FR2790326A1 - Monitoring centering pin lock in nuclear Pressurized Water Reactor fuel assemblies comprises applying shock to pin and registering signal detected by vibration sensor - Google Patents

Abstract

The procedure consists of applying a shock to the centering pin (3) and registering the delayed signal from the shock detected by a vibration sensor (25) located close to the pin. The signal delivered by the sensor is processed and analyses in a Fourier series, and a frequency corresponding to the maximum value of the response spectrum is selected and compared with a reference value to determined whether the pin is properly locked. The apparatus used for the procedure includes a system for lowering a frame (11) with a supporting plate (12) into the water, a swinging hammer (16), a positioning system (26, 35, 36, 37) for the vibration detector. a hammer actuating mechanism (20, 21, 22), and signal registering and processing systems.

Description

The subject of the present invention is a method and a device for controlling

  underwater tightening of a centering pin of a fuel assembly on a support plate

  of a pressurized water nuclear power plant.

  In pressurized water nuclear power plants,

  the fuel assemblies are fixed at their lower part

  superior, on a heart support plate placed in the

  nuclear reactor vessel and which is filled with water.

  Conventionally, this core support plate has water passage orifices as well as

  centering elements for fuel elements.

  The centering members of each element

  bustible are made up of two pawns which are the most

  often attached to the core support plate by screwing.

  At regular intervals, the screwing of the centering pins of the fuel elements must be checked in order to prevent one of these pins from unscrewing and circulating in the primary circuit up to a water box of a steam generator. The object of the invention is to propose a method and a device for controlling the centering pins of the fuel assemblies at a distance and under water.

  The subject of the invention is therefore a method of

  underwater testing of the tightening of an assembly centering pin

  combustible wiring on a core support plate of a

  pressurized water nuclear bale, characterized in that: - a shock is produced on the pawn to be checked, - the time signal produced during this shock is recorded and detected by a vibration sensor placed close to said pawn, - treatment and we analyze in Fourier series the signal delivered by the sensor and we select the value

  of the natural frequency obtained by spectral analysis of the

  general delivered by said vibration sensor corresponding to the maximum value of the response spectrum obtained by the Fourier transforms of the time signal, - and the value of the natural frequency is compared

  obtained by analysis at a reference value to determine

  ner if said centering pin is properly tightened on

the heart support plate.

  According to another characteristic of the invention, the vibration sensor is placed directly on the centering pin. The invention also relates to an underwater control device for tightening a centering pin of a fuel assembly on a core support plate of a pressurized water nuclear power station, characterized in that it comprises: means of descent from the surface of the water of a frame, a support plate on the upper face of the core support plate of the frame,

  - a hammer mounted tilting in a vertical plane

  cal between a position separated from the centering pin and a position of contact with this pin, - means for positioning a vibration sensor near the centering pin,

  means for controlling the tilting of the market;

  sheet to produce a shock on said centering pin, - means for recording the time signal detected by the vibration sensor,

  - means of processing and analysis in se-

  Fourier lines of the signal delivered by the vibration sensor

  tions, - means for selecting the value of

  the natural frequency obtained by the spectral analysis of the

  general delivered by the vibration sensor corresponding to the

  maximum value of the response spectrum obtained by trans-

  Fourier formed from the time signal, - and means for comparing the value of

  the natural frequency obtained by analysis at a value of

  reference to determine whether said centering pin is suitable

  fairly tight on the heart support plate.

  According to other characteristics of the invention: - the frame comprises means of pre-centering on the core support plate, - the pre-centering means are formed by two pins fixed on the underside of the support plate of the frame and intended to cooperate with two water passage orifices of said core support plate arranged on a

  diagonal of a fuel assembly receiving area

  ble, - the hammer is attached to the lower end

  a pendulum mounted on a horizontal axis and the end of which

  opposite mite comprises a pivot cooperating with the means for controlling the tilting of said hammer,

  the means for controlling the tilting of the market;

  shank are formed by a jack supported by the frame and whose piston rod comprises an end piece movable by said jack between a first position in contact with the pendulum pivot to bring the hammer into said position away from the centering pin and a second position disengaged from this pivot and located beyond the first position to release said pendulum and said hammer,

  the means for positioning the vi sensor

  brations comprise a bell provided with an imprint of a shape complementary to the centering pin and supporting said vibration sensor, said bell being supported by the frame and movable between, on the one hand, a separated position

  of the centering pin and, on the other hand, an overlapping position

  of said pin, - the bell is brought to bear on the centering pin by a jack carried by the frame, - the bell is provided with a lateral opening for the passage of the hammer,

  - the vibration sensor is mounted on a collar

  elastic tie applied to the centering pin when the bell is placed on said pin,

  - the vibration sensor is formed by an ac-

  celerometer or microphone or any receiver suitable for the

  frequency range of the vibration spectrum.

  The characteristics and advantages of the invention

  will appear during the description which follows,

  born as an example and made with reference to the drawings an-

attached, on which:

  - Fig. 1 is a schematic perspective view

  part of a heart support plate of a cent

  nuclear pressurized water treatment, - Fig. 2 is a schematic elevation view

  a device for controlling the tightening of a center pin

  trale, according to the invention, and during positioning on the core support plate, - FIG. 3 is a schematic top view of the control device according to the invention, - FIG. 4 is a perspective view of the

  positioning bell of the vibration sensor of the device

  control device according to the invention, - FIG. 5 is a view in longitudinal section of the bell shown in FIG. 4, - Figs. 6 to 8 are schematic views in

  elevation showing the operation of the con-

  trole according to the invention, - Figs. 9 and 10 represent two frequency response curves obtained underwater respectively for a tight centering pin and a loose centering pin, - Fig.ll represents two curves showing the natural frequency of two centering pins as a function of

  the clamping force of each of these pins.

  In Fig. 1, a part of a core support plate 1 of a pressurized water nuclear power station is shown schematically and which comprises a multitude

  orifices 2 for the passage of water passing through this top plate

heart port 1. -

  The core support plate 1 is fixed to the

  lower part of a nuclear reactor vessel which is replaced

plaice of water.

  In the embodiment shown in the figures, the orifices 2 are uniformly distributed in groups of four to each form a reception area

  of a fuel assembly, not shown.

  The reception area thus defined for each fuel assembly has the shape of a square and comprises two centering pins 3 arranged along a diagonal of this square. Each centering pin 3 is fixed to the core support plate 1 by screwing and is projecting from the face

  upper of said core support plate 1, as shown

felt in FIG. 2.

  The device according to the invention designated as a whole by the reference 10 makes it possible to control the tightening of each centering pin 3 directly on the core support plate 1, that is to say at the bottom of the tank and under

water.

  As shown in Figs. 2 and 3, the provision

  control device 10 comprises a frame 11 comprising a plate

  that horizontal 12 of support on the upper face of the plate

  that core support 1 and which is in the form of a

triangular plate.

  The frame 11 also comprises, on one of the edges of the support plate 12, a plate 13 which is presented

  substantially in the form of an L and which extends perpendicular to

  lairement to said support plate 12.

  The frame 11 is equipped at its upper part with a hooking element 14 with for example a handling pole, not shown and which makes it possible to lower the control device 10 from the surface of the water to

the heart support plate 1.

  In general, the frame 11 supports:

  - means of pre-centering on the upper plate

  core port 1, - an element for producing a shock on the centering pin 3 to be checked, - means for positioning a vibration sensor near the centering pin 3, - means for controlling the element intended at

  produce the shock on said centering pin 3.

  As shown in Figs. 2 and 3, the means for pre-centering the frame 11 on the support plate

  core 1 are formed by two pins 15 fixed on the underside

  of the support plate 12 and intended to cooperate each

  cun with an opening 2 of the core support plate 1 during

  the descent of the control device.

  The pre-centering pins 15 are distributed over

  below the support plate 12 so as to cooperate with two orifices 2 arranged along a diagonal of an area of

  receipt of a fuel assembly.

  The element for producing a shock on the centering pin 3 to be checked so as to determine if the centering pin 3 is properly tightened on the core support plate 1 by analysis of the vibrations produced on said centering pin 3 during the impact, are formed by a hammer 16 fixed to the lower end 17a of a balance 17 mounted on a horizontal axis 18 supported by the plate 13 of the frame 11. The end 17b of the balance 17 opposite to that

  17a provided with the hammer 16 comprises a pivot 19.

  The assembly formed by the hammer 16, the pendulum 17 and the pivot 19 is pivotally mounted around the axis 18 between, on the one hand, a position spaced from the centering pin 3 to be checked and shown in FIG. 7 and, on the other hand, a position of contact with this pin and shown in FIG. 8;

  The means for controlling the tilting of the market

  plate 16 and of the pendulum 17 around the axis 18 are formed by a jack 20 supported by the plate 13 of the frame 11 and whose piston rod 21 comprises an end piece 22 displaceable by

  said cylinder 20 so as to cooperate with pivot 19 and

  command the tilting of the hammer 16 around the axis 18.

  The control device 10 is also

  pe of a vibration sensor 25 placed near the centering pin 3 to be checked and which allows, during the impact

  duit by the hammer 16 on said centering pin 3 of

  tect the time signal produced during said shock.

  Preferably, the means for positioning the vibration sensor 25 are constituted by a bell 26 provided with an imprint 27 of shape complementary to the pin of

  centering 3, as shown in Figs. 4 and 5.

  This bell 26 has a lateral opening 26a for the passage of the hammer 16 and a cutout 29 for the

  positioning the vibration sensor 25.

  This vibration sensor 25 is mounted on an elastic collar 30 which makes it possible to apply said vibration sensor 25 to the centering pin 3 at the time of the

  placing the bell 26 on said pin 3.

  The assembly formed by the vibration sensor 25 and the elastic collar 30 is held in position in the

  bell 26 by means of a cover 31 fixed on the inner part

  of said bell 26 by means of screws, not shown

  tees. Furthermore, the bell 26 has a passage 32 for positioning the connecting wire 33 of the sensor.

  vibrations 25 with the different means of analysis and

  recording of the signal detected by said sensor 25.

  The connecting wire 33 is held in the housing

ment 32 by a rod 34.

  The bell 26 supporting the vibration sensor

  is carried by the plate 13 of the frame 11 by means of a support

port 28 fixed on said plate 13.

  When fitting the frame 11 on the support plate

  of heart 1, the bell 26 completely covers the pawn of cent

trage 3.

  To keep this bell 26 in its position of covering the centering pin 3, the plate 13 of the frame 11 supports a jack 35 whose piston rod 36 is located

in the axis of said bell 26.

  The piston rod 36 of the jack 35 comprises, at its free end, an element 37 for bearing on the head 26b of the bell 26. Finally, the control device comprises: - means for recording the time signal detected by the vibration sensor 25,

  - means of processing and analysis in se-

  Fourier lines of the signal delivered by the vibration sensor

  25, - means for selecting the natural frequency value obtained by the spectral analysis of the signal delivered by the vibration sensor 25 corresponding to the

  maximum value of the response spectrum obtained by trans-

  Fourier formed from the time signal, - and means for comparing the value of

  the natural frequency obtained by analysis at a value of

  reference to determine whether said centering pin 3 is con-

  tightly tightened on the core support plate 1.

  These means are of known type and commonly used.

  used to process and analyze this kind of signal.

  The tightening of the centering pin 3 on the core support plate 1 is checked directly under

water and as follows.

  First, we descend from the surface of the water and using a handling pole fixed on

  the attachment member 14, the frame 11 supporting the various

  rents elements to carry out the check of the pin tightening

3 to check.

  During the descent of the frame 11, the pre-centering pins 15 progressively penetrate into the orifices 2 of the corresponding water passage until the support plate 12 comes into contact with the core support plate 1. The bell 26 is kept pressed on the support

  28 by the jack 35, as shown in FIG. 2.

  When the frame 11 is placed on the core support plate 1 shown in FIG. 6, the bell 26 is raised and released from the support 28. During the descent of the frame 11, the bell 26 is gradually tightened on the centering pin 3. After this positioning phase, the jack 35 is actuated to return the rod 36 and separate the bell 26 from the frame 11 thus making this bell 26 integral

  centering pin 3 thanks to the elastic collar 30.

  The tilting of the hammer 16 is then controlled,

as shown in Fig. 7.

  To this end, the jack 20 is actuated in such a way that the end piece 22 comes into contact with the pivot 19 of the pendulum 17 so as to bring, by tilting this pendulum 17 around the axis 18, the hammer 16 in the separated position.

  of the centering pin 3, as shown in FIG. 7.

  The position of the bell 26 on the pawn of cent

  trage 3 is determined so that the opening 26a is

  in the hammer tilt plane 16.

  Under the action of the actuator 20, the endpiece 22 continues to run and passes beyond the end of the pivot 19, as shown in FIG. 8, which has the effect of releasing the balance 17 so that this balance 17 and the

  hammer 16 pivot around axis 18.

  - During this tilting, the hammer 16 passes through the opening 26a of the bell 26 and comes into contact with the

  centering pin 3 to control what produces a shock.

  During this shock, the tempo signal is recorded.

  rel produced and detected by the vibration sensor 25.

  Then we process and analyze in series of

  Fourier the signal delivered by the sensor 25 and we select

  the value of the natural frequency obtained by the analysis

  spectral lysis of the signal delivered by said vibration sensor

  corresponding to the maximum value of the spectrum of

  response obtained by the Fourier transforms of the time signal

  porel. By way of example, there is shown in FIG. 9 a frequency response curve obtained underwater with a centering pin 3 tightened to 60mN and in FIG. 10 a run of

  frequency response obtained underwater with a cent pawn

  track 3 loose. The presence of a double peak on the curve of the

  Fig. 9 is due to the detection of two different transverse modes

  because of the presence, at the base of the pawn, of a me-

centering plate.

  Using the curve shown in FIG. 11,

  we compare the value of the natural frequency obtained by ana-

  lysis to a reference value to determine whether the controlled centering pin 3 is properly tightened on the plate

heart support 1.

  For example, a response between 3000 and 4500 Hz guarantees a minimum tightening torque of

  around 10mN, as shown in FIG. 11.

  The process thus implemented makes it possible to control

  underwater tighten the centering pins of the assemblies

  fuel on the core support plate of a pressurized water nuclear power plant and to determine whether these centering pins are properly tightened or in the process of loosening. After checking a first centering pin,

  the end piece 22 is returned to its initial position under the ac-

  tion of the actuator 20 by passing over the pivot 19.

  This removal is possible because the pendulum

  17 is at rest in a substantially vertical position

  wedge and moved away from the contact position on the pin

  centering 3, as shown in FIG. 2.

  Then, the control device 10 is moved

  using the handling pole to position it

  ner on a new centering pin.

  The vibration sensor can be constituted by

  an accelerometer or a microphone or an ultra-sensor

  trasons or by any other appropriate sensor.

Claims (12)

  1. Method for checking under water the tightening of a centering pin (3) of a fuel assembly on a core support plate (1) of a pressurized water nuclear power station, characterized in that: - a impact on the centering pin (3) to be checked, - the time signal produced during   of this shock and detected by a vibration sensor (25) placed   cé near said pawn (3), - we process and analyze in Fourier series   the signal delivered by the sensor 25 and the value is selected   their from the natural frequency obtained by spectral analysis   of the signal delivered by said vibration sensor (25) cor-   corresponding to the maximum value of the response spectrum obtained by the Fourier transforms of the time signal, - and we compare the value of the natural frequency   obtained by analysis at a reference value to determine   ner if said centering pin (3) is properly tightened on the heart support plate (1).   2. Control method according to claim 1, characterized in that the vibration sensor is placed   (25) directly on the centering pin (3).   3. Device for monitoring under water the tightening of a centering pin (3) of a fuel assembly on a core support plate (1) of a pressurized water nuclear power station, characterized in that it comprises: means of descent from the water surface of a frame (11),   - a support plate (12) on the upper face   lower of the core support plate (1) of the frame (11), - a hammer (16) mounted tilting in a vertical plane between a position spaced from the centering pin (3) and a position of contact with this pin (3) ,   - means (26, 27, 35, 36, 37) for positioning -   ment of a vibration sensor (25) near the centering pin (3),   - means (20, 21, 22) for controlling the tilting   Lement of the hammer (16) to produce a shock on said centering pin, means for recording the time signal detected by the vibration sensor (25),   - means of processing and analysis in se-   Fourier lines of the signal delivered by the vibration sensor   tions (25), - means for selecting the value of   the natural frequency obtained by the spectral analysis of the   general delivered by the vibration sensor (25) corresponding to the maximum value of the response spectrum obtained by the Fourier transforms of the time signal, - and means for comparing the value of the natural frequency obtained by the analysis with a value for determining whether said centering pin (3) is   suitably tightened on the core support plate (1).   4. Control device according to the claim   tion 3, characterized in that the frame (11) comprises means (15) for pre-centering on the core support plate (1).   5. Control device according to the claim   tion 4, characterized in that the pre-centering means are formed by two pins (15) fixed on the underside of the support plate (12) of the frame (11) and intended to cooperate   with two orifices (2) for the passage of water from said top plate   heart port (1) arranged on a diagonal of an area of   receipt of a fuel assembly.   6. Control device according to claim   3, characterized in that the hammer (16) is fixed at the end   lower part (17a) of a pendulum (17) mounted on a horizontal axis (18) and the opposite end (17b) of which   a pivot (19) cooperating with the means (20, 21, 22) of   command to tilt said hammer (16).   7. Control device according to claim   3 or 6, characterized in that the control means of the lower   hammer base (16) are formed by a cylinder (20) sup-   carried by the frame (11) and the piston rod (21) of which   carries a tip (22) movable by said cylinder (20) between   a first position in contact with the pivot (19) of the base   lance (17) for bringing the hammer (16) into said posi-   tion moved away from the centering pin (3) and a second position released from this pivot (19) and located beyond the first position to release said balance (17) and said hammer (16). 8. Control device according to claim 3, characterized in that the means for positioning the vibration sensor (25) comprise a bell (26) provided   an imprint (27) of a shape complementary to the pawn of cent   trage (3) and supporting said vibration sensor (25),   said bell (26) being supported by the frame (11) and   can be placed between, on the one hand, a position spaced from the centering pin and, on the other hand, an overlapping position of said pawn (3).   9. Control device according to claim 8, characterized in that the bell (26) is brought to bear on the centering pin (3) by a jack (35, 36, 37) carried by the frame (11).   10. Control device according to the claims   tions 8 and 9, characterized in that the bell (26) is provided with a lateral opening (26a) for the passage of the hammer (16). -   11. Control device according to claims   1 and 8, characterized in that the vibration sensor (25) is mounted on an elastic collar (30) applied to the centering pin (3) when the bell (26) is installed on said pawn (3).   12. Control device according to any one   as in claims 3 to 11, characterized in that the cap-   vibration generator (25) is formed by an accelerometer or microphone or any receiver adapted to the frequency range of the vibrational spectrum.