JPH05249268A - Fuel assembly - Google Patents

Abstract

PURPOSE:To make a plurality of vertical grooves for forming a thick water film connected to a float stopper provided on the inner face of a channel box and obtain a fuel assembly superior in output effect with supply to fuel bundles of coolant smoothed. CONSTITUTION:A fuel assembly consists of a plurality of fuel rod 2 wherein an upper tie plate 5 and a lower tie plate 6 are arranged in upper and lower parts respectively, an upper end is held on the upper tie plate 5 and a lower end is kept on the lower tie plate 6, and whose inside is filled with a plurality of pellets, a fuel bundle 23 wherein a plurality of spacers 21a, 21b for holding the fuel rods 2 at intervals are arranged between upper and lower tie plates and a cylindrical channel box wherein the fuel bundle 23 is surrounded and a coolant passage is formed. With a float ripper composed of a plurality of vertical grooves provided on the inner face of the channel box 24, coolant flow in the inside of the channel box 24 is turned to the fuel bundle 23 and a plurality of the vertical grooves reaching the float ripper from the lower part of the channel box 24 are provided at the position corresponding to the fuel rods 2 on the outer circumferential part of the fuel bundle 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coolant passage in a boiling water reactor, and more particularly to cooling a fuel bundle inside a fuel assembly and improving output efficiency.

[0002]

2. Description of the Related Art A fuel assembly in a boiling water reactor is shown in FIG.
As shown in the perspective view of FIG. 14, the fuel assembly 1 includes a large number of fuel rods 2 containing a nuclear fuel material, one or a plurality of water rods 3, and these fuel rods 2 and the water rods 3 at predetermined intervals. Holding multiple spacers 4
And these, upper tie plate 5 and lower tie plate 6
The fuel bundle 7 mounted on the above is surrounded by a square tubular channel box 8. The thickness of the channel box 8 is uniform in the vertical and circumferential directions, and the channel box 8 divides the fuel assembly 1 into the inside and the outside of the fuel assembly.

Inside the fuel assembly 1, vapor voids of water, which is a coolant, are generated due to heat transfer from the fuel rods 2.
Since there is little heat transfer or heat generation outside the fuel assembly 1, vapor voids do not occur. Especially in boiling water reactors,
The coolant outside the fuel assembly 1 has a high water density so as to effectively suppress the neutron moderation, and the characteristics of the flow inside and outside the channel box 8 are set so that vapor voids do not occur. A cross-shaped control rod (not shown) is arranged on the outside of the channel box 8 so that the control rod can be smoothly inserted into and removed from the core by using the smooth outer surface of the channel box 8 as a guide.

Further, in a boiling water nuclear reactor in which steam voids are directly generated in the core, the amount of voids generated in the fuel assembly 1 varies depending on the output of the fuel assembly 1, so that the channels in each fuel assembly 1 are different. If the box 8 is not installed and the coolant flow path is not restricted in the lateral direction, a cross flow between the two-phase fuel bundles 7 (cross flow) occurs, and from the periphery of the fuel bundle with a large heat output to the fuel bundle with a small heat output. The coolant escapes and the cooling capacity of the fuel decreases. Therefore, there is a pressure difference between the inside and the outside of the channel box 8 provided for such a purpose, and the internal pressure is higher.

As a result, the channel box 8 expands outward due to the effects of heat and neutron irradiation. In order to suppress the expansion amount and smooth the insertion of the control rod to secure the rigidity of the fuel assembly 1, the channel box 8 is made of a zirconium alloy with a small neutron absorption, and is made of a thick plate to some extent. .. Conventionally, such a channel box 8 is manufactured by bending a plate material to form a half of a square tube of a shape, and combining two of these to weld them together to form a square tube.

As shown in the enlarged vertical sectional view of the main part of FIG. 15, in the vicinity of the lower end of the channel box 8, there is a region where the water of the coolant 9 is heated from below the saturation temperature to the saturation temperature,
There is no steam inside the channel box 8 and the coolant 9 fills the inside of the fuel assembly 1. However, in the majority of the axial direction inside the channel box 8, the coolant flow consists of a mixture of steam 10 and water, forming a layer of water film 11 on the inner surface of the channel box 8 and also on the surface of each fuel rod 2. The water film 11 of one layer contacts. Note that reference numeral 12 indicates a water drop.

As the coolant flow goes upward in the axial direction, the volume occupied by the steam 10 generated on the surface of the fuel rod 2 in the coolant flow increases, and the thickness of the water film 11 contacting the surface of the fuel rod 2 increases. Is reduced. If the thickness of the water film 11 in contact with the fuel rod 2 is too small and the heat generation of the fuel rod 2 is great there, overheating and thermal instability occur (transition boiling, film boiling occur and insufficient cooling occurs). become). Water also flows upward by forming a water film 11 in contact with the inner surface of the channel box 8 surrounding the fuel bundle 7.

However, unlike the fuel rods 2, the channel box 8 is heated mainly by neutrons and γ rays, and the amount of heating is small. As a result, the water film 11 in contact with the inner surface of the channel box 8 flows upward while remaining thick, and is relatively independent of the fuel bundle output, the amount of cooling water into the fuel bundle 7, and the axial height.

Further, in the result of the numerical analysis of the flow distribution in the horizontal cross section in the channel box 8, the water film 11 contacting the inner surface of the channel box 8 shows the enlarged cross section of the main part of FIG. As shown in the plan view, it is wavy, and the small gap between the outermost fuel rod 2 of the fuel bundle 7 and the inner wall of the channel box 8 is thin.
In the recent fuel assembly design, the maximum thermal neutron flux and the maximum local power are generated in the fuel rod 2 adjacent to the wall of the channel box 8.

To solve this problem, JP-A-63-2611
In No. 91, as shown in the enlarged vertical cross-sectional view of the main part of FIG. 17, the inside of the upper part of the channel box 8 is provided with a slope-shaped lateral groove by cutting and the flow tripper 13 is provided. The water film 11 flowing upward on the surface wall is inverted by the flow tripper 13 and the edge portion 13a toward the fuel rod 2 adjacent to the channel box 8 and used to cool the fuel bundle 7 and adjacent to the channel box 8. It is disclosed that the occurrence of transition boiling of the fuel rod 2 is suppressed, and as a result, the limit output of the entire fuel bundle 7 (the maximum output of the fuel bundle at which transition boiling starts to occur somewhere in the fuel bundle) is disclosed.

In addition to the above, as a method of positively guiding the coolant 9 to the upper portion of the fuel bundle 7, as shown in the partially cut front view of the fuel assembly in FIG. Two channel boxes 15 are arranged in a double manner, and a channel 16 is formed in a gap between the channel box 8 and the second channel box 15, and a lower opening 17 and an upper opening opened in the second channel box 15. A fuel assembly 19 configured to communicate with 18 is known. The fuel assembly 19 guides the coolant from the lower opening 17 to the upper opening 18 through the flow path 16 and supplies it to the fuel bundle 7 above the fuel assembly 19.

[0012]

The fuel assembly 1 and the fuel assembly 19 have the following problems.
That is, in the fuel assembly 1, the distribution of the thickness of the water film 11 formed on the inner surface of the channel box 8 in the circumferential direction is in the vicinity of the outermost fuel rod 2 on the upper part of the channel box 8 where the coolant 9 is most required. Since it is difficult to efficiently supply the coolant 9 to the upper part of the fuel rods at the outermost periphery of the fuel bundle through the flow tripper 13, it is difficult to improve the limit output by the flow tripper 13.

The flow tripper 13 is formed by a lateral groove formed in a slanting shape on the inner surface of the upper portion of the channel box 8. When the channel box 8 is mounted from the upper portion of the fuel bundle 7, the flow tripper 13 is placed on the outermost periphery of the fuel bundle 7. The protrusion of the side band of a certain spacer 4 and the edge portion 13a of the flow tripper 13 are caught, so that an inconvenience is likely to occur in the assembly of the fuel assembly 1.

Further, the channel box 8 is manufactured by welding two shape members each having a shape in which a square tube is divided into two.
In the welding operation in the 13 part of the flow tripper, the cross-section thickness changes in the axial direction, so that it is difficult to control the welding heat input and it is difficult to perform good welding. In the fuel assembly 19, the structure and fabrication of the dual channel box forming the flow path 16 are complicated,
Moreover, there is a problem that the shape becomes large.

The object of the present invention is to engrave a plurality of vertical grooves which form a thick water film connected to a flow tripper provided on the inner surface of the channel box to facilitate the supply of the coolant to the fuel bundle. And to provide a fuel assembly with excellent output efficiency.

[0016]

An upper tie plate and a lower tie plate are respectively arranged at upper and lower parts, and an upper end is held by the upper tie plate and a lower end is held by a lower tie plate, and a plurality of fuel pellets are filled inside. A plurality of fuel rods, a fuel bundle in which a plurality of spacers for holding the fuel rods at intervals are arranged between the upper and lower tie plates, and a tubular channel box surrounding the fuel bundle to form a coolant flow path. In the fuel assembly consisting of a plurality of transverse grooves are provided on the inner surface of the channel box to divert the coolant flow on the inner surface of the channel box to the fuel bundle, and to reach the flow tripper from the lower part of the channel box. Is provided at a position corresponding to the fuel rod on the outer peripheral portion of the fuel bundle.

[0017]

[Function] The water film rising from the lower part of the inner surface of the channel box is effectively thicker than the inner surface by the vertical groove provided in the portion where the water film is apt to be thin on the front surface of the fuel rod, and therefore the cooling reaches the lowermost flow tripper. The amount of wood supply increases. As a result, the amount of water drops peeled off from the inner wall of the channel box at the flow tripper portion and deflected in the direction of the fuel rod at the outermost periphery of the fuel bundle is increased, the transition boiling of the fuel rod is suppressed, and the limit output is improved.

Further, in the channel box, the flow tripper and the vertical groove provided on the inner surface are slidable on the welded portion at the time of assembling and the projection of the side band of the spacer, and further on the lower tie plate at the lower end of the channel box. Since it is not provided in the part that moves and fits, the welding work is easy, and during the assembly process of the fuel assembly where the channel box is mounted from above the fuel bundle, the sliding of the channel box and the spacer is improved and the spacer Will not be damaged.

Further, even in the portion where the flow tripper is not provided due to the local shape of the lateral end of the flow tripper, the coolant is guided from the adjacent flow tripper, so that the cooling effect on the fuel rods at the outermost periphery of the fuel bundle is obtained. Be homogenized.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. It should be noted that the same components as those of the above-described conventional technique are denoted by the same reference numerals and detailed description thereof will be omitted. As shown in the longitudinal sectional view of FIG. 1, the fuel assembly 20 includes a large number of elongated fuel rods 2 and water rods 3, which are supported between an upper tie plate 5 and a lower tie plate 6. Has been done.

The fuel rod 2 passes through a plurality of spacers 21a and 21b. The spacers 21a and 21b serve as an intermediate supporting means to hold the fuel rods 2 apart from each other and suppress horizontal vibration. Each of the fuel rods 2 has pellets of fissionable fuel in an elongated tube and has a lower end plug 22a and an upper end plug 22.
It is sealed with b. The lower end plug 22a is fitted and supported in a support hole formed in the lower tie plate 6, and the upper end plug 22b is formed with an extension portion and fitted in a support hole provided in the upper tie plate 5.

Some of the support holes in the lower tie plate 6 (eg, holes at specific locations on the periphery) are threaded to threadably connect the fuel rod 2 with the threaded lower end plug. The extension portion of the upper end plug 22b of the same fuel rod 2 penetrates through the support hole of the upper tie plate 5 and projects to the upper surface of the upper tie plate 5, and is screwed by a holding nut (not shown) so that the fuel bundle 23
Is configured. Further, the outer periphery of the fuel bundle 23 is surrounded by a thin plate with a channel box 24 in the shape of a rectangular tube to form a fuel assembly 20.

The channel box 24 has a substantially square horizontal cross section, and has a slip fit structure on the upper and lower tie plates 5 and 6 and the spacers 21a and 21b. The channel box 24 is bolted to the fuel bundle by a piece material welded to the upper end. Fix at 23. A tip piece is formed on the lower tie plate 6, and the tip piece is inserted into an opening of a fuel support fitting of a core support plate (not shown).

Further, as shown in the perspective view of FIG. 2 and the partially cut perspective view of FIG. 3, the inside of the channel box 24 is filled with the fuel effective portion of the fuel bundle 23 (the fuel pellets in the fuel rods are filled. Upper part) to 1/4 to 1/2
A plurality of lateral groove flow trippers 13 are provided in the section.
Further, a vertical groove 25 reaching the lowermost stage of the plurality of flow trippers 13 is carved from the lower part of the channel box 24, and the vertical groove 25 has a width of 10 mm or less and is provided in parallel in the axial direction.

The flow tripper 13 and the vertical groove
25 is engraved on the inner surface of the channel box 24 by processing such as cutting, electric discharge, electrolysis, and corrosion etching. When the channel box 24 is attached to the fuel bundle 23, the sides of the spacers 21a and 21b shown in FIGS. Protrusion 32 of band 30
Neither the flow tripper 13 nor the vertical groove 25 is disposed on the inner surface portion 26 that slides with the inner surface portion that slides with the lower tie plate 6 at the lower end of the channel box 24, and the inner surface is flat in the axial direction. ..

The vertical groove 25 is AA in FIG. 4 in FIG.
As shown in the sectional view taken in the direction of the arrow, it is provided so as to be located in front of the fuel rod 2 on the inner surface of the channel box 24. The spacer 21a shown in FIG. 4 and the spacer 21b shown in the cross-sectional view taken along the line BB in FIG. 1 are all examples of ferrule spacers, and the active fuel length is divided into approximately 7 in the axial direction. In this example, a spacer is arranged at the upper end of the divided section.

In this example, in order to improve the two-phase flow pressure loss in the upper part of the fuel assembly 20 and the reactor shutdown margin, the sixth,
The seventh spacers 21b, 21b have voids 27 in which eight fuel rods 2 are not arranged. The fuel rod 2 in the 27th part of this space is
A partial length fuel rod 28 is arranged whose upper end ends at a position where it penetrates the fifth spacer 21a. This spacer
21a and 21b are formed by arranging the same number of cylindrical sleeves 29 as the fuel rods 2 in a grid pattern, and further enclosing the outer periphery of the bundle of the cylindrical sleeves 29 with a band-shaped side band 30.

The cylindrical sleeves 29 arranged in a grid pattern are adjacent to each other and are joined by spot welding. Two projections are provided on the upper and lower ends of the cylindrical sleeve 29. These protrusions are formed by projecting a part of the cylindrical sleeve 29 inward. Further, a continuous loop spring 31 is installed so as to straddle two adjacent cylindrical sleeves 29, and the shape of the continuous loop spring 31 is such that the central portion in the height direction projects outward.

On the outside of the side bands 30 of the spacers 21a and 21b, keep a distance from the inner wall of the channel box 24,
Further, two protrusions 32, which serve as sliding parts between the spacers 21a and 21b and the channel box 24, are provided on each side near the corners of the outer peripheries of the spacers 21a and 21b. Further, a plurality of flow tabs 33 are provided on the upper ends of the side bands 30 of the spacers 21a and 21b at regular intervals.

Next, the operation of the above configuration will be described. Water, which is the coolant of the nuclear reactor, enters the cooling channel in the channel box 24 from the lower opening of the lower tie plate 6 through the opening of the fuel support frame. Coolant is fuel rod 2
And, the heat from the partial length fuel rod 28 is received to reach the saturation temperature,
Furthermore, vapor voids are generated. The amount of voids in this vapor void increases as it rises in the axial direction.

Therefore, such a two-phase flow is generated by the surfaces of the fuel rods 2 and the partial length fuel rods 28, the inner surface of the channel box 24, and the water rods 3 as shown in the enlarged longitudinal sectional view of the main part of FIG. A thin water film 11 of a coolant is formed on the surface, and the thickness of the water film 11 becomes thinner in the axial direction in the fuel rods 2 and the partial length fuel rods 28 where heat is generated. In the space between the fuel rod 2 and the partial length fuel rod 28, water droplets 12
The amount of water droplets 12 in the steam flow decreases as it goes upwards.

Between the fuel rod assemblies 20 mounted on the core of a boiling water reactor, there is a water gap outside the channel box 24, where neutrons are efficiently heat-treated. The thermal neutron flux is large near the outermost periphery of the fuel bundle 23, and the heat generation of the fuel rods 2 is also larger than that of the central portion of the fuel bundle 23. Therefore, the coolant 9 is larger in the lower half or 3/4 region of the fuel bundle 23 of the fuel assembly 20 with respect to the fuel effective portion (portion filled with the fuel pellets in the fuel rod), and the outermost peripheral portion Unlike the conventional flat inner surface of the channel box 8, a thick water film 11a is formed between the fuel rods 2 and the inner surface of the channel box 24 due to the surface tension of the vertical groove 25 provided on the inner surface of the channel box 24. It is played and flows.

Furthermore, as the coolant flow in the fuel bundle 23 rises in the axial direction, the volume occupied by the steam increases, and the water film 11 on the surfaces of the fuel rods 2 and the partial length fuel rods 28 becomes thin, which tends to occur. At the outermost fuel rods 2 of the strong fuel bundle 23, the margin with respect to the condition for starting the boiling transition that deteriorates the cooling of the fuel rods 2 becomes small, and the flow is made at a position of 1/2 to 3/4 from below the active fuel length. More coolant is supplied to the tripper 13. Further, at this time, a large amount of the coolant supplied to the flow tripper 13 becomes a thick water film 11a due to the vertical groove 25, and the water droplets 12 are efficiently collected on the fuel rod 2 in front of the fuel rod 2. Biased.

The interval between the outermost fuel rod 2 of the fuel bundle 23 and the inner surface of the channel box 24 is increased over the entire inner surface in the circumferential direction of the channel box 24 from the region where the number of vapor voids is small in the lower portion of the fuel bundle 23. Then, the flow of the cooling water is excessively offset to the outer periphery of the fuel bundle 23, and conversely, the fuel rods 2 and the partial length fuel rods 28 inside the fuel bundle 23 are insufficiently cooled, or the water film attached to the inner surface of the channel box 24 11 is stripped off by the high-speed two-phase flow, flows as water droplets 12 into the space between the inner surface of the channel box 24 and the outermost fuel rod 2, and the amount of water supplied to the flow tripper 13 does not increase. , Does not contribute to the cooling of the fuel rod 2.

Therefore, as shown in the enlarged cross-sectional view of the main part of FIG. 7, the width of the vertical groove 25 is the water film on the inner surface of the channel box 24.
It is conceivable to reduce the width of the vertical groove 25 so as to utilize the surface tension between the water film 11 and the inner surface of the channel box 24 so that 11 is not stripped by the two-phase flow. For example, if it is 3 mm or less, about 1 mm is desirable because of the balance between processing and use of surface tension.

Further, a flow tripper in which a slanted groove is cut in the inner surface of the channel box 24 in the upper 1/4 to 1/2 portion of the fuel where cooling of the fuel rods 2 on the outer periphery of the fuel bundle 23 becomes poor.
By forming 13, the membranous water flow that is effectively thickened by the flutes 25 along the inner surface of the unheated channel box 24 and rises is formed in the bottommost flow tripper 13
Flow into the lateral groove of the fuel cell 2 and then are deflected toward the fuel bundle 23 at the edge portion 13a above the lateral groove and toward the adjacent exothermic fuel rods 2.

The lower edge of the lateral groove is tapered so that the flow of the water film 11 can smoothly flow in. This taper has a shallow angle so that flow separation does not occur, and the water flow separated from the inner surface of the channel box 24 at the upper edge portion 13a of the groove of the flow tripper 13 becomes a water droplet 12 and a part of the fuel is adjacent to the fuel. It adheres to the surface of the rod 2 and prevents the transition from nucleate boiling and heating of the fuel rod 2.

The edge part of the first flow tripper 13
The water film 11 that was not peeled off by 13a is the next flow tripper.
Supplied to 13. Thus, as shown in FIG.
The flow tripper shown in Fig. 3 is lower than that of the conventional channel box 8 with a smooth inner surface below the flow tripper 13.
The cooling effect of the outermost fuel rod 2 by 13 is extremely improved.

Furthermore, since the flow tabs 33 for attracting the cooling water flow inside the fuel bundle 23 are provided on the upper edges of the side bands 30 of the spacers 21a and 21b holding the fuel bundle 23, the flow tabs 33 , The cooling water flow between the inner surface of the channel box 24 and the outermost fuel rods 2 of the fuel bundle 23 is changed to the outermost fuel rods 2 and the second outermost fuel rods 2.
And turn to the partial length fuel rod 28. As a result, spacer 21
A large amount of water droplets 12 in the cooling water flow passing through a and 21b adhere to the surfaces of the fuel rods 2 and the partial length fuel rods 28 to prevent transition from nucleate boiling and overheating of the fuel rods 2 and the partial length fuel rods 28. ..

When the flow tripper 13 for machining the inner surface of the channel box 24 and the vertical groove 25 are engraved, the welded portion 14 of the channel box 24 and the protrusions 32 of the side bands 30 of the spacers 21a and 21b are slid. Neither the flow tripper 13 nor the vertical groove 25 is processed on the moving inner surface portion.

In the process of assembling the channel box 24 by welding two shape members of a rectangular tube into two parts, if the flow tripper 13 and the vertical groove 25 are formed in the welded portion 14, the welded portion The cross-sectional thickness at 14 changes in the axial direction, making it difficult to control the welding heat input. That is, in the thin portion, the welded portion 14 is excessively melted, the weld strength is lowered due to the formation of a pit, the size of the metal crystal grains, the phase is changed, and the corrosion resistance is lowered. 14
If there is no change in the thickness at, the above problems do not occur and welding can be performed easily and firmly.

Further, in the process of assembling the fuel assembly 20 by covering the lower end opening of the channel box 24 from above the fuel bundle 23, the inner surface of the channel box 24 and the projections 32 on the side bands 30 of the spacers 21a and 21b are formed. Since the inner surface of the channel box 24 is smooth at the sliding part, the sliding is good. In particular, the groove of the flow tripper 13 has a sloped shape, the lower edge is tapered, and the upper edge is a vertical edge portion 13a. Without this structure, the channel box 24 is mounted from above the fuel bundle 23. It is easy to get caught in the protrusion 32 of the side band 30 during the work.

The section of the inner surface of the lower end of the channel box 24 that slides with the lower tie plate 6 is the channel box.
Since the cooling water flows from the gap between the inner surface of 24 and the side surface of the lower tie plate 6 to the bypass area, the wall thickness of the channel box 24 at the lower end is also reduced in order to suppress the flow rate of this portion, and the gap is creeped. Therefore, it is better not to provide the vertical groove 25 on the inner surface of the lower end of the channel box 24 in order to prevent the channel box from becoming large during use.

Further, since the vertical groove 25 is provided in the lower non-boiling water region of the fuel assembly 20, the flow rectifying effect of the coolant by the vertical groove 25 is obtained, and the disturbance of the coolant in the non-boiling water region is obtained. The flow is suppressed and the friction pressure loss is reduced. In order to increase the flow rate of the coolant around the outermost peripheral fuel rods 2 above the fuel bundle 23, which determines the maximum thermal power that does not cause the transition boiling of the fuel assembly 20,
25 provides more water film flow to the flow tripper 13.

Sidebands of the spacers 21a and 21b
The flow tab 33 of 30 and the flow tripper 13 on the inner surface of the channel box 24 attract the water film 11 rising along the inner surface of the channel box 24 to the fuel bundle 23 in the form of water droplets 12, thereby transitioning the fuel bundle 23. The start of boiling and overheating are prevented, and the limit output of the fuel assembly 20 is improved. Although the structure of the spacers 21a and 21b has been described above by taking the ferrule type as an example, the same action and effect as above can be obtained by other methods such as an egg plate type.

Next, a modification of the present invention relating to the flow tripper and the like will be described. 8 is a perspective view of a channel box showing a second embodiment, FIG. 9 is a partially cutaway perspective view of the channel box, and FIG. 10 is an enlarged perspective view of a flow tripper. As shown in FIG. 8, a plurality of lateral grooved flow trippers 41 are provided at the upper part of the inner surface of the square tubular channel box 40, and a plurality of vertical grooves 25 are provided at the lower part of the flow trippers 41 at the uppermost end of the flow tripper 41. Of the fuel assembly shown in FIG. 1 is cut to a position avoiding a portion where the lower tie plate 6 is fitted.

The flow tripper 41 includes the welded portion 14 when the channel box 40 is assembled, and the side bands of the spacers 21a and 21b of the fuel bundle 23 shown in FIGS. 1 and 4 and 5 which are inserted into the channel box 40. It is not provided in the sliding part 26 with 30. Therefore, in the fuel rods 2 adjacent to this vicinity, the water film 11 from the inner surface of the channel box 40 is hardly peeled off and attached. Therefore, at the left and right ends of the flow tripper 41, as shown by the arrows in FIG. 10, the water film 11 is guided in the left and right outer directions to increase the peeling adhesion at both ends. It is characterized by being formed in. This angle is 45 degrees or more.

A partially cutaway perspective view of the channel box shown in FIG. 11 is a third embodiment, and the corners of the inner surface of the channel box 50 having a square tubular shape are shown in FIGS.
Side bands of the spacers 21a and 21b of the fuel bundle 23 shown in FIG.
A portion which does not slide with 30 is provided with a flow tripper 51 and a vertical groove 52 having the same shape as the flow tripper 13 and the vertical groove 25 shown in FIG.

A partially cutaway perspective view of the channel box shown in FIG. 12 shows the channel box 60 according to the fourth embodiment.
At the corners of the inner surface of the fuel cell, the flow stripper 41 and the vertical groove shown in FIG. 9 are also provided in the portions of the fuel bundle 23 shown in FIGS. This is an example in which a flow tripper 61 and a vertical groove 62 having the same shape as 25 are engraved. In the channel boxes 50 and 60 of the third and fourth embodiments, transition boiling and overheating are also prevented in the fuel rods 2 at the outermost corners of the fuel bundle 23.

The above-mentioned embodiments are examples of the fuel assembly having the structure in which the fuel bundle 23 is surrounded by the rectangular channel box, but as the fifth embodiment, the fuel assembly of FIG. As shown in the transverse cross-sectional view of the body, the fuel assembly 70 includes a cooling channel partition plate 72 in an outer cylinder 71 having a rectangular tubular shape, and a cross-shaped water cloth (water gap) inside the fuel assembly 70. The flow tripper 1 is provided on the inner surface of the outer cylinder 71 and on the small fuel bundle 74 side of the cooling channel partition plate 72 with respect to each small fuel bundle 74 divided into four by the water cloth 73.
3 and a vertical groove (not shown). The reference numeral 75 indicates a control rod, and the spacer (not shown) in the small fuel bundle 74 and the arrangement thereof are the same as those in the above-described embodiment, so that the same operation and effect can be obtained.

[0051]

As described above, according to the present invention, a layer of water formed on the inner surface of the channel box and flowing upward is effectively increased in thickness by the vertical grooves and rectified to provide the flow on the upper portion of the channel box. The amount of water droplets for the fuel bundle is effectively increased and supplied from the tripper to be used for effective cooling of the fuel bundle, and the transition boiling of the fuel rod is suppressed. As a result, the limit output of the entire fuel bundle in the fuel assembly is improved. Further, since the flow tripper is not provided at the welded portion of the channel box or the like, there is an effect that the assembly of the channel box becomes easy.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a fuel assembly according to an embodiment of the present invention.

FIG. 2 is a perspective view of a channel box according to an embodiment of the present invention.

FIG. 3 is a partially cutaway perspective view of a channel box according to an embodiment of the present invention.

FIG. 4 is a sectional view taken along the line AA of FIG.

5 is a cross-sectional view taken along the line BB of FIG.

FIG. 6 is an enlarged vertical cross-sectional view of a main part of a channel box of one embodiment according to the present invention.

FIG. 7 is an enlarged transverse cross-sectional view of a main part of the channel box of the embodiment according to the present invention.

FIG. 8 is a perspective view of a channel box showing a second embodiment according to the present invention.

FIG. 9 is a partially cutaway perspective view of a channel box showing a second embodiment according to the present invention.

FIG. 10 is an enlarged perspective view of a flow tripper showing a second embodiment according to the present invention.

FIG. 11 is a partially cutaway perspective view of a channel box showing a third embodiment according to the present invention.

FIG. 12 is a partially cutaway perspective view of a channel box showing a fourth embodiment according to the present invention.

FIG. 13 is a cross-sectional view of a fuel assembly showing a fifth embodiment according to the present invention.

FIG. 14 is a partially cutaway perspective view of a conventional fuel assembly.

FIG. 15 is an enlarged vertical sectional view of a main part of a conventional fuel assembly.

FIG. 16 is an enlarged cross-sectional view of a main part of a conventional channel box.

FIG. 17 is an enlarged vertical sectional view of a main part of a conventional channel box.

FIG. 18 is a partially cutaway perspective view of a conventional dual channel box type fuel assembly.

[Explanation of symbols]

2 ... Fuel rod, 3 ... Water rod, 5 ... Upper tie plate, 6 ... Lower tie plate, 10 ... Steam void, 11 ... Water film, 11a ... Thick water film, 12 ... Water drop, 13, 41, 51, 61 ... Flow tripper, 13a ... Edge part, 14 ... Welded part, 20, 70 ...
Fuel assembly, 21a, 21b ... Spacer, 23 ... Fuel bundle, 2
4, 40, 50, 60 ... Channel box, 25, 52, 62 ... Vertical groove, 26 ... Sliding part, 27 ... Vacancy, 28 ... Partial length fuel rod, 29 ... Cylindrical sleeve, 30 ... Side band, 31 ... Continuous loop spring,
32 ... Sideband protrusions, 33 ... Sideband flow tabs, 71 ... Outer cylinder, 72 ... Cooling channel partition plate, 73 ... Water cloth, 74 ... Small fuel bundle.

Claims (1)

[Claims] 1. A plurality of fuels, each of which has an upper tie plate and a lower tie plate disposed at the upper and lower parts thereof, and has an upper end held by the upper tie plate and a lower end held by the lower tie plate and filled with a plurality of fuel pellets therein. A fuel assembly consisting of a rod, a fuel bundle in which a plurality of spacers holding the fuel rods at intervals are arranged between the upper and lower tie plates, and a tubular channel box surrounding the fuel bundle and forming a coolant flow path. In the body, a flow tripper consisting of a plurality of lateral grooves is provided on the inner surface of the channel box to divert the coolant flow on the inner surface of the channel box to the fuel bundle, and a plurality of vertical grooves reaching the flow tripper from the lower part of the channel box are provided. A fuel assembly provided at a position corresponding to a fuel rod on an outer peripheral portion of the fuel bundle.