Method for treating packaging for radioactive material against corrosion

Abstract

The invention relates to a method for treating at least one surface of packaging for transporting, warehousing and / or storing radioactive material against corrosion, the at least one surface of the packaging being a surface that is intended to accommodate at least one seal of the packaging. This method is implemented by means of an electrolytic device comprising an anode, a cathode and an electrolytic solution, the electrolytic solution comprising at least one metal M in cationic form, the method comprising the following consecutive steps (a) to (d): (a) bringing the surface of the packaging into contact with at least one applicator impregnated with the electrolytic solution, the packaging forming the cathode and the applicator forming the anode, the anode and the cathode being connected to a power supply; (b) applying a voltage delivered by the power supply across the cathode and the anode with a value U of between 5 V and 30 V; (c) keeping the voltage at this value U so as to reduce the metal M in cationic form, whereby a layer of the metal M is formed on the surface of the packaging in contact with the applicator; and (d) removing the applicator from the coated surface of the packaging, the electrolytic solution comprising a nickel sulphamate, a silver salt and / or a copper salt.

Description

[0001]DESCRIPTION Method for treating a radioactive material container against corrosion Technical field of the invention The invention relates to a method for treating a radioactive material container against corrosion. The invention relates more particularly to a method for treating at least one surface against corrosion of a radioactive material transport, storage and / or storage container. This surface advantageously corresponds to a surface intended to receive a seal fitted to said container. The invention also relates to a radioactive material transport, storage and / or storage container comprising at least one surface treated against corrosion by the above-mentioned corrosion treatment method. State of the art Among the known corrosion treatment methods in the field of radioactive material transport, storage and / or storage containers,we can cite the process of producing an anti-corrosion coating, typically nickel, at least at the level of the packaging cavity, that is to say on the internal surface of the packaging, or even on the internal and external surfaces of the packaging. To do this, the body of the packaging, comprising a base and a side wall extending from the base, is placed in a tank within which an electrolytic deposit of nickel is carried out, typically of the order of 300 µm. Such a process has many disadvantages, including those related to the handling of the packaging bodies in view of their large dimensions, to material costs since at least the internal surface, or even the internal and external surfaces, of the packaging are coated and to the associated processing times. However,such a process is somewhat oversized in the case where it is only desired to protect from corrosion the surfaces of the packaging which are intended to receive the sealing gasket(s), which correspond to the so-called "seal bearing" surfaces. In addition, it is necessary to carry out an additional step of machining the surfaces in order to obtain the required roughness. Thus, in order to treat only the surfaces corresponding to the seal bearings and, in doing so, to limit the material and implementation costs in connection with the ^ dimensional constraints, more targeted (localized) anti-corrosion treatment processes have been proposed. This includes in particular a treatment process consisting of depositing, by arc welding, a localized stainless steel coating on said seal bearing surfaces. However,such a process requires not only significant welding times but also additional machining steps. Document JP S5793895 U describes a nuclear reactor containment vessel provided with a flange joint whose joint surface is coated with a plating layer in order to prevent rust. This plating layer is produced by applying, to the surface to be coated, a sponge or a brush impregnated with a solution,the sponge and the surface forming the anode and the cathode respectively. This document does not, however, specify the composition of the solution or the operating conditions which are implemented to obtain the plating layer. The aim of the present invention is therefore to overcome the drawbacks of the methods of the prior art and to propose a method for treating a radioactive material container against corrosion which is characterized by the deposition of a protective coating which is localized at the surfaces of the container more particularly intended to be protected from corrosion such as the surfaces of the seals mentioned above. This method must also be more economical than those of the prior art, by allowing this protection against corrosion by means of a coating of reduced and constant thickness, without there being any need to resort to an additional rectification step, for example by machining,of said coating. Statement of the invention These and other aims are achieved, firstly, by a method for treating against corrosion at least one surface of a packaging for transporting, storing and / or storing radioactive material, said at least one surface of the packaging being a surface intended to receive at least one seal of the packaging. According to the invention, this method is implemented by means of an electrolytic device comprising an anode, a cathode and an electrolytic solution, the electrolytic solution comprising at least one metal M in cationic form, and comprises the following successive steps (a) to (d): (a) bringing at least one applicator impregnated with the electrolytic solution into contact with the surface of the packaging, the packaging forming the cathode and the applicator forming the anode, the anode and the cathode being connected to an electrical power supply,(b) applying an electrical voltage delivered by the power supply between the cathode and the anode at a value U of between 5 V and 30 V, (c) maintaining the electrical voltage at this value U so as to reduce the metal M to cationic form, whereby a layer of the metal M is formed on the surface of the packaging in contact with the applicator, and (d) removing the applicator from the coated surface of the packaging, the electrolytic solution comprising a nickel sulfamate, a silver salt and / or a copper salt. The method according to the invention makes it possible to produce an anti-corrosion coating formed by a metallic layer consisting of the metal M, this metal M being in this case Ni, Ag or Cu, or by a metallic alloy of two, or of these three, metals M. This anti-corrosion coating is deposited electrolytically on a localized surface of the packaging,it being specified that this localized surface corresponds to the surface of the packaging which is in contact with the applicator, the localized surface being electrically conductive. The anti-corrosion coating is formed by the electrolytic reduction of the metal M in cationic form in the electrolytic solution impregnating the applicator, it being specified that this electrolytic reduction occurs on the surface of the cathode constituted by the packaging. This anti-corrosion electrolytic coating, which has a substantially constant thickness, retains the initial roughness of the localized surface on which it has been applied and therefore does not need to be machined at the end of the process to give it the desired roughness. In addition to being substantially constant,the thickness of the coating is less than that of the anti-corrosion coatings produced by the methods of the prior art and thus makes it possible to accompany any deformations of the body of the packaging. This thickness is advantageously between 20 µm and 100 µm and, preferably, between 40 µm and 70 µm. It is specified that the expression "between … and …", which has just been cited and which is used in the present application, must be understood as defining not only the values ​​of the interval, but also the values ​​of the limits of this interval. It may be noted that the surface to be treated may represent only the first part of a total surface considered, the surface of this first part then necessarily being electrically conductive. On the other hand, the second part is then electrically insulated in order to avoid any deposit of metal on the latter. ^ As indicated above,step (a) of bringing the packaging into contact with at least one applicator impregnated with the electrolytic solution determines the surface of the packaging on which the anti-corrosion coating will be deposited electrolytically. As indicated previously, this surface of the packaging on which the anti-corrosion coating is deposited electrolytically corresponds at least to the surfaces of the packaging intended to receive the sealing gasket(s) of the packaging or, in other words, to the gasket bearing surfaces. In an advantageous embodiment, during step (b), the value U of the electrical voltage applied between the cathode and the anode is between 8 V and 15 V. In one embodiment of the method according to the invention, the surface of the packaging is a surface of revolution whose axis of revolution corresponds to the longitudinal axis of the packaging. Thus,this surface may be a cylindrical surface which is then parallel to this longitudinal axis of the packaging. This surface may also be in the form of a disc which is then perpendicular to this longitudinal axis of the packaging. In a first variant of the method according to the invention, during steps (a) to (c), the contact between the surface of the packaging and the applicator is achieved by a fixed positioning of the applicator on all or part of the surface of the packaging. In a second variant of the method according to the invention, during steps (a) to (c), the contact between the surface of the packaging and the applicator is achieved by a relative movement of the applicator with respect to the surface of the packaging. According to a particular embodiment, the speed of the relative movement of the applicator with respect to the surface of the packaging is between 1 m / min and 40 m / min and, advantageously,between 5 m / min and 30 m / min. This relative movement can be ensured either by a rotation of the packaging around its longitudinal axis, the applicator then being fixed, or by a rotation of the applicator around the longitudinal axis of the packaging, the packaging being fixed. This second variant of the method according to the invention has the advantage of implementing an applicator of reduced size compared to the surface of the packaging to be treated against corrosion. For example, the surface of the applicator in contact with the packaging can represent at most 50% and, advantageously, at most 30% of the surface of the packaging to be treated. A first advantage associated with this reduction in the size of the applicator is to facilitate the impregnation of the applicator by the electrolytic solution. A second advantage is to reduce the power of the generator providing the electrical supply and, in doing so,to ^ reduce the risks of an increase in temperature by Joule effect of the electrolytic solution. According to a particular embodiment, in particular when the surface of the packaging to be treated against corrosion is a cylindrical surface, the longitudinal dimension of the applicator is greater than or equal to the longitudinal dimension of this surface of the packaging to be treated. According to another particular embodiment, in particular when the surface of the packaging to be treated against corrosion is in the form of a disc, the radial dimension of the applicator is greater than or equal to the radial dimension of this surface of the packaging to be treated. Alternatively,the surface treatment can also be obtained by combining the rotation of the packaging with a movement of the applicator in a direction parallel or perpendicular to the axis of the packaging depending on whether the surface is cylindrical or disc-shaped. Whether the first variant or the second variant of the method according to the invention is considered, the applicator is kept in contact with the surface of the packaging to be treated against corrosion during each of steps (a) to (c). This contact is achieved by applying pressure from the applicator to the surface of the packaging to be treated. This pressure exerted by the applicator on the surface of the packaging is preferably constant so as to obtain an anti-corrosion coating of substantially constant thickness. According to a particular embodiment, during these steps (a) to (c), the pressure exerted by the applicator on the surface of the packaging is less than or equal to 20.10, -4MPa. Advantageously, this pressure exerted by the applicator on the surface of the packaging is between 10 -4 MPa and 15.10 -4MPa. The method according to the invention may use only one applicator. However, nothing prevents the use of two, three, or even more applicators from being considered, especially since the use of several applicators makes it possible to optimize the wettability of the surface to be treated and, more generally, to reduce the overall duration of the anti-corrosion treatment. Thus, according to an advantageous embodiment, the method according to the invention uses two applicators, these two applicators being diametrically opposed relative to the axis of the packaging. It is specified that throughout the present description, the term "applicator" used in the singular covers both the use of a single applicator and several applicators. ^ According to one embodiment, the applicator is made of a conductive material and, preferably, graphite or nickel.According to an advantageous embodiment, the applicator is pierced throughout and / or is provided with grooves. These perforations and / or grooves made in the applicator not only allow good impregnation of this applicator by the electrolytic solution but also facilitate the degassing of dihydrogen formed during the electrolytic reduction reaction which occurs on the surface of the packaging (cathode). As indicated previously, the electrolytic solution which impregnates the applicator comprises at least one metal M in cationic form, the metal M being chosen from Ni, Ag and Cu. The electrolytic solution comprises a nickel sulfamate, a silver salt and / or a copper salt. Thus, the method according to the invention makes it possible to produce an anti-corrosion coating formed by a metallic layer consisting of nickel, silver or metallic copper, by a metallic alloy of two of these metals or of these three metals.Such metals and metal alloys are well known to be corrosion resistant. In the case where the metal M in cationic form is a silver salt, this silver salt may be a silver cyanide. In the case where the metal M in cationic form is a copper salt, this copper salt may be a cupric sulfate or a cupric fluoborate. In a more particularly advantageous variant, the electrolytic solution comprises a nickel sulfamate.The use of an electrolytic solution comprising a nickel sulfamate makes it possible to obtain a protective coating that is particularly resistant to corrosion, which resists thermal shocks during operation of the container, in particular when the latter is suddenly immersed for underwater loading of nuclear fuels, and which does not crack under accidental transport conditions, in particular under the effect of ovalization of the cylindrical body of the container and, therefore, of the joint bearing surfaces. According to a particular embodiment, the temperature of the electrolytic solution impregnated in the applicator is between 15°C and 80°C. The method according to the invention therefore has the advantage of being able to be implemented at ambient temperature, i.e. at a temperature typically between 18°C ​​and 25°C.To reduce the overall duration of the anti-corrosion treatment, this temperature of the electrolytic solution impregnated in the applicator can be advantageously brought to a temperature between 30°C and 70°C and, preferably, between 50°C and 70°C. According to one embodiment, the current density (DI) per unit area (S) which is applied during step (c) and which is noted DI / S, is between 4 Ah / dm. 2 and 12 Ah / dm 2 . It is specified that S corresponds to the surface treated during step (c). Controlling the parameter that is the current density per unit area makes it possible to control the final thickness of the metal layer M forming the anti-corrosion coating. Advantageously, the current density per unit area applied during step (c) is between 6 Ah / dm 2 and 8 Ah / dm 2. According to one embodiment, the method according to the invention further comprises one or more of the following steps (i) to (iv), steps (i) to (iii) being implemented prior to step (a) and steps (iv) and (v) being implemented after step (d): (i) applying a masking to a surface of the packaging other than the surface to be treated, (ii) applying a cleaning solution to the surface of the packaging followed by rinsing with water, (iii) applying an activating solution to the surface of the packaging followed by rinsing with water, (iv) rinsing the coated surface of the packaging with water, and (v) removing the masking. The implementation of step (i) makes it possible to protect one or more surfaces of the packaging which are not intended to be treated by the method according to the invention.This step can also make it possible to protect a specific part of the surface to be treated and thus only make a deposit on the unprotected part of the surface. The implementation of one and / or the other of steps (ii) and (iii) makes it possible to optimize the subsequent adhesion of the layer of metal M constituting the anti-corrosion coating. In a particular embodiment, the cleaning solution of step (ii) comprises a sodium salt. This sodium salt is preferably chosen from sodium hydroxide and sodium carbonate. In a particular embodiment, the activation solution of step (iii) comprises an inorganic acid which is preferably sulfuric acid.In a particular embodiment, one and / or the other of steps (ii) and (iii) can be carried out electrolytically; the cleaning and / or activation solutions then constitute the electrolytic solutions of an electrolytic device in which the cathode is formed by the packaging and the anode by at least one applicator impregnated with one and / or the other of these solutions, by analogy with the corrosion treatment method described above. The method according to the invention makes it possible to treat at least one surface of a radioactive material transport, storage and / or storage container against corrosion, in particular the surface(s) intended to receive at least one seal. Such a radioactive material transport, storage and / or storage container typically comprises a packaging body, consisting of a bottom and a side wall extending from the bottom, as well as a system for closing this body.The surface of the packaging coated by the treatment method according to the invention corresponds at least to the receiving surface of at least one seal ensuring the seal between the body and the closing system in the closed position of the packaging.Brief description of the figures Other advantages, aims and particular characteristics of the present invention will emerge from the following non-limiting description of at least one particular embodiment of the method according to the invention, with reference to the appended drawings, in which: - Figure 1 is a schematic perspective view of a packaging for transporting, storing and / or storing radioactive material; - Figure 2 is a schematic sectional view of the body of the packaging shown in Figure 1; - Figure 3 is an enlargement of the upper part of the packaging body; and - Figure 4 is a front view of the upper end of the body of the packaging, in particular of the surface S2 identified in Figure 3 and provided with two anodes.Detailed description of a particular embodiment The method according to the invention is implemented on the radioactive material transport, storage and / or disposal container 10 shown schematically in Figure 1. The container 10 comprises a cylindrical body 12 as well as a closure system or lid 14. As illustrated in Figure 2, the body 12 of the container 10 comprises a bottom 16 and a side wall 18 extending from the bottom 16. The body 12 is centered around the longitudinal axis A and is of circular section. ^ The upper part 12' of the body 12, which corresponds to the part opposite the bottom 16, is intended to receive at least one seal mounted on the inner surface of the lid (not shown). This or these seals make it possible to ensure sealing between the body 12 and the closure system 14 in the closed position of the container 10.With reference to Figure 3, which corresponds to an enlargement of the upper part 12' of the body 12, it can be seen that this upper part 12' comprises the surfaces identified by the references S1, S2, S3, S4 and S5. The surfaces S1, S3 and S5 on the one hand, and S2 and S4 on the other hand, correspond to surfaces which are respectively longitudinal (cylindrical) and radial (disc-shaped) relative to the longitudinal axis A. If all of the surfaces S1 to S5 are treated by the anti-corrosion treatment method according to the invention, the description below will focus on the treatment of the surface S2 alone. The surface S2 has an annular shape and corresponds to the receiving surface of two seals (not shown) arranged on the lower surface of the cover 14 of the packaging 10 and making it possible to ensure sealing between the body 12 and the cover 14 in the closed position of the body 12 of the packaging 10.Typically, the surface S2 to be treated has a surface area of ​​approximately 5840 cm² and a radial dimension of the order of 10 cm. In a first step (i) prior to the anti-corrosion treatment of the surface S2, the other surfaces S1, S3, S4 and S5 are masked by applying a protective coating. Such a protective coating can be formed by an adhesive tape of the aluminum scotch type, by paint and / or by a peelable varnish. In Figure 3, these masked surfaces S1 and S3 to S5 are marked by a thicker line than that marking the surface S2. In a second step (ii), an electrolytic cleaning step is carried out on the surface S2. To do this, the surface S2 is brought into contact with two graphite applicators, or anodes, A1 and A2, each having a surface area of ​​228 cm² (19 cm x 12 cm), the contact surface between the applicators A1, A2 and the surface S2 therefore representing approximately 4% of the total surface area of ​​S2.These applicators A1 and A2 are impregnated with a cleaning solution comprising sodium hydroxide and the temperature of which is between 15°C and 40°C. The impregnation of the applicators A1, A2 is maintained during step (ii) by means of a continuous supply, by means of a hose, at a flow rate greater than 4 L / min of cleaning solution. These applicators A1 and A2 are arranged diametrically opposite as illustrated in FIG. 4. The body 12 is then rotated about its longitudinal axis A so as to have a relative displacement between the anodes A1, A2 and the surface S2 of approximately 15 m / min. An electrical voltage is then applied between the surface S2 and the anodes A1, A2 with a value between 8 V and 10 V. When the current density reaches a value of the order of 22 Ah, the electrical voltage is cut off, the anodes A1, A2 are removed and the rotation of the body 12 is interrupted.In a third step (iii), an electrolytic activation step is carried out on the surface S2 which was cleaned during step (ii). To do this, the surface S2 is brought into contact with two other applicators, or anodes, A1' and A2' specific for this step (iii), impregnated with an activation solution comprising sulfuric acid and whose temperature is between 15 °C and 40 °C. The impregnation of the applicators A1', A2' is maintained during step (iii) by means of a continuous supply, by means of a hose, at a flow rate greater than 3 L / min of activation solution. As in step (ii), in step (iii), the applicators A1' and A2' are arranged diametrically opposite each other (figure 4). An electrical voltage of the order of 8 V is then applied between the surface S2 and the anodes A1', A2'.The body 12 is then rotated about its longitudinal axis A so as to have a relative displacement between the anodes A1', A2' and the surface S2 of approximately 15 m / min. When the current density reaches a value of the order of 32 Ah, the electrical voltage is cut off, the anodes A1', A2' are removed and the rotation of the body 12 is interrupted. In a fourth step, the anti-corrosion treatment method according to the invention is implemented, making it possible to carry out a deposit of metallic nickel by electrolytic means on the surface S2 which was activated during step (iii). To do this, the surface S2 is brought into contact with two new applicators, or anodes, A1" and A2" impregnated with a solution comprising nickel sulfamate and having a temperature of between 50°C and 70°C.The impregnation of the applicators A1", A2" is maintained during this fourth step by means of a continuous supply, by means of a hose, at a flow rate greater than 10 L / min of nickel sulfamate solution. As in steps (ii) and (iii), in this fourth step, the applicators A1" and A2" are arranged diametrically opposite each other (figure 4). An electrical voltage of the order of 15 V and an amperage of approximately 200 A are then applied per anode between the surface S2 and the anodes A1", A2". The body 12 is then rotated about its longitudinal axis A so as to have a relative displacement between the anodes A1", A2" and the surface S2 of approximately 15 m / min. When the current density reaches a value of the order of 400 Ah, which corresponds to a current density value per unit area of ​​6.8 Ah / dm. 2, the electrical voltage is cut off, the anodes A1", A2" are removed and the rotation of the body 12 is interrupted. At the end of this fourth step, the surface S2 is completely coated with a layer of metallic nickel having a constant thickness of the order of 50 µm. In a fifth step, the maskings are removed from the untreated surfaces S1, S3, S4 and S5, in order to carry out the possible subsequent treatment of one or more of these surfaces. Each of the second, third and fourth steps can be carried out automatically.

Claims

^ CLAIMS 1. Method for treating against corrosion at least one surface of a radioactive material transport, storage and / or warehousing container (10) by means of an electrolytic device comprising an anode (A1", A2"), a cathode and an electrolytic solution, said at least one surface of the container being a surface intended to receive at least one seal of the container and the electrolytic solution comprising at least one metal M in cationic form, this method comprising the following successive steps (a) to (d): (a) bringing at least one applicator (A1", A2") impregnated with the electrolytic solution into contact with the surface of the container (10), the container (10) forming the cathode and the applicator (A1", A2") forming the anode, the anode and the cathode being connected to an electrical power supply,(b) applying an electrical voltage delivered by the power supply between the cathode and the anode at a value U of between 5 V and 30 V and, advantageously, between 8 V and 15 V, (c) maintaining the electrical voltage at this value U so as to reduce the metal M in cationic form, whereby a layer of the metal M, having a thickness advantageously between 20 µm and 100 µm and, preferably, between 40 µm and 70 µm, is formed on the surface of the package (10) in contact with the applicator (A1", A2"), and (d) removing the applicator (A1", A2") from the coated surface of the package (10), the electrolytic solution comprising a nickel sulfamate, a silver salt and / or a copper salt.

2. Method according to claim 1, wherein the surface of the package (10) is a surface of revolution, for example a cylindrical surface or a disc-shaped surface.

3. Method according to claim 2, wherein,during steps (a) to (c), the contact between the surface of the packaging (10) and the applicator (A1", A2") is achieved by a relative movement of the applicator (A1", A2") with respect to the surface of the packaging (10), the relative movement being ensured either by a rotation of the packaging (10) around its axis, ^ longitudinal, the applicator (A1", A2") being fixed, or by a rotation of the applicator (A1", A2") around the longitudinal axis of the packaging (10), the packaging (10) being fixed.

4. Method according to claim 3, wherein the speed of the relative movement of the applicator (A1", A2") with respect to the surface of the packaging (10) is between 1 m / min and 40 m / min and, advantageously, between 5 m / min and 30 m / min.

5. Method according to any one of claims 1 to 4, wherein, during steps (a) to (c), the pressure exerted by the applicator (A1", A2") on the surface of the packaging (10) is less than or equal to 20.10 -4MPa and, advantageously, between 10 -4 MPa and 15.10 -4MPa.

6. Method according to any one of claims 1 to 5, wherein the surface of the applicator (A1", A2") in contact with the packaging (10) represents at most 50% and, advantageously, at most 30% of the surface to be treated.

7. Method according to any one of claims 2 to 6, wherein the radial dimension of the applicator (A1", A2") is greater than or equal to the radial dimension of the surface to be treated.

8. Method according to any one of claims 2 to 6, wherein the longitudinal dimension of the applicator (A1", A2") is greater than or equal to the longitudinal dimension of the surface to be treated.

9. Method according to any one of claims 1 to 8, wherein the silver salt is a silver cyanide.

10. A method according to any one of claims 1 to 9, wherein the copper salt is a cupric sulfate or a cupric fluoborate. 11.Method according to any one of claims 1 to 10, in which the applicator (A1", A2") is made of a conductive material, preferably graphite or nickel and is advantageously pierced throughout and / or is provided with grooves. ^ 12. Method according to any one of claims 1 to 11, in which two applicators (A1", A2") diametrically opposed with respect to the axis (A) of the packaging (10) are implemented.

13. Method according to any one of claims 1 to 12, in which the temperature of the electrolytic solution impregnated in the applicator (A1", A2") is between 15 °C and 80 °C, advantageously between 30 °C and 70 °C and, preferably, between 50 °C and 70 °C.

14. Method according to any one of claims 1 to 13, in which the current density applied during step (c) is between 4 Ah / dm 2 and 12 Ah / dm 2 , and, advantageously, between 6 Ah / dm 2 and 8 Ah / dm 2.

15. A method according to any one of claims 1 to 14, further comprising one or more of the following steps (i) to (v), wherein steps (i) to (iii) are performed prior to step (a) and steps (iv) and (v) are performed after step (d): (i) applying a masking to a surface of the package (10) other than the surface to be treated, (ii) applying a cleaning solution to the surface of the package (10) followed by rinsing with water, (iii) applying an activating solution to the surface of the package (10) followed by rinsing with water, (iv) rinsing the coated surface of the package (10) with water, and (v) removing the masking. 16.Method according to any one of claims 1 to 15, in which, the packaging (10) comprising a body (12), this body (12) being formed by a bottom (16) and a side wall (18) extending from the bottom (16), and a closure system (14) of the body (12), the coated surface of the packaging (10) corresponds at least to the receiving surface of at least one seal ensuring the seal between the body (12) and the closure system (14) in the closed position of the packaging (10).

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