JP4245489B2 - In-furnace work method and apparatus - Google Patents

Description

  The present invention relates to an in-core work method and apparatus capable of efficiently performing inspection and inspection and preventive maintenance work in a reactor pressure vessel in a boiling water reactor power plant.

  In order to access the in-core working device to the conventional reactor bottom, the fuel and control rod drive mechanism is removed, and the in-core working device is passed through the reactor core to access the reactor bottom ( For example, Patent Document 1).

  In addition, when accessing the inside of the jet pump, the upper opening of the jet pump is not an opening through which the inside can be seen from above, so a guide mechanism is attached to the inlet mixer of the jet pump from the upper part of the furnace. The in-furnace working device was smoothly inserted into the jet pump for access (for example, Patent Document 2).

JP 2001-281386 A

JP 2001-159696 A

  However, in the former method, it is necessary to remove the fuel, the control rod, and the control rod drive mechanism from the reactor before installing the in-core work device at the bottom of the reactor. In the latter method, the jet pump has a guide mechanism. It is necessary to install it, and it takes a lot of time and labor to install it.

  The present invention has been made in view of the circumstances as described above, and the working apparatus main body is placed inside the jet pump and the atoms without removing the fuel, the control rod and the control rod drive mechanism, and without attaching the guide mechanism to the jet pump. It is an object of the present invention to provide an in-furnace working method and apparatus accessible to the furnace bottom.

  In order to achieve the above object, the present invention constitutes an in-furnace working apparatus by the following means.

In an in-reactor working method for performing an operation by inserting a main body of a working device from an upper part of the reactor into a jet pump for circulating reactor water in a reactor pressure vessel, the main body at an end of the working device. A guide provided at an end of the working device is inserted into an opening on a side surface of the jet pump so that the center axis of the work device is deviated by a predetermined angle with respect to the center axis in a state where the center axis is in a vertical direction, It is inserted into the jet pump following the guide.

  In this case, the angle of the guide with respect to the central axis of the main body can be adjusted, and when the guide is inserted into the opening, the guide is biased to the predetermined angle, and the main body is disposed inside the jet pump. The guide can also be used as a work tool after it is inserted into the tool.

  The main body may be pulled into the jet pump by gravity acting on the guide.

Furthermore, the present invention provides a main body inserted from the upper part of the reactor into a jet pump for circulating reactor water in a reactor pressure vessel, and the central axis in a state where the central axis of the main body is in a vertical direction. And a guide that can be inserted into an opening on a side surface of the jet pump provided at a lower portion of the main body so as to be deviated by a predetermined angle .

  Further, the guide can be a guide bar attached to the lower end of the main body at a predetermined angle with respect to the central axis, and the guide is freely supported by the main body and has its own weight. The guide may be configured to be deviated by a predetermined angle with respect to the vertical direction, or the guide may be supported by the main body so as to be restored to the position deviated by the predetermined angle with respect to the central axis of the main body.

  Furthermore, the guide may be configured to be able to control a deflection angle of the main body with respect to the central axis, and in this case, the guide may be used as a work tool.

  The main body includes at least three parts connected by a plurality of joints, and the main body includes a plurality of supports that can be engaged with an inner wall of the jet pump and that can be stored in the main body. May be.

Furthermore, the present invention provides a main body inserted from the upper part of the reactor into a jet pump for circulating reactor water in a reactor pressure vessel, and the central axis in a state where the central axis of the main body is in a vertical direction. And a guide that can be inserted into the opening of the side surface of the jet pump provided at the lower part of the main body so as to be deviated by a predetermined angle, and has a surface that is deviated with respect to the central axis .

  According to the present invention, the in-reactor operation allows the work device main body to be accessed inside the jet pump and the reactor bottom without removing the fuel, the control rod, and the control rod drive mechanism, and without attaching the guide mechanism to the jet pump. Methods and apparatus can be provided.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing the overall configuration of a first embodiment of an in-furnace working apparatus according to the present invention.
The in-furnace working device includes a working device main body 1, a wire rope 2 attached to the upper end portion of the working device main body 1, a lower end portion of the working device main body 1, an opening on a side surface of the jet pump, That is, the guide mechanism 3 is sized to be inserted between the inlet mixer and the nozzle.

  The working device body 1 is composed of an elongated tubular body 1a having a plurality of holes on the peripheral surface, and is suspended by a wire rope 2 using a hoist on the furnace upper portion (not shown), and at the upper opening end of the tubular body 1a. A hose 4 is connected, and water in the jet pump can be sucked through a hole 1b provided in the peripheral surface of the tubular body 1a by a pump (not shown) connected to the hose 4.

  The guide mechanism 3 has a guide bar 5 attached with a tip portion thereof being deviated by a predetermined angle with respect to a vertical direction that is the central axis of the work apparatus main body 1, and the posture of the guide mechanism 3 is not changed greatly when the guide bar 5 is inserted. The guide bar 5 is attached to the lower part of the weight 6. Further, the guide mechanism 3 is fixed to the lower part of the work apparatus body 1 through a joint 7 such as a universal joint, and its peripheral part is covered with a bellows 8 made of an elastic member such as rubber.

  Next, the operation of the in-furnace working apparatus configured as described above will be described with reference to FIG.

  Now, as shown in FIG. 2, when the work apparatus body 1 is suspended from the upper part of the furnace into the furnace by the wire rope 2 to the vicinity of the opening existing between the inlet mixer 11 and the nozzle 12 of the jet pump 10, first the work apparatus body The tip of the guide bar 5 of the guide mechanism 3 connected to the lower part of 1 is gradually inserted into the inlet mixer 11 along the tapered surface of the opening.

  Further, when the work apparatus main body 1 is suspended, the work apparatus main body 1 is pulled by the action of gravity by the weight 6 of the guide mechanism 3 that has already entered the jet pump 10. Thereby, the work apparatus body 1 is inserted so as to be drawn into the jet pump 10 following the guide mechanism 3 in a state in which the attitude of the entire apparatus does not change. Here, the periphery of the joint 7 connecting the guide mechanism 3 and the lower part of the work apparatus main body 1 is covered with a bellows 8, whereby the guide mechanism 3 has its distal end portion connected to the central axis of the work apparatus main body 1. In contrast, a restoring force is applied so as to return to a position deviated by a predetermined angle. Therefore, the gravity of the weight 6 of the guide mechanism 3 and the action of the restoring force by the bellows 8 can be smoothly drawn into the jet pump 10 without greatly changing the posture of the work apparatus body 1.

The weight of the weight 6 and the magnitude of the restoring force due to the bellows 8 are determined appropriately depending on the size of the opening between the nozzle of the jet pump 10 and the inlet mixer, etc. The mechanism 3 can be reliably inserted into the jet pump 10 without being caught in the jet pump 10. Further, the guide rod 3 can be configured to also serve as the weight 6, and the bellows 8 can be configured not to have a restoring force. When the bellows 8 is configured so as not to have a restoring force, the guide mechanism 3 is free-supported, that is, point-supported by the work apparatus main body 1, but if the weight 6 is appropriately set, the guide mechanism 3 is similarly provided. 3 can be smoothly inserted into the jet pump 10.
When these operations are performed, the wire rope 2 is suspended and the amount of movement can be confirmed from the outside of the furnace.

  When a pump (not shown) is operated with the work apparatus main body 1 inserted at a predetermined position, water in the jet pump 10 is connected to the upper open end of the tubular body 1a through a hole 1b provided in the peripheral surface of the tubular body 1a. Then, the air is sucked through the hose 4 and led to the analysis filter outside the furnace from the pump outlet. The water that has been collected and purified by this analysis filter with an appropriate amount of contaminants is returned to the reactor water.

  As described above, when the operation of collecting the pollutants and the like in the jet pump 10 is completed, the work apparatus main body 1 is lifted to the upper part of the furnace by the reverse operation to the above, and the series of operations is completed.

  In the above embodiment, the contaminants and the like in the jet pump 10 are collected. However, when the inside of the jet pump 10 is inspected, a TV camera and an eddy current probe are inserted into the hole 1b provided on the peripheral surface of the tubular body 1a. In addition to mounting the array and ultrasonic probe, instead of the hose connected to the upper open end of the tubular body 1a, these devices are connected to a control device installed outside the furnace via signal cables. By doing so, the test | inspection in the jet pump 10 can be implemented easily.

  In the above-described embodiment, the work apparatus main body 1 is constituted by the tubular body 1a having a plurality of holes on the peripheral surface. However, the tubular body 1a is provided with three or more arms deployed or stored around the axis at equal intervals. The fixing mechanism provided is installed, the fixing mechanism is set in the retracted state, the work apparatus body 1 is inserted to a predetermined position in the jet pump 10, and the fixing mechanism is deployed at that position. You may enable it to fix the working device main body 1 to an inner wall stably.

  Furthermore, in the said Example, although it is a case where the contaminant in the jet pump 10 is removed and test | inspected for the working apparatus main body 1, when inserting into the reactor bottom part, the work inserted in the jet pump 10 is carried out. The apparatus body 1 is further suspended by the wire rope 2 through the opening at the bottom of the jet pump 10 to the bottom of the reactor, and inspected in the same manner as described above using a TV camera, eddy current probe, array type ultrasonic probe, etc. Can be implemented.

  As described above, in the first embodiment of the present invention, the guide rod 5 has a dimension that can be inserted from the opening between the inlet mixer 11 and the nozzle 12 on the side surface of the jet pump 10 and is provided at the lowermost end of the work apparatus body 1. Since the tip portion is attached with a predetermined angle offset with respect to the vertical axis of the work apparatus main body 1, the work apparatus main body 1 is attached to the predetermined inside of the jet pump without attaching a guide mechanism to the jet pump 10 as in the prior art. In addition to being smoothly inserted at the position, it can be further inserted into the reactor bottom through the opening at the bottom of the jet pump 10.

  Further, since the guide bar 5 is attached to the lower part of the work apparatus main body 1 via the weight 6, when the guide bar 5 is inserted into the jet pump 10, the weight 6 always works in the vertical direction to work. The main body 1 acts so as to retract, so that the posture of the entire apparatus does not change greatly, and the working apparatus main body is guided by the guide mechanism 3 to the opening existing between the inlet mixer 11 and the nozzle 12 of the jet pump 10. 1 can be inserted smoothly.

Furthermore, since the bellows 8 made of an elastic body is provided between the root portion of the tubular body 1a and the weight 6 so as to cover the periphery of the joint 7, when inserting the working device body 1 into the jet pump 10, It is possible to prevent the joint portion from hitting the inlet mixer 11 or the nozzle 12 and causing damage.
Further, since the bellows 8 gives a restoring force such that the tip of the guide mechanism 3 returns to a position deviated by a predetermined angle with respect to the central axis of the work apparatus main body 1, the work apparatus main body 1 is inserted into the jet pump 10. The posture when doing can be kept more stable.

  3 (a) and 3 (b) are perspective views of the overall configuration showing a second embodiment of the in-furnace working apparatus according to the present invention. In addition, the same code | symbol is attached | subjected about the structure same as 1st Example, and the detailed description is abbreviate | omitted.

  Similarly to the first embodiment, the in-furnace working apparatus according to the present embodiment is attached to the working apparatus main body 1, the wire rope 2 attached to the upper end portion of the working apparatus main body 1, and the lowermost end portion of the working apparatus main body 1. The guide mechanism 3 has a size that can be inserted from the opening on the side surface of the jet pump, that is, between the inlet mixer and the nozzle.

  In this embodiment, instead of the guide bar 5 shown in FIG. 1 in the guide mechanism 3, the surface of the lower portion of the weight 6 is inclined 5a as shown in FIGS. 3 (a) and 3 (b). , 5b. Here, the inclined surfaces 5a and 5b have surfaces that are deviated by a predetermined angle with respect to the vertical direction serving as the central axis of the work apparatus body 1 like the guide bar 5 shown in FIG. Here, the inclined surfaces 5a and 5b may be conical surfaces as shown in FIG. 3 (a), or may be elliptical surfaces obtained by cutting a cylinder by a plane as shown in FIG. 3 (b).

  Even with this configuration, when the work apparatus body 1 is suspended from the furnace top to the furnace by a wire rope to the vicinity of the opening existing between the inlet mixer and the nozzle of the jet pump, as in the first embodiment, The inclined surfaces 5a and 5b at the tip of the guide mechanism 3 connected to the lower part of the work apparatus main body 1 are gradually inserted into the inlet mixer along the tapered surface of the opening. In this state, the work apparatus main body 1 is pulled by the action of gravity by the weight 6 of the guide mechanism 3, so that the work apparatus main body 1 is moved into the jet pump 10 following the guide mechanism 3 without changing the attitude of the entire apparatus. It can be inserted as if it was pulled in.

  As described above, in the second embodiment of the present invention, the weight 6 is provided with inclined surfaces 5a and 5b on the lower side thereof, the surface of which the guide mechanism 3 is deviated by a predetermined angle with respect to the vertical direction serving as the central axis of the work apparatus body. This also provides the same effect as that of the first embodiment.

  4 (a) and 4 (b) are perspective views of an overall configuration showing a second embodiment of the in-furnace working apparatus according to the present invention, wherein (a) is a storage state of the working apparatus main body, and (b) is a working apparatus main body. The expanded state of is shown.

  The work device main body 21 is connected to the wire rope 2 and suspended from a position fixing mechanism 22, and is coaxially connected to the position fixing mechanism 22, and has a shaft rotary joint 23 a that can rotate about a root portion and a tip portion. 23b and three bending joints 23c, 23d, and 23e between the rotary shaft joints 23a and 23b, and a link mechanism 24 in which the rotary joints are coupled to each other by a link, and the rotary shaft joint 23b at the tip. And a guide bar 26 attached to the bending joint 23e on the distal end side.

  As the work tool 25 at the distal end, any one of a TV camera, an ultrasonic probe, a phased array UT head, an eddy current flaw detection head, a laser irradiation head, and a water ejection nozzle is attached in a replaceable manner.

  The root position fixing mechanism 22 is provided with at least three support bodies 27 that are developed from the work apparatus main body 21 around the axis in two stages in the vertical direction.

  Here, the work device main body 21 is suspended by the wire rope 2 using a hoist at the top of the furnace, and is connected to a control device (not shown) installed outside the furnace via a cable, an optical fiber, a tube, and the like. .

  Next, the operation of the in-furnace working apparatus configured as described above will be described with reference to FIGS. 5 (a) and 5 (b).

  Now, with the position fixing portion 22 retracted, the work tool 25 is bent so as to be folded upward by the bending joint 23e on the distal end side of the link mechanism 24, and the guide rod 26 is bent to the vertical axis of the work apparatus main body 21. On the other hand, it is held in a state where it protrudes outward at an appropriate angle.

  In this state, the working device main body 21 suspended by the wire rope 2 into the furnace using the hoist at the upper part of the furnace is opened between the inlet mixer and the nozzle of the jet pump as in the first embodiment. When suspended to the vicinity, first, the tip of the guide rod 26 connected to the bending joint 23e of the link mechanism 24 of the work apparatus main body 21 is gradually inserted into the inlet mixer along the tapered surface of the opening.

  Further, the work device main body 21 is suspended, and when it is confirmed that the work device main body 21 is inserted into a predetermined position in the jet pump, the control device installed outside the furnace causes the work device main body 21 to be placed at the base of the work device main body 21. The position fixing mechanism 22 is operated.

  When this position fixing mechanism 22 operates, as shown in FIGS. 5 (a) and 5 (b), the three support bodies 27 that are mounted in two upper and lower stages so as to be freely opened and closed are deployed outward from the axial center, One end thereof is engaged with and fixed to the inner peripheral surface of the cylindrical diffuser 13. In this case, the work apparatus main body 21 is firmly held on the inner peripheral surface of the diffuser 13 with the work apparatus main body 21 positioned at the center of the diffuser 13 by the three upper and lower support bodies 27. In the jet pump 10, 14 is a baffle plate and 15 is a shroud.

  Next, when the five rotary joints 23a to 23e in which the links are linearly connected are driven, each link is rotated according to the rotation angle of the rotary joints 23a to 23e, and the work attached to the tip portion thereof. The tool 25 moves to the work target site inside the jet pump 10. Therefore, inspection and repair in the jet pump 10 can be carried out by attaching the work tool 25 of any one of a camera, an ultrasonic probe, a phased array UT head, an eddy current flaw detection head, and a laser irradiation head to the work head. When these operations are completed, the work apparatus main body 21 is lifted to the upper part of the furnace by the reverse operation to the above, and a series of operations is completed.

  In the above description, the work apparatus main body 21 is inspected and repaired in the jet pump 10, but when the reactor bottom is inspected, the work apparatus main body 21 inserted in the jet pump is further connected to the wire rope 2. Thus, it is suspended from the bottom of the reactor through the opening at the bottom of the jet pump 10 and inspected by a TV camera, eddy current probe, array type ultrasonic probe, or the like.

  As described above, in this embodiment, the guide rod 26 that enters the work apparatus main body 21 along the tapered surface of the opening existing between the inlet mixer and the nozzle on the side surface of the jet pump is bent on the distal end side of the link mechanism 24. Since the working device main body 21 can be inserted into the jet pump 10 simply by being attached to the joint 23e, the inside of the jet pump can be installed without attaching a funnel-shaped guide device to the inlet mixer portion of the jet pump as in the prior art. Work such as inspection and repair or repair can be easily performed in a short time.

  In addition, since the work apparatus main body 21 constitutes the position fixing mechanism 22 by arranging the three support bodies 27 that can be deployed at the root portion in two upper and lower stages, the holding force for fixing the position in the cylinder can be increased. .

  Further, a link mechanism 24 is formed by connecting the five rotary joints 23a to 23e with links in a straight line below the position fixing mechanism 22, and the work tool 25 is detachable at the tip thereof. Therefore, it is possible to easily access a work head such as a camera or an ultrasonic probe to a required position in the jet pump.

  On the other hand, when working at the bottom of the reactor, the working device body 21 inserted into the jet pump is suspended from the bottom of the jet pump through the opening at the bottom of the jet pump, so that a TV camera or an eddy current probe is suspended. Inspection can be performed with a contactor, array-type ultrasonic probe, etc., so there is no need to remove the fuel assembly, fuel support bracket, control rod, and control rod drive mechanism as before, greatly increasing work time. Can be shortened.

  6 (a) and 6 (b) are perspective views showing a fourth embodiment of the in-furnace working apparatus according to the present invention, wherein (a) shows the overall configuration, and (b) is when inserted into the jet pump. The structure of is shown. In addition, the same code | symbol is attached | subjected about the structure similar to a 3rd Example, and the detailed description is abbreviate | omitted.

  As in the third embodiment, the in-furnace working apparatus according to the present embodiment is connected to the wire rope 2 and suspended from the position fixing mechanism 22, and is coaxially connected to the position fixing mechanism 22, and has a root portion and a tip. There are shaft rotary joints 23a and 23b that can rotate about the shaft, and three bending joints 23c, 23d, and 23e between the shaft rotary joints 23a and 23b, and a link mechanism 24 in which these rotary joints are connected by a link. And a working tool 25 connected to the shaft rotary joint 23b at the tip, and the joints 23a, 23b, 23c, 23d, and 23e are configured to be controllable, but in the third embodiment, 4A is different in that the guide rod 26 is not provided.

  In this embodiment, the work tool 25 provided at the tip is used as a guide 26a for insertion into the jet pump. That is, in this embodiment, the guide 26 a is a work tool 25 that can control the deflection angle with respect to the central axis of the work apparatus main body 21. Then, as shown in FIG. 6B, when the working device is inserted into the jet pump, the bending joint 23e to which the working tool 25 is attached is controlled to deviate from the central axis of the working device body by a predetermined angle. Thus, the guide 26a is obtained.

  In other words, in the present embodiment, the work tool 25 is configured so that the angle with respect to the central axis of the work apparatus main body can be adjusted, and also serves as the guide 26a. When the working device is inserted into the opening located between the inlet mixer and the nozzle on the side of the jet pump, the working tool 25 is biased to a predetermined angle and used as a guide 26a, and the entire device is placed inside the jet pump. After the insertion, the angle of the work tool 25 used as the guide 26a is further controlled by the bending joint 23, and the work is performed similarly to the third embodiment.

  Thereby, the operation | work tool 25 can be made to perform the same effect | action as the guide bar | rod 26 in Fig.4 (a), (b). When the working device body 21 is further inserted into the jet pump, the entire device can be inserted into the jet pump more smoothly by controlling the bending joints 23c and 23d as appropriate.

  As described above, according to the present embodiment, the work tool 25 attached to the tip of the work apparatus main body can be used as the guide 26b by controlling the bending joint 23e. The same effect as the embodiment can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS The perspective view of the whole structure which shows the 1st Example of the in-furnace working apparatus by this invention. The perspective view which shows the state which inserts a working device main body into the inside of a jet pump in the Example. The perspective view of the whole structure which shows the 2nd Example of the in-furnace working apparatus by this invention. It is a front view of the whole structure which shows the 3rd Example of the in-furnace working apparatus by this invention, (a) is the storage state of a working device main body, (b) is a figure which shows the expansion | deployment state of a working device main body, respectively. In the same Example, the working apparatus main body inserted in the inside of a jet pump expands a fixing mechanism, and shows the state which enters into working posture by a link mechanism, (a) is a front view, (b) is a perspective view. . It is a perspective view of the whole structure which shows the 3rd Example of the working apparatus in a furnace by this invention, (a) shows the whole structure, (b) is a figure which shows the state inserted in the inside of a jet pump.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Work apparatus main body 1a ... Tubular body 1b ... Hole 2 ... Wire rope 3 ... Guide mechanism 4 ... Hose 5 ... Guide rod 5a, 5b ... Inclined surface 6 ... Weight 7 ... Joint 8 …… Bellows 21 …… Working device main body 22 …… Fixing mechanism 23a-23e …… Rotating joint 24 …… Link mechanism 25 …… Working tool 26 …… Guide rod 26a …… Guide 27 …… Support

Claims (14)

In the in-reactor working method of performing the work by inserting the main body of the working device from the upper part of the reactor into the jet pump that circulates the reactor water in the pressure vessel of the reactor,
Inserting a guide provided at the end of the working device into the opening on the side surface of the jet pump so that the central axis of the main body is deviated by a predetermined angle with respect to the central axis in a state where the central axis is in a vertical direction ,
An in-furnace working method, wherein the main body is inserted into the jet pump following the guide. In the furnace operation method according to claim 1,
An in-furnace working method characterized in that an angle of the guide with respect to a central axis of the main body is adjustable, and the guide is biased to the predetermined angle when the guide is inserted into the opening. In the furnace working method according to claim 2,
An in-furnace working method, wherein the work is performed by controlling the angle of the guide after the main body is inserted into the jet pump. The in-furnace working method according to claim 1, wherein the main body is pulled into the jet pump by gravity acting on the guide. A main body inserted from the top of the reactor into a jet pump that circulates reactor water in the reactor pressure vessel;
A guide that can be inserted into an opening of a side surface of the jet pump provided at a lower portion of the main body so as to be deviated by a predetermined angle with respect to the central axis in a state where the central axis of the main body is in a vertical direction. An in-furnace working device. The in-furnace working device according to claim 5,
A joint attached to the lower end of the main body, a bellows covering the periphery of the joint, and a weight attached to the lower end of the joint, and the guide is provided at the lower part of the main body via the weight. An in-furnace working device. In the in-furnace working device according to claim 5,
The in-furnace working apparatus according to claim 1, wherein the guide is a guide bar attached to the lower end of the main body with a predetermined angle with respect to the central axis. In the in-furnace working device according to claim 5,
The in-furnace working apparatus according to claim 1, wherein the guide is freely supported by the main body and is configured to be deviated by a predetermined angle with respect to a vertical direction by the weight of the guide. In the in-furnace working device according to claim 5,
The in-furnace working apparatus, wherein the guide is supported by the main body so as to be restored to a position deviated by the predetermined angle with respect to a central axis of the main body. The in-furnace working device according to claim 5,
The in-furnace working apparatus, wherein the guide is configured to be able to control a deflection angle of the main body with respect to the central axis. The in-furnace working device according to claim 5,
The in-furnace working apparatus characterized in that the guide also serves as a working tool used inside the jet pump. In the furnace working device according to claim 11 ,
The main body includes at least three portions connected by a plurality of joints, and the main body includes a plurality of supports that can be engaged with an inner wall of the jet pump and can be accommodated in the main body. In-furnace working device. 13. The in-furnace working apparatus according to claim 12 , wherein the plurality of joints include a shaft rotary joint that can rotate around a central axis of the main body, and a bending joint that can adjust an angle with respect to the central axis. In-furnace working device. 6. The in-furnace working apparatus according to claim 5, wherein the guide has a surface that is biased with respect to the central axis.

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