JPH05281386A - Method for transforming reactor incore component material - Google Patents

Abstract

PURPOSE:To obtain a method for transforming reactor incore component material, by which the degraded part of a material is transformed without taking reactor incore structure out of the reactor and improve the corrosion resistivity of a channel box. CONSTITUTION:In the method for transforming reactor incore component, a high frequency induction coil 6 is arranged in welding thermal effect part 5 which is a sensitized region of a shroud as an incore structure in reactor pressure vessel. The method is constituted of a process using this high frequency induction coil 6 for heating and of a process arranging the high frequency induction coil at a channel box and heating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is capable of recovering sensitization due to welding of reactor internals and material deterioration due to neutron irradiation, and further improving corrosion resistance of a channel box forming a fuel assembly. The present invention relates to a material reforming method for equipment in a nuclear reactor.

[0002]

2. Description of the Related Art Boiling water nuclear reactor (hereinafter referred to as BWR)
In general, the operating life of a plant is generally set to about 40 years in consideration of the safety factor. However, it is considered that the practical life of nuclear power plant structures is much longer than this, and in recent years, the extension of the life of nuclear power plants has been studied and quantitatively evaluated.
The welds of some reactor internals become sensitized by the heat input from welding during manufacturing, and the sensitization of the material also progresses in this part by irradiation with neutrons during subsequent operation, and its toughness slightly decreases. Is being considered. This degree of toughness reduction is one of the important issues when quantitatively evaluating the life extension period of a plant, and is currently being actively studied. In addition to the welded parts, it is considered that the material in the reactor internal structure deteriorates to some extent by neutron irradiation, but this is also an important subject for consideration when determining the life extension period of the plant. ing.

When extending the life of such a plant, the life extension period may be limited depending on the evaluation result of the degree of deterioration of the material. Therefore, for the replaceable reactor internal structures, the replacement method is being developed in parallel. However, most of the reactor internal structure is difficult to replace due to its structure, or even if it can be replaced, a large investment is required for developing the construction method.

On the other hand, although the channel box forming the fuel assembly installed in the reactor is a replaceable part, it is exposed to the severe corrosive environment of the core of the reactor, and its life is expected to increase in the future. In order to develop a high burnup fuel with a long life, it is necessary to further improve its corrosion resistance compared to the present.

[0005]

Therefore, when extending the life of the plant, there is a strong demand for the development of a method for recovering only the material-deteriorated portion without removing such internal structure from the nuclear reactor. At present, various methods such as a technique for modifying the surface of a material using a laser beam are being studied, but up to now, no one technically applicable to a plant has been developed.

Further, various materials have been vigorously developed for improving the corrosion resistance of the high burnup channel box, but no technique for improving the corrosion resistance by surface modification at the time of manufacturing the current material has been developed. ..

The present invention has been made in consideration of the above points, and it is possible to remove the internal reactor structure without removing it from the reactor.
An object of the present invention is to obtain a material reforming method for reactor internal equipment which can recover a portion where the material is deteriorated by neutron irradiation during welding or operation, and can further improve its corrosion resistance at the time of manufacturing a channel box.

[0008]

In order to achieve the above object, the present invention provides a method for modifying a material in a reactor internal equipment, which is used for modifying a material in a reactor internal equipment, comprising: Reactor characterized in that a high-frequency induction coil is arranged in a sensitized region generated during welding of an internal structure in the furnace, and the sensitized region is recovered by high-frequency induction heating using the high-frequency induction coil. Provided is a material reforming method for reactor internal equipment, which is used for material reforming of reactor internal equipment, comprising: a reactor deteriorated by neutron irradiation during reactor operation; A high-frequency induction coil is arranged in a structure, and a material reforming method for reactor internal equipment, characterized in that the deteriorated reactor internal structure is recovered by high-frequency induction heating using the high-frequency induction coil, It In the material reforming method of reactor internal equipment used for material reforming of reactor internal equipment, a high frequency induction coil is arranged in a zirconium alloy channel box at the time of manufacturing to form a fuel assembly. Provided is a method for modifying the material of reactor internal equipment, characterized in that the channel box is heat-treated by high-frequency induction heating using the high-frequency induction coil.

[0009]

With this structure, the high-frequency induction coil is used to continuously heat the material surface of the reactor internal structure deteriorated by welding or neutron irradiation, thereby sensitizing the material by welding or neutron irradiation. The material-deteriorated portion can be solution-treated and recovered.

Further, by heating the surface of a zirconium alloy channel box using the same high frequency induction coil, a layer having excellent corrosion resistance can be formed on the surface, and the corrosion resistance is remarkably improved. be able to.

[0011]

FIG. 1 is a schematic diagram of a shroud which is one of the reactor internals to which the first embodiment of the present invention is applied.
In the figure, the shroud 2 is arranged in the reactor pressure vessel 1 and forms a boundary between a boiling region and a non-boiling peripheral region in the reactor. The shroud 2 is made of several austenitic stainless steel plates by several circumferential joint welds 3 and vertical seam welds 4 in that shape. FIG. 2 is an enlarged view of the core portion of the shroud 2, especially the fuel loaded therein. FIG. 3 shows the first of the present invention.
It is a block diagram of an Example and is an example which applied the present invention to vertical seam welding part 4 of shroud 2. Generally, the weld zone has a weld heat affected zone 5 that is affected by the heat input during welding along the weld line, and has a particularly high carbon content (generally C> 0.03%) stainless steel. In the case of steel, this region is sensitized and the resistance to stress corrosion cracking is inferior to the other. Further, the welding heat affected zone 5 may be further sensitized by neutron irradiation during the operation of the reactor. In the first embodiment, a high frequency induction coil 6 incorporated in a mobile robot with a remote control (not shown) is arranged in this portion at a position of 3 mm to 5 mm with respect to the welding heat affected zone 5. FIG. 4 is a block diagram of a high frequency heating system for heating by a high frequency induction coil. An inverter 7 connected to an external power source and a transformer 8 are connected by a cable 9. The transformer 8 and the high frequency induction coil 6 are integrated. Next, the operation of the first embodiment having such a configuration will be described.

About 100 K using high frequency induction heating system
When a high frequency of Hz is applied to the heating coil 6, the region 5 sensitized by neutron irradiation during welding and subsequent operation in FIG. 3 is the solution temperature of stainless steel by induction heating.
Temperature rises from 1050 to 1100 ℃. A phenomenon in which the soundness of a reactor internal structure becomes a problem due to its sensitization is a phenomenon of a material surface in contact with reactor water, which causes stress corrosion cracking, corrosion fatigue, and the like. Therefore, it is sufficient that only the surface of the shroud (the range of up to about 2 mm toward the inner surface) is restored by this method. The high frequency condition for this is about 100 KHz
It is a degree. The high-frequency heating coil 6 is incorporated in a mobile robot with remote control (not shown), and the high-frequency induction coil 6 is continuous so that the welding heat-affected zone 5 is held at 1050 to 1100 ° C for 5 to 30 seconds by this mobile robot. Move to.

As described above, according to the first embodiment, the region sensitized by the welding of the shroud and the subsequent neutron irradiation is maintained at the solution temperature for a certain period of time, so that the sensitization is completely eliminated and the material state is improved. Can be recovered. Further, since the first embodiment uses induction heating by high frequency, only the material surface portion is heated, and the central portion of the wall thickness is hardly affected by the heating.

By the way, in general, stainless steel and the like have a cooling rate of 400 to 800 during the cooling process when the cooling rate after the solution treatment is low.
It is said that heat sensitization occurs again at a temperature between ° C. However, the reactor pressure vessel is always filled with a large amount of reactor water, and since the high frequency induction heating of the first embodiment can be performed in this reactor water, this reactor water acts as a coolant during high frequency induction heating, The shroud surface can be cooled from the solution temperature to a low temperature region in a short time. Therefore, in the first embodiment, the re-sensitization in the cooling process after the solution heat treatment by the high frequency induction heating can be completely prevented. The first embodiment can be applied in the same manner to the peripheral joint welded portion of the shroud and the sensitized portion due to welding of other nuclear reactor structures. Next, a second embodiment of the present invention will be described.

It is conceivable that, of the nuclear reactor internal structures arranged close to the core part, not only the welded part but the entire material surface is deteriorated in corrosion resistance and toughness to some extent by neutron irradiation. The solution treatment method for the surface of the welded material by high-frequency induction heating according to the present invention is extremely effective for recovery of the neutron-irradiated portion on the entire surface of such a structure. This method is exactly the same as the first embodiment of the present invention. When the entire structure surface is subjected to solution treatment, the high frequency induction coil may be shifted by a predetermined interval by a remote mobile robot so that the entire structure surface can be completely solution-treated. The heating conditions at this time may be the same as in the first embodiment. Next, a third embodiment of the present invention will be described.

FIG. 5 is a block diagram of a channel box constituting a fuel assembly to which the third embodiment of the present invention is applied. In FIG. 5, the channel box 11 is made of zirconium alloy. This channel box is made from a zirconium alloy ingot with a diameter of about 600 mm, hot forging, hot rolling, and cold rolling.
A thin plate is manufactured, and this is processed and welded to manufacture a shape as shown in FIG. During this time, a number of heat histories are traced, but a different metallographic structure is exhibited depending on the heat histories. Depending on this metal structure, there is a possibility that it may not show good corrosion resistance during use in a nuclear reactor, and now it is passed a strict acceptance inspection and delivered to the plant.

In general, it is known that a structure obtained by quenching from the β region has good corrosion resistance in a nuclear reactor, but it is highly necessary to maintain the β quenched structure through the above manufacturing process. In need of technology. Therefore, the third embodiment was devised to form a β-quenched structure on the surface of the channel box near the final stage of the manufacturing process.

FIG. 6 is a block diagram of a third embodiment in which the present invention is applied to the channel box manufactured by the above manufacturing process. In the third embodiment, a high frequency induction coil in which a high frequency induction coil 14 incorporated in a mobile robot with a remote control (not shown) is arranged on the surface of the manufactured channel box.
The configuration of the high-frequency heating system for heating by 14 is the same as in FIG. Next, the operation of the third embodiment having such a configuration will be described.

About 50 to 10 using a high frequency induction heating system
When a high frequency of 0 KHz is applied to the heating coil 14, the surface 12 of the channel box in FIG. 6 is partially melted by induction heating or rises to the β phase region. Whether it is melting or heating to the β-phase region depends on the moving speed of the coil. The phenomenon in which the corrosion resistance of the channel box is a problem is the phenomenon of the material surface in contact with the reactor water. For this reason, only the surface of the channel box (up to about 0.5 mm toward the inner surface) is sufficient for the system to melt or heat to the β range. The high frequency condition for this is in the range of about 50 to 100 KHz. The high-frequency heating coil 14 is incorporated in a mobile robot with remote control (not shown), and the entire surface of the channel box is melted or β by this mobile robot.
The high frequency induction heating coil 14 is continuously moved at a predetermined speed so as to be held in the phase region for 5 to 30 seconds.

As described above, according to the third embodiment, the surface layer of the channel box having a thickness of about 0.5 mm is melted or held in the β phase region for a certain period of time by high frequency induction heating to form a complete β quenched structure. The corrosion resistance of the surface becomes extremely good. Further, since the third embodiment uses induction heating by high frequency, only the material surface portion is heated, and the thickness center portion is hardly affected by the heating.

By the way, in general, zirconium alloy is β
It is said that when the cooling rate of quenching from the phase is low, a structure with poor corrosion resistance is generated during this cooling process. However, in the third embodiment, the high frequency induction heating is applied to the channel box formed into a thin plate having a thickness of about 2 mm, and the channel box surface can be melted or cooled from the β phase region to the low temperature region in an extremely short time. it can. Therefore, in the third embodiment, the change in the metal structure during the cooling process can be prevented by the high frequency induction heating.

Although the third embodiment is applied to the entire surface of the channel box, even if it is applied only to the surface adjacent to the stainless steel such as the control rod which is the most severe corrosive environment, a considerable improvement effect can be obtained. Obtainable.

[0023]

As described above, according to the material reforming method for the reactor internal equipment according to the present invention, the reactor internal structure deteriorated by welding or neutron irradiation using the high frequency induction coil. By heating and holding the surface, the material-deteriorated portion such as sensitization due to welding or neutron irradiation is completely solution-treated, and the material-deteriorated portion can be recovered. As a result, the soundness of the reactor internals is guaranteed, which can contribute to extending the life of the plant.

Further, in the present invention, by heating the whole or a part of the surface of the channel box forming the fuel assembly by using the high frequency induction coil, a layer having excellent corrosion resistance can be formed on the surface. It is possible to significantly improve the corrosion resistance of the channel box, which can contribute to the reliability of the high burnup fuel.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a partially cut shroud, which is one of reactor internal structures to which the first and second embodiments of the present invention are applied.

FIG. 2 is an enlarged bird's-eye view of the shroud shown in FIG.

FIG. 3 is a configuration diagram according to a material reforming method for reactor internal equipment, which is a first and a second embodiment of the present invention.

FIG. 4 is a configuration diagram of a system relating to a material reforming method for reactor internal equipment according to the first and second embodiments of the present invention.

FIG. 5 is a perspective view showing a channel box to which a third embodiment of the present invention is applied.

FIG. 6 is a configuration diagram according to a material reforming method for a channel box, which is a third embodiment of the present invention.

[Explanation of symbols]

 1 ... Reactor pressure vessel 2 ... Shroud 3 ... Circumferential joint weld 4 ... Vertical seam weld 5 ... Welding heat affected zone 6 ... High frequency induction coil 11 ... Channel box 14 ... High frequency induction coil

Claims (3)

[Claims] 1. A material reforming method for reactor internal equipment used for material reforming of reactor internal equipment, comprising: a sensitization region generated during welding of internal reactor internals in a reactor. A method for modifying a material for reactor internal equipment, comprising disposing a high frequency induction coil, and recovering the sensitized region by high frequency induction heating using the high frequency induction coil. 2. A high-frequency induction coil for a reactor internal structure which has been deteriorated by neutron irradiation during reactor operation in a method for modifying a reactor internal device material used for modifying a reactor internal material. Is arranged, and the deteriorated reactor internal structure is recovered by high-frequency induction heating using the high-frequency induction coil. 3. A high-frequency induction coil in a zirconium alloy channel box at the time of manufacturing for forming a fuel assembly in a material reforming method for reactor internal equipment used for material reforming of nuclear reactor internal equipment. And heat treating the channel box by high frequency induction heating using the high frequency induction coil.