GB2250944A

GB2250944A - Radioactive source storage installation

Info

Publication number: GB2250944A
Application number: GB9124980A
Authority: GB
Inventors: Michel Rodriguez; Guillou Georges Le
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 1990-12-20
Filing date: 1991-11-25
Publication date: 1992-06-24
Anticipated expiration: 2011-11-25
Also published as: GB2250944B; JP2713321B2; FR2670946B1; FR2670946A1; JPH05119194A; GB9124980D0

Abstract

For the storage, replacement and transportation of radioactive sources (44) used in a confinement enclosure (12), an installation is proposed, which comprises a mobile storage casket (14), an engagement member (88) mounted on one wall (10) of the enclosure, first cable sections (46) carrying the radioactive sources and second cable sections (104) which can be connected to the first sections. The storage casket (14) incorporates a rotary body (22) having at least two inwardly curved storage tubes (40), each of which is able to receive a source (44) and the first cable section (46) carrying the latter. This section is normally locked by a locking pin (54), which automatically releases the first cable section when the casket (14) is engaged on the engagement member. The corresponding storage tube (40) is then aligned with a guide tube (96) and the source can be transferred between the enclosure (12) and the casket. <IMAGE>

Description

RADIOACTIVE SOURCE STORAGE INSTALLATION DESCRIPTION The invention relates to an installation making it possible to store one or more radioactive sources normally placed in a confinement enclosure, externally of said enclosure, when said sources are not used. This installation also allows the replacement of spent sources and their transportation.

In the state of the art, the storage and transportation of radioactive sources outside the confinement enclosures in which said sources are normally placed take place by means of transportation and storage caskets or flasks, which are not designed to receive these sources. There are consequently difficult - to so-lve problems with respect to the protection of personnel against radiation emitted by the sources during their transfer between the confinement enclosure and the casket. Moreover, the replacement of a spent source requires particularly long handling operations, because two different caskets must be used for evacuating the spent source and for bringing in the new source.

FR-A-2 544 542 discloses-a mobile tubular enclosure by means of which contaminated parts placed within the confinement enclosure can be replaced and transported from one place to another. This mobile enclosure makes it possible to solve the problems caused by conventional transportation caskets. However, it is particularly complex and costly, so that its use must be reserved for the replacement of special parts and it is not suitable for replacing radioactive sources.

The invention specifically relates to an installation for the storage of radioactive sources, whose original design enables it to carry out, in a particularly simple and risk-free manner for personnel, the storage, replacement and transportation of radioactive sources normally contained in confinement enclosures.

In its broadest definition, such a radioactive source storage installation is characterized in that it comprises a biological protection or storage casket containing a rotary drum, in which are housed at least two inwardly curved storage tubes issuing at one end of the rotary drum; at least one first cable section carrying a radioactive source at a first end, said cable section being receivable with said source in one of the storage tubes, so that a second end of the cable section is accessible at said end of the rotary drum when the source is in the bottom of the storage tube; and means for locking the cable section in the rotary drum associated with each of the storage tubes.

As a result of the inwardly curved nature of the storage tubes housed in the rotary drum of the casket, operators are protected against radiation emitted by the source or sources, which can be located in the bottom of each of the tubes. Therefore the operators can safely carry out a number of operations before or after the transfer of a source between the casket and a tight enclosure, which is not the case with caskets having the conventional design, where the source is received in a rectilinear recess.

Moreover, the rotary drum of the casket has several storage tubes making it possible to replace one or several radioactive sources (three in the embodiment) with the aid of a single casket, which was not previously possible.

Advantageously, the installation according to the invention also comprises an engagement member mounted on one wall of an enclosure able to contain the source and on which can be engaged the said end of the rotary drum, so that each of the storage tubes can be aligned with a guide tube traversing the wall and the engagement member by a rotation of said drum; and a second cable end, which can be received in the guide tube and whereof a first end can be coupled to the second end of the first cable section.

in a preferred embodiment of the invention, said end of the rotary drum has a cylindrical portion projecting beyond an end surface of the storage casket and which can bear against an abutment surface of the engagement member, said cylindrical portion then penetrating a complementary cylindrical recess formed in the engagement member.

Preferably, the locking means comprise an element able to cooperate with the engagement member in order to release the first cable section, when said rotary drum end is engaged on the engagement member. Said element can in particular be constituted by a locking pin slidingly received in a bore formed in said rotary drum end and intersecting one of the storage tubes, a passage formed in the locking pin being aligned with said storage tube when one end of the locking pin is flush with the outer surface of said rotary drum end, as well as elastic means acting on the locking pin in order to move it towards a locking position for the first cable section, in which said end of the locking pin projects beyond said end surface.

Advantageously, the installation according to the invention also comprises a trolley or carriage, which carries the storage casket, in such a way that an axis of the engagement member is aligned with the rotation axis of the rotary drum.

The storage casket can also comprise rotary drum rotation indexing means determining positions in which each of the storage tubes is aligned with the guide tube.

The invention is described in greater detail hereinafter relative to a preferred embodiment of the invention and with reference to the attached drawings, wherein show: Fig. 1 a side view, in part longitudinal section of a radioactive source storage installation according to the invention.

Fig. 2 a cross-sectional view along line II-II of fig. 1.

Figs. 3A and 3B diagrammatic side views illustrating in longitudinal sections two stages of the realization of the installation of fig.

1 during the replacement of a radioactive source.

In fig. 1, the reference numeral 10 designates one wall of a confinement enclosure 12, in which radioactive sources can be used.

The installation according to the invention permits the provisional storage of one or more such sources outside the confinement enclosure 12, so as to e.g. carry out the replacement thereof.

This installation mainly comprises a storage casket or flask designated in general terms by the reference numeral 14. This generally cylindrical transportation casket 14 comprises a thick wall 16 made from a material absorbing the radiation emitted by the radioactive sources, such as lead and/or compound. Along the axis XX' of the storage casket 14, said wall 16 defines a cylindrical recess 18 closed at one end and whose opposite end issues onto a front face 20 of the wall 16.

A cylindrical drum or body 22 is mounted in rotary manner within the recess 18. The rotary drum 22 is partly supported by a first bearing 24, mounted in a part 26 detachably fitted in the bottom of the recess 18 and in which is received an extension 28 of the body 22. The supporting action is also fulfilled by a second bearing 30, mounted in a flange 32 fixed, e.g. by means of the screws 34, to the front face 20 of the wall 16, so that a cylindrical portion 33 of the body 22, projecting beyond the front face 20, is received in the said bearing 30.

The cylindrical body 22 comprises a metal wall 36 forming the outer envelope of the drum, as well as the cylindrical portion 33. Within the said wall 36 is placed a filling material 38 such as lead and/or compound able to absorb the radiation emitted by the radioactive sources.

At least two inwardly curved storage tubes 40 are mounted in the cylindrical body 22. The bottom of these storage tubes 40 is placed in the filling material 38 in the vicinity of the end of the cylindrical body 22 supported by the bearing 24, whilst the opposite end of each of the tubes.40 issues onto the front face 42 of the cylindrical portion 33. The curvature of each of the tubes 40 is such that the bottom of these tubes is at a very small distance from the axis XX', whereas the end of the tubes issuing onto the front face 42 is at a relatively large distance from said axis.

When a radioactive source 44 is placed in the bottom of one of the storage tubes 40, the curvature of the latter makes it possible to ensure that direct radiation emitted by said source does not diffuse along the tube so as to pass out through its open end.

To each of the radioactive sources 44 is welded a cable section 46, whose length is such that the end of said section projects beyond the front face 42 when the radioactive source 44 is placed in the bottom of the tube 40.

On the front face 42 of the projecting portion of the cylindrical body 22, each of the storage tubes 40 carries an end fitting 48 to which can be screwed a protection and safety sleeve 50, in which is housed the projecting end of the cable section 46.

As is more particularly illustrated in fig. 2, the cable sections 46 carrying the radioactive sources 44 are normally immobilized within the storage tubes 40 by locking means designated by the reference 52.

For each of the storage tubes 40, said locking means 52 comprise a locking pin 54 slidingly received in a bore 56 radially traversing the projecting portion of the cylindrical body 22 and whose axis intersects the axis of the corresponding tube 40. The locking pin 54 is traversed by a passage 58 having the same diameter as the tube 40 and which can be aligned with the latter or displaced with respect thereto, as a function of the position occupied by the locking pin within the bore 56.

A pin 60 is placed in the projecting portion of the cylindrical body 22, so as to intersect the axis of the bore 56 passing through an oblong recess 62 formed in the locking pin 54. The cooperation between the pin 60 and the oblong recess 62 limits the deflection of the locking pin 54 in one or other direction within the bore 56.

A first end of the locking pin 54 in the vicinity of the axis XX' bears on a helical compression spring 64 also located in the bore 56. The opposite end of said spring 64 bears on the end of a screw 66 received in a tapped end portion of the bore 56.

Thus, the spring 64 normally keeps the locking pin 54 in a locked position, in which the end of the oblong recess 62 closest to the spring 64 bears against the pin 60. In this position of the locking pin 54, the axes of the passage 58 and the storage tube 40 are displaced by a value substantially equal to the diameter of the passage and the tube. Consequently, when a radioactive source 44 is present in the bottom of the tube 40, the cable section 46 welded to said source is locked in the tube 40 by the locking pin 54 under the action of the spring 64 and as illustrated in fig. 2.

Advantageously, to ensure that the locking in translation of the cable section 46 is more effective, a pin 68 traverses the locking pin 54 perpendicular to its axis, so as to intersect the passage 58 according to a secant on the side of the spring 64.

In the locking position of the locking pin 54 illustrated in fig.

2, the end of said pin opposite to the spring 64, which is hemispherical, projects beyond the outer cylindrical surface 70 of the projecting cylindrical portion 33 of the drum 22. As will be shown hereinafter, this characteristic makes it possible to push back the locking pin 54 into an unlocked position, in which the passage 58 is aligned with the corresponding storage tube 40, by acting on the hemispherical projecting end of said pin, so that it is flush with the outer cylindrical surface 70.

It is also possible to regulate the calibration of the spring 64, i.e. the tension with which the cable section 46 is locked by the locking pin 54, by screwing or unscrewing to a greater or lesser extent the screw 66. The bores 56 containing the locking pins 54 associated with each of the storage tubes 40 are reciprocately displaced in accordance with the axis x The storage casket 14 also has indexing means making it possible during the rotation of the cylindrical body 22, to pinpoint the angular positions of the latter for which each of the storage tubes 40 is located in a relative angular position determined with respect to the casket wall 16.When the latter is mounted on a transportation trolley 72 (fig. 1) travelling on wheels 74 in such a way that its axis XX' is oriented horizontally, said angular position is such that the axis of the storage tube 40 in question is placed in a vertical plane containing the axis XX' and above said axis in the embodiment shown in the drawings.

In practice and as is shown in greater detail in fig. 2, said indexing means e.g. comprise a ball 76 carried by a screw 78 radially traversing the flange 32 and applied by a compression spring 80 against the cylindrical outer surface of the portion 33 of the cylindrical body 22 located within the flange 32. Axial grooves 82 having a circular arc section and formed on said external surface receive the ball 76 when one of the storage tubes 40 is located in the angular position defined hereinbefore.

Thus, when an operator controls the rotation of the cylindrical body 22 within the wall 16, e.g. by means of a not shown spanner engaging in the blind holes 84 formed on the cylindrical outer surface of the cylindrical body portion 33, he stops this rotation when he feels the click caused by the penetration of the ball 76 in the groove 82 corresponding to the storage tube 40 in which a radioactive source is tb be introduced or from which it is to be removed.

Finally, the storage casket 14 has a protective cap 86, shown in mixed line form in fig. 1, which is dismantlably fixed to the front face 20 of the wall 16, so as to cover the entire projecting portion of the cylindrical body 22, the flange 32 and the sleeves 50.

To allow the transfer of a radioactive source 40 between the storage casket 14 and the confinement enclosure 12 defined by the partition 10, the latter is equipped with an engagement member in the form of a flange 88, which is fixed to the outer surface of the wall 10, e.g. by means of screws 90, as illustrated in fig. 1. It is important to note that the axis of said flange 88 coincides with the axis XX' of the casket 14, when the latter is mounted on the trolley or carriage 72.

On its outer face, the flange 88 has a ring-shaped portion, which internally defines a cylindrical recess 92 open towards the outside and complementary of the cylindrical portion of the casket body 22 projecting beyond the end face 94 of the flange 32.

A rectilinear guide tube 96 traverses the wall 10 and the flange 88, so as to issue into the bottom of the cylindrical recess 92 at a point located above the axis XX', so that the axis of said guide tube is located in a vertical plane passing through the axis XX' and at a distance equal to the distance separating the ends of the storage tubes 40 from said axis XX'. In this way, the guide tube 96 is automatically placed in the alignment of the storage tube 40 pinpointed by the indexing means equipping the storage casket 14.

Blind holes 98 are also formed in the wall 10 and in the flange 88, so as to issue into the recess 92 in front of each of the other storage tubes 40 of the casket 14, when one of said tubes is located in the extensionof the guide tube 96. The dimensioning of these blind holes 98 makes it possible to house there protective sleeves 50 sealing the other storage tubes 40 when the cylindrical portion of the body 22, which projects beyond the surface 94, is received in the complementary cylindrical recess 92.

It should be noted that when said cylindrical portion of the body 22, which projects beyond the surface 94 is received in the recess 92, the locking pins 54 are automatically overridden by the cooperation of the hemispherical ends of said pins with a bevelled portion 100 formed at the entrance of the recess 92. The radioactive source or sources 44 present in the storage tubes 40 are consequently automatically released when the surface 94 bears against the end face 102, forming the abutment surface of the flange 88.

Finally, the installation according to the invention comprises a second cable section 104 to be received in the guide tube 96 and whose end is equipped with a coupling device 106 for fixing to a complementary coupling device 108 mounted at the end of the cable section 46 carrying the radioactive source 44. The coupling devices 106,108 can be constituted by fast screw or bayonet couplings, or any equivalent mechanism.

An example of the use of the storage installation according to the invention for replacing a radioactive source normally located within a confinement enclosure 12 will now be described whilst successively referring to figs. 3A and 3B.

As illustrated in fig. 3A, the storage casket 14 is firstly brought on the trolley 72 (fig. 1) into the vicinity of the engagement flange 88. After removing the protective cap 86, an operator manually rotates the cylindrical body 22, so as to bring an empty storage tube 40 in front of the guide tube 96, whilst making use of the previously described indexing means. He then removes the protective sleeve 50 from said empty storage tube, engages the casket 14 on the engagement flange 88 by moving the trolley 72 on the rails 74, so as to make the cylindrical end 33 of the body 22 penetrate the recess 92 of the flange 88.

In this position illustrated in fig. 3B, an operator moves back with the aid of remote manipulating means located within the confinement enclosure 12, an assembly constituted by the radioactive source 44 to be replaced, the cable section 46 welded to said source and the cable section 104 coupled to the section 46 with the aid of the devices 106 and 108. Under the effect of this thrust, the radioactive source to be replaced travels in the guide tube 96 and then in the storage tube 40 located in the extension of said guide tube until it abuts with the radioactive source 44 in the bottom of the tube 40 (arrow-F).

It should be noted that the displacement of the source and the associated cable sections is not prejudiced by the locking means 52. Thus, the latter then occupy their release position, in view of the fact that the locking pins 54 have been forced back during the entrance of the cylindrical portion 33 of the body 22 into the interior of the recess 92.

The operator then slightly moves back the trolley 72 carrying the casket 14, so as to free the cylindrical projecting portion of the body 22 from the recess 92. During this return movement, the thrust force exerted on the cable section 104 from the interior of the cell 12 is maintained until the locking pins 54 pass out of the recess 92. A locking of the cable section 46 under the action of the spring 64 acting on the corresponding locking pin 54 is then automatically obtained.

Under these conditions, the coupling devices 106,108 become accessible and can be disconnected by the operator. The protective sleeve 50 of the corresponding storage tube 40 is immediately put into place. The operator can then introduce a new radioactive source into the confinement enclosure 12. For this purpose, he again manually rotates the cylindrical body 22, so as to bring into the extension of the guide tube 96 another storage tube 40 containing a new radioactive source fixed to a cable section 46. After removing the protective sleeve 50 from said storage tube, the operator couples the coupling device 108 to the coupling device 106 of a cable section previously introduced into the guide tube 96.

The engagement of the casket 14 on the flange 88 is then carried out, which has the effect of freeing the cable section 46. By acting from the interior of the confinement enclosure 12, the operator can thus transfer the new radioactive source into the interior of said enclosure.

In order to complete the operation, the operator again moves back the trolley 72 carrying the storage casket 14 and then puts back into place the protective sleeve 50 of the corresponding storage tube 40, as well as the protective cap 86. The spent source can then be transported to another site with the aid of the casket 14.

It should be noted that during these operations, the working personnel is protected against the radiation emitted by the radioactive sources by the inwardly curved nature of the storage tubes 40 on the side of the casket 14.

Obviously, the invention is not limited to the embodiment described hereinbefore and covers all variants thereof. Thus, it is readily apparent that the number of storage tubes 40 in the cylindrical body 22 can be higher or can be equal to two within the scope of the overall dimensions which it is wished to give to the storage casket. Moreover, the locking means 52 could be differently constructed and the sliding locking pins could be replaced by pivoting elements. In addition, the search for a particularly simple and inexpensive solution has led to the design of a storage casket in which the rotation of the cylindrical body is manually controlled, but this could easily be controlled by'a motor. Finally, the horizontal orientation of the common axis of the casket and the engagement means provided on the confinement enclosure wall is not imperative, provided that the casket can be placed on a system ensuring in simple manner its alignment with the engagement device.

Claims

1. Installation for the storage of radioactive sources, chara cterized in that it comprises a storage casket (14) containing a rotary drum (22), in which are located at least two inwardly curved storage tubes (40) issuing at one end of the rotary drum; at least one first cable section (46) carrying a radio active source (44) at a first end, said cable section being received with said source in one of the storage tubes1 so that a second end of the cable section is accessible at said end of the rotary drum when the source is in the bottom of the storage tube; and means (52) for locking the cable section in the rotary drum associated with each of the storage tubes.

2. Installation according to claim 1, characterized in that it also comprises an engagement member (88) mounted on a wall (10) of an enclosure (12) able to contain the source and on which can be engaged said end of the rotary drum, so that each of the storage tubes (40) can be aligned with a guide tube (96) traversing the wall and the engagement member by a rotation of said drum; and a second cable sections (104) received in the guide tube and whereof a first end can be coupled to the second end of the first cable section.

3. Installation according to claim 2, characterized in that said end of the rotary drum (22) has a cylindrical portion (33), which projects beyond an end surface (94) of the storage casket (14) and which can bear against an abutment surface (102) of the engagement member, said cylindrical portion then pene trating a complementary cylindrical recess (92) formed in the engagement member.

4. Installation according to any one of the claims 2 and 3, char acterized in that the locking means (52) incorporate an element (54) able to cooperate with the engagement member (88) to release the first cable section (46) when said rotary drum end is engaged on the engagement member.

5. Installation according to claims 3 and 4 in combination, char acterized in that said element is a locking finger (54) slid ingly received in a bore (56) formed in said end of the rotary drum (22) and intersecting one of the storage tubes (40), a passage (58) formed in the locking pin being aligned with said storage tube when one end of the locking pin is flush with the outer surface of said end of the rotary drum, and elastic means (64) acting on the locking pin (54) in order to move it towards a locking position of the first cable sect ion, in which said locking pin end projects beyond said outer surface.

6. Installation according to any one of the claims 2 to 5, chara cterized in that it comprises a trolley (72) carrying the storage casket and running on rails (74), so that an axis of the engagement member is aligned with the rotation axis of the rotary drum (22).

7. Installation according to claim 6, characterized in that the storage casket (14) comprises means (52) for the indexing in rotation of the rotary drum (22) determining positions in which one of the storage tubes (40) is aligned with the guide tube (96).

8. Installation according to any one of the preceding claims, characterized in that it comprises at least two detachable sealing sleeves (50), which can be fixed to said rotary drum end, in the extension of each of the storage tubes (40), so as to be able to close the second end of the first cable sect ion (46) received in said storage tube.

9. Installation according to claim 8, combined with any one of the claims 2 to 7, characterized in that the engagement member (88) comprises at least one blind hole (98), which can receive a protective sleeve (50), when the end of the rotary drum is engaged on the engagement member with a storage tube (40), from which the sleeve has been removed, aligned with the guide tube (96).

10. Installation according to any one of the preceding claims, characterized in that it also comprises a removable protective cap (86), which can be fixed to the transportation casket (14) around the end of the rotary drum (22).

11. Installation substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.