JP3256484B2 - Shroud tube and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shroud pipe for a fuel element and a control element of a nuclear reactor, and more particularly to a shroud pipe for a control element and a method of manufacturing the same.

[0002]

2. Description of the Related Art Absorber pellets 2 of control elements loaded in a nuclear reactor are cracked due to neutron irradiation effects, temperature distribution in the absorber pellets, and the like. The broken fragments 4 accumulate at the lower part of the absorber pellet. This is called relocation. When the absorber pellets 2 are irradiated with neutrons, a volume expansion behavior called swelling occurs. On the other hand, the control element has a structure in which a gap 5 capable of absorbing the swelling of the absorber pellets is provided in advance so that the soundness of the cladding tube is not impaired by the volume expansion of the absorber pellets due to swelling. However, when relocation occurs, the fragments 4 of the absorber pellets 2 fill the gap 5 between the absorber pellets 2 and the cladding tube 3 as shown in FIG. A forced displacement is applied, which causes the cladding tube 3 to break. Therefore, in the conventional control element 1a, a shroud tube 6a for holding the absorber pellets is used in order to prevent relocation of the absorber pellets 2. FIG. 6 shows an example of the structure of a conventional shroud tube 6a. The conventional shroud tube 6a has a tubular shape in which the absorbent pellets 2 are arranged in a line and contained therein, and these are arranged inside the cladding tube 3.

[0003]

In such a conventional structure, since the shroud pipe 6a is subjected to the forced displacement due to the swelling of the absorber pellets 2, a large strain is generated in the shroud pipe 6a, and the shroud pipe 6a is damaged by exceeding the allowable value. This causes a problem that relocation of the absorber pellets 2 cannot be prevented. This was due to the fact that in the tubular shroud tube 6a, the circumferential protrusion became large with respect to the displacement due to the swelling of the absorber pellets.

In order to solve such a problem, it is necessary to develop a shroud tube which does not cause a large strain in the shroud tube by absorbing displacement even when the absorber pellet swells and which satisfies the pellet holding effect. Is desired.

[0005] The present invention has been made in view of the above circumstances, and even if the absorber pellets swell, the displacement can be absorbed and no large distortion is generated. It is an object of the present invention to provide a shroud tube that satisfies the effect of retaining the fragments and a method of manufacturing the shroud tube.

[0006]

In response to this object, a shroud tube according to the present invention has a tubular shape capable of accommodating a plurality of absorbent pellets in a line, and the left and right ends of the material are left and right. It is characterized in that the overlapping portions are formed along the longitudinal axis. Further, the method for manufacturing a shroud tube of the present invention has a tubular shape capable of accommodating a plurality of absorbent pellets in a state of being aligned in a line, and the overlapping portion where the left and right side edges of the material overlap along the longitudinal axis. A method for manufacturing a shroud tube that has been formed, wherein a slit is formed on a side surface of a metal tube, and then pressed inward to overlap the left and right ends to form the overlapped portion, or a metal plate is rolled. It is characterized by forming.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings showing an embodiment in which the present invention is applied to a shroud tube for a control element.

In FIG. 1, reference numeral 1 denotes a control element. The control element 1 is configured by filling a plurality of absorbent pellets 2 in a line in a cladding tube 3. The absorber pellets 2 are housed in the cladding tube 3 in a state of being included in the shroud tube 6.

The shroud pipe 6 includes a plurality of absorbent pellets 2.
Are arranged in a line and have a body 7 in the shape of a tube that can be densely stored. The body 7 is formed by rounding a metal plate made of a material (for example, austenitic stainless steel) having ductility even when irradiated with thin neutrons, and forming it into a tubular shape. An overlapping portion 8 is formed on the side of the body 7 along the longitudinal axis. The overlapping portion 8 is a portion where the left and right side ends 12 and 13 of the metal plate 11 overlap.

In order to manufacture the body 7, the metal plate 11 may be rounded and formed into a tube shape so as to form the overlapped portion 8 as described above. Alternatively, a slit may be formed in the longitudinal direction, and the metal part may be uniformly pressed inward from the outside to perform plastic working to form the overlapped portion 8. The overlapping amount W of the overlapping portion 8 is determined by estimating the swelling amount of the absorber pellets 2.
In some cases, some leakage of the fragments of the absorber pellets 2 from the shroud pipe 6 is acceptable. In this case, the overlapping amount W is zero or the side end portions 12 of the overlapping portion 8,
13 may be slightly separated and some slits may be formed. The inner diameter D of the body 7 is slightly smaller than the outer diameter of the absorbent pellet 2 before swelling, and the elastic pellet 2 is held by utilizing the elastic restoring force of the body 7.

Next, the operation of the shroud tube configured as described above will be described. FIG. 4 shows a state of the shroud tube before being loaded into the nuclear reactor and a deformation of the shroud tube when loaded into the nuclear reactor and subjected to displacement due to swelling of the absorber pellets. As shown in Figure 4a, before being loaded into the reactor shroud tube 6 holds the absorber pellets 2, superposition amount W ₁ in this case overlapping portion 8 is large, also, the shroud tube 6 clearance D ₁ is large between the cladding tube 3 and. Next, the control element 1 is loaded in the nuclear reactor, and the absorber pellets 2 undergo neutron irradiation to cause swelling, but the displacement of the absorber pellets 2 is absorbed by the elastic deformation of the shroud tube 6. This case is smaller superposition amount W ₂ of overlapping portions 8 and gaps D ₂ also decreases the shroud tube 6 and the cladding 3. Thus, in the present invention, the shroud tube absorbs the swelling of the absorber pellets in the circumferential direction and does not stretch in the circumferential direction, so that no large stress is generated in the shroud tube and the shroud tube loses soundness. Nothing. In addition, by providing the shroud tube with an overlapping portion in advance, even when the circumferential length of the shroud tube is extended due to swelling of the absorber pellets, it is possible to prevent the fragments of the pellets from falling and causing relocation.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of the design of a shroud tube is shown below. Shroud tube material: SUS316 Shroud tube thickness: 0.2 mm Shroud tube outer diameter: 12.6 mm Shroud tube overlapping portion width (before irradiation): 5 mm Shroud tube overlapping portion width (after irradiation): 1 .2mm

[0013]

As is apparent from the above description, according to the present invention, even when the absorber pellets swell, the displacement can be absorbed and no large strain is generated, and the absorber pellets and the fragments thereof can be absorbed. And a method for manufacturing the same can be obtained.

Although the above description is of an embodiment in which the present invention is applied to a control element shroud pipe, the present invention can also be applied to a fuel element shroud pipe.

[Brief description of the drawings]

FIG. 1 is a perspective explanatory view of a partially broken control element.

FIG. 2 is a sectional view taken along the line AA in FIG.

FIG. 3 is an explanatory perspective view of a shroud tube.

FIG. 4 is a cross-sectional view of a control element.

FIG. 5 is an explanatory perspective view of a conventional control element with a shroud pipe removed;

FIG. 6 is an explanatory perspective view of a conventional control element.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 control element 2 absorber pellet 3 cladding tube 4 debris 5 gap 6 a shroud tube 6 shroud tube 7 trunk 8 superposition

Claims (5)

(57) [Claims] 1. A tubular shape capable of accommodating a plurality of absorbent pellets arranged in a line, and a superposed portion where left and right ends of a raw material are overlapped is formed along a longitudinal axis. A characteristic shroud tube. 2. The shroud tube according to claim 1, wherein said shroud tube is made of a metal material. 3. The shroud tube according to claim 1, wherein said material is austenitic stainless steel. 4. A shroud tube having a tubular shape capable of accommodating a plurality of absorbent pellets in a line, and having a superposed portion formed along the longitudinal axis where left and right ends of the material overlap each other. The method for manufacturing a shroud tube according to claim 1, wherein a slit is formed in a side surface of the metal tube, and then the metal tube is pressed inward to overlap the left and right ends to form the overlapped portion. 5. A tubular shape capable of accommodating a plurality of absorbent pellets arranged in a line, and a superposed portion where left and right ends of a material overlap each other is formed along a longitudinal axis. A method for manufacturing a shroud tube, characterized by rolling and forming a metal plate.