JP2517034B2 - Decay heat removal device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a decay heat removal apparatus for a nuclear reactor, and more specifically, to a heat exchanger for transferring heat generated in the core to a secondary system and a heat exchanger. The present invention relates to a decay heat removal device combined with a pipe.

[Conventional technology]

A decay heat removal device that removes decay heat after a reactor shutdown is
Generally, it is composed of a circulation pump and a cooler.

Further, as described in JP-A-58-118988, there has been proposed a method of removing decay heat after a reactor shutdown by using a heat pipe without using a dynamic device such as a circulation pump.

In addition, A.N.S., Transactions 47
Volume (1984) pp. 292-293 (ANS, Trans., Vol.47
(1984) p292-293),
A method of directing the vapor of the primary system directly to the condenser has also been proposed.

[Problems to be solved by the invention]

However, among the above-mentioned conventional techniques, the decay heat removal device including the circulation pump and the cooler inevitably requires a large-scale emergency power source to drive the circulation pump.

Further, in the conventional decay heat removal device using a heat pipe, the heat generating part of the heat pipe is inserted into the furnace, so that the structure of inserting the heat generating part of the heat pipe into the furnace becomes complicated. At the same time, the furnace container must be enlarged.

Furthermore, in the decay heat removal device that directly guides the vapor of the primary system to the condenser, the number of pipes that should be assumed to break increases, and with the purpose of absorbing the decay heat, a large capacity A cooling water pool is required.

An object of the present invention is to provide a decay heat removal apparatus that is simple in equipment by effectively utilizing the existing equipment of a conventional reactor and is also excellent in reliability in terms of decay heat removal after a reactor shutdown. To do.

[Means for solving problems]

The purpose is to contain a nuclear fuel, a heat exchanger for transferring heat generated in the core to a secondary system, a water supply drum arranged upstream of the heat exchanger, and a water supply for supplying water to the water supply drum. In a nuclear reactor equipped with a pipe and a main steam pipe arranged downstream of the heat exchanger to discharge steam generated in the heat exchanger, above the water supply drum of the heat exchanger, the heat branched from the water supply drum. This is achieved by providing a pipe and a control device that closes the valve of the water supply pipe after the reactor is shut down and closes the valve of the main steam pipe after the water level in the heat pipe drops below a set value.

[Action]

In the above structure, so-called subcooled water having a saturation temperature or lower flows into the water supply drum of the heat exchanger during normal operation of the reactor. Then, the water receives heat from the core through the heat transfer tubes of the heat exchanger, boils into steam, and is guided to the steam turbine through the steam drum.

Thus, in the present invention, the heat pipe is installed above the water supply drum of the heat exchanger as described above,
When the inside of the heat pipe is degassed to be filled with water at the initial stage, after that, the pressure loss on the heat exchanger side is larger than the hydrostatic head in the heat pipe, so that the filled state is maintained.

When the valve of the water supply pipe is closed after the reactor is stopped, the cooling water in the heat transfer pipe continues to boil due to the decay heat of the core, but part of the generated steam rises due to buoyancy, cooling the heat pipe. Replace with water. Since the condensing part of the heat pipe is installed in the cooling water pool outside the containment vessel, when the water level in the heat pipe drops and almost reaches the position of the water supply drum, the valve of the main steam pipe is closed. After that, the heat generated in the core is conducted from the heat exchanger to the cooling water pool outside the containment vessel through the heat pipe.

〔Example〕

Hereinafter, the present invention will be described based on one embodiment of FIG. 1 and FIG. 2. FIG. 1 is an overall configuration explanatory view of a decay heat removal device according to the present invention, and FIG. It is a figure which shows the time-dependent behavioral change of the coolant in the heat exchanger and the heat pipe part shown by numerals 4 and 20.

In FIG. 1, a core 2 loaded in a pressure vessel 1
Is surrounded by shell 3. The steam generated in the core 2 is condensed on the surface of the heat transfer tube of the heat exchanger 4, and transfers the steam heat to the cooling water inside the heat transfer tube. The cooling water flows into the heat exchanger 4 from the water supply pipe 10 through the water supply drum 11, but is boiled by the heat from the core 2 in the heat exchanger 4 and becomes steam. This steam is guided from the steam drum 12 through the main steam pipe 13 to the steam turbine 14, and power is generated by a generator 15 driven by the steam turbine 14. The steam that has left the steam turbine 14 is condensed in the condenser 16 to return to water, is driven by the pump 17, and is guided to the water supply pipe 10.

Therefore, in the present invention, the heat pipe 20 is connected above the water supply drum 11 in the heat exchanger 4 portion, and in FIG. 1, 21 is a differential pressure gauge for measuring the water level in the heat pipe 20, 22 and 23 are valves for isolating the heat exchanger 4, one valve 22 of which is provided in the middle of the water supply pipe 10. The other valve 23 is connected in the middle of the main steam pipe 13.

In the above configuration, the non-condensable gas in the heat pipe 20 is discharged to the outside by a water pressure from a discharge valve (not shown) provided in the upper part of the heat pipe 20 before the operation of the nuclear reactor is started.

During normal reactor operation, the pressure loss ΔP _F when the cooling water passes through the heat exchanger 4 is larger than the static water head ΔP _SH in the heat pipe 20, so , The cooling water is full.

On the other hand, if the reactor core 2 is scrammed due to a loss of cooling water and the reactor operation is stopped, the amount of heat generated in the reactor core 2 is rapidly reduced, and the amount of steam generated in the heat exchanger 4 is also reduced. Due to the decrease, the steam turbine 14 cannot continue to rotate, the feed water pump 17 also stops, and the steam turbine 14 and the feed water pump 17 are separated from the heat exchanger 4. In such a case, In this embodiment, the heat pipe 20 is activated as shown in FIG.

That is, FIG. 2 (a) shows the flow state of the coolant during the normal operation of the reactor, in which the cooling water flowing into the heat exchanger 4 with a subcooling degree is heated in that portion,
It boils and forms steam and then comes out. After shutting down the reactor, first, as shown in FIG. 2 (b), the valve 22 is closed,
In the core 2 portion of FIG. 1, since the heat generation by the fission products continues, the cooling water in the heat exchanger 4 continues to boil. Then, part of the steam generated as described above rises in the heat pipe 20 due to buoyancy, and the cooling water in the heat pipe 20 is gradually replaced with the steam. When the water level in the heat pipe 20 reaches a set level (for example, the lower end of the heat pipe 20), the valve 23 is closed, as shown in FIG. The heat generated in the core is efficiently emitted to the outside through the heat generating portion of 20. This concrete control method will be described with reference to FIG. 1. In FIG. 1, the scrum signal of the core 2 and the stop signal of the feedwater pump 17 are sent to the main controller 25, and both signals are sent. When the main controller 25
Sends a signal to the valve switch 26 to close the valve 22. Further, the water level in the heat pipe 20 is obtained from the signal of the differential pressure gauge 21 and the signal of the pressure gauge 24 by density correction in the calculator 28, and the signal is sent to the main controller 25. When the water level reaches a set value (for example, the lower end of the heat pipe 20), the valve 23
Is sent to the valve opening / closing device 27, and after that, the second
As described in FIG. (C), the heat generated in the core is efficiently sent from the heat exchanger 4 to the cooling water pool 29 located outside the containment vessel 5 through the heat pipe 20. For a plant with a heat output of 2000 MW, 10
When considering a decay heat removal device that removes decay thermal 42 MW after minutes, assuming that the inner diameter of the heat pipe 20 is 8 cm, the number of heat pipes 20 is calculated from the limitation of the heat transport amount due to the scattering limit. Approximately 150 units are required, and during normal operation of the reactor, heat is released to the outside by natural convection inside the heat pipe, but the value is small at about 0.6 MW.

Also, in an actual plant, several heat exchangers are installed, but since the heat transfer area of the heat exchanger is large, the decay heat removal device according to the present invention described above is used for one heat exchanger. According to the present invention, there is an effect that the facility can be simplified by effectively utilizing the heat exchanger, which is a normal reactor system, as a part of the decay heat removal device. Since a circulation pump, which is a mechanical device, is unnecessary,
By making this type of device passivating, it is possible to provide a decay heat removal device which is reliable and has no failure.

FIG. 3 is a diagram for explaining the overall configuration of a second embodiment of the device of the present invention, and FIG. 4 is a diagram showing the behavioral change of the coolant in the heat exchanger and the heat pipe portion indicated by reference numerals 4 and 20 in FIG. FIG.

In FIG. 3, the difference from the embodiment shown in FIG.
The heat pipe 20 is a separate type, the steam side pipe 31 is provided above the water supply drum 11, and the cooling water side pipe 32 is provided on the side of the water supply drum 11. In addition, in FIG. 3, the steam side pipe 31,
The cooling water side pipe 32 and the condensing unit 30 are collectively referred to as a heat pipe.

Then, in FIG. 3, the inside of the heat pipe 20 is the same as in the case of the embodiment shown in FIG.
Filled with cooling water. The procedure for opening and closing the valves 22 and 23 after the reactor is shut down is also the same as in the embodiment shown in FIG. 1, and the flow state of the coolant in the heat pipe 20 at this time will be described with reference to FIG. Then, in FIG. 3, the steam generated in the heat exchanger 4 rises due to buoyancy,
As shown in FIG. 4 (a), the water flows from the water supply drum 11 into the steam side pipe 31. Then, when the steam flows into the steam side pipe 31, the still water head in the steam side pipe 31 becomes the cooling water side pipe 32.
And the sum of the static water heads in the condensing part 30 becomes smaller, so the cooling water flows from the cooling water side pipe 32 to the steam side pipe 31 via the water supply drum 11, passes through the condensing part 30, and the cooling water side pipe. 32
The natural circulation is generated, and the steam generated in the heat exchanger 4 is entrained in the natural circulation and is connected to the steam side pipe 31.
As shown in FIG. 4 (b), the inside of the steam side pipe 31 is quickly filled with steam. Steam side piping
When the cooling water runs out in the heat exchanger 31, the steam generated in the heat exchanger 4 rises in the steam side pipe 31 and returns to water in the condensing unit 30, and flows into the water supply drum 11 through the cooling water side pipe 32. In this way, the decay heat generated in the core is efficiently released to the outside.

Thus, in the present embodiment, since the flow paths of steam and water are separated, the heat transfer amount is large, and for example, when removing the decay heat of 42 MW, the inner diameter of the steam side pipe 31 is 15 cm, the cooling water. Assuming that the inner diameter of the side pipe 32 is 5 cm, the number of the above-mentioned pipes 31 and 32 may be 10 in calculation, and in that case, the amount of heat radiated through the pipe during normal reactor operation is about 0.03 MW. Becomes smaller. That is, according to the present embodiment, the steam generated in the heat exchanger 4 is quickly replaced with the cooling water in the heat pipe 20, so that the operation of the heat pipe 20 is quick and the heat transport amount is large. Therefore, the number of pipes is reduced, and the heat radiation during the normal operation of the reactor is also small.

FIG. 5 is an explanatory view of the overall configuration showing a third embodiment of the device of the present invention.

In FIG. 5, the difference from the embodiment shown in FIG.
On the steam side pipe 31 of the heat pipe 20, the discharge pipe 40 and the discharge valve
41 is installed.

Therefore, in the embodiment shown in FIG. 5, after the reactor and the feed water pump are stopped, the valves 22 and 23 are simultaneously closed,
Next, when the discharge valve 41 is opened by the valve switch 42, due to the pressure difference between the steam side pipe 31 and the cooling water pool 29, the steam side pipe 31
The cooling water inside is promptly discharged to the cooling water pool 29, and the water level in the steam side pipe 31 has a certain set value, for example, the steam side pipe 31.
When the discharge valve 41 is closed, the steam generated in the heat exchanger 4 thereafter rises from the water supply drum 11 to the steam side pipe 31 and becomes water in the condensing section 30 to reach the cooling water side. Plumbing 32
The natural circulation from the water to the water supply drum 11 is established, and the decay heat is released to the cooling water pool 29 located outside the containment vessel 5.

That is, according to the present embodiment, since the water level in the steam side pipe 31 is rapidly lowered, the heat pipe constituted by the condenser 30, the cooling water side pipe 32 and the steam side pipe 31 is also quickly operated. be able to.

FIG. 6 is an explanatory diagram of the overall configuration showing a fourth embodiment of the device of the present invention.

In FIG. 6, the difference from the embodiment shown in FIG. 3 is that the steam side pipe 31 of the heat pipe 20 is installed above the steam drum 12, and the check valve 50 is attached to the steam side pipe 31. There is a point.

Therefore, in the embodiment of FIG. 6, during normal reactor operation, the pressure loss ΔP _F when the cooling water passes through the heat exchanger 4 is smaller than the condensation portion 30 and the cooling water side pipe 32. Since it is larger than the sum of the static heads of ΔP _SH , the check valve 50 is still closed, and most of the inside of the steam side pipe 31 is filled with steam (note that It is desirable to sufficiently insulate the steam side pipe 31), and even after the reactor shutdown, most of the inside of the steam side pipe 31 is filled with steam and the static head is small. , The steam generated in the heat exchanger 4, the steam drum 12,
Furthermore, the natural circulation that rises in the steam side pipe 31 and becomes water in the condensing section 30 and returns from the cooling water side pipe 32 to the water supply drum 11 is quickly established.

That is, according to this embodiment as well, the operation of the heat pipe 20 is quick, and since the coolant flows through the heat exchanger 4, the heat removal amount in the heat exchanger 4 portion can be increased.

〔The invention's effect〕

The present invention is as described above, and as is clear from the description of the illustrated embodiments, according to the present invention, by effectively utilizing a heat exchanger, which is a common reactor system, as a part of the decay heat removal apparatus. , Because it has the effect of simplifying the equipment and does not require a circulating pump that is a dynamic device, it has made the decay heat removal device with no failure and excellent reliability by making this kind of device passive. can do.

[Brief description of drawings]

FIG. 1 is an explanatory view of the overall configuration showing an embodiment of the decay heat removal apparatus according to the present invention, and FIG. 2 is a time chart of the coolant in the heat exchanger and the heat pipe portion shown by reference numerals 4 and 20 in FIG. 1, respectively. Showing the change in dynamic behavior, FIG. 3 is an explanatory view of the overall configuration showing the second embodiment of the device of the present invention, and FIG. 4 is cooling in the heat exchanger and heat pipe portions indicated by reference numerals 4 and 20 in FIG. FIG. 5 is a diagram showing the change in behavior of the material over time, FIG. 5 is an overall configuration explanatory diagram showing a third embodiment of the present invention device, and FIG. 6 is an overall configuration explanatory diagram showing a fourth embodiment of the present invention device. is there. 2 ... Reactor core, 4 ... Heat exchanger, 10 ... Water supply piping, 11 ...
Water supply drum, 12 …… Steam drum, 13 …… Main steam pipe, 20
...... Heat pipe, 21 …… Differential pressure gauge, 22,23 …… Valve, 24…
… Pressure gauge, 25 …… Main controller, 26, 27 …… Valve opener, 28…
… Calculator.

Claims (4)

(57) [Claims] 1. A core for containing nuclear fuel, a heat exchanger for transferring heat generated in the core to a secondary system, a water supply drum disposed upstream of the heat exchanger, and water for supplying water to the water supply drum. In a nuclear reactor comprising a water supply pipe and a main steam pipe arranged downstream of the heat exchanger for discharging steam generated in the heat exchanger, above the water supply drum of the heat exchanger, branched from the water supply drum. Decay heat characterized by the provision of a heat pipe and a control device that closes the valve of the water supply pipe after the reactor is shut down and closes the valve of the main steam pipe after the water level in the heat pipe drops below a set value. Removal device. 2. The steam pipe of the heat pipe and the cooling water pipe are separated from each other according to claim 1, the steam pipe is provided above the water supply drum of the heat exchanger, and the cooling water pipe is provided. Decay heat removal device provided on the side of the water supply drum. 3. The discharge pipe according to claim 2, wherein a discharge pipe and a discharge valve are provided above the steam side pipe of the heat pipe, and after the reactor is shut down, the valves of the water supply pipe and the main steam pipe are closed. A decay heat removal device provided with a control device that opens the valve and closes the discharge valve after the water level in the heat pipe drops below a set value. 4. The steam pipe of the heat pipe is provided above the steam drum according to claim 2, and cooling water passes through the heat pipe from the steam drum to the steam pipe of the heat pipe. A decay heat removal device equipped with a check valve that flows only in the direction of the water supply drum.