EP0019544B1 - Transport container closure device for an assemblage irradiated in a nuclear reactor - Google Patents

Description

The present invention relates to a device for closing the transport case of an irradiated assembly in a nuclear reactor.

We know that transport castles are used to transport the irradiated assemblies from the nuclear reactor to the reprocessing plant. Each castle generally contains several irradiated assemblies, each assembly being sealed in a case.

The present invention relates to a device for closing such a case, this device being designed so as to meet the required safety and operating requirements.

DE-A-2 738 592 discloses a device for closing the transport case of an irradiated assembly in a nuclear reactor comprising a circular plug housed in the head of the case, a seal located between the case head and the stopper and a lock provided with fingers engaging in a groove made in the case head to stop said lock in translation, means being further provided on the lock for applying the stopper against the joint and sealing between the latter and the case head.

The subject of the invention is a device for closing the transport case of an irradiated assembly of this type, the safety of which is increased by the presence of a secondary seal located downstream of the primary seal produced by the seal. . In addition, the device of the invention comprises a circular flange fixed on the case head, the presence of which makes it possible to preserve the secondary seal from any impact.

More specifically, the closure device is characterized in that the latch and the plug are joined to one another by a fastening means allowing rotation of the latch relative to the plug, the latch comprising a gripping head ; at least one radial finger coming from the plug immobilizes the latter in rotation by engaging in at least one groove made in the case head; a circular flange is fixed to the case head by distributed screws; and a secondary seal is located downstream of the primary seal, said secondary seal being constituted by a cover, a cylindrical part of which engages inside the case head.

With regard to the primary seal, the presence of means for securing between the latch and the plug, these means allowing rotation of the latch relative to the plug, allows these two parts to be put in place quickly in a single operation.

According to a first preferred embodiment, the means for sealing between the cover and the case head consists of a fusible joint formed by a deep annular groove filled with a fusible alloy at low temperature and by a blade provided with the cover and dipping into said alloy.

Preferably, the diameter of the cover in its cylindrical part is slightly less than that of the bore, made in the case head, in which it engages, thus providing an annular chamber delimiting a thin layer of gas between the mass of the cover and the fuse seal device.

According to a second preferred embodiment, the means for sealing between the cover and the case head consists of two horizontal lips, a first lip having come from the cover, a second having come from the case head, these two lips being joined to each other by a weld made at their ends, and held in contact with each other by the circular flange fixed to the case head by distributed screws.

Preferably, the cover further comprises a piston-mounted seal inside a groove formed on the cover in its cylindrical part.

According to another characteristic of a preferred embodiment of the invention, the device for closing the case further comprises a locking device stopping in translation said cover after its introduction into the case head. This locking device is constituted by at least two radial fingers from the cover and located in its cylindrical part, first engaging in grooves made in the case head, then then engaging by rotation inside. a groove made in said case head.

According to a preferred embodiment of the lock, the latter is hollowed out in its central part, and the means for securing said plug with its lock consists of radial screws, each of these screws, terminated by a stud, sinking into a groove practiced in said plug.

According to another characteristic of a preferred embodiment of the invention, the stopper comprises, integrated into its face facing the inside of the case, a cavity filled with an insulator with compressed metal fabrics and closed by a sheet welded to the periphery of said plug.

• la fig. 1 représente une vue générale en coupe axiale de l'étui de transport d'un assemblage irradié;
• la fig. 2 représente une demi-vue en coupe axiale d'une première variante de réalisation d'un dispositif de fermeture de l'étui;
• la fig. 3 représente une demi-vue en coupe axiale d'une deuxième variante de réalisation du dispositif de fermeture de l'étui.

In any case, the characteristics and advantages of the invention will appear better after the description which follows, of embodiments given by way of explanation and in no way limiting, with reference to FIGS. 1, 2 and 3, in which:

• fig. 1 shows a general view in axial section of the transport case of an irradiated assembly;
• fig. 2 shows a half view in axial section of a first alternative embodiment of a device for closing the case;
• fig. 3 shows a half-view in axial section of a second alternative embodiment of the device for closing the case.

In fig. 1, reference 1 designates the carrying case. This is in the form of a long hollow cylinder about six meters in length and 0.3 meters in diameter. At its upper end, the case head 2, a piece of revolution of reinforced thickness, is welded to the body of the case 3. Inside the case head 2, the plug 4 is shown diagrammatically making a primary seal and the cover 5 providing a secondary seal, located downstream of said primary seal. The assembly 6, after irradiation in the core of the nuclear reactor, is introduced by the case head 2 inside the sock 9 where it is immersed in sodium 8 used as a coolant. The plug 4 is put in place as soon as the assembly is holstered; it seals the case for transits at the power station from the berth in the handling corridor to the storage well and at the work station for its packaging; similar functions are entrusted to it at the reprocessing plant and for the repatriation of the case to the central. The cover 5 must alone seal the case in the event of failure of the primary seal.

FIG. 2 represents a half-section view of an alternative embodiment of a device for closing the case according to the present invention. The case head 2, welded to the body of case 1 is a very thick piece of revolution. Inside this case head 2 are housed a primary seal constituted by the plug 10 and a secondary seal constituted by the cover 30, this secondary seal being that which is most important, because it is located downstream. the primary seal provided by the plug 10.

The primary seal consists of two main parts: the plug 10 and its latch 11. These two parts are joined to one another by a securing device making it possible to simultaneously handle the plug 10 and the latch 11 at the using a single gripping head 20 during their introduction inside the case head or during their extraction from the same case head 2. In the particular case of the example of embodiment shown in FIG. 2, this securing device consists of a pin 21 welded to the bolt 11, introduced inside a cylindrical hole made in the plug 10 and immobilized in translation relative to the plug 10 by a cylindrical key 23. However, this device allows the latch 11 to rotate relative to the plug 10.

The plug 10 has in its upper part three fingers 24, coming from the plug 10, and located at 120 ° from one another. The latch 11 likewise comprises three fingers 14 at 120 ° from one another, these fingers 14 being similar to the fingers 24 coming from the body of the plug 10. Inside the case head 2 are formed three longitudinal grooves such as 19. To introduce the assembly constituted by the plug 10 and by the latch 11 inside the case head 2, each of the three fingers 24 of the plug 10 is first introduced inside one of the longitudinal grooves 19, then the fingers 24 of the plug are made to slide in said grooves 19, until each of the fingers 14 of the latch 11 can be introduced inside these same grooves 19. We then move in translation all of these two parts until the plug 10 comes to bear on its seat 12 on which a seal 13 has previously been placed. Thus, the plug is immobilized in rotation by each of the fingers 24 engaged in the longitudinal grooves such as 19. This flat seal 13 can be of different types. It can be in particular as compressed asbestos or even asbestos compressed and reinforced by stainless steel wires. The compatibility of such a seal with sodium is not always ensured with time and temperature, but it is nevertheless sufficient to ensure the sealing of the case during the period of transport of the latter from the nuclear power plant. at the reprocessing plant, and during its return to the plant. A circular groove 15 is provided in the case head 2 allowing, by rotation of the lock 11 1 by 60 ° relative to the plug 10, the erasure of each of the fingers 14 inside said circular groove 15. In addition, the latch 11 comprises, distributed over its periphery, six screws such as 16, each terminated by a crimped ball 17. These six screws 16 make it possible to exert a force on the plug 10 and thus compress the seal 13. In in fact, after the plug 10 and the cover 11 have been placed inside the case head, the rotation of an angle of 60 ° of the latch 11 relative to the plug 10, immobilized in rotation, each brings six balls 17 ending each of the screws 16 above an equal number of conical impressions 18 made in the upper face of the plug 10. The lock 11 is therefore stopped in translation by each of the fingers 14, each is then tightened screws 16 and the seal 13 is thus compressed, which achieves the desired primary seal.

Downstream of the primary seal, there is a secondary seal constituted by a cover 30. This cover has a cylindrical part 31 which engages inside the case head 2. It is provided in its upper part with 'a gripping head 32, identical to the gripping head 20 of the latch 11, allowing its manipulation using a clamp 33 shown in phantom. At its upper part, the cover 30 has a lip 34 coming to be pressed, once said cover 30 inserted inside the case head, against a second lip 35 coming from the massive part of the case head 2 After the cover 30 has been put in place, the lips 34 and 35 are joined to one another by a butt weld 36. This leaktight seal 36 constitutes the so-called secondary seal located downstream of the primary seal produced. by seal 13.

In addition, a circular flange 40 is fixed to the case head by distributed screws 41. The circular flange 40 has a conical part 42 which, exerting a force on the lip 34 of the cover, keeps it in contact with the head d case 2. This solution makes it possible to avoid, in the event that the plug 10 leaks, that the gas pressure is exerted on the weld 36 made at the end of the lips 34 and 35. The circular flange 40 comprises also a gripping head 43, which allows its manipulation via a clamp 44 shown in phantom.

The cover 30 also includes a circular groove 37 for housing an elastomeric seal which seals with the cylindrical part of the case head. This seal is only used for the return of the case 1 to the power station, when the case is cold, the sodium solidified, and without the irradiated assembly, the lip weld 36 not being carried out.

The cover 30 also has at its lower part a locking system. This locking system comprises three radial fingers 50 coming from the cover 30. Each of these fingers 50 is introduced during the positioning of the cover 30 inside the case head 2, in a longitudinal groove such as 19 Once lip 34 has come of the cover 30 in abutment with the upper part of the case head 2, the cover 30 is rotated on itself by an angle of 60 °, in order to engage each of the fingers 50 in a circular groove 51 made in the case head 2. This locking device stops the cover 30 in translation and thus makes it possible to avoid making the weld 36 work during handling, when the circular flange 40 is not yet in place.

The advantages presented by this secondary sealing are the following: firstly, the sealing functions and those of mechanical resistance are independent of each other. Indeed, the weld 36 has the sole function of ensuring a seal between the lips 34 and 35. It undergoes no mechanical force. The forces or shocks undergone by the case are transmitted by the flange 40 to the case 2 without being exerted on the cover 30. This results in increased security of this seal. On the other hand, the lip weld can be redone several times, approximately four times, after leveling the weld 36 for disassembly, and without any particular machining for its production at the power station. Finally, this solution facilitates the mounting of the cover 30 and the circular flange 40.

Fig. 3 shows a view in axial half-section of a second alternative embodiment of a closure device for an irradiated assembly transport case. As the solution described in connection with fig. 2, it comprises a primary seal provided by a plug 100 blocked on its seat 12 by a latch 101, and a secondary seal provided by a cover 140, located downstream of the primary seal.

The primary seal produced in this second embodiment has a general organization identical to that described in FIG. 2. Indeed, the plug 100 and the latch 101 secured to one another are introduced in a single operation inside the case head 2. The system for stopping the rotation of the plug 100 and the stop system in translation of the lock 101 relative to the case head 2 are the same as those which have been described in the previous figure. However, the device for blocking the plug 100 on its seat 12 and for compressing the flat seal 13 in order to achieve the desired primary seal is different. Indeed, the latch 111 is hollowed out in its central part to allow passage to a piston, not shown in the figure, imparting a compressive force to the seal 13 by means of the plug 100. The six screws 16 distributed at the periphery of the lock 101 are each terminated by a crimped ball 17. In a manner identical to that of FIG. 2, the rotation of the latch 101 relative to the plug 100 which is immobilized in rotation, brings each of the balls 17 above an imprint 18, of conical shape, formed in the upper face of the plug 100. The screws 16 are then tight. In this way, it avoids working these screws 16 and particularly the balls 17, which avoids seizure of the latter. As mentioned above, the plug 100 and the latch 101 are secured to one another during their introduction inside the case head, this fastening device having nevertheless to allow the rotation of one relative to the other, in order to allow the locking of the latch 101. This is achieved by radial screws 103, each terminated by a stud 104 and sinking into a groove 105 formed in the plug 100. Each of the pins 104 are mounted with play in each of the grooves 105. The angular movement is adjusted by welding segment segments at the bottom of the groove 105.

Furthermore, a damping device 110 is integrated into the plug 100 on its face facing the inside of the case 1. This damping device 110 is constituted by a circular cavity made in the plug 100 and filled with an insulator with metallic fabrics. 111. The practical cavity in the plug 100 is closed by a sheet 112 welded at 113 at the periphery of said plug 100. This shock absorbing device 110 makes it possible to absorb the shocks of the assembly 6, shown in phantom and immersed in liquid sodium 8, against the cap 100.

The device shown in fig. 3 also includes a secondary seal, located downstream of the primary seal, provided by the cover 140. The seal between the case head 2 and the cover 140 is provided by a device called "fusible joint". This fusible joint is constituted by a deep annular groove 120 formed in the case head 2 and filled with a low-temperature fusible alloy 121 and by a blade 122 coming from the cover and dipping into the alloy 121. According to the temperature reached by the case head, this fusible alloy 121 can be constituted by white metals with low melting point, or silver solders for higher temperatures. The blade 122 has holes 123 distributed on two levels at its lower part. These holes serve as a lock, when the alloy 121 is solid, improving the resistance to tearing of the fusible joint. They also make it possible, when the alloy 121 is liquid, to limit the difference in level between the two faces of the blade 122 when there is a difference between the pressures prevailing inside and outside the case 1, the gases escaping through said holes 123. The groove 120 constituting the retention tank for the alloy 121 is thinned at its lower part so that with the plunging blade 122, the forces of capillaries are taken into account, thus increasing the shear coefficient of the alloy 121. The lateral clearance between the tank 120 and the blade 122 is of the order of 1 mm on either side. At its upper part, the tank widens so as to provide a volume 124 which makes it possible to avoid overflow of the liquid alloy 121 under the effect of the pressure prevailing inside the case 1. The sealing is carried out, the alloy 121 being liquid or solid, but only the latter state is to be taken into consideration for the operation of the secondary sealing. The establishment and disassembly of the cover 140 is carried out by melting the alloy 121 by means of an inductor ring, not shown in the figure, mounted remotely on the case head 2 around the groove 120 formed in that -this. Such an induction heating system allows the rapid melting of the alloy 121 and consequently a rapid installation and disassembly of the cover 140. Although the induction heating of the alloy 121 does not heat up the nearby solid parts very much, has however provided, in order to thermally isolate the cover 140 from the case head 2, particularly in the part where the circular groove 120 containing the fusible alloy 121 is arranged, an annular chamber delimiting a thin strip of gas between the mass of the cover 140 and the device of the fusible joint. This gas slide 125 constitutes thermal protection for the cover 140.

The cover 140 further comprises at its lower part a locking device making it possible to stop it in translation relative to the case head 2. The locking device constituted by three fingers 50 located at 120 ° one of the other and engaging in a circular groove 51 is identical to that which has been described in connection with FIG. 2. This locking device makes it possible to avoid making the fusible joint work, particularly during shearing, during handling.

It will also be noted that the elastomeric seal 37 sealing the cover 30 of FIG. 2 during the return of the case 1 from the reprocessing plant to the central unit is no longer necessary. In fact, the fusible joint ensures sealing on the outward journey as on the return of the case 1.

The secondary sealing device further comprises a circular flange 130 closed by a sheet 131 welded at 132 to the circular flange 130. This circular flange 130 is fixed to the case head 2 by screws 133 distributed. It is observed that, because of this arrangement, the cover 140 is completely protected against shocks which could occur during the transport of the case. There is thus a separation of the sealing and mechanical resistance functions.

Furthermore, the sheet 131 prevents the fall of dust or impurities inside the fusible joint.

The major advantages of this secondary sealing solution by a fusible joint are as follows: firstly, it allows rapid fitting of the cover 140 without requiring the use of complex and bulky machines, such as screwdrivers , cylinders, etc., which should be installed in the cell. All that is needed is the inductor ring allowing the melting of the alloy 121. On the other hand, each of the parts constituting this secondary sealing device can be reused ad infinitum, which is not the case, in particular. , seals made by welding. In fact, at most, the weld can be redone after leveling, three or four times. Consequently, the cost of the sealing system described in this solution is reduced.

Claims (9)

1. Closure device for a transport container for an assembly irradiated in a nuclear reactor comprising a circular cap (10) lodged in the container top (2), a gasket (13) located between the container top (2) and the said cap (10), and a locking member (11), at least two radial fingers (14) extending from the locking member (14) and engaging in a groove (15) formed in the containertop (2) and preventing translational movement of said locking member (14), means being provided on the locking member (11) to urge the cap (10) against the gasket (13) and provide a seal, referred to as a primary seal, between the latter and the container top (2), characterized in that:

- said locking member (11) and said cap (10) are joined together by a link means permitting rotation of the locking member relative to the cap, the locking member (11) having a gripping head (20);

- at least one finger (24) extends from cap (10) preventing rotation of the cap by engaging in at least one recess (19) formed in the container top (2);

- a circular flange (40) is fixed on the container top (2) by circumferentially-distributed bolts (41);

- a secondary seal is located downstream of the primary seal, said secondary seal comprising a lid (30) having a cylindrical part engaging in the interior of the container top (2).

2. Closure device according to Claim 1, characterized in that the means provided on the locking member (11) to urge the cap (10) against the gasket (13) comprise regularly distributed bolts (16) each ending in an inset ball (17) engaging in indentations formed in the upper surface of the cap (10) facing said bolts, thereby settling said cap on its seating (12) and compressing the flat gasket (13).

3. Closure device according to either of Claims 1 and 2, characterized in that the means providing a seal between the lid (30) and the container top (2) comprise a fusible junction formed by a deep annular groove (120) filled with a low-melting alloy (121) and by a thin sheet (122) leading from the lid and dipping into the alloy.

4. Closure device according to Claim 3, characterized in that the diameter of the cylindrical portion of the lid (140) is slightly less than that of the bore formed in the container top (2) into which it fits, thereby leaving an annular chamber enclosing a thin layer of gas between the bulk of the lid and the fusible junction.

5. Closure device according to either of Claims 1 and 2, characterized in that the means providing a fluid-tight seal between the lid (30) and the container top (2) comprise two horizontal lips (34, 35), a first lip (34) extending from the lid, and a second lip (35) extending from the container top (2), the two lips being held together by a weld (36) at their peripheries, and kept in contact with one another by a circular flange (40) fixed to the container top (2) by regularly distributed bolts.

6. Closure device according to Claim 5, characterized in that the lid (30) additionally comprises a sealing ring (37) mounted in a groove formed in the cylindrical portion (31) of the lid.

7. Closure device according to any one of Claims 1 to 6, characterized in that it additionally comprises locking means for preventing linear movement of said lid (30, 140) after it is introduced into the containertop (2), said locking means comprising at least two radial fingers (50, 120) extending from the cylindrical portion of the lid, engaging in longitudinal grooves formed in the container top (2) and rotatably engaging in a groove encircling the container top (2).

8. Closure device according to any one of Claims 1 to 7, characterized in that the locking member (102) has an open central portion and that the link means between the cap (100) and the locking member comprises radial bolts (103) each terminating in a stud (104) engaging in a recess formed in the said cap.

9. Closure device according to any one of Claims 1 to 8, characterized in that the cap (10, 100) comprises, within its face directed towards the interior of the container, a cavity filled with compressed metal foil insulation (111) which is closed by a plate welded to the periphery of said cap (100).

Images