JPH04125497A - Heat exchanger for fast reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat exchanger for a nuclear reactor, and particularly to a heat exchanger suitable for use in a heat exchanger for a fast reactor.

[Conventional technology]

Regarding the structure of a conventional fast reactor heat exchanger, see [Hitachi Review VoQ0.67 NFll (1985-
11) p., 891-892.

In a tank-type fast reactor that uses liquid metal sodium (hereinafter referred to as sodium) as a coolant, as shown in FIG. 2, a reactor vessel 9 is filled with sodium, and a reactor core 2.
Upper core mechanism 7. Multiple heat exchangers1. A plurality of pumps 11 are installed.

Furthermore, inside the reactor vessel 9, there is a partition wall 10 that separates the high temperature sodium flowing out from the reactor core 2 and the low temperature sodium flowing out from the heat exchanger 1 during normal rated operation. It is separated into a lower low temperature plenum 5. The upper part of the reactor vessel 9 is the roof slab 1
2 (lid plate). During normal rated operation, the pump 11 ensures a circulation flow rate of approximately 360
The sodium in the cold plenum at 11.℃ is pumped. It passes through the high-pressure plenum 3, exchanges heat with the reactor core 2, becomes sodium at about 530°C, and flows into the high-temperature plenum 4. The sodium in the hot plenum 4 passes through the heat exchanger 1 and is cooled before flowing into the cold plenum 5. When a nuclear reactor is shut down and scrammed, a heat exchanger for removing decay heat is activated, and a small pump called a pony motor and natural circulation inside the reactor are used to remove decay heat after the reactor shuts down. 10 when fully rated
A circulating flow rate of approximately 3% to 3% is ensured.

[Problem to be solved by the invention]

The problems of the above-mentioned conventional technology will be explained using figures.

FIG. 3 shows the temperature T1 of the outlet 13 of the heat exchanger 1 and the low temperature plenum 5 after the reactor is shut down. The figure shows an outline of an example of a change in T2 over time. During normal rated operation before reactor shutdown, the temperature of high-temperature plenum 4 is 530°C, and the temperature of low-temperature plenum 5 is 3.
Assume that the coolant is circulating at 60°C. When the nuclear reactor is shut down, the circulating flow rate decreases rapidly as described above. However, since the heat exchanger 1 contains the low-temperature fluid of the secondary cooling system inside, due to the influence of its heat capacity, the flow rate of the primary system fluid decreases at the beginning of the scram, as shown in Figure 3. It is then cooled to a temperature lower than the rated outflow temperature, that is, the temperature of the low-temperature plenum 5. - In the calculation example, as shown in Figure 3, due to the effect of the heat capacity of the secondary cooling system of heat exchanger 1,
This will result in a temperature drop of up to 100°C. Then, as the difference in fluid temperature between the secondary cooling system and the primary system of the heat exchanger 1 decreases, the temperature at the heat exchanger outlet 13 gradually increases, and the temperature depends on the cooling of the auxiliary heat exchanger for decay heat removal. become. At the rated time, that is, before scram, the fluid flows out from the heat exchanger outlet 13 to the low-temperature plenum 5 due to the circulation force of the pump at a temperature of T t =T x as shown in FIG. 4(a). After the scrum, T 1 < T 2 as mentioned above.
Therefore, due to the influence of buoyancy, the fluid from the heat exchanger outlet 13 descends as shown in FIG. flow inside. Since the temperature inside heat exchanger 1 is T1, T
By flowing the fluid at temperature 2 into the interior and mixing it,
Maximum fluctuation range ITI-T2+ as outlined in Figure 3
temperature fluctuations occur. This temperature fluctuation may cause thermal cycles or thermal fatigue to occur in the internal structure of the heat exchanger 1.

An object of the present invention is to prevent fluid from entering the heat exchanger 1 from the low-temperature plenum 5 at the initial stage of a scram, and to prevent thermal fatigue that may occur within the heat exchanger 1.

[Means to solve the problem]

The above object is achieved by providing a pipe with an internal throttle installed at the outlet of the heat exchanger, and providing a hole in the pipe surface at a position below the throttle.

[Effect]

At the outlet of the heat exchanger of a fast reactor, a pipe with an internal restrictor is provided, and by providing a hole in the piping surface at the bottom of the restrictor, the reactor is stopped and the circulation flow rate is reduced, allowing heat exchange. When the temperature of the fluid at the outlet drops below the fluid temperature in the cold plenum, the restriction speeds up the fluid exiting the heat exchanger and directs it through the center of the piping and out into the cold plenum. Fluid having a higher temperature than the fluid flowing out from the heat exchanger of the low temperature plenum rises inside the pipe along the outer periphery of the pipe. The rising fluid from the cold plenum is prevented from rising by a restriction provided on the inner surface of the pipe. However, this rise in fluid is caused by buoyancy due to the temperature difference between the fluid in the heat exchanger and the fluid in the low-temperature plenum. accumulates and eventually exceeds the aperture and rises even higher than the aperture. Therefore, in the present invention, a hole is further provided in the piping surface at the bottom of the restriction, and the fluid that has been prevented from rising by the restriction in the piping escapes to the outside of the piping through the hole in the piping surface, thereby preventing fluid from entering above the restriction. prevent. This results in
This prevents temperature fluctuations caused by mixing of the fluid in the heat exchanger with the fluid in the low-temperature plenum that entered the heat exchanger at the beginning of the scram.
Heat fatigue can be prevented.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example in which the fast reactor heat exchanger of the present invention is used as a heat exchanger for a tank-type fast reactor. A constriction 14 and a hole 15 are provided in the piping of the outlet 13 of the heat exchanger 1. The reactor shuts down, the circulating flow rate decreases, and the heat exchanger outlet 1
When the temperature of the fluid in the heat exchanger 3 falls below the fluid temperature in the cold plenum 5, the throttle 14 speeds up the fluid exiting the heat exchanger 1, as shown in FIG. and drain into the cold plenum 5. The fluid having a higher temperature than the fluid flowing out from the heat exchanger 1 of the low temperature plenum 5 rises inside the pipe 13 along the outer periphery of the outlet pipe 13.

The rising fluid from the low-temperature plenum 5 is prevented from rising by a throttle 14 provided on the inner surface of the pipe 13. Furthermore, the fluid whose rise is blocked by the throttle 14 is allowed to escape to the outside of the plumber 3 through the hole 15 provided in the piping surface below the throttle 14, thereby preventing the fluid from entering above the throttle 14.

As a result, as shown in the outline of the temperature change in FIG. 6, the fluid in the low-temperature plenum 5 that entered the heat exchanger outlet piping 3 at the initial stage of the scram further enters the heat exchanger 1 and mixes. This can prevent temperature fluctuations caused by heat exchanger 1 and thermal fatigue of the structural materials inside the heat exchanger 1.

FIG. 7 shows an embodiment in which the heat exchanger of the present invention is applied to a loop-type fast reactor. A piping having a restriction 14 and a hole 15 is provided at the outlet 13 of the primary system fluid that exchanges heat with the secondary cooling system inside the vessel of the heat exchanger 1 which is connected to the outside of the reactor vessel by piping.

FIG. 8 shows another embodiment of the present invention. A plurality of throttles and holes are provided in the piping of the heat exchanger outlet 13, and the structure for preventing fluid from entering the heat exchanger 1 from the low-temperature plenum 5 is multiplied, thereby increasing the effect.

〔Effect of the invention〕

According to the present invention, a pipe with an internal throttle installed is provided at the outlet of the heat exchanger of a fast reactor, and a hole is provided in the piping surface at the □ position below the throttle, so that the reactor can be stopped and the circulation flow rate reduced. When the temperature of the fluid at the exit of the heat exchanger drops below the temperature of the fluid in the cold plenum, the restriction speeds up the fluid exiting the heat exchanger and directs it through the center of the piping and into the cold plenum. .

Fluid having a higher temperature than the fluid flowing out from the heat exchanger of the low temperature plenum rises inside the pipe along the outer periphery of the pipe. The rising fluid from the cold plenum is prevented from rising by a restriction provided on the inner surface of the pipe. Furthermore, this fluid can be allowed to escape from the pipe through a hole provided in the piping surface below the throttle, thereby preventing the fluid from entering above the throttle. This prevents temperature fluctuations caused by mixing of the fluid in the heat exchanger with the fluid in the low-temperature plenum that entered the heat exchanger at the initial stage of the scram, thereby preventing thermal fatigue.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a heat exchanger of a fast reactor according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of a tank-type fast reactor, and Fig. 3 is an explanatory diagram of a heat exchanger outlet temperature at reactor shutdown in a conventional technology. FIG. 4 is an explanatory diagram of the flow and temperature at the outlet of the heat exchanger before and after scram in the conventional technology, and FIG. 5 is a diagram showing the flow and temperature at the outlet of the heat exchanger after scram in the present invention. An explanatory diagram, FIG. 6 is a characteristic diagram of the transient change in the heat exchanger outlet temperature during reactor shutdown in the present invention, FIG. 7 is an explanatory diagram of an embodiment of the loop type fast reactor of the present invention, and FIG. FIG. 7 is an explanatory diagram of main parts of another embodiment of the present invention. 1... Heat exchanger, 2... Core, 3... High pressure plenum, 4... High temperature plenum, 5... Low temperature plenum, 6
・Connection piping, 7... Core upper mechanism, 8 ・Free liquid level,
9. Reactor vessel, 10... Partition wall, 11... Pump, 1
2... Roof slab, 13... Heat exchanger outlet, 14...
... Throttle, 15... Hole, 16... Heat exchanger inlet. Rino diagram 6th cause diagram 7

Claims (1)

[Scope of Claims] 1. In a heat exchanger for a fast reactor in which a primary coolant is built in the reactor vessel, a pipe with a throttle installed inside is provided at the outlet of the heat exchanger, and a pipe at the bottom of the throttle is provided. A heat exchanger for a fast reactor characterized by having holes provided on the piping surface at the positions. 2. The fast reactor heat exchanger according to claim 1, wherein the piping of the heat exchanger is directly connected to the heat exchanger. 3. The heat exchanger for a fast reactor according to claim 1, wherein the piping of the heat exchanger is connected to the heat exchanger via the piping of the heat exchanger. 4. The heat exchanger for a fast reactor according to claim 1, wherein the piping of the heat exchanger has a single aperture and a single hole. 5. The heat exchanger for a fast reactor according to claim 1, wherein the piping of the heat exchanger has a plurality of apertures and holes.