JP2016003901A - Nuclear reactor automatic depressurization system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nuclear reactor automatic depressurization system that depressurizes a reactor pressure vessel even when a total loss of power in a nuclear power plant occurs, and reduces time and cost for the recovery operation.SOLUTION: An automatic depressurization system comprises: an exhaust pipe 4 that communicates with the inside of a reactor pressure vessel 2 through a main steam pipe 3; and an automatic depressurization valve 5 installed on the exhaust pipe 4. The automatic depressurization valve 5 includes a disk 9 located to close a seat 8, a stem 10 that has one end connected to the disk 9, and a fusible-material housing chamber 12 that houses a fusible material 11 for regulating the other end of the stem 10. Liquefaction of the fusible material 11 with a rise in temperature in the exhaust pipe 4 allows the stem 10 and the disk 9 to move, and pressure from the upstream side of the automatic depressurization valve 5 moves the disk 9 to open the seat 8.

Description

  The present invention relates to a boiling water type or pressurized water type nuclear reactor, and more particularly, to an automatic pressure reducing device for reducing the pressure inside a reactor pressure vessel.

  A boiling water type or pressurized water type nuclear reactor is provided with an emergency core cooling system (ECCS: Emergency Core Cooling System) for cooling the core in the event of a loss of coolant accident, for example. The emergency core cooling system for boiling water reactors consists of a high pressure core water injection device that can inject water into a pressure vessel under high pressure, a low pressure core water injection device that can inject water into a pressure vessel under low pressure, and a pressure reduction in the pressure vessel. And an automatic pressure reducing device. The pressure reduction in the pressure vessel by the automatic pressure reducing device promotes the water injection of the high pressure core water injection device and plays the role of accelerating the operation timing of the low pressure core water injection device. On the other hand, an emergency core cooling device for a pressurized water reactor generally has a high pressure core water injection device and a low pressure core water injection device, but does not have an automatic pressure reduction device. However, if the automatic decompression device is provided, it is possible to enjoy the above-described advantages.

  Automatic depressurization devices are generally adapted to operate by electrical means. For this reason, if the in-house power supply of the nuclear power plant is completely lost, the pressure in the pressure vessel cannot be reduced. That is, water injection of the high pressure core water injection device cannot be promoted, and the operation timing of the low pressure core water injection device cannot be advanced.

  Therefore, as an auxiliary automatic pressure reducing device (pressure reducing mechanism), for example, one end side is located inside the reactor pressure vessel (specifically, the upper side of the reactor core) and the other end side is located outside the reactor pressure vessel. And the thing provided with the fusible stopper provided in the one end side of this piping is proposed (refer patent document 1).

  The fusible plug includes a plate that covers the opening at the end of the pipe, and bolts, nuts, collars, and the like that support the plate. The collar is made of a soluble metal (specifically, a metal having a melting point of 300 to 700 ° C., for example). If the high-pressure core water injection device does not operate for some reason and the temperature of the steam in the reactor pressure vessel rises when a loss of coolant accident occurs, the collar melts and the plate opens at the end of the pipe. Detach from (ie, unplug). Thereby, the steam in the reactor pressure vessel is discharged through the piping, and the inside of the reactor pressure vessel is depressurized.

Japanese Patent Laid-Open No. 7-5286

  However, there are the following problems in the above prior art. That is, the color of the fusible plug described in Patent Document 1 cannot be reused if it is melted. For this reason, it is necessary to perform a restoration work for re-installing the collar, which causes labor and cost.

  An object of the present invention is to provide an automatic depressurization device for a nuclear reactor that can depressurize the reactor pressure vessel and reduce the labor and cost of recovery work even when the in-house power supply of the nuclear power plant is completely lost. There is.

  To achieve the above object, the present invention provides an automatic reactor depressurization apparatus comprising an exhaust pipe that communicates directly or indirectly with the inside of a reactor pressure vessel, and an automatic decompression valve provided in the exhaust pipe. The automatic pressure reducing valve accommodates a valve body disposed so as to close a valve seat, a valve stem having one end connected to the valve body, and a fusible material that regulates the other end of the valve stem. A fusible material storage chamber, and if the fusible material is liquefied as the temperature of the exhaust pipe rises, the valve stem and the valve body can be moved by the pressure upstream of the automatic pressure reducing valve. The valve body is configured to move to open the valve seat.

  In the present invention, when a coolant loss accident or the like occurs, if the high pressure core water injection device does not operate for some reason and the temperature of the reactor pressure vessel rises, the temperature of the exhaust pipe also rises. When the fusible material of the automatic pressure reducing valve is heated and liquefied by heat conduction, the valve rod and the valve body are movable. Then, the valve body is moved by the pressure upstream of the automatic pressure reducing valve to open the valve seat. Thereby, the fluid in the reactor pressure vessel is discharged through the exhaust pipe, and the pressure in the reactor pressure vessel is reduced. Therefore, even if the total loss of the on-site power source of the nuclear power plant occurs, the pressure inside the reactor pressure vessel can be reduced.

  Further, the automatic pressure reducing valve can be reused even after the operation. That is, if the upstream side pressure of the automatic pressure reducing valve is low and the temperature of the exhaust pipe decreases, the fusible material solidifies in a state where the valve body is disposed so as to close the valve seat. Therefore, it is not necessary to perform a restoration work for re-installing the parts, and the labor and cost can be reduced.

  According to the present invention, the reactor pressure vessel can be depressurized even when the in-house power source of the nuclear power plant is completely lost. Also, it is possible to reduce the labor and cost of recovery work.

It is the schematic showing the structure of the automatic pressure reduction apparatus of the reactor in one Embodiment of this invention. It is sectional drawing showing the structure of the automatic pressure reducing valve in one Embodiment of this invention.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram showing a configuration of an automatic depressurization device for a nuclear reactor in the present embodiment. FIG. 2 is a sectional view showing the structure of the automatic pressure reducing valve in the present embodiment.

  The automatic pressure reducing device 1 for a nuclear reactor according to this embodiment includes an exhaust pipe 4 branched from a main steam pipe 3 connected to a reactor pressure vessel 2, an automatic pressure reducing valve 5 provided in the exhaust pipe 4, and a remote operation. And an on-off valve 6 of a type (specifically, mechanical type or electric type). Normally, the automatic pressure reducing valve 5 is closed and the on-off valve 6 is open. In this embodiment, the on-off valve 6 is provided on the upstream side of the automatic pressure reducing valve 5, but may be provided on the downstream side of the automatic pressure reducing valve 5.

  The automatic pressure reducing valve 5 includes a body (valve box) 7 that forms a flow path, a seat (valve seat) 8 that is formed in the flow path, and a disk (valve element) 9 that is disposed so as to close the seat 8. And a stem (valve rod) 10 whose one end side (lower side in FIG. 2) is connected to the disk 9, and a fusible material 11 (in this embodiment) that regulates the other end side (upper side in FIG. 2) of the stem 10 And a fusible material storage chamber 12 in which a metal having a relatively low melting point is stored. One specific example of the fusible substance 11 is a lead-bismuth alloy whose melting point can be changed within a range of 120 to 800 ° C. depending on its metal composition. In the present embodiment, the melting point of the fusible material 11 is set to about 600 ° C.

  And if the reactor pressure vessel 2 is normal temperature (for example, about 273 ° C.) and the main steam pipe 3 and the exhaust pipe 4 are also normal temperature, the fusible material 11 of the automatic pressure reducing valve 5 remains solid. Therefore, since the fusible material 11 restricts the movement of the stem 10 (that is, the movement of the disk 9), the disk 9 remains in the state where the seat 8 is closed regardless of the vapor pressure upstream of the automatic pressure reducing valve 5. Become.

  On the other hand, for example, when a coolant loss accident occurs, if the high pressure core water injection device does not operate for some reason and the temperature of the reactor pressure vessel 2 rises, the temperatures of the main steam pipe 3 and the exhaust pipe 4 also rise. When the fusible material 11 is heated and liquefied by heat conduction, the stem 10 and the disk 9 are movable. Then, the disk 9 is lifted by the vapor pressure upstream of the automatic pressure reducing valve 5 to open the seat 8. As a result, the steam in the reactor pressure vessel 2 is discharged to the suppression chamber (pressure suppression chamber) 13 through the exhaust pipe 4 to depressurize the reactor pressure vessel 2. If the pressure in the reactor pressure vessel 2 (that is, the steam pressure on the upstream side of the automatic pressure reducing valve 5) is sufficiently reduced, the disk 9 falls due to its own weight and closes the seat 8 (check valve function). .

  As described above, in the present embodiment, the reactor pressure vessel 2 can be depressurized even when the on-site power supply of the nuclear power plant is completely lost. Further, unlike the fusible plug described in Patent Document 1, the automatic pressure reducing valve 5 can be reused even after operation. That is, if the temperature of the exhaust pipe 4 decreases while the vapor pressure on the upstream side of the automatic pressure reducing valve 5 is low, the fusible material 11 is solidified in a state where the disk 9 is disposed so as to close the seat 8. Therefore, it is not necessary to perform a restoration work for re-installing the parts, and the labor and cost can be reduced.

  Further, in this embodiment, when the temperature of the reactor pressure vessel 2 remains high (that is, the automatic pressure reducing valve 5 remains open) and the inside of the reactor pressure vessel 2 is desired to be pressurized again, it can be remotely operated. The valve 6 may be closed. Thereby, repressurization in the reactor pressure vessel 2 can be performed.

  In the above-described embodiment, the case where a metal having a relatively low melting point is used as the fusible material 11 has been described as an example. However, the present invention is not limited to this, and the scope and spirit of the present invention are not deviated. Deformation is possible. That is, for example, a wax or the like may be employed. In this case, the same effect as described above can be obtained.

  In the above embodiment, when the exhaust pipe 4 is provided so as to branch from the main steam pipe 3 connected to the reactor pressure vessel 2 when applied to the boiling water reactor (that is, the reactor pressure vessel). The case where the exhaust pipe 4 is provided so as to indirectly communicate with the inside of the second example) has been described as an example. However, the present invention is not limited to this, and modifications can be made without departing from the spirit and technical idea of the present invention. That is, for example, an exhaust pipe may be provided so as to branch from a main coolant pipe connected to a pressurized water reactor and connected to a reactor pressure vessel. Further, for example, an exhaust pipe may be provided so that one end side is located inside the reactor pressure vessel 2 and the other end side is located outside the reactor pressure vessel 2 (that is, the inside of the reactor pressure vessel 2 and An exhaust pipe may be provided so as to communicate directly). In these cases, the same effect as described above can be obtained.

DESCRIPTION OF SYMBOLS 1 Automatic pressure-reduction apparatus 2 Reactor pressure vessel 4 Exhaust pipe 5 Automatic pressure-reduction valve 6 Remote operation type on-off valve 9 Valve body 10 Valve rod 11 Fusible material 12 Fusible material storage chamber

Claims (3)

In an automatic depressurization device for a reactor, comprising an exhaust pipe communicating directly or indirectly with the inside of a reactor pressure vessel, and an automatic depressurization valve provided in the exhaust pipe,
The automatic pressure reducing valve is
A valve body disposed so as to close the valve seat; a valve rod having one end connected to the valve body; and a fusible material storage chamber containing a fusible material that restricts the other end of the valve rod. And
If the fusible material is liquefied as the temperature of the exhaust pipe rises, the valve rod and the valve body can be moved, and the valve body is moved by the pressure on the upstream side of the automatic pressure reducing valve, so that the valve seat An automatic depressurization device for a nuclear reactor characterized in that it is configured to open the reactor. The automatic depressurization device for a nuclear reactor according to claim 1,
The automatic decompression device for a nuclear reactor, wherein the fusible material is a lead-bismuth alloy. The automatic depressurization device for a nuclear reactor according to claim 1,
An automatic depressurization device for a nuclear reactor, comprising a remotely operated on-off valve provided in the exhaust pipe.

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