JPH05323070A - Channel box - Google Patents

Abstract

PURPOSE:To improve the insertion properties of a control rod, to suppress the occurrence of local corrosion and to prevent the exfoliation of an oxide film by preventing curvature of a channel box due to an irradiation growth. CONSTITUTION:Over a region of 50 to 90% of an area between two base lines, i.e., a base line passing a point located in the height region in the axial direction of a channel box 11, that is, about 70mm above the lower end of the box, and a base line passing a point located about 500mm below from the upper end thereof in this region, a beta-quenched region 10 of a tissue formed by rapid cooling from a beta region temperature is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a channel box of a fuel assembly for a boiling water reactor, in particular, the control rod insertion property is improved, bending deformation does not occur, and the upper grid is resistant to high temperature water corrosion. The present invention relates to a channel box made of a zirconium-based alloy having excellent corrosion resistance in a plate facing portion.

[0002]

2. Description of the Related Art A channel box of a boiling water reactor fuel assembly forms a passage for a control rod to smoothly move between adjacent fuel assemblies, and also secures a passage of high temperature and high pressure. Also plays an important role.

FIG. 5 is an elevational view showing a partial cross section of a fuel assembly for a boiling water reactor. Reference numeral 1 in the figure indicates a square rectangular channel box.

The channel box 1 surrounds the fuel bundle. In the fuel bundle, a plurality of fuel rods 2 having UO ₂ fuel loaded in a cladding tube are squarely arranged with a spacer 3 interposed, and each fuel rod 2 is drilled in an upper tie plate 4 and a lower tie plate 5. It is assembled by inserting the respective upper end plug and lower end plug into the formed support holes. A channel box 1 surrounds these fuel bundles to form a fuel assembly.

As shown in FIG. 6 (a), the channel box 1 has a stainless steel projection called a spacer pad 6 attached to the upper part of the two surfaces facing the control rod via rivets 7. Further, as shown in FIG. 6B, a pair of channel clips 8 are welded to the upper end surface at symmetrical positions. The channel clip 8 is provided with a leaf spring called a channel fastener 9, and the channel fastener 9 and the spacer pad 6 form a gap between the control rod and four fuel assemblies surrounding the control rod.
Hundreds of such fuel assemblies are loaded into one reactor.

From the viewpoint of neutron economy and corrosion resistance at high temperatures, the constituent materials of so-called core structures are as follows.
A zirconium-based alloy has been put to practical use, and it is also called Zircaloy-4, which is usually made of zirconium with about 1.5% tin, about 0.2% iron, and about 0.1% chromium added to the material of the channel box. Zirconium based alloys are used.

The manufacturing process of a typical channel box will be described with reference to FIG. First, the plate material that is the material of the channel box is received (step 1), and this is press-formed into a U-shape to manufacture a channel half (step 2), and two channel halves are welded together to form a zircaloy square tube. Produce (step 3).

After this, insert a stainless steel core into the
By heating and annealing to 600 ° C., the channel box is finished to a specified size, and the residual stress in the previous step (step 3) is removed (step 4). In this method, heat molding is performed by utilizing the difference between the coefficient of thermal expansion of stainless steel (17 × 10 ⁻⁶ in / in / ° C.) and the coefficient of thermal expansion of zircaloy (5 × 10 ⁻⁶ in / in / ° C.).

Next, the dimple processing and the channel clip, which are the contact points with the upper tie plate of the fuel assembly, are welded (step 5), polished (step 6), and spacer pad welded (step 7), followed by final inspection (step). 8) is implemented and completed. When the stainless steel core is inserted into the Zircaloy square cylinder in (Step 4), it is technically difficult because the gap between the Zircaloy square cylinder and the stainless steel core is very small.
Therefore, when welding the channel halves in (Step 3), a step of incorporating the core in advance is also performed. Further, as a means for improving the corrosion resistance of the channel box, α + β quenching may be carried out on the Zircaloy square tube in the previous step of (Step 4).

[0010]

By the way, a channel box made of a zirconium-based alloy is exposed to a large amount of neutrons during its use, so that it is elongated in the longitudinal direction. This mechanism is due to the fact that the crystal structure of zirconium is a dense hexagonal crystal.

In the rolling process at the time of manufacturing the zircaloy plate material which is the material of the channel box, the C axis of the dense hexagonal crystal is aligned substantially perpendicular to the surface of the zircaloy plate material, so that a strong texture is formed in the channel box. There is. Also, zirconium crystals are irradiated with neutrons,
Since the channel box shrinks in the C-axis direction and grows in the direction perpendicular to the C-axis, the channel box is elongated in the longitudinal direction.

When the two surfaces facing the channel box have different amounts of expansion, the channel box is bent and deformed. This bending deformation has a large amount of fast neutron irradiation, and a surface with a large elongation becomes convex, and the maximum bending occurs in the central portion in the axial direction. The inter-channel fastener gap for the movement of the control rod is secured by the fuel support fitting at the lower end of the fuel assembly and the spacer pad and channel fastener at the upper end.

However, since the bending of the channel box occurs at the central portion in the axial direction, when the four channel boxes sandwiching the control rod bend toward the control rod side, interference with the control rod occurs and the control rod is inserted. It can be difficult and can be an important issue for reactor safety.

Further, in recent years, fuel has been advanced to have a high burnup from the viewpoint of economy and the like, and it is expected that the amount of bending due to the above-mentioned increase.

On the surface of the channel box made of the above-mentioned zirconium-based alloy, corrosion may occur during operation, and an oxide film may gradually grow and sometimes peel off. In particular, it is known that corrosion locally progresses in the vicinity of stainless steel such as the portion facing the upper lattice plate, the portion adjacent to the in-core instrumentation pipe, and the portion facing the control rod handle.

When the oxide film is peeled off, the oxide film activated in the core accumulates on the bottom of the furnace and the amount of radioactive material near the bottom of the furnace increases, which may adversely affect the human body during a regular inspection, for example. Occurs. Further, the decrease in the thickness of the channel box due to the peeling of the oxide film may lead to a decrease in the mechanical strength of the channel box. further,
Fuel assemblies are in the direction of higher burnup for the purpose of improving economic efficiency, and in that sense also, the corrosion resistance of the channel box must be improved.

On the other hand, such a channel box is manufactured, for example, through the manufacturing process shown in FIG. 4 (excluding the stainless steel plate attaching process in FIG. 4) described later.

In the prior art, the entire final product is α +
It has been proposed that a β treatment, an α + β treatment or a β treatment for a product before the final product is achieved to achieve fine dispersion precipitation of an intermetallic compound and improve corrosion resistance.

However, although the conventional technique can improve the corrosion resistance to some extent, it has a problem that the above-mentioned local corrosion is not sufficient.

The present invention has been made to solve the above-mentioned problems, and prevents the bending of the channel box due to irradiation growth to improve the insertability of the control rod, and the upper grid plate against corrosion by hot water. An object of the present invention is to provide a channel box that has excellent corrosion resistance in the facing portion and can suppress peeling of an oxide film.

[0021]

A first aspect of the present invention is a fuel in which a large number of fuel rods are aligned and arranged with spacers interposed, and both ends of these fuel rods are fixed to an upper tie plate and a lower tie plate, respectively. In a channel box of a fuel assembly for a boiling water reactor for enclosing a rod bundle, about 70 above the lower end along the axial height of the channel box.
The base point is the point of mm, the base point is about 500 mm from the upper end, and the area between 50% and 90% between both base lines is provided with the β-quenched structure produced by rapid cooling from the β region temperature. It is characterized by

A second aspect of the present invention is for enclosing a fuel rod bundle constituted by arranging a large number of fuel rods in an array with a spacer interposed therebetween, and fixing both ends of these fuel rods to the upper and lower tie plates, respectively. In the channel box of the fuel assembly for a boiling water reactor, the stainless steel is attached to the outer surface of the channel box facing the upper lattice plate of the channel box when the fuel assembly is loaded in the core. It is characterized by

[0023]

In the first aspect of the present invention, the strong texture of the channel box is improved, and the channel box does not stretch in the longitudinal direction even when irradiated with fast neutrons. In at least 50% or more of the whole is β-quenched.

If the crystal structure of the channel box has a β-quenched structure, it is possible to prevent irradiation growth, which is the main cause of irradiation growth, and also to prevent channel bending due to irradiation growth.

When β-quenching is performed on a channel box, which is a Zircaloy rectangular tube, the β region (about 1000 ° C.)
In the above, there is a problem that the strength of the channel box is lowered and the channel box is easily deformed. In the present invention, β-quenching is performed with the core inserted in order to maintain the shape of the channel box, so that deformation of the channel box during β-quenching is suppressed.

In the second aspect of the invention, the local corrosion of the upper lattice plate facing portion is caused by the formation of a local battery due to the difference in the corrosion potential of each metal when different kinds of metals come into contact with each other in the reactor water. The so-called galvanic corrosion is considered to be the cause of this problem.Therefore, in the plate material manufacturing process or channel box manufacturing process, a stainless steel plate is affixed to the outer surface of the channel box molding plate material or pre-channel that faces the upper lattice plate of the channel box. To do.

As a result, the stainless steel plate is attached to the portion of the channel box facing the upper lattice plate, the difference in corrosion potential between the upper lattice plate and the outer surface of the channel box disappears, and the problem of corrosion on the surface of the upper portion of the channel box facing the upper lattice plate is eliminated. Will be resolved.

Further, at the interface between the stainless steel attached to the outer surface of the channel box and the zircaloy, that is, the interface with the base material of the channel box, local corrosion similar to the above may occur, but the base material and the stainless steel adhere to each other. Therefore, the corrosive environment is improved as compared with the conventional example. Further, peeling of the generated oxide film is suppressed by the attached stainless steel.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the channel box according to the present invention will be described with reference to FIGS. In addition,
The first embodiment corresponds to the first invention described in claim 1.

FIG. 1 (a) is an elevational view showing the channel box 11 of the first invention, and the hatched portion is a β-quenched region.
10 is shown, and FIG. 1 (b) shows a top view of FIG. 1 (a).

The shape and structure of the channel box 11 shown in FIG. 1 is essentially the same as that of the channel box 1 shown in FIG. 6, but is characterized in that the β-quenched region 10 is added to the shaded portion. And

That is, reference numeral 10 indicates a region to which a β-quenched structure is added. In this embodiment, β quenching is performed in the region 10 corresponding to the active fuel length portion of the fuel assembly in which the fast neutron irradiation dose of the normal channel box increases. The β-quenched area 10 has a base point at the lower end of the channel box 11 and is blank up to about 70 mm from the base point.
50% to 90% between both base lines with the base line at about 500 mm from the upper end of the channel box 11 from above.
Area. Therefore, channel box 11
It is blank from the upper end to 500 mm below, and no β-quenched structure is attached.

The reason why the β-quenched region is selected is due to the mechanical properties of the β-structure. Zircaloy has a lower ductility as compared with the α-annealed structure, though the β-quenched structure has an increased strength. It is necessary to keep the area of β-quenched structure within a small range.

Therefore, in the present embodiment, quenching is performed in about 90% of the area of the central area excluding the upper and lower areas of the channel box. Note that such β
By applying the tissue to 50% or more of the entire area of the channel box 11, an effective bending effect can be obtained.

Next, referring to FIG. 2, the channel box 11
The manufacturing method of will be described. The same parts as those in FIG. 7 are designated by the same reference numerals.

First, a plate material which is a material for the channel box is received (step 1), and this is press-formed into a U-shape to manufacture a channel half (step 2). Two channel halves are welded together to form a zircaloy corner. A cylinder is manufactured (step 3).

Here, insert a stainless steel core,
Β consisting of a high-frequency heating device (not shown) incorporating a high-frequency coil for β-quenching and a water jet cooling device (not shown) with the core inserted in a Zircaloy square tube
The square tube is installed in a quenching device (not shown) to perform β quenching (step 3-1).

A high frequency heating device is used to heat the square tube. The reason is that the difference in electrical resistance between zircaloy and stainless steel is large, and zircaloy is heated at a high temperature, whereas the temperature rise of stainless steel core is smaller than that of zircaloy, so the zircaloy square cylinder due to thermal expansion of the core is used. No deformation occurs, and the problem of thermal fatigue of the core that is repeatedly used does not occur.

After high frequency heating, a square tube made of zircaloy with a stainless steel core inserted therein is heated to about 600 ° C. and annealed to finish the channel box to a specified size and to reduce residual stress in the previous step. Are removed (step 4). This is the coefficient of thermal expansion of stainless steel (17 × 10 ^-6
in / in / ℃) and the coefficient of thermal expansion of Zircaloy (5 × 10 ^-6 in / in
/ ° C.) is utilized to perform heat molding.

Next, the dimple processing and the channel clip, which are the contact points with the upper tie plate of the fuel assembly, are welded (step 5), polished (step 6), and spacer pad welded (step 7), followed by final inspection (step). 8) is implemented and completed.

According to the above embodiment, the β-quenched structure is added to the specific region of the channel box to suppress the irradiation growth and prevent the bending accompanying the irradiation growth. Further, when the channel is β-quenched, deformation of the channel easily occurs, but in order to suppress the deformation at the time of manufacturing, β-quenching is performed with the core inserted. This can prevent the control rod from being difficult to insert due to interference with the control rod in the reactor.

Next, a second embodiment of the channel box according to the present invention will be described with reference to FIGS. 3 and 4.
The second embodiment corresponds to the second invention described in claim 2.

FIG. 3 (a) is an elevational view showing the main part of the channel box 12 of the second invention, FIG. 3 (b) is a transverse sectional view taken along the line AA of FIG. 3 (a), and FIG. c) is BB of FIG.
FIG.

The channel box 12 of this embodiment is made of a zirconium-based alloy, and when the fuel assembly is loaded into the reactor core, it is shown in FIG. 3 on the outer surface of the channel box facing the upper lattice plate of the reactor core. As described above, the stainless steel plate 13 is attached. The stainless steel plate 13 can be attached and installed by riveting, crimping, welding metal bonding, or the like.

Channel box 12 stainless steel plate 13
A spacer pad 6 is provided on the upper side surface where is not attached, and a channel clip 8 is provided on the upper end surface.

Next, referring to FIG. 4, the channel box 12
The manufacturing method of will be described. 4 (a) and 4 (b)
And correspond to each alphabet.

That is, a zirconium-based alloy plate is subjected to an acceptance inspection a, and this is press-formed into a U shape to produce a channel half. This channel half is groove processed c
Then, two channel halves are combined to form a rectangular tube shape, and then electron beam welding d and heat treatment forming e are performed.

Next, the length f is determined as a process for attaching the stainless steel plate, and the dimple process g, the clip welding h,
After drilling i and backwashing j, affixing stainless steel plate o
I do. Finally spacer pad welding 1 and final inspection m
To complete the channel box 12.

As a step of applying the stainless steel as described above, the outer surface of the pre-channel that faces the upper lattice plate of the channel box is attached at the time of length f during the channel box manufacturing process. Cut according to the dimensions of the stainless steel to be used.

Next, after the pickling process, stainless steel is attached to a predetermined portion by riveting. This makes it possible to manufacture a channel box having excellent corrosion resistance in the upper lattice plate facing portion and suppressing peeling of the oxide film.

The process of applying the stainless steel in the above embodiment is not limited to the step of determining the length f in the channel box manufacturing process, and the process of applying the stainless steel plate is performed after the pickling treatment. Is not limited.

The first embodiment has a step of β-quenching with a core inserted in the channel box before the final molding in the channel manufacturing process using the core annealing method as the final molding method. ..

After the β-quenching step in which the core is inserted into the channel box, final hot forming is performed using the inserted core. Further β-quenching process (3-1)
Is by induction heating and water quenching.

[0054]

According to the first aspect of the present invention, the growth due to fast neutron irradiation does not occur, and the problem of channel bending due to irradiation growth of Zircaloy is solved.

According to the second aspect of the present invention, the stainless steel plate is attached to the outer surface of the upper lattice plate facing portion of the channel box, so that the local corrosion and the oxide film peeling at the upper lattice plate facing portion in the nuclear reactor are effective. In addition to the above, it is possible to improve the soundness of the channel box with respect to high burnup.

[Brief description of drawings]

FIG. 1A is an elevation view showing a first embodiment of a channel box according to the present invention, and FIG. 1B is a top view of the channel box in FIG.

FIG. 2 is a process drawing showing the manufacturing method of the channel box in FIG.

FIG. 3 (a) is an elevational view showing an essential part of a second embodiment of the channel box according to the present invention, and FIG. 3 (b) is an A- of FIG.
The cross-sectional view which cuts and shows the A arrow direction, and (c) is a longitudinal cross-sectional view which cut | disconnects the BB arrow direction of (a).

4A is a process diagram showing a method of manufacturing the channel box in FIG. 3, and FIG. 4B is a perspective view of a process sequence facing FIG.

FIG. 5 is an elevation view showing a conventional boiling water reactor fuel assembly in a partial cross section.

6 (a) is an elevation view showing the channel box in FIG. 5, (b) is a top view of (a), and (c) is a bottom view of (a).

FIG. 7 is a process drawing showing the manufacturing method of the channel box in FIG.

[Explanation of symbols]

1 ... Channel box, 2 ... Fuel rod, 3 ... Spacer,
4 ... Upper tie plate, 5 ... Lower tie plate, 6 ... Spacer pad, 7 ... Rivet, 8 ... Channel clip, 9 ... Channel fastener, 10 ... β quenching area, 11 ...
Channel box (first invention), 12 ... Channel box (second invention), 13 ... Stainless steel plate, 14 ... Dimple.

Claims (2)

[Claims] 1. Boiling water for enclosing a fuel rod bundle constituted by arranging a large number of fuel rods in an array with a spacer interposed therebetween, and fixing both ends of these fuel rods to an upper and a lower tie plate, respectively. In the channel box of a fuel assembly for a nuclear reactor, a point along the axial height of the channel box is about 70 mm from the lower end to the base line, and a point about 500 mm from the upper end is the base line, and the distance between both base lines is 50 mm. % To 90%
A channel box characterized by being provided with a β-quenched structure produced by being rapidly cooled from the β-region temperature to the region. 2. Boiling water for enclosing a fuel rod bundle constituted by arranging a large number of fuel rods with spacers in between and fixing both ends of these fuel rods to an upper and a lower tie plate, respectively. In a channel box of a fuel assembly for a nuclear reactor, characterized in that stainless steel is attached to an outer surface of the channel box facing the upper lattice plate when the fuel assembly is loaded in the core. And the channel box.