JP2000111684A - Heating object fluid mixing promoting structure in reactor vessel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heating object fluid mixing promoting structure in a reactor vessel having a shape and arrangement capable of promoting to level a temperature of a heating object fluid flowing in an outlet nozzle and capable of reducing passage resistance in an upper plenum. SOLUTION: In an upper plenum 40 defined in the upper part of a reactor core 33 where a heating object fluid separately flows to a low temperature area (a) and a high temperature area (d) and fluidly communicated with an outlet nozzle 12 provided in the side part of a reactor vessel 10, a heating object fluid (b') flowing out of the low temperature area of the reactor core 33 is guided up to the vicinity of the outlet nozzle 12, 2/3 or more is diametrically thinned, and a heating object fluid guide member 1 composed of the thin diameter part 6 and the thick diameter part 5 having a diametrically contracting rate not less than at least 15% is arranged in the upper plenum 40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal structure of a pressurized water reactor in which a heating element and a fluid to be heated exchange heat, and more particularly to an internal structure near an outlet nozzle of an upper plenum. The shape and arrangement of the

[0002]

2. Description of the Related Art A power reactor is a device for cooling nuclear reaction heat generated inside a fuel rod with a coolant such as light water, that is, heat is exchanged between the nuclear fuel and the coolant. FIG. 9 shows the internal structure of a pressurized water reactor, which is a typical example of a nuclear reactor. Inside the reactor vessel 10, there are reactor internals, nuclear fuel assemblies, and coolant. Briefly describing these, a reactor core vessel 30 is suspended and supported in a reactor vessel 10 integrally formed with an inlet nozzle 11 and an outlet nozzle 12 of a reactor coolant, which is light water. Inlet nozzle 11
The number of outlet nozzles 12 and the number of coolant circulation loops corresponding to the output of the nuclear reactor correspond to the number of coolant circulation loops, usually two to four, respectively. They are arranged at intervals in the circumferential direction.
A lower core support plate 32 and a lower core plate 31 extending horizontally are provided below the inside of the core tank 30, and a lower plenum 41 is formed below them.

[0003] A large number of fuel assemblies 33 are loaded adjacent to each other on a lower core plate 31 to form a core. On the upper part of the fuel assembly 33, an upper core plate 21 is supported by an upper core support plate 20 via an upper core support column 23, and the upper core plate 21 presses the fuel assembly 33 to form a coolant flow. Floating and the like are prevented. A plurality of control rod cluster guide tubes 2
The lower end of 2 is supported by a support pin (not shown) or the like, and the control rod cluster guide tube 22 extends upward through the upper core support plate 20. By drawing a control rod cluster (not shown) from the core into the control rod cluster guide tube 22 or inserting the control rod cluster from the control rod cluster guide tube 22 into the fuel assembly 33 of the core, the heat output of the core is reduced. Adjusted.

FIG. 10 is an enlarged view showing the structure of the upper part of the fuel assembly 33. As shown in FIG. As shown in this figure, the upper core plate 21 and the upper core support plate 20 are
The control rod cluster guide tube 22 which is structurally connected to maintain the strength and penetrates the upper core support plate 20 is also fixed to the upper core support plate 20 and is supported in the lateral direction. An upper plenum 40 is defined between the upper core plate 21 and the upper core support plate 20 connected as described above.

Next, the flow of light water as a coolant inside the reactor vessel 10 configured as described above will be described. The low-temperature light water flowing from the inlet nozzle 11 flows as shown by arrows in FIGS. 9 and 10. That is, it flows down the annular descending space between the core vessel 30 and the inner surface of the reactor vessel 10, and is inverted by the lower plenum 41. Light water that changed its direction upwards,
It flows into the core through the lower core support plate 32 and the lower core plate 31. The light water rising in the reactor core flows as a substantially parallel flow, deprives the fuel rods of the fuel assembly 33 of the nuclear reaction heat, and the temperature rises. After passing through the upper core plate 21, it turns laterally, flows out of the outlet nozzle 12, and flows out of the outlet pipe 42.
Through to a steam generator (not shown).

[0006] Here, a core composed of a plurality of fuel assemblies 33 is usually composed of fuel assemblies having different burnups in three cycles in order to exchange about 1/3 of the fuel every cycle. The output of each fuel assembly differs depending on the burnup. In addition, the neutron flux leaks out of the reactor at the fuel position where the control rods controlling the reactor power are loaded and the neutron flux leaks out of the reactor. Will be lower.

Therefore, when the flow of light water in the reactor core is examined in more detail, the flow of the arrow d flowing through the center where fission reactions are active is relatively well heated due to the influence of the neutron flux distribution in the reactor core. As a result, it becomes relatively hot and enters the upper plenum 40 from the core. Then, it flows inside and around the control rod cluster guide tube 22, and flows into the upper core support plate 20.
, And is guided in the lateral direction, and the arrow e in FIG.
It flows like f and g and flows into the outlet nozzle 12.

On the other hand, the peripheral stream a flowing through the periphery of the core having a relatively low neutron flux density is heated but flows out of the core into the upper plenum 40 at a relatively low temperature as compared with the center. The flow of the arrow b from the core outlet of the peripheral flow toward the outlet nozzle 12 flows through a region where there is no upper core structure inside the core tank 30 and a relatively low resistance, so that the outlet nozzle flows through a direct or short flow path. It flows into 12.

Accordingly, in the outlet pipe 42 connected to the outlet nozzle 12, a relatively low-temperature peripheral flow flows through the bottom of the pipe as shown by the arrow c, and a relatively high-temperature core flow flows. It flows through the ceiling as shown by arrow g. That is, in the outlet pipe 42 and the outlet nozzle 12, a high-temperature layer of the coolant is formed in the upper part and a low-temperature layer of the coolant is formed in the lower part, causing a stratification phenomenon, and a temperature distribution having a large thermal gradient in the outlet pipe and the like. Becomes In addition, when the flow with this temperature difference generates a vortex when passing through the internal structure of the reactor, the temperature of the fluid fluctuates. Easily become obstacles.

Therefore, a structure for promoting mixing to reduce the temperature difference of the heated fluid by changing the flow of the heated fluid depending on the shape of the reactor internal structure installed in the reactor vessel is disclosed in Japanese Patent Application Laid-Open No. H10-157,873. It is disclosed in Japanese Patent Application Laid-Open No. 9-72985, and FIG. 11 shows its structure. In this conventional example, the pipes 24 with slots are arranged on the entire outer peripheral portion of the heat generating portion, and a part of the flow of the arrow a with the low temperature light water flowing out from the outer peripheral portion is appropriately arranged as shown by the arrow b ′. Flows into the slotted tube 24 and then flows out of the upper slot into the upper plenum 40 and toward the outlet nozzle 12 as shown by arrow c '. With this flow, a part of the relatively low-temperature peripheral flow flowing through the slotted tube 24 and the above-described central flows d and e mix moderately inside the upper plenum 40, and the outlet nozzle The temperature of the light water as the coolant flowing into the cooling water 12 is averaged, and the sufficiently mixed light water flows through the outlet pipe 42.

[0011]

However, as described above, low-temperature light water is introduced into the inside of a tubular slotted tube 24 having a large outer diameter, and the light water is introduced from the position of the upper core plate 21 to the outlet nozzle 12. Since the structure that guides upward to near the upper height has a larger outer diameter than the upper core support column 23 having a shape that does not allow light water to pass through, the lateral flow passage toward the outlet nozzle 12 in the upper plenum 40 becomes narrower, The flow resistance of the structure increases. As a result, the fluid load on the upper core support column 23 and the control rod cluster guide tube 22 increases, which may affect the structural integrity of the control rod cluster guide tube 22.

At all positions other than the control rod cluster guide tubes on the upper part of the fuel assembly corresponding to the core outer peripheral portion, slotted tubes 24 are arranged between the upper core plate 21 and the upper core support plate 20. When installing, the upper plenum 40
The flow resistance of the structure in the inside becomes large, and the fluid load applied to the control rod cluster guide tube 22 is limited to the slotted tube 2.
It is about twice or more than when 4 is not attached. In particular, since the lower end of the control rod cluster guide tube 22 is pinned to the upper core plate 21 with the support pin or the like as described above, it is not preferable that the fluid load increases from the viewpoint of safety.

Therefore, in order to solve the above-mentioned problems, the present invention promotes the averaging of the temperature of the coolant flowing into the outlet nozzle and reduces the flow resistance in the upper plenum. It is an object of the present invention to provide a heated fluid mixing promoting structure in a nuclear reactor vessel having an arrangement.

[0014]

In order to achieve the above object, according to the present invention, a fluid to be heated is defined at an upper part of a core where the fluid flows separately in a low temperature region and a high temperature region.
In the upper plenum, which is in fluid communication with an outlet nozzle provided on the side of the reactor vessel, the fluid to be heated flowing out of the low-temperature region of the core is guided to the vicinity of the outlet nozzle, and at least 2/3 of the diameter is reduced. A heated fluid mixing promoting structure in a reactor vessel, wherein a heated fluid guide member having a small diameter portion and a large diameter portion having a diameter reduction ratio of at least 15% or more is provided in the upper plenum.

It is preferable that a plurality of elongated slots are provided in the small diameter portion of the heated fluid guiding member at positions and lengths substantially corresponding to the inner diameter of the outlet nozzle. Further, a tapered portion is provided between the large-diameter portion and the small-diameter portion of the heated fluid guide member so as to be connected, and a plurality of window holes may be provided in the tapered portion. Further, it is desirable that the heated fluid guide member is disposed at a position of an existing upper core support column provided on an outer peripheral portion of the upper plenum and is exchanged.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

FIG. 1 is a sectional view showing the whole of a pressurized water reactor equipped with a heated fluid guide tube according to the present invention.
3 is an enlarged view showing details of the upper plenum 40. FIG.
In these figures, since the internal structure of the pressurized water reactor is largely the same as that of the conventional structure described above,
Description of overlapping parts is omitted. The part different from the above-described conventional structure is the shape of the slotted tube 1 as the heated fluid guide tube. The slotted tube 1 has an upper plenum 4
It may be completely new within zero. Outlet nozzle 1
The slotted pipe 1 may be provided in place of an existing member other than the control rod cluster guide pipe adjacent to the outflow side to 2.

FIG. 3 is an enlarged side view of the slotted tube 1. The slotted tube 1 is formed in a tubular shape, and its lower end 3 is open. When the slotted tube 1 is mounted on the upper core plate 21, the tube 1 communicates with the core through a hole in the upper core plate 21. Thus, the coolant flowing out of the core flows through the inside of the tube 1 with the slot. The upper end side of the slotted tube 1 is attached and fixed to the upper core support plate 20 in the same manner as the upper core support column 23 described above.
A small-diameter mounting portion 4 and a flange portion 4a are formed.

The portion from the lower end 3 of the slotted tube 1 to the lower end of the flange portion 4a, that is, the portion located in the upper plenum 40 when installed and excluding the flange portion 4a, has a lower side. The upper side of the large diameter portion 5 is formed by a small diameter portion 6, and a tapered portion 7 is provided at a portion where the large diameter portion 5 transitions to the small diameter portion 6. Here, the length ratio between the large-diameter portion 5 and the small-diameter portion 6 is at least 1: 3, that is, since the slotted tube 1 has the tapered portion 7 and the flange portion 4a, it is located in the upper plenum 40. It is preferable that at least two-thirds of the part to be formed be the small diameter part 6. Further, the outer diameter of the small diameter portion 6 is smaller than that of the large diameter portion 5 by at least 15% or more.

Next, the upper plenum 4 of the slotted tube 1
FIG. 4 shows the arrangement position within 0. FIG. 4 shows a quarter of the cross section of the reactor vessel 10 in the upper plenum 40, and shows only a main part of each structure. The open square is the control rod crester guide tube 22, the X-shaped is the upper core support column 23, and the round is the position where the conventional slotted tube 24 is provided. , The position where the slotted tube 1 according to the invention is mounted. As can be seen from this figure, conventionally, the tubes 24 with slots are provided at all positions corresponding to the outer peripheral portion of the core (the positions of white and hatched circles in the figure). Is limited to a position where the existing upper core support column 23 is located, and the slotted tube 1 is disposed in place of the upper core support column 23 (the position of the hatched circle in the figure). .

Here, FIGS. 5 to 8 model the arrangement positions of the respective structures in FIG. 4, and FIG. 5 shows a four-loop structure of a conventional general existing furnace without any slotted pipe. FIG. 6 shows the arrangement of the plant, and FIG.
FIG. 7 is a layout view in which the upper core support column 23 arranged on the outer peripheral portion of the existing furnace is replaced with a slotted tube 24, and FIG. 8 is a layout view in FIG. FIG. 2 is a diagram in which a tube with a slot 24 is replaced with a tube with a slot 1 according to the present invention and arranged. Table 1 shows the analysis results of the change in the fluid load acting on the control rod cluster guide tube 22 at the arrangement position of the slotted tube 1 and the reduction ratio of the outer diameter in these FIGS.

[0022]

[Table 1]

In Table 2, the reduction rate of the outer diameter is based on the outer diameter of the conventional slotted tube 24 having a large outer diameter.
As the slotted tube 1 according to the present invention, a tube having the small-diameter portion 6 reduced by about 20% is used, and the reduction ratio is about 0.8. Also, the reduction ratio of the upper core support column 23 of the existing furnace is 0.5 compared to the conventional thick slotted tube 24. On the other hand, control rod cluster guide tube 2
The fluid load acting on 2 is based on the existing furnace shown in FIG.

As can be seen from Table 1, when the conventional thick-walled tube 24 having an outer diameter is disposed at all positions above the fuel assembly corresponding to the outer periphery of the core (arrangement in FIG. 6). In addition, the flow path closing rate increases, and the fluid load acting on the structure around the outlet nozzle 12 in the upper plenum 40, for example, the control rod cluster guide tube 22 increases to 2.5 times that of the existing furnace, thereby affecting the flow. large. Next, as shown in FIG. 7, the control rods are arranged only when the arrangement according to the present invention, that is, when the upper core support column 23 arranged on the outer peripheral portion of the existing furnace is replaced with a tube 24 having a large outside diameter and a slot. Cluster guide tube 2
2 can be suppressed to about 1.5 times. Further, as shown in FIG. 8, when the conventional thick slotted tube 24 is replaced with the slotted tube 1 according to the present invention, the fluid load acting on the control rod cluster guide tube 22 is 1.3 times that of the existing furnace. It turns out that it can only be done. According to the experiments, the mixing of the coolant at a high temperature and a low temperature is promoted by merely arranging the slotted tube 1 at the position shown in FIG. It turns out that you can.

Returning to FIG. 3, the small-diameter portion 6 of the slotted tube 1
When the pipe 1 with a slot is attached, the outlet of the fluid to be heated and the flow passage close to the outlet nozzle 12 at the portion where the lateral flow is large are minimized. At the position corresponding to (see FIG. 2)
A plurality of elongated slots 2 are provided.

The flow resistance (pressure loss) of the coolant flowing through the slotted tube 1 with respect to the axial flow increases in the tapered portion 7 where the outer diameter is reduced from the large diameter portion 5. If the flow resistance is too large, the flow rate of the coolant passing through the upper core plate 21 (see FIG. 2) may be uneven, which may cause a side flow in the core. Therefore, in order to avoid the non-uniform flow rate, a plurality of window holes 8 having a flow path cross-sectional area of a considerable amount or more that the flow path cross-section is reduced in the small-diameter portion 6 are provided in the tapered portion 7 of the slotted tube 1. A part of the coolant is discharged from the hole 8. Table 2 shows the experimental results of the flow resistance of the window 8 provided in the tapered portion 7, that is, the reduction ratio of the pressure loss.

[0027]

[Table 2]

As is apparent from Table 2 above, by disposing the window hole 8 below the outlet nozzle 12 as shown in FIG. 2, the pressure loss is reduced. Further, the direction of the window hole 8 is a direction that is effective for discharging the coolant from the slotted tube 1 with respect to the flow inside the slotted tube 1.

Next, the flow of light water in the reactor core when the slotted tube 1 having the above-described configuration is disposed in the upper plenum 40 inside the reactor vessel 10 will be described. However, since the flow is largely the same as the previous example, the description is omitted, and the flow from the upper plenum 40 to the outlet nozzle 12 will be described in detail with reference to FIG.

As described above, the flow of the arrow d in which the fission reaction flows through the center of the core is heated relatively well and becomes relatively high temperature, enters the upper plenum 40 from the core, and flows through the control rod cluster guide tube 22. It flows inside and around to the lower surface of the upper core support plate 20, and is guided laterally toward the outlet nozzle 12 as shown by arrows e and f in FIG. On the other hand, the peripheral flow a that has flowed around the core where the neutron flux density is relatively small flows out of the core into the upper plenum 40 at a relatively low temperature while being heated. A part of the flow flows into the appropriately disposed slotted tube 1 and flows from the slot 2 provided at a position corresponding to the outlet nozzle 12 as shown by the arrow b ′ in the upper plenum 40. Leaked into
Heads to outlet nozzle 12.

As described above, by flowing the relatively low-temperature coolant through the slotted pipe 1, the low-temperature peripheral flow and the high-temperature central flow are mixed appropriately, and the outlet nozzle 12 The temperature of light water as coolant flows in like a flow, and the temperature of light water is averaged.
Flowing inside. In addition, since the slot 2 is provided in the slotted tube 1 over the position and length corresponding to the outlet nozzle 12, it is possible to minimize the plugging of the passage in the portion where the lateral flow of the coolant in the upper plenum 40 is large. Can be.

The diameter of the small diameter portion 6 having a length of 2/3 of the upper part of the slotted tube 1 is smaller than the large diameter portion 5 by 15% or more. In order to reduce the fluid load acting on the
Flows smoothly toward the outlet nozzle 12 through the slot 2 of the slotted tube 1 as shown in FIG. Further, mixing of the cold peripheral stream and the hot central stream can be facilitated.

Further, the slotted tube 1 has a large diameter portion 5.
Since the window hole 8 is provided in the tapered portion 7 that transitions from the inside to the small diameter portion 6, the flow rate corresponding to the diameter reduction can be discharged from the inside of the slotted tube 1 to the upper plenum 40 before reaching the small diameter portion 6. . Therefore, a decrease in the axial flow rate passing through the inside of the slotted tube 1 is avoided, the flow rate of the coolant passing through the flow passage holes of the upper core plate 21 is not uneven, and the flow rate of the coolant at a low temperature is reduced. Mixing with the high-temperature coolant is further promoted, so that the temperature equalization proceeds.

[0034]

According to the first aspect of the present invention, a fluid to be heated is defined at an upper portion of a reactor core where the fluid flows separately in a low temperature region and a high temperature region, and a fluid is supplied to an outlet nozzle provided on a side portion of the reactor vessel. In the communicating upper plenum, the fluid to be heated flowing out of the low temperature region of the core is guided to the vicinity of the outlet nozzle, and the diameter is reduced to 2/3 or more and the diameter reduction rate is at least 15% or more. The heated fluid guide member comprising a portion and a large diameter portion has a heated fluid mixing promoting structure in the reactor vessel provided in the upper plenum, so that the low-temperature heated fluid flowing through the low-temperature region on the outer peripheral portion of the core, Since the flow of the high-temperature heated fluid flowing through the high-temperature region is guided and mixed into the flow and the increase in the fluid load of the structure inside the upper plenum due to the non-heated fluid guide member can be reduced, the pipe following the outlet nozzle can be used. To prevent the occurrence of thermal stratification phenomenon in,
In addition, the soundness of structures such as the control rod cluster guide tube is improved.

According to the second aspect of the present invention, since a plurality of elongated slots are provided in the small diameter portion of the heated fluid guide member at positions and lengths substantially corresponding to the inner diameter of the outlet nozzle. The flow passage of the heated fluid toward the outlet nozzle can be smoothed, and the fluid load of the structure inside the upper plenum can be further reduced by minimizing the flow passage closure in the portion where the lateral flow of the coolant is large in the upper plenum. Along with
Mixing of the heated fluid in the outlet nozzle is promoted.

According to a third aspect of the present invention, a tapered portion is provided between the large-diameter portion and the small-diameter portion of the heated fluid guide member so as to be connected thereto, and a plurality of tapered portions are provided in the tapered portion. Since the window hole is provided, the flow rate corresponding to the diameter reduction inside the heated fluid guide member can be discharged from the heated fluid guide member to the upper plenum before reaching the small diameter portion, and the heated fluid guide member can be released. By avoiding a decrease in the internal axial flow rate, a lateral flow in the core is prevented, and the mixing of the low-temperature heated fluid and the high-temperature heated fluid in the upper plenum is promoted, so that the temperature becomes even.

According to a fourth aspect of the present invention, since the heated fluid guide member is disposed at a position of an existing upper core support column provided on an outer peripheral portion of the upper plenum and is exchanged, the upper portion is disposed in the upper plenum. The fluid load acting on the structure inside the plenum can be further reduced, and the soundness of the structure is further enhanced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a main part of a pressurized water reactor according to an embodiment of the present invention.

FIG. 2 is a partially enlarged sectional view showing a main part near an upper plenum of the embodiment.

FIG. 3 is a partially cut-away enlarged side view of a slotted tube.

FIG. 4 is a quarter showing the arrangement of structures in the upper plenum.
FIG.

FIG. 5 is a diagram modeling the arrangement of structures in an upper plenum.

FIG. 6 is a diagram modeling an arrangement of structures in an upper plenum.

FIG. 7 is a diagram modeling the arrangement of structures in an upper plenum.

FIG. 8 is a diagram modeling the arrangement of structures in an upper plenum.

FIG. 9 is a longitudinal sectional view showing a main part of an existing general pressurized water reactor.

10 is a partially enlarged cross-sectional view showing a main part in the vicinity of an upper plenum of the pressurized water reactor of FIG.

FIG. 11 is a partially enlarged cross-sectional view showing a main part near an upper plenum to which a conventional slotted tube is attached.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Tube with a slot (small diameter type), 2 ... Slot, 3 ... Lower end, 4 ... Mounting part, 5 ... Large diameter part, 6 ... Small diameter part, 7 ... Tapered part, 8 ... Window hole, 10 ... Nuclear reactor Container, 11 ... inlet nozzle,
12 outlet nozzle, 20 upper core support plate, 21 upper core plate, 22 control rod cluster guide tube, 23 upper core support column, 24 pipe with slot (conventional type: large diameter type), 3
0: core tank, 31: lower core plate, 32: lower core support plate, 33: fuel assembly, 40: upper plenum, 41: lower plenum, 42: outlet piping.

[Procedure amendment]

[Submission date] September 22, 1999 (September 9, 1999
2)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

[0014]

In order to achieve the above object, according to the present invention, a fluid to be heated is defined at an upper part of a core where the fluid flows separately in a low temperature region and a high temperature region.
In an upper plenum that is in fluid communication with an outlet nozzle provided on a side of the reactor vessel, the fluid to be heated flowing out of the low-temperature region of the core is guided to the vicinity of the outlet nozzle, and the inner diameter of the outlet nozzle is substantially equal to that of the outlet nozzle. Corresponding position
A heated fluid mixing promoting structure in a reactor vessel, in which a heated fluid guide member having a small diameter portion and a large diameter portion provided with a plurality of elongated slots over the length of the pipe is provided in the upper plenum. provide.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

[0015] provided a tapered portion so and to articulate between the large diameter portion and the small diameter portion of the heated fluid guide member,
A plurality of window holes can be provided in the tapered portion . Also ,
It is preferable that the heated fluid guide member is disposed at a position of an existing upper core support column provided on an outer peripheral portion of the upper plenum and is exchanged.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction contents]

[0034]

According to the first aspect of the present invention, a fluid to be heated is defined at an upper portion of a reactor core where the fluid flows separately in a low temperature region and a high temperature region, and a fluid is supplied to an outlet nozzle provided on a side portion of the reactor vessel. In the communicating upper plenum, the heated fluid flowing out of the low temperature region of the core is guided to the vicinity of the outlet nozzle, and substantially corresponds to the inner diameter of the outlet nozzle.
A plurality of elongate slots over the location and length
The heated fluid guide member comprising the small-diameter portion and the large-diameter portion is provided in the upper plenum so as to promote mixing of the heated fluid in the reactor vessel. The heated fluid is guided into and mixed with the flow of the high-temperature heated fluid flowing through the high-temperature region, and enters the upper plenum.
The flow passage of the coolant in the area where the lateral flow of the coolant is large
Since the increase in the fluid load of the structure inside the upper plenum by the unheated fluid guiding member can be reduced, the occurrence of thermal stratification in the pipe following the outlet nozzle can be prevented and the control can be performed. Improve the soundness of structures such as rod cluster guide tubes.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Deleted

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction contents]

According to a second aspect of the present invention, a tapered portion is provided between the large-diameter portion and the small-diameter portion of the heated fluid guide member so as to be connected to each other. Since the window hole is provided, the flow rate corresponding to the diameter reduction inside the heated fluid guide member can be discharged from the heated fluid guide member to the upper plenum before reaching the small diameter portion, and the heated fluid guide member can be released. By avoiding a decrease in the internal axial flow rate, a lateral flow in the core is prevented, and the mixing of the low-temperature heated fluid and the high-temperature heated fluid in the upper plenum is promoted, so that the temperature becomes even.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0037

[Correction method] Change

[Correction contents]

According to the third aspect of the present invention, since the heated fluid guide member is disposed at the position of an existing upper core support column provided on the outer peripheral portion of the upper plenum and is exchanged with the existing upper plenum, The fluid load acting on the structure inside the plenum can be further reduced, and the soundness of the structure is further enhanced.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takehiko Tsutsui 1-1-1 Wadasaki-cho, Hyogo-ku, Kobe-shi, Hyogo Mitsubishi Heavy Industries, Ltd. 1-1-1, Tazakicho Mitsubishi Heavy Industries, Ltd., Kobe Shipyard (72) Inventor Izumimoto 2-1-1, Araicho, Araimachi, Takasago-shi, Hyogo Pref.

Claims (4)

[Claims] 1. An upper plenum in which a fluid to be heated is defined at an upper portion of a core flowing separately in a low-temperature region and a high-temperature region, and is in fluid communication with an outlet nozzle provided on a side of a reactor vessel. Guiding the heated fluid flowing out of the low-temperature region to a position near the outlet nozzle,
A heated fluid mixing promoting structure in a reactor vessel, wherein a heated fluid guide member having a small diameter portion and a large diameter portion having a small diameter of at least 3 and a diameter reduction ratio of at least 15% is disposed in the upper plenum. . 2. The small diameter portion of the heated fluid guide member is provided with a plurality of elongated slots at positions and lengths substantially corresponding to the inner diameter of the outlet nozzle.
4. The structure for promoting mixing of a fluid to be heated in a nuclear reactor vessel according to claim 1. 3. A tapered portion is provided between the large-diameter portion and the small-diameter portion of the heated fluid guide member so as to be connected to each other, and a plurality of window holes are provided in the tapered portion. Item 3. A structure for promoting mixing of a fluid to be heated in a reactor vessel according to Item 1 or 2. 4. The method according to claim 1, wherein the fluid guide member to be heated is disposed at a position of an existing upper core support column provided on an outer peripheral portion of the upper plenum and is exchanged. A mixed fluid promoting structure in a reactor vessel as described in the above.