Patent Application
20120213320
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.
The invention also relates to a method for assisting in the underwater extraction or insertion of an elongate element disposed in a pipe.
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.
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.
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.
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.
There are generally from two or four thermocouple columns.
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.
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.
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.
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.
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.
It is therefore necessary to replace these thermocouples during scheduled maintenance operations of the nuclear reactor.
The replacement of the thermocouples is done after stopping and cooling the reactor and after disassembling the cover.
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.
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.
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.
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.
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.
In other cases, despite successful pulling, it can be difficult or even impossible to introduce a new thermocouple into the pipe.
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.
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.
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.
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.
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.
Embodiments of the invention may include other features:
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,
the clamping member is formed by a cylinder,
the vibrator is a pneumatic vibrator,
the measuring member is formed by an accelerometer, and
the housing is fastened at the end of a remote handling pole.
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:
the housing is lowered into the water using the handling pole,
the jaws of the gripper are kept in the spaced-apart position,
the jaws of the gripper are placed on either side of the pipe of the elongate element to be extracted,
the clamping member is controlled remotely to move the jaws in the clamping position of the pipe,
the vibrator is commanded to vibrate the pipe using the housing and the gripper,
the vibration created by the vibrator on the pipe is measured to determine the optimum vibration,
the vibrator is adjusted to the optimum vibration, and
pulling is simultaneously exerted in the axial direction on the elongate element.
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:
the housing is lowered into the water using the handling pole,
the jaws of the gripper are kept in the spaced-apart position,
the jaws of the gripper are placed on either side of the pipe of the elongate element to be inserted,
the clamping member is controlled remotely to move the jaws in the clamping position of the pipe,
the vibrator is commanded to vibrate the pipe using the gripper,
the vibration created by the vibrator on the pipe is measured to determine the optimum vibration,
the vibrator is adjusted to the optimum vibration, and
thrust is simultaneously exerted in the axial direction on the elongate element.
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:
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.
This device can be used to assist with the extraction or insertion of any other elongate element in a pipe.
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.
As shown in
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 9a 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 9b with a generally substantially square cross-section with rounded corners. Each of the parts 9a and 9b 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 1a of the vat 1.
Placed between the support plate 8 of the upper internal equipment 6 and the upper core plate 7, in addition to the lower parts 9b 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.
As shown in
In this figure, a limited number of the upper pipe 21 has been shown so as not to overload the figure.
After a certain operating time of the nuclear reactor, the reactor is stopped and cooled for maintenance and to reload with fuel assemblies.
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.
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
As shown in
As shown more particularly in
The sealed housing 41 bears a gripper 43 made from two jaws, 43a and 43b, respectively, extending, in the clamping position, substantially parallel to one another. These jaws 43a and 43b each bear a pad, for example made from plastic, on the surface intended to be in contact with the pipe 21.
In the embodiment illustrated in
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 43b. To that end, the yoke 47 is connected to a transverse axis 48 that bears the mobile jaw 43b.
The mobile jaw 43b is kept in position spaced away from the stationary jaw 43 for example by a spring (not shown), or by any other suitable member.
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.
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.
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.
In the case of an extraction of a defective thermocouple 22, the free end 22a of said thermocouple 22 protruding relative to the column 20 is connected, as shown in
In the case of an insertion of a new thermocouple 22 in the corresponding pipe 21, the free end 22a protruding relative to the column 20 is connected to a thrust device on said thermocouple 22.
To extract a thermocouple 22 that is stuck in its pipe 21, the operators placed on the bridge 35 proceed as follows.
First, the operators connect the free end 22a of the thermocouple 22 to be extracted to the hoist 60, as shown in
Next, the operators lower the housing 41 of the assembly 40 into the water of the pool using the handling pole 54. The jaws 43a and 43b 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, 43a and 43b, 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.
Using the control cabinet 55, the operators remotely control the cylinder 45 so as to move the mobile jaw 43b 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 43b 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.
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.
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.
According to one alternative, several assemblies 40 can be placed on a same pipe.
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.
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.
According to another embodiment shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 09 56354 | Sep 2009 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR10/51913 | 9/15/2010 | WO | 00 | 5/9/2012 |
