TIGHT CLOSURE Of a CASE OF CONTAINMENT HAS MULTIPLE USES FOR NUCLEAR FUEL ASSEMBLIES IRRADIATE OR WASTE HAS HIGH ACTIVITY

Device for sealing a housing containment for irradiated nuclear fuel assemblies or high activity

The invention relates to a device for module multi-purpose containment, for example for irradiated nuclear fuel assemblies or high activity waste material, using joints.

One technique for transportation and storage of irradiated nuclear fuel assemblies is under development.

It consists schematically:

-introducing a thin-walled metal case and fully opening at one end thereof, in a thick-walled metal overwrap also hermetically closable; said casing can ensure confinement of the radioactive material while having sufficient mechanical strength. The overwrap thick provides shielding radioactive sufficient and most of the mechanical hold for that the entire parcel, and consisting of the outer packaging, the containment casing and the content of radioactive materials that it is provided of placing, is transportable, i.e. can meeting the requirements in the event of an accident severe regulatory (for example drop),

-introducing the container assembly, i.e. the overpack and the housing, are stored in the pool where the irradiated nuclear fuel assemblies to be transported,

-to load said fuel assemblies irradiated in the housing,

-placing the cover of the housing so as to ensure confinement of the radioactive material to be emptied and the housing,

-performing drying the cavity of the housing optionally out pool, and to seal the resulting package.

The package can then be safely transported and caused to destination. The containment casing will then be extracted from the overwrap to be stored at the desired location.

The housing multi-purpose containment is also known as English of "multi-purpose canister" (MPC) and the outer packaging as of "over-pack" (OP).

Typically, the end for complete opening of the housing is sealingly closed with a lid welded to, reversibly, by the O-clamped between a cover and a flange attached to the open end of said case.

Figure 1 illustrates such a reversible closure joint.

This is sees (1) the thin wall of the containment casing to multiple use (MPC), (2) in the inner cavity of the housing wherein the irradiated nuclear fuel assemblies are introduced, in (3) the clip fixed to the upper end for complete opening of the housing, (4) in the cover comprising two seals (5), in their housings, sealing after closing using the bolts (6).

With a closing device of this type, see that after the cassette is inserted into the overpack, the flange (3) rests on the upper end of the overwrap (7) (OP).

Thus introducing as extracting said seal housing reversible, respectively into and out of the overpack, that may be engaged by said upper end of the overwrap, which involves a cell or shielded device, operation or a swimming pool, to provide the radiation shield that the housing does not have (MPC).

To facilitate the operation of removing the overwrap in a vertical position and unnecessary to use such a shielded device intermediate between the overpack (OP) and the desired storage location, it is advantageous to use an overwrap having a total opening not only at its upper end, but also at its lower end; and after removing the bottom of the overwrap the package and is conveyed directly above the storage location, can then be used to extract the housing charged fuel assemblies irradiated by the lower end of said overwrap by sliding the one relative to the other.

It appears evident that the presence of a flange on the housing prevents such apparatus wherein the housing is inserted into the overpack by its upper end and is extracted by its lower end.

It is essential to facilitate the apparatus a housing having an outer wall perfectly smooth, in particular, without any flange. The invention has thus sought to develop such a housing that simultaneously has a reversible closure reliably, but also simple to produce or to implement and having no element that projects from the outer cylindrical wall of the housing.

The present invention is a device for removable sealing a metal housing confinement multiple use (MPC) for irradiated nuclear fuel assemblies, consisting essentially of a tubular body or cylindrical, generally with a circular cross-section, having a long axis, a lower end closed by a sealed bottom and an upper end fully open, said housing being adapted to be wholly included in a thick-walled metal overpack, said sealing device comprising:

-at least two solid discs removable metal entirely located within said tubular body, bearing directly or via a disk or bearing ring, on a shoulder formed in the inner wall of the tubular body along all or part of its periphery, near its upper end, each of said solid discs and sealing means located at their periphery cooperating with a vertical portion of the inner wall of the tubular body,

-a clamping device, also within the tubular body above said metal solid discs and acting on them, for sealing.

The solid discs are stacked on each other and in the sealing is in particular between the sealing means located at the periphery of the metal solid discs and the vertical wall of the tubular body as will be seen in more detail further.

The supporting plate may also be a crown. Furthermore the solid disc most lower sealing means can be supported directly on said shoulder without through the disk or bearing ring.

Typically, and as will be seen further in detail, the sealing means generally comprise O-rings which are compressed using the clamping device which can be of known type.

The thickness of the tubular body of the housing (MPC) is thin, typically between 1 and 10 cm, but most often between 2 to 5 cm and despite this the device according to the invention makes it possible to provide the seal of the case in the time. Compared the thick walls of the overpack (OP) are generally in the order of 10 to 30 cm, but most often between 15 and 25 cm. On the other hand, the order of magnitude of the diameter of the housing (MPC) is between 0.5 and 2.5 m m (usually in the range 1.5 m and 2 m) and its length, bonded to the fuel assemblies contained, can vary between 3 and 5 m.

The solid discs and the disc or bearing ring generally have a thickness of at least 15 mm which is related to the thickness of the gasket and is capable of avoiding any deformation in the clamping sealing. Their thickness is usually less than 50 mm to avoid any adverse weighting of the container or to leave more space available the fuel elements introduced into the cavity.

The closure device according to the invention can additionally carry devices for testing the sealing. In this regard, the use according to the invention of at least two discs solid metal with their sealing means makes it possible to control and thereby assure said sealing.

Such a locking device consists of at least two elements (i.e. a metal disk and a clamping device) can be penetrated by a port having its own sealing system, for example having two controllable sealing joints.

Figure 2 illustrates the invention. It appears very easy to make or to implement and the entire container has an outer wall perfectly cylindrical, smooth, without edges being formed along its length.

On Figure 2 see in (1) the thin wall of the tubular body of the containment casing to multiple use (MPC), (2) in the inner cavity for receiving the irradiated fuel assemblies stored in a suitable basket. The upper end (10) of the tubular body may be the same thickness as the body, but here it has been welded and has a slight additional thickness to the inside of said tubular body; it has, as well as the tubular body, a circular cross-section except optionally in sections, for example at point cuts type (20) or when the supporting shoulder (11) does not occupy the entire periphery of the inner wall of the tubular body, as will be seen farther; vertical herein the outer walls of the tubular body and its end optionally insert (10) are aligned such that they do not have projecting portion at the outside of the housing that may interfere with. The internal thickening, possible, provides the upper end (10) of the housing a greater stiffness such that the protecting device according to the invention is improved without reducing the capacity of said housing.

The upper end (10) has a shoulder (11) formed in the inner wall; said shoulder can be provided on all or only a portion of the periphery of said inner wall. It is such that the disc or bearing ring (12) can rest stably; the disc or bearing ring is circular and has an upper face, a bottom face and a cylindrical side wall.

On the upper face of the circular disc or bearing ring (12) takes place a first circular solid disc (13), which solid disk (13) has at its periphery sealing means comprising a chamfer (14) provided at the place of its lower peripheral edge and an O-ring the metal more often (15) taking place in the housing created by said chamfer (14). The metal joint may be of the type [...] (registered trademark) or other metal gasket having similar properties.

An alternative embodiment is that the lower disc (13) is supported directly on the shoulder (11).

The sealing condition is provided by the metal gasket (15) between the vertical inner wall cylindrical with a circular cross-section of the end piece (10) [or from the end of the tubular body (1) in the case where there is no specific end piece added] and one or the other of the surface of the chamfer or the horizontal upper face of the supporting disc.

The embodiment with a supporting disc is particularly advantageous to compress the seal (15) and sealing when the shoulder (11) is not performed on the entire periphery of the inner wall, by in particular to the fact that said sealing is obtained at least partly by supporting the seal on the vertical portion of the interior wall.

To have better guarantee sealing and to improve the control, a second solid disc (13 ') identical to the disc (13), with its chamfer (14') and its metal gasket (15'), is placed on the upper surface of the plate (13);

the seal (15') is of the same compressed by reaction on the upper face of the solid disk (13) lower on which it sits.

The clamping device, not shown, is located entirely within the end piece (10) [or optionally of the tubular body (1)]. Typically it is of known type and provided with clamping means cooperating with the inner wall that provide a fluid seal of the close the housing by compression on the seals (15,15 ') by pressing vertically on the upper disc.

Referring is that by tightening compresses the seals (15,15 ') to provide a fluid tight seal between the chamfers of the solid discs (13) and (13') and the inner wall of the end piece (10) [or optionally from the end of the tubular body (1)].

In simple modular and the number of solid discs can be increased to the request to further enhance the degree of securing the seal.

II appears that the closure device according to the invention can be implemented easily, authorises the switch to entire housing (MPC) through an overwrap (OP) from one end to the other and simultaneously achieves a high sealing and mechanical strength safety regulatory requirements.