JPH0447797B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a nuclear reactor shutdown device used as a back-up reactor shutdown device for a gas-cooled nuclear reactor. [Technical Background of the Invention] Generally, a gas-cooled nuclear reactor is constructed as shown in FIGS. 1 and 2. That is, numeral 1 in the figure is a nuclear reactor vessel, and a reactor core 2 is accommodated within this reactor vessel 1. In this core 2, graphite blocks are stacked as a moderator, and fuel rods 3 are loaded in the graphite blocks. A coolant such as helium gas flows into the reactor vessel 1 from the inlet pipe 4, passes through the reactor core 2 from above, is heated, and flows out from the outlet pipe 5. The high-temperature coolant flowing out from the outlet pipe 5 exchanges heat with the external coolant through the heat exchanger 6, and then is returned to the reactor vessel 1 through the inlet pipe 5 by the circulation pump 7. It is configured as follows. Further, a control rod guide tube 8 is inserted into the reactor core 3 from above, and this control rod guide tube 8 is inserted into the reactor core 3 from above.
A control rod 9 is housed inside the core 2 so as to be able to move up and down, and the control rod 9 can be inserted into or pulled out of the core 2.
It is configured to perform output control. This control rod 9 is driven by a control rod drive mechanism 10 . The control rod drive mechanism 10 includes a wire rope 11 connected to a control rod 9, a drum 12 for winding in and letting out the wire rope 11, and a motor 1 for rotationally driving the drum 12.
It is composed of 3. And this motor 13
The drum 12 is driven by the wire rope 11.
It is configured to take in and pay out the control rod 9, and to raise and lower the control rod 9. Further, in this way, the nuclear reactor is provided with a backup reactor shutdown device 14 assuming that the control rods 9 cannot be inserted. Although a plurality of each of the fuel rods 3, control rods 9, control rod drive mechanism 10 , and back-up reactor shutdown device 14 are actually provided, only one of each is shown in FIG. There is. The backup reactor shutdown device 14 has a structure and operating principle different from those of the control rod drive mechanism 10 , so that it will not fail due to the same cause as the control rod drive mechanism 10 . It is configured as follows. The backup reactor shutdown device 14 is constructed as shown in FIG. 2. That is,
In the figure, reference numeral 15 denotes a guide tube, which is inserted into the reactor core 2 from above, and its upper end is open. A neutron absorbing material storage hopper 16 is provided above the guide tube 15. In this neutron absorbing material storage hopper 16, a neutron absorbing material 17 is stored, which is made of a neutron absorbing material such as boron carbide (B ₄ C) formed into particles, such as small spheres. A neutron absorbing material falling port 18 is formed in the lower part of this neutron absorbing material storage hopper 16, and this neutron absorbing material falling port 18 is connected to the guide tube 1.
It faces the upper end opening of 5. This neutron absorbing material falling port 18 is closed by a labyrinth disk 19. Further, one end of a high pressure gas supply pipe 20 is connected to the inside of the neutron absorbing material storage hopper 16, and the other end of this high pressure gas supply pipe 20 is connected to a high pressure gas supply source 22 via an on-off valve 21. When the backup reactor shutdown device 14 is to be operated, the on-off valve 21 is opened and high pressure gas is supplied from the high pressure gas supply source 22 into the neutron absorbing material storage hopper 16. The yard disk 19 is broken, and the small spherical neutron absorber 17 is dropped from the neutron absorber drop port 18 into the guide tube 15, and the reactor is stopped. In this case, since the neutron absorbing material 17 is small spherical, the graphite block of the reactor core 2 may shift due to an earthquake, etc., and the guide tube 15
Even if it is slightly deformed, it will surely fall into this guide tube 15. [Problems with the Background Art] In the conventional back-up reactor shutdown device 14 described above, repeated loads act on the rupture disk 19 due to fluctuations in reactor pressure, and the rupture disk 1
There is a possibility that the neutron absorbing material 17 may suffer fatigue failure, or may be damaged due to corrosion or deterioration of the material due to neutron irradiation.In such a case, the neutron absorbing material 17 may fall into the guide tube 15, and the reactor may stop unexpectedly. Also, Rapture Disc 19
If a crack occurs in the rupture disk 1, a leak will occur when high pressure gas is supplied, and this rupture disk 1
9 may not be able to be broken. Furthermore, if the rupture disk 19 breaks, the breakage may fall into the core 2 and block the coolant passage within the core 2. Furthermore, the biggest drawback of using such a rupture disk 19 is that it is not possible to conduct an operation test while the reactor is operating. That is, such a backup reactor shutdown device 1
4 does not operate normally, but must operate reliably when operation is required. Therefore, it is desirable to frequently test the operation of such devices to ensure their reliability.
However, if such a device is subjected to an operation test, the rupture disk 19 will break, the neutron absorber 17 will fall into the guide tube 15, and the reactor will stop, so the operation test must be carried out while the reactor is operating. cannot be implemented. Furthermore, after performing the operation test, the Lapture Disk 19 must be replaced with a new one, which is a cumbersome work, and the removed Lapture Disk 19 must be disposed of as solid radioactive waste. Processing was troublesome. Further, even when an operation test was conducted when the nuclear reactor was shut down, it was troublesome to replace the rupture disk after the test, collect the neutron absorbing material that had fallen into the guide tube, etc., and the work was inefficient. [Purpose of the Invention] The present invention was made based on the above circumstances, and its purpose is to prevent malfunctions and to perform operation tests at any time regardless of whether the reactor is in operation or stopped. The objective is to obtain a nuclear reactor drive mechanism that can be easily repaired after testing. [Summary of the Invention] A nuclear reactor shutdown device according to the present invention includes: a guide tube inserted into the reactor core from above; a neutron absorber storage hopper provided above the guide tube and having a neutron absorber drop port at the lower end; A valve body that is provided in the neutron absorbing material storage hopper so as to be movable up and down and that closes the neutron absorbing material falling port, a drive unit that drives the valve body up and down in the vertical direction, and a position detector that detects the position of the valve body. The drive unit includes a drive motor, a ball screw shaft that is rotationally driven by the drive motor, and a ball nut that is connected to the valve body via a connecting rod and converts rotation of the ball screw into linear motion. and an electromagnetic brake that applies a braking force to the ball screw shaft to stop the valve body from moving up and down. That is, when the reactor is in normal operation, the neutron absorbing material falling port is closed by the valve body, and the neutron absorbing material in the neutron absorbing material storage hopper does not fall into the reactor. When an emergency situation occurs and the reactor is to be shut down, the valve body is raised by the drive unit and the neutron absorbing material in the neutron absorbing material storage hopper is dropped into the reactor from the neutron absorbing material falling port. Further, during the operation test, the vertical position of the valve body is detected by a position detector, and the valve body is moved up and down by the drive unit within a range that does not completely separate from the neutron absorbing material drop port. Therefore, since the operation test can be performed without dropping the neutron absorbing material into the reactor, the operation test can be performed not only when the reactor is shut down but also when it is in operation. As a result, normal functions can be maintained at all times, and reliability can be improved. In addition, unlike the conventional rupture disk, which causes the neutron absorbing material to fall by breaking under a certain pressure, the strength of components such as valve bodies and connecting rods can be made sufficiently strong, which can be used to prevent fluctuations in reactor pressure, neutron irradiation, etc. Damage caused by this can be prevented and malfunctions can be eliminated, and since the valve body protection tube is provided, the valve body can be moved up and down smoothly. Even during operation tests, the neutron absorbing material does not fall into the reactor, and no debris is generated, so there is no need for conventional work such as replacing the rupture disk. Repairs are easier, and there is no need to dispose of solid radioactive waste, so work efficiency can be significantly improved. Further, since conventional high-pressure gas supply equipment, piping, etc. are not required, costs can also be reduced. [Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 3 to 8. In the figure, 101 is a nuclear reactor vessel, and a reactor core 102 is accommodated within this reactor vessel 101.
In this core 102, graphite blocks are stacked as a moderator, and fuel 103 is loaded in the graphite blocks. Then, a coolant such as helium gas flows into the reactor vessel 101 from the inlet pipe 104, passes through the reactor core 102, is heated, and is heated by the outlet pipe 104.
It is configured to flow out from 5. and,
The high-temperature coolant flowing out from the outlet pipe 105 exchanges heat with an external coolant via a heat exchanger 106 and is then returned to the reactor vessel 101 from the inlet pipe 104 by a circulation pump 107. It is configured. Further, a control rod guide tube 108 is inserted into the reactor core 102 from above, and a control rod 109 is accommodated in the control rod guide tube 108 so as to be able to move up and down.
It is configured to control the output of the reactor core 102 by being inserted into or pulled out of the reactor core 102. This control rod 109 is driven by a control rod drive mechanism 110. This control rod drive mechanism 110 includes a wire rope 111 connected to the control rod 109,
It is composed of a drum 112 for winding in and letting out the wire rope 111, and a motor 113 for rotating the drum 112. The motor 113 drives the drum 112, winds in and lets out the wire rope 111, and moves the control rod 109 up and down. In addition, in such a reactor, the control rod 1 is
A back-up reactor shutdown device 114 is provided assuming that the reactor 09 cannot be inserted. In addition, the fuel rod 103, control rod 109, control rod drive mechanism 1
Although a plurality of each of 10 and backup reactor shutdown device 114 are actually provided, only one of each is shown in FIG. The backup reactor shutdown device 114 has a structure and operating principle different from those of the control rod drive mechanism 110, so that it will not fail due to the same cause as the control rod drive mechanism 110. It is configured as follows. The backup reactor shutdown system 114 is constructed as shown in FIGS. 4 to 8. That is, in the figure, reference numeral 115 is a guide tube that is inserted into the core 102 from above, and its upper end is open. A neutron absorbing material storage hopper 116 is provided above the guide tube 115. And this neutron absorbing material storage hopper 1
A neutron absorbing material 117 in which a neutron absorbing material such as boron carbide (B ₄ C) is formed into particles, such as small spheres, is stored in the chamber 16 . A neutron absorbing material falling port 118 is formed in the lower part of this neutron absorbing material storage hopper 116, and this neutron absorbing material falling port 118 faces the upper end opening of the guide tube 115. Above neutron absorber falling port 1
A cylindrical valve body 119 is fitted in 18 , and this valve body 119 is connected to a drive section 121 provided above via a connecting rod 120 . A valve protection pipe 122 is provided between the connecting rod 120 and the neutron absorber storage hopper 116. That is, the valve body 119 is configured to move up and down along the valve body protection tube 122 by the drive unit 121, thereby opening and closing the neutron absorbing material drop port 118. The drive section 121 is constructed as shown in FIGS. 5 and 6. Reference numeral 123 in the figure indicates a frame. At the top of this frame 123 is a drive motor 12.
4 is fixed, and a gear 125 is attached to a shaft 124A protruding from the lower end of this drive motor 124. A gear 126 meshes with this gear 125 . This gear 126 has a ball screw shaft 12
7 is attached, and a ball nut 128 meshes with this ball screw shaft 127. The ball screw shaft 127 has ball bearings 129 and 13 at its upper and lower parts.
0, and the ball nut 128 is fixed to the connecting plate 131.
The aforementioned connecting rod 120 is connected to this connecting plate 131 by a bolt 132. The rotational motion of the drive motor 124 transmitted by the gears 125 and 126 is converted into vertical linear motion by the ball screw shaft 127 and ball nut 128, and the connecting rod 120 is thereby connected via the connecting plate 131. move up and down. The connecting rod 120 is supported by a guide bearing 133 fixed to the lower part of the frame 123, and the guide bearing 133 prevents the connecting rod 120 from swinging and the ball nut 128 from rotating. The frame body 123
The lower limit position detection limit switch 134 detects the lower limit position of the valve body 119 and the upper limit position detection limit switch 13 detects the upper limit position of the valve body 119.
5 are installed respectively. On the other hand, the connection plate 1
31 is the lower limit position detection limit switch 13.
A contact 136 that contacts the upper limit position detection limit switch 135 and a contact 137 that contacts the upper limit position detection limit switch 135 are provided, respectively. An encoder 138 as a position detector is attached coaxially to the lower part of the gear 125, and the encoder 138 detects the vertical position of the valve body 119 that moves up and down. Note that this encoder 138 alone is enough to control the valve body 1.
In this embodiment, the lower limit position detection limit switch 134 and the upper limit position detection limit switch 135 are provided to increase safety. Further, an electromagnetic brake 139 is attached to the upper end of the ball screw shaft 127 that protrudes above the gear 126, and the braking force of the electromagnetic brake 139 improves the accuracy of the stopping position when stopping the valve body 119, for example. The operation will be explained based on the above configuration. When the nuclear reactor is in normal operation, the valve body 119 is lowered to the lower limit position, as shown in FIG. 7, and closes the neutron absorber drop port 118.
At this time, the valve body 119 is connected to the neutron absorber falling port 118.
It is in a fitted state with the neutron absorbing material drop port 118 over the entire length of the axial direction length _L1 . Next, when an emergency situation occurs and the reactor is to be stopped, an emergency activation signal is output from a reactor safety protection system (not shown), and the drive motor 124 automatically rotates forward in response to this emergency activation signal. The forward rotation of the drive motor 124 is transmitted to the ball screw shaft 127 via gears 125 and 126, and the ball screw shaft 127 also rotates forward. This ball screw shaft 127
The forward rotation of the ball nut 128 causes the ball nut 128 to rise, and the connecting rod 120 and the valve body 119, which are connected to the ball nut 128 via the connecting plate 131, to rise. Then, as shown by the two-dot chain line in the figure, the ascending distance is
When reaching _L3 , the contact 137 contacts the upper limit position detection limit switch 135, and an upper limit position detection signal is output. This upper limit position detection signal causes the drive motor 124 to stop driving, and at the same time, the electromagnetic brake 139 operates to stop the valve body 119 at the position of the rising distance _L3 . Above ascent distance L ₃
is from the lower end of the neutron absorber falling port 118 to the valve body 119
is the distance to the lower end of the valve body 119 when stopped at the upper limit position, which is larger than the axial length _L1 of the neutron absorber drop port 118, so the neutron absorber drop port 118 is in the open state, The neutron absorber 117 stored in the neutron absorber storage hopper 116 falls into the reactor through the neutron absorber drop port 118. This shuts down the reactor. After that, to return to the original state, the drive motor 124 is reversed. Drive motor 124
Due to the reverse rotation, the ball screw shaft 127 is also reversed through the gears 125 and 126, and accordingly, the ball nut 128 and the connecting plate 13 are connected to the ball nut 128.
A connecting rod 120 and a valve body 1 connected via 1
19 descends. When the contactor 136 contacts the lower limit position detection limit switch 134, a lower limit position detection signal is output. The drive motor 124 is stopped by this lower limit position detection signal, and at the same time, the electromagnetic brake 139 is activated. With this, the valve body 11
9 stops and returns to its original state. Next, a case in which an operation test is performed will be explained with reference to FIG. First, a signal is sent to the drive motor 124 to rotate the drive motor 124 in the forward direction. Due to the forward rotation of the drive motor 124, the ball screw shaft 127 rotates forward through the gears 125 and 126, and the ball nut 128 and the connection plate 131 are connected to the ball nut 128.
The connecting rod 120 and the valve body 119, which are connected via the valve body 119, rise. When the rising distance reaches _L2 , the encoder 138 detects this and outputs a detection signal to stop the drive motor 124, and also activates the electromagnetic brake 139 to stop the valve body 119 at the position of the rising distance _L2 . . The above rising distance L ₂ is the distance between the valve body 119 and the lower end of the neutron absorber drop port 118.
Valve body 119 when a part thereof is fitted into neutron absorber drop port 118 and stopped as shown by the dotted chain line
is the distance to the lower end of the neutron absorber 117 stored in the neutron absorber storage hopper 116.
will not fall. Note that the encoder 138
The detection signal from the sensor is generated only during operation tests and is electrically interlocked so that it does not occur during normal operation. After the valve body 119 is raised to the lifting distance _L2 , the drive motor 124 is reversed to reverse the ball screw shaft 127. This causes the connecting rod 120 and the valve body 119 to descend. The contactor 136 is the lower limit position detection limit switch 1.
34, a lower limit position detection signal is output. This lower limit position detection signal causes the drive motor 1 to
24 is stopped, and at the same time, the electromagnetic brake 139 is activated to stop the valve body 119. At this time, valve body 1
19 is the axial length of the neutron absorbing material falling port 118
Neutron absorber drop port 118 along the entire length of L ₁
are in a mated state. Thereafter, by repeating such rising and falling operations, the neutron absorbing material 117
Operation tests can be performed without dropping the device. According to the reactor shutdown device according to this embodiment,
Valve body 119, connecting rod 120, and drive unit 12 without dropping neutron absorber 117 into the reactor.
Since it is possible to perform the operation test described in 1 above, it is possible to perform an operation test at any time not only when the reactor is shut down, but also when the reactor is operating, ensuring normal function at all times and greatly improving reliability. be able to. Also, unlike the conventional rupture disk, which causes the neutron absorber 117 to fall by breaking under a certain pressure, the strength of the valve body 119, connecting rod 120, and other members can be made sufficiently strong to prevent fluctuations in reactor pressure. Damage due to neutron irradiation or the like can be prevented, malfunctions are eliminated, and since the valve body protection layer 122 is provided, the valve body 119 can be moved up and down smoothly. Even when the operation test is performed, the neutron absorber 117 does not fall into the reactor, and no fragments are generated, and there is no need for conventional work such as converting the rupture disk. Subsequent repairs are easier, and workability can be significantly improved since there is no need to dispose of solid radioactive waste. Further, since conventional high-pressure gas supply devices, piping, etc. are no longer necessary, costs can also be reduced. [Effects of the Invention] In the nuclear reactor shutdown device according to the present invention, the valve body that closes the neutron absorber fall port is provided in the neutron absorber storage hopper so that it can be moved up and down, so the position of the valve body can be detected by a position detector. However, by raising and lowering the valve body by a predetermined stroke, it is possible to conduct an operation test of the reactor shutdown device without causing the neutron absorber stored in the neutron absorber storage hopper to fall from the neutron absorber drop port. Further, in the present invention, a drive unit that drives the valve body up and down is connected to a drive motor, a ball screw shaft rotationally driven by the drive motor, and the valve body through a connecting rod, so that the rotation of the ball screw is converted into a linear motion. Since the structure includes a ball nut for conversion and an electromagnetic brake that applies braking force to the ball screw shaft to stop the valve body from moving up and down, it is possible to move the valve body up and down with a simple configuration, and also to drive the valve body. The valve body can be stopped at a predetermined position by the electromagnetic brake without being affected by the inertial force of the motor.

[Brief explanation of the drawing]

1 and 2 are diagrams showing a conventional example, in which FIG. 1 is a diagram showing a schematic configuration of a gas-cooled nuclear reactor, and FIG. 2 is a longitudinal sectional view of a nuclear reactor shutdown device. Figures 3 to 8 are diagrams showing one embodiment of the present invention, in which Figure 3 is a diagram showing a schematic configuration of a gas-cooled nuclear reactor, Figure 4 is a vertical cross-sectional view of a reactor shutdown device, and Figure 5 is a diagram showing a schematic configuration of a gas-cooled reactor. is a partially enlarged view of Fig. 4, Fig. 6 is a view in the - arrow direction of Fig. 5, and Fig. 7 is a partially enlarged view of Fig. 4.
This figure and FIG. 8 are longitudinal cross-sectional views for explaining the operation. 102...Reactor core, 114...Reactor shutdown device,
115... Guide pipe, 116... Neutron absorbing material storage hopper, 117... Neutron absorbing material, 118... Neutron absorbing material falling port, 119... Valve body, 120...
Connecting rod, 121... Drive unit, 122... Valve protection tube, 138... Encoder (position detector).

Claims (1)

[Claims] 1. A guide tube inserted into the reactor core from above, a neutron absorber storage hopper provided above the guide tube and having a neutron absorber drop port at the lower end, and a neutron absorber storage hopper installed in the neutron absorber storage hopper so as to be able to rise and fall freely. It includes a valve body that closes the neutron absorbing material falling port, a drive unit that drives the valve body up and down in the vertical direction, and a position detector that detects the position of the valve body, and the drive unit is connected to a drive motor. a ball screw shaft that is rotationally driven by the drive motor; a ball nut that is connected to the valve body via a connecting rod and converts the rotation of the ball screw into linear motion; and a ball nut that applies braking force to the ball screw shaft to drive the valve body. A nuclear reactor shutdown device characterized by comprising an electromagnetic brake for stopping the vertical movement of a nuclear reactor.