FI104760B - Method for monitoring gap between a drive nut and a drive screw in a nuclear reactor - Google Patents

Description

x 104760

Method for monitoring the play between the drive nut and the screw in a nuclear reactor - Method 5: För övervakning av glapp mellan en drivdonsskruv i en kärnreaktor 5

The operation of the nuclear reactor is controlled by a plurality of joysticks which are inserted into or withdrawn from the reactor core, in this case from the bottom 10. There are actuators for controlling each joystick, each comprising an actuator nut (actuator nut) extending along the actuator screw, whereby this screw is rotated through the gear and motor. Above the drive screw is a piston tube 15, one end of which is supported by a quick stop sleeve against the drive nut, the other end being connected to the joystick. No oil can be used to lubricate the drive nut and the drive screw because this part of the drive is located in the environment 20, which is in direct contact with the nuclear reactor pressure vessel. This has caused the drive nut to be fitted with graphite threads and a metal safety thread. The safety thread prevents the joystick from falling out: from the fuel chamber when the graphite thread breaks or becomes too hot. However, it is important that the drive is not operated without lubrication, ie. when the graphite layer is ··· so worn that the nut leans against the safety thread.

: This may cause the screw and nut threads to be damaged and the wear-caused metal-30 chips to spread to the drive, causing danger. . with respect to the passage of the chips into the reactor water through the drive flushing stream through the drive means · · · *.

i 0 ':; "" p5 The drive nuts have a 2.5 mm thick graphite «·« layer that may wear out before contact is reached • f · ·' between the drive nut safety screws and the drive screw • i · • f 2 104760 . The need for servicing of actuators is thus largely determined by the wear on the graphite threads of the drive nuts. The clearance of the new drive nut turns the screw about 15-20 ° before the nut moves along the screw. In this case, the 1 ° rotation of the 5 screws corresponds to a 0.027 mm axial movement of the nut in the thread pitch used in the present case (other pitches can of course also be used). For example, if a maximum absolute clearance of about 70 ° is allowed, this corresponds to a wear of a graphite thread of a nut of delta (70 ° 20 °) x 0.0027 mm = 1.35 mm.

According to a known clearance measurement method, the gear unit gear and motor are omitted and replaced by 15 manual measuring clamps. The play is then measured by moving the drive nut to its lower end position so that it leans against the drive flange. In this position, the scale of the measuring clamp is reset, after which the screw is further rotated by the palm of the mit-20 clamp until it stops, thereby achieving a mechanical lock between the actuator nut and the screw. The degree of rotation of the crank is then read from the dial and indicates the play: the magnitude. This measurement process is complicated and expensive because, as mentioned above, among other things, the motor housing itself must be removed from the drive flange. This must: · · be confined in a confined space in front of the concrete shield and, in addition to the • difficulty of the work, will require the maintenance personnel to be exposed to certain radiation. Because the number of actuators required for the reactor can be up to 150 units. . and even greater, it is easy to understand that any improvement in the method described can lead to great savings.

It is an object of the present invention to provide a method for controlling the gap between the drive screw and the nut, 104760 for controlling the bottom of a nuclear reactor. a joystick inserted into the active heart.

According to the invention, the actuator is provided with a sensor 5 which detects the revolutions and revolutions that the actuator screw rotates in connection with the control. When the actuator nut is worn, it is moved to a predetermined detection position, for example from the upper mechanical to the stop, and the actuator screw is stopped at the first rev-10 read position, which the sensor reads. After a certain time of operation, the drive nut is again moved to the same detection position, for example, from the upper mechanical to the stop, and the sensor reads the second speed of the drive screw. The difference between turns and / or revolutions between said revolution positions is then determined, which difference corresponds to the wear of the nut during the service life.

If, for example, this difference is 20o in one turn, the aforementioned thread has a lifetime of 20 x 0.027 mm = 0.54 mm. Assuming that the nut was completely new at the beginning of the measurement, it can be assumed that it can still be used for some time. Thus, the method does not determine: absolute clearance, but only measures the change in clearance from one situation to another. However, this is quite sufficient if at the beginning of the measurement the state of the nut ···, ie. the degree of wear of the graphite thread is known, and. ·: the clearance measured in degrees of rotation of the drive screw to which it corresponds. Subsequent measurements then indicate an increase in play and thus an increase in wear. Above. . 50 °, corresponding to a wear of about 1.35 mm, before the * · * nut needs to be replaced.

A suitable device for carrying out this method comprises a sensor equipped with a cam having a plurality of ridges at its periphery. This cam wheel is set to rotate in conjunction with the 4 104760 actuator screws and the ridges are designed to influence the inductive sensor so that each pulse generated corresponds to a specific rotation of the actuator screw. The ridges must be evenly distributed around the cam ring 5 with the exception of one ridge which has been removed. The removed ridge provides a clear reference point for each full turn of the drive screw.

A new test of the actuators described above may be performed at appropriate times during the actuation cycle, whereby the actuator nut play is monitored and each actuator maintenance need can be determined. These measurements can be made from a central measuring station "within the joystick" without the need to remove the actuators, which is a major advantage over the prior art method.

One important point to note in this context is that measurements must be made mainly at the same operating temperature of the drive, otherwise erroneous results may be obtained. The difference of more than 20 ° C between different measuring procedures must be corrected at discretion.

The invention can best be understood with reference to the accompanying Figures 1 through 2, wherein Figures 1 and 2 schematically illustrate the operation of the actuators, Fig. 3 the location of the sensor in the actuator, Fig. 4 above the displacement of the actuator nut. - .. - towards the mechanical stop and Fig. 5 of the measuring device «. electrical wiring diagram.

ψ · «30. In Figure 1, the number 1 denotes the reactor vessel. The reactor core with the cartridges 2 and '·]' joysticks 3 is placed therein. These joysticks 3 are controlled by actuators comprising, inter alia, an actuator housing 4 connected via a actuator flange 5 to a quick coupling 6 and a gear motor 7.

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Fig. 2 shows the positioning of the drive nut 8 on the drive screw 9 inside the guide tube 10 of the drive housing 4. The drive screw 9 extends to the upper end of this guide tube 10. A piston tube 5i is disposed about the actuator screw 3, which rests against the actuator nut 8 via a sleeve for the quick stop. The piston tube 11 is connected in the upward direction to the joystick 3. The sleeve 12 and the drive nut 8 are provided with guide members 13 which run along guide strips 10 not visible in the figures and prevent the drive nut 9 from rotating with the drive screw 9.

Figure 3 uses the same notations as above. Figure 3 further shows a tube 14 containing a tongue element 15, 15 which cooperates with the drive nut 8 and the magnets 16 for position detection of the sleeve 12.

3, the cam screw 17 and the inductive sensor 18 are also provided on the shaft of the drive screw 9. In this case, the cam 17 wheel is provided with 72 ridges corresponding to a rotation of 5 ° towards the ridge. Each ridge induces a pulse in the inductive sensor and these pulses are further passed to the pulse counter. Contrary to the foregoing, with respect to the uniform distribution of the ridges ', i,' 25, one of the ridges is removed around the cam 17, which results in a clear reference point for each rotation of the screw; j from the printer connected to the pulse counter. Pulse- • «, ·: ·. thus also calculates each revolution and divides the rotation of the drive 30 screw 9. For example, if the wear-resistant. . the actuator nut 8 with graphite thread is moved towards the upper mechanical stop, · · using the pulse counter, it is possible to determine the rotation position of the screw 9,: T: in this case, at 5 ° intervals. When the measurement is made from the same mechanical: "'35 for the stops, the pulse counter, again at 5 ° intervals, can be used to determine how much further the · · * \ * screw 9 can be rotated through the graphite of the drive nut 8.

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6 104760 on the basis of thread wear. This measurement is facilitated by the use of a fixed reference point per revolution corresponding to the ridge removed as proposed. As mentioned above, the difference between the two measurement values is allowed up to a maximum of 50 °, in other words substantially less than one turn, which of course facilitates the determination of wear.

To further simplify the measurement, the pulses 10 may be passed to a measurement converter which directly converts the pulses to the magnitude of the rotation angle of the screw 9.

All of these operations can be performed at the measurement center 19, which is located at the biological protection site, i. inside the concrete shell 15, which is schematically marked on the walls 20. From the control room, sensors 18 of different actuators can be connected to one another and the increased play is measured, after which the measurement value is transmitted to a measurement computer 21 in the control room.

Figure 4 schematically illustrates how to move the actuator nut 8 v: towards the upper mechanical stop 22. In order to do this:,:.: 25, the upper limit switch of the actuator must be bypassed. In the figure, the number 8 denotes, as in the past, a drive nut fitted with a · · · · · ·; graphite thread 23, the total amount of wear (about • t ......-------- 2.5 mm) is indicated by the lined areas 34.

30 The number 35 denotes a nuts nut made of inconel. . a number 13 t r t · r denotes a graphite control member extending along the guide 24 * * *. The figure further schematically shows how the cam V * i wheel 17 is connected to the drive screw 9 and how the pulses induced by the sensor 35 are further transmitted to the pulse counter 25. It should also be understood that the more the thickness of the wear surface 34 decreases, the more the screw 9 may be rotated before it locks when the drive nut comes against the mechanical stop 22. This mechanical stop will of course comprise a fixed measuring point, but in theory the measuring method described above may be implemented using some drive detection position, e.g. "rod inside" or "drive nut inside" instead of coming against the mechanical stop, but such a method of measurement is somewhat more uncertain.

Figure 5 finally shows a wiring diagram of a measuring device in which inductive sensors are designated 18, 18 ', 1811 and 1811'. These sensors 18 communicate with the pulse calculator 25 via a plurality of interleaver cards inserted in the relevant terminal 26. Computer 27 collects 15 measurement data from various sensors 18 and transmits them via modem 28, coaxial cable 29 and modem 30 to measurement computer 31 equipped with hard drive 32 and with a printer 33. The measured values can be stored on this computer in the control room 31.

From the control room, a signal may be transmitted from the computer 31 to the relevant terminal 26 for connection of a new sensor 18 '. In this way, from the control room, the operation of all the actuators can be gradually controlled for increased nut clearance and the measurement results stored in the measuring computer 31.

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Claims (4)

Method for monitoring gap between a drive screw 5 (9) and a drive nut (8) for operating a control rod (3) which is inserted from below into the core of a nuclear reactor, characterized in that the drive is provided with a sensor (18) indicating turns and portions of a turn that the actuator screw (9) rotates during actuation, that in the case of undigested actuator nut (8) it is driven towards a certain definite indication position, preferably its upper mechanical stop (22), wherein the actuator screw (9) is stopped in a first rpm position which is read via the transducer (18), that after a certain operating time the nut (8) eats is driven to the same indication position, preferably its upper mechanical stop (22), and the second rpm position of the drive screw (9) is read, where after the difference in turns and / or in parts of a revolution between said speed positions is determined, said difference corresponding to the nut wear occurred during the elapsed operating time. Device for carrying out the method according to claim 1, characterized in that the encoder consists of a cam wheel (17) having a plurality of chambers around the circumference and arranged to rotate with the drive screw (9), said chambers intended to operate an inductive encoder ( 18), wherein each induction row corresponds to a certain angular rotation of the driver screw (9). • · e 3. Device according to claim 2, characterized in that the cams on the cam wheel (17) are evenly distributed around the circumference of the cam wheel except for a cam which has been removed. Device according to claim 2, characterized in that the inductive sensor (18) cooperates with a pulse counter (25) or printer for recording the number of pulses received from the sensor (18) during the rotation of the drive screw (35).