JPS6219677B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a flow path structure of a heat exchanger, and in particular,
The present invention relates to a flow path structure of an intermediate heat exchanger provided in a reactor vessel of a tank-type nuclear reactor.

[Conventional technology]

Heat generated in the core of a tank-type nuclear reactor is absorbed by the primary coolant and extracted by the secondary coolant via an intermediate heat exchanger provided within the reactor vessel. An example of the structure of such a tank-type nuclear reactor is shown in FIG.

In the figure, the reactor vessel 10 includes a partition structure 11
The reactor core 12 is partitioned into a hot plenum 14 housing the core 12 in the center of the lower part, and a cold plenum 16 formed around the hot plenum 14. A plurality of circulation pumps 18 are installed in the cold plenum 16,
Liquid metal sodium 22 (hereinafter referred to as sodium), which is a coolant in the cold plenum, is sent to the hot plenum 14 via the primary system piping 20. In addition, the intermediate heat exchanger 24 (hereinafter referred to as a heat exchanger), which has a flow path whose upper part opens to the hot plenum 14 and whose lower part opens to the cold plenum, has a secondary system, which is a coolant flowing in the secondary system piping 26. A sodium flow path is formed, and heat exchange is performed between the primary system sodium 22, which has cooled and warmed the core 12, and the secondary system sodium. That is, core 1
The primary sodium, which has risen inside the hot plenum 14 while cooling the sodium, enters the heat exchanger from the upper part of the heat exchanger 24 arranged around the hot plenum 14, warms the secondary sodium, and cools itself. and flows down through the heat exchanger 24 and into the cold plenum 16. On the other hand, secondary sodium is
It is heated to a high temperature in the heat exchanger 24, and the secondary system piping 2
6 to a steam generator (not shown).

Note that the reference numeral 28 indicates the free liquid level of the sodium 22 in the hot plenum 14, and the reference numeral 30 indicates the free liquid level of the sodium 22 in the cold plenum 16.

The conventional flow path structure of the heat exchanger provided in the tank-type nuclear reactor is shown in FIGS. 4 and 5.

Figure 4 shows a gate valve type heat exchanger.
The upper flange 32 of 25 of the main body of the heat exchanger 24 is attached to the roof slab 34 of the reactor containment vessel, and a downcomer pipe 36 through which secondary system sodium flows down is formed integrally with the secondary system piping 26 at the center. There is. Surrounding this downcomer pipe 36 is a secondary sodium riser pipe 38, which is connected to the secondary system piping 26 at the upper part. An upper tube plate 42 is formed at the upper end of the large diameter portion 40 of the riser pipe 38, and a lower tube plate 44 is formed at the lower end. Further, the upper tube plate 42, the large diameter portion 4
0, a large number of heat transfer tubes 46 are provided passing through the lower tube plate 44, and communicate the hot plenum 14 and the cold plenum 16 via the upper inlet portion 48 and opening 50 of the upper tube plate 42. . Note that the upper end of the opening 50 is located at a position lower than the free sodium liquid level 28 of the hot plenum 14.

A partition plate 52 is provided around the main body 25 of the heat exchanger 24 to separate the hot plenum 14 and the cold plenum 16. The upper end of the partition plate 52 is located at approximately the same height as the lower end of the opening 50. A seal portion 54 is formed between the main body 25 and the partition plate 52 at an intermediate portion of the partition plate 52, and a seal portion 54 is formed between the main body 25 and the partition plate 52.
4 and Cold Plenum 16 have been cut off. Further, a flange 56 is provided on the circumferential side near the upper end of the partition plate, and the lower end of the gate of the gate valve 58 that moves up and down is received on the upper surface of the flange 56, thereby making it possible to cut off communication between the hot plenum 14 and the cold plenum 16.

Gas is injected from a gas nozzle 62 into a gas injection chamber 60 formed by the main body 25, the partition plate 52, the seal portion 54, the flange 56, and the gate valve 58 to adjust the height of the liquid level.

FIG. 5 shows a gas pressure type heat exchanger that shuts off the flow path using gas pressure. In the figure, a substantially hemispherical chamber 64 communicating with the lower end of the downcomer pipe 36 is formed below the lower tube plate 44 . A large number of heat transfer tubes 68 are provided between the chamber 64 and the confluence section 66 above the upper tube plate 42 to guide the secondary sodium coming in from the downcomer pipe 36 to the riser pipe 38 . Further, between the upper tube plate 42 and the lower tube plate 44, an upper opening 70 and a lower opening 7 are provided.
The primary sodium 22 in the hot plenum 14 flows through the heat transfer tube 68.
It flows down into the cold plenum 16 while contacting the cold plenum 16. In other words, between the gate valve type heat exchanger shown in Figure 4 and the gas pressure type heat exchanger shown in Figure 5, there is a difference in whether the sodium flowing in the heat transfer tubes is primary sodium or secondary sodium. , there is no difference in the function of the heat exchange part.

Unlike the type shown in FIG. 4, the partition plate 52 does not have a flange, and a partition wall 72 is provided around the upper part of the main body 25 in place of the gate valve. Bulkhead 7
The lower end of 2 reaches into the primary sodium 22 in the hot plenum 14, and together with the main body 25, forms a gas injection chamber 74 that opens downward. Note that the reference numeral 76 is the sodium free liquid level when inert gas is pressurized into the gas injection chamber 74.

A tank-type nuclear reactor is provided with a plurality of heat exchangers, and when maintenance is required for one of the heat exchangers, the tube bundle of the heat exchanger is pulled out and isolated as follows.

In the gate valve method shown in FIG. 4, the gate valve 58 is lowered and brought into contact with the flange 56 to cut off communication between the hot plenum 14 and the cold plenum 16, and inert gas is injected into the gas injection chamber 60 from the gas nozzle 62. This prevents the primary sodium 22 from flowing into the heat transfer tube 46 before performing the necessary work.

On the other hand, in the gas pressure method shown in Fig. 5, the gas nozzle 6
2, the free liquid level of the primary sodium 22 in the gas injection chamber 74 is raised to the upper opening 70.
This is done by pushing it further down and blocking the flow of the primary sodium 22.

[Problem that the invention seeks to solve]

However, in the gate valve method, as the equipment becomes larger, the gate valve 58 and flange 56 are
The seal between the
In addition, while the partition plate 52 expands in the radial direction due to the temperature rise accompanying the increase in the output of the reactor core 12, the main body 25 expands in the radial direction.
Because it is attached to a relatively cold roof slab, it is maintained at a low temperature and has a relatively small amount of expansion.
Therefore, due to the difference in expansion between the partition plate 52 and the main body 25, the sealing performance at the seal portion 54 deteriorates.
There is a possibility that the flow of primary sodium 22 cannot be sufficiently blocked.

In one gas pressure method, the gas injection chamber 74
Since the inert gas is pressurized into the main body 25, there is a risk that the free liquid level of the primary sodium will recover due to gas leakage in the gas piping system, and the primary sodium 22 will flow inside the main body 25. Furthermore, when the output of the core 12 changes, the free liquid level 28 changes, and the free liquid level 76 also changes accordingly, and there is a risk that the inert gas that has been injected will exceed the lower end of the partition wall 72 and be drawn into the sodium 22. There is. Furthermore, the portion 75 near the top of the upper tube plate 42 that corresponds to the sodium free liquid level is subject to thermal stress due to the temperature difference between the primary sodium system and the secondary system sodium during thermal transients such as when the power of the reactor core 12 increases. arise.

An object of the present invention is to provide a flow path structure for a heat exchanger that can completely block the flow of primary sodium when maintenance of the heat exchanger is required.

[Means for solving problems]

In order to achieve the above object, the present invention has a flow path that communicates a hot plenum with a cold plenum located below the hot plenum and allows a high temperature primary coolant in the hot plenum to flow into the cold plenum, and is in thermal contact with the flow path. The basic structure of a heat exchanger is that the secondary coolant flowing in the opposite direction absorbs the heat of the high-temperature primary coolant and performs heat exchange. A partition wall that opens into the primary coolant and forms a decompression chamber is installed, sealing the hot plenum and cold plenum, and rising from the partition structure of both plenums to the decompression chamber along the circumference of the heat exchanger, with the upper end serving as the high-temperature primary cooling inside the hot plenum. A partition plate is set higher than the free liquid level of the material, and the pressure inside the vacuum chamber is reduced to allow the high temperature primary coolant to overcome the partition plate and flow into the heat exchanger. This paper proposes a flow path structure for a heat exchanger that is equipped with a pressure reducing means that lowers the liquid level below the upper end of the partition plate and stops the inflow.

[Effect]

In the present invention, a partition plate having an upper end higher than the free liquid level is disposed in a reduced pressure chamber formed by the partition wall inserted below the free liquid level of the primary coolant and the outer wall of the heat exchanger body, If you want to let the primary coolant flow in, you can reduce the pressure in the vacuum chamber and use the siphon effect to cross the partition plate, while if you want to block the inflow of the primary coolant, you just need to release the pressure reduction and stop the siphon effect. Therefore, a flow path structure of the heat exchanger that can completely block the flow of the primary coolant can be obtained.

Therefore, when a malfunction occurs in the primary coolant flow path blocking mechanism, in the conventional example, the primary coolant flows, but in the present invention, unless the pressure is reduced again, the primary coolant flows.
Since there is no need to worry about the primary coolant flowing out, subsequent work such as maintenance is highly safe.

〔Example〕

Next, a preferred embodiment of the flow path structure of a heat exchanger according to the present invention will be described with reference to FIGS. 1 and 2. Note that parts corresponding to those described in the prior art are given the same reference numerals, and the description thereof will be omitted.

FIG. 1 is a diagram showing an embodiment of the flow path structure of a heat exchanger according to the present invention. In the figure, heat exchanger 8
0 is a heat exchanger having a structure in which secondary sodium flows through heat transfer tubes 68, and is of a type corresponding to the conventional example shown in FIG. In this heat exchanger 80,
The upper end of the partition plate 82 that separates the hot plenum 14 and the cold plenum 16 is located at the free liquid level 28 of the primary sodium 22 in the hot plenum 14.
It's higher. A partition wall 86 having an inverted L-shaped cross section is formed along the circumference of the main body 84 with its tip 88 facing downward on the upper peripheral side surface of the main body 84 of the heat exchanger 80 . The partition wall 86 has a tip 88 that is connected to the partition plate 82.
It is located further outward, is immersed in the primary sodium system 22, and forms, together with the main body 84, a decompression chamber 90 that opens into the sodium 22. Decompression chamber 90
An opening 92 is provided at the upper end of the opening 9.
2, a pressure reducing pipe 9 connected to a vacuum pump (not shown)
4 is connected.

The operation of this embodiment having the above configuration is as follows. When heat exchange is performed between the primary sodium 22 and the secondary sodium flowing through the heat transfer tube 68, first, a vacuum pump (not shown) is driven to create a negative pressure in the decompression chamber 90. And hot plenum 1
The primary sodium 22 in 4 is sucked up from the pressure reduction chamber 90 into the pressure reduction pipe 94 by negative pressure, and the sucked up sodium 22 is solidified in the pressure reduction pipe 94 by closing a valve (not shown), thereby performing a so-called sodium freeze. Therefore, the interior of the decompression chamber 90 is maintained at a negative pressure state even when the vacuum pump is stopped, and the sodium in the hot plenum 14 enters the decompression chamber 90 and reaches the partition plate 82 located at a position higher than the free liquid level 28.
and flows into the upper opening 70 by a so-called siphon effect. And sodium 22
comes into contact with the heat transfer tube 70 to exchange heat with the secondary sodium, flows down the flow path in the main body 84 while being cooled, and enters the cold plenum 16 through the lower opening 72. On the other hand, the secondary sodium introduced into the main body 84 by the downcomer pipe 36 is reversed in the lower chamber 64 and enters the heat exchanger tube 68, and rises while being heated within the heat exchanger tube 68, and reaches the confluence part 66 and the riser pipe 38. It enters the secondary system piping 26 through the , and is sent to a steam generator (not shown).

Now, when maintenance of the heat exchanger 80 is required and it is desired to shut off the flow of the primary sodium 22, the solidified sodium in the pressure reducing pipe 94 is melted by an appropriate method.

The sodium in the decompression chamber 94 is melted and flows down into the decompression chamber 90 when a valve (not shown) is opened, and the pressure in the decompression chamber returns to the pressure in the hot plenum 14 . Therefore, the free liquid level in the decompression chamber 90 drops to a position equivalent to the free liquid level 28 in the hot plenum 14,
The partition plate 82 prevents the flow of the primary sodium 22 into the upper opening 70, thereby blocking the flow of the primary sodium 22.

In this way, when maintenance is required for one of the plurality of heat exchangers installed in a tank-type nuclear reactor, the sodium in the pressure reducing tube of that heat exchanger is melted and the pressure inside the pressure reducing chamber 90 is reduced. When the siphon action is cut off and the flow of primary sodium 22 is blocked,
Maintenance is easy.

Furthermore, during thermal transients such as when the output of a nuclear reactor increases,
Thermal stress that conventionally occurred in a portion 73 near the upper tube plate 42 can be reduced because this portion 73 is wetted by the primary sodium 22.

FIG. 2 is a diagram showing the flow path structure of another embodiment according to the present invention, and corresponds to the conventional example in FIG. 4. In this embodiment, the primary sodium 22 flows through the heat exchanger tube 46, and the secondary sodium flows through the heat exchanger tube 46.
It flows around the area. In this case too,
As in the embodiment shown in FIG. 1, if the inside of the decompression chamber 90 is maintained at a negative pressure, the primary sodium system can flow into the heat exchanger 80, and if the depressurization is stopped, the flow of the secondary system sodium can be cut off. .

In any case, the primary sodium stops flowing when the reduced pressure is removed, creating a so-called fail-safe structure, compared to conventional examples in which the primary sodium flows when a failure occurs in the flow path blocking mechanism. Therefore, it is extremely safe. In addition, although the above-mentioned embodiment described an intermediate heat exchanger used in a tank-type nuclear reactor, the present invention provides an intermediate heat exchanger for an auxiliary core cooling system, a cold trap, etc. between a hot plenum and a cold plenum. It can also be applied to devices having flow paths.

〔Effect of the invention〕

According to the present invention, it is possible to obtain a heat exchanger flow path structure that allows primary sodium to flow into the heat exchanger while reducing the pressure in the decompression chamber, while completely blocking the flow of the primary sodium when this depressurization is stopped. .

In particular, when a failure occurs in the flow path blocking mechanism,
Unlike the conventional example in which the primary sodium flows, the present invention has a fail-safe structure in which the flow of the primary sodium stops if the reduced pressure state for flowing the primary sodium is broken. Extremely safe.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the flow path structure of a heat exchanger according to the present invention, FIG. 2 is a diagram showing another embodiment, and FIG. 3 is a diagram showing an example of the structure of a tank-type nuclear reactor. , FIG. 4 is a diagram showing the flow path structure of a conventional gate valve type heat exchanger, and FIG. 5 is a diagram showing the flow path structure of a conventional gas pressure type heat exchanger. 14...Hot plenum, 16...Cold plenum, 24...Heat exchanger, 26...Secondary system piping, 36...Down pipe, 38...Rising pipe, 46...
Heat exchanger tube, 52... Partition plate, 54... Seal portion, 5
8...Gate valve, 60...Gas injection chamber, 62
... Gas injection nozzle, 68 ... Heat exchanger tube, 72 ...
Partition wall, 74... gas injection chamber, 80... heat exchanger,
82... Partition plate, 86... Partition wall, 90... Decompression chamber, 94... Decompression pipe.

Claims (1)

[Scope of Claims] 1. A partition structure that separates a hot plenum that accommodates a primary coolant that has become high temperature after absorbing heat from a heat source, and a cold plenum that accommodates a relatively low-temperature primary coolant before being sent to the heat source section. The hot plenum is disposed through the hot plenum and the cold plenum located below the hot plenum is connected to the cold plenum, and the hot plenum is connected to the cold plenum. In the flow path structure of the heat exchanger for performing heat exchange by absorbing the heat of the high temperature primary coolant into the secondary coolant flowing through the heat exchanger, a partition wall opening into the high-temperature primary coolant and forming a decompression chamber; and a partition wall that extends from the partition structure along the circumference of the heat exchanger to the decompression chamber while sealing the hot plenum and the cold plenum, and has an upper end connected to the decompression chamber in the hot plenum. a partition plate set higher than the free liquid level of the high-temperature primary coolant, and reducing the pressure in the vacuum chamber to cause the high-temperature primary coolant to overcome the partition plate and flow into the heat exchanger; A flow path structure for a heat exchanger, comprising a pressure reducing means for lowering the liquid level of the high-temperature primary coolant below the upper end of the partition plate and stopping the inflow.