JPH0555839B2 - - Google Patents

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention is directed to a boiling water reactor (hereinafter referred to as BWR).
Regarding the neutron flux measurement tube loaded in the reactor core, especially when loading the neutron flux measurement tube into the reactor core, it is necessary to insert not only the shuttle tube but also the drive tube, detector, and cable into the drive tube in advance. Concerning what makes it possible to keep things.

(Prior Art) A conventional example will be described with reference to FIGS. 8 to 16. Figure 8 is a diagram showing the schematic configuration of BWR,
Reference numeral 1 in the figure is a reactor pressure vessel. This reactor pressure vessel 1 is mounted and fixed on a reactor pressure vessel pedestal 2. A coolant 3 and a reactor core 4 are housed within the reactor pressure vessel 1 . core 4
is composed of a plurality of fuel assemblies, control rods, etc. (not shown). The reactor core 4 is the reactor pressure vessel 1
It is housed in a shroud 5 installed on the inner circumferential side of. A neutron flux measurement housing 6 and a control rod drive mechanism housing 7 are disposed through the lower part of the reactor pressure vessel 1 . A control rod drive mechanism 8 is housed within the control rod drive mechanism housing 7 .

The neutron flux measurement housing 6 is connected to a neutron flux measurement guide pipe 9 in the reactor pressure vessel 1, and the neutron flux measurement guide pipe 9 is located approximately in the axial center of the shroud 5 and supports the reactor core 4 from below. It is connected to the core support plate 10 and is open.

At the opening 9a of the neutron flux measurement guide tube 9,
As shown in the figure, a neutron flux measuring tube 11 is inserted and removably inserted from above. This neutron flux measurement tube 1
1 reaches the neutron flux measurement flange 13 of the lower part of the neutron flux measurement housing 6 arranged in the inner space (pedestal space) 12 of the pedestal 2 for the reactor pressure vessel. It is accommodated. On the other hand, a plunger 14 is installed at the top of the neutron flux measurement tube 11,
This plunger 14 is pressed by the spring force of a coil spring (not shown) housed in the upper part of the neutron flux measuring tube 11 to the bottom of the intersection of the upper grid plate 15 provided at the upper part of the shroud 2 and supporting the reactor core 4 from above. ing. This supports the upper part of the neutron flux measurement tube 11.

The neutron flux measuring tube 11 has an atmospheric atmosphere inside, and is equipped with a dry tube 17 as a pressure tube that receives the operating pressure of the nuclear reactor as external pressure, and a shuttle tube 18 is inside the dry tube 17 and can be moved up and down. is housed in. A detector 20 surrounded by glass wool 19 and a cable 21 are housed within the shuttle tube 18 . The surface of the detector 20 is coated with uranium 235, and this uranium 235 absorbs thermal neutrons in the reactor and becomes fragments, which ionizes the argon gas sealed within the detector 20. The ionization current generated by the ionization of the argon gas enters each electrode and becomes an ionization signal proportional to the number of neutrons.

The lower end of the shuttle tube 18 is connected to a drive tube 22 which is a long member as shown in FIG.
It is connected to the. i.e. drive tube 2
A recess 22a is formed at the upper end of the recess 2.
A male thread 22b is formed on the outer peripheral surface of 2a. The lower end of the shuttle tube 18 is inserted into the upper recess 22a from above, and a nut 23 having a female thread 24 is screwed into the male thread 22b from its outer periphery.
8 and the drive tube 22 are fastened.
An O-ring 26 is installed between the lower end surface of the shuttle tube 18 and the counterbore surface 25 of the drive tube 22, thereby maintaining an insulating atmosphere around the cable 21 due to nitrogen gas. A stopper 27 is annularly protruded from the lower side surface of the shuttle tube 18, and this stopper 27 prevents the shuttle tube 18 from coming out upward from the nut 23. The drive tube 22 is connected to a neutron flux measuring flange 13 disposed within the pedestal space 12 as shown in FIG.
The drive tube 22 is connected to a drive device 27 through which the drive tube 22 is moved up and down.

Next, the configuration of the drive mechanism 27 will be explained with reference to FIG. 12. FIG. 12 is a sectional view showing the structure of the drive mechanism 27, and the reference numeral 28 in the figure is a bearing bracket. This bearing bracket 2
Bearings 29 and 30 are mounted above and below 8, respectively. The drive tube 22 is supported by these bearings 29 and 30 so that it can move up and down and rotate. Further, a cable 21 is inserted into the drive tube 22. A rack portion 31 is formed on the outer peripheral surface of the drive tube 22, and a sprocket 32 meshes with the rack portion 31. Note that a guide roller 33 is arranged on the opposite side of this sprocket 32. The sprocket 32 is connected to a drive section (not shown) via a worm 33 and an intermediate shaft 34, and is rotated in a desired direction by this drive section. Further, a cable guard 35 shown in FIG. 8 is attached to the lower part of the drive mechanism 27, and the cable guard 35 is connected to a signal cable 36 from the central control room.
is connected.

In the neutron flux measurement system having such a configuration, the drive tube 22 and the shuttle tube 18 are moved up and down by rotating the sprocket 32 according to the output state of the nuclear reactor, and thereby the drive tube 22 and the shuttle tube 18 are moved up and down. The detector 20 is inserted into or pulled out from the reactor core 4. After the detector 20 detects neutrons in the core 4, the detection signal is transmitted to the central control room and the neutron flux distribution is monitored from there.

By the way, when a nuclear reactor is operated for a long period of time, the uranium-235 coated on the upper end of the detector 20 is damaged, and therefore it is necessary to periodically replace it with a new neutron flux measurement tube 11. be.
Therefore, the installation work of the neutron flux measuring tube 11 will be explained with reference to FIGS. 13 and 14. FIG. 13 is a sectional view showing details of the lower end of the neutron flux measurement tube 11. Before installing the neutron flux measurement tube 11 in the reactor core 4, the shuttle tube 18 is inserted into the dry tube 17 in advance. I'll keep it. Next, the nose cap 37 is screwed into the lower end of the dry tube 17 to close it off. In the figure, reference numeral 38 is a male threaded portion formed on the nose cap 37, and reference numeral 39 is a female threaded portion formed on the lower end of the dry tube 17. Note that the detector 20 and cable 21 are not attached at this point.

Next, the dry tube 17 with the shuttle tube 18 assembled therein is lifted up so that the nose cap 37 is positioned below, and suspended into the core 4 from above the core 4 shown in FIG. The hemispherical lower end of the nose cap 37 is inserted into the neutron flux measurement guide tube 9 opened on the core support plate 10. When the dry tube 17 continues to be suspended, the nose cap 37 appears below the neutron flux measurement housing 9.

Next, FIG. 14 is a diagram showing a state in which the dry tube 17 is supported within the neutron flux measurement flange 13 at the lower part of the neutron flux measurement housing 6, and the lower outer peripheral surface of the dry tube 17 has a tapered sealing surface 40. is formed. On the other hand, a similarly tapered flange sealing surface 41 is formed on the neutron flux measuring flange 13 side, and the dry tube 17 is supported by the neutron flux measuring flange 13 by engaging the sealing surface 40 with the sealing surface 41 from above. .

After the dry tube 17 is supported by the neutron flux measurement flange 13, as shown in FIG. Press and engage the bottom of the intersection. Through such a procedure, loading of the neutron flux measurement tube 11 into the reactor core 4 is completed.

Next, as shown in FIG. 8, the pedestal space 12
Remove the nose cap 37 inside and screw the drive tube 22 into the nut 23. This completes the connection between the drive tube 22 and the shuttle tube 18.

Next, the drive tube 22 is connected to the drive mechanism 27. That is, the drive tube 22 is inserted into the bearing bracket 28, and the threaded portion 31 of the drive tube 22 is screwed into the sprocket 32. Finally, a detector 20 covered with glass wool 19 and a cable 21 are inserted into the drive tube 22 in the pedestal space 12, and the end of the cable 21 and the end of the signal cable from the central control room are connected. , this connection portion is covered by a cable guard 35.

According to the above configuration, the drive tube 22 and the shuttle tube 1 are operated in the pedestal space 12.
8, insertion of the detector 20 and cable 21 into the drive tube 22, etc. are difficult and time-consuming because the pedestal space 12 is very narrow. Since the inside of the space 12 is under high radiation doses, there is a concern that workers may be exposed to radiation.

In particular, when inserting the detector 20 and cable 21 into the drive tube 22, the entire length is about 12 m, the diameter is small, and the glass wool 19 is covered. It was very difficult to carry out the work, as it was necessary to always take into account the slackness of the parts.

Therefore, the following methods have been considered as a means to solve such problems. That is, this is a method in which the drive tube 22, the detector 20, and the cable 21 are installed in the dry tube 17 in advance, and the reactor core 4 is loaded in this state. In other words,
Before loading the neutron flux measurement tube 11 into the reactor core 4, the shuttle tube 18 and drive tube 22 are fastened together as shown in FIG. After covering the detector 20 and cable 21, they are inserted into the drive tube 22. After this, the nose cap 37 is screwed into the lower end of the dry tube 17.

FIG. 16 shows the state of the lower end of the dry tube 17 when installed by this method. Note that the reference numeral 43 in the figure is a connector. As shown in the figure, when the dry tube 17 is raised to load the reactor core 4, the shuttle tube 18, drive tube 22, etc. move downward due to their own weight. At this time, since the connector 43 connected to the end of the cable 21 receives the load of the shuttle tube 18 and the drive tube 22, the connector 43 or the cable 21 may be deformed. If such deformation occurs, it may become unusable. Therefore, such a method has not been adopted in the past.

(Problems to be Solved by the Invention) In this way, with the conventional configuration, workers are forced to perform difficult work within a space, which not only reduces the operating rate due to longer working hours, but also causes problems for workers. There is a problem that radiation exposure is a concern, and the present invention was made based on this point.
The purpose is to provide a neutron flux measurement tube that can prevent damage to the signal cable pulled out from the lower end opening of the drive tube and the connector attached to the end of the cable.

[Structure of the Invention] (Means for Solving the Problems) That is, the present invention provides a dry tube that penetrates the bottom of a reactor vessel and is inserted into the reactor core, and a shuttle that is inserted from the lower end opening of the dry tube. a drive tube connected to the lower end of the shuttle tube and configured to move the shuttle tube in the axial direction of the dry tube; a neutron detector provided at an upper portion within the shuttle tube; a signal cable inserted through the shuttle tube and pulled out from the lower end opening of the drive tube; and a connector attached to the end of the signal cable;
In the neutron flux measuring tube, the lower end of the drive tube is provided with a cylindrical nose cap that is screwed onto the lower end of the dry tube when the dry tube is inserted into the reactor core. It is characterized by forming a stepped portion that abuts.

(Function) That is, in the present invention, a stepped portion is formed on the upper inner surface of the nose cap, and the stepped portion receives the loads of the shuttle tube and the drive tube.

(Embodiment) The first embodiment of the present invention will be described below with reference to FIGS. 1 to 5.
An example will be explained. Incidentally, the same parts as in the prior art are denoted by the same reference numerals, and the explanation thereof will be omitted. First, the nose cap 101 in this embodiment is composed of the above-mentioned cap 102 and a lower cap 103. The upper cap 102 is screwed into the lower end of the dry tube 17 through a male threaded end 102a, and the lower cap 103 is connected to the upper cap 10 through a female threaded end 103a.
It is screwed into the rear end male threaded portion 102b of No. 2.

A chamfered portion 10 is provided on the outer periphery of the upper cap 102.
4 are formed intermittently in the axial direction. These chamfered portions 104 are formed in consideration of the case where a jig (for example, a spanner) not shown is used.
Further, a stepped portion 105 serving as a holding mechanism is formed on the inner peripheral side of the lower end of the upper cap 102. The lower end of the drive tube 22, which has already been inserted into the dry tube 17, engages with this stepped portion 105 from above. Drive tube 2
It supports the load of the upper members including 2.

On the other hand, regarding the lower cap 103, there is also a chamfered portion 106 on the upper outer peripheral surface of the lower cap 103.
The purpose is the same as the chamfered portion 104 formed on the upper cap 102 side. A protective cover 107 as a holding mechanism is disposed within the lower cap 103. The protective cover 107 is composed of an upper protective cover 108 and a lower protective cover 109, and the upper protective cover 108 and the lower protective cover 109 have different inner diameters. That is, the inner diameter of the upper protective cover 108 is larger than that of the lower protective cover 109. The inner diameter of the protective cover upper part 108 substantially matches the outer diameter of the maximum outer diameter portion 43a of the connector 43. Therefore, a stepped portion 110 is formed between the protective cover upper part 108 and the protective cover lower part 109. A screw hole is formed in the upper part of the protective cover upper part 108, and a set screw 111 is screwed into the screw hole.

The operation will be explained based on the above configuration. First, the dry tube 17 is placed horizontally, and as shown in FIG. 2, the shuttle tube 18 and the drive tube 22 connected through the nut 23 are inserted into the dry tube 17 in the direction shown by arrow a in the figure. After this insertion is completed, the glass wool 19 is inserted as shown in FIG.
The detector 20 and the cable 21 covered with the above are inserted into the drive tube 22 as shown by the arrow b in the figure. In addition, this detector 20 and cable 21
The insertion operation may be performed before inserting the shuttle tube 18 and drive tube 22 into the dry tube 17.

Next, as shown in FIG. 4, the cap 102 is screwed onto the lower end of the dry tube 17. Next, as shown in FIG. 5, the connector 43 is surrounded by the protective cover 107, and the setscrew 111 is screwed in. As shown in the figure, the tip of the set screw 111 is located above the stepped portion at the connecting portion between the cable 21 and the connector 43, so that the protective cover 107 is reliably prevented from falling. Next, the lower cap 103 is screwed into the upper cap 102 to form the state shown in FIG. The assembly is now complete.

When the assembly is completed, the dry tube 17 is erected to be loaded into the reactor core 4. As the neutron flux measuring tube 11 rises, the shuttle tube 18, drive tube 22, etc. housed inside move downward, but as described above, the lower end of the drive tube 22 is formed on the lower inner peripheral surface of the upper cap 102. Since the cable 21 is engaged with and supported from above by the stepped part 105, a large load is not applied to the lower part of the cable 21, the connector 43, etc.
At this time, the detector 20 and cable 21 housed in the shuttle tube 18 and drive tube 22 are covered with glass wool 19, and the frictional resistance of this glass wool 19 acts, so that they will not fall.

As described above, in this embodiment, the nose cap 1
By forming the stepped portion 105 on the upper part of the inner surface of 01, the stepped portion 105 can receive the load of the shuttle tube 18 and the drive tube 22. Therefore, when the dry tube 17 incorporating the shuttle tube 18 and the drive tube 22 is inserted into the reactor core, the load of the shuttle tube 18 and the drive tube 22 does not act on the cable 21 or the connector 43, and the shuttle tube 18 and drive tube 22
Accidents of damage to the cable 21 and connector 43 due to the load can be prevented. Therefore, the installation work of the neutron flux measuring tube 11 becomes easy, and even when it needs to be replaced, it is a simple work, and the radiation exposure of the workers can also be reduced.

Further, the nose cap 101 of this embodiment is composed of an upper cap 102 and a lower cap 103, and the nose cap can be attached by simply screwing the upper cap 102 into the dry tube 17 and screwing the lower cap 103 into the upper cap 102. This is possible, and the attachment and detachment work is also extremely easy.

Further, chamfered portions 104 and 10 are provided on the outer peripheral surfaces of the upper cap 102 and the lower cap 103, respectively.
6 is formed in order to facilitate operation using the jig, so the workability is also extremely good.

Further, since a set screw 111 is attached to the upper end of the protective cover 107 disposed in the lower cap 103 to prevent the protective cover 107 from falling, the protective cover 107 will fall when the neutron flux measurement tube 11 is attached or detached. There's nothing to do.

Next, a second embodiment will be described with reference to FIG. In this second embodiment, the nose cap is not divided into two parts as in the first embodiment, but is integrated. First, nose cap 20
A male threaded portion 202 is formed on the outer periphery of the upper end of the nose cap 201, and the nose cap 201 is screwed into the dry tube 17 via this male threaded portion 202. Further, a chamfered portion 203 is formed on the outer peripheral surface of the nose cap 201 at a position below the male threaded portion 202, and this chamfered portion 203 facilitates operation with a jig (not shown). A stepped portion 204 is formed on the inner peripheral side of the nose cap 201, and the lower end surface of the drive tube 22 engages with this stepped portion 204 from above, thereby allowing the drive tube 22, shuttle tube 18, etc. Support the load. The lower part of the stepped part 204 has a smaller diameter than the upper part, and another stepped part 205 is formed. The lower part of this stepped part 205 has an even smaller diameter, and the maximum outer diameter part 43 of the connector 43
The inner diameter is approximately the same as the outer diameter of a. This portion supports the connector 43 to prevent damage due to vibrations and the like.

As described above, according to the second embodiment, not only can the same effects as in the first embodiment be achieved, but also because the nose cap 201 is integrated, the number of parts is small and the work is easy. , which is also preferable in terms of cost.

Next, a third embodiment will be described with reference to FIG. In this third embodiment, the nose cap is divided into two parts as in the first embodiment. First, the nose cap 301 is the cap 3 above.
02 and a lower cap 303. First, the upper cap 302 has a male threaded portion 304 formed at its upper end, and is screwed into the dry tube 17 via this male threaded portion 304. A chamfered portion 3 is provided on the outer peripheral surface of the male threaded portion 304 at a lower position.
05 is formed to facilitate operation using a jig (not shown). Above upper cap 3
02 extends further downward in the axial direction than the upper cap of the first embodiment, and has a female threaded portion 306 formed at its lower end. Also, this female thread part 3
A chamfered portion 307 is formed above the chamfered portion 306, and as in the case of the chamfered portion 305 described above, operation using a jig (not shown) is facilitated.

On the other hand, the lower cap 303 is inserted into the upper cap 302 from below, and the male threaded portion 308 formed on the outer peripheral surface of the lower portion is screwed into the female threaded portion 306, thereby forming the upper cap 302. It has been concluded. A protective cover 309 for protecting the connector 43 is integrally formed on the upper part of the lower cap 303, and the inner diameter of this protective cover 309 is
This substantially coincides with the outer diameter of the maximum outer diameter portion 43a of No. 3.
This protective cover 309 prevents damage to the connector 43 due to vibration. Moreover, the above protective cover 309
The lower end surface of the drive tube 22 engages with the upper end surface from above, thereby causing the drive tube 2
2 and the shuttle tube 18. That is, in this third embodiment, the upper end surface of the protective cover 309 is the stepped portion 310 of the nose cap 301.

As described above, in the case of the third embodiment, the same effects as in the first and second embodiments can be achieved, and furthermore, the attachment and detachment operations are extremely simple.

[Effects of the Invention] As described in detail above, in the present invention, a stepped portion is formed on the upper inner surface of the nose cap, and this stepped portion receives the loads of the shuttle tube and the drive tube. Therefore, when the dry tube in which the shuttle tube and drive tube are installed is inserted into the reactor core, the load of the shuttle tube and drive tube is transferred to the signal cable pulled out from the lower end opening of the drive tube and the signal cable attached to the end of the cable. It does not act on the connector, and damage to the signal cable and connector can be prevented.

[Brief explanation of drawings]

1 to 5 are diagrams showing the first embodiment of the present invention, FIG. 1 is a sectional view showing the configuration of the nose cap and its vicinity, and FIG. 2 is a diagram showing the shuttle tube and drive tube inside the neutron flux measurement tube. 3 is a sectional view showing the state in which the detector and cable are inserted, FIG. 4 is a sectional view showing the state in which the upper cap is attached, and FIG. 5 is a sectional view showing the state in which the lower cap is attached. 6 is a sectional view showing the structure of the nose cap and its vicinity according to the second embodiment; FIG. 7 is a sectional view showing the structure of the nose cap and its vicinity according to the third embodiment; Figures 8 to 16 are diagrams used to explain conventional examples; Figure 8 is a cross-sectional view showing the configuration of a part of a boiling water reactor; Figure 9 is a cross-sectional view showing the configuration of a neutron flux measurement tube. 10 is a sectional view showing a part of the neutron flux measurement tube in detail, FIG. 11 is a sectional view showing the connection structure with the shuttle tube and the drive tube,
Fig. 12 is a sectional view of the drive mechanism, Fig. 13 is a sectional view of the nose cap, Fig. 14 is a sectional view showing the engagement structure between the neutron flux measurement tube and the neutron flux measurement flange, and Fig. 15 is a sectional view of the detector and the neutron flux measurement flange. FIG. 16 is a diagram showing the cable insertion operation, and FIG. 16 is a diagram showing the modification of the cable and the connector. 1...Reactor pressure vessel, 4...Reactor core, 11...
Neutron flux measurement tube, 17...Dry tube, 18
...Shuttle tube, 20...Detector, 21...
...Cable, 22...Drive tube, 101
...Nose cap, 102...Upper cap,
103...Lower cap, 105...Stepped portion (support mechanism), 107...Protective cover (protection mechanism).

Claims (1)

[Claims] 1. A dry tube inserted into the reactor core through the bottom of the reactor vessel, a shuttle tube inserted from the lower end opening of the dry tube, and a shuttle tube connected to the lower end of the dry tube. A drive tube that is moved in the axial direction, a neutron detector provided at the upper part of the shuttle tube, and a signal cable that is connected to the neutron detector, passes through the shuttle tube, and is pulled out from the lower end opening of the drive tube. A neutron flux measuring tube comprising: a connector attached to an end of the signal cable; and a cylindrical nose cap screwed onto the lower end of the dry tube when the dry tube is inserted into the reactor core. . A neutron flux measuring tube, characterized in that a stepped portion is formed on the upper inner surface of the nose cap, with which the lower end of the drive tube comes into contact.