Abstract:
A device for assisting in the underwater extraction or insertion of an elongate element disposed in a pipe is provided. The device includes a clamping and vibration-generating assembly including a sealed housing bearing a gripper and including a member for tightening the gripper on the pipe, an adjustable vibrator for vibrating the housing and the gripper, and a member for measuring the vibration produced by the vibrator on the pipe in order to determine the optimum vibration The device also includes a controller for remotely controlling the gripper and the vibrator. A method for assisting in the extraction or insertion of an elongate element is also provided.

Description:
[0001]    The present invention relates to a device for assisting in the underwater extraction or insertion of an elongate element disposed in a pipe, and in particular a thermocouple disposed in a measuring pipe for the upper internal equipment of a pressurized water nuclear reactor. 
         [0002]    The invention also relates to a method for assisting in the underwater extraction or insertion of an elongate element disposed in a pipe. 
       BACKGROUND 
       [0003]    Pressurized water nuclear reactors comprise, inside a vat, the core of the nuclear reactor made up of fuel assemblies having a prismatic shape with their vertical axis and, above the core, upper internal equipment in particular comprising a set of vertical guide-tubes making it possible to ensure the guiding of the control rods formed by bundles of rods placed parallel to one another and containing a material absorbing neutrons. 
         [0004]    To control the reactors by adjusting the reactivity of the core, the clusters of absorber rods are moved in the vertical direction, during operation of the reactor, so that the absorber rods are introduced over a greater or lesser height inside certain fuel assemblies of the core. 
         [0005]    The upper internal equipment generally comprises an upper plate, also called support plate, and a lower plate constituting the upper plate of the core of the nuclear reactor bearing on the upper end of the fuel assemblies, when the upper internal equipment is in the service position in the core of the reactor. The vertical guide-tubes guiding the control rods are connected to the support plate and the lower plate, which each comprise a first part inserted between the support plate and the lower plate and a second part fastened above said support plate. Support columns disposed between the support plate and the lower plate, parallel to the guide-tubes, make it possible to maintain these plates and ensure the rigidity of the upper internal equipment. 
         [0006]    The upper internal equipment also comprises instrument columns, such as cylindrical thermocouple columns. Arranged in each of the thermocouple columns is a set of thermocouples making it possible to measure the temperature of the coolant at the outlet of a preselected set of fuel assemblies of the core of the reactor. 
         [0007]    There are generally from two or four thermocouple columns. 
         [0008]    Each thermocouple column is not fastened on the support plate of the upper internal equipment, but is guided by a spindle extending vertically above said plate and penetrating the thermocouple column. However, each thermocouple column is made integral with the cover of the vat of the reactor only by upper sealing means, disposed between a tubing of an adapter secured in an opening of the cover and the upper part of the column. 
         [0009]    Several thermocouples are therefore disposed in a column and leave that column through peripheral openings, formed at the base of the column to each rejoin a bleed passing through the support plate. To that end, each bleed is provided with a guide tube positioned aligned with an opening formed in the support plate substantially overhanging a zone where the temperature measurement must be done. The thermocouple is introduced into an upper guide pipe supported by the thermocouple column and by a lower guide pipe disposed in the tube of the corresponding bleed. The sensitive measuring end of the thermocouple is positioned at the predetermined measuring zone. 
         [0010]    Part of the thermocouples is intended to measure the temperature of the coolant of the reactor, at the outlet of the core, below the upper plate of the core, near the upper tip of the fuel assemblies. 
         [0011]    The thermocouples introduced into the pipes are subject to high temperature and pressure stresses, with the result that some of them may have operating defects after a certain residence time in the vat of the reactor. 
         [0012]    Thus, it is no longer possible to have a reliable and representative image of the actual temperature of the coolant of the core of the reactor. 
         [0013]    It is therefore necessary to replace these thermocouples during scheduled maintenance operations of the nuclear reactor. 
         [0014]    The replacement of the thermocouples is done after stopping and cooling the reactor and after disassembling the cover. 
         [0015]    Before disassembling the cover, the connections of the thermocouples are disconnected and the control rods of the corresponding absorber clusters are separated. The upper internal equipment of the reactor is disassembled and placed in a storage area in the pool of the reactor. 
         [0016]    To extract the defective thermocouples, one pulls, from the upper level of the pool, remotely and underwater, on the thermocouple using a tool engaged with the extension of the thermocouple outside the corresponding column. It may be necessary to exert very strong pulling on the thermocouple to remove it. 
         [0017]    In fact, because the thermocouple is mounted with very little, and even practically no play in certain parts of the pipes, the frictional forces, during removal of the thermocouples, can be very significant. 
         [0018]    In certain cases, the thermocouple is blocked in the pipe and cannot be removed by pulling without risk of rupture. In this case, the measuring pipe is lost, which causes the loss of a measuring point. 
         [0019]    In certain long pipes with several curves, it is fairly unlikely that it will be possible to remove the thermocouple, the gripping being sufficient to create a blocking situation. 
         [0020]    In other cases, despite successful pulling, it can be difficult or even impossible to introduce a new thermocouple into the pipe. 
         [0021]    Lastly, simple pulling on the thermocouple can lead to damage to the wall of the corresponding pipe, which is detrimental to the insertion of a new thermocouple. 
         [0022]    It is known to facilitate the removal of the thermocouples by propagating ultrasounds in the thermocouple from its end, on which a pulling force is exerted in its axial direction. 
         [0023]    However, in the case of thermocouples whereof the blocking part is situated in the lower end of the pipe, i.e. at a significant distance from the thermocouple on which the pulling is exerted and through which the ultrasounds are transmitted, this known method is ineffective. 
       SUMMARY OF THE INVENTION 
       [0024]    An object of the invention is to provide a device and method for assisting in the extraction or insertion of an elongate element disposed in a pipe that makes it possible, through easy-to-use means, to avoid these drawbacks and facilitate the extraction or insertion of the elongate element. 
         [0025]    A device for assisting in the underwater extraction or insertion of an elongate element disposed in a pipe and in particular a thermocouple disposed in a measuring pipe of the upper internal equipment of a pressurized water nuclear reactor is provided. The devices includes a clamping and vibration-generating assembly comprising a sealed housing bearing a gripper and including a member for tightening the gripper on the pipe, an adjustable vibrator for vibrating the housing and the gripper, and a member for measuring the vibration produced by the vibrator on the pipe in order to determine the optimum vibration and, on the other hand, a controller for remotely controlling the gripper and the vibrator. 
         [0026]    Embodiments of the invention may include other features: 
         [0027]    the gripper comprises a stationary jaw and a movable jaw that can be moved by a clamping member between a position close to the stationary jaw and a position spaced away from said stationary jaw, 
         [0028]    the clamping member is formed by a cylinder, 
         [0029]    the vibrator is a pneumatic vibrator, 
         [0030]    the measuring member is formed by an accelerometer, and 
         [0031]    the housing is fastened at the end of a remote handling pole. 
         [0032]    A method for assisting in the underwater extraction of an elongate element disposed in a pipe and in particular a thermocouple disposed in a measuring pipe of the upper internal equipment of a pressurized water nuclear reactor, using an extraction device as previously defined, is also provided. The method includes: 
         [0033]    the housing is lowered into the water using the handling pole, 
         [0034]    the jaws of the gripper are kept in the spaced-apart position, 
         [0035]    the jaws of the gripper are placed on either side of the pipe of the elongate element to be extracted, 
         [0036]    the clamping member is controlled remotely to move the jaws in the clamping position of the pipe, 
         [0037]    the vibrator is commanded to vibrate the pipe using the housing and the gripper, 
         [0038]    the vibration created by the vibrator on the pipe is measured to determine the optimum vibration, 
         [0039]    the vibrator is adjusted to the optimum vibration, and 
         [0040]    pulling is simultaneously exerted in the axial direction on the elongate element. 
         [0041]    A method for assisting in the underwater insertion of an elongate element disposed in a pipe and in particular a thermocouple disposed in a measuring pipe of the upper internal equipment of a pressurized water nuclear reactor, using an insertion device as previously defined, is also provided. The method includes: 
         [0042]    the housing is lowered into the water using the handling pole, 
         [0043]    the jaws of the gripper are kept in the spaced-apart position, 
         [0044]    the jaws of the gripper are placed on either side of the pipe of the elongate element to be inserted, 
         [0045]    the clamping member is controlled remotely to move the jaws in the clamping position of the pipe, 
         [0046]    the vibrator is commanded to vibrate the pipe using the gripper, 
         [0047]    the vibration created by the vibrator on the pipe is measured to determine the optimum vibration, 
         [0048]    the vibrator is adjusted to the optimum vibration, and 
         [0049]    thrust is simultaneously exerted in the axial direction on the elongate element. 
     
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
         [0050]    The invention will be better understood upon reading the following description, provided as an example and done in reference to the appended drawings, in which: 
           [0051]      FIG. 1  is a diagrammatic cross-sectional view through a vertical plane of symmetry of a vat of a pressurized water nuclear reactor, 
           [0052]      FIG. 2  is a diagrammatic partial perspective view of the upper internal equipment of a nuclear reactor in position on an operating stand in the pool of the reactor, for an operation to replace at least one thermocouple using the assistance device, according to the invention, 
           [0053]      FIG. 3  is a diagrammatic side view of a clamping and vibration-generating assembly of the assistance device, according to the invention, 
           [0054]      FIG. 4  is a diagrammatic perspective view of the clamping and vibration-generating assembly of the assistance device according to the invention, and 
           [0055]      FIG. 5  is a diagrammatic perspective view of an alternative of the clamping and vibration-generating assembly of the assistance device according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0056]    In the following description, the device according to embodiments of the invention will be described to assist in the extraction or insertion of an elongate element formed by a thermocouple disposed in a measuring pipe of the upper internal equipment of a pressurized water nuclear reactor. 
         [0057]    This device can be used to assist with the extraction or insertion of any other elongate element in a pipe. 
         [0058]      FIG. 1  diagrammatically illustrates a vat of a pressurized water nuclear reactor designated by reference  1 . Traditionally, disposed inside the vat  1  of the nuclear reactor is the core  2  formed by fuel assemblies  3  juxtaposed so that the longitudinal axis of the fuel assemblies is vertical. The core  2  of the reactor is disposed inside lower internal equipment designated by general reference  4  and in particular comprising the partition  5  of the core. 
         [0059]    The nuclear reactor also comprises upper internal equipment designated by general reference  6  that rests on the upper plate of the assemblies of the core, via an upper core plate  7 . 
         [0060]    As shown in  FIG. 1 , the upper internal equipment  6  comprises a support plate  8  of the guide-tubes that will hereafter be called support plate  8 . This support plate  8  extends parallel to the upper core plate  7  constituting the lower portion of the upper internal equipment  6  and which is made so as to ensure fastening of the upper internal equipment  6  inside the vat  1 . 
         [0061]    The upper internal equipment  6  comprises the guide-tubes designated by general reference  9 , which are made up, each above the support plate  8 , of an upper portion  9   a  with a circular section and, between the support plate  8  of the upper internal equipment  6  and the upper core plate  7 , a lower portion  9   b  with a generally substantially square cross-section with rounded corners. Each of the parts  9   a  and  9   b  constitutes a guide-tube  9  of the upper internal equipment  6  making it possible to move a cluster in the vertical direction to adjust the reactivity in the core of the nuclear reactor, connected to a suspension and movement rod, the vertical movement of which is ensured by a mechanism, not shown, situated above the cover  1   a  of the vat  1 . 
         [0062]    Placed between the support plate  8  of the upper internal equipment  6  and the upper core plate  7 , in addition to the lower parts  9   b  of the guide-tubes  9 , are bracing columns  10  ensuring the maintenance and spacing of the upper core plate  7  relative to the support plate  8 . 
         [0063]      FIG. 2  shows, diagrammatically and in perspective view, the upper surface of the support plate  8  that supports the upper parts  9   a  of the guide-tubes  9  and in the embodiment shown in that figure, two thermocouple columns  20  that extend parallel to the guide-tubes  9 , above the support plate  8 . Traditionally, disposed in each of the thermocouple columns  20  is a set of upper guide pipes  21  each of a thermocouple  22  making it possible to measure the temperature of the coolant at the outlet of a preselected assembly set of the core of the nuclear reactor. 
         [0064]    As shown in  FIG. 2 , several upper guide pipes  21  are disposed in a column  20  and leave that column through peripheral openings formed above the foot of the thermocouple column  20  to each join a bleed designated by general reference  30  and intended to pass through the support plate  8  of a thermocouple  22 . 
         [0065]    In this figure, a limited number of the upper pipe  21  has been shown so as not to overload the figure. 
         [0066]    After a certain operating time of the nuclear reactor, the reactor is stopped and cooled for maintenance and to reload with fuel assemblies. 
         [0067]    To perform the maintenance and repair operations for this internal equipment of the vat of the reactor, the cover is removed after cooling the reactor and the upper internal equipment  6  can be removed from the reactor and placed in a storage area in the pool of the reactor. In the event one or more thermocouples  22  used to measure the temperature of the coolant at the outlet of the core have become defective during use, they must be replaced. This operation to replace the thermocouples is done on the upper internal equipment disposed in its storage area and requires that the defective thermocouple  22  first be extracted from that pipe  21 , and that a new thermocouple  22  be inserted in that pipe  21 . 
         [0068]    The extraction or insertion of a thermocouple  22  in the corresponding pipe  21  is facilitated by the assistance device, according to the invention, and which comprises a clamping and vibration-generating assembly of the corresponding pipe  21 , this assembly being designated by general reference  40  in  FIGS. 2 to 5 . 
         [0069]    As shown in  FIG. 2 , to place the clamping and vibration-generating assembly on the pipe  21  of the thermocouple  22  to be extracted or inserted, the operators work from a bridge  35  placed above the upper level of the water in the pool in which the upper internal equipment is disposed. 
         [0070]    As shown more particularly in  FIGS. 3 to 5 , the assembly  40  comprises a sealed housing  41  equipped, on one of its surfaces, with a removable cover  42 . The housing  41  is mounted at the end of a pole  54 , thereby allowing operators to work from the bridge  35  and to bring the housing  41  close to the pipe  21  of the thermocouple  22  to be extracted or inserted. 
         [0071]    The sealed housing  41  bears a gripper  43  made from two jaws,  43   a  and  43   b,  respectively, extending, in the clamping position, substantially parallel to one another. These jaws  43   a  and  43   b  each bear a pad, for example made from plastic, on the surface intended to be in contact with the pipe  21 . 
         [0072]    In the embodiment illustrated in  FIGS. 3 to 5 , the jaw  43   a  is stationary and the jaw  43   b  is mobile. The mobile jaw  43   b  can be moved by a clamping member  45  disposed inside the housing  41  ( FIG. 4 ) between a position close to the stationary jaw  43   a  to clamp the conduit  21  and a position spaced away from said stationary jaw  43   a  shown in broken lines in  FIG. 3  so as to allow the gripper  43  to be positioned on the pipe  21  or to allow the removal of that gripper  43 . 
         [0073]    The clamping member  45  is preferably formed by a cylinder. This cylinder  45 , for example pneumatic, traditionally comprises a piston  46  that acts on a handling yoke  47  of the mobile jaw  43   b.  To that end, the yoke  47  is connected to a transverse axis  48  that bears the mobile jaw  43   b.    
         [0074]    The mobile jaw  43   b  is kept in position spaced away from the stationary jaw  43  for example by a spring (not shown), or by any other suitable member. 
         [0075]    The housing  41  of the assembly  40  generally contains an adjustable vibrator  49 , for example pneumatic and of a known type, that makes it possible to vibrate said housing  41  and the gripper  43  supported by said housing  41 . 
         [0076]    Lastly, the housing  41  contains a measuring member  50  for measuring the vibration created by the vibrator  49  on the pipe  21  to determine the optimum vibration for the pipe  21  so as to enable the extraction or insertion of the thermocouple  22  in that pipe  21 . This measuring member  50  is formed by an accelerometer or any other suitable element. 
         [0077]    The cylinder  45 , the vibrator  49  and the accelerometer  50  are connected by electric and pneumatic connections to a controller in the form of a control and monitoring cabinet  55  mounted on the bridge  35 . These electric and pneumatic connecting elements pass inside the handling pole  54 . This handling pole  54  is formed from several elements mounted successively to form a sealed pole. 
         [0078]    In the case of an extraction of a defective thermocouple  22 , the free end  22   a  of said thermocouple  22  protruding relative to the column  20  is connected, as shown in  FIG. 2 , to a pulling device  60  of said thermocouple  22  for example made up of a hoist. 
         [0079]    In the case of an insertion of a new thermocouple  22  in the corresponding pipe  21 , the free end  22   a  protruding relative to the column  20  is connected to a thrust device on said thermocouple  22 . 
         [0080]    To extract a thermocouple  22  that is stuck in its pipe  21 , the operators placed on the bridge  35  proceed as follows. 
         [0081]    First, the operators connect the free end  22   a  of the thermocouple  22  to be extracted to the hoist  60 , as shown in  FIG. 2 . 
         [0082]    Next, the operators lower the housing  41  of the assembly  40  into the water of the pool using the handling pole  54 . The jaws  43   a  and  43   b  of the gripper  43  are kept in the spaced apart position, thereby allowing the operators to place the pipe  21  of the thermocouple  22  to be extracted between said jaws,  43   a  and  43   b,  respectively. The operators can be helped by a viewing device, for example such as an underwater camera placed at the bottom of a handling pole. 
         [0083]    Using the control cabinet  55 , the operators remotely control the cylinder  45  so as to move the mobile jaw  43   b  and bring the gripper  43  into a clamping position via the piston  46  of the cylinder  45 , which acts on the yoke  47  so as to pivot the mobile jaw  43   b  around the transverse axis  48 . After clamping the gripper  43  on the pipe  21  of the thermocouple  22  to be extracted, the operators actuate the vibrators  49  to vibrate the pipe  21  via the housing  41  and the gripper  43 . The accelerometer  50  measures the vibration created by the vibrator  49  on the pipe  21  and the value thus measured is displayed on the control housing  55 , thereby making it possible to determine the optimum vibration created in the pipe  21 . The operators adjust the vibrator  49  to the optimum vibration. 
         [0084]    At the same time, the hoist  60  exerts a pulling force in the axial direction on the thermocouple  22  so as to extract it from its pipe  21 . 
         [0085]    The vibrations thus created in the pipe  21  of the thermocouple  22  to be extracted during the pulling phase make it possible to create micro-delaminations between the thermocouple and the pipe and to reduce the coefficient of friction between said thermocouple and said pipe. In this way, the potential damage of the pipe is reduced and the chances of successfully extracting the thermocouple are increased. 
         [0086]    According to one alternative, several assemblies  40  can be placed on a same pipe. 
         [0087]    According to another alternative, vibrations can also be created in the thermocouple itself In that case, a vibrator, not shown, is mounted in series with the pulling device, i.e. with the hoist  60 . 
         [0088]    To introduce a new thermocouple  22  into a pipe  21  after extracting a defective thermocouple, the operators proceed in the same way, but instead of pulling on the thermocouple, they use a suitable system to exert thrust on the thermocouple to be introduced into the pipe. 
         [0089]    According to another embodiment shown in  FIG. 5 , the jaws  43   a  and  43   b  of the gripper  43  are disposed horizontally, while in the embodiment previously described, these jaws are disposed vertically.