JPH0310198A - Intermediate heat exchanger of tank typed fast breeder reactor - Google Patents

Abstract

PURPOSE:To detect with a high sensitivity and within a rather short time a leakage from a heat transfer tube which has relatively high leaking probability by detecting a fluctuation of a liquid surface of a secondary coolant at the moment when a down- comer is pressurized by an inert gas after drainage of the secondary coolant. CONSTITUTION:In the case of confirmation of a leakage from a heat transfer tube 18, a secondary coolant 20 in a downcomer 24 is drained, for the first place. In this case, not all the secondary coolant 20 can be drained by an ordinary drain operation and, at an upper position higher than a roof slab of a downcomer, a liquid surface of the secondary coolant 20 is formed. Then, the secondary coolant is replaced with an inert gas and, with pressurizing the inert gas, a fluctuation of the liquid surface is detected by an electro-magnetic induction coil 33 which is a detecting measure of a liquid surface fluctuation. The liquid surface of the secondary coolant is formed inside an inner side tube 22 and an outer side tube 23 by a drainage of the secondary coolant 20 and the electro-magnetic induction coil 33 detects the liquid surface fluctua tion under a pressurized condition, and consequently, when the liquid surface goes down, it is judged that a leakage in a heat transfer tube 18 exists.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an intermediate heat exchanger used in a tank-type fast breeder reactor, and in particular, the present invention relates to an intermediate heat exchanger used in a tank-type fast breeder reactor. This article relates to an intermediate heat exchanger for a tank-type fast breeder reactor that can be well detected.

(Prior Art) Figure 4 shows a conventional tank-type fast breeder reactor, in which the reactor vessel 1 has a double structure consisting of an inner main vessel 1a and a guard vessel 1b for safety. It is supported in a downwardly extending manner within a shaped cavity wall 2. The reactor vessel 1 and cavity wall 2 are closed off by a roof slab 3.

In the lower part of the main vessel 1a, a blemish part 5 and a core 6 are sequentially stacked with a core support 4 interposed therebetween. At the top of this core 6, a core upper mechanism 7 is attached to the roof slab 3.
is provided. Further, at the exact upper end position of the core 6, a partition wall 8 is provided by a partition wall support 8a to partition the inside of the main machine la into an upper hot pool 9 and a lower cold pool 10.

Further, as shown in FIG. 4, from the roof slab 3, a plurality of one-stop circulation pumps 11 for circulating the primary coolant 15 in the main container 1a are suspended at equal intervals in the circumferential direction. A thin cylindrical body 12 surrounding the outside of these stop circulation pumps 11 is provided to vertically penetrate the partition wall 8 . Furnace pipes 13 are led out from the lower ends of each one-stop circulation pumps 11, and their tips are connected to the blemish part 5.

Further, from the roof slab 3, a plurality of intermediate heat exchangers 14 for exchanging heat between the secondary coolant and the secondary coolant are suspended in the main container 1 at equal intervals in the circumferential direction, and the lower ends of the intermediate heat exchangers 14 are suspended at equal intervals in the circumferential direction. The portion penetrates through the through hole 8b of the partition wall 8 and reaches into the cold pool 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 (not shown) 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 cooling 15 flows into the intermediate heat exchanger 14 from above, transfers heat energy to the liquid metal serving as the secondary coolant, and the temperature of the secondary cooling 15 drops and flows down into the cold pool 10.

On the other hand, the primary coolant 15 in the cold pool 10 rises within the thin-walled cylindrical body 12, is pressurized by the one-stop circulation bomb 11, and is returned to the blennium section 5 through the in-furnace piping 13.

Next, the structure and operation of the intermediate heat exchanger 14 will be explained with reference to FIGS. 5 and 6.

As shown in FIG. 5, the intermediate heat exchanger 14 has an elongated hollow outer shell 16, and a flange 16a formed at the upper end of the outer shell 16 is supported by the roof slab 3. The entire vessel 14 is suspended. The lower end of this outer body 16 is tapered in diameter and inserted into a through hole 8b of the partition wall 8 to open into the cold pool 10 with an outlet nozzle 16b.

Further, in the lower part of the outer shell 16, as shown in FIG.
is stored. And the entrance window 1 opened in the outer body 16
The primary coolant 15 (inuyama arrow) flowing from 9 onto the upper tube plate 17a flows down inside each heat transfer tube 18, flows out from the lower tube plate 17b, passes through the outlet nozzle 16b, and enters the cold pool 10.
flow down inside.

Further, as shown in FIGS. 5 and 6, a secondary coolant 20 (large black arrow) made of liquid metal such as liquid sodium is applied to the upper and lower tube plates at the center of the outer shell 16 from the outside of the roof slab 3. An inner pipe 22 is fed into the space 21 between 17a and 17b through a lower end opening 22a, and a secondary coolant 20 heated by heat exchange with the primary coolant 15 from the space 21.
A downcomer 24 is provided, which is formed by an outer pipe 23 that takes out the roof slab 3 and leads it out of the roof slab 3.

Note that the penetration portion of the lower end of the inner tube 22 with the tube plate 17b is configured as an end plate 25 because the secondary coolant 20 comes into direct contact therewith.

Furthermore, a radiation shielding body 27 filled with steel balls is provided at the upper end of the outer shell 16 for radiation shielding.

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

The primary coolant 15 flows into the outer shell 16 from the entrance window 19 in the hot pool 9, as shown by the large arrow in FIG.

On the other hand, the secondary coolant 20 flows down inside the inner tube 22 of the downcomer 24 and flows into the space 21 through the lower end opening 22a, as shown by the large black arrow in FIG. The primary coolant 15 flowing down in the heat transfer tube 18 and the secondary coolant 20 rising in the space 21 exchange heat with each other. After this heat exchange, the primary coolant 15 in a low temperature state flows into the outer shell 16 from the lower end opening of the heat transfer tube 18, and flows into the cold pool 10 through the outlet nozzle 16b.

On the other hand, the secondary coolant 20, which has reached a high temperature, is in the upper pipe! 12
It flows into the outer pipe 23 of the downcomer 24 at a portion 17a and is fed to a steam generator (not shown) of the secondary main coolant system.

In the intermediate heat exchanger of the conventional tank-type fast breeder reactor having the above configuration, the pressure on the secondary side is designed to be higher than that on the primary side if only one of the heat exchanger tubes 18 occurs. , the secondary coolant 20 will flow out to the primary side. Conventionally, the leakage of the secondary coolant 20 has been detected by monitoring the liquid level of the steam generator or the secondary main circulation pump.

(Problems to be Solved by the Invention) In the conventional tank-type fast breeder reactor, the intermediate heat exchanger 14 forms a boundary with the activated primary coolant 15 and the non-activated secondary coolant 20.

Therefore, in the event that a leak occurs due to damage to a portion constituting the boundary, it is necessary to pull out the intermediate heat exchanger 14, clean the adhering coolant sodium, decontaminate it, and repair it.

Among the constituent members of the intermediate heat exchanger 14, the main part that forms the boundary between the secondary coolant 15 and the secondary coolant 20 is the outer shell 1.
6 and heat exchanger tubes 18.

Of these, the probability that a leak will occur in the outer shell 16 is considered to be very low, but since the heat exchanger tubes 18 have a large number and a relatively thin structure, the probability that a leak will occur is relatively high. it is conceivable that.

By the way, when repairing the intermediate heat exchanger 14 by pulling it out, the number of heat transfer tubes 18 is approximately several thousand, so identifying the leak location, that is, the part to be repaired, is a critical issue that affects the repair organization. It becomes a pass.

Regarding the identification of the leakage position in the heat exchanger tube 18, it is possible to identify the leakage position in a relatively short time by employing a detection method using bubbles as shown in, for example, Japanese Patent Laid-Open No. 60-73292. . However, before identifying a leaky heat transfer tube, it is necessary to confirm whether a leak has occurred or not. Conventionally, as mentioned above, the sodium level in the steam generator or secondary main circulation pump was checked. Adopt a monitoring method.

However, in the case of the conventional monitoring method, the liquid level of the steam generator is about 10rrl'', and the liquid level of the secondary main circulation pump is about 6rrf.
Therefore, even if a leak occurs, the liquid level change is small and the detection sensitivity is poor.

The present invention has been made with these points in mind, and has therefore been developed to provide a tank-type heat exchanger that can quickly and sensitively detect leaks from heat exchanger tubes, which have a relatively high leakage probability among the components of an intermediate heat exchanger. The purpose is to provide an intermediate heat exchanger for fast breeder reactors.

[Structure of the invention]

(Means for Solving the Problems) As a means for achieving the above object, the present invention provides a downcomer that handles a secondary coolant, and a liquid level of the secondary coolant formed in the downcomer after draining the secondary coolant. The present invention is characterized in that a liquid level fluctuation detection means is provided for detecting fluctuations when the inside of the downcomer is pressurized with an inert gas.

(Function) In the intermediate heat exchanger for the tank-type fast breeder reactor according to the present invention, when checking for the presence or absence of leakage from the heat transfer tubes, the secondary coolant is first drained. At this time, in a normal draining operation, all of the secondary coolant in the downcomer is not drained, and a liquid level of the secondary coolant is formed above the roof slab of the downcomer. Therefore, the secondary coolant system was replaced with an inert gas, and while pressurizing this inert gas,
Fluctuations in the liquid level are detected by liquid level fluctuation detection means. In other words, if there is a leak in the heat transfer tube, the liquid level will drop, so
By detecting this with the liquid level fluctuation detection means, it is possible to detect the presence or absence of a leak.

The liquid level fluctuation detection means may be an electromagnetic induction coil mounted on the outer circumference of the outer tube, an electromagnetic induction type liquid level sensor 1 inserted into the inner tube from above, or the like.

(Example) An example of the present invention will be described below with reference to FIGS. 1 and 2. The present invention is characterized only by the intermediate heat exchanger, and the rest of the structure of the tank-type fast breeder reactor is exactly the same as the conventional one shown in FIG. Only the characteristic parts will be illustrated and explained.

FIG. 2 shows an example of an intermediate heat exchanger according to the present invention, and this intermediate heat exchanger 14 has a flange 1 formed at the upper end.
The intermediate heat exchanger 14 is provided with an elongated hollow outer shell 16 supported by the roof slab 3 via 6a, and the intermediate heat exchanger 14 is suspended and supported by the outer shell 16.

On the other hand, at a position corresponding to the outer body 16 of the partition wall 8 that divides the inside of the main container (not shown) into an upper hot pool 6 and a lower cold pool 10 and the partition wall support 8a that supports the partition wall 8, as shown in FIG. A through hole 8b is provided as shown in FIG.
A stand pipe 30 is inserted and fixed into this through hole 8b. The lower part of the outer body 16 is loosely fitted into the stand pipe 30.

As shown in FIG. 2, the lower end of the outer shell 16 is tapered to form an outlet nozzle 16b, and the inside of the outer shell 16 is connected to the cold pool 10 through the outlet nozzle 16b. It's communicating.

Further, between the outlet nozzle 16b and the lower end of the stand vibe 30, and between the outlet nozzle 16b and the lower front lN1 described later,
7b, a bellows 31 is installed to absorb expansion and contraction due to thermal expansion.

As shown in FIG. 2, in the part of the outer shell 16 located inside the stand vibe 30, there is an upper tube plate 17 that partitions the inside of the outer shell 16.
A and a lower tube plate 17b are respectively provided, and a large number of heat exchanger tubes 18 are supported through the tube plates 17a and 17b.

The primary coolant 15 (inuyama arrow) that flows into the upper tube plate 17a from one inlet window provided at the upper part of the outer shell 16 flows down inside each heat transfer tube 18 and flows out from the lower tube plate 17b. ,
It is adapted to flow down into the cold pool 10 through the outlet nozzle 16b.

At the center of the outer shell 16, as shown in FIGS. 1 and 2, a downcomer 24 is provided which has a double pipe structure including an inner pipe 22 and an outer pipe 23.

The inner tube 22 feeds a secondary coolant 20 (large black arrow) made of liquid metal such as liquid sodium from the outside of the roof slab 3 into the space 21 between the tube plates 17a and 17b through the lower end opening 22a. In addition, the outer pipe 23 takes out the secondary coolant 20 heated by exchanging heat with the primary coolant 15 in the space 21 and leads it out of the roof slab 3. ing.

Further, as shown in FIG. 2, the penetrating portion of the lower end of the inner tube 22 with the lower tube plate 17b is configured as an end plate 25 because the secondary coolant 20 comes into direct contact with it, and the central portion of the inner tube 22 A dip tube 32 is inserted therein.

Additionally, inside the upper end of the outer shell 16, as shown in FIG.
A radiation shield 27 filled with steel balls is provided to block radiation, and an electromagnetic induction coil 33 is attached to the upper part of the radiation shield 27 of the outer tube 23, as shown in FIGS. 1 and 2. has been done.

As shown in FIG.
Fluctuations in the liquid level 34 of the secondary coolant 20 formed inside the heat exchanger tube 18 under pressure are detected, and if the liquid level 34 drops, it is detected that there is a leak in the heat transfer tube 18. This will be detailed later.

Next, the operation of this embodiment will be explained. Note that the heat exchange action in the intermediate heat exchanger 14 is exactly the same as the conventional one shown in FIG. 5, so only the method for detecting leakage in the heat exchanger tubes 18 will be described below.

If there is a possibility that a leak has occurred in the heat exchanger tubes 18 of the intermediate heat exchanger 14 due to a change in the liquid level of the steam generator or the secondary main circulation pump, first drain the secondary coolant 20 by a normal drain operation. Drain.

By the way, in a normal draining operation, the secondary coolant 20 in the downcomer 24 of the intermediate heat exchanger 14 is not completely drained, and as shown in FIG.
A liquid level 34 of the secondary coolant 20 is formed within the outer tube 23 . In this embodiment, leak detection is performed by effectively utilizing this liquid level 34.

That is, as shown in FIG. 1, once a liquid level 34 is formed in the downcomer 24, the secondary coolant system is replaced with an inert gas, and this inert gas is pressurized. As a result, the liquid level 34 is pressed from above.

At this time, if there is a leak in the heat exchanger tube 18, the liquid level 34 will gradually drop, so this liquid level fluctuation is reflected by the electromagnetic induction coil 34.
3, leaks in the heat exchanger tubes 18 can be detected in a short time and with high sensitivity.

Note that the heat exchanger tube 18 in which a leak has occurred can be identified by using, for example, the bubble method detection disclosed in Japanese Patent Application Laid-Open No. 60-73292.

Furthermore, even during regular periodic inspections, leakage in the heat transfer tubes 18 can be confirmed by inspecting in the same manner as described above when the secondary coolant 20 is drained.

FIG. 3 shows another embodiment of the present invention, in which the electromagnetic induction coil 3 in the above embodiment is used as a liquid level fluctuation detection means.
3, an electromagnetic induction type liquid metal level needle 35 is used.

That is, as shown in FIG. 3, the upper end of the inner tube 22 of the downcomer 24 is provided with a flange portion 36 and a liquid metal level needle well 37. A liquid metal level needle 35 is inserted from the
It is fixed to the flange portion 36.

Even with this configuration, the presence or absence of a leak in the heat exchanger tube 18 can be detected with high sensitivity in a short time by performing leak detection using the same method as in the above embodiment.

〔Effect of the invention〕

As explained above, the present invention provides a liquid level fluctuation detection means provided in the downcomer that detects fluctuations in the secondary coolant liquid level formed in the downcomer after the secondary coolant is drained under pressure by an inert gas. Since it is designed to detect heat exchanger tube leaks in a short time and with high sensitivity,
It is possible to shorten the repair period and reduce radiation exposure during repair.

Furthermore, since a leak test can be easily performed during periodic inspections, operational efficiency can be improved.

[Brief explanation of drawings]

, FIG. 1 is a main enlarged cross-sectional view of an intermediate heat exchanger according to an embodiment of the present invention, FIG. 2 is a cross-sectional view showing a similar overall configuration, and FIG. 3 is a cross-sectional view showing another embodiment of the present invention. Figure 1 is a diagram equivalent to Figure 1, Figure 4 is a partial cross-sectional view showing a conventional tank-type fast breeder reactor, Figure 5 is a cross-sectional view showing the configuration of the intermediate heat exchanger in Figure 4, and Figure 6 is a diagram showing the main points of Figure 5. It is an enlarged view of the part. DESCRIPTION OF SYMBOLS 1... Reactor vessel, 1a... Main vessel, 3... Roof slab, 8... Partition wall, 9... Hot pool, 10
... Cold pool, 14 ... Intermediate heat exchanger, 15
...-Next coolant, 16...Outer shell, 16b...Outlet nozzle, 17a...Upper tube plate, 17b...Lower tube plate, 1
8... Heat exchanger tube, 19... Inlet window, 20... Secondary coolant, 21... Space, 22... Inner tube, 23...
Outer tube, 24...downcomer, 32...electromagnetic induction coil, 34...liquid level, 35...liquid metal level needle.

Claims (1)

[Claims] A tank-type fast breeder reactor that penetrates the roof slab covering the main vessel and is suspended within the main vessel, and its lower end divides the main vessel into an upper hot pool and a lower cold pool. An outer shell that penetrates the partition wall, and an upper tube plate and a lower tube plate provided in the outer shell are arranged to penetrate through the outer shell, and the high temperature primary coolant flowing from the hot pool onto the upper tube plate is passed through the inside. A large number of heat transfer tubes are arranged to flow down and discharged into the cold pool from an outlet nozzle at the lower end of the outer shell; an inner tube that exchanges heat with the primary coolant that flows through each heat transfer tube; an outer pipe for leading out the secondary coolant to the outside of the roof slab; 1. An intermediate heat exchanger for a tank-type fast breeder reactor, characterized in that the downcomer is provided with liquid level fluctuation detection means for detecting fluctuations in the surface of the downcomer when the inside of the downcomer is pressurized with an inert gas.