JPH08278390A - Shroud and its repairing method - Google Patents

Abstract

PURPOSE: To provide a shroud and a repairing method for shroud capable of preventing crack generation and increase of the generated crack. CONSTITUTION: On the edge surfaces 41a, 41b, 42a and 42b of connection parts (diameter difference parts) 41 and 42 of shroud surface of which lamination of parent metal of a shroud 2 arranged in a reactor pressure vessel has exposed in contact with reactor water, melting treatment is applied by non-filler TIG welding, and the edge surfaces 41a, 41b, 42a and 42b are covered with molten metal 10 so that the initiation of cracking owing to lamination of plate material is avoided and progression is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a shroud which is a core supporting structure of a reactor pressure vessel and a repair method thereof.

[0002]

2. Description of the Related Art FIG. 9 is a schematic sectional view of a reactor core support structure of a conventional boiling water reactor. In the figure, a shroud 2 is arranged in a reactor pressure vessel 1, and a fuel 15 is stored in the shroud 2. The shroud 2 functions as a horizontal support for the fuel 15 and a partition wall of the reactor water flow path. An upper lattice plate 3 is provided on the upper portion of the shroud 2, and a lower portion thereof is supported by a shroud support leg 8 from a lower portion of the pressure vessel 1 by an annular shroud support cylinder 7. Generally, the shroud 2 is provided with two different diameter portions 4, the upper diameter difference portion 42 is provided with the upper lattice plate 3, and the lower diameter difference portion 41 is provided with the core support plate 9. There is. A control rod 16 is provided on the core support plate 9.
Is supported so that it can be raised and lowered, and fuel 1 is attached to the upper end of each control rod 16.
5 is attached. A shroud support plate 6 is provided on the outer peripheral portion of the shroud support cylinder 7 to regulate the distance from the pressure vessel 1 and to position the shroud 2 in the pressure vessel 1. Further, a jet jet is provided on the upper surface of the plate 6. A pump 5 is arranged to forcibly circulate water between the pressure vessel 1 and the outer peripheral surface of the shroud 2.

The shroud 2 has the different diameter portions 41, 42.
Since different members are welded to form stepped parts with different diameters, the end faces are exposed at the inner and outer peripheral parts of the annular member formed of the plate material forming the stepped part, but recently, on the end faces Cracks may be found. It is considered that the cracks are formed at the time of molding and occur along the lamination layer exposed on the end face, and further propagate, but the shroud 2
If cracks occur in the
Naturally, repair or reinforcement of the part is required. Note that the lamination means a layered structure, and since a plurality of different parts of the structure are exposed on the end face formed across the layer, the cracks generated from the end face where the layered part is exposed are concerned. It is considered that it progresses along the layer, in other words, parallel to the layer.

Stress corrosion cracking is considered as one of the causes for the occurrence or development of cracks. For this stress corrosion cracking, a corrosion-resistant material containing delta ferrite is built up on the surface that comes into contact with the corrosive fluid, and then the built-up toe is heated to 5 k
A method of performing melt processing at J / cm or less is known (Japanese Patent Publication No. 59-21711). This method is intended to eliminate the chromium-deficient layer formed by the thermal effect of the build-up of the corrosion resistant material and to produce a structure having excellent corrosion resistance containing delta ferrite.

A method is also known in which one of the front and back surfaces is cooled while the opposite surface is melted (JP-A-2-258190). This method is intended to melt-process one surface to form a structure having excellent corrosion resistance containing delta ferrite, and to reduce residual stress on the other surface.

Further, there is also known a method of melting the surface of the welded portion of the internal structure of the nuclear reactor in contact with the reactor water with a laser (Japanese Patent Laid-Open No. 2-161397). According to this method, the heat-affected zone or segregation zone having poor corrosion resistance is subjected to a surface treatment by a laser, melted and then rapidly cooled to be made into two phases, thereby improving the corrosion resistance.

[0007]

By the way, in the above-mentioned conventional example, the purpose is to repair cracks occurring in any part of the shroud, and consideration is given to prevention or suppression of cracks. I didn't. In particular, no consideration was given to preventing or suppressing cracks caused by the lamination of shrouds made of sheet material that would cause initiation. Therefore, the surface where the lamination of the shroud is exposed in layers, in other words, the portion where the surface formed across the lamination contacts the reactor water is modified,
Alternatively, it is considered that a structure in which the layered exposed portion of the shroud does not come into contact with the reactor water is preferable.

The present invention has been made in view of the above-mentioned circumstances of the prior art, and an object thereof is to provide a shroud and a method for repairing the shroud which can prevent the occurrence of cracks and the progress of the cracks. Especially.

[0009]

Means for Solving the Problems The above-mentioned object is to make the lamination of the plate material exposed in layers in the shroud, melt the surface layer portion in contact with the reactor water, and make the state equivalent to the weld metal, or the shroud. This can be achieved by manufacturing the whole or a part of the shroud by forging to prevent the cut surface of the plate material from being exposed.

That is, in order to achieve the above object, the first
The means is characterized in that, in the shroud arranged in the reactor pressure vessel, the portion of the surface of the shroud where the lamination of the base material is exposed is in contact with the reactor water is subjected to the melting treatment. In this case, for example, non-filler TIG welding can be applied as the melting process.

The second means is characterized in that, in a shroud of the same premise, a weld overlay is applied to a portion of the surface of the shroud where the lamination of the base material is exposed, which is in contact with the reactor water. In this case, filler TIG welding can be applied as the weld overlay.

The third means is characterized in that, in the shroud of the same premise, the shroud is integrally formed by forging.

The fourth means is characterized in that, in the shroud of the same premise, the adjacent portion of the different diameter portion of the shroud is formed by forging.

A fifth means is a shroud repairing method for repairing a shroud arranged in a reactor pressure vessel, in which a portion of the surface of the shroud where the lamination of the base material is exposed is melted and treated. It is characterized by that.

A sixth means is a shroud repairing method based on the same premise, in which a portion of the surface of the shroud where the lamination of the base material is exposed is in contact with the reactor water is weld-padded.

In this case, for example, filler TIG welding may be applied as the weld overlay, and non-filler TIG welding may be applied as the melting process.

[0017]

In the shroud, the portion where the lamination of the plate material is exposed in layers, that is, the surface formed across the lamination is subjected to the melting treatment so that the lamination does not come into direct contact with the reactor water. As a result, corrosion does not progress between the lamination layers, and cracks from the layers can be prevented. In addition, as the melting treatment, melting by non-filler TIG welding or the like or welding overlay such as filler TIG welding can be applied, whereby crack initiation due to lamination of the plate material can be prevented. In addition, a melting process such as non-filler TIG welding, or a weld overlay such as filler TIG welding is applied to the crack generation site on the inner surface and the outer surface of the shroud. Thereby, the crack generated in the shroud can be contained inside the shroud, and the crack can be prevented from progressing.

Further, even if the shroud is integrally forged or a part of the shroud is forged so that the layered portion of the lamination of the plate material is not exposed on the inner and outer surfaces of the shroud, the initiation of cracking is prevented. Can be prevented.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of essential parts showing a shroud and a pressure vessel according to a first embodiment of the present invention. In the following description, the same reference numerals are attached to the respective units that can be regarded as equivalent to the above-described conventional example, and the duplicated description will be omitted.

In FIG. 1, a connecting portion (diameter difference portion) 41 between a lowermost small-diameter body portion 21 of the shroud 2 and a larger-diameter body portion 22 above the shroud 2, and the uppermost portion of the body portion 22 and its upper portion. Connection part (diameter difference part) 4 with the larger-diameter body part 23 of
The end faces 41a, 41 in which the lamination of 2 is exposed in layers
The entire surface of b and 42a, 42b is covered with the molten metal 10, and the surface state is improved by the delta ferrite produced by melting and solidifying. In this embodiment, the molten metal 10 is formed by non-filler TIG welding,
The lamination of the cut surface of the plate material covers the exposed portion in layers. FIG. 2 is an enlarged view showing a state in which the end surfaces 42a and 42b are melt-processed by non-filler TIG welding.

In TIG (tungsten / inert gas arc) welding, heat is input by the arc, but the arc is generated in a circular shape with a diameter of several millimeters, and the welding torch is moved to advance the welding. Becomes a bead shape, and the end faces 41a, 41b, 42a, 42b are melt-processed so as to be covered with beads.

FIG. 3 shows an end surface 42a according to the second embodiment,
It is an enlarged view which shows the state which carried out the melting process of 42b. That is, as schematically shown in FIG. 3, when a through crack 11 or a non-through crack 12 is formed on the surface of the plate material cut surface of the connection portion (diameter difference portion) 42 of the shroud 2, the end surface where lamination is exposed in layers 42a, 42b non-filler TIG
When welding is performed, the through crack 11 or the non-through crack 12 can be contained inside the shroud difference portion 4.

FIG. 4 shows an end surface 42a according to the third embodiment,
It is an enlarged view which shows the state which carried out the melting process of 42b. This embodiment is an example in which filler TIG welding is applied to the entire surfaces of the end faces 42a and 42b of the connecting portion (diameter reducing portion) 42 of the shroud 2. That is, in the example in which the entire surface of the end surface of the connecting portion 42 of the shroud 2 is filler TIG welded to cover the lamination of the end surfaces 42a and 42b with the weld metal 13 and the surface state of the end surfaces 42a and 42b is improved. is there.

FIG. 5 shows an end surface 42a according to the fourth embodiment,
It is an enlarged view which shows the state which carried out the melting process of 42b. In this embodiment, the through crack 11 or the non-through crack 1 is formed on the surfaces of the end surfaces 42a and 42b of the connecting portion (diameter reducing portion) 42 of the shroud 2.
When 2 occurs, it is an example in which the through crack 11 or the non-through crack 12 is enclosed in the shroud different diameter portion 4 by performing filler TIG welding.

FIG. 6 shows a shroud 2 according to the fifth embodiment.
FIG. In this embodiment, the entire shroud 2 is integrally forged to prevent the lamination from being exposed at the end faces of the connection portions (reduced diameter portions) 41, 42. This lamination appears when the plate material is manufactured in the can manufacturing process, and when it is integrally formed by forging, the lamination is not exposed on the end faces of the connecting portions 41 and 42. Therefore, the initiation of cracking caused by lamination can be eliminated.

FIG. 7 is a sectional view of the essential parts of a shroud according to the sixth embodiment.

In this embodiment, the connecting portion (diameter difference portion) 42 of the shroud 2 is manufactured by forging into a hook-shaped cross section, and is welded by butting against the body portions 22 and 23 of the shroud 2. By doing so, the reduced diameter portion 42 of the shroud 2
Since the lamination is not exposed, the cause of crack initiation can be eliminated. In addition, the code | symbol 14 shows the welded part.

FIG. 8 is a sectional view of the essential parts of a shroud according to the seventh embodiment.

In this embodiment, the connecting portion (diameter difference portion) 42 of the shroud 2 is formed into an annular shape, and the outer peripheral surface of the upper end of the body portion 22 and the inner peripheral surface of the lower end portion of the body portion 23 are butted. It is an example of welding. Even with this configuration, the connecting portion 4
Since the end face where the lamination No. 2 is exposed does not come into contact with the reactor water, it is possible to eliminate the initiation cause of cracking.

[0031]

As is apparent from the above description, according to the present invention configured as described above, the lamination is not exposed on the end faces of the portions (connection portions) having different diameters of the shroud, and Therefore, since the end surface does not come into contact with the reactor water, it is possible to eliminate the initiation cause of the crack of the shroud due to the lamination and prevent the development of the crack generated in the shroud.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a shroud according to a first embodiment of the present invention.

FIG. 2 is a partial perspective view showing a state of a melting process of a connecting portion of the shroud in FIG.

FIG. 3 is a partial perspective view showing a state of a melting process of a connecting portion of a shroud according to a second embodiment.

FIG. 4 is a partial perspective view showing a state of a melting process of a connecting portion of a shroud according to a third embodiment.

FIG. 5 is a partial perspective view showing a state of a melting process of a connecting portion of a shroud according to a fourth embodiment.

FIG. 6 is a cross-sectional view of essential parts of a shroud integrally formed by forging according to a fifth embodiment.

FIG. 7 is a partial perspective view showing a state of a connecting portion of a shroud according to a sixth embodiment, with a part thereof being cross-sectioned.

FIG. 8 is a partial perspective view showing a state of a connecting portion of a shroud according to a seventh embodiment, which is a partial cross section.

FIG. 9 is a cross-sectional view showing a conventional reactor internal structure.

[Explanation of symbols]

 1 Reactor Pressure Vessel 2 Shroud 21, 22, 23 Shroud Body 3 Upper Lattice Plate 4, 41, 42 Shroud Connection (Different Diameter) 5 Jet Pump 6 Shroud Support Plate 7 Shroud Support Cylinder 8 Shroud Support Leg 9 Core support plate 10 Molten metal 11 Through crack 12 Non-through crack 13 Weld metal 14 Weld

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideyasu Furukawa 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory

Claims (10)

[Claims] 1. A shroud arranged in a reactor pressure vessel, wherein a portion of the surface of the shroud exposed by lamination of the base material which is in contact with the reactor water is subjected to a melting treatment. 2. The shroud according to claim 1, wherein the melting process is a non-filler TIG welding process. 3. A shroud arranged in a reactor pressure vessel, wherein a portion of the surface of the shroud where the lamination of the base material is exposed is in contact with the reactor water and a weld overlay is applied to the shroud. 4. The shroud according to claim 2, wherein the weld overlay is a filler TIG weld overlay. 5. A shroud arranged in a reactor pressure vessel, wherein the shroud is integrally formed by forging. 6. A shroud arranged in a reactor pressure vessel, wherein a portion adjacent to the different diameter portion of the shroud is formed by forging. 7. A shroud repairing method for repairing a shroud arranged in a reactor pressure vessel, characterized in that a portion of the surface of the shroud where the lamination of the base material is exposed is in contact with the reactor water is melted. Shroud repair method. 8. The shroud repair method according to claim 7, wherein the melting process is a process by non-filler TIG welding. 9. A shroud repairing method for repairing a shroud arranged in a reactor pressure vessel, which comprises applying a weld overlay to a portion of the shroud surface exposed by lamination of the base material which is in contact with reactor water. A characteristic shroud repair method. 10. The method for repairing a shroud according to claim 9, wherein the weld overlay is a filler TIG weld overlay.