JPS61272596A - Intermediate heat exchanger - Google Patents

Abstract

PURPOSE:To secure soundness of bellows themselves, by providing the bellows comprising multiple layers in the vicinity of the lower ends of an outer drum and an inner drum, fixing the bellows by a folded tube, sealing the outer drum and the inner drum with the relatively short bellows, and absorbing the difference in thermal expansions by the temperature difference among the outer drum, an upper tube plate, a heat transfer pipe, a lower tube plate and the inner drum. CONSTITUTION:Outer and inner double bellows 34a and 34b are provided between an outer drum 19 and an inner drum 33 and have the double-bellows shape. The upper end of the outer bellows 34a is fixed to the outer drum 19, and the lower end is coupled and fixed to the lower end of the a folded tube 38. The upper end of the inner bellows 34b is fixed to the upper end of the folded tube 38, and the lower end is coupled and fixed to the lower end of the inner drum 33. The difference in thermal expansions at the lower end parts of the outer drum 19 and the inner drum 33, which is caused by the temperature difference among the outer drum 19, an upper tube plate 20a, a heat transfer pipe 21, a lower tube plate 20b and the inner drum 33, is absorbed by the expansion and the contraction of the outer bellows 34a and the inner bellows 34b, which are provided between the outer drum 29 and the inner drum 33, in the axial direction.

Description

Detailed Description of the Invention [Technical Field of the Invention 1] The present invention relates to an intermediate heat exchanger used in a tank-type fast breeder reactor, and particularly to an intermediate heat exchanger having a structure that absorbs a difference in thermal expansion between a shell and a tube bundle. Regarding.

[Technical background of the invention and its problems] Conventionally, in tank-type fast breeder reactors, long cylindrical shell-and-tube intermediate heat exchangers are installed on the roof slab of the reactor vessel alternately with the primary main circulation bomb in the circumferential direction. There are multiple units suspended at intervals.

This intermediate heat exchanger performs heat exchange between the primary coolant and the secondary coolant within the reactor vessel. The intermediate heat exchanger has a vertical outer shell that circulates the primary coolant, and inner and outer tubes that are arranged concentrically around the axis of the outer shell and that circulate the secondary coolant. The lower end of this intermediate heat exchanger is inserted into a through hole along the vertical direction of a horizontal partition wall that defines a hot pool and a cold pool in the upper and lower parts of the reactor vessel,
The outer shell is sealed and held by a stand pipe provided along the periphery of the through hole in the partition wall. The high-temperature primary coolant from the hot pool flows in through the window hole drilled in the outer shell of the intermediate heat exchanger, and the secondary coolant flows through the inner and outer tubes through the heat transfer tube section provided inside the external heat exchanger. It exchanges heat, becomes low temperature, and flows into the cold pool from the lower end of the outer shell. In addition,
The low-temperature primary coolant in the cold boule is forcibly introduced into the lower core by the primary main circulation pump, heated in the core, rises, and reaches the hot boule.

By the way, in a fast breeder reactor equipped with an intermediate heat exchanger as described above, the temperature distribution occurring in the intermediate heat exchanger in various operating modes of the reactor will be considered. Here, the temperature of the primary coolant flowing into the heat transfer tube section from the window hole provided in the outer shell is TPH1, and the temperature of the primary coolant flowing out from the lower end of the outer shell into the cold pool is TPO. In addition, the temperature of the secondary coolant flowing through the inner tube and flowing into the heat exchanger tube section and the temperature of the secondary coolant flowing through the outer tube and flowing out from the heat exchanger tube section are calculated by TSC.
and TSH. Therefore, let us consider the temperature difference between the heat exchanger tube portion and the outer shell, which has the same height. The primary coolant flows downward inside the heat exchanger tube, and the secondary coolant flows upward while being in contact with the outside, so the temperature of the heat exchanger tube is between the temperatures of the primary coolant and the secondary coolant. temperature, and the temperature distribution differs in the height direction.

Therefore, the temperature near the lower tube sheet is between TPO and TSC, and the temperature near the upper tube sheet is between TPH and TSH.

On the other hand, the temperature of the outer shell is determined by the fact that the inside and secondary coolant flows upward through the heat transfer tube, and the outside is filled with the primary coolant that hardly flows between it and the standpipe. , is considered to be approximately equal to the temperature of the secondary coolant. Therefore, the temperature of the outer shell is T near the lower tube plate.
SG, it is about TSH near the upper tube plate.

As mentioned above, it is thought that a temperature difference always exists between the heat exchanger tube and the outer shell, and the difference in thermal expansion caused by this temperature difference can cause excessive thermal stress on the outer shell or the heat exchanger tube. Therefore, it is necessary to install a mechanism to absorb this difference in thermal expansion.

In order to estimate the temperature difference between the outer shell and the heat transfer tube, which causes this difference in thermal expansion, on the safe side in terms of design, it is assumed that the temperature of the heat transfer tube is equal to the temperature of the primary coolant passing through it, and the temperature of the outer shell is is assumed to be equal to the secondary coolant temperature passing through. Therefore, the temperature difference between the outer shell and the heat transfer tube is TPO near the lower tube sheet.
-TSCl, and near the upper tube sheet, it is about TPH-TSH. These values depend on the temperature changes of the primary and secondary coolants based on the overall system design of the tank-type fast breeder reactor, but during normal operation they are approximately 40-50°C.
It is assumed that the temperature is around ℃. However, transient changes in primary and secondary coolant temperatures that occur with the operating temperature of a nuclear reactor can result in fairly large temperature differences, especially in hot conditions where the secondary cooling system shuts down. In the event of a shock, it is necessary to consider that this temperature difference will be approximately 150 degrees Celsius near the lower tube sheet, even if it is estimated to be large considering safety. Further, since the length of the heat exchanger tube portion in the vertical direction is generally about 5 to 6 m, the difference in thermal expansion caused by this temperature difference (assumed to be uniform in the vertical direction) is approximately 15 to 1811 m. If such a large difference in thermal expansion is left unaddressed, compressive stress generated in the heat exchanger tubes may cause buckling of the heat exchanger tubes, which may adversely affect the maintenance of the integrity of the intermediate heat exchanger equipment.

A conventional solution to this problem has been to provide a bellows for absorbing the difference in thermal expansion between the outer shell and the inner shell forming the lower plenum at the lower end of the intermediate heat exchanger. This bellows has the property of easily absorbing displacement in the axial direction of the intermediate heat exchanger, thereby absorbing the difference in thermal expansion between the heat exchanger tube and the outer shell.

FIG. 4 shows an enlarged view of the conventional structure of the bellows, in which a single bellows 34 is installed between the vicinity of the lower end of the lower tapered portion of the outer shell 19 and the lower end of the inner shell 33. The inner shell 33 is integral with the lower tube sheet 20b, and the lower tube sheet 20b and an unillustrated upper tube sheet are connected with great rigidity by welding or the like via the heat transfer tubes 21. Further, the upper tube plate is welded to the outer shell 19 again by welding or the like around the upper tube plate. Therefore, the temperature of the outer shell below the level of the upper tube sheet, the upper tube sheet, the heat transfer tube 21, and the lower tube sheet 2
Outer shell 1 caused by the difference in temperature between 0b and inner shell 33
Almost all of the relative displacement in the axial direction between the lower end of the inner shell 33 and the lower end of the inner shell 33 is absorbed by the bellows 34, thereby relieving the thermal stress generated in the outer shell 19 and the heat transfer tubes 21. The bellows 34 also has an outer shell 19 and an inner shell 1113 filled with secondary coolant.
The boundary is formed by supporting the differential pressure between the pressure in the tapered annulus space 36 formed by the annulus 3 and the pressure of the primary coolant in the lower plenum 10.

Note that a stand vibrator 30 is fixed to a partition wall (not shown) and a partition wall support disposed below the partition wall, along the periphery of a through hole for inserting an intermediate heat exchanger.

This stand vibe 30 extends further downward than the lower end of the outer shell 19 at the location where the intermediate heat exchanger 14 is installed. A bellows 35 is provided between the stand vibe 30 and the outer body 19, and seals between the hot boule and the cold boule 10, and the stand vibe 30
The difference in thermal expansion between the outer shell 19 and the outer shell 19 can be absorbed.

By the way, in such a conventional intermediate heat exchanger, most of the parts other than the bellows are considered to be rigid bodies, and displacement, that is, strain, tends to be concentrated on the bellows 34.35, so the structural integrity of the bellows 34.35 is not guaranteed. Gender becomes an issue. The main loads acting on the bellows 34, 35 are the axial displacement control type load due to the thermal expansion difference and the pressure difference between the primary and secondary coolants. Particularly in the case of a tank-type fast breeder reactor, the pressure of the secondary coolant is low, and the pressure difference acts as a fairly large primary load. Therefore, if a load due to the difference in thermal expansion is superimposed on this, there is a risk of causing excessive deformation behavior such as ratchet deformation of the bellows. In order to prevent this, it is necessary to reduce the stress due to the difference in thermal expansion as much as possible, and for this purpose, measures have been considered to increase the axial length of the bellows and increase the number of ridges on the bellows. However, in this case, the overall length of the intermediate heat exchanger inevitably increases, which limits the size of the reactor vessel in the depth direction, which in turn leads to an increase in the cost of the tank-type fast breeder reactor.

[Object of the invention] - The present invention has been made to solve these problems, and includes a double inner and outer shell between the outer shell and the inner shell near the lower end of the intermediate heat exchanger to absorb the difference in thermal expansion. To provide an intermediate heat exchanger in which the structural soundness of the bellows itself is ensured by providing a bellows, and the thermal stress generated in the heat exchanger tubes and external use of the intermediate heat exchanger can be significantly alleviated, leading to cost reduction. It is in.

[Summary of the Invention] In order to achieve this object, the present invention installs a multi-layered bellows between an outer shell and an inner shell near the lower end of an intermediate heat exchanger, one of the bellows is attached to the outer shell, and the other is attached to the outer shell. is fixed to the inner body,
By installing cylindrical folded tubes between the multi-layered bellows, a large number of short tubes can be installed in series, absorbing the large relative displacement between the outer shell and the inner shell, and reducing the primary and secondary bellows. Next, a coolant boundary is formed.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In addition, in FIGS. 1 to 3, the same parts are given the same reference numerals, and the explanation of the overlapping parts will be omitted.

First, the entire tank-type fast breeder reactor will be explained with reference to FIG.

For safety, the reactor vessel 1 has a double structure consisting of an inner main vessel 1a and a guard vessel 1b, and is suspended and supported within a cylindrical cavity wall 2. The reactor vessel 1 and cavity wall 2 are closed by a roof slab 3.

A plenum portion 5 and a core 6 are sequentially stacked with a core support 4 interposed in the lower part of the main vessel 1a. A core upper mechanism 7 is provided on the roof slab 3 above the core 6 . Further, at the exact upper end position of the core 6, a partition wall 8 that partitions the inside of the main vessel 1a into an upper hot boule 9 and a lower cold boule 10 is attached to a partition wall support 8b.
established by.

Further, a plurality of secondary main circulation bombs 11 that circulate the primary coolant 15 within the main container 1a are suspended from the roof slab 3 at equal intervals in the circumferential direction. A thin cylindrical body 12 surrounding the outside of these primary circulation pumps 11 is provided to vertically penetrate the partition wall 8. Further, an in-furnace pipe 13 is led out from the lower end of each primary main circulation bomb 11, and its tip is connected to the plenum part 5.

Further, from the roof slab 3, a plurality of intermediate heat exchangers 14 for exchanging heat between the primary coolant and the secondary coolant are suspended in the main container 1 at equal intervals in the circumferential direction, and their lower ends are connected to the partition wall. 8 and reaches into the cold boule 10. This roof slab 3 is designed to prevent heating by circulating and supplying cooling gas to the internal cavity by a gas circulation device 17 installed outside the main container 1. Further, the space between the lower surface of the roof slab 3 and the upper surface of the primary coolant 15 is filled with an inert cover gas.

Here, the operation of the tank-type fast breeder reactor configured as described above will be explained.

First, the primary coolant 15 made of a liquid metal such as liquid sodium is heated to a high temperature by receiving thermal energy from a nuclear reaction while passing upward through the reactor core 6, and passes through a window hole in the upper core mechanism 7 to a hot temperature. It flows into the pool 9. Then, the secondary coolant 15 flows into the intermediate heat exchanger 14 from above, transfers heat energy to the liquid metal serving as the secondary coolant, cools itself, and flows into the cold boule 10.

On the other hand, the primary coolant 15 in the cold boule 10 rises within the thin-walled cylindrical body 12, is pressurized by the primary main circulation bomb 11, and is returned to the plenum portion 5 through the furnace piping 13.

Next, the structure and operation of the intermediate heat exchanger will be explained with reference to FIG.

The intermediate heat exchanger 14 has a long hollow outer shell 19, a flange 19a formed at the upper end of the outer shell 19 is supported by the roof slab 3, and the entire intermediate heat exchanger 14 is suspended. . The lower end of this outer body 19 has a tapered diameter, is pushed through a through hole 8a of the partition wall 8, and opens into the cold boule 10 with an outlet nozzle 19b.

Further, a large number of heat transfer tubes 21 are housed in the lower part of the outer shell 19 and are supported through the upper and lower tube plates 20a and 2ob.

Then, from the entrance window 22 made in the outer shell 19, the upper tube plate 2Oa is opened.
The primary coolant 15 (large curved arrow) that has flowed upward flows down inside each heat transfer tube 21, flows out from the lower tube plate 20b, and flows down into the cold boule 10 through the outlet nozzle 19b.

In addition, a secondary coolant 23 made of liquid metal such as liquid sodium is supplied from the outside of the roof slab 3 to the center of the outer shell 19.
(Daikoku arrow) is the space 2Oc between the upper and lower tube plates 20a and 2Ob.
an inner pipe 24 that feeds the inside through the lower end opening 24a, and an outer pipe 25 that takes out the secondary coolant 23 heated by heat exchange with the primary coolant 15 from the space 20G and leads it out to the outside of the roof slab 3. A down cuff 26 is provided.

The penetrating portion with the lower tube plate 20b at the lower end of the inner tube is configured as an end plate 31 because the secondary coolant 23 comes into direct contact with it.

Furthermore, a heat shield plate 27 for preventing radiant heat from the primary coolant 15 and a radiation shield 28 filled with steel balls for blocking radiation are provided at the upper end of the outer shell 19. On the outside of the outer shell 19 in the hot pool 9, there is a skirt 2 that rectifies the primary coolant flowing into the outer shell 19 from the inlet window 22.
9 hangs down from the lower surface of the roof slab 3.

Here, the heat exchange action in the intermediate heat exchanger 14 will be explained.

As shown by the large curved arrow in FIG. 3, the primary coolant 15 passes between one outer shell and the skirt 29 in the hot pool 9, and flows into the outer shell 19 from the inlet window 22 in a rectified state. do.

On the other hand, the secondary coolant 23 flows down inside the inner tube 24 of the down cuff 26, as shown by the large black arrow, and flows into the space 2Oc through the lower end opening 24a.

The primary coolant 15 flowing down in the heat transfer tube 21 and the secondary coolant 23 rising in the space 20c exchange heat with each other. After this heat exchange, the primary coolant 15 is in a low temperature state.
flows out into the outer shell 19 from the opening of the heat exchanger tube 21, and flows into the corbibourg 10 through the outlet nozzle 19b.

On the other hand, the secondary coolant 23 that has reached a high temperature is transferred to the upper tube plate 20.
It flows into the outer tube 25 of the down cuff 26 at a portion a, and is fed to a steam generator (not shown) of the secondary main coolant system.

Next, the structure of the outer blank bellows 34a and 34b provided between the outer shell 19 and the inner shell 33 will be described.

FIG. 1 is an enlarged sectional view showing only the left half of the white bellows 34a, 34b, and 35 outside the intermediate heat exchanger in FIG. The outer and inner double bellows 34a and 34b are installed between the outer shell 19 and the inner shell 33, and the outer shell 19
Outer bellows 34a on the side and inner bellows 34b on the inner body 33 side
It takes the form of a double bellows. The upper end of the outer bellows 34a is connected to the outside 1119, the lower end is connected and fixed to the lower end of the folded tube 38, and the upper end of the inner bellows 34b is fixed to the folded tube 38.
The upper end and the lower end are fixedly connected to the lower end of the inner shell 33.

Next, the operation of one embodiment of the above configuration will be explained with reference to FIG.

Outer shell 19, upper tube sheet 20a, heat transfer tube 21, lower tube sheet 20
b and the inner shell 33 caused by the temperature difference.
The difference in thermal expansion that appears at the lower ends of the outer rIA 19 and the inner bellows 33 is absorbed by the axial expansion and contraction of the outer bellows 34a and the inner bellows 34b installed between the outer rIA 19 and the inner shell 33. - For example, during normal operation of a fast breeder reactor, the outer shell 19, upper tube sheet 20a, heat transfer tube 21, lower tube sheet 20b
Let us consider the case where there is a temperature difference of about 40° C. between the inner shell 33 and the inner shell 33. In this case, the relative displacement due to the difference in thermal expansion occurring at the lower end portions of the outer shell 19 and the inner shell 33 is considered to be about 400 mm, although it depends on the detailed dimensions of the intermediate heat exchanger 14. Also, at this time, since the temperature on the outer shell 19 side is low, the lower end of the inner shell 33 extends 4n downwards than the lower end of the outer shell 19. The double bellows 34a and 34b have almost the same shape except for a slight difference in diameter.
dimensions, their displacements are approximately equally 2
It is considered that the number is distributed in n increments. Therefore, compared to the conventional example shown in FIG. 4 in which the bellows are single-layered, the secondary stress generated by the bellows itself to absorb the difference in thermal expansion is halved, and even in the event of a hot shock that stops the secondary cooling system, Even thermal expansion due to an excessive temperature difference that occurs in the bellows can be absorbed while ensuring the integrity of the bellows. In particular, in tank-type fast breeder reactors, the pressure difference between the secondary coolant and the primary coolant is large, and the primary stress generated in the bellows due to this is large, and on top of this, when the primary stress due to the thermal expansion difference is repeatedly applied. However, according to the present invention, by using a bellows with approximately half the length, a thermal expansion absorption mechanism that does not cause such excessive deformation can be provided. can.

Note that the present invention is not limited to the above-mentioned embodiments, and may be applied to an intermediate heat exchanger of a type in which a heat exchanger tube (not shown) for removing decay heat is provided in the upper space of the upper tube plate 20a in FIG. The present invention can be applied to.

The effects of this example will be described. In this type of intermediate heat exchanger, during the decay heat removal operation, heat exchange is performed in the space above the upper tube sheet 20a, so the secondary coolant 15 is in a cold state above the upper tube sheet 20a, and the heat transfer is The heat tube 21 also becomes cold. On the other hand, the outer shell 19 is exposed to relatively high temperatures because it is thermally affected by the hot boule 9.
As a result, the bellows 34 undergoes a large thermal expansion displacement that is opposite to that during normal operation.

In such an intermediate heat exchanger, the bellows of the present invention exhibits even more effects.

[Effects of the Invention] As explained above, the present invention provides a multi-layered bellows near the lower end of the outer shell and inner shell of an intermediate heat exchanger, and fixes these in series with a folded tube, thereby connecting the outer shell and the inner shell. is sealed by a relatively short bellows. Therefore, the difference in thermal expansion caused by the temperature difference between the outer shell, the upper tube sheet, the heat transfer tube, the lower tube sheet, and the inner shell can be absorbed, and the integrity of the oven itself can be ensured. In addition, it is possible to provide an intermediate heat exchanger that is short in the axial direction at a relatively low cost, contributing to a reduction in the depth of the main vessel of a tank-type fast breeder reactor, and ultimately leading to a reduction in the cost of the entire reactor. can.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view showing only the vicinity of the lower end of an intermediate heat exchanger in an embodiment of the present invention, FIG. 2 is a sectional view showing the entire reactor vessel, and FIG. 3 is an intermediate heat exchanger according to the present invention. A sectional view showing an exchanger. FIG. 4 is a partial sectional view showing an enlarged lower end portion of a conventional intermediate heat exchanger. 1...Reactor vessel 3...Roof slab 19...Outer shell 20a...Upper tube plate 20b... ...Lower tube plate 21 ...Heat transfer tube 33 ...Inner shell 34a ...Outer bellows 34b ...Inner bellows 37 ......End hardware 38...Guide rail Fig. 1 Fig. 2 Fig. 3

Claims (2)

[Claims] (1) Outer shell and primary cooling that penetrate the roof slab that covers the main vessel of a tank-type fast breeder reactor and are suspended into the main vessel, separating the secondary coolant outside the heat transfer tubes from the primary coolant inside the main vessel. In an intermediate heat exchanger having an inner shell forming a lower plenum containing a material therein with a lower tube sheet, a multi-layered bellows is installed between the outer shell and the inner shell, and one of the outermost layer bellows is disposed between the outer shell and the inner shell. An intermediate heat exchanger characterized in that one of the innermost layer bellows is fixed to the inner shell on the outer shell, a cylindrical folded tube is installed between the multilayered bellows, and the bellows are sequentially fixed to this. vessel. (2) The intermediate heat exchanger according to claim 1, wherein a heat exchanger tube coil for removing decay heat is provided in the upper space of the upper tube plate in the outer shell.