JPS61237992A - Intermediate heat exchanger - Google Patents

Abstract

PURPOSE:To compact the heat exchanger and obtain the intermediate heat exchanger, excellent in the reliability of structure, by a method wherein a material, having a thermal expansion coefficient larger than the same of the material of heat transfer tube, is employed for the material of a lower cylinder of the intermediate heat exchanger for a nuclear reactor. CONSTITUTION:The intermediate heat exchanger 33 consists of a hollow tubular upper cylinder 38 and a lower cylinder 39, hung vertically from a roof slub 2. An upper tube plate 41 is provided at the connecting section between the upper cylinder 38 and the lower cylinder 39, while a lower tube plate 42 is provided horizontally at the lower end of the lower cylinder 39. 39Cr series ferrite steel or the like, excellent in high-temperature strength and having comparatively small thermal expansion coefficient, is employed for the materials of the upper tube plate 41, the lower tube plate 42 and the heat transfer tube 43 while stainless steel, excellent in high-temperature strength and having comparatively larger thermal expansion coefficient, is employed for the material of one part of the lower cylinder 39 and both of them are connected through a different material coupling 23. According to this constitution, a tension load, applied on the heat transfer tube 43, effects in a direction of mitigating the load when the temperature of the tube 43 is increased suddenly and the tube 43 expands further in the case of hot-shock accident and whereby Euler buckle of the heat transfer tube 43, which is caused in case the tube 43 and the lower cylinder 39 are made of the same material, may be avoided.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an intermediate cooling system installed in a reactor vessel used for heat exchange between a primary cooling system and a secondary cooling system of a liquid metal cooling tank fast breeder reactor, for example. The present invention relates to a heat exchanger, and particularly to an intermediate heat exchanger with an improved method of absorbing the difference in thermal expansion between a heat exchanger tube bundle and a shell.

[Technical background of the invention and its problems]

Liquid Metal Cooling Tank In current fast breeder reactors, liquid metal, such as liquid sodium, is used in the primary coolant in the tank main vessel, which serves as the reactor vessel, and in the secondary coolant circulating in the secondary cooling system including the steam generator. An intermediate heat exchanger for exchanging heat between the primary coolant and the secondary coolant is installed inside the tank main vessel. That is, as shown in FIG. 3, the upper part of the tank main vessel 1 is covered with a roof slab 2, and on this roof slab 2, a plurality of intermediate heat exchangers 3 are installed at intervals along with a primary circulation pump 5 around the core 4. is suspended from. It should be noted that a safety container 7 is installed outside the tank main passenger equipment 1 in case the primary coolant 6 leaks. In addition, in the figure, 30 is the liquid level of the coolant 6.

As shown in FIG. 4, for example, the intermediate heat exchanger 3 has a hollow cylindrical upper part vertically suspended from the roof slab 2. The upper body V has a plurality of primary coolant inlet windows 20 in the upper part of the peripheral wall. The upper tube plate 11 is provided at intervals in the circumferential direction and is provided between the coolant inlet window 20 and the primary coolant outlet nozzle 10 of the lower body V.
A large number of heat exchanger tubes 13 whose upper and lower ends are supported by a lower tube plate 12 are arranged vertically, and the primary coolant 6 is supplied to the heat exchanger tubes 1
It is designed to flow down within 3. Further, a secondary coolant inlet nozzle 14 and a secondary coolant outlet nozzle 15 are provided at the upper end of the upper body 8, and a downcomer pipe 16 communicating with the secondary coolant inlet nozzle 14 is provided at the axial center of the lower body 9. A rising pipe 17 that hangs down to the lower tube sheet 12 and communicates with the secondary coolant outlet nozzle 15 surrounds the down pipe 16 and hangs down to the upper tube sheet 11. The descending pipe 16 and the rising pipe 17 communicate with each other through communication ports 16a and 17B in a chamber formed between the upper tube sheet 11 and the lower tube sheet 12, that is, a heat exchange chamber 18, thereby providing secondary cooling. When the material flows from the downcomer pipe 16 to the riser pipe [7], it comes into contact with the outer peripheral surface of the heat transfer tube 13 in the heat exchange chamber 18 and exchanges heat with the primary coolant 6.

In the tank main vessel 1, the high temperature primary coolant 6 above the reactor core 4 flows into the intermediate heat exchanger 3 through the primary coolant inlet window 20 of the upper shell 8, and as it flows down inside the heat transfer tube 13. After exchanging heat with the secondary coolant, it flows out from the primary coolant outlet nozzle 10, passes through the primary circulation pump 5, and cools the core 4 again.

In addition, the secondary coolant flows into the intermediate heat exchanger 3 from the secondary coolant nozzle 14 at the upper part, and enters the heat exchanger tube 13 in the heat exchange chamber 18.
After contacting the outer circumferential surface of the coolant and exchanging heat with the primary coolant, the coolant is circulated through the secondary coolant outlet nozzle 15 to the secondary cooling system.

On the other hand, in the intermediate heat exchanger 3, a bellows 22 is provided to surround the primary coolant outlet nozzle 10 in order to absorb the difference in thermal expansion between the lower shell 9 and the heat exchanger tubes 13. The thermal expansion of the heat transfer tube 13 is transmitted to the primary coolant outlet nozzle 10 via the lower tube plate 12 and the lower head 21.
0 and the relative thermal displacement at the lower end of the lower shell 9 is the bellows 22
is absorbed by. Further, the bellows 22 forms a boundary between the primary coolant and the secondary coolant, and needs to satisfy design requirements as a primary coolant boundary.

This type of intermediate heat exchanger requires a space (11) below the lower tube plate 12 for the lower head 21 and the primary coolant outlet nozzle 10. Primary coolant outlet nozzle 10
The length of the lower head 21 must be greater than or equal to the required length of the bellows 22 provided around it, and the length of the lower head 21 must be such that the primary coolant flowing out from the lower tube sheet 12 can be smoothly absorbed into the primary coolant. It needs to be long enough to lead to the exit nozzle 10. 1
In an intermediate heat exchanger having an exchange heat amount of about 650 MWt used in a 00100O class tank-type fast breeder reactor, the above-mentioned space is about 2.5 m, which puts restrictions on the length of the heat transfer tube. Primary coolant outlet nozzle 1
0, the flow of the primary coolant is throttled, giving a pressure loss of about o, o s Ky/d on the primary side of the intermediate heat exchanger. This is approximately 1/3 of the total pressure loss on the primary side of the intermediate heat exchanger. Furthermore, although the bellows 22 serves as a primary coolant boundary, there are still developmental elements to confirm its structural reliability.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an intermediate heat exchanger that is compact and has excellent structural reliability.

[Summary of the invention]

In the present invention, an upper shell is installed vertically in the reactor vessel of a nuclear reactor and has a primary coolant inlet window, a lower shell is connected to the upper shell, and an upper shell is provided at the upper end of the lower shell. A tube sheet, a lower tube sheet provided at the lower end of the lower shell, a number of heat transfer tubes connecting the upper tube sheet and the lower tube sheet, and a downcomer pipe and a secondary coolant provided in the lower shell. The intermediate heat exchanger is characterized by using a material having a larger thermal expansion coefficient than the material used for the lower body ν and the heat transfer tube.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. The intermediate heat exchanger 33 of this embodiment is mainly composed of a hollow cylindrical upper shell and a lower shell 39 vertically suspended from the roof slab 2.

In the upper passage, a plurality of primary cooling member inlet windows 50 are bored at intervals in the upper part of the peripheral wall. An upper tube plate 41 is provided horizontally at the connection portion between the upper body 38 and the lower body 39, and a lower tube plate 42 is provided horizontally at the lower end of the lower body 39.

The upper and lower ends of a large number of heat transfer tubes 43 passing through the upper tube sheet 41 and the lower tube sheet 42 are supported.

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A secondary cooling member delivery nozzle 45 is provided.

The descending pipe 46 communicating with the nozzle material containing the secondary cooling member descends through the narrow part of the lower body 39 to the lower tube plate 42 .
It opens at a nearby lower opening 46a. An ascending pipe 47 communicating with the secondary cooling member outlet nozzle 45 surrounds the descending pipe 46 and hangs down to the upper tube plate 41, and opens at an upper opening 47a below the upper tube plate 41.

In the intermediate heat exchanger according to this embodiment, the upper tube plate 41,
The lower tube plate 42 and the heat exchanger tubes 43 are made of a material that has excellent high-temperature strength and a relatively small coefficient of thermal expansion, such as 39Cr.
A part of the lower shell 39 is made of a material with excellent high-temperature strength and a relatively large coefficient of thermal expansion, such as stainless steel (S
02, 304, etc.) and are joined by a dissimilar material joint 23. Part 3 of the lower body 39 that uses stainless steel
The length of 9b is calculated from the temperature distribution of the lower shell 39 and the heat exchanger tube 43 during operation, and the difference in thermal expansion between the lower shell 39 and the heat exchanger tube 43 is approximately equal, and the tensile load and The lower body 39 is set so that a slight compressive load acts on it.

In the intermediate heat exchanger section having the above configuration, the primary coolant 6 is
The primary cooling member flows into the upper body 38 through the inlet window 50, passes through the upper tube sheet 41, flows into the heat transfer tubes 43, descends here and transfers heat to the secondary coolant, and then flows from the lower tube sheet 42. Flows downward. Further, the secondary coolant flows from the secondary coolant-filled nozzle to the lower shell 3 through the downcomer pipe 46 and the lower opening 46a.
It is sent to the space 48 outside the heat exchanger tube 43 in 9. Next, this secondary coolant receives heat from the heat exchanger tube 43 while rising in the space 48, and its temperature increases, and from the upper opening position, the temperature of the secondary coolant increases.
．． The steam generator outside the furnace (
(not shown).

During normal operation, the temperatures of the heat exchanger tubes and the lower shell 39 are approximately equal when considered as an average in the vertical direction. In this case, the heat exchanger tube 43 is in a higher temperature state than at the time of manufacture (room temperature), and the thermal expansion of the heat exchanger tube 43 is smaller than that of the lower body 39, so the heat exchanger tube 43
A tensile load acts on the lower body 39, and a compressive load acts on the lower body 39.

Next, when the temperature of the heat exchanger tube 43 rises rapidly due to a hot shock accident, the heat exchanger tube 43 further thermally expands, but in this case, the tensile load that was previously on the heat exchanger tube 43 acts in a direction to be relieved.

Therefore, no large compressive load is applied to the heat exchanger tubes 43,
Euler buckling of the heat exchanger tube 43, which occurs when the heat exchanger tube 43 and the lower body 39 are made of the same material, can be avoided. Although a compressive load is applied to the lower shell 39, the lower shell 39 has a larger diameter than the heat transfer tubes 43, and has a margin against buckling.

For example, if the length of the heat exchanger tube 43 is 8 m, the tensile stress of the heat exchanger tube cage and the compressive stress of the lower shell 39 during normal operation are 50 m.
6K with negligible creep during the design life at a temperature of 0°C
If p/ad or less is set, the length of the stainless steel portion 39b of the lower body 39 will be about 20 mm. For this design, assuming the hot shock accident described above, the average metal temperature of the heat exchanger tube 43 at the time of a hot shock accident was set to 450°.
Assuming that the average metal temperature of the C1 lower body 39 is 400°C,
A compressive stress of approximately 2K9Ad is applied to the heat exchanger tube 43, but there is sufficient margin for the Euler buckling limit.

〔Effect of the invention〕

As detailed in the above embodiments, the intermediate heat exchanger according to the present invention eliminates the lower head, the primary cooling member outlet nozzle, and the bellows that were conventionally installed at the lower part of the intermediate heat exchanger. By making the entire length of the intermediate heat converter in the furnace vessel the same, the effective heat transfer section can be made longer.

Therefore, if the required heat transfer area is kept the same, the number of heat transfer tubes can be significantly reduced, and the body diameter of the intermediate heat exchanger can be reduced.

Reducing the number of heat transfer tubes may increase the pressure loss on the primary side, but in the present invention, the pressure loss on the primary side is offset by the reduction in pressure loss due to the removal of the primary cooling nozzle, and the pressure loss on the primary side is reduced. can also be suppressed to an allowable value.

On the other hand, from the viewpoint of structural reliability, the bellows, which remains a development element, is no longer necessary, and even if some heat exchanger tubes become hot due to non-uniform flow etc. and a relative compressive load is applied, Since the normal load is a tensile load, it is canceled out and cannot become a compressive load that would cause buckling, contributing to improved structural reliability.

Furthermore, the reduction in the intermediate heat exchanger body diameter also leads to a reduction in the size of the reactor vessel, resulting in significant effects such as contributing to the downsizing of the entire nuclear couple.

[Brief explanation of drawings]

1 and 2 show an embodiment of the present invention,
Figure 1 is a longitudinal sectional view of an intermediate heat exchanger, Figure 2 is a partial longitudinal sectional view showing an enlarged view of the lower shell, Figure 3 is a longitudinal sectional view of a conventional fast breeder reactor, and Figure 4 is a longitudinal sectional view of a conventional intermediate heat exchanger. FIG. 3 is a longitudinal cross-sectional view of the heat exchanger. 1...Furnace vessel O...Intermediate heat exchanger 38
... Upper body 39... Lower body 41...
Upper tube plate 42... Lower tube plate 43... Heat exchanger tube 46... Descending pipe 47... Rising pipe
50...Primary coolant inlet window agent Patent attorney
Noriyuki Kensuke Chika (and 1 other person) Redemption I M Figure 2 Figure 3 Figure 4

Claims (2)

[Claims] (1) An upper shell that is arranged vertically in the reactor vessel of a nuclear reactor and has a primary coolant inlet window, a lower shell that is connected to the lower part of the upper shell, and the upper and lower ends of this lower shell. an upper tube sheet and a lower tube sheet installed horizontally in each, a large number of heat transfer tubes connecting these upper tube sheets and lower tube sheets, and a downcomer pipe and a riser pipe for secondary coolant provided in the lower body. An intermediate heat exchanger comprising: a material having a higher coefficient of thermal expansion than a material for the heat transfer tubes as a material for the lower shell. (2) The intermediate heat exchanger according to claim 1, wherein a material having a higher coefficient of thermal expansion than the material of the heat exchanger tubes is used for a portion of the lower shell.