JP2016080301A - Cooling system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance heat removal performance of an air cooling type cooling system.SOLUTION: A cooling system 100 is applied to a nuclear power plant, and includes: a cooling tower 1 including an air suction port 4 for suctioned air; an air cooling heat exchanger 2 housed in the cooling tower 1, and provided on a flow passage of suctioned air in the cooling tower 1; a supply source 6 for fluid having smaller density than suctioned air, provided outside the cooling tower 1; and a supply pipeline 5 connected to the supply source 6 and the cooling tower 1, and supply fluid to the cooling tower 1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a cooling system applied to a nuclear power plant.

  Nuclear power plants need to cool the reactor by removing the decay heat of the core even if the power supply is lost in an emergency. As a cooling system that does not require a power source, an air-cooled system that utilizes natural circulation of air has been proposed (see Patent Document 1).

JP 2013-174447 A

  However, in general, an air-cooled cooling system using natural circulation has a low heat removal efficiency, and thus it is necessary to enlarge the system in order to ensure a large heat removal performance.

  The present invention has been made in view of the above, and an object thereof is to improve the heat removal performance of an air-cooled cooling system.

  In order to achieve the above object, the present invention provides a cooling tower having an air intake port for intake air, an air-cooled heat exchanger housed in the cooling tower and provided on a flow path of intake air in the cooling tower, A fluid supply source having a density lower than that of the intake air provided outside the cooling tower; and a supply pipe that connects the supply source and the cooling tower and supplies the fluid to the cooling tower. Features.

  ADVANTAGE OF THE INVENTION According to this invention, the heat removal performance of an air cooling type cooling system can be improved.

It is a longitudinal section showing a schematic structure of one example of composition of a cooling system concerning a 1st embodiment of the present invention. It is a longitudinal cross-sectional view showing the schematic structure of one structural example of the nuclear power plant to which the cooling system which concerns on 2nd Embodiment of this invention is applied. It is a longitudinal cross-sectional view showing the schematic structure of one structural example of the nuclear power plant to which the cooling system which concerns on 3rd Embodiment of this invention is applied. It is a figure which illustrates the relationship between the supply amount of steam, and the natural circulation flow rate.

<First Embodiment>
(Constitution)
FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of a configuration example of the cooling system according to the present embodiment.

  As shown in FIG. 1, the cooling system 100 according to this embodiment includes a cooling tower 1, an air-cooled heat exchanger 2, a supply pipe 5, and a tank (supply source) 6.

  The cooling tower 1 is formed in a chimney shape extending upward, for example, and an upper cooling tower outlet 8 is opened. The cooling tower 1 includes an air intake 4 for intake air. External air is taken into the cooling tower 1 as intake air through the air intake 4. The air intake 4 is provided in at least a part of the wall surface constituting the cooling tower 1 in the vicinity of the air-cooling heat exchanger 2 (in FIG. 1, two locations at the lower end of the cooling tower 1).

  The air-cooling heat exchanger 2 is accommodated in the cooling tower 1 and is provided on the air flow path in the cooling tower 1 (between the air intake 4 and the cooling tower outlet 8). The air cooling heat exchanger 2 includes a plurality of heat transfer tubes 3. A cooled fluid supply pipe (first pipe) 34 is connected to one end side of the heat transfer pipe 3, and a cooled fluid that is hotter than the surrounding air is supplied via the first pipe 34. The air-cooled heat exchanger 2 cools the cooled fluid by exchanging heat between the cooled fluid supplied from the facility that has generated the cooled fluid via the first pipe 34 and the air in the cooling tower 1. A cooled fluid return pipe (second pipe) 35 is connected to the other end side of the heat transfer tube 3, and the cooled fluid cooled by heat exchange in the air-cooled heat exchanger 2 is returned to the source equipment. In addition, the number of the heat exchanger tubes 3 of the air-cooling heat exchanger 2 can be arbitrarily set in consideration of necessary heat removal performance.

  The tank 6 is provided outside the cooling tower 1 as a supply source of a fluid (supply fluid) having a density lower than that of air taken into the cooling tower 1. Examples of the supply fluid supplied from the tank 6 to the cooling tower 1 include a gas that is lighter than air at the same temperature, such as helium, in addition to steam.

  The supply pipe 5 connects the tank 6 and the cooling tower 1. Although it is only necessary that the outlet opening faces the inside of the cooling tower 1, in this embodiment, the supply pipe 5 extends through the wall surface of the cooling tower 1 to the inside of the cooling tower 1 and opens upward. . In the present embodiment, the supply pipe 5 is connected to the cooling tower 1 at a position above the air-cooling heat exchanger 2 and is opened at a position above the air-cooling heat exchanger 2 in the cooling tower 1. The supply pipe 5 is provided with a flow rate adjusting valve 32. By operating the flow rate adjusting valve 32, the flow rate of the supply fluid supplied to the cooling tower 1 can be adjusted. The flow rate adjustment valve 32 may be operated manually or may be operated by a signal from a central control room (not shown).

(Operation)
When the fluid to be cooled is supplied to the heat transfer tube 3 of the air-cooling heat exchanger 2 and heat exchange is performed between the fluid to be cooled and the air in the air-cooling heat exchanger 2, the temperature of the air increases and the temperature of the fluid to be cooled decreases. To do. Since the density of air generally decreases as the temperature rises, the air whose temperature has risen due to heat exchange in the air-cooled heat exchanger 2 rises in the cooling tower 1 by buoyancy, and enters the atmosphere from the outlet 8 of the cooling tower. Is released. When the air in the cooling tower 1 is released into the atmosphere, an amount of air corresponding to the amount of released air is newly taken into the cooling tower 1 from the air intake 4. In this way, natural circulation in which air is naturally taken into the cooling tower 1 occurs. Hereinafter, the flow rate of air taken into the cooling tower 1 by natural force is referred to as a natural circulation flow rate.

By the way, the buoyancy F acting on the warmed air is expressed by Expression (1).
F = (ρ _∞ −ρ _h ) gH (1)
Where ρ _∞ : density of air outside the cooling tower, ρ _h : density of air inside the cooling tower, g: gravitational acceleration, H: cooling tower height

In order to increase the natural circulation flow rate, the air buoyancy in the cooling tower 1 may be increased to increase the amount of air released from the cooling tower 1 into the atmosphere. From formula (1), in order to increase the buoyancy of the air in the cooling tower 1, the cooling tower height H of the cooling tower 1 should be increased or the air density ρ _h in the cooling tower 1 should be reduced. I understand.

In the present embodiment, the supply fluid is supplied into the cooling tower 1 at a position above the air-cooling heat exchanger 2 from the tank 6 through the supply pipe 5 by operating the flow rate adjustment valve 32. As described above, since the density of the supply fluid is smaller than the density of the air in the cooling tower 1, the density ρ _m of the mixture of the air in the cooling tower 1 and the supply fluid after the supply fluid is supplied is the supply gas. It becomes smaller than the density ρ _h of the air in the cooling tower 1 before supplying. Therefore, as shown in the equation (1), the buoyancy of the air-fuel mixture in the cooling tower 1 after supplying the supply gas is larger than the buoyancy of the air in the cooling tower 1 before supplying the supply gas. As a result, the amount of air released from the cooling tower 1 into the atmosphere increases, and the natural circulation flow rate increases.

Example 1
In this embodiment, the atmospheric pressure condition in the density [rho _∞ of 30 ° C. in air to about 1.17 kg / ^{m 3,} the density of the air became 100 ° C. warmed in heat exchanger [rho _h a 0.93 kg / ^{m 3} The density of steam at 100 ° C. is 0.60 kg / m ³ .

When an amount of supply fluid corresponding to 20% of the air mass flow rate in the cooling tower 1 is supplied into the cooling tower 1, the density ρ _m of the air-fuel mixture in the cooling tower 1 becomes 0.84 kg / m ³ . As a result, the density difference between the density [rho _∞ density [rho _m with external air cooling tower 1 of the air-fuel mixture inside the cooling tower 1 is increased from 0.24 kg / ^{m 3} to 0.33 kg / ^{m 3,} As shown in Equation (1), the buoyancy of the air-fuel mixture in the cooling tower 1 after supplying the supply gas is increased by about 38% compared to the buoyancy of the air in the cooling tower 1 before supplying the supply gas. As described above, when the buoyancy of the air-fuel mixture in the cooling tower 1 increases, the natural circulation flow rate increases. When the natural circulation flow rate increases, the flow rate of the air taken into the cooling tower 1 also increases, so that the pressure loss in the heat transfer tube 3 of the air-cooled heat exchanger 2 increases. The flow rate of the air taken into the cooling tower 1 is determined so that the increase in pressure loss and the increase in buoyancy coincide. Since the pressure loss is proportional to the square of the air flow velocity, the flow velocity of the air taken into the cooling tower 1 increases by about 17% when the buoyancy increases by 38%. Since the forced convection heat transfer coefficient of the single-phase flow is generally proportional to the 0.8th power of the flow velocity, the heat transfer amount in the air-cooled heat exchanger 2 is improved by about 13%.

(effect)
(1) According to this embodiment, the buoyancy of the air-fuel mixture in the cooling tower 1 can be increased by supplying the supply fluid having a density lower than that of air into the cooling tower 1. As a result, the amount of air released from the cooling tower 1 into the atmosphere can be increased, and the natural circulation flow rate can be increased. When the natural circulation flow rate increases, the flow rate of the air taken into the cooling tower 1 increases, so that the heat transfer amount in the air-cooling heat exchanger 2 can be increased and the heat removal performance of the cooling system 100 can be enhanced.

  (2) Generally, as a method for improving the heat removal performance of a cooling system using natural circulation of air, fins are attached to heat transfer tubes used in heat exchangers to increase the heat transfer area. There is a method of increasing the natural circulation flow rate of air by increasing the height. However, these methods increase the size of the heat exchanger and the cooling tower. In addition, the cost may increase significantly.

  On the other hand, in this embodiment, the tank 6 and the cooling tower 1 are connected by the supply pipe 5, and the supply fluid is supplied from the tank 6 to the cooling tower 1 through the supply pipe 5, thereby removing heat from the cooling system 100. Improves performance. Thereby, it can be set as a highly efficient cooling system, making a magnitude | size equivalent. Therefore, the air-cooling heat exchanger 2 and the cooling tower 1 are not increased in size. Furthermore, a significant increase in cost can be suppressed.

  (3) In the present embodiment, the number of heat transfer tubes 3 provided in the air-cooling heat exchanger 2 is reduced, the length of the heat transfer tubes 3 is shortened, or cooling is performed by the amount that the heat removal performance of the cooling system 100 is improved. Even if the height of the tower 1 is lowered to downsize the cooling system 100, sufficient heat removal performance can be ensured. Thereby, it can be set as the cooling system reduced in size, making performance equivalent. Therefore, cost can be reduced. Moreover, the convenience of the cooling system 100 can be improved and the applicable range can be expanded.

  (4) Even when supplying a supply fluid (for example, steam) higher than the intake air from below the air-cooling heat exchanger 2, the density of the air-fuel mixture in the cooling tower 1 decreases and the buoyancy increases as described above. In addition, the effect of improving the heat removal performance can be obtained. However, since the air cooling heat exchanger 2 is provided with a large number of heat transfer tubes 3 and the flow path area is narrow, the flow rate of the air-fuel mixture around the heat transfer tubes 3 increases. When the flow velocity of the air-fuel mixture around the heat transfer tube 3 increases, the pressure loss of the heat transfer tube 3 increases, so the amount of new air taken into the cooling tower 1 decreases, and the effect of improving the heat removal performance is weakened accordingly. . In addition, the temperature of the air-fuel mixture mixed with the high-temperature steam is higher than that of the intake air, and the heat removal performance is improved by the amount that the temperature difference from the fluid to be cooled supplied to the heat transfer pipe 3 of the air-cooling heat exchanger 2 becomes smaller. Work adversely in getting the effect.

  On the other hand, in the present embodiment, the supply pipe 5 is disposed so as to open at a position above the air-cooling heat exchanger 2 in the cooling tower 1, and the supply fluid is cooled at a position above the air-cooling heat exchanger 2. Supplying to the tower 1. Therefore, an increase in pressure loss of the heat transfer tube 3 can be suppressed. Since the space above the air-cooling heat exchanger 2 has a large flow path area, the increase in pressure loss is sufficiently small relative to the increase in buoyancy even if the flow rate of the air-fuel mixture increases. Further, the fluid to be cooled supplied to the heat transfer tube 3 can be heat-exchanged with normal-temperature (unheated) air taken into the cooling tower 1. Therefore, the heat removal performance of the cooling system 100 can be improved more effectively.

  (5) If the supply fluid becomes excessively supplied, the release of the air-fuel mixture through the cooling tower outlet 8 cannot catch up, and the intake from the air intake 4 is hindered or reduced, and there is a concern that the heat removal effect may be reduced. The On the other hand, in the present embodiment, the flow rate adjustment valve 32 is provided in the supply pipe 5, and the flow rate of the supply fluid supplied from the supply source 6 to the cooling tower 1 can be adjusted. Therefore, it is possible to suppress a decrease in the amount of air taken into the cooling tower 1 through the air intake 4 due to excessive supply fluid supplied from the supply source 6 to the cooling tower 1.

  (6) In the present embodiment, air naturally circulates in the cooling tower 1. Therefore, the fluid to be cooled can be cooled without the need for a power source.

Second Embodiment
(Constitution)
FIG. 2 is a longitudinal sectional view showing a schematic configuration of a configuration example of a nuclear power plant to which the cooling system according to the present embodiment is applied. In FIG. 2, parts that are the same as in the first embodiment are given the same reference numerals, and descriptions thereof are omitted as appropriate.

  As shown in FIG. 2, the nuclear power plant 200 according to this embodiment includes a nuclear reactor containment facility 201 and a cooling system 202. Hereinafter, each component will be described.

1. Reactor containment facility The reactor containment facility 201 includes a reactor pressure vessel 10, a reactor containment vessel 11, and a reactor building 12. A reactor containment vessel 11 is stored in the reactor building 12. A reactor pressure vessel 10 is stored in the reactor containment vessel 11. A reactor core 15 is disposed in the reactor pressure vessel 10. Although not particularly illustrated, steam generated in the reactor pressure vessel 10 by the reactor core 15 is supplied to the turbine to drive the turbine, and the rotational power of the turbine is transmitted to the generator to generate power. A suppression chamber 43 is provided inside the reactor containment vessel 11 so as to surround the lower end side of the reactor pressure vessel 10. Water is stored in the suppression chamber 43. The suppression chamber 43 is provided with a suction pipe 45. One end side of the suction pipe 45 is disposed in the water of the suppression chamber 43, and the other end side is connected to the pump 46. One end of a discharge pipe 47 is connected to the pump 46. The other end side of the discharge pipe 47 is connected to the reactor pressure vessel 10. The pump 46 is connected to a turbine 48 that is driven by the steam flow from the reactor pressure vessel 10. Therefore, the pump 46 is driven by the steam turbine 48 without an external power source, sucks up water in the suppression chamber 43 through the suction pipe 45, and supplies water to the reactor pressure vessel 10 through the discharge pipe 47.

2. Cooling System The cooling system 202 according to this embodiment includes a water cooling system 203 and an air cooling system 204. The cooling system 202 according to the present embodiment is different from the cooling system 100 of the first embodiment in that a water cooling system 203 is provided as a supply source of the supply fluid instead of the tank 6. Description will be made sequentially focusing on differences from the first embodiment.

Water cooling system The water cooling system 203 is provided in the reactor building 12, and includes a water cooling heat exchanger 21, a cooling water pool 23, a cooled fluid supply pipe (third pipe) 39, and a cooled fluid recovery pipe (fourth Piping) 40 is provided.

  The cooling water pool 23 is provided at a position lower than the reactor pressure vessel 10, and is provided at a position lower than the ground in this embodiment. Cooling water 24 is stored inside the cooling water pool 23. As the cooling water 24, pure water is preferable, but seawater or the like may be used for emergency. The cooling water pool 23 is configured to be able to supply cooling water from the outside.

  The third pipe 39 is connected to the reactor pressure vessel 10 and supplies the fluid to be cooled (steam) generated in the reactor pressure vessel 10 in the event of an emergency such as power loss to the water cooling system 203. By opening the shut-off valves 51 and 52, the water cooling system 203 is activated. The shut-off valves 51 and 52 are closed when the nuclear power plant 200 is in a normal operation state, and are opened in an emergency such as loss of power. The shut-off valves 51 and 52 may be operated manually, or may be operated by a signal from a central control room (not shown). A choking orifice 41 is provided in the third pipe 39. By providing the choking orifice 41, the flow rate of the fluid to be cooled to be supplied to the water-cooled heat exchanger 21 can be set with the opening area. This is because the upper limit of the speed of the fluid to be cooled in the choking orifice 41 can be limited because the flow velocity does not exceed the speed of sound.

  The water cooling heat exchanger 21 is accommodated in the cooling water 24 of the cooling water pool 23 and includes a plurality of heat transfer tubes 22. One end of the heat transfer tube 22 is connected to the reactor pressure vessel 10 via a third pipe 39, and steam generated in the reactor pressure vessel 10 is supplied as a cooled fluid via the third pipe 39. The water-cooled heat exchanger 21 cools the cooled fluid by exchanging heat between the cooled fluid supplied from the reactor pressure vessel 10 via the third pipe 39 and the cooling water 24 in the cooling water pool 23. The other end side of the heat transfer tube 22 is connected to the suppression chamber 43 via the fourth pipe 40, and the fluid to be cooled that has been cooled by heat exchange in the water-cooled heat exchanger 21 is sent to the suppression chamber 43. The fourth piping 40 is provided with a choking orifice 42. The choking orifice 42 is the same as the choking orifice 41 provided in the third pipe 39. In addition, the number of the heat exchanger tubes 22 of the water-cooled heat exchanger 21 can be arbitrarily set in consideration of necessary heat removal performance.

2-2. Air Cooling System In this embodiment, the supply pipe 5 of the air cooling system 204 connects the cooling water pool 23 of the water cooling system 203 and the cooling tower 1. That is, in this embodiment, steam generated in the cooling water pool 23 by heat exchange in the water-cooled heat exchanger 21 is supplied to the cooling tower 1 via the supply pipe 5.

  A discharge pipe 7 branches from a position upstream of the flow rate adjustment valve 32 in the supply pipe 5. The discharge pipe 7 discharges a part of the steam supplied from the cooling water pool 23 to the cooling tower 1 through the supply pipe 5 into the atmosphere. The discharge pipe 7 is provided with a flow rate adjusting valve 33. By operating the flow rate adjusting valve 33, the amount of steam released into the atmosphere can be adjusted. For example, the amount of steam supplied to the cooling tower 1 is adjusted by the opening degree of the flow rate adjusting valves 32 and 33. The flow rate adjustment valve 33 may be operated manually as in the case of the flow rate adjustment valve 32, or may be operated by a signal from a central control room (not shown).

  In the air cooling system 204 of the present embodiment, the first pipe 34 and the second pipe 35 are connected to the heat exchanger 13 provided in the reactor pressure vessel 10. In the present embodiment, the fluid to be cooled generated in the reactor pressure vessel 10 in the event of an emergency such as power loss is supplied to the heat transfer tube 3 of the air-cooled heat exchanger 2 through the heat exchanger 13 through the first pipe 34. It is cooled by heat exchange in the cold heat exchanger 2, returned to the heat exchanger 13 through the second pipe 35, and exchanges heat with the cooled fluid generated in the reactor pressure vessel 10. In the present embodiment, the first pipe 34 and the second pipe 35 are provided with a shutoff valve (first valve) 36 and a shutoff valve (second valve) 37. The first valve 36 and the second valve 37 are closed when the nuclear power plant is in a normal operation state, and are opened in an emergency such as loss of power. The first valve 36 and the second valve 37 may be operated manually, or may be operated by a signal from a central control room (not shown).

  In the present embodiment, the third pipe 39 is connected to the reactor pressure vessel 10 at a position above the heat exchanger 13. The first pipe 34 is connected to the heat exchanger 13 at a position above the second pipe 35.

(Operation)
This embodiment is used only when necessary, and the cooling fluid is cooled using both the water cooling system 203 and the air cooling system 204 during a period in which the decay heat after the start of use is large. Is used to cool the fluid to be cooled. This will be specifically described below.

  When the first valve 36 and the second valve 37 of the air cooling system 204 are opened, the cooling system 202 is activated. When the first valve 36 is opened, the heat generated in the reactor pressure vessel 10 is supplied to the air-cooled heat exchanger 2 through the heat exchanger 13 through the first pipe 34 and released to the atmosphere. The to-be-cooled fluid cooled by the air-cooling heat exchanger 2 is returned to the heat exchanger 13 through the second pipe 35 and exchanges heat with the steam generated in the reactor pressure vessel 10. In this manner, the decay fluid in the reactor pressure vessel 10 is removed by circulating the fluid to be cooled between the heat exchanger 13 and the air-cooled heat exchanger 2.

  The air whose temperature has risen due to heat exchange of the air-cooling heat exchanger 2 gains buoyancy, rises in the cooling tower 1, and is discharged from the cooling tower outlet 8 into the atmosphere. An amount of air corresponding to the amount of air released from the cooling tower outlet 8 into the atmosphere is newly taken into the cooling tower 1 through the air intake 4.

  On the other hand, the steam generated in the reactor pressure vessel 10 is supplied from the reactor pressure vessel 10 to the heat transfer tube 22 of the water-cooled heat exchanger 21 due to the pressure difference between the inlet of the third pipe 39 and the suppression chamber 43, The heat transfer tube 22 condenses in the heat transfer tube 22. The latent heat generated by the condensation of the steam is transferred to the cooling water 24 of the cooling water pool 23 through the heat transfer pipe 22, and the steam is condensed. The condensed water is sent to the suppression chamber 43 through the fourth pipe 40. In the cooling water pool 23, the cooling water 24 boils and steam is generated. Steam generated in the cooling water pool 23 is guided to the outside of the reactor building 12 through the supply pipe 5 and supplied to the cooling tower 1. If necessary, the flow rate adjusting valves 32 and 33 provided in the supply pipe 5 and the discharge pipe 7 are operated to control the amount of steam supplied to the cooling tower 1 and the remaining steam is released into the atmosphere via the discharge pipe 7. May be released.

  The steam supplied to the cooling tower 1 has a lower density than the air in the cooling tower 1 whose temperature has been raised by heat exchange in the air-cooling heat exchanger 2, and rises in the cooling tower 1 by buoyancy. The steam mixes with air while rising in the cooling tower 1 and is discharged from the cooling tower outlet 8 into the atmosphere. As described in the first embodiment, by supplying a supply fluid having a density lower than that of air to the cooling tower 1, the amount of air taken into the cooling tower 1 is increased and the heat transfer performance of the air cooling system 204 is improved. To do.

  Thereafter, after the supply of steam from the water cooling system 203 is stopped, the reactor containment facility 201 is cooled only by the air cooling system 204.

(effect)
With the above configuration, also in the present embodiment, a supply fluid having a density lower than that of air is supplied into the cooling tower 1, the outlet of the steam supply pipe 5 is installed above the air-cooling heat exchanger 2, and the flow control valve is connected to the supply pipe 5. Since 32 is provided, the same effect as the first embodiment can be obtained. As described above, since the water cooling system 203 is operated by the pressure difference between the third pipe 39 and the suppression chamber 43, there is also a merit that no power source is required in this embodiment. In addition, the following effects can be obtained in the present embodiment.

  In the present embodiment, the water cooling system 203 can be reduced in size because the heat removal performance of the air cooling system 204 is improved and the amount of heat removal is increased. Therefore, the cooling water 24 in the cooling water pool 23 can be saved. Moreover, since the cooling water pool 23 can be reduced in size, the freedom degree of arrangement | positioning of the cooling water pool 23 increases.

  Moreover, the nuclear power plant 200 of this embodiment uses the water cooling system 203 relatively together with the air cooling system 204 in the period with a large decay heat immediately after starting. If the air cooling system 204 is operated independently from the start-up, it is necessary to enlarge the air cooling system 204 in order to ensure certain performance. On the other hand, in this embodiment, the air cooling system 204 can be reduced in size by using the water cooling system 203 with high heat removal performance and cooling the steam efficiently during a period of large decay heat. This also contributes to cost reduction.

  Moreover, in this embodiment, the cooling water pool 23 and the cooling tower 1 are connected by the supply piping 5, and the vapor | steam generated in the cooling water pool 23 is supplied to the cooling tower 1 as a supply fluid. In other words, if there is an existing nuclear power plant equipped with the air-cooled heat exchanger 2 and the water-cooled heat exchanger 21, a cooling system with high heat removal performance can be constructed simply by adding the supply pipe 5, the flow rate adjusting valve 32, and the like. it can.

<Third Embodiment>
(Constitution)
FIG. 3 is a longitudinal sectional view showing a schematic configuration of a configuration example of a nuclear power plant to which the cooling system according to the present embodiment is applied. In FIG. 3, the same parts as those in the second embodiment are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

  This embodiment differs from the second embodiment in that a choking orifice 44 is provided in the supply pipe 5 in place of the flow rate adjustment valve 32. The description will focus on the differences from the second embodiment.

  The inventors of the present application have obtained the following knowledge as a result of intensive studies.

  The inventors of the present invention have a sensitivity with respect to changes in the natural circulation flow rate by supplying steam to the cooling tower 1 with the pressure loss coefficient of the heat transfer tube 3, the height of the cooling tower 1, and the pressure loss coefficient in the cooling tower 1 as parameters. Analysis was performed and the results of FIG. 4 were obtained. FIG. 4 is a diagram illustrating the relationship between the supply amount of steam and the natural circulation flow rate. The horizontal axis represents the ratio of the mass flow rate of steam (steam mass flow rate) supplied to the cooling tower 1 to the mass flow rate of air taken into the cooling tower 1 (air mass flow rate), and the vertical axis represents the air mass flow rate after steam supply. The value divided by the air mass flow before supply is shown. In FIG. 4, the solid line indicates the case where the pressure loss coefficient of the heat transfer tube 3, the height of the cooling tower 1 and the pressure loss coefficient in the cooling tower 1 are set to arbitrary values (hereinafter referred to as reference values) (first case). It shows the change of natural circulation flow. The dotted line shows the change in the natural circulation flow rate when the height of the cooling tower 1 is made higher than the reference value (second case). The change of the natural circulation flow rate in the case (third case) is shown. As shown in FIG. 4, when steam of about 15 to 25% of the air mass flow rate is supplied to the cooling tower 1, the natural circulation flow rate is maximized or increased to some extent in any of the first to third cases. I understand that.

  Since the natural circulation flow rate is determined by the balance between the buoyancy generated in the cooling tower 1 and the pressure loss generated in the cooling tower 1 and the air-cooled heat exchanger 2, it can be predicted in advance. Therefore, for example, in the configuration of the second embodiment, in order to maximize the heat removal performance of the air cooling system 204, the natural circulation flow rate of 15 to 15 predicted by controlling the opening degree of the flow rate adjustment valve 32 of the supply pipe 5 is used. What is necessary is just to supply about 25% of steam to the cooling tower 1.

  In the present embodiment, a choking orifice 44 is provided in the supply pipe 5 instead of the flow rate adjustment valve 32. In this embodiment, the opening area of the choking orifice 44 is set so that steam of about 15 to 25% of the predicted natural circulation flow rate can be supplied to the cooling tower 1. Other configurations are the same as those of the choking orifice 41.

(effect)
When the pressure difference between the upstream side and the downstream side of the choking orifice 44 exceeds the pressure loss when steam passes through the choking orifice 44 at the speed of sound, the flow rate of the steam flowing through the choking orifice 44 becomes constant. Therefore, in this embodiment, the amount of steam supplied to the cooling tower 1 without a power source can be set to a flow rate that maximizes the heat removal amount of the air cooling system. Further, excessive supply of steam to the cooling tower 1 can be suppressed.

<Others>
The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to one having all the configurations described. For example, part of the configuration of one embodiment can be replaced with the configuration of another embodiment. It is also possible to delete and replace a part of the configuration of each embodiment.

  For example, the case where the first valve 36 and the second valve 37 are shut-off valves has been described as an example. However, the essential effect of the present invention is to enhance the heat removal performance of the air-cooled cooling system, and the configuration is not necessarily limited to this configuration as long as the essential effect is obtained. For example, the first valve 36 and the second valve 37 may be switching valves.

  Further, the case where the choking orifices 41 and 42 are provided in the third pipe 39 and the fourth pipe 40 has been described as an example. However, as long as the above-described essential effect of the present invention is obtained, this configuration is not necessarily used. It is not limited. For example, the third piping 39 and the fourth piping 40 may be provided with a flow rate adjusting valve instead of the choking orifices 41 and 42.

DESCRIPTION OF SYMBOLS 1 Cooling tower 2 Air cooling heat exchanger 4 Air intake port 5 Supply piping 6 Supply source 7 Release piping 10 Reactor pressure vessel 11 Reactor containment vessel 21 Water cooling heat exchanger 23 Cooling water pool 32, 33 Flow rate adjustment valves 41, 42 44 Choking orifice 203 Water cooling system

Claims (10)

A cooling tower having an air intake for intake;
An air-cooled heat exchanger housed in the cooling tower and provided on a flow path of intake air in the cooling tower;
A source of fluid having a density lower than that of the intake air provided outside the cooling tower;
A cooling system comprising: a supply pipe for connecting the supply source and the cooling tower and supplying the fluid to the cooling tower. The cooling system of claim 1, wherein
A water cooling system comprising a water cooling heat exchanger and a cooling water pool that houses the water cooling heat exchanger is provided as the supply source,
The cooling system characterized in that the supply pipe connects the cooling water pool and the cooling tower. The cooling system according to claim 1 and claim 2,
The cooling system according to claim 1, wherein the supply pipe is opened at a position above the air-cooling heat exchanger. The cooling system according to claim 2, wherein
A discharge pipe branched from the supply pipe;
A cooling system comprising: a flow rate adjusting valve provided in the supply pipe and the discharge pipe. The cooling system according to claim 2, wherein
A discharge pipe branched from the supply pipe;
A choking orifice provided in the supply pipe;
A cooling system comprising: a flow rate adjusting valve provided in the discharge pipe. The cooling system according to claim 5, wherein
The cooling system is characterized in that the choking orifice is set so that a mass flow rate of a fluid supplied to the cooling tower is 15 to 25% of a mass flow rate of intake air in the cooling tower. A cooling system according to claim 2;
A reactor pressure vessel connected to a water-cooled heat exchanger of the cooling water pool;
A nuclear power plant comprising a reactor containment vessel for housing the reactor pressure vessel.   A cooling method, wherein a fluid having a density lower than that of intake air is supplied to the cooling tower from the outside of the cooling tower that houses the air-cooled heat exchanger. The cooling method according to claim 8, wherein
A cooling method characterized by supplying steam generated by cooling steam generated in a reactor pressure vessel to the cooling tower as the fluid. The cooling method according to claim 9, wherein
A cooling method characterized in that a mass flow rate of steam supplied to the cooling tower is 15 to 25% of a mass flow rate of intake air in the cooling tower.

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