JPH05196765A - Channel box and fuel assembly - Google Patents

Abstract

(57) [Summary] (Revised) [Purpose] Irradiation of a rectangular box-shaped channel box body used for a fuel assembly for boiling water reactors, which is cured by heat effect on a predetermined part of its side surface. By utilizing the deformation of the side surface due to, the heat removal efficiency of the fuel rod by the coolant is improved and its output is increased. In a channel box main body 10 having a plurality of side faces and formed in a rectangular tube shape, a desired side face is provided in the vicinity of an upstream side of a spacer 5 when assembled in a fuel assembly. ,
A provisional welded portion 11 in the width direction by an electron beam or the like, that is, a welded heat-affected zone or a cured portion by a partially molten portion is provided. [Effect] By the bulge 10f that is generated when the lower side of the temporary welding portion 11 that is difficult to deform is deformed to the outside, the coolant is turned to the arrow G and applied to the fuel rod 3 in the spacer 5, so that the liquid phase The heat removal efficiency of the fuel rod portion where is easily peeled off is increased to increase the output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a channel box surrounding a fuel bundle and a fuel assembly formed by using the channel box. Particularly, the deformation of the channel box is utilized to improve the limit output of the fuel assembly. It is the one that tries to make it.

[0002]

2. Description of the Related Art As is well known, a fuel assembly for a boiling water reactor (BWR) has an upper tie plate 1, a lower tie plate 2, a plurality of fuel rods 3, a water rod 4, as shown in FIG. It is provided with a plurality of spacers 5, a rod spring 6, a channel box body 7, and the like. A large number of fuel rods 3 and water rods 4 are vertically connected between the upper tie plate 1 and the lower tie plate 2, and these fuel rods 3 and water rods 4 are vertically arranged in a predetermined direction. A fuel bundle 8 is formed by being elastically supported at a uniform interval by the plurality of spacers 5 arranged at intervals, and further, the channel box body 7 surrounding the fuel bundle 8 is The upper tie plate 1 and the lower tie plate 2 are fitted and fixed.

By the way, the channel box body 7 is made of Zircaloy-4, and a plurality of (4
The number of side surfaces 7a is formed in a rectangular tube shape, and a fuel assembly incorporating this is loaded with a plurality of adjacent fuel cells in a square matrix in the BWR. The coolant flows from the lower side to the upper side, and at this time, the heat transfer phenomenon accompanied by boiling removes heat from the fuel rods 3 and the like.

Here, as is known, the heat removal action is performed so that the spatial separation state of the gas phase and the liquid phase in the coolant is intermediate with the lower portion A of the channel box body 7 as shown in FIG. A bubble flow D, a slab flow E, and an annular flow F are formed in the portion B and the upper portion C, respectively. Here, the bubbly flow D is actively generated from the heat transfer surface, which is the surface of the fuel rod 3 or the like,
Small vapor bubbles (voids) 9a are generated, and these are mixed in the liquid phase coolant.

Next, the slab flow E in the intermediate portion B is
As a result of the small voids converging, a small vapor nodule 9b larger than the void is shown in the coolant, and further, in the annular flow F in the upper part C of the fuel assembly, The vapor lumps 9b are aggregated to form larger vapor lumps 9c, and as is also known, the surface of the fuel rods 3 is coated with a liquid coolant. Is present.

The maximum heat output of the fuel assembly in which the coolant is present in the form of a film is defined by the heat removal capacity of the coolant, and when a heat output exceeding this heat removal capacity occurs. The coolant which has been present in the form of the above film is separated from the surface of the fuel rod 3 or the like. As a result, the surface of the fuel rod 3 etc. is directly covered with the vapor film (boiling transition).
Then, the temperature rapidly rises, the fuel rods 3 are burned out (burned out), and the fissile products having high radioactivity flow out, so that the output of the fuel assembly is constant. It must be kept below the output (limit output).

On the surface of the fuel rod 3 as a heating element, the gas-liquid distribution of the coolant is as described above, whereas the side surface 7a of the channel box body 7 which is a non-heating element is in contrast to this.
A liquid film of a coolant thicker than the liquid film on the surface of the fuel rod 3 exists on the inner surface of the fuel rod 3 and the outer surface of the water rod 4.

On the other hand, as described above, the fuel assembly is in the reactor interior loading period, and due to the pressure loss of the coolant flowing in the fuel assembly, the inner pressure of the channel box body 7 is larger than the outer pressure. Therefore, it is also known that the side surface 7a bulges outward, and when such deformation occurs, a known control rod for adjusting the reactivity of the nuclear reactor is attached to the channel box body of each fuel assembly. 7 There is a risk that it will be difficult or difficult to insert them into the mutual gap.

[0009] Such a problem is presently present in BWRs,
Considering that high burnup of fuel is being promoted in order to reduce the fuel cost, it is expected that the deformation of the channel box body 7 due to the outward bulge will be much larger than ever. Therefore, the countermeasures have become more important.

Therefore, although measures for preventing the above-mentioned undesired deformation have already been proposed, Japanese Patent Publication No. 13075/1989, Japanese Patent Laid-Open No. 253290/1988, and Japanese Patent Laid-Open No. 1-227991.
In Japanese Patent Laid-Open No. 1-269085, etc., the shape itself has peculiarities such as setting unevenness by making the wall thickness different at the four corners and the central part of the channel box body. Although they have their own effects, they are not satisfactory because the manufacturing process is troublesome and the flow of the coolant is affected.

[0011]

In view of the drawbacks of the above-mentioned conventional example, the present application has the following problems.
On the side surface of the channel box body formed in a rectangular tube shape,
By applying a thermal effect to the proper place by the electron beam, the deformation due to the bulge of the side surface is less likely to occur, which makes it easy to perform thermal treatment only on the proper place on the same channel box body as before. To provide a highly reliable channel box at low cost
That is the first purpose.

However, in the invention of claim 1 according to the present application,
Further, by not only suppressing the above deformation but also effectively utilizing the deformation, the flow direction of the coolant is directed from the inside of the side surface of the channel box main body to the vicinity of the spacer support portion of the fuel rod. , This improves the cooling effect for the relevant part of the fuel rod where the liquid film is peeled off due to the turbulence of the coolant flow due to the spacer, thereby increasing the output of the fuel rod and the flow rate of the coolant. I am trying to enable driving with less.

Next, in the second aspect of the present invention, in the above-mentioned annular flow adhering to the surface of the fuel rod, the thermal effect is exerted at the position particularly on the upper side of the side surface. An attempt is made to effectively improve the cooling effect on the fuel rods by eliminating steam lumps and the like by diverting due to the deflection of the coolant.

Further, in the fuel assembly according to claim 3, by incorporating the channel box according to claim 1, it is possible to exhibit a sufficient heat removal effect even in a BWR having a high burnup. In this way, the purpose is to prevent the high burnup from being hindered by the cooling performance.

[0015]

In order to achieve the above object, the present invention provides a channel box body having a plurality of side faces and formed in a rectangular tube shape. Provided with a channel box characterized in that a temporary welding portion in the width direction is formed at a position near the upstream side of the spacer when assembled in the fuel assembly on the side surface. Trying to.

According to a second aspect of the present invention, in the channel box according to the first aspect, the temporary welding portion formed on the side surface of the channel box is located on the upper side of the spacer when it is incorporated into the fuel assembly. The contents are arranged near the upstream side.

In the third aspect, the channel box of the first aspect is used, and a large number of fuel rods and water rods are vertically connected and connected between the upper tie plate and the lower tie plate. A fuel bundle is formed by elastically supporting the fuel rod and the water rod at a uniform interval by a plurality of spacers arranged at a predetermined distance in the vertical direction. When the channel box body surrounding the above is fixedly mounted on the above-mentioned upper tie plate and lower tie plate, and the plurality of side faces formed in the rectangular tube shape of the above channel box body are assembled into the fuel assembly. An object of the present invention is to provide a nuclear fuel assembly characterized in that a temporary welding portion in the width direction is formed at a position near the upstream side of the spacer.

[0018]

In the channel box according to the first aspect, the temporary welding portion is formed at a desired side surface of the channel box body, and the temporary welding is not performed to adhere the object to the object by the welding means. This is to form a welding heat affected zone or a line-shaped partially melted zone by using an electron beam or the like.

Therefore, the zircaloy at the temporary welding location is
By heating to the β region or α + β region and then cooling, β-quenching or α + β-quenching is locally performed, which increases the hardness and thus the deformation, and the outward pressure based on the pressure loss of the coolant. Swelling will be suppressed. Here, in the present invention, since the temporary welding portion is formed in the vicinity of the upstream side of the spacer and in the width direction, the temporary welding portion does not swell and the upper and lower sides thereof are outward. Since it swells, the coolant of the channel box body is deflected and flows from this temporary welding portion toward the fuel rod portion elastically supported by the spacer.

Here, at the above-mentioned spacer portion, the flow of the coolant is disturbed, and the liquid film of the coolant formed on the surface of the fuel rod is easily separated due to the turbulent flow.
Therefore, the above-mentioned vapor bubbles 9a, small vapor masses 9b, and small vapor masses 9c having a low heat transfer coefficient are present in the separated portion, but these are removed by the diverted coolant, The coolant comes into direct contact with the fuel rods, and the heat removal action of the relevant portion of the fuel rods is improved.

According to the channel box of claim 2, the temporary welding portion is on the side surface and is formed on the upper side where the small vapor mass 9b or the small steam mass 9c is present, so that the heat removal effect is efficient. Therefore, the output of the fuel assembly can be further improved.

In the fuel assembly according to the third aspect, the channel box main body performs the above-described operation, so that reliable and high-power operation of the nuclear reactor is guaranteed.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A channel box according to claim 1 will be described in detail with reference to FIGS. 1 and 2. FIG.
1B is a front view of a fuel assembly incorporating the channel box body 10 with a part cut away, and FIG. 1B is an enlarged partial vertical sectional front view showing the vicinity of the spacer 5 in the fuel assembly. 2 shows the channel box body 1 described above.
The perspective view which showed the upper end side of 0 is shown.

Also in the present invention, the channel box main body 10 has a plurality of side faces 10a, 10b, 10c, 10d such as four sides as in the conventional example, so that the channel box body 10 is formed into a rectangular tube shape.
Are formed, and moreover, one or more of the side faces are
When this is incorporated into a fuel assembly, a temporary welding spot 11 is formed by an electron beam or the like in the vicinity of the upstream side of the coolant in the spacer 5 in the width direction of the side face.

Here, the temporary welding spot 11 indicates a spot where a welding heat affected zone or a line-shaped partial fusion zone is formed. To form this, a vacuum atmosphere (10 ⁻⁴ To
rr or less), electron beam acceleration voltage 100 to 50
The electron beam irradiation may be performed under the conditions of 0 KV and an electron beam current of 10 to 50 mA. Of course, since there are various thicknesses of the channel box body 10, it is necessary to perform a treatment corresponding to this, and the temporary welded portion 11 is affected by heat more than other portions, and its hardness is large. However, if the penetration depth of the temporary welded portion 11 is changed, the hardness is also changed. Therefore, the above conditions must be changed depending on the channel box main body itself and its usage conditions.

Here, in the channel box body 10 shown in FIG. 2, when the channel box body 10 is formed of Zircaloy-4, both side edges bent into a quadrangle are butted and welded to each other. The welding line 12 formed on the side face 10d is formed in a rectangular tube and is shown by a dotted line in the same figure. When such a welding line 12 is formed, the hardness of only the side surface 10d increases the elongation due to irradiation, while the side surface 10d, which is the opposite side thereof, decreases.
Since b becomes easier to stretch, and as a result, the channel box body 10 becomes easier to bend, the channel box body 10 also has an existing temporary welding portion 12 'formed on the side surface 10b as shown by the dotted line. ing.

In the illustrated embodiment, the temporary welding points 11 formed in the width direction are all linear, but of course, the curved shape and the sawtooth shape can be formed. The tentative welded portion 11 formed as described above has a zircaloy of β due to the electron beam as explained in the section of action.
After being heated to the region and the α + β region, they are rapidly cooled to be β-quenched and α + β-quenched, respectively, which increases hardness and strengthens deformation. As a result, as clearly shown in FIG. 1B, on the upper and lower sides of the temporary welding portion 11 on the side surface 10b, the bulge 1 toward the outside due to the pressure difference between the inside and outside due to the pressure loss of the coolant in the channel box body 10.
0e and 10f are generated, and the temporary welding portion 11 and the bulge 10f, which are not easily deformed, cause the coolant that has flowed directly upward to the fuel rod 3 as indicated by an arrow G.
It will be turned to the side.

By forming the temporary welded portion 11 in this way, not only the undesired deformation of the side surface is suppressed, but also the flow of the coolant becomes as indicated by the arrow G. Therefore, the coolant is a spacer. 5 will flow toward the portion of the fuel rod 3 which is elastically supported by the fuel rod 5, and at this time, due to the disturbance of the coolant due to the presence of the spacer 5, the liquid film on the surface of the fuel rod 3 will flow. Despite the easy peeling, the deflected coolant is directly flowed, and as a result, the cooling action of the portion with the worst heat exchange is improved.

Here, in the embodiment shown in FIGS. 1 and 2,
Although the temporary welding spots 11 are formed on all the side faces, the effect can be improved even with only one side face, and the temporary welding spots 11 are provided correspondingly to all the spacers 5 over the entire length. However, this can also be provided only on the desired spacer 5, and at this time, as shown in claim 2, it is more efficient to provide the temporary welding portion 11 on the upper side. A good cooling effect can be realized. The reason for this is that when it is incorporated into the fuel assembly as described above, the number of voids increases toward the downstream side of the channel box body 10 and the voids grow to a large extent. This is because the fuel rod is less likely to be cooled by the coolant toward the side, and these voids are removed from the surface of the fuel rod by the deflected coolant.

The fuel assembly according to claim 3 is the same as that shown in FIG.
It is obtained by incorporating the channel box body 10 of the above-mentioned claim 1 in place of the channel box body 7 in the conventional fuel assembly described in detail above.

[0031]

Since the present invention is constituted as described above, according to the first aspect, the channel box main body is formed with appropriate unevenness so that the cooling water flowing along the inner surface of the channel box main body is prevented. , The direction of the fuel rod can be changed so that it flows toward the elastically supported portion by the spacer, which effectively improves the heat removal effect of the coolant, and the output of the fuel rod can be improved. Increased operation or operation with reduced coolant flow is possible.

Further, according to the second aspect, the effect of the first aspect can be more efficiently exhibited by providing the temporary welding portion on the upper side of the channel box body. Further, according to the fuel assembly of claim 3, since the above-mentioned channel box main body is provided, deformation is suppressed and high reliability can be ensured, and heat removal effect is improved, even when the combustion is advanced. Due to
It is possible to satisfy the demand for advanced combustion.

[Brief description of drawings]

FIG. 1A is a partially cutaway front view showing a fuel assembly having a channel box body according to the present invention, and FIG.
FIG. 3 is a partially longitudinally enlarged front view showing the main part thereof.

FIG. 2 is a perspective view showing an upper end side of the same channel box body.

FIG. 3 is a front view in which a channel box is cut away showing a fuel assembly for a conventional boiling water reactor.

FIG. 4 is a longitudinal distribution explanatory view showing a spatially separated state of a gas phase and a liquid phase of a coolant in a conventional channel box body.

[Explanation of Codes] 1 Upper tie plate 2 Lower tie plate 3 Fuel rod 4 Water rod 5 Spacer 8 Fuel bundle 10 Channel box body 10a Side face 10b Side face 10c Side face 10d Side face 11 Temporary welding point

Claims (3)

[Claims] 1. A channel box main body having a plurality of side faces and formed in a rectangular tube shape, wherein the side faces are near the upstream side of the spacer when assembled in a fuel assembly. A channel box characterized in that a temporary welding portion in the width direction is formed at the position. 2. The temporary welded portion formed on the side surface is arranged near the upstream side of the spacer at a position that is an upper side of the temporary welded portion when the temporary welded portion is incorporated into the fuel assembly. The listed channel box. 3. A large number of fuel rods and water rods are vertically connected in a state of being aligned between the upper tie plate and the lower tie plate, and these fuel rods and water rods are vertically arranged in a predetermined direction. A fuel bundle is formed by being elastically supported at a uniform interval by a plurality of spacers arranged at intervals, and the channel box body surrounding the fuel bundle is attached to the upper tie plate and the lower tie plate. A plurality of side faces formed in a rectangular tube shape of the channel box main body, which are mounted and fixed to the fuel cell assembly, and when assembled in a fuel assembly, at a position near the spacer upstream side, in the width direction. The nuclear fuel assembly is characterized in that the temporary welding points of are formed.