Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F5/00—Transportable or portable shielded containers
  • G21F5/06—Details of, or accessories to, the containers
  • G21F5/12—Closures for containers; Sealing arrangements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D19/00—Casting in, on, or around objects which form part of the product
  • B22D19/04—Casting in, on, or around objects which form part of the product for joining parts

Definitions

• the present invention relates to a container for radioactive materials such as waste or exothermic nuclear materials, the container essentially consisting of a hollow main body inside which are capable of being housed the radioactive materials, as well as a cover intended to close off the hollow main body.
• the invention also relates to a method for closing such a container.
• the invention finds a very particular application in the fields of treatment and conditioning of nuclear waste.
• Containers for radioactive materials are first known, the hollow main body and the cover of which are assembled by welding. If this technique used remains generally satisfactory for containers made of ordinary steels or stainless steels, it is however not suitable for containers made of cast iron, this material being however often retained because of its possibility of being obtained by recycling of very slightly contaminated metallic elements, coming from the dismantling of nuclear installations.
• welds of small thicknesses namely not exceeding 5 to 6 mm, can be envisaged on cast iron.
• the conditioning constraints of radioactive materials impose a weld which extends over the full thickness of the container, which is usually between approximately 30 and 130 mm.
• the welds obtained on thicknesses such as those mentioned above are the seat of significant residual stresses, which can be detrimental to the durability of the container. .
• the thermal stress relieving treatments carried out during the implementation of methods for conditioning nuclear waste would be difficult to carry out, and not entirely effective on large wall thicknesses of the container.
• a cast iron container comprising a cover fixed by sealing on the hollow main body, by projection of molten lead in a groove formed by the cover and the body main hollow of this container.
• the cast lead solidifies in the groove provided for this purpose, and forms a fixing element securing the two main components of the container. Note that the joining of these elements comes essentially from the particular geometry of the groove, having at the level of the hollow main body a lateral surface with two portions inclined relative to the vertical at acute and opposite angles, so as to create an effect of wedge preventing the cover from detaching from the hollow main body.
• the lead seal obtained is in no way suitable for withstanding high temperatures, and therefore cannot authorize the storage of exothermic nuclear material.
• the lead melting temperature being only 327 ° C, this value then acts as a limit not to be exceeded to maintain mechanical retention between the two main elements constituting the container, this value even being able to be reduced by because of the sharp drop in the mechanical characteristics of lead beyond a certain temperature.
• the invention therefore aims to provide a container for radioactive materials comprising a hollow main body and a cover made of at least one first metallic material, the container at least partially overcoming the drawbacks mentioned above relating to the embodiments of the invention. prior art.
• the object of the invention is to present a container whose mechanical connection and sealing between the cover and the hollow main body are considerably improved compared to the solutions already proposed.
• the object of the invention is to propose a method for closing such a container.
• the invention firstly relates to a container for radioactive materials comprising a hollow main body and a cover made of at least one first metallic material, the cover being capable of being fixed to the hollow main body by means of sealing means made of a second metallic material cast in a groove defined by the lid and the hollow main body of the container.
• the cover and the hollow main body are secured to the sealing means by means of a connection zone, formed by chemical reaction between the first and second metallic materials.
• the essential characteristic of the invention according to which the second metallic material poured into the groove is capable of reacting chemically with each first metallic material allows the formation of a bonding zone made up of intermetallic compounds ensuring a true tight metallurgical bond between on the one hand the sealing means, and on the other hand the cover and the hollow main body of the container.
• the reliability of maintaining the lid in a sealed manner on the hollow main body of the container is therefore greatly increased, in particular compared to the solution described in document FR-A-2 733 966.
• the sealing means provided in this art previous take the form of lead poured into a cast iron groove, the latter having a specific geometry ensuring the maintenance of the cover on the hollow main body, when the lead is solidified in the groove.
• no chemical reaction occurs between lead and cast iron due to the nonexistence of iron-lead intermetallic compounds, this property thus prohibiting the presence of this type of compound at the interface between sealing means and the groove.
• each first metallic material is of the cast iron or steel type.
• the second metallic material can be a cast iron, zinc or one of its alloys, steel, or even aluminum or one of its alloys.
• the bonding zone can then be made of alloys of the iron-carbon, iron-zinc or iron-aluminum type, these materials being capable of ensuring perfect mechanical resistance between the sealing means and the two main container components.
• the metallic materials indicated above, capable of being used to produce the sealing means advantageously have a higher melting temperature than that of lead used in the prior art, and are therefore able to bear the presence of exothermic radioactive materials inside the container.
• the value of this temperature nevertheless advantageously makes it possible to envisage a reopening of the relatively easy cover, using conventional means capable of causing the sealing means to merge.
• connection zone has an average thickness of between approximately 10 ⁇ m and 5 mm, so that the mechanical connection generated between the cover and the hollow main body of the container is durably resistant and waterproof.
• the cover has an external lateral surface partially defining the groove and comprising two adjacent portions inclined respectively by an angle ⁇ and by an angle ⁇ relative to a direction parallel to a main longitudinal axis of the container, the angles ⁇ and ⁇ being acute and opposite in order to obtain a wedge effect.
• the invention also relates to a method of closing a container for radioactive materials comprising a hollow main body and a cover made of at least one first metallic material, the method comprising a step of placing place the cover on the body main hollow of the container so as to form a groove between these two elements, followed by a step of producing sealing means ensuring the fixing of the cover to the hollow main body of the container by pouring a second metallic material into the groove.
• the second metallic material is chosen so that it is capable of reacting chemically with each first metallic material, so as to form a bonding zone between on the one hand the sealing means, and on the other hand the lid and the hollow main body of the container.
• the step of fitting the cover is followed by a step of preheating the first material constituting the groove, this last step can also be preceded by a preparation of the surfaces of the groove.
• the step of producing the sealing means is preceded by a step of excessively casting the second metallic material into the groove for a determined period, so as to cause heating of the first metallic material. constituting the groove, as well as washing the surfaces of this groove.
• the step of producing the sealing means by casting the second metallic material in the groove is followed by a step of heating this second material resting in the groove, in order to promote the chemical reaction between the first and second metallic materials.
• Figure 1 shows a partial schematic sectional view of an upper portion of a container for radioactive materials, according to a preferred embodiment of the invention, and before the sealing means have been put in place
• Figure 2 shows a partial schematic sectional view of an upper portion of the container shown in Figure 1, after solidification of the sealing means in the groove
• Figure 3 shows a schematic perspective view of a particular arrangement, for performing the step of making the sealing means for the method of closing a container according to the invention.
• FIG. 1 there is shown partially and schematically a container 1 for radioactive materials, according to a preferred embodiment of the present invention.
• the container 1 comprises a hollow main body 2, defining a space 4 inside which can be housed the radioactive materials, such as exothermic nuclear waste.
• the container 1 has a cover 6 capable of being fitted into the hollow main body 2, so as to obtain a space 4 completely closed.
• the space 4, preferably of circular section, is delimited on the one hand with the aid of a lateral surface 8 and a bottom (not shown) formed by the hollow main body 2, and on the other hand at l using an upper surface 10 formed by the cover 6, the latter as well as the hollow main body 2 being arranged coaxially.
• the hollow main body 2 and the cover 6 respectively have annular contact surfaces 12 and 14, allowing the stop in translation of the cover 6 relative to the hollow main body 2, when the interlocking of these two elements 2 and 6.
• the contact surfaces 12 and 14 are preferably designed so that the cover 6 can be housed in the hollow main body 2 without protruding outside of it, and that their respective upper surfaces 13 and 15 lie substantially in the same plane perpendicular to a longitudinal main axis (not shown in these figures) of the container 1.
• the clearance 16 can be of the order of 0.5 mm.
• the container 1 in which the container 1 is shown while the cover 6 has not yet been fixed on the hollow main body 2, the latter has an inner lateral surface 20 in its upper portion, while that the cover 6 has an outer side surface 22.
• the adjacent and continuous side surfaces 20 and 22 form a groove 24 preferably extending all around the axis main longitudinal section of the container 1 along a variable horizontal section, this groove 24 being open to the outside of this container 1. It is specified that the groove 24 could naturally extend only partially around the main longitudinal axis of the container 1, for example to form portions of angularly spaced grooves, without departing from the scope of the invention.
• the groove 24 can also be produced so as to have a constant horizontal section, the shape of this groove being easily modular, by simple adaptation of the internal lateral surface 20 and the external lateral surface 22.
• the groove 24 thus obtained makes it possible to offer a space in which sealing means 26
• the cover 6 and the hollow main body 2 on the one hand, and the sealing means 26 on the other part are separated by a connecting zone 28, having a shape substantially identical to that of the wall of the groove 24 initially provided, over a thickness 29 which can range from 10 ⁇ m to 5 mm, and preferably being of the order of 2 mm.
• connection zone 28 located substantially at the initial location of the external lateral surface 22 and the internal lateral surface 20, results from a chemical reaction produced between the cover 6 and the hollow main body 2 on the one hand, and the sealing means 26 on the other hand, during the casting of the sealing means 26 in the groove 24.
• the connection zone 28 provides a rigid mechanical connection between the sealing means 26 and the two main elements 2 and 6 of the container 1, this specific feature of the invention ensuring perfect sealing of the container.
• the hollow main body 2 and the cover 6 are made from at least one first metallic material, and preferably from the same material such as steel or cast iron.
• the sealing means 26 are made of a second metallic material, such as cast iron, zinc or one of its alloys, steel, aluminum or one of its alloys, or still any other metallic material capable of exhibiting reactivity with the first metallic material retained, in order to chemically react with the latter and to constitute a bonding zone 28 comprising intermetallic compounds.
• the cover 6 and the hollow main body 2 are made of steel and the sealing means 26 are made of cast iron, these two materials are capable of reacting with each other when the cast iron is still liquid, so as to form a bonding zone 28 composed of an iron-carbon alloy, obtained by diffusion of the carbon from the cast iron to the steel.
• the bonding zone 28 has a carbon gradient in a direction going from the sealing means 26 towards the cover 6 or the hollow main body 2 of the container 1, and the structure of this connection zone 28 evolves from a mixture of ferrite and perlite to a cast iron, passing through a structure of eutectoid steel then hyper-eutectoid .
• connection zones 28 obtained are respectively composed of an iron-zinc alloy and an iron-alloy aluminum, ensuring rigid mechanical maintenance between the sealing means 26 and the two main elements 2 and 6 of the container 1.
• connection zone 28 had a structure similar to that which can be observed in the case of galvanizing operations carried out by quenching steel elements in liquid zinc.
• first and second materials are made of steel, these then being chosen so that carbon diffusion is possible when the sealing means 26 are in the liquid state, in order to obtain a connection zone 28 of iron-carbon alloy having a carbon gradient in a direction going from the sealing means 26 towards the cover 6 or the hollow main body 2 of the container 1.
• the external lateral surface 22 of the cover 6 may comprise two adjacent portions 30 and 32 inclined respectively by an angle ⁇ and by an angle ⁇ relative to a direction 34 parallel to the main longitudinal axis of the container 1, the angles ⁇ and ⁇ being acute and opposite in order to obtain a wedge effect when it is desired to extract the cover 6 from the hollow main body 2.
• the upper portion 32 is inclined so as to approach the main longitudinal axis away from the upper portion of the container 1, while the lower portion 30 is inclined so as to approach the main longitudinal axis in s' moving towards a lower portion of the container 1.
• the inner lateral surface 20 of the hollow main body 2 can also include a portion 36 inclined in the same way as the upper portion 32 of the outer lateral surface 22, namely so as to approach the main axis. longitudinal away from the upper portion of the container 1, this portion 36 preferably being opposite the upper portion 32 of the outer lateral surface 22.
• the sealing means 26 take place in the groove 24, the part of these sealing means 26 located between the portions 32 and 36 initially provided, takes substantially the form of a cap providing additional mechanical retention of the cover 6 on the hollow main body 2.
• the shape of the groove 24 can be designed in any other way aimed at providing a geometry ensuring maintenance of the cover 6 on the hollow main body 2, when the sealing means 26 are solidified inside this initially planned groove 24, without departing from the scope of the invention.
• the groove 24 has a variable width, which can for example extend between 10 and 20 mm, and being of the order of 15 mm at the portions 32 and 36 opposite.
• the invention also relates to a container closure method, such as that which has just been described above.
• the first metallic material chosen to make the cover 6 and the hollow main body 2 is steel, for example of the E24 type, while that the second cast metallic material used to form the sealing means 26 is a cast iron, for example of the EN-GJS-400-15 type.
• the first step in this process consists in placing the cover 6 on the hollow main body 2 of the container 1, so as to form the groove 24, as can be seen in FIG. 1.
• the surfaces 20 and 22 can be prepared using a mechanical technique such as sandblasting, a chemical technique such as degreasing or pickling, an electrochemical technique or a deposit of a layer of metallic material such as zinc or nickel.
• the surfaces 20 and 22 of the groove 24 can be nickel-plated in order to avoid oxidation of these surfaces during their rise in temperature and in the presence of air.
• the possible techniques for depositing the layer of metallic material are taken from the conventional metallic deposition techniques, such as that of galvanization for the deposition of zinc.
• the step of preparing the surfaces 20 and 22 of the groove 24 can consist of the combination of several of the techniques mentioned above.
• these surfaces 20 and 22 of the groove 24 can then undergo a step of preheating at low temperature to avoid their oxidation, for example of the order of 400 ° C., using collars electric heaters or any other means ensuring such a function. Note that this operation can be carried out under neutral gas to completely avoid the harmful effects that an oxidation of the surfaces 20 and 22 of the groove 24 could cause. Then, the cast iron is poured into the groove 24, so as to form the sealing means 26 shown in FIG. 2.
• means for casting the iron 40 assembled on the cover 6 of the container 1, comprise a container 42 in which the iron is located in the liquid state.
• the container 42 is pivotally mounted on a support 44 secured to the end of an arm 46, the latter being able to pivot around the main longitudinal axis 38 of the container 1.
• the liquid cast iron resting in the container is capable of being poured into an orifice taking the form of a funnel 48, also mounted on the arm 46 of the means 40.
• the funnel 48 then communicates with a discharge duct 50, of which the end 52 is oriented close to and facing the groove 24.
• the funnel 48 is moreover capable of pivoting along an axis parallel to the axis of rotation between the container 42 and the support 44, this specificity being provided to ensure a clean discharge of the liquid iron into the funnel 48, regardless of the quantity of iron present in the container 42.
• the rotations of the elements 42 and 48 relative to the support 44 can be performed manually, using handles 54 and 56 respectively.
• the end 52 of the iron discharge duct 50 can describe a circular movement allowing it to be constantly facing the bottom of the groove 24, this characteristic specific then ensuring the possibility of taking advantage of a uniform distribution of the cast iron inside this groove 24, during the implementation of the casting operation.
• the pig iron is then poured into the groove 24, for example at a temperature of around 1470 ° C.
• the casting of the cast iron is carried out by putting the arm 46 of the means 40 in rotation about the main longitudinal axis 38, either manually or automatically.
• the cast iron can be poured in excess and continuously, in order to heat and wash the surfaces 20 and 22 of the groove 24, previously nickel-plated.
• a system for recovering excess cast iron can then consist of means for discharging the cast iron located at the bottom of the groove 24, or alternatively in means arranged on the surface for recovering the cast iron overflowing from this groove.
• the excess casting period can in particular be determined as a function of the optimum temperature to be reached for the surfaces 20 and 22 of the groove 24, therefore taking into account various parameters such as the surface area of these surfaces 20 and 22, the flow rate iron, iron temperature, etc. Furthermore, it is noted that this period may also depend on the thickness of the metal deposit previously made on the surfaces 20 and 22 of the groove 2.
• the filling time is approximately 40 seconds and the quantity of excess cast iron for washing and heating is of the order of 250 kg, or a washing rate of 0.06 kg / s. cm 2 .
• a final step consists in heating the cast iron so that it remains liquid in the groove 24.
• This step has main objective of promoting the diffusion of carbon from the melting of the sealing means 26, to the steel of the hollow main body 2 and of the cover 6 of the container 1. The diffusion of carbon then makes it possible to obtain a connection zone 28 in iron-carbon alloy, ensuring a mechanical connection and sealed, directly between the sealing means 26 on the one hand, and the hollow main body 2 and the cover 6 on the other.
• This step of heating the cast iron in the groove 24 can be carried out using conventional heating means such as electric heating collars (not shown), at a temperature of the order of 500 ° C. for approximately 2 hours. . It is specified that the heating time can be adapted so that the chemical reaction between the first and second metallic materials is completed, or so that the bonding zone 28 is large enough to generate a perfect tight mechanical bond. between the cover 6 and the hollow main body 2 of the container 1.
• connection zone 28 obtained following the implementation of such a method, has a microstructure evolving over a thickness 29 of approximately 2 mm, from a mixture from ferrite and perlite to a cast iron, passing through a eutectoid then hyper-eutectoid steel structure.
• the bonding zone 28 had a breaking strength of approximately 276 MPa, for an elastic limit of 146 MPa at 0.2%, and an elongation at break of the '' around 33.1%.
• the surfaces 20 and 22 of the groove 24 do not undergo preparation by metallic deposition such as nickel, but are pickled so as to obtain surfaces 20 and 22 capable of reacting easily with the cast zinc.
• connection zone 28 is composed of an iron-zinc alloy, substantially identical to that obtained during a galvanization carried out by quenching steel parts in liquid zinc.
• the use of zinc or one of its alloys as second metallic material is advantageous in the sense that the reopening of the cover 6 can easily be envisaged by melting sealing means 26, due to the low melting temperature of this type of material.
• the steps are similar to those described previously in the first two preferred embodiments, with the difference that the casting step is preferably carried out under protection of a neutral gas.
• the reopening of the cover 6 sealed on the hollow main body 2 of the container 1 can easily be carried out by fusion of the sealing means 26.
• This fusion is preferably carried out using a torch heating. , laser, induction or resistors.

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• 2002
  • 2002-10-01 FR FR0212115A patent/FR2845196B1/fr not_active Expired - Fee Related
• 2003
  • 2003-09-29 JP JP2004540859A patent/JP2006501457A/ja not_active Ceased
  • 2003-09-29 EP EP03772388A patent/EP1547097A1/de not_active Withdrawn
  • 2003-09-29 US US10/529,616 patent/US7321128B2/en not_active Expired - Fee Related
  • 2003-09-29 WO PCT/FR2003/002852 patent/WO2004032152A1/fr not_active Application Discontinuation

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