Patent Description:
In more detail, the present invention fits into the context of the cylindrical casks intended for conditioning, storage and disposal of solid radioactive waste of medium activity with reduced Alpha-emitting radionuclide (MA-Beta) content. It is understood that the cask of the invention is suitable for use in the conditioning, storage and disposal of other types of waste.

It is known that the casks for conditioning, storage and disposal of solid waste of medium activity have to meet stringent requirements, generally set by national or international standards which, albeit with some differences, establish substantially equivalent criteria. For Italy, the reference standard is UNI <NUM>:<NUM>.

Among the casks available to date, cylindrical casks made of suitable metal materials, e.g. made by casting spheroidal cast iron or forging carbon steel, are particularly well known.

In general, the casks of this type consist of a main body provided with an access opening, and of a lid closing the opening of the body and fixed to the body by screws. A sealing system is placed between the body and the lid, which according to standards (such as the already mentioned Italian standard UNI <NUM>:<NUM>) must consist of two gaskets in series.

The known casks, although generally efficient, may have some drawbacks in certain cases and still seem to have room for improvement.

In particular, some known casks are provided with sealing systems with combined axial and radial gaskets, which besides being relatively complicated and costly to manufacture and install, may in some cases not be entirely satisfactory in use.

In general, the known casks have recesses, defined for example by the seats formed in the lid and into which the lid closing screws are recessed, and by the heads of the screws themselves, which are normally cylindrical with a hexagonal socket. The presence of recesses poses problems during the usual operations of decontamination of the cask, as washing liquid and contaminated particulate matter can stagnate there or enter into the gaps left between the seats of the bolted connections.

Even the lid itself, if it is in turn recessed between the sides of the main body of the cask, creates an additional closed recess, a potential source of water stagnations or contaminated particulate matter, especially in the case wherein, as is often the case, the cask is filled under a water head and subsequently drained, dried and decontaminated.

An example of the above-mentioned kind of casks is disclosed by <CIT>.

It is an aim of the present invention to provide a cask for conditioning, storage and disposal of radioactive waste, in particular solid radioactive waste of medium activity, which is free of the drawbacks highlighted herein of the prior art.

In particular, it is an aim of the invention to provide a cask that is simple, inexpensive to make and use, and at the same time fully efficient.

It is a particular aim of the invention to provide a cask that is fully efficient in the sealing function and capable of effectively protecting the sealing system, for example in case of accidental events such as shocks and/or fires and which at the same time allows to simplify decontamination operations.

A further aim of the invention is to improve the sealing function not only of the primary sealing system (operating between the lid and the body of the cask) but also of the secondary sealing systems (operating on openings formed in the lid and in the body of the cask for draining, venting and the internal pressure and leakage checks during operation).

In accordance with these aims, the present invention relates to a cask for conditioning, storage and disposal of radioactive waste, in particular solid radioactive waste of medium activity, as defined in essential terms in the appended claim <NUM> and, in its additional characters, in the dependent claims.

The cask of the invention is fully effective in its functions, meeting in particular the requirements of the UNI <NUM>:<NUM> standard, while at the same time being particularly simple and inexpensive to make and use.

The cask of the invention enables in particular a simplification of the assembly and commissioning operations, allowing, among other things, the required performance of the main sealing system to be maintained for each design condition, whether it is normal, abnormal or incidental.

In accordance with the invention, in fact, the primary sealing system (acting between lid and body of the cask) consists of two axial gaskets in series, which are coplanar and tightened in a coaxial direction to the (cylindrical) body of the cask, guaranteeing sealing performance under all design conditions; this results in a significant saving in manufacturing costs compared to other solutions and at the same time high sealing efficiency.

In addition, the gaskets of the primary sealing system are protected against accidental events and therefore maintain their sealing efficiency even in the event of accidents (shocks and fires). In fact, the conical coupling surfaces are coupled to each other with a play less than the play existing between each lid closing screw and the respective through hole formed in the lid, thus ensuring the protection of the lid closing screws in the event of shocks. The gap between the radially outer portions of the flanges, on which the lid closing screws are placed, makes it possible to compensate, in the event of fire, for any differential thermal expansion and consequent tension and deformation states.

According to further aspects of the invention, which are the subject-matter of the dependent claims, the cask of the invention also has further features that allow to optimise the decontaminability of the outer surfaces of the cask, avoiding possible stagnations of liquids or solid particles. In particular, the lid closing screws are recessed in seats provided with radial outflow openings.

According to a further aspect of the invention, the so-called secondary sealing systems, acting on auxiliary openings formed on the body and on the lid of the cask, are also particularly simple and effective, as they consist of metal sealing rings, for example of C-Ring type, used together with threaded caps, in particular conical thread caps (NPT caps) treated with a solid lubricant and anti-seize paste that acts as a gas-tight sealing material. In this way, a significant saving in mechanical machining costs is achieved; in fact, the housing of an NPT cap is in fact definitely simpler and less costly than the construction of a seat for a second metal sealing ring, with the associated surface roughnesses, dimensional and geometric tolerances. In addition, commercially available NPT caps made of galvanised carbon steel can be used, which are definitely cheaper than custom-made sealing rings of C-Ring type made of high-grade Nickel alloys (e.g. Alloy <NUM>) coated with Silver on the surface.

Further features and advantages of the present invention will become clear from the description of the following non-limiting embodiments, with reference to the figures of the accompanying drawings, wherein:.

In <FIG> and <FIG>, <FIG> denotes as a whole a cask for conditioning, storage and disposal of radioactive waste, in particular solid radioactive waste of medium activity.

The cask <NUM> comprises: a main hollow body <NUM>, e.g. cylindrical, extending along and about a longitudinal axis A and provided with an access opening <NUM>; a lid <NUM>, e.g. with circular plan, closing the opening <NUM> and fixed to the body <NUM> by closing screws <NUM>; and a primary sealing system <NUM> arranged between the lid <NUM> and the body <NUM>.

The body <NUM> is in particular a cylindrical body having a cylindrical side wall <NUM> that extends along and about the axis A between a lower end <NUM>, closed by a bottom wall <NUM>, and an upper end <NUM>, provided with the opening <NUM>.

The body <NUM> has, at the upper end <NUM>, a flange <NUM> that extends about the opening <NUM> and cooperates with the lid <NUM> to close the opening <NUM>.

with reference also to <FIG> and <FIG>, the flange <NUM> has an annular sealing surface <NUM> substantially flat and perpendicular to the axis A and a radially outer portion <NUM> that is axially offset with respect to the sealing surface <NUM>, joined to the sealing surface <NUM> by a step <NUM>.

The body <NUM> also has a conical coupling surface <NUM> that extends from a radially inner edge of the sealing surface <NUM> towards the axis A and towards the lower end <NUM>; and optionally (but not necessarily) an annular outflow surface <NUM> that extends from the sealing surface <NUM> towards the axis A and is slightly inclined downwards, i.e. towards the lower end <NUM>.

The portion <NUM> of the flange <NUM> is provided with a plurality of threaded blind holes <NUM>, parallel to the axis A and arranged angularly spaced about the axis A to receive respective closing screws <NUM>.

Each hole <NUM> is connected to a drainage hole <NUM>, formed radially through the side wall <NUM> at one bottom end of the respective hole <NUM> and communicating with the outside of the cask <NUM>.

The body <NUM> also comprises a lifting bead <NUM> that protrudes radially from the side wall <NUM> of the body <NUM> around the flange <NUM> and can be grasped by special lifting devices for manoeuvring the cask <NUM>. Advantageously, the bead <NUM> has an upper outflow surface <NUM> inclined downwards (i.e. towards the lower end <NUM>) with respect to the axis A and to the side wall <NUM>.

The lid <NUM> has a central portion <NUM> and a radially outer flange <NUM>, facing the flange <NUM> of the body <NUM>.

Specifically, the flange <NUM> comprises a sealing surface <NUM> cooperating with the sealing surface <NUM> of the body <NUM>; and a radially outer portion <NUM> facing the portion <NUM> of the flange <NUM> of the body <NUM>.

The sealing surfaces <NUM>, <NUM> are parallel to one another and perpendicular to the axis A.

The central portion <NUM> has a conical coupling surface <NUM> adjacent to the sealing surface <NUM>; the coupling surface <NUM> is defined by a side surface of the central portion <NUM> inclined towards the axis A and towards the lower end <NUM> and has a shape corresponding to the coupling surface <NUM> of the body <NUM>.

Portion <NUM> has a plurality of through holes <NUM> aligned to respective holes <NUM> of the body <NUM> to receive the closing screws <NUM>.

Each hole <NUM> comprises an enlarged upper portion <NUM> shaped to house a head <NUM> of the respective closing screw <NUM>. The portion <NUM> has an annular bottom surface <NUM> from which a side wall <NUM> extends which surrounds the head <NUM> of the closing screw <NUM> but has a radial opening <NUM> facing toward a radially outer peripheral edge of the lid <NUM> and flush with the bottom surface <NUM>.

The lid <NUM> also comprises a lifting bead <NUM> that protrudes radially from the side wall <NUM> of the lid <NUM> around the flange <NUM> and can be grasped by special lifting devices. Advantageously, the bead <NUM> has an upper outflow surface <NUM> located flush with the bottom surface <NUM> and inclined downwards (i.e. towards the lower end <NUM>) with respect to the axis A.

The sealing system <NUM> comprises two gaskets <NUM> in series acting between the sealing surfaces <NUM>, <NUM>.

In particular, the gaskets <NUM> are axial gaskets acting parallel to the axis A between the sealing surfaces <NUM>, <NUM>, which are parallel to one another and perpendicular to the axis A.

The gaskets <NUM> consist of respective metal sealing rings, for example metal O-rings or, preferably, energized metal C-Rings.

For example, the gaskets <NUM> are housed in respective grooves <NUM> formed on one of the sealing surfaces <NUM>, <NUM> and protrude axially out of the grooves <NUM> to contact the opposite sealing surface <NUM>, <NUM>. Preferably, the grooves <NUM> are formed on the sealing surface <NUM> of the lid <NUM> to prevent the gaskets <NUM> from being damaged when loading the waste into the cask <NUM>.

Appropriately, the gaskets <NUM> are fixed to the lid <NUM> and held in the respective grooves <NUM> by means of clips screwed into special recesses within the grooves <NUM>.

When the lid <NUM> is mounted on the body <NUM> and fixed to it by closing screws <NUM>, the closing screws <NUM> are inserted through respective holes <NUM> and engage respective holes <NUM> to tighten the flanges <NUM>, <NUM> against each other.

Preferably, the closing screws <NUM> are hexagonal head screws, for example (but not necessarily) made of galvanised steel. This avoids the presence of a recessed hexagon, a potential site for stagnations and contaminated particulate matter, and screws supplied in a hot-dip galvanised state can be used, which are more resistant to general corrosion than electrolytic galvanisation. In this way, it is also possible to meet the regulatory requirements that envisage <NUM> years for a design life of the cask, which can be extended by a further <NUM> years in the event of scheduled maintenance intervention, e.g. for the replacement of components (gaskets, bolts, etc.) with incipient corrosion.

The closing screws <NUM> are recessed, in use, in a respective hole <NUM> formed in the lid <NUM> so that they do not project axially out of hole <NUM>. In particular, the head <NUM> of each closing screw <NUM> is housed in the portion <NUM> of the hole <NUM> and abuts, optionally with interposition of a washer, onto the bottom surface <NUM> of the portion <NUM>.

Advantageously, the closing screws <NUM> are tightened in use with a load higher than the minimum nominal load required to make contact between the flanges <NUM>, <NUM>, i.e. to obtain complete deformation of the gaskets <NUM> and bring the sealing surfaces <NUM>, <NUM> in contact with each other (so-called metal-to-metal contact as indicated by the manufacturer). This margin on the tightening load has two indirect beneficial effects on the gaskets <NUM>.

Firstly, there is an increase in the friction force between the sealing surfaces <NUM>, <NUM> of the flanges <NUM>, <NUM>: in the event of a transverse shock, more energy is required for the relative sliding to occur between the flanges <NUM>, <NUM> and thus the relative "creeping" between the gaskets <NUM> and the respective sealing surfaces <NUM>, <NUM>.

Secondly, by increasing the tightening load, in the event of breakage of one or more closing screws <NUM> (again due to accidental falls of the cask <NUM>), the other remaining closing screws <NUM> more effectively compensate for the tightening "amount" that is lacking: experimental and analytical tests carried out on prototypes and FEM models of the cask <NUM> have demonstrated to maintain sealing performance even after the breakage of several contiguous closing screws (a situation simulating an accidental shock event).

The body <NUM> and the lid <NUM> are in contact by means of the respective conical coupling surfaces <NUM>, <NUM> and the respective sealing surfaces <NUM>, <NUM>, which tighten the gaskets <NUM> together.

On the other hand, the radially outer portions <NUM>, <NUM> of the flanges <NUM>, <NUM> remain axially spaced from each other by a gap <NUM> defined by the step <NUM>. The gap <NUM> allow the preservation of the integrity of the closing screws <NUM> (and thus of the performance of the gaskets <NUM> they tighten) in the event of a fire, because it keeps the differential thermal expansions and the resulting tension and deformation states under control.

Advantageously, the conical coupling surfaces <NUM>, <NUM> are coupled to each other with a play less than the play existing between each closing screw <NUM> and the respective through hole <NUM> formed in the lid <NUM>.

In this way, in the event of a transverse shock on the cask <NUM>, the energy of the impact is absorbed by the conical coupling between the coupling surfaces <NUM>, <NUM> preventing direct and impulsive contact between the lid <NUM> and the closing screws <NUM> and thus avoiding the potential shear failure of the closing screws <NUM> and the consequent localised loss of the tightening load on the gaskets <NUM>. In essence, the coupling surfaces <NUM>, <NUM> of the body <NUM> and of the lid <NUM> fulfil the function of preventing the transverse sliding of the body <NUM> with respect to the lid <NUM>, as well as the function of acting as a lead-in and centring while mounting the lid <NUM>; in addition, the coupling surfaces <NUM>, <NUM> increase the shielding of the cask <NUM> (with a zig-zag effect on radiations). The coupling surfaces <NUM>, <NUM> instead are not supposed to have a sealing function: in fact, the gaskets <NUM> of the primary sealing system <NUM> both work axially and are not affected by any transverse shock.

The cask <NUM> also comprises one or more auxiliary openings <NUM> formed passing-through in the body <NUM> and in the lid <NUM> for draining, venting and the internal pressure and leakage checks during operation; for example, auxiliary openings <NUM> are located in the middle of the lid <NUM> (<FIG> and <FIG>) and in the side wall <NUM> of the body <NUM> at the lower end <NUM> (<FIG>).

Each auxiliary opening <NUM> is provided with a double-gasket closing and sealing device <NUM>.

Each device <NUM> comprises a blind flange <NUM> housed in a seat <NUM> aligned with the auxiliary opening <NUM>; the blind flange <NUM> is fixed to the seat <NUM> by fixing screws <NUM> which engage respective threaded holes <NUM> formed on a bottom surface <NUM> of the seat <NUM> around the auxiliary opening <NUM>.

The device <NUM> also comprises a first auxiliary gasket <NUM> and a second auxiliary gasket <NUM> in series interposed between the blind flange <NUM> and the seat <NUM>.

The first auxiliary gasket <NUM> is defined by a metal sealing ring, for example an energized C-Ring, placed around the auxiliary opening <NUM> and interposed between a sealing surface <NUM> of the blind flange <NUM> and the bottom surface <NUM> of the seat <NUM>, facing each other; for example, the auxiliary gasket <NUM> is housed in an annular groove <NUM> formed on the sealing surface <NUM> of the blind flange <NUM> and projecting from the groove <NUM>.

The second auxiliary gasket <NUM> is defined by a conical thread cap <NUM>, specifically an NPT cap, which engages a corresponding conical threaded seat <NUM> formed in the auxiliary opening <NUM>; the cap <NUM> has a thread <NUM> provided with a covering layer of solid lubricant and anti-seize paste which is interposed between the thread <NUM> of the cap <NUM> and the conical threaded seat <NUM> and acts as a gas-tight sealing material.

The solid lubricant and anti-seize paste is in particular the same as the one used for the closing screws <NUM> and in general for all the threaded connections on the cask <NUM>.

Essentially, a product normally used in a lubricant and anti-seize function on threaded parts is used for a sealing function.

For example, the commercial product Molykote P-<NUM> (Dow Corning) was used, which is a composition of mineral oils and solid lubricants, containing in particular zirconium oxide, mineral oils, graphite, calcium hydroxide, with an operating temperature of over <NUM>. It is understood that other similar lubricant and anti-seize pastes can be used, even with different components.

The combination of the conical thread cap <NUM> with the solid lubricant and anti-seize paste applied to its thread <NUM> guarantees sealing performance at the same level as a metal C-Ring, as demonstrated in experimental tests.

Advantageously, in order to allow inspection in use of the so-called "control volume", i.e. the interspace defined between the auxiliary gaskets <NUM>, <NUM> in series, the blind flange <NUM> has an inspection opening <NUM> formed through the blind flange <NUM> and aligned with the auxiliary opening <NUM>; the inspection opening <NUM> is closed by an inspection cap <NUM> which is also a conical thread cap (NPT cap) having a thread <NUM> provided with a covering layer of solid lubricant and anti-seize paste, screwed in a respective conical threaded seat <NUM> formed in the inspection opening <NUM>; also in this case, the covering layer of solid lubricant and anti-seize paste is interposed between the thread <NUM> of the inspection cap <NUM> and the conical threaded seat <NUM> and acts as a gas-tight sealing material.

Optionally, a shielding pin <NUM> (having essentially the function of radiation containment) is placed inside the auxiliary opening <NUM>, further inwards the opening <NUM> of the inspection cap <NUM>.

Similarly, as shown in <FIG>, the control volume defined between the gaskets <NUM> of the primary sealing system <NUM> is also accessible for inspections through one or more inspection openings <NUM>, formed through the flange <NUM> of the lid <NUM>. In the example shown, there are two diametrically opposed inspection openings <NUM> on the lid <NUM>. Each inspection opening <NUM> extends through the lid <NUM> as far as the sealing surface <NUM> where it is placed between the two gaskets <NUM>. Each inspection opening <NUM> is also closed by an inspection cap <NUM> which is also a conical thread cap (NPT cap) having a thread <NUM> provided with a covering layer of solid lubricant and anti-seize paste, screwed in a respective conical threaded seat <NUM> formed in the inspection opening <NUM>; also in this case, the covering layer of solid lubricant and anti-seize paste is interposed between the thread <NUM> of the inspection cap <NUM> and the conical threaded seat <NUM> and acts as a gas-tight sealing material.

Preferably, a shielding pin <NUM> having radiation containment function is placed inside the inspection opening <NUM>, further inwards in the inspection opening <NUM> than the inspection cap <NUM>.

Advantageously, the fixing screws <NUM> of the blind flanges <NUM> are also hexagonal head screws, for example (but not necessarily) made of galvanised steel, and are recessed in the respective blind flange <NUM>. In this case, it is not possible to completely eliminate the formation of stagnations in the same way as for the closing screws <NUM> of the lid <NUM>; however, the blind flanges <NUM> are normally mounted at least once drainage has been completed (and often after a drying phase), so the problem is less significant; in addition, the enlarged seat of the fixing screws <NUM> required to be able to access their hexagonal head with the socket spanner favours the decontamination of the surfaces enclosed therein.

In the variant shown in <FIG> and <FIG>, the double-gasket closing and sealing device <NUM> of one or more of the auxiliary openings <NUM> (for example, as shown in <FIG>, the auxiliary opening <NUM> located on the body <NUM> at the lower end <NUM>) is provided for connection to an external instrument, for example a manometer.

The device <NUM> still comprises a blind flange <NUM>, housed in a seat <NUM> aligned with the auxiliary opening <NUM>, and a first auxiliary gasket <NUM> and a second auxiliary gasket <NUM> in series interposed between the blind flange <NUM> and the seat <NUM>.

Also in this case, the blind flange <NUM> is fixed to the housing <NUM> by fixing screws <NUM> that engage respective threaded holes formed on the bottom surface <NUM> of the seat <NUM> around the auxiliary opening <NUM>.

The first auxiliary gasket <NUM> is still defined by a metal sealing ring, for example an energized C-Ring, placed around the auxiliary opening <NUM> and interposed between the blind flange <NUM> and the bottom surface <NUM> of the seat <NUM>; for example, the auxiliary gasket <NUM> is housed in an annular groove <NUM>, formed on a sealing surface <NUM> of the blind flange <NUM> facing the bottom surface <NUM>, and projects from the groove <NUM>.

In this case, the cap <NUM> described above is replaced by a connection element <NUM> comprising a quick coupling joint <NUM> and, if necessary, an adapter nipple <NUM>; the connection element <NUM> has a first threaded end <NUM> (for example, on the nipple <NUM> if present) engaging a corresponding conical threaded seat <NUM> formed in the auxiliary opening <NUM> by means of a thread <NUM> with conical thread, in particular with an NPT thread; and a second end <NUM> (in particular, on the joint <NUM>) provided with a quick coupling seat <NUM> shaped to receive an external instrument, for example a manometer. Appropriately, the quick coupling seat <NUM> is provided with metal inner sealing elements (cooperating in use with the instrument being coupled to the joint <NUM>). It is understood that joint <NUM> may be directly screwed in the conical threaded seat <NUM> with no need for the adapter nipple <NUM>: in other words, the connection element <NUM> may consist of the joint <NUM> alone, or, like in the example shown, of an assembly formed by the joint <NUM> and by the nipple <NUM>: in this case, the joint <NUM> is joined to the nipple <NUM>, for example, by means of a conical threaded connection <NUM>.

Also in this case, a shielding pin <NUM> (having essentially the function of radiation containment) is advantageously placed inside the auxiliary opening <NUM>, further inwards in the opening <NUM> of the connection element <NUM>.

Similarly to what has been described above, the thread <NUM> of the connection element <NUM> and, if present the nipple <NUM>, also the threaded connection <NUM>, are provided with covering layers of solid lubricant and anti-seize paste that also acts as a gas-tight sealing material.

Also in this case, the blind flange <NUM> has an inspection opening <NUM>, formed through the blind flange <NUM> and aligned with the auxiliary opening <NUM> and closed by a conical thread inspection cap <NUM> (NPT cap) having a thread provided with a covering layer of solid lubricant and anti-seize paste, screwed in a respective conical threaded seat formed in the inspection opening <NUM> with also the function of gas-tight sealing material. Clearly, the inspection cap <NUM> can take on different shapes and sizes: for example, while in the embodiment described above with reference to <FIG> the inspection cap <NUM> is a hexagonal head cap, in the variant shown in <FIG> the inspection cap <NUM> is a hexagonal recessed cap (i.e. having an inner hexagonal seat for being screwed/unscrewed).

Advantageously, various surfaces of the cask <NUM> are inclined with respect to the axis A so as to favour the drainage of the cask <NUM> after loading under water head; for example, as described above, the outflow surface <NUM> adjacent to the coupling surfaces <NUM>, <NUM>, and the outflow surfaces <NUM>, <NUM> of the beads <NUM>, <NUM> are inclined. In addition, the bottom wall <NUM> of the body <NUM> has an outflow surface <NUM> inclined downwards and towards the side wall <NUM>, so as to convey the liquids towards the auxiliary opening <NUM> placed at the bottom of the body <NUM>.

Optionally, in order to avoid the risk of stagnation and contamination, any gaps present on the cask <NUM>, such as the gap <NUM> between the flanges <NUM>, <NUM> and the volume determined by the play existing between the blind flanges <NUM> and the respective seats <NUM> on the body <NUM> and on the lid <NUM>, can be filled with a sealing filler material (without structural functions), e.g. with neoprene strips, expanded graphite, etc. As these areas are sufficiently shielded from the content of the cask <NUM>, it is not necessary for the sealing filler material to have special characteristics of resistance/integrity to ionising radiations.

Clearly, the choice of the materials with which to make the cask <NUM> and its various components must take into account the specific intended use. For example, all bolts are made of galvanised carbon steel (hot-dip galvanised or by electrolysis) in order to prevent the occurrence of galvanic corrosion if materials with different potential are used. If the storage environment were aggressive, the galvanisation might also suffer in the long run (especially for the elements exposed to the outside environment), and in such a case the bolts can be made of stainless steel.

The surfaces of the cask <NUM> can be painted as is usual in the industry. Preferably, the surfaces of the body <NUM> and of the lid <NUM> that are in mutual contact after closing and tightening the lid <NUM> are not painted. Thus, the sealing surface <NUM> of the body <NUM> and the sealing surface <NUM> of the lid <NUM> are only partially painted, i.e. only outside the contact area between the flanges <NUM>, <NUM>, while their respective portions facing the gap <NUM> are not painted. Similarly, for each blind flange <NUM>, the bottom surface <NUM> of the seat <NUM> and the corresponding sealing surface <NUM> of the blind flange <NUM>, in contact with each other, are not painted.

Claim 1:
A cask (<NUM>) for conditioning, storage and disposal of radioactive waste, in particular solid radioactive waste of medium activity, comprising: a main hollow body (<NUM>) extending along and about a longitudinal axis (A) and provided with an access opening (<NUM>); a lid (<NUM>) closing the opening (<NUM>) and fixed to the body (<NUM>) by closing screws (<NUM>) which tighten respective flanges (<NUM>, <NUM>) of the body (<NUM>) and the lid (<NUM>) against each other and are inserted in respective through holes (<NUM>) formed in the lid (<NUM>) and in respective threaded blind holes (<NUM>) formed in the body (<NUM>); and a primary sealing system (<NUM>) arranged between the body (<NUM>) and the lid (<NUM>) and comprising two gaskets (<NUM>) in series; wherein the body (<NUM>) and the lid (<NUM>) are provided with respective conical coupling surfaces (<NUM>, <NUM>) adjacent to said respective flanges (<NUM>, <NUM>) and in contact with each other and coupled to each other with a play less than the play existing between each closing screw (<NUM>) and the respective hole (<NUM>) formed in the lid (<NUM>); and in that said gaskets (<NUM>) in series of the primary sealing system (<NUM>) are axial gaskets acting parallel to the axis (A) between respective sealing surfaces (<NUM>, <NUM>), parallel to one another and perpendicular to the axis (A), of said flanges (<NUM>, <NUM>) of the body (<NUM>) and the lid (<NUM>); said flanges (<NUM>, <NUM>) being in contact with each other by means of said respective sealing surfaces (<NUM>, <NUM>), and comprising respective radially outer portions (<NUM>, <NUM>) axially spaced apart from each other by a gap (<NUM>), said portions (<NUM>, <NUM>) being provided with said through holes (<NUM>) of the lid (<NUM>) and said threaded blind holes (<NUM>) of the body (<NUM>) which receive the closing screws (<NUM>).