage the intersection angle between the plurality of lattice plate groups 30 arranged in the X direction and the plurality of lattice plate groups 30 arranged in the Y direction.

  Further, when the positioning member 23 has a hollow shape, it can be used as a drain pipe of the cask 1. That is, when the spent nuclear fuel 7 is accommodated in the cask 1 in the fuel pool, the cask 1 holds a large amount of water inside. After the spent nuclear fuel 7 is accommodated and the cask 1 is pulled up from the fuel pool, it is necessary to drain the water retained inside the cask 1. Therefore, by making the positioning member 23 hollow, it can be used as a water drainage path inside the cask 1.

  Furthermore, the basket 2 according to the present embodiment is assembled by simply stacking the convex portions 14 of the lattice plates 21 and 21a in a lattice shape so as to fit into the holes 20 of the lattice support plates 19 and 19a. As a result, when the basket 2 is assembled, a fastening jig such as a bolt or welding is not used, so that the structure is simple, the assembling work is facilitated, and the cost can be reduced.

  In addition, since the lattice support plates 19 and 19a according to the present embodiment require fewer parts than the conventional basket structure, the procurement of materials and parts, the management cost, the assembling procedure of the basket 2 and the number of assembling steps can be simplified. The manufacturing cost can be reduced by the reduction.

(Appendix)
By the way, in the basket 2 for storing the spent nuclear fuel for PWR, (a) structural strength for safely holding the spent nuclear fuel, and (b) the heat generated by the spent nuclear fuel are transmitted to the inner container 3. (C) The characteristic (subcritical characteristic) for maintaining a subcritical state is required.

  Among them, regarding the subcritical characteristics of (c), the gap 15 (see FIG. 3) whose dimensions are controlled by the grid widths G, H, J, and K of the grid support plate 19 is formed, so that the demand is met. ing. However, in the case of the structure in which the lattice plates 21 and 21a having the recesses 13 for insertion are laminated in a lattice shape, there are problems in the structural aspect regarding the above-described (a) structural strength and (b) heat transfer characteristics.

Therefore, in the present embodiment, by using the grid support plates 19 and 19a, the strength characteristics are improved and the heat transfer performance is slightly improved, and the problems of the grid-like assembly structure are solved.
Specifically, FIG. 12 is a diagram for explaining the problem of the conventional basket 2 in which the lattice support plate 19 is not provided, and the first-stage lattice plate group 30-1 and the third-stage stacked in the axial direction. The grid plate group 30-3 is shown. In the portion where the recess 13 for insertion is formed, the orthogonal lattice plates 21 intersect.

  In such a conventional basket structure, for example, consider a case where the cask 1 is in a sideways posture and gravity in the direction of arrow F (X direction) acts on the spent nuclear fuel 7. In this case, the load of the spent nuclear fuel 7 is applied to the lattice plate 31 between the adjacent recesses 13. However, since the insertion recess 13 is formed in the belt-like region B, the portion of the lattice plate 31 that can bear the load of the spent nuclear fuel 7 is substantially only the portion of the belt-like region A. That is, in the case of the structure in which the lattice plates 31 having the insertion recesses 13 are laminated in a lattice shape, the portion of the belt-like region B is not effectively used for the load load, and an improvement in the strength of the structure has been desired. . Therefore, in the conventional basket structure, the load of the spent nuclear fuel 7 is borne by increasing the thickness of the lattice plate 31 in order to increase the structural strength.

  However, if the thickness of the lattice plate 31 is increased while maintaining the gap 15 (see FIG. 11B), the mass and cross-sectional area of the cask 1 increase. Generally, since the mass and diameter of the cask 1 are limited based on facility equipment such as a crane, it has been a problem to suppress an increase in the mass and diameter of the cask.

  On the other hand, in this embodiment, in order to solve such a problem, the lattice support plates 19 and 19a are used. FIG. 13 shows the first to third stage lattice support plates 19a, 19, and 19 and the first to third stage lattice plate groups 30-1 to 30-3.

  In FIG. 13, a case is considered in which a load is applied to the spent nuclear fuel 7 in the depth direction of the drawing as in FIG. 12. The grid support plate 19 in contact with the hatched portion E of the grid plate groups 30-1 to 30-3 bears a load, and deformation due to the load is suppressed. That is, the cross-sectional secondary moment of the lattice plate group 30 is increased, and the structural strength of the basket 2 is improved.

  The lattice support plates 19 and 19a formed of a material having excellent heat transfer characteristics (aluminum, aluminum alloy, etc.) are assembled so as to be in contact with the respective lattice plates 21 and 21a. Therefore, the heat of the convex portion 14 of each lattice plate 21, 21 a is transmitted to the adjacent convex portion 14 via the lattice support plates 19, 19 a, and the other lattice plate 21 in contact with the lattice support plate 19, 21a is also transmitted. Thereby, the heat-transfer characteristic of the longitudinal direction of the lattice board 21 which was a subject can be improved.

  As mentioned above, although several embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Used nuclear fuel container (cask), 2 ... Support structure (basket), 3 ... Inner container, 4 ... Neutron shielding material, 5 ... Heat transfer fin, 6 ... Outer container, 7 ... Used nuclear fuel, 8-10 ... Lid, 12a ... Neutron shielding plate, 12b ... Plate-like member, 13 ... Recess, 14 ... Projection, 15 ... Gap, 19 ... Lattice support plate, 19a ... Lattice support plate (base plate), 20 ... Hole, 21, 21a DESCRIPTION OF SYMBOLS ... Grid plate, 22 ... Step part, 23 ... Positioning member, 24 ... Positioning hole, 30, 30-1-30-n ... Grid plate group, 31 ... Grid plate, 32 ... Through-hole, 33 ... Communication member.

Claims (7)

A lattice plate in which a plurality of convex portions and concave portions are formed on the upper side and the lower side, a first lattice plate group composed of the plurality of lattice plates arranged in parallel, and orthogonal to the first lattice plate group A spent nuclear fuel support structure comprising: a second grid plate group including a plurality of the grid plates arranged in parallel; and a plate-like grid support plate having a plurality of holes arranged in a grid pattern inside. Because
The support structure for spent nuclear fuel, wherein the support structure has a configuration in which the first lattice plate group, the lattice support plate, and the second lattice plate group are alternately fitted.   The spent nuclear fuel support structure according to claim 1, wherein the convex portion of the lattice plate is fitted into a hole of the lattice support plate.   The spent nuclear fuel support structure according to claim 1 or 2, wherein a plurality of positioning holes through which positioning members are inserted are provided on an outer periphery of the lattice support plate.   The grid support plates disposed at the upper and lower ends of the support structure are provided with stepped portions, and the upper side or lower piece of the grid plate fitted into the stepped portions of the grid support plate is configured to be flat. The spent nuclear fuel support structure according to any one of claims 1 to 3, wherein the spent nuclear fuel support structure is provided.   5. The spent nuclear fuel support structure according to claim 1, wherein the lattice plate is made of a metal or alloy plate having a neutron absorber and a plate having high thermal conductivity. 6. A grid plate in which a plurality of convex portions and concave portions are formed on the upper side and the lower side, a first grid plate group composed of a plurality of grid plates arranged in parallel, and in parallel so as to be orthogonal to the first grid plate group Of a spent nuclear fuel support structure having a second lattice plate group composed of a plurality of lattice plates arranged in a plate, and a plate-like lattice support plate having a plurality of holes arranged in a lattice shape inside A method,
A method of manufacturing a support structure, wherein the first lattice plate group, the lattice support plate, and the second lattice plate group are alternately fitted together.   A spent nuclear fuel container comprising the spent nuclear fuel support structure according to any one of claims 1 to 5 inside.

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