JPS645277B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device used to release a neutron measurement tube inserted into the core of a nuclear reactor from sticking to a guide tube or the like.

A boiling water reactor is equipped with a neutron measurement tube that penetrates the bottom of the reactor pressure vessel. This neutron measurement tube is supported by inserting its lower part into the in-core guide tube, but impurities such as crud brought into the reactor during reactor operation can get between the guide tube and the neutron measurement tube. It is necessary to assume the situation where the neutron measurement tube becomes stuck to the guide tube. If such sticking occurs, it may become impossible to lift the neutron measurement tube from the upper part of the reactor when replacing the neutron measurement tube during periodic inspection or the like.

This invention was made based on the above circumstances, and its purpose is to apply direct external force to the neutron measurement tube from the bottom side of the reactor pressure vessel in the axial and circumferential directions when the neutron measurement tube becomes stuck. It is an object of the present invention to provide a fixation release device for a neutron measurement tube, which can release the fixation without damaging the neutron measurement tube.

The present invention will be described below with reference to an illustrative embodiment. In the figure, 1 is a neutron measurement tube. The neutron measurement tube 1 has its lower half inserted into the in-core guide tube 2, and its upper half exposed in the core region S between the core support plate 3 and the upper grid plate 4. This core region S is loaded with fuel assemblies (not shown). Further, the head 1a of the neutron measuring tube 1 is constructed so as to be able to protrude from the lower main body 1b, and is biased in the protruding direction by a spring 5 to fit into the locking recess 6 of the upper grid plate 4. is supported. 7 and 8 are large-diameter guide sections provided in the middle of the neutron measurement tube 1, and these guide sections 7 and 8 are connected to the in-core guide tube 2.
It is designed to be able to slide freely against the surface. Further, the lower end of the in-core guide tube 2 penetrates the bottom of the reactor pressure vessel 10 and is connected to the housing 11 at the lowermost end.
has been formed. A flange portion 13 is fixed to the lower surface of the housing 11 with a sealing material 12 interposed therebetween by bolts 14. The lower part of the neutron measurement tube 1 passes through the through hole 15 provided in the housing 11 and the flange portion 13.
Further, a male threaded surface 16 is formed on the outer peripheral surface of the neutron measuring tube 1 in the middle of the lower part thereof. This male thread surface 16
During normal reactor operation, a tightening nut (not shown) is screwed into the flange portion 13 to tighten the neutron measuring tube 1 downward between the flange portion 13 and the lower surface of the flange portion 13. By this tightening, the sealing step part 18 of the neutron measurement tube 1 comes into close contact with the tapered valve seat part 17 formed in the flange part 13, and the inside of the in-core guide tube 2 can be kept watertight. ing. Further, a removable nose piece 19 that covers the terminal of the sensor is screwed onto the lowermost end of the neutron measurement tube 1. This nose piece 19 is screwed on when replacing the neutron measurement tube 1, and after replacement, it is removed and a signal cable is connected to the sensor terminal.

Further, a threaded portion 20 is provided on the inner surface of the opening 15a of the through hole 15, and the fixing release device 2 of the present application utilizes this threaded portion 20 and the male threaded surface 16.
5 can be installed. The configuration of this fixing release device 25 will be explained below.
is a fixed outer tube, and this fixed outer tube 26 has a threaded portion provided on the outer circumferential surface of its upper end portion which is screwed into the threaded portion 20 and tightened to form a flange portion 13.
is fixed in a liquid-tight manner. The threaded portion 20 is a so-called tapered thread with a smaller diameter on the inner side to improve watertightness. Further, a drain port 27 is provided at the lower end of the fixed outer tube 26, and this drain port 27 is communicated with a drain pit of the pedestal via a drain hose (not shown). Further, a sleeve 28 is fixed to the lowermost end of the fixed outer tube 26, and a first force transmitting body 29 is rotatably attached to the outer surface of the sleeve 28. A plurality of through holes 30 are formed in the force transmitting body 29 at equal intervals in the circumferential direction. Connection bolts 41, which will be described later, are inserted into these through holes 30, and nuts 31 are screwed into them.

A movable shaft 32 is inserted into the fixed outer tube 26. A pipe-shaped inner tube portion 32a into which the lower end portion of the neutron measurement tube 1 is inserted is provided at the upper portion of the movable shaft 32. A female threaded surface 33 is formed on the inner surface of the distal end of this inner tube portion 32a, and this female threaded surface 33 can be screwed into the male threaded surface 16 of the neutron measurement tube 1. Numerals 34 and 34 are sealing materials for maintaining fluid tightness between the fixed outer tube 26 and the movable shaft 32. Furthermore, a thrust bearing 35 is provided in the large diameter portion 32b formed at the lower part of the movable shaft 32.
A second force transmitting body 40 is rotatably mounted via radial bearings 36 and 37. Connecting bolts 41 are fixed vertically to the upper surface of this force transmitting body 40. And these connecting bolts 41
... are inserted through the through holes 30 of the force transmitting body 29 described above, and nuts 31 are screwed together. That is, by changing the screwing position of these nuts 31..., the force transmitting body 40 on the movable shaft side is raised and lowered, and along with this movement, the movable shaft 32 is moved in the axial direction with respect to the fixed outer tube 26. It's summery. That is, the force transmitting bodies 29, 40, the connecting bolts 41, the nuts 31, and the like constitute an axial drive mechanism 38. A dust cover 42 prevents dust from entering the thrust bearing 35. Further, 43 is a cover that covers the lower surface of the force transmitting body 40, and is fixed with bolts 44,44. Further, the radial bearing 37 is fixed by a nut 45. In addition, the movable shaft 32
A sealing material 46 is attached to the sliding surface between.

Further, at the lowermost end of the movable shaft 32, there is provided an operating section 47 for rotating the movable shaft, which has a non-circular cross-section, for example, a square head shape. By turning, the rotation shaft 32 rotates together.

Next, the operation of the device of the above embodiment will be explained. During normal operation of the nuclear reactor, the unsticking device 25 is removed from the flange portion 13 and is instead tightened onto the externally threaded surface 16 by a tightening nut (not shown). As a result, the sealing step portion 18 of the neutron measurement tube 1 is pressed against the valve seat portion 17, and watertightness is ensured. Further, the nose piece 19 has been removed, and a signal cable has been led out from the terminal of the sensor.

Then, during periodic inspections, etc., the neutron measurement tube 1
When replacing the above tightening nut,
6, remove the signal cable, and attach the nose piece 19. Then, the equipment handling device installed on the auxiliary hoist provided on the fuel exchange platform is lowered into the reactor core, engaged with the head 1a of the neutron measurement tube 1, and this head 1a is attached to the spring 5.
The neutron measuring tube 1 can be lifted out by raising the hoist again by pushing it toward the main body 1b side against the elastic force of the neutron measuring tube 1, thereby disengaging the fitting from the locking recess 6. However, at this time, if for some reason, for example, the sealing step part 18 is stuck to the valve seat part 17 or the guide parts 7 and 8 are stuck to the inner surface of the in-core guide tube 2, it is difficult to lift the neutron measurement tube 1. Therefore, if you try to forcefully lift the neutron measurement tube 1, there is a risk that the neutron measurement tube 1 will be damaged.

Therefore, in this case, the fixing release device 25 is used. First, the female threaded surface 33 at the tip of the movable shaft is screwed into the male threaded surface 16 of the neutron measurement tube 1. At this time, the fixed outer tube 26 is placed on the cover 42 together with the force transmitting body 29 due to its own weight, and a wide gap is secured between the upper end of the fixed outer tube 26 and the flange portion 13. Therefore, the screwing operation of the female thread surface 33 can be easily performed. Next, the fixed outer tube 26
The tip threaded portion of the flange portion 13 is screwed into the threaded portion 20 of the flange portion 13 and tightened. Then, the nuts 31... are tightened to the connecting bolts 41..., and the force transmitting bodies 29, 4
0 Shorten the distance between each other. By doing this,
Since the second force transmitting body 40 rises relatively, the movable shaft 32 receives a rising force via the thrust bearing 35. Therefore, the sealing step portion 18 can be raised from the valve seat portion 17. At this time, the reactor water in the in-core guide tube 2 passes through the valve seat part 17 and enters the gap between the fixed outer tube 26 and the movable shaft 32, but since the fixed outer tube 26 is installed in a liquid-tight manner, Water never leaks.

Next, a torque wrench is fitted to the operating portion 47 of the movable shaft 32, and the movable shaft 32 is rotated to forcibly rotate the neutron measurement tube 1. This makes it possible to release the fixation of the neutron measurement tube 1. Note that the torque wrench is designed to be able to transmit torque with a safe torque that does not damage the neutron measurement tube 1.

When the fixation can be released as described above and the neutron measurement tube 1 can rotate sufficiently smoothly, loosen the nuts 31 again and lower the neutron measurement tube 1.
A sealing step part 18 is brought into close contact with a valve seat part 17 to achieve self-shielding. and drain port 2
The reactor water in the fixed outer pipe 26 is discharged to the drain pit through a drain hose (not shown) connected to the pipe 7.
When the drainage is completed, the fixed outer tube 26 is removed from the flange portion 13 and lowered onto the force transmitting body 40 on the lower side. Next, the operation part 47 is turned with a wrench to release the threaded engagement between the female threaded surface 33 and the male threaded surface 16 at the tip of the fixed shaft, and the fixing release device 25 is lowered onto the workbench.
By screwing a drain pipe (not shown) into the opening 15a of the flange portion 13, a standard style is created in which the neutron measurement tube 1 can be lifted.
A signal is sent to the fuel exchange platform to lift up the neutron measurement tube 1 and replace it with a new neutron measurement tube.

As described above, according to this embodiment, even if the neutron measuring tube 1 is stuck, the sticking can be effectively released by directly applying a lifting force and rotational force to the neutron measuring tube 1. Additionally, there is no leakage of reactor water during work, and the amount of radiation exposure associated with work is low. In addition, since the neutron measurement tube 1 can be rotated with the sealing step portion 18 raised above the valve seat portion 17, damage to the valve seat portion 17 can be prevented.

Furthermore, since the movable shaft 32 is fixed by using the existing male threaded surface 16 into which a tightening nut is screwed during reactor operation, there is no need to perform any new processing on the neutron measurement tube 1. There is also an advantage.

In the above embodiment, the second force transmitting body 40 is moved up and down by adjusting the amount of screwing of the nut 31. However, for example, it is possible to move the bolt into a threaded hole formed on the upper surface of the force transmitting body 40. The force transmitting body 40 may be raised and lowered by inserting a screw into the bolt and changing the amount of screwing of this bolt. In short, the present invention only needs to include an axial drive mechanism that can change the relative position of the movable shaft in the axial direction with respect to the fixed outer tube. Therefore, it is also possible to employ a mechanism that uses a hydraulic jack or the like to move the movable shaft in the axial direction.

As explained above, this invention enables the neutron measurement tube to be forcibly moved directly in the axial direction and the circumferential direction via the movable shaft detachably attached to the neutron measurement tube, and is simply a hoist. Compared to the case where the upper end of the neutron measurement tube is grasped and lifted with a tool, the fixation can be released without damaging the neutron measurement tube. In addition, the fixed outer tube is liquid-tightly screwed into the opening of the inner-core guide tube flange, and work can be carried out while maintaining the inner-core guide tube liquid-tight, which prevents reactor water from scattering.
This method is effective in efficiently and safely removing stuck neutron measurement tubes, since the amount of radiation exposure during work is small, and the operating rate of the reactor can be improved.

[Brief explanation of the drawing]

The drawing is a longitudinal sectional view showing an embodiment of the present invention. 1... Neutron measurement tube, 2... In-core guide tube,
10...Reactor pressure vessel, 13...In-core guide pipe flange portion, 15...Through hole, 15a...Opening portion, 16...Male thread surface, 25...Fixing release device,
26... fixed outer tube, 29... first force transmitting body, 3
2... Movable shaft, 33... Female threaded surface, 38... Axial drive mechanism, 40... Second force transmission body, 41...
Connection bolt, 47...operation unit.

Claims (1)

[Scope of Claims] 1. A fixed outer tube whose upper end is removably and liquid-tightly screwed into the opening of an in-core guide tube flange attached to the bottom of the reactor pressure vessel, and a fixed outer tube with a liquid-tight structure inside the outer tube. It is inserted into the neutron measuring tube and is movable in the axial and circumferential directions with respect to the outer tube, and has a female threaded surface on the inner surface of the upper end. It is characterized by comprising a movable shaft to which the movable shaft is screwed, an axial drive mechanism for driving the movable shaft in the axial direction with respect to the fixed outer tube, and an operating part for rotating the movable shaft formed on the movable shaft. Neutron measurement tube fixation release device. 2 The above-mentioned axial drive mechanism includes a first force transmitting body attached to a fixed outer tube, a second force transmitting body attached to a movable shaft, and a connection between these two force transmitting bodies with the two force transmitting bodies separated and facing each other. 2. A neutron measurement tube fixation release device according to claim 1, comprising a bolt mechanism that can freely adjust the amount of screw movement.