JPH1164557A - Fuel assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel assembly preventing foreign matters flowing along with a coolant, from flowing into the fuel assembly so as to maintain the soundness of fuel rods satisfactorily by installing an extension part of each coolant flow hole, a foreign matter inflow preventive plate, and a projecting part provided at the lower end plug of each fuel rod in a lower tie plate which is a coolant inflow part in the fuel assembly. SOLUTION: The upper and lower ends of a plurality of fuel rods 3 are supported by an upper tie plate and a lower tie plate 15. The mutual spaces of the fuel rods 3 are held by a plurality of fuel spacers between both tie plates, and the outer periphery is surrounded by a fuel channel 2. In a fuel assembly 14 of such constitution, coolant flow holes 13 provided piercing the lower tie plate 15 are extended in the direction of internal space of the lower tie plate 15 through flow hole extension parts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel assembly loaded in a nuclear reactor, and more particularly to a fuel assembly for preventing foreign matter mixed in coolant from flowing into the fuel assembly.

[0002]

2. Description of the Related Art A fuel assembly for a boiling water reactor is shown in FIG.
As shown in a partially cutaway vertical sectional view of FIG. 1, the fuel assembly 1 has a large number of fuel rods 3 and at least one water rod 4 housed in a rectangular tubular fuel channel 2.

An upper tie plate 5 and a lower tie plate 6 are mounted on the upper and lower portions of the fuel assembly 1, respectively. The upper tie plate 5 and the lower tie plate 6 have the fuel rod 3 and the water rod 4 attached thereto. Both ends are held by an upper end plug 7 and a lower end plug 8. A plurality of fuel spacers 9 are attached to the water rod 4 at predetermined intervals in the axial direction, and the plurality of fuel rods 3 are aligned and supported by the plurality of fuel spacers 9. It prevents bending.

FIG. 23 is a plan view showing the network portion 10 of the lower tie plate 6. In this network portion 10, a lower end plug 8 is inserted to support the fuel rod 3 and the water rod 4. A lower end plug support receiving cylinder 11 and a coolant flow hole 13 through which a coolant 12 whose flow direction is indicated by an arrow in FIG.

[0005] As shown in an enlarged longitudinal sectional view of the main part of FIG. 24, the coolant 12 flows into the fuel assembly 1 from the lower tie plate 6 located at the lower end of the fuel assembly 1, The fuel flows through the coolant flow holes 13 provided in the portion 10 and flows around the fuel rods 3 in the fuel channel 2 toward the upper part of the fuel assembly 1 while removing heat generated by the fuel rods 3.

In the fuel assembly 1, a part of the coolant 12 passes through the water rod 4, and at the upper part of the fuel assembly 1, the coolant 12 flows around the fuel rod 3. Together, the fuel assembly 1 from the upper tie plate 5
Spills out of the

[0007]

When the reactor is shut down and periodic inspection is performed, the reactor pressure vessel (not shown) is opened to fill the coolant 12 therein, and the fuel assembly 1 Although replacement and other operations are performed, metal pieces such as wires used in various operations may fall into the reactor pressure vessel during this periodic inspection. Further, there is a possibility that a part of the reactor structure may be peeled off due to oxidation or other causes, and the peeled pieces may fall into the reactor pressure vessel.

[0008] Therefore, when foreign matter such as metal pieces and exfoliated pieces enter the coolant 12, the weight is usually small. Therefore, when the operation of the nuclear reactor is restarted, it is led to the core with the flow of the coolant 12. I will At this time, when a part of the fuel flows into the fuel assembly 1 via the lower tie plate 6, there is a possibility that the fuel may be caught in the fuel assembly 1.

If the foreign matter is caught in the fuel assembly 1 and comes into contact with the fuel cladding tube forming the jacket of the fuel rod 3 due to a change in the flow rate of the coolant 12 or the like, the fuel fretting phenomenon occurs. Damage to the cladding will cause fuel rod 3
In addition, there was a problem that the reliability of the fuel assembly 1 was reduced.

An object of the present invention is to provide an extension of a coolant flow hole, a foreign matter inflow prevention plate, and a lower end of a fuel rod in a lower tie plate which is a coolant inflow portion in a fuel assembly to be loaded into a nuclear reactor. An overhang is installed on the stopper to prevent foreign matter flowing with the coolant from flowing into the fuel assembly.
An object of the present invention is to provide a fuel assembly that maintains good fuel rod integrity.

[0011]

According to a first aspect of the present invention, there is provided a fuel assembly for supporting an upper and lower end of a plurality of fuel rods with an upper tie plate and a lower tie plate. In a fuel assembly in which the intervals between fuel rods are held by a plurality of fuel spacers between the rates and the outer circumference is surrounded by a fuel channel, the coolant flow holes provided through the lower tie plate extend in the lower tie plate internal space direction. It is characterized by having been extended to.

[0012] The foreign matter mixed into the coolant and flowing is guided to the outside of a portion of the coolant flow hole extending in the lower tie plate internal space direction, and is trapped in the lower tie plate internal space at the base. It does not flow into the fuel assembly through the material flow holes. In addition, the foreign matter that has flown with the coolant and guided into the coolant circulation hole is not sufficiently buoyant inside the coolant circulation hole because the length of the passage is longer. Does not flow into the fuel assembly.

[0013] A fuel assembly according to a second aspect of the present invention includes:
According to the first aspect of the present invention, the inside of a portion of the coolant flow hole provided in the lower tie plate extending in the direction of the inner space of the lower tie plate has a spiral shape.

Since the inside of the lower tie plate coolant flow hole extending in the direction of the lower tie plate internal space has a helical shape, the projected cross-sectional area is small and the flow passage is bent, so that it has an elongated shape. Foreign matter that damages the fuel cladding tube, which has poor flexibility, cannot pass through, and is prevented from flowing in near the inlet of the coolant circulation hole. Further, since the flow passage is extended and elongated, foreign matter does not flow into the fuel assembly.

[0015] A fuel assembly according to a third aspect of the present invention includes:
In claim 1, the inside of a portion of the coolant flow hole provided in the lower tie plate that extends in the direction of the inner space of the lower tie plate is formed into a hook shape.

Since the inside of a portion of the coolant flow hole in the lower tie plate which extends in the direction of the inner space of the lower tie plate has a key shape, the projected cross-sectional area is small and the flow passage is bent, so that it has an elongated shape. Foreign matter that damages the fuel cladding tube, which has poor flexibility, cannot pass through, and is prevented from flowing in near the inlet of the coolant circulation hole. Further, since the flow passage is extended and elongated, it does not flow into the fuel assembly.

According to a fourth aspect of the present invention, there is provided a fuel assembly comprising:
According to the first aspect of the present invention, in the coolant flow holes provided in the lower tie plate, the inside of a portion extending in the direction of the lower tie plate internal space is formed in a V shape.

Since the inside of the coolant flow hole of the lower tie plate extending in the direction of the inner space of the lower tie plate has a V-shape, the projected cross-sectional area is small and the flow passage is bent, so that it is elongated. Foreign matter that damages the fuel cladding tube, which has a low flexibility in shape, cannot pass through, and is prevented from flowing in near the inlet of the coolant flow hole. Further, since the flow passage is extended and elongated, it does not flow into the fuel assembly.

A fuel assembly according to a fifth aspect of the present invention comprises:
According to the first aspect of the present invention, a portion of the coolant flow hole provided in the lower tie plate, which extends in the direction of the lower tie plate internal space, is inclined with respect to the axial direction of the fuel assembly.

Since the portion where the coolant flow hole of the lower tie plate extends in the direction of the inner space of the lower tie plate is slanted, foreign matters are easily guided to the outside of the extended portion, and the trapping effect is high. Also, while the flow passage is bent,
Since the flow passage is elongated, it does not flow into the fuel assembly.

[0021] The fuel assembly according to the invention of claim 6 is:
In Claims 1 to 5, a taper is provided on the outside of the tip of a portion of the coolant flowing hole provided in the lower tie plate extending in the lower tie plate internal space direction. The foreign matter flowing together with the coolant is guided to the outside of the portion extended in the direction of the lower tie plate internal space by the taper toward the outside of the tip, so that the foreign matter trapping effect outside the extended portion can be improved.

A fuel assembly according to a seventh aspect of the present invention comprises:
A fuel assembly in which the upper and lower ends of a plurality of fuel rods are supported by an upper tie plate and a lower tie plate, and the interval between the fuel rods is held between the tie plates by a plurality of fuel spacers and the outer periphery is surrounded by a fuel channel. In the above, the same size holes are provided at the same positions as the plurality of lower end plug support receiving cylinders for inserting and supporting lower end plugs such as fuel rods provided in the network portion of the lower tie plate and cooling provided in the network portion. A foreign matter inflow prevention plate provided with a small-diameter hole as a coolant flow passage at the same position as the material flow hole is provided on the upper surface of the network portion and is sandwiched by a lower end plug of the fuel rod.

The foreign matter flowing along with the coolant and passing through the coolant flow hole of the lower tie plate is caught by the small diameter hole of the foreign matter inflow prevention plate. Does not flow.

Further, the pressure loss of the passing coolant can be changed according to the size of the small-diameter hole, and the effect of capturing foreign matter mixed in the coolant can be changed. The installation of the foreign matter inflow prevention plate can be easily performed together with the operation of inserting the fuel rod into the lower tie plate without the need for a tool or the like.

[0025] The fuel assembly according to the invention of claim 8 is:
A seventh aspect of the present invention is characterized in that the coolant flow path in the foreign matter inflow prevention plate has a mesh shape. Since the coolant channels are formed in a network, the number of mesh holes can be increased to reduce the pressure loss of the passing coolant, and the size of the mesh holes can be reduced to capture foreign substances mixed in the coolant. Can be higher.

A fuel assembly according to a ninth aspect of the present invention is:
According to a seventh aspect of the present invention, the coolant flow path in the foreign matter inflow prevention plate is formed in a small circular porous shape. Since the coolant flow path is small circular porous, the number of small circular holes can be increased to reduce the pressure loss of the coolant passing therethrough. Can increase the capturing effect.

A fuel assembly according to a tenth aspect of the present invention is:
According to a seventh aspect of the present invention, the coolant flow path in the foreign matter inflow prevention plate is formed in a slit shape. Since the coolant passage is slit-shaped, the number of slits can be increased to reduce the pressure loss of the passing coolant, and the size of the slit can be reduced to increase the effect of capturing foreign matter mixed in the coolant. be able to.

[0028] The fuel assembly according to claim 11 is:
In the seventh to tenth aspects, the coolant passage in the foreign matter inflow prevention plate is inclined with respect to the axial direction of the fuel assembly. Since the coolant flow path in the foreign matter inflow prevention plate that captures foreign matter mixed in the coolant is inclined,
Since the projected cross-sectional area is small, the effect of capturing foreign matter is further improved without changing the pressure loss.

[0029] The fuel assembly according to the invention of claim 12 is:
A fuel assembly in which the upper and lower ends of a plurality of fuel rods are supported by an upper tie plate and a lower tie plate, and the interval between the fuel rods is held between the tie plates by a plurality of fuel spacers and the outer periphery is surrounded by a fuel channel. Wherein a horizontal projection is provided on the outer periphery of the lower end plug of the fuel rod.

With the horizontal overhang of the lower end plug,
Since the flow path of the coolant is narrowed downstream of the lower tie plate, foreign matter flowing with the coolant and passing through the coolant flow hole of the lower tie plate is caught by the overhang portion, and the fuel in the fuel assembly Foreign matter does not reach around the rod.

The fuel assembly according to the invention according to claim 13 is:
A twelfth aspect of the present invention is characterized in that the position of the horizontal protrusion provided on the outer periphery of the lower end plug of the fuel rod is different in the axial direction between adjacent fuel rods. The protrusion of the lower end plug of the fuel rod has a different height between adjacent fuel rods, so the effect of capturing foreign matter that has passed through the coolant flow hole of the lower tie plate at the lower end plug protrusion is further improved. I do.

A fuel assembly according to a fourteenth aspect of the present invention is:
A fuel assembly in which the upper and lower ends of a plurality of fuel rods are supported by an upper tie plate and a lower tie plate, and the interval between the fuel rods is held between the tie plates by a plurality of fuel spacers and the outer periphery is surrounded by a fuel channel. In the above, a narrow portion is provided at the tip of the lower end plug of the fuel rod, and at the same position as the plurality of lower end plug support receiving cylinders in the network section of the lower tie plate, the tip diameter of the lower end plug of the fuel rod is substantially A lower end for inserting and supporting a water rod lower end plug provided in the network portion by providing a through hole connecting a hole having an equivalent diameter and a cut portion having a width substantially equal to a diameter of a constricted portion of the lower end plug. A hole having a diameter substantially equal to the tip diameter of the lower end plug of the water rod is provided at the same position as the stopper support receiving cylinder, and a small diameter coolant passage is provided at the same position as the coolant circulation hole in the network portion. A foreign matter inflow prevention plate provided with a gasket is installed on the lower surface of the network portion, and is engaged with a cut portion of the foreign matter inflow prevention plate at a narrow portion of a lower end plug of a fuel rod inserted into the lower end plug support receiving cylinder. And

The foreign matter flowing together with the coolant is captured by the small-diameter hole of the foreign matter inflow prevention plate just before the coolant flow hole in the lower tie plate, so that the foreign matter does not flow into the fuel assembly. In addition, the installation of the foreign matter inflow prevention plate can be easily performed without tools or the like.

[0034] The fuel assembly according to claim 15 is:
In claim 14, the coolant flow path in the foreign matter inflow prevention plate is formed in a mesh shape. Since there are a plurality of meshed coolant channels, increasing the number of mesh holes can reduce the pressure loss of the passing coolant, and reduce the size of the mesh holes to capture foreign matter mixed in the coolant. The effect can be enhanced.

A fuel assembly according to a sixteenth aspect of the present invention is
In claim 14, the coolant flow path in the foreign matter inflow prevention plate is formed in a small circular porous shape. Since the coolant flow path is a small circular porous, by increasing the number of small circular holes, it is possible to reduce the pressure loss of the coolant passing therethrough,
By reducing the size of the holes, the effect of capturing foreign matter mixed in the coolant can be increased.

[0036] The fuel assembly according to claim 17 is:
In claim 14, the coolant flow path in the foreign matter inflow prevention plate has a plurality of slits. Since the coolant channel is slit-shaped, increasing the number of slits can reduce the pressure loss of the coolant passing through it, and reducing the size of the slit to increase the effect of capturing foreign matter mixed in the coolant. can do.

The fuel assembly according to the invention according to claim 18 is:
In Claims 14 to 17, the coolant passage in the foreign matter inflow prevention plate is inclined with respect to the axial direction of the fuel assembly. Since the coolant flow path in the foreign matter inflow prevention plate that captures foreign matter mixed in the coolant is inclined,
Since the projected cross-sectional area is small, the effect of capturing foreign matter is further improved without changing the pressure loss.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. Note that the same components as those of the above-described related art are denoted by the same reference numerals, and detailed description thereof will be omitted. In the first embodiment, the fuel assembly 14 includes a plurality of fuel rods 3 and a lower end of a water rod 4 (not shown). A lower end plug support receiving cylinder 11 for inserting and supporting the plug 8 and a lower tie plate 15 provided with a coolant circulation hole 13 into which a coolant 12 indicated by an arrow flows are provided.

In the lower tie plate 15, on the lower surface 10 a of the network part 10 of the network part 10, a circulation hole extending part 16 having a cylindrical inside and communicating with the coolant circulation hole 13 into which the coolant 12 flows is provided. Thereby, the coolant flow hole 13 is extended to the space side inside the lower tie plate.

Next, the operation of the above configuration will be described. During operation of the reactor, the coolant 12 is supplied from the inside to the fuel assembly 14 disposed in the reactor core, below the lower tie plate 15 (upstream side), from the inside of the flow hole extension 16 and the coolant flow hole 13.
Through the fuel channel 2. At this time, if foreign matter is mixed in the coolant 12, the foreign matter flows into the lower tie plate 15 together with the coolant 12.

In the coolant 12, the coolant directly flowing into the fuel assembly 14 from the flow hole extension 16 via the coolant flow hole 13 and the flow hole extension 16 are connected to the lower tie plate 15.
Is extended from the lower surface 10a of the network portion toward the space side (lower side) inside the lower tie plate.
a circulates into the flow hole extension 16.

However, foreign matter that can flow into the fuel assembly 14 and damage the fuel cladding tube (not shown) that covers the fuel rods 3 can pass through the coolant flow holes 13. It is assumed to be an elongated solid with high hardness and poor surface flexibility.

As described above, when the foreign matter that may damage the fuel cladding tube is directly led to the flow hole extension 16 by the flow of the coolant 12, the shape of the flow hole extension 16
Blocked near 16 entrance. Further, in the flow hole extension portion 16 and the coolant flow hole 13, since the flow passages are long due to communication with each other, foreign matters cannot obtain sufficient buoyancy inside the long flow passages. Inflow into channel 2 becomes difficult.

Further, foreign matter is caused by the coolant 12 to extend the flow hole extension.
When guided to the outer peripheral portion of the lower portion 16, since the flow hole extension portion 16 protrudes from the lower surface 10 a of the network portion and extends toward the space inside the lower tie plate, it is trapped at the lower surface 10 a of the network portion, which is the bottom portion. Is done. As a result, most of the foreign matter that may damage the fuel cladding tube is difficult to flow into the fuel assembly 14.

Therefore, in the fuel assembly 14, foreign matter that does not hinder the inflow of the coolant 12 for removing heat generated from the fuel rods 3 and damages the fuel cladding tube of the fuel rods 3 is considered. Since the flow into the fuel assembly 14 is prevented, the soundness of the fuel assembly 14 together with the fuel rods 3 can be maintained well.

In the lower tie plate 15, the pressure loss of the coolant 12 passing therethrough is made equal to that of the conventional lower tie plate 6 in consideration of the flow passage area of the flow hole extension 16, so that the core It is easy to make the pressure loss of the coolant 12 equal to that of the related art and to make the core characteristics equal.

Since the second embodiment is a modification of the first embodiment according to the second aspect, the description of the same components, operations and effects as those of the first embodiment will be omitted. Therefore, the different parts will be mainly described. As shown in the enlarged longitudinal sectional view of the main part of FIG. 2, the fuel assembly 17 is provided on the lower surface 10a of the network portion of the lower tie plate 18 with a flow hole extension portion 19 communicating with the coolant flow hole 13 and having a helical interior. Is provided, so that the coolant flow holes 13 are extended toward the space inside the lower tie plate.

Regarding the operation of the above configuration, even if a foreign substance is mixed into the coolant 12 and flows into the lower tie plate 18, the inside of the flow hole extension 19 in the coolant 12 is spirally formed. , And flows around the fuel rod 3 in the fuel channel 2 via the coolant flow hole 13.

However, as for foreign matter, the flow hole extension 19
When guided to the inside, the inside of the flow hole extension portion 19 is helical, so the projected cross-sectional area is small and the passage is bent, so that the solid shape in the elongated shape that may damage the fuel cladding tube Foreign matter cannot pass through and the flow hole extension 19
Near the entrance of the vessel. In addition, the circulation hole extension
Since the flow path is long in 19 and the coolant flow hole 13, it is difficult for foreign matter to pass through the long flow path.

In addition, foreign matter is formed by the coolant 12 through the flow hole extension.
When guided to the outer peripheral portion of 19, the flow hole extension portion 19 is extended to the space side inside the lower tie plate, and is caught at the network portion lower surface 10a which is the bottom portion. Therefore, most of the foreign matter that may damage the fuel cladding tube hardly flows into the fuel assembly 17, and the soundness of the fuel assembly 17 together with the fuel rods 3 can be maintained well.

Since the third embodiment is a modification of the first embodiment according to the third aspect, the description of the same components, operations and effects as those of the first embodiment will be omitted. Therefore, the different parts will be mainly described. As shown in the enlarged vertical sectional view of the main part of FIG. 3, the fuel assembly 20 is provided on the lower surface 10a of the network portion of the lower tie plate 21 so as to communicate with the coolant flow hole 13 and to form a hook-shaped flow hole extension inside. With the provision of 22, the coolant flow holes 13 extend to the space side inside the lower tie plate.

Regarding the operation of the above configuration, even if foreign matter enters the coolant 12 and flows into the lower tie plate 21, the coolant 12 has a hook-like shape inside the flow hole extension 22. To the coolant passage 13
Flows around the fuel rod 3 in the fuel channel 2 via

However, as for foreign matter, the flow hole extension 22
When guided to, the inside of the flow hole extension 22 is bent in a hook shape, the projected cross-sectional area is small and the passage is bent, so that solid foreign matter in an elongated shape cannot pass, Inflow is blocked near the inlet of the flow hole extension 22. Further, in the flow hole extension portion 22 and the coolant flow hole 13,
Due to the length of the flow passage, foreign matter is difficult to pass through this long flow passage.

In addition, foreign matter is formed by the coolant 12 due to the flow hole extension.
When guided to the outer peripheral portion of 22, the flow hole extension portion 22 extends to the space side inside the lower tie plate, and is caught at the network portion lower surface 10a which is the bottom portion. Therefore, most of the foreign matter that may damage the fuel cladding tube hardly flows into the fuel assembly 20, and the soundness of the fuel assembly 20 together with the fuel rods 3 can be maintained well.

Since the fourth embodiment is a modification of the first embodiment, it will not be described with respect to the same components, functions and effects as those of the first embodiment. Therefore, the different parts will be mainly described. As shown in the enlarged vertical sectional view of the main part of FIG. 4, the fuel assembly 23 is formed on the lower surface 10a of the lower tie plate 24 so as to communicate with the coolant flow hole 13 so as to extend the flow hole having a V shape inside. By providing the part 25, the coolant circulation hole 13 is configured to extend toward the space inside the lower tie plate.

Regarding the operation of the above configuration, even if a foreign substance is mixed into the coolant 12 and flows into the lower tie plate 24, the coolant 12 passes through the inside of the flow hole extension 25. It refracts in the shape of a letter and passes without hindrance, and flows into the fuel channel 2 via the coolant flow holes 13.

However, as for foreign matter, the flow hole extension portion 25
When guided to, the inside of the flow hole extension 25 is bent in a C-shape, the projected cross-sectional area is small and the passage is bent, so that solid foreign matter in an elongated shape cannot pass, Inflow is blocked near the inlet of the flow hole extension 25.
Further, since the flow passage is long in the flow hole extension 25 and the coolant flow hole 13, it is difficult for foreign matter to pass through the long flow passage.

In addition, the foreign matter is formed by the coolant 12 due to the flow hole extension.
When guided to the outer peripheral portion of 25, since the circulation hole extension portion 25 extends to the space side inside the lower tie plate, it is caught at the network portion lower surface 10a which is the bottom portion. Therefore, most of the foreign matter that may damage the fuel cladding tube hardly flows into the fuel assembly 23, and the soundness of the fuel assembly 23 together with the fuel rods 3 can be maintained well.

The fifth embodiment relates to claim 5 and is a modification of the first embodiment. Therefore, the description of the same components, operations and effects as those of the first embodiment will be omitted. Therefore, the different parts will be mainly described.

As shown in the enlarged vertical sectional view of the main part of FIG. 5, the fuel assembly 26 is provided on the lower surface 10a of the network of the lower tie plate 27 so as to communicate with the coolant flow hole 13 so as to form the coolant flow hole.
By providing a flow hole extension 28 inclined with the 13 axis,
The coolant flow holes 13 are configured to extend obliquely with respect to the axial direction of the fuel assembly 26 toward the space inside the lower tie plate.

Regarding the operation of the above structure, even if foreign matter enters the coolant 12 and flows into the lower tie plate 27, the coolant 12 passes through the through-hole extension 28 in the coolant 12. After turning obliquely at the outlet, it flows into the fuel channel 2 through the coolant flow holes 13 without any trouble.

However, as for foreign matter, the flow hole extension portion 28
When it is led to the flow hole extension 286, the entrance of the flow hole extension 286 is inclined and bent at the exit, so that a solid object having a slender shape cannot pass through and flows into the flow hole extension 28. Is blocked. Furthermore, in the flow hole extension 28 and the coolant flow hole 13, since the flow path is long,
Foreign matter is difficult to pass through this long flow passage.

In addition, foreign matter is formed by the coolant 12 due to
When guided to the outer periphery of 28, since the flow hole extension 28 is inclined and extended to the space side inside the lower tie plate, it is easy to be guided to the bottom along this flow hole extension 28, It is captured on the network unit lower surface 10a. Therefore, most of the foreign matter that may damage the fuel cladding tube hardly flows into the fuel assembly 26, and the soundness of the fuel assembly 26 together with the fuel rods 3 can be maintained well.

Since the sixth embodiment is a modification of the first embodiment according to the sixth aspect, the description of the same components, operations and effects as those of the first embodiment will be omitted. Therefore, the different parts will be mainly described. As shown in the enlarged vertical sectional view of the main part of FIG. 6, the fuel assembly 29 has a network hole lower surface 10a in the lower tie plate 30 which communicates with the coolant circulation hole 13 and has a flow hole extension formed with a taper on the outside of the tip. With the provision of 31, the coolant flow holes 13 extend to the space side inside the lower tie plate.

Regarding the operation of the above configuration, even if foreign matter enters the coolant 12 and flows into the lower tie plate 30, the coolant 12 is not It flows into the fuel channel 2 via the hole 13. However, when the foreign matter is led to the flow hole extension 31, the entrance is tapered on the outside. Therefore, it is highly effective that the foreign material is guided to the outside along this taper. Guided to the bottom of the network
Captured at 10a.

Further, the flow hole extension 31 and the coolant flow hole
In 13, since the flow path is long, foreign matter is difficult to pass through the long flow path. Therefore, most of the foreign matter that could damage the fuel cladding is
It is difficult to flow into the fuel assembly 29, and the soundness of the fuel assembly 29 together with the fuel rods 3 can be favorably maintained.

The lower tie plates 18, 21, 24, 27, 30 of the second to sixth embodiments described above also have respective flow hole extension portions 19, 22, 25, 28, 31. By making the pressure loss of the coolant 12 passing through equal to that of the conventional lower tie plate 6 in consideration of the flow path area of the above, the pressure loss of the coolant 12 in the core is made equal to the conventional one, and the core characteristics are equivalent. And can be.

As shown in FIG. 7, the fuel assembly 32 has a plurality of fuel rods 3 and a lower part of a water rod 4 (not shown). A lower end plug support receiving cylinder 11 for inserting and supporting the end plug 8,
A lower tie plate 6 provided with a coolant flow hole 13 into which a coolant 12 indicated by an arrow flows is provided. A foreign matter inflow prevention plate 33 is provided on the upper surface 10b of the network portion 10 of the lower tie plate 6, and is held by being sandwiched between the upper surface 10b of the network portion and the fuel rod 3.

As shown in the plan view of FIG. 8, the foreign matter inflow prevention plate 33 has a network portion of the lower tie plate 6.
A lower end plug insertion hole 34 of the same size is provided at the same position as a number of lower end plug support receiving cylinders 11 for inserting and supporting the lower end plug 8 of the fuel rod at 10.
And a coolant passage hole in the network section 10.
At the same position as 13, a small-diameter hole of the coolant channel 35 that blocks the passage of foreign matter is provided.

Next, the operation of the above configuration will be described. The coolant 12 flows into the fuel channel 2 from the inside of the lower tie plate 6 through the coolant circulation holes 13 of the network portion 10 and subsequently through the small-diameter holes that are the coolant flow passages 35 of the foreign matter inflow prevention plate 33. . At this time, if foreign matter is mixed in the coolant 12, even if the foreign matter passes through the coolant circulation hole 13, the coolant flow path 35
Is stopped and trapped in the small diameter hole.

As a result, foreign matter does not reach around the fuel rods 3 in the fuel channel 2, so that the fuel cladding tube is not damaged, and the soundness of the fuel assembly 32 is maintained with the fuel rods 3. be able to. The attachment of the foreign matter inflow prevention plate 33 is performed by inserting the fuel rod 3 and the lower end plug 8 of the water rod 4 into the lower end plug support receiving cylinder 11 on the upper surface 10b of the network portion 10 when the fuel rod 3 and the lower end plug 8 are inserted. Is easily retained.

For this reason, the installation is extremely simple without the need for a special mounting device, and the foreign matter inflow prevention plate 33 does not require any processing such as screw holes. Is easy to fabricate because it is possible.

Since the eighth embodiment relates to claim 8 and is a modification of the seventh embodiment, description of the same components, operations and effects as those of the seventh embodiment will be omitted. Therefore, the different parts will be mainly described. As shown in the enlarged plan view of the main part of FIG. 9, the foreign matter inflow prevention plate 36 has a coolant flow passage 37 provided between the lower end plug insertion holes 34 for inserting and supporting the lower end plug 8 by a plurality of corners. It is configured to be provided in a mesh shape by holes.

The operation of the above configuration is as follows.
37 is a mesh shape and a plurality of square holes, and by increasing the number of square holes, the pressure loss of the coolant 12 passing therethrough can be reduced, and the effect of capturing foreign matter mixed in the coolant 12 is high, and By reducing the size of each square hole, the capturing effect can be further improved.

Therefore, by considering the flow passage area of the coolant flow passage 37, the foreign matter trapping effect is high, and the pressure loss of the coolant 12 passing therethrough is reduced by the conventional lower tie plate without the foreign matter inflow prevention plate 36. 6, the pressure loss of the coolant 12 in the core can be made equal to the conventional case, and the core characteristics can be made equal.

Since the ninth embodiment is a modification of the seventh embodiment, a description of the same components, operations and effects as those of the seventh embodiment will be omitted. Therefore, the different parts will be mainly described. As shown in the main part enlarged plan view of FIG. 10, the foreign matter inflow prevention plate 38 has a small circular coolant passage 39 provided between the lower end plug insertion holes 34 for inserting and supporting the lower end plug 8 in a small circular shape. It is configured to be provided in a porous shape.

The operation of the above structure is as follows.
By increasing the number of small circular holes or increasing the number of small circular holes, the pressure loss of the coolant 12 passing therethrough can be reduced, and the effect of capturing foreign matter mixed in the coolant 12 is high, and The capture effect is further improved by reducing the small circular hole.

Since the tenth embodiment is a modification of the seventh embodiment, a description of the same components, operations and effects as those of the seventh embodiment will be omitted. Therefore, the different parts will be mainly described. As shown in the enlarged plan view of the main part of FIG. 11, the foreign matter inflow prevention plate 40 has a plurality of slits formed in the coolant passage 41 provided between the lower end plug insertion holes 34 for inserting and supporting the lower end plug 8. It is a configuration provided in a shape.

The operation of the above arrangement is as follows.
41 is a plurality of slits and, by increasing the number of slits, it is possible to reduce the pressure loss of the coolant 12 passing therethrough, and the effect of capturing foreign matter mixed in the coolant 12 is high, and
The trapping effect is further improved by making the slit smaller.

Since the eleventh embodiment is a modification of the seventh to tenth embodiments according to claim 11, the same components, operations and effects as those of the seventh to tenth embodiments are provided. Is omitted, and different parts will be mainly described. The enlarged vertical sectional view of the main part of FIG.
The cross section taken along the -A line is shown as an example, and the foreign matter inflow prevention plate 42 has a mesh-shaped coolant passage 43 formed by a plurality of square holes.
The fuel assembly 32 is configured to be inclined with respect to the axial direction.

As a function of the above configuration, since the coolant flow passage 43 provided in the foreign matter inflow prevention plate 42 is inclined with respect to the axial direction of the fuel assembly 32, there is no hindrance to the pressure loss of the coolant 12. There is no. However, since the projected cross-sectional area in the flow direction of the coolant 12 is reduced, the passage of foreign matter is more difficult than in the foreign matter inflow prevention plate 36 in the eighth embodiment, and the capturing effect can be improved. . In addition,
In addition to forming the mesh like the coolant channel 43, the coolant channel 3
Similar effects can be obtained by using small holes, porous holes, and slits in 5, 39, and 41.

The twelfth embodiment is directed to a twelfth embodiment. As shown in an enlarged vertical sectional view of a main part of FIG. 13, a fuel assembly 44 has a plurality of fuel rods 45 and a lower part of a water rod 4 (not shown). A lower end plug support receiving cylinder 11 for inserting and supporting the end plug 8,
A lower tie plate 6 provided with a coolant flow hole 13 into which a coolant 12 indicated by an arrow flows is provided. In the fuel rods 45, a horizontal overhang 46 is provided in the outer periphery of the lower end plug 8 in a blung manner, and the overhang 46 has a size and shape such that adjacent fuel rods 45 do not abut each other. Make up.

Next, the operation of the above configuration will be described. On the downstream side of the network portion 10 of the lower tie plate 6, a coolant flow path is formed between adjacent overhangs 46 on the outer periphery of the lower end plug 8 of the fuel rod 45. Coolant
12 flows from the inside of the lower tie plate 6 through the coolant flow holes 13 of the network section 10 and flows into the fuel channel 2.

At this time, if foreign matter is mixed in the coolant 12, the coolant 12 flows through the coolant passage formed between the adjacent overhangs 46 without any trouble. Flows around the fuel rod 45.

However, as for foreign matter,
The passage is blocked and trapped because the coolant flow path formed by the above is narrow. Accordingly, foreign matter does not reach around the fuel rod 45 in the fuel channel 2. Therefore, the soundness of the fuel assembly 44 together with the fuel rods 45 can be favorably maintained without damaging the fuel cladding tube.

The thirteenth embodiment is directed to a thirteenth embodiment.
Since this is a modification of the twelfth embodiment, description of the same components, operations and effects as those of the twelfth embodiment will be omitted, and different portions will be mainly described. As shown in the main part enlarged plan view of FIG. 14, the fuel assembly 47 includes a plurality of fuel rods 45a,
Although the fuel rods 45b are inserted and supported, the fuel rods 45a and the fuel rods 45b are alternately arranged adjacent to each other.

The fuel rod 45a is provided with a horizontal overhang 46a in the form of a plunge around the lower end plug 8, and the fuel rod 45b is provided with an overhang 46b. Further, the overhanging portion 46a of the fuel rod 45a and the overhanging portion 46b of the fuel rod 45b are located at the installation positions of the fuel rod 45a.
In the flow direction of the coolant 12, which is the axial direction of 45a and 45b, the directions are different from each other. Here, the overhang portion 46a is located above the overhang portion 46b.

As an effect of the above configuration, the fuel assembly 47
In the above, the coolant flow path on the downstream side of the network portion 10 of the lower tie plate 6 is narrowed by the overhang portions 46a and 46b, and the overhang portions 46a and 46b
Is formed by refraction due to the difference in the installation position of the. As a result, the coolant 12 that has passed through the coolant circulation holes 13
It refracts between 46a and 46b and passes without hindrance, is guided into the fuel channel 2 and flows around the fuel rods 45a and 45b.

However, foreign matter mixed in the coolant 12 is prevented from passing through the overhang portions 46a and 46b and is captured, so that the soundness of the fuel assembly 47 together with the fuel rods 45a and 45b is maintained well. Can be. The fuel rod 45
a, 45b, overhanging portions 46a, 46 provided on the outer periphery of lower end plug 8
With respect to the shape of b and the installation position in the flow path direction which is the axial direction, the position and the shape with high efficiency are considered in consideration of the assembling work and the pressure loss and the foreign matter capturing effect of the coolant 12 together with the twelfth embodiment. Can be easily set as appropriate.

That is, when the installation positions of the overhang portions 46a and 46b in the flow path direction are close to each other and when the overhang portions 46a and 46b come close to each other, the pressure loss of the coolant 12 increases, but the foreign matter capturing effect is low. improves. Also, the overhang portions 46a,
Even if the 46b interferes with each other on the projection plane in the axial direction, if the installation positions in the flow path direction are far apart, the fuel rod 45b should be inserted first and the fuel rod 45a should be removed first. Therefore, no trouble occurs in the assembly work.

The fourteenth embodiment relates to claim 14, wherein
The same components as those in the seventh to twelfth embodiments are denoted by the same reference numerals. As shown in the enlarged vertical sectional view of the main part of FIG. 15, the fuel assembly 48 has a lower end plug 50 of a plurality of fuel rods 49 and a lower end plug 8 of the water rod 4 (not shown) at its lower part.
The lower tie plate 6 is provided with a lower end plug support receiving cylinder 11 for inserting and supporting a coolant and a coolant flow hole 13 into which a coolant 12 indicated by an arrow flows.

In the network portion 10 of the lower tie plate 6, a foreign substance inflow prevention plate 51 is provided on the lower surface 10a of the network portion, and engages with a constricted portion 52 provided on the lower end plug 50 of the fuel rod 49. And hold it.
As shown in the main part enlarged front view of FIG.
A constricted portion 52 is provided at the tip of the lower end plug 50.

As shown in the plan view of FIG. 17, the foreign matter inflow prevention plate 51 is provided with a plurality of lower end plug support receiving cylinders 11 for inserting and supporting the lower end plugs 50 of the fuel rods 49 in the network portion 10. At the same position, a through-hole is provided that connects an insertion hole 53 having a diameter substantially equal to the tip diameter of the lower end plug 50 and a semicircular cutout 54 having a width substantially equal to the diameter of the constricted portion 52.

Further, a lower end plug support receiving cylinder for inserting and supporting the lower end plug 8 of the water rod 4 in the network section 10.
A support hole 55 having a diameter substantially equal to the tip diameter of the lower end plug 8 of the water rod 4 is provided at the same position as the coolant rod 11, and a coolant flow path is provided at the same position as the coolant circulation hole 13 in the network unit 10.
It is configured with 35 small diameter holes.

Next, the operation of the above configuration will be described. When the lower end plug 50 of all the fuel rods 49 is inserted into the lower end plug support receiving cylinder 11 of the lower tie plate 6, the distal end of the lower end plug 50 and the constricted portion 52 protrude from the network portion lower surface 10a.

The insertion hole 53 of the foreign substance inflow prevention plate 51 is inserted into the distal end of the lower end plug 50 so that the foreign substance inflow prevention plate
When the member 51 is horizontally moved in the engagement direction indicated by the white arrow 56 in FIG. 17, each semicircular cut portion 54 of the foreign matter inflow prevention plate 51 is engaged with the constricted portion 52 of each lower end plug 50, and foreign matter inflow is caused. Prevention plate
51 is held vertically.

Thereafter, when the lower end plug 8 of the water rod 4 (not shown) is inserted into the lower end plug support receiving cylinder 11 of the lower tie plate 6, the lower end plug 8 of the water rod 4 is inserted.
Is supported by the lower end plug support receiving cylinder 11, and the distal end thereof is inserted into the support hole 55 of the foreign matter inflow prevention plate 51.

As a result, the foreign matter inflow prevention plate 51 is prevented from moving horizontally.
Is held. The removal of the foreign matter inflow prevention plate 51 and the fuel rod 49 from the lower tie plate 6 can be easily performed by first taking out the water rod 4 in the reverse procedure.

In the fuel assembly 48, even in the event that foreign matter is mixed into the coolant 12 and flows into the lower tie plate 6, the coolant 12 is also prevented from flowing into the small tie plate 6 by the foreign matter inflow prevention plate 51. After passing through the coolant flow 35 and passing through the coolant flow holes 13 of the lower tie plate 6, it is guided around the fuel rod 49 in the fuel channel 2 without any problem.

However, the foreign matter is prevented and trapped by the coolant passage 35 having the small diameter hole in the foreign matter inflow prevention plate 51, so that the foreign matter does not flow around the fuel rod 49 in the fuel channel 2, so that the fuel does not flow. The soundness of the fuel assembly 48 together with the cladding is well maintained.

Further, after the lower end plug 50 of the fuel rod 49 is inserted into the lower end plug support receiving cylinder 11, the constricted portion 52 is engaged with the semicircular cut portion 54 of the foreign matter inflow prevention plate 51, whereby the height is increased. Direction, and then the lower end plug 8 of the water rod 4
To maintain the horizontal direction. Therefore, it is not necessary to form a screw hole or the like in the foreign matter inflow prevention plate 51, and the manufacturing can be easily performed only by pressing.

In a fuel assembly using a short fuel rod (not shown) having a shorter length than a standard fuel rod, the upper part of the short fuel rod is not held by the upper tie plate 5. However, since the fourteenth embodiment is configured to be supported by the lower tie plate 6 in the vertical direction via the foreign matter inflow prevention plate 51, during the transportation of the fuel assembly and the operation of the reactor,
The short fuel rod does not come off from the lower tie plate 6, and the short fuel rod also has a detachment prevention effect.

The fifteenth embodiment is as set forth in claim 15, wherein
Since this is a modification of the fourteenth embodiment, the description of the same components, operations, and effects as those of the fourteenth embodiment will be omitted, and different portions will be mainly described. As shown in the main part enlarged plan view of FIG. 18, the foreign matter inflow prevention plate 57 is provided with a coolant flow provided between the semicircular cut portions 54 connecting the insertion holes 53 for inserting and supporting the lower end plug 50. The path 37 is configured to be provided in a mesh shape by a plurality of square holes.

The operation of the above configuration is as follows.
37 is a mesh shape and a plurality of square holes, and by increasing the number of square holes, the pressure loss of the coolant 12 passing therethrough can be reduced, and the effect of capturing foreign matter mixed in the coolant 12 is high, and By reducing the size of each square hole, the capturing effect can be further improved.

Therefore, by considering the flow passage area in the coolant flow passage 37, the foreign matter trapping effect is high, and the pressure loss of the coolant 12 passing therethrough is reduced by the conventional lower tie plate without the foreign matter inflow prevention plate 576. 6, the pressure loss of the coolant 12 in the core can be made equal to the conventional case, and the core characteristics can be made equal.

The sixteenth embodiment is directed to claim 16, wherein
Since this is a modification of the fourteenth embodiment, the description of the same components, operations, and effects as those of the fourteenth embodiment will be omitted, and different portions will be mainly described. As shown in the enlarged plan view of the main part of FIG. 19, the foreign matter inflow prevention plate 58 is provided between the semicircular cut portions 54 connecting the insertion holes 53 for inserting and supporting the lower end plug 8, and the coolant flow The path 39 is configured to be provided in a small circular porous shape.

The operation of the above structure is as follows.
By increasing the number of small circular holes or increasing the number of small circular holes, the pressure loss of the coolant 12 passing therethrough can be reduced, and the effect of capturing foreign matter mixed in the coolant 12 is high, and The capture effect is further improved by reducing the small circular hole.

The seventeenth embodiment is directed to claim 17, wherein
Since this is a modification of the fourteenth embodiment, the description of the same components, operations, and effects as those of the fourteenth embodiment will be omitted, and different portions will be mainly described. As shown in the enlarged plan view of the main part of FIG. 20, the foreign matter inflow prevention plate 59 is provided between the square cut portions 60 connected to the insertion holes 53, which are through holes for inserting and supporting the lower end plug 8. Coolant channel 41
Are provided in a plurality of slits.

The operation of the above configuration is as follows.
41 is a plurality of slits and, by increasing the number of slits, it is possible to reduce the pressure loss of the coolant 12 passing therethrough, and the effect of capturing foreign matter mixed in the coolant 12 is high, and
The trapping effect is further improved by making the slit smaller. Further, according to the square cut portion 60 in which the insertion hole 53 is connected to the through hole, the narrow portion 52 of the lower end plug 50 of the fuel rod 49 is formed into a square having the same size as the square cut portion 60, The rotation of the fuel rod 49 can be regulated and held.

The eighteenth embodiment relates to claim 18, wherein
Since this is a modification of the fourteenth to seventeenth embodiments,
The description of the same components, operations and effects as those of the fourteenth to seventeenth embodiments will be omitted, and different portions will be mainly described. The enlarged vertical sectional view of the main part of FIG.
The cross section along the -B line is shown as an example, and the foreign matter inflow prevention plate 61 has a mesh-shaped coolant passage 43 formed by a plurality of square holes.
The fuel assembly 48 is configured to be inclined with respect to the axial direction.

As a function of the above configuration, since the coolant flow passage 43 provided in the foreign matter inflow prevention plate 61 is inclined with respect to the axial direction of the fuel assembly 48, the pressure loss of the coolant 12 is not affected. There is no. However, since the projected cross-sectional area of the coolant 12 in the flow direction is reduced, the passage of foreign matter is more difficult than in the foreign matter inflow prevention plate 57 in the fifteenth embodiment, and the trapping effect is improved.

[0112] In addition to forming the coolant flow path in a mesh shape like the coolant flow path 43, the same effect can be obtained by making the coolant flow paths 35, 39 and 41 small holes, porous and slit shapes. be able to.

The lower tie plate 6 in the fourteenth to eighteenth embodiments has a foreign matter inflow prevention plate.
51, 57 to 59, 61 need to have a structure that can be mounted in the internal space of the lower tie plate 6. This includes, for example,
As in the lower tie plate disclosed in JP-A-8-179069 `` Fuel assembly '', the network part for inserting the lower end plug 50 of the fuel rod 49 and the lower nozzle into which the coolant 12 flows from the outside can be separated. By doing so, the foreign matter inflow prevention plates 51 and 57
Nos. 59 and 61 can be easily attached to the network unit.

[0114]

As described above, according to the present invention, a foreign substance mixed in and flowing into the coolant is guided to the outside of the extended portion of the coolant flow hole and captured before the coolant flow hole of the lower tie plate. Even when the coolant is guided into the coolant flow hole, the long coolant flow hole and its flow path shape prevent foreign matter from flowing into the fuel assembly.

Further, in order to prevent foreign matters mixed into the coolant and flowing into the fuel assembly, the installation work is easy and the manufacturing is easy on the upstream or downstream side of the coolant flow hole in the lower tie plate. In addition to providing a foreign matter inflow prevention plate, various shapes of the coolant flow path are selected.

Further, a horizontal projection is provided at the lower end plug of the fuel rod, and foreign matters flowing together with the coolant are captured at the projection between adjacent fuel rods. This prevents foreign matter from reaching the periphery of the fuel cladding tube in the fuel assembly, so that the soundness of the fuel assembly together with the fuel rods can be favorably maintained.

[Brief description of the drawings]

FIG. 1 is an enlarged longitudinal sectional view of a main part of a fuel assembly according to a first embodiment of the present invention.

FIG. 2 is an enlarged longitudinal sectional view of a main part of a fuel assembly according to a second embodiment of the present invention.

FIG. 3 is an enlarged longitudinal sectional view of a main part of a fuel assembly according to a third embodiment of the present invention.

FIG. 4 is an enlarged longitudinal sectional view of a main part of a fuel assembly according to a fourth embodiment of the present invention.

FIG. 5 is an enlarged longitudinal sectional view of a main part of a fuel assembly according to a fifth embodiment of the present invention.

FIG. 6 is an enlarged longitudinal sectional view of a main part of a fuel assembly according to a sixth embodiment of the present invention.

FIG. 7 is an enlarged longitudinal sectional view of a main part of a fuel assembly according to a seventh embodiment of the present invention.

FIG. 8 is a plan view of a foreign matter inflow prevention plate according to a seventh embodiment of the present invention.

FIG. 9 is an enlarged plan view of a main part of a foreign matter inflow prevention plate according to an eighth embodiment of the present invention.

FIG. 10 is an enlarged plan view of a main part of a foreign matter inflow prevention plate according to a ninth embodiment of the present invention.

FIG. 11 is an enlarged plan view of a main part of a foreign matter inflow prevention plate according to a tenth embodiment of the present invention.

FIG. 12 is an enlarged vertical sectional view of the foreign matter inflow prevention plate according to the eleventh embodiment of the present invention, taken along line AA in FIG. 9;

FIG. 13 is an enlarged longitudinal sectional view of a main part of a fuel assembly according to a twelfth embodiment of the present invention.

FIG. 14 is an enlarged longitudinal sectional view of a main part of a fuel assembly according to a thirteenth embodiment of the present invention.

FIG. 15 is an enlarged longitudinal sectional view of a main part of a fuel assembly according to a fourteenth embodiment of the present invention.

FIG. 16 is an enlarged front view of a main part of a fuel rod according to a fourteenth embodiment of the present invention.

FIG. 17 is a plan view of a foreign matter inflow prevention plate according to a fourteenth embodiment of the present invention.

FIG. 18 is an enlarged plan view of a main part of a foreign matter inflow prevention plate according to a fifteenth embodiment of the present invention.

FIG. 19 is an enlarged plan view of a main part of a foreign matter inflow prevention plate according to a sixteenth embodiment of the present invention.

FIG. 20 is an enlarged plan view of a main part of a foreign matter inflow prevention plate according to a seventeenth embodiment of the present invention.

FIG. 21 is an enlarged vertical sectional view of the foreign matter inflow prevention plate according to the eighteenth embodiment of the present invention, taken along line BB in FIG. 18;

FIG. 22 is a partially cutaway longitudinal sectional view of a conventional fuel assembly.

FIG. 23 is a plan view of a conventional lower tie plate network unit.

FIG. 24 is an enlarged sectional view of a main part of a conventional fuel assembly.

[Explanation of symbols]

1, 14, 17, 20, 23, 26, 29, 32, 44, 47, 48 ... fuel assembly, 2 ... fuel channel, 3, 45, 45a, 45b, 49 ...
Fuel rod, 4 ... water rod, 5 ... upper tie plate,
6, 15, 18, 21, 24, 27, 30 ... Lower tie plate, 7 ...
Upper end plug, 8,50 ... lower end plug, 9 ... fuel spacer, 10 ...
Network part, 10a: Network part lower surface, 10b: Network part upper surface, 11: Lower end plug support receiving cylinder, 12: Coolant (flow direction arrow), 13: Coolant flow hole, 16, 19, 22, 2
5, 28, 31 ... distribution hole extension, 33, 36, 38, 40, 42, 51, 5
7-59, 61 ... foreign matter inflow prevention plate, 34 ... lower end plug insertion hole, 35
... coolant passage with small diameter holes, 37 ... mesh-like coolant passage, 39 ...
Porous coolant channel, 41 ... Slit-shaped coolant channel, 43
... Refrigerant flow channels in a mesh shape, 46, 46a, 46b. Overhangs, 52. Constriction of lower end plug, 53. Insertion hole, 54. Semicircle cut, 55. Support hole, 56. (Engagement direction),
60 ... Square cut part.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shigeyuki Ishida 66-2 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Toshiba Engineering Corporation

Claims (18)

[Claims] An upper end and a lower end of a plurality of fuel rods are supported by an upper tie plate and a lower tie plate, and an interval between fuel rods is held between the two tie plates by a plurality of fuel spacers, and an outer periphery is formed by a fuel channel. In the enclosed fuel assembly, a coolant flow hole provided through the lower tie plate is extended in a direction of an inner space of the lower tie plate. 2. The fuel assembly according to claim 1, wherein a portion of the coolant flow hole provided in the lower tie plate, which extends in the direction of the inner space of the lower tie plate, has a spiral shape. 3. The fuel assembly according to claim 1, wherein a portion of the coolant passage hole provided in the lower tie plate extending in the direction of the inner space of the lower tie plate has a hook shape. 4. A coolant flow hole provided in the lower tie plate, wherein a portion extending in a direction of an inner space of the lower tie plate has a V shape.
The fuel assembly as described. 5. A coolant circulation hole provided in the lower tie plate, wherein a portion extending in a lower tie plate internal space direction is inclined with respect to an axial direction of the fuel assembly. The fuel assembly as described. 6. The coolant flow hole provided in the lower tie plate, wherein a taper is provided at a tip outer side of a portion extended in a direction of an inner space of the lower tie plate. Fuel assembly. 7. Upper and lower ends of a plurality of fuel rods are supported by an upper tie plate and a lower tie plate, and an interval between the fuel rods is held between the two tie plates by a plurality of fuel spacers, and an outer periphery is formed by a fuel channel. In the enclosed fuel assembly, holes of the same size are provided at the same position as a plurality of lower end plug support receiving cylinders for inserting and supporting lower end plugs such as fuel rods provided in the lower tie plate network portion, and the network portion is provided. A foreign matter inflow prevention plate provided with a small-diameter hole as a coolant flow passage at the same position as a coolant flow hole provided in the network portion is provided on the upper surface of the network portion and is sandwiched by lower end plugs of the fuel rods. Fuel assembly. 8. The fuel assembly according to claim 7, wherein the coolant flow passage in the foreign matter inflow prevention plate is formed in a mesh shape. 9. The fuel assembly according to claim 7, wherein the coolant flow passage in the foreign matter inflow prevention plate has a small circular porous shape. 10. The fuel assembly according to claim 7, wherein the coolant flow passage in the foreign matter inflow prevention plate has a slit shape. 11. The fuel assembly according to claim 7, wherein the coolant passage in the foreign matter inflow prevention plate is inclined with respect to the axial direction of the fuel assembly. 12. The upper and lower ends of a plurality of fuel rods are supported by an upper tie plate and a lower tie plate, and an interval between the fuel rods is held between the tie plates by a plurality of fuel spacers, and the outer periphery is formed by a fuel channel. In the enclosed fuel assembly, a horizontal projection is provided on an outer periphery of a lower end plug of the fuel rod. 13. The fuel assembly according to claim 12, wherein the position of the horizontal projection provided on the outer periphery of the lower end plug of the fuel rod is different in the axial direction between adjacent fuel rods. . 14. Upper and lower ends of a plurality of fuel rods are supported by an upper tie plate and a lower tie plate, and an interval between the fuel rods is held between the two tie plates by a plurality of fuel spacers, and an outer periphery is formed by a fuel channel. In the enclosed fuel assembly, a constriction is provided at the tip of the lower end plug of the fuel rod, and the lower end plug of the fuel rod is located at the same position as a plurality of lower end plug support receiving cylinders in the network section of the lower tie plate. A through-hole is provided that connects a hole having a diameter substantially equal to the tip diameter of the lower end plug and a cut portion having a width substantially equal to the diameter of the constricted portion of the lower end plug, and a water rod lower end plug in the network portion is provided. A hole having a diameter substantially equal to the tip diameter of the lower end plug of the water rod is provided at the same position as the lower end plug support receiving cylinder to be inserted and supported, and a coolant is provided at the same position as the coolant circulation hole in the network portion. A foreign substance inflow prevention plate provided with a small diameter hole as a flow path is installed on the lower surface of the network portion, and a cutout portion of the foreign matter inflow prevention plate at a narrow portion of a lower end plug of a fuel rod inserted into the lower end plug support receiving cylinder. A fuel assembly for engaging. 15. The fuel assembly according to claim 14, wherein the coolant flow path in the foreign matter inflow prevention plate has a mesh shape. 16. The coolant flow path in the foreign matter inflow prevention plate is formed in a small circular porous shape.
The fuel assembly as described. 17. The coolant flow path in the foreign matter inflow prevention plate has a plurality of slits.
5. The fuel assembly according to 4. 18. The fuel assembly according to claim 14, wherein the coolant passage in the foreign matter inflow prevention plate is inclined with respect to the axial direction of the fuel assembly.