JPH11287886A - Shroud tube and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To absorb displacement by swelling, by constituting a tube shape shell capable of containing absorber pellets in a line with element tubes having a slit, and duplicating inside and outside and covering the inner slit by the outer element pipe. SOLUTION: A control element 1 is constituted by aligning and charging a plurality of absorber pellets 2 in a clad 3. The absorber pellets 2 are contained in the clad in the state contained in a shroud tube 6. The shroud 6 has a shell part 7 having a tube shape capable of densely containing a plurality of absorber pellets 2. The shell part 7 is constituted by duplicating the shell part elements 8a and 8b coaxially inside and outside thereof. The shell part element tubes 8a and 8b are made of austenic group stainless steel and a slit 11 is arranged alternately along the longitudinal axis on the side part and the outer element tube 8b covers the slit of inner element tube 8a with the element tube 8b. By constituting in this manner, the shroud tube 6 can absorb the swelling of the absorber pellets 2 by the displacement in the circumferential direction.

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 satisfying the effect of retaining the fragments and a method of manufacturing the shroud tube.

[0006]

SUMMARY OF THE INVENTION In response to this object, a shroud tube according to the present invention has a tubular body capable of accommodating a plurality of absorbent pellets in a line, Consists of a plurality of pipes overlapping inward and outward,
Each said base tube has a slit along a longitudinal axis,
It is characterized in that the slit of the inner tube overlaps with the outer tube to cover it.

The method of manufacturing a shroud tube according to the present invention includes a body having a tubular shape capable of accommodating a plurality of absorbent pellets arranged in a line, wherein the body has a plurality of elements overlapping inward and outward. A method of manufacturing a shroud pipe, wherein each of the raw pipes has a slit along a longitudinal axis, and the outer raw pipe covers the slit of the inner raw pipe. Is characterized in that at least one of them is formed by forming a slit on the side surface of a metal tube or by rounding a metal plate.

[0008]

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 tube 6 has a body 7 having a tubular shape capable of densely storing a plurality of absorber pellets in a line.
Having.

The body 7 is constituted by a plurality of body pipes having slightly different diameters, in this embodiment, two body pipes 8a and 8b concentrically overlapping inward and outward. Each of the body shells 8a and 8b is made of a material (for example, austenitic stainless steel) having ductility even when irradiated with thin neutrons.
Slits 11 are formed on each side along the longitudinal axis, and are arranged such that the slits of the body shells are alternated. Thus, the slit of the inner body tube 8a is closed by the outer body tube 8b.

In order to manufacture the body part 7, the metal plate may be rounded and formed into a tubular shape so that the left and right ends 12, 13 are slightly apart to form the slit 11, or a thin metal plate may be formed. A slit 11 may be formed in the longitudinal direction on the side using a tube. The inner diameter D of the innermost body tube 8a is slightly smaller than the outer diameter of the absorbent pellet 2 before swelling, and the outermost body tube 8b is located outside the outer diameter.
Have inner diameters of the body shells 8a located adjacent to the inner side, respectively.
Is slightly smaller than the outer diameter of the body pellet, so that the elastic pellet 2 and the other body shell adjacent to the inside are held by utilizing the elastic restoring force of the body shell.

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, in this case the barrel blank tube 8a, the width W _a1, W _b2 of the slit 11 of 8b small, also the gap D ₁ is large between the shroud tube 6 and the cladding 3. Next, the control element 1 is loaded into the reactor, and the absorber pellets 2 undergo neutron irradiation to cause swelling.
Is absorbed by the elastic deformation of the shroud tube 6. In this case, the width W _a1 of the slit 11 of the body shell 8a, 8b,
W _b2 becomes large, and smaller gap _{D 2} between the shroud tube 6 and the cladding 3.

Thus, according to the present invention, the shroud pipe 6 absorbs the swelling of the absorber pellets by circumferential displacement and does not project in the circumferential direction, so that no large stress is generated in the shroud pipe and the shroud pipe is There is no loss of soundness. In addition, since the slit that allows the circumferential displacement of the body tube is always closed by the outer body tube, even if the circumferential length of the shroud tube is extended due to swelling of the absorber pellets, debris of the pellet is not removed. Can be prevented from spilling and causing relocation.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of the design of a shroud tube is shown below. Material of inner and outer trunk pipes: SUS316 Thickness of inner and outer trunk pipes: 0.2 mm / 0.2 mm Outer diameter of inner and outer trunk pipes: 12.6 mm / 13.0 mm Inner and outer trunk pipes Slit width (before irradiation): 0 mm / 0
mm Width of slits (after irradiation) of inner and outer trunk shells: 3.8 mm
/3.8mm

[0015]

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.

In the embodiment described above, the body shell constituting the body is composed of two bodies indicated by reference numerals 8a and 8b.
The body may be composed of three or more body shells.

Although the above description has been made with respect to an embodiment in which the present invention is applied to a shroud pipe for a control element, the present invention can also be applied to a shroud pipe for a fuel element.

[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 an explanatory 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 a, 8 b trunk tube 11 slit

Claims (5)

[Claims] 1. A body having a tubular shape capable of accommodating a plurality of absorber pellets in a state of being arranged in a line, wherein the body comprises a plurality of base tubes overlapping inward and outward, and each of the base tubes is A shroud tube having a slit along a longitudinal axis, wherein the shroud tube overlaps such that an outer tube covers the slit of the inner tube. 2. The shroud tube according to claim 1, wherein the body is made of a metal material. 3. The shroud tube according to claim 1, wherein at least one of said plurality of tubes is austenitic stainless steel. 4. A body having a tubular shape capable of accommodating a plurality of absorber pellets in a state of being aligned in a line, wherein the body comprises a plurality of base tubes overlapping inward and outward, and each of the base tubes is A method for manufacturing a shroud tube having a slit along a longitudinal axis, wherein an outer tube overlaps a slit of an inner tube, wherein at least one of the tubes is slit on a side surface of a metal tube. A method for manufacturing a shroud tube, characterized by forming and manufacturing a shroud tube. 5. A body having a tubular shape capable of accommodating a plurality of absorber pellets in a state of being aligned in a line, wherein the body comprises a plurality of base tubes overlapping inward and outward, and each of the base tubes is A method of manufacturing a shroud tube having a slit along a longitudinal axis, wherein an outer tube overlaps a slit of an inner tube, wherein at least one of the tubes is formed by rolling a metal plate. A method for manufacturing a shroud tube, characterized by being formed.