JP2014137239A - Cooling device of spent fuel pool and cooling method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for passively cooling a spent fuel pool, which can easily be additionally installed in even an existing plant without reducing a preservation space for spent fuel.SOLUTION: A cooling device 10 for a spent fuel pool includes: a coolant which is liquid when pool water 12 for removing decay heat of a spent fuel 11 is at a normal set temperature, and is evaporated at a temperature higher than the normal set temperature; a heat receiving part 20 which holds the coolant and is immersed in the pool water 12; a transfer circuit 14 which transfers a coolant 25 evaporated in the heat receiving part 20 to a heat dissipation part 13; a return circuit 15 which returns a liquid coolant 26 condensed in the heat dissipation part 13 to the heat receiving part 20.

Description

  Embodiments of the present invention relate to a technique for passively cooling pool water from which decay heat of spent fuel has been removed without using external power.

Spent fuel used in the nuclear reactor is temporarily stored in a storage pool filled with pool water in order to remove the decay heat generated.
The pool water heated by absorbing the decay heat is cooled and the water quality is maintained by an existing fuel pool cooling and filtering system (FPC).

  By the way, when the situation where the external power supply including emergency is lost occurs and the fuel pool cooling and purification system (FPC) becomes unusable, the pool water continues to rise in temperature and is lost due to evaporation, and the spent fuel collapses. Heat cannot be removed.

In this way, assuming a case where the fuel pool cooling and purification system becomes unusable, a technique for cooling pool water has been studied even in a situation where external power cannot be used.
Specifically, a technique for installing a heat transfer pipe and releasing the heat in the storage pool to the outside has been proposed (for example, Patent Document 1).

JP-A-6-294891

However, according to the above-described known technique, a large amount of installation space for the heat transfer pipe is used inside the storage pool, and the storage space for spent fuel is reduced.
In addition, there is a concern about the increase in the amount of construction work when it is added to the existing plant.
Furthermore, when the upper space of the spent fuel storage pool is occupied by a part of the heat transfer pipe, there are design restrictions to avoid interference with the crane handling the fuel assembly.

  The present invention has been made in view of such circumstances, and provides a passive cooling technique for a spent fuel pool that can be easily added to an existing plant without reducing the storage space for spent fuel. The purpose is to do.

  In the spent fuel pool cooling device, when the pool water for removing decay heat of the spent fuel is at a normal set temperature, the liquid shows a liquid state and vaporizes at a temperature exceeding the normal set temperature, and holds the refrigerant A heat receiving part immersed in the pool water, a transfer circuit for transferring the refrigerant vaporized in the heat receiving part to the heat radiating part, and a return circuit for returning the liquid refrigerant condensed in the heat radiating part to the heat receiving part. .

  The embodiment of the present invention provides a passive cooling technique for a spent fuel pool that can be easily added to an existing plant without reducing the storage space for spent fuel.

The block diagram which shows embodiment of the cooling apparatus of the spent fuel pool which concerns on this invention. (A) The block diagram which shows embodiment of the heat receiving part applied to the cooling device of a spent fuel pool, (B) Sectional drawing of the heat exchanger tube which comprises a heat receiving part. The flowchart explaining operation | movement of the cooling device of the spent fuel pool which concerns on embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, the spent fuel pool cooling device 10 is liquid when the pool water 12 for removing decay heat of the spent fuel 11 is at a normal set temperature, and vaporizes at a temperature exceeding the normal set temperature. And the heat receiving part 20 that holds the refrigerant and is immersed in the pool water 12, the transfer circuit 14 that transfers the refrigerant 25 vaporized in the heat receiving part 20 to the heat radiating part 13, and the heat radiating part 13 is condensed. And a return circuit 15 that returns the liquid refrigerant 26 to the heat receiving unit 20.

Spent nuclear fuel discharged from the nuclear reactor is accommodated in units of fuel assemblies in a fuel rack in which a plurality of square tubes are arranged in a grid. And it cools for a certain period in the storage pool 18 until radiation and decay | disintegration heat decay.
The spent fuel 11 shown in FIG. 1 shows a state where a plurality of spent fuel assemblies (not shown) are accommodated in a fuel rack and arranged at the bottom of the storage pool 18.

The fuel assembly is hung by a crane (not shown) provided at the upper part of the storage pool 18 and is taken in and out of the fuel rack.
The storage pool 18 is provided with a fuel pool cooling and purification system (FPC: not shown) for cooling the pool water 12 that rises in temperature by absorbing the decay heat of the spent fuel 11.
This fuel pool cooling and purification system (FPC) is normally set so that the temperature of the pool water 12 is about 50 ° C. and about 65 ° C. or less even when an abnormality occurs.

By the way, when the power supply is lost due to damage such as natural disasters and the function of the fuel pool cooling and purification system (FPC) is lost, the pool water 12 evaporates due to decay heat, and the spent fuel 11 exposed to the air further increases in temperature. There is a risk of damage.
The cooling device 10 according to the present embodiment performs cooling of the pool water 12 whose temperature has been increased without requiring external power even when the power supply is lost in this way.

In the present embodiment, water is used as the refrigerant held inside the heat receiving unit 20.
The internal pressure of the heat receiving unit 20 is reduced by the pressure reducing circuit 30 so that the refrigerant water being held is vaporized at a temperature lower than the boiling temperature of the pool water 12.
In addition, the refrigerant | coolant hold | maintained inside the heat receiving part 20 is not limited to water, If the pool water 12 is liquid and shows vaporization at the temperature exceeding this normal setting temperature, when it is normal setting temperature, Are employed as appropriate.
In addition, when a refrigerant boiling at a temperature sufficiently lower than the boiling point (100 ° C.) of the pool water 12 is employed at atmospheric pressure, the decompression circuit 30 can be omitted.

The heat receiving part 20 is provided in the gap between the inner wall of the storage pool 18 and the spent fuel 11 so as to be immersed in the pool water 12.
And the heat receiving part 20 and the storage pool 18 are being fixed by the fixing member 27 in the bottom part.

As a result, the heat receiving section 20 can be additionally installed without extracting the spent fuel 11 in the existing nuclear power plant, and the operation of the crane above the storage pool 18 is not hindered.
Furthermore, since the gap between the inner wall of the storage pool 18 and the spent fuel 11 is eliminated, the horizontal earthquake resistance is also improved.

  As shown in FIG. 2 (A), the heat receiving section 20 is connected to a plurality of heat transfer tubes 21 arranged in the vertical direction and the lower ends of the plurality of heat transfer tubes 21 and connected to the return circuit 15. A liquid header 22 and a steam header 23 that connects the upper ends of the plurality of heat transfer tubes 21 and is connected to the transfer circuit 14 are provided.

The inside of the heat transfer tube 21 is filled with a liquid refrigerant, which absorbs heat from the pool water 12 and boils. And the boiled vapor | steam raises the inner side of the several heat exchanger tube 21 which aligns a longitudinal direction up and down.
In addition, as shown in the cross-sectional view of FIG. 2B, the heat transfer tube 21 is provided with fins 24 on its outer surface for increasing the contact area with the pool water 12.

Thereby, since the amount of heat transfer from the pool water 12 to the heat transfer tube 21 is increased, the heat removal from the pool water 12 that has reached a high temperature can be efficiently performed.
The fins 24 are preferably provided in a vertical shape so that the circulation of the pool water 12 around the heat transfer tubes 21 is not hindered.

The condensate header 22 receives the liquid refrigerant 26 returned from the heat radiating unit 13 via the return circuit 15, and distributes and supplies this refrigerant to the plurality of heat transfer tubes 21 connected and connected.
The steam header 23 joins the refrigerant 25 (steam) boiled and vaporized inside the plurality of connected heat transfer tubes 21, and transfers the steam to the heat radiating unit 13 via the transfer circuit 14.

In addition, each of the heat exchanger tube 21, the condensate header 22, and the steam header 23 is stored and fixed inside a rack (not shown).
Thus, since the main components are integrated, the heat receiving unit 20 is easily installed in the gap between the inner wall of the storage pool 18 and the spent fuel 11 without extracting the spent fuel 11 in an existing nuclear power plant. be able to.

The heat dissipating unit 13 has an upper end connected to the transfer circuit 14 and inputs the vaporized refrigerant 25 (steam) transferred from the heat receiving unit 20 to be air-cooled.
The latent heat of the air-cooled vapor is released to the outside by the heat dissipating unit 13, condenses and becomes a liquid refrigerant 26, and moves downward by gravity.
The condensed liquid refrigerant 26 is returned to the heat receiving unit 20 via the return circuit 15 connected to the lower end of the heat radiating unit 13.

The cover 16 is provided so as to cover the heat radiating portion 13 and has a lower opening 34 and an upper opening 35.
Inside the cover 16, an ascending air current 19 that flows from the lower opening 34 to the upper opening 35 is generated due to the chimney effect based on heat exchange with the heat radiating portion 13.
The rising airflow 19 efficiently cools the heat dissipating part 13, and all of the introduced steam is condensed into a liquid refrigerant 26 and further cooled.

The transfer circuit 14 and the return circuit 15 are fixed to the peripheral portion of the storage pool 18 by a fixing member 28, and are divided into parts connected to the heat receiving part 20 and parts connected to the heat radiating part 13. Connected by a flange 17.
By having such a connection structure, the heat receiving unit 20 can be integrated with the transfer circuit 14 and the return circuit 15.
As a result, the cooling device 10 can be easily installed in the existing nuclear power plant without extracting the spent fuel 11.

  In the decompression circuit 30, the decompression pump 31 that decompresses the pressure applied to the refrigerant held in the heat receiving unit 20, and the decompression circuit 30 is changed from the open state to the closed state in conjunction with the stop of the decompression pump 31 due to the loss of power. An on-off valve 32 and a throttle valve 33 that adjusts the opening so that the pressure value is included in the set range during pressure reduction are provided.

When the on-off valve 32 operates in an open state, the decompression pump 31 decompresses the system in the heat radiating unit 13, the transfer circuit 14, and the heat receiving unit 20 to a pressure lower than the atmospheric pressure. Thereby, the boiling point of the refrigerant | coolant hold | maintained at the heat receiving part 20 falls.
In order to set the boiling point of the refrigerant in the system, the opening of the throttle valve 33 is adjusted so that the pressure value of the reduced pressure is included in the setting range.

When a power loss occurs, as the power supply is stopped, the decompression pump 31 is stopped and the on-off valve 32 is also closed.
Then, the system of the heat radiating unit 13, the transfer circuit 14, the return circuit 15 and the heat receiving unit 20 is hermetically sealed while maintaining the set reduced pressure state.
Then, due to the decay heat of the spent fuel 11, the temperature of the pool water 12 rises, and when the refrigerant reaches the set boiling point, the pool water 12 is removed by boiling and vaporizing the refrigerant in the heat receiving unit 20.

The operation of the spent fuel pool cooling device according to the embodiment will be described with reference to FIG. 3 (see FIG. 1 as appropriate).
First, in a normal state in which the nuclear reactor plant is operating normally (S11 to S14: No), the on-off valve 32 is set to an open state (S11), and the decompression pump 31 is operating (S12).
Then, the opening of the throttle valve 33 is adjusted so that the pressure value in the system is included in the setting range (S13), and the boiling temperature of the refrigerant in the heat receiving unit 20 is set.

Then, it is assumed that an emergency occurs (S14: Yes) and the fuel pool cooling and purification system (FPC) is stopped due to the loss of power (S15: Yes).
Then, with this power loss, the decompression pump 31 is stopped (S16), and the on-off valve 32 is also closed (S17).
When the temperature of the pool water 12 rises due to the decay heat of the spent fuel 11 (S18: No) and exceeds the normal set temperature (S18: Yes), the liquid refrigerant held in the heat receiving unit 20 is vaporized. Start (S19).

By the vaporization of the refrigerant, the pool water 12 is removed from heat (S20), and the vaporized refrigerant is transferred to the heat radiating portion 13 via the transfer circuit 14 (S21) and condensed to be a liquid refrigerant ( (S22) and returned to the heat receiving unit 20 (S23).
Then, the flow of (S19) to (S23) is repeated until the operation of the fuel pool cooling and purification system (FPC) is recovered (S15: No).

  According to the spent fuel pool cooling device of at least one embodiment described above, the heat receiving part immersed in the pool water and the air cooling type heat radiating part are connected by a closed loop circuit, so that passive power is not required. Thus, it becomes possible to cool the pool water.

  Although the embodiments of the present invention have been described, these embodiments are presented as examples, and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10 ... Cooling device, 11 ... Spent fuel, 12 ... Pool water, 13 ... Radiation part, 14 ... Transfer circuit, 15 ... Return circuit, 16 ... Cover, 17 ... Flange, 18 ... Storage pool, 19 ... Updraft, 20 DESCRIPTION OF SYMBOLS ... Heat-receiving part, 21 ... Heat exchanger tube, 22 ... Condensate header, 23 ... Steam header, 24 ... Fin, 25 ... Evaporated refrigerant, 26 ... Liquid refrigerant, 27, 28 ... Fixed member, 30 ... Decompression circuit, 31 ... Depressurization pump, 32 ... open / close valve, 33 ... throttle valve, 34 ... lower opening, 35 ... upper opening.

Claims (10)

A refrigerant that shows liquid when the pool water that removes decay heat of spent fuel is at a normal set temperature and vaporizes at a temperature exceeding the normal set temperature;
A heat receiving part that holds the refrigerant and is immersed in the pool water;
A transfer circuit for transferring the refrigerant vaporized in the heat receiving part to the heat radiating part;
A spent fuel pool cooling apparatus, comprising: a return circuit that returns the liquid refrigerant condensed in the heat radiating unit to the heat receiving unit.   The spent fuel pool cooling device according to claim 1, further comprising a decompression circuit including a decompression pump that decompresses an atmospheric pressure applied to the refrigerant held in the heat receiving unit.   The spent fuel pool cooling device according to claim 2, wherein the decompression circuit further includes an on-off valve that switches the decompression circuit from an open state to a closed state in conjunction with a stop of the decompression pump due to power loss.   4. The spent fuel pool cooling device according to claim 2, wherein the decompression circuit further includes a throttle valve that adjusts an opening degree so that a pressure value is included in a set range during the decompression. 5.   The spent heat pool cooling device according to any one of claims 1 to 4, wherein the heat receiving unit is provided in a gap between an inner wall of the pool that stores the pool water and the spent fuel. The heat receiving part is
A plurality of heat transfer tubes arranged vertically and vertically,
A condensate header connecting the lower ends of the plurality of heat transfer tubes and connecting to the return circuit;
The spent fuel pool cooling device according to any one of claims 1 to 5, further comprising: a steam header that connects upper ends of the plurality of heat transfer tubes and is connected to the transfer circuit.   The spent fuel pool cooling device according to claim 6, wherein fins for expanding a contact area with the pool water are provided on an outer surface of the heat transfer tube.   The spent fuel pool cooling device according to any one of claims 1 to 7, wherein a cover for generating an updraft by heat exchange with the heat radiating portion is disposed.   The used part according to any one of claims 1 to 8, wherein the transfer circuit and the return circuit are formed by flange-connecting a part connected to the heat receiving part and a part connected to the heat radiating part. Fuel pool cooling system. A step in which pool water for removing decay heat of spent fuel exceeds a normal set temperature;
A step of vaporizing the liquid refrigerant held in the heat receiving part immersed in the pool water;
Transferring the vaporized refrigerant to a heat dissipation unit;
Returning the liquid refrigerant condensed in the heat radiating section to the heat receiving section.

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