JP2525850B2 - Neutron absorption element recovery device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a device for recovering, from the inside of a core, a neutron absorbing element that has been dropped into the core from a backup reactor shutdown device of a gas-cooled reactor, for example.

[Technical background of the invention]

In general, control of nuclear reactivity in a nuclear reactor is performed by inserting the control rod into the core by using a control rod drive device, or by pulling out from the core.To shut down the reactor, fully insert the control rod into the core. It is done by.

The reactor shutdown function is extremely important, and it is necessary to surely shut it down, for example, when the reactor is abnormal. For this reason, in actual reactors, in addition to the control rod drive device, a backup reactor shutdown device whose operating principle is different from that of the control rod drive device is provided to take sufficient safety measures.

Figure 1 shows the schematic configuration of a gas-cooled reactor.
In the figure, 1 is a reactor vessel, and 2 is a reactor core provided in the reactor vessel 1. The core 2 is constructed by stacking graphite blocks as moderators and loading fuel rods 3 therein. An inlet pipe 4 for allowing a coolant such as helium gas to flow in is connected to the bottom of the reactor vessel 1, and an outlet pipe 5 is inserted into the inlet pipe 4. The coolant flowing into the reactor vessel 1 passes through the core 2 from the upper side to the lower side, is heated by the nuclear reaction heat of the core 2, and then flows out from the outlet pipe 5.

On the other hand, a heat exchanger 6 is provided outside the reactor vessel 1, and after the high temperature coolant flowing out from the outlet pipe 5 is heat-exchanged with the secondary coolant in the heat exchanger 6, the circulation pump is used. It is returned to the reactor vessel 1 again through the inlet pipe 4 by 7.

Further, a control rod guide tube 8 is inserted into the core 2 from above, and a control rod 9 is housed in the control rod guide tube 8 so as to be vertically movable. The output of the core 2 is controlled by inserting / pulling out the control rod 9 into / from the core 2. The control rod 9 is driven by a control rod drive mechanism 10 provided at the upper end of the reactor vessel 1. The control rod drive mechanism 10 connects a wire rope 11 to the control rod 9, and the wire rope 11 The drum
It is wound around 12, and this drum 12 is rotationally driven by a motor 13,
The control rod 9 is moved up and down by winding the wire rope 11 or unwinding it.

On the other hand, in case of emergency such that the control rod 9 cannot be inserted, the backup reactor shutdown device 14 is provided.

A plurality of the fuel rods 3, the control rods 9, the control rod drive mechanism 10 and the backup reactor shutdown device 14 are all provided, but in the figure, each is shown in a simplified manner.

By the way, the backup reactor shutdown device 14 is different from the control rod drive mechanism 10 in terms of structure and operation principle so as not to cause a redundant failure due to a common cause with the control rod drive mechanism 10.

That is, FIG. 2 shows a backup reactor shutdown device 14, and reference numeral 15 in the drawing is a guide tube. The guide tube 15 is inserted into the core 2 from above, and its upper end is opened. A neutron absorber storage hopper 16 is provided above the guide tube 15. In this hopper 16, for example, boron carbide (B ₄
A neutron absorbing element 17 in which a neutron-absorbing substance such as C) is formed into a pellet shape having a diameter of about 10 mm or a diameter and height of about 10 mm is stored. The lower end of the neutron absorbing element storage hopper 16 has a conical shape having a smaller diameter at the lower side, and the lower end opening is a neutron absorbing element drop opening 18, which is located above the guide tube 15. The neutron absorbing element drop port 18 is closed by a thin plate-shaped rupture disk (rupture plate) 19. This rupture disk 19 always bears the weight of the neutron absorbing material 17, but has strength that never breaks by itself.

On the other hand, a high-pressure gas supply device 21 is connected to the neutron absorber storage hopper 16. This has a structure in which an accumulator 22 storing high-pressure gas is connected to a hopper 16 via a gas supply pipe 23, and an opening / closing valve 24 is inserted in the middle of the gas supply pipe 23.

Therefore, in order to operate the backup reactor shutdown device 14, the open / close valve 24 may be opened to supply the high-pressure gas into the hopper 16. Then, the rupture disc
19 breaks due to the pressure increase in the hopper 16, the neutron absorbing element 17 in the hopper 16 falls into the core 2 through the guide tube 15, stops the nuclear reaction in the core 2, and causes an emergency stop of the nuclear reactor.

By the way, since the neutron absorbing element 17 is dropped into the reactor core 2 when the backup reactor shutdown device 14 is operated, the neutron absorbing device 17 is used to restart the reactor when the reactor is restarted. It is necessary to collect from 2.

[Problems of background technology]

As a device for recovering neutron absorbing elements that have been dropped into the core from a backup reactor shutdown device, etc., it is necessary to be able to recover efficiently without causing diffusion of radioactivity, and not to reduce the safety and operating rate of the reactor. Is.

[Object of the Invention]

The present invention has been made based on such circumstances, the object is to efficiently collect the neutron absorbing element dropped in the core, without causing the diffusion of radioactivity,
It is an object of the present invention to provide a neutron absorbing element recovery device capable of improving the safety and operating rate of a nuclear reactor.

[Outline of Invention]

In order to achieve the above objects, the neutron absorbing element recovery apparatus of the present invention, a door valve that is detachably installed on the operating floor above the reactor vessel, and the door valve and the reactor vessel interposed between the inside of the reactor A spacer tube forming a pressure boundary, a housing cylinder provided on the door valve equipped with a hoist, a recovery guide tube reaching the core of the reactor vessel from within the spacer tube, and a recovered neutron absorbing element A recovery device main body that has a hopper that stores the above and is housed in the collection guide tube so as to be able to move up and down, is hung by the hoist, and is housed in the housing cylinder together with the collection guide tube.
A vacuum pump that is attached to the main body of the recovery device and that makes the inside of the hopper lower than the internal pressure of the furnace, and a neutron absorbing element that is led out from the inside of the recovery device below the recovery guide tube and is dropped into the core of the hopper. It is characterized in that it is provided with a recovery pipe for sucking the inside.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. 3 and 4. The same parts as those in FIGS. 1 and 2 are designated by the same reference numerals.

FIG. 3 is a vertical cross-sectional view of the neutron absorbing element recovery device 25. This device 25 is attached to the reactor vessel 1 after removing the backup reactor shutdown device 14 at the same position as this device 14.

Reference numeral 26 is an operating floor provided above the reactor vessel 1, and has a handling port 27 at a position above the guide pipe 15.
A door valve 28 is provided on the handling port 26 so as to block the handling port 27.
The housing cylinder 29 is attached via the. The accommodating cylinder 29 has a cylindrical shape, and has a wire rope winding drum type electric hoist 30 at the upper end. Further, a spacer tube 31 for forming a pressure boundary is provided between the door valve 28 and the introduction pipe portion 1a of the reactor vessel 1. A recovery guide tube 32 is provided inside the spacer tube 31,
The lower end of the recovery guide tube 32 reaches the upper part of the core 2.
The recovery guide tube 32 has a flange portion 32a that abuts on the upper end of the introduction tube 1a, and a hollow fitting protrusion 33 that fits on the upper portion of the guide tube 15 at the lower end, and the vicinity of the guide tube 15 on the upper part of the core 2. Positioning projection that fits into the positioning recess 34 formed at the position
35 are provided. Inside the recovery guide tube 32, a recovery device main body 36 is housed so as to be vertically movable. An upper end of the recovery device main body 36 is closed by a lid plate 37, and a central portion of the lid plate 37 is suspended from the electric hoist 30 by a wire rope 38.
In addition, it is suspended via the load cell 39. A recovery pipe 40 is led out from the lower end of the recovery device body 36. The lower end of the recovery tube 40 is introduced into the guide tube 15 through the fitting protrusion 33. A nozzle 41 is provided at the lower end of the recovery pipe 40.

FIG. 4 shows the structure of the recovery device main body 36, and reference numeral 42 is a cylindrical hopper. Below the hopper 42, a conical bottom plate 43 having a high center is connected by a connecting member 44, and a gap between the lower end of the hopper 42 and the connecting member 44 is closed by an outer cylinder 45. The outer cylinder 45 is fitted to the lower outer periphery of the hopper 42 so as to be able to move up and down, and is constantly urged downward by a compression coil spring 46, and its lower end is pressed against the bottom plate 43. The lower end of the outer cylinder 45 and the bottom plate 43
The space between and is sealed airtight by an appropriate means such as an O-ring (not shown). Further, the hopper 42 and the outer cylinder 45 are also properly airtightly sealed by a welding bellows or the like (not shown).

A guide pipe 47 is vertically arranged in the hopper 42, and the recovery pipe 40 is inserted into the guide pipe 47. The upper end of the recovery pipe 40 is bent in an arc shape and is located in the upper part of the hopper 42, and the lower end penetrates the bottom plate 43. The recovery pipe 40 and a through hole provided in the bottom plate 43 The gap between them is hermetically sealed by a welded bellows 48.

The upper end of the hopper 42 is closed by an upper end plate 49, and a vacuum pump 50 is attached to the upper surface of the upper end plate 49. The suction port of the vacuum pump 50 communicates with the inside of the hopper 42 through the center of the upper end plate 49, and the communication port at the center of the upper end plate 49 is closed by a filter 51 attached to the lower surface of the lower end plate 49.

A suspension rod 52 and a recovery detection rod 53 are further inserted through the upper end plate 49. The lower end of the suspension rod 52 is attached to the recovery pipe 40, and the upper end has a spring bearing plate 54.
A compression coil spring 55 inserted between the spring receiving plate 54 and the upper end plate 49 is constantly biased upward. The elasticity of the coil spring 55 is balanced with the weight of the recovery pipe 40, so that the relative position between the recovery pipe 40 and the hopper 42 is kept constant. A limit switch 56 is installed in the vicinity of the spring receiving plate 54, and when the recovery pipe 40 rises with respect to the hopper 42, the limit switch 56 detects the rise. A welding bellows 57 is attached between the spring receiving plate 54 and the upper end plate 49 to seal a hole for inserting the suspension rod 52 provided in the upper end plate 49. On the other hand, a rack 58 is formed in the lower half of the recovery detection rod 53, and the rack 58 is meshed with a pinion 59 mounted in the hopper 42. Flapper 60 in this rack
Is attached so as to face the upper open end of the recovery pipe 40. Further, the recovery detection rod 53 has a spring receiving plate 61 at its upper end, and is constantly urged upward by a compression coil spring 62 inserted between the spring receiving plate 61 and the upper end plate 49. The elasticity of the coil spring 62 is balanced with the weight of the recovery detection rod 53, and thus the recovery detection rod 53
The relative position between 53 and the hopper 42 is kept constant, and the tilt of the flapper 60 is kept constant. A potentiometer 63 that detects the amount of displacement of the recovery detection rod 53 with respect to the hopper 42 is installed above the spring receiving plate 61. A welding bellows is provided between the spring receiving plate 61 and the upper end plate 49 to seal a hole for inserting the recovery detection rod 53 provided in the upper end plate 49.
64 is installed.

The cover plate 37 is connected to a position above the upper end plate 49 via a connecting member 65, and a suspension rod 66 is inserted through the central portion thereof. A bottomed cylindrical spring receiving member 67 is connected to the lower end of the suspension rod 66, and a compression coil spring 68 is interposed between the inner bottom surface of the spring receiving member 67 and the lower surface of the lid plate 37. Further, a limit switch 69 is attached to the lower surface of the cover plate 37, and the limit switch 69 is configured to detect the lowering of the suspension rod 66 with respect to the cover plate 37, that is, the looseness of the wire rope 38. In FIG. 4, reference numerals
70 is a guide rail provided vertically on the inner peripheral surface of the recovery guide tube 32, and 71a and 71b are the upper surface of the lid plate 37 and the hopper 42, respectively.
The guide roller is attached to the outer peripheral surface and rolls along the guide rail 70.

 Next, the operation will be described.

If the control rod 9 cannot be inserted into the core 2 due to an unforeseen situation, the backup reactor shutdown device 14 is promptly activated, and the neutron absorbing element 17 is introduced into the core 2 through the guide tube 15. Drop and shut down the reactor.

After the reactor is shut down, the backup reactor shutdown device 14 is taken out of the reactor by a dedicated handling machine (not shown) such as a fuel exchanger, and the inlet pipe 1a of the reactor vessel 1 is closed with a plug.

After that, the neutron absorbing element recovery device 25 is attached in the following procedure. That is, first, the spacer tube 31 and the door valve 28 are installed, the stopper is removed by a dedicated handling machine, and the door valve 28 is closed. Next, the neutron absorbing element recovery device 25 excluding the door valve 28 and the spacer tube 31 is carried out from the storage chamber (not shown) by a crane (not shown). At this time, the recovery device 25 has a recovery guide tube inside the storage cylinder 29.
32, the recovery device main body 36 and the like are accommodated.
Therefore, the lower end of the containing cylinder 29 is connected to the door valve 28, and after the inside of the containing cylinder 29 is evacuated and replaced with helium gas,
The door valve 28 is opened. Next, the hoisting machine 30 is rotated in the forward direction to lower the recovery guide tube 32, the recovery device body 36, and the recovery tube 40, and the fitting projection 33 at the lower end of the recovery tube 40 is fitted to the upper end of the guide tube 15 and positioned. The projection 35 is fitted into the positioning recess 34, and the flange 32a of the recovery guide tube 32 is brought into contact with the upper end of the introduction tube 1a to position the recovery guide tube 32.
Then, when the hoisting machine 30 is further rotated in the forward direction, the recovery device body 36
And only the recovery pipe 40 descends. In this way, the nozzle 41 at the tip of the recovery tube 40 is brought close to the neutron absorbing element 17 inside the guide tube 15.

Next, when the vacuum pump 50 is started to make the pressure inside the hopper 42 lower than the furnace pressure, the neutron absorbing element 17 is sucked from the nozzle 41, rises in the recovery pipe 40, and is recovered from the upper end into the hopper 42.

In this recovery operation, the recovery device main body 36 and the recovery pipe 40 are lowered by the hoisting machine 30, and the neutron absorption element 17 from the core 2 is removed.
Is performed while balancing the recovery speed of the recovery pipe and the descending speed of the recovery pipe 40. At this time, while the neutron absorbing element 17 is falling from the upper opening of the recovery pipe 40, the element 17 is covered by the flapper.
Upon hitting 60, the flapper 60 has rotated to the position shown by the phantom line in FIG. Then, this rotation is converted into the lowering operation of the rack 58 and detected by the potentiometer 63. It should be noted that the closed state of the recovery pipe 40 or the nozzle 41 can be detected by detecting the pressure inside the hopper 42 as necessary. When the outflow of the neutron absorbing element 17 from the recovery tube 40 is stopped, the flapper 60 returns to the position indicated by the solid line in FIG. 4, so that it can be detected that the element 17 is not recovered. Further, when the balance between the recovery speed of the element 17 and the descending speed of the recovery tube 40 becomes unbalanced, and the descending speed of the recovery tube 40 increases, the reaction force from the neutron absorbing element 17 acts upward on the nozzle 41, and the recovery tube Such a condition is detected by limit switch 56 as 40 rises relative to hopper 42.

After recovering the neutron absorbing element 17 from the core 2 in this way, the hoisting machine 30 is reversed to first raise the recovery device body 36 and the recovery pipe 40. And the cover plate 37 is the collection guide tube 32.
After contacting the flange portion 32a of the
Also rises integrally with the recovery device main body 36 and the recovery pipe 40, and is stored in the storage cylinder 29.

Therefore, the door valve 28 is closed, the neutron absorbing element recovery device 25 is removed from the door valve 28, and the crane is transported to the storage room. Further, the introduction pipe portion 1a is closed with a stopper by a dedicated handling machine, and the spacer tube 31 and the door valve 28 are removed.

On the other hand, the neutron absorbing element recovery device 25 transferred to the storage room
As for, the outer cylinder 45 is raised against the spring 46 by using a dedicated device (not shown), and the lower end of the hopper 42 and the bottom plate are
The neutron absorption element 17 in the hopper 42 is discharged through the opening by opening between the opening 43 and 43.

Therefore, with the above configuration, the neutron absorbing element recovery device can be operated without breaking the pressure boundary in the reactor vessel 1.
25 can be installed and removed. In addition, the neutron absorption element
The recovery work of 17 can also be easily performed by the vacuum pump 50, there is no need to circulate piping outside the reactor, the diffusion of radioactivity can be prevented, and the safety and operating rate of the nuclear reactor can be improved. When recovering the neutron absorbing element 17, the recovery pipe 40
Limit switch 56 detects the upward movement of
By controlling the vacuum pump 50 and the hoisting machine 30 while recognizing the recovery state of the neutron absorbing element 17 by detecting the inclination of the flapper 60 with the potentiometer 63, the recovery work of the neutron absorbing element 17 can be performed safely and efficiently. Can be done.

〔The invention's effect〕

As described above in detail, according to the present invention, the neutron absorbing element dropped in the reactor core can be efficiently collected without causing the diffusion of radioactivity, and the safety and operating rate of the reactor can be improved. A neutron absorbing element recovery device can be provided.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a schematic configuration of a gas-cooled reactor,
FIG. 2 is a vertical cross-sectional view of a backup reactor shutdown device, FIGS. 3 and 4 show an embodiment of the present invention, and FIG. 3 is a vertical cross-sectional view of a neutron absorbing element recovery device, FIG. FIG. 3 is a vertical cross-sectional view showing a peripheral portion of a recovery device body of the same device. 1 ... Reactor vessel, 17 ... Neutron absorbing element, 26 ... Operating floor, 28
… Door valve, 30… Electric hoist, 31… Spacer tube, 32… Recovery guide tube, 40… Recovery tube, 42… Hopper, 50…
Vacuum pump, 56 ... Limit switch, 60 ... Flapper, 63
… Potentiometer.

Claims (1)

(57) [Claims] 1. A door valve detachably installed on the operation floor above the reactor vessel, a spacer tube interposed between the door valve and the reactor vessel to form a pressure boundary in the reactor, and a hoisting machine. In the recovery guide tube having a storage cylinder installed on the door valve, a recovery guide tube that reaches the core of the reactor vessel from the spacer tube, and a hopper that stores the recovered neutron absorbing element And a recovery device main body that is housed in the storage cylinder body and is lifted up and down by the hoisting machine and stored in the storage cylinder together with the recovery guide tube. The inside of the hopper is made lower in pressure than the furnace pressure by being attached to the recovery device main body. A vacuum pump; and a recovery pipe for sucking up into the hopper the neutron absorbing element that is drawn out from the inside of the recovery device from the recovery guide pipe and is dropped into the core. Neutron absorbing element recovery apparatus characterized by.