EP1624466A1 - Process for decontamination of objects made from lead - Google Patents

Abstract

The procedure consists of placing the lead or lead alloy objects, such as nuclear reactor screen blocks, in contact with an alkaline aqueous solution, rinsing with water or an aqueous rinsing solution, followed by contact with an acid aqueous solution and rinsing again. The alkaline solution is of soda or potassium, preferably in a 30 per cent concentration and at a temperature of 60 degrees C, in which the objects are immersed for 10 to 80 minutes as it is agitated. The acid solution is of nitric or acetic acid of similar concentration, at ambient temperature, in which the objects are immersed for preferably 30 minutes. The final rinsing stage is followed by drying.

Description

The invention relates to a method for decontaminating, that is to say removing contaminants, lead objects.

More specifically, the invention relates to a method for decontaminating lead objects contaminated with radioactive contaminants.

The method of the invention is particularly applicable to the decontamination of lead bricks, optionally coated, for example, possibly painted, which are contaminated with radioactive elements.

The technical field of the invention may, in general, be defined as that of the decontamination of metals such as lead, and in particular that of the decontamination of metal surfaces such as lead surfaces.

Lead or lead alloys in the form of bricks, sheets, plates or others is widely used as a protective material, screen material in nuclear facilities, such as nuclear power plants, radioactive waste reprocessing plants, nuclear fuel fabrication plants and laboratories where radioactive material is used.

For example, bricks, sheets or sheets of lead or lead alloys may be used for raising walls or protective partitions around radioactive areas.

When objects made of lead or lead alloys are contaminated by radioactivity, they can then either be stored or treated to decontaminate them and eliminate the radioactive elements that are found especially on the surface of these objects.

The storage of lead contributes significantly to increasing the volume of radioactive waste and requires numerous and complex preliminary operations.

Treatment to remove radioactive contamination from lead or lead alloy objects may consist of melting the objects in melting furnaces for reuse. This type of treatment is not usable in the case of objects, such as bricks, provided with a coating, for example in the case of bricks provided with one or more layers of paint, and / or in the case of bricks contaminated by alpha emitters such as uranium, curium, americium, and plutonium.

Decontamination can be achieved by mechanical treatment, such as planing or brushing; this type of treatment has been shown to result in incrustation rather than elimination of contamination. In addition, this mechanical treatment must generally be followed by a step of melting the lead object free of its surface contamination because the object can not be reused as is.

Contamination can also be removed by a wet process, using a decontamination liquid. Such methods are described for example in GB-A-2 284 702, US-A-5 591 270, US-A-5 678 232, US-A-5 340 505, the document GB-A-1 229 395, EP-A-0 247 933, GB-A-1 458 239, and US-A-5 093 072.

These different processes make it possible to decontaminate lead objects by etching the oxide layer on the lead surface. They do not make it possible to decontaminate objects provided with coatings, for example layers of paint. In addition, these processes use, at high temperature, namely generally between 85 ° C and 125 ° C, inorganic and organic acids and complex oxidizing agents, difficult to reprocess afterwards. The kinetics of the decontamination is very slow and the lead precipitation reaction in solution envisaged in these processes generates gases during the reaction.

There is therefore a need for a method of decontaminating lead or lead alloy objects that allows the effective and total removal of contaminants, regardless of the nature, form, number and quantity thereof.

In particular, there is a need for a method of decontaminating objects made of lead or lead alloys which ensures the elimination of radioactive contaminants, whatever they may be, and in particular alpha emitters.

In addition, there is a need for a method for decontaminating lead or lead alloy articles that allows the decontamination of lead or lead alloy objects regardless of the surface state thereof and which allows and in particular the decontamination of coated objects having one or more layers of different nature and / or thickness, over which, in or between which there may be different contaminants.

Finally, there is a need for a process which allows the decontamination of lead or lead alloy articles and their immediate reuse at the end of the process without the need for destruction, re-shaping of the object, for example during a merge step.

This decontamination process must also be simple, fast, reliable, safe and have a limited number of simple steps.

The object of the present invention is to provide a method of decontaminating a lead object or a lead alloy that meets the needs listed above, among others, and meets the requirements listed above.

The object of the present invention is also to provide a method for decontaminating an object made of lead or lead alloy which does not have the disadvantages, defects, limitations and disadvantages of the processes of the prior art and which solves the problems of the processes of the prior art, in particular liquid methods.

• a) on met en contact l'objet avec une solution aqueuse basique ;
• a1) on met en contact l'objet avec de l'eau ou une solution de rinçage aqueuse ;
• b) on met en contact l'objet avec une solution aqueuse acide ;
• b1) on met en contact l'objet avec de l'eau ou une solution de rinçage aqueuse.

This and other objects are achieved in accordance with the present invention by a method of decontaminating an object made of lead or lead alloy, wherein the following steps are carried out:

• a) the object is brought into contact with a basic aqueous solution;
• a1) the object is brought into contact with water or an aqueous rinsing solution;
• b) the object is brought into contact with an acidic aqueous solution;
• b1) the object is brought into contact with water or an aqueous rinsing solution.

The treated lead or lead alloy articles may be provided with a coating comprising one or more layers.

This or these layers can be in particular layers of paint.

When the coating comprises several layers, the layers may differ in composition and / or thickness and / or the nature of the contaminant (s) on and / or in each of the layers.

The process according to the invention is advantageously applied to the case where the contaminant (s) are radioactive elements.

The method according to the invention comprises a specific sequence of specific steps, using specific reagents which is neither described nor suggested in the prior art, as represented in particular by the documents mentioned above.

Surprisingly, and because of this series of specific steps, the process according to the invention for the decontamination of lead or lead alloys solves the problems of the processes of the prior art, in particular lead decontamination processes by wet way of the prior art. It meets all the needs and requirements listed above for decontamination processes, and it does not have the drawbacks, limitations, defects and disadvantages of lead decontamination processes of the prior art, in particular decontamination processes. wet method of the prior art.

The process according to the invention is a simple, reliable, inexpensive, rapid process with a limited number of steps using readily available reagents. Similarly, the method according to the invention can be implemented with a simple material, inexpensive readily available. The decontamination, the removal of contaminants obtained with the process according to the invention is very effective, whatever the substrate, the lead or lead alloy object on which it is used and in particular whatever the form, the surface state of it. In particular, the process according to the invention gives excellent results on the objects provided with a coating, whatever the nature of the latter, and the nature and / or the composition of the layers which constitute it. The method according to the invention allows the very effective removal of contaminants of any kind and in particular of all radioactive contaminants. The effluents generated by the The method according to the invention can be regenerated, which limits the volume of the effluents, and they can be easily treated at the end of the process by simple methods.

The surprising advantages and effects of the process of the invention result from the specific steps of the process, from their succession in the order indicated, and from the reagents used in each step.

The solution of step a) is a basic solution which is generally chosen from aqueous sodium hydroxide solutions and aqueous potassium hydroxide solutions.

The basic solution, for example the aqueous sodium hydroxide solution of step a), generally has a mass concentration of 0.5 to 90%, preferably 30%.

The contacting of the object with the basic solution, for example the aqueous sodium hydroxide solution, is generally carried out at a temperature of 25 to 90.degree. C., preferably this contacting is carried out hot, namely at a temperature of generally from 40 to 90 ° C, for example 60 ° C.

It has indeed been found that the effectiveness of the treatment with the basic solution, for example with the aqueous solution of sodium hydroxide, was better when operated under hot conditions.

The duration of bringing the object into contact with the basic solution, for example the aqueous sodium hydroxide solution, depends on the expected result. If it is a degreasing of uncoated lead parts, the duration of the contacting of the object with the solution will be less important than in the case of a coating stripping. In this case, the duration of the contacting will correspond to the time required for stripping. This duration is generally between 10 min and 1:20.

The contacting is generally carried out by immersing the object to be decontaminated in a bath of the basic solution, for example aqueous sodium hydroxide solution, preferably stirred.

At the end of step a), the treated objects are rinsed with water or an aqueous solution (step a1). This rinsing makes it possible to wash the surface of the objects so as not to pollute the acid solution of step b) with the solution of step a). This rinse usually lasts 5 to 15 minutes. This rinsing step is then followed by step b).

The solution used in step b) is an acidic aqueous solution. For example, an aqueous solution of nitric acid or an aqueous solution of acetic acid can be used.

Nitric acid is preferred because nitric acid is more effective at solubilizing contaminants, particularly radioelements. Indeed, in addition to its "acid" power, nitric acid has significant oxidizing power in contrast to acetic acid. This oxidizing power makes it possible to oxidize contaminants such as radioelements and to form compounds with high oxidation levels. However, it is in particular known that the more a radioelement is oxidized, the more soluble it is.

The acid solution of step b) in the case where it is a nitric acid solution generally has a mass concentration of 0.5% to 90%, preferably 30%.

The acid solution of step b) in the case where it is an acetic acid solution generally has a mass concentration of 0.5% to 90%, preferably 30%.

The contacting of the object resulting from the rinsing step a1) after step a) with the acidic solution, for example nitric acid or acetic acid, is generally carried out at ambient temperature, namely from 15.degree. at 30 ° C, preferably 20 to 25 ° C. Indeed, during step b), heating is not necessary for the implementation of the method.

The effectiveness of the decontamination performed in this step is very high at room temperature, which avoids the need for heating and results in energy savings.

The duration of the contacting of step b) depends on the expected result expressed for example in terms of decontamination factor.

The longer the immersion time of the object is important, and the more decontamination is important, especially the decontamination factor is important. Generally, the duration of the contacting is 15 minutes to 1 hour, preferably 30 minutes.

The contacting of the object resulting from the rinsing step a1) after step a) is generally carried out by immersion of the object in a bath of the acid solution for example acetic acid or nitric acid.

It is not necessary to resort to agitation of the acid bath unlike the soda bath.

It is advantageous to use a basket to immerse, to immerse, objects such as bricks, contaminated in the acid bath for example of nitric acid or acetic acid, it will be possible to operate the same in step a ) and rinsing steps a1) and b1).

Advantageously, it is possible to envisage a closed-loop recirculation of the basic solution and / or of the acid solution forming the baths, with possible recovery of the waste, residues, resulting in particular from the possible coating of which objects such as bricks were provided. This recovery can be done for example by skimming or filtration.

In the case of radioactive contaminants the recirculation of the acid solutions can be carried out until the solutions are saturated.

Obligatorily, at the end of step b), a rinsing (step b1)) of treated objects such as bricks, for example with water or an aqueous solution. This rinsing makes it possible to put an end to the attack reaction of the lead.

This rinse usually lasts 5 to 15 minutes.

It is usually followed by a drying step.

Other advantages of the invention will appear on reading the detailed description which follows.

The invention relates to a decontamination process, that is, a method for removing contaminants from a lead or lead alloy object.

By object lead or lead alloys is generally meant in the sense of the invention an object comprising predominantly lead or a lead alloy.

Generally lead or lead alloy constitutes at least one surface of said object.

The objects treated by the process of the invention generally consist entirely of lead or a lead alloy, that is to say that they are massive objects possibly provided with a coating.

The lead alloys may be chosen for example from lead-tin, lead-barium, and tin-lead-antimony alloys.

The object treated by the method of the invention may have any shape. It could be for example a brick, a plate, a sheet ....

The object treated by the process according to the invention may comprise a coating on the surface of lead or lead alloy, and this coating may comprise one or more layers, for example from one to ten layers or a few dozens of layers, for example 20, 30, 50.

The layer or layers may be layers of paint, for example acrylic paint, glycerophthalic, urethane alkyd, epoxy, ....

In the case where the coating comprises several layers, these may differ by their composition and / or their thickness and / or the nature of the contaminant on and / or in each of the layers.

Thus, the coating may comprise several layers of paint and the contamination may be on the surface of the upper layer and / or between the layers and / or in the layers. It is indeed common for a coating to include several layers of paint in the case, for example, where to fix the contamination on a contaminated painted wall, is covered with the layer of contaminated paint with another layer.

In general, it should be noted that contaminants are found mainly on the surface of objects, such as lead bricks or lead alloys or sub-surface.

In principle, there can be no migration of contaminants, such as radioelements in lead which is a massive, non-porous material.

The contaminants may be of various natures, but the process according to the invention preferably applies to the removal of contaminants which are radioactive elements, emitters α, β and y; the invention makes it possible in particular to eliminate the contaminants which are alpha emitters such as uranium, curium, americium and plutonium.

Other contaminants that could be removed by the process of the invention include greases and oxide deposits present on the surface of the metal.

The first step of the method according to the invention is the contacting of the object with a solution basic aqueous solution, for example an aqueous solution of sodium hydroxide.

This step can be defined generally, simply as a surface treatment of the object such as brick, and this basic attack has various effects depending on whether one proceeds to the treatment of uncoated objects, for example unpainted bricks, or treating coated articles, for example bricks coated with one or more layers of paint.

In the case of uncoated objects, this treatment ensures the degreasing of the surface with the basic solution, for example the aqueous sodium hydroxide solution; it is preferably carried out hot and it allows the removal of surface contaminants, for example certain radioelements which are soluble in basic media. If the contaminants are radioelements, this first step is actually a slight decontamination.

In the case of coated articles which are, for example, provided with one or more layers of paint, treatment with the basic solution, for example the aqueous solution of sodium hydroxide, makes it possible to etch and degrade this coating, for example this or these layers of painting.

The basic solution, for example the aqueous solution of sodium hydroxide, has a mass concentration of generally from 0.5 to 90%, preferably 30%.

The contacting of the object such as a brick can be carried out in different ways, for example by spraying, coating the solution or the like. But in a preferred embodiment, this step Basic etching is performed by dipping, immersing, the object in a bath of the basic solution, for example aqueous sodium hydroxide solution. This way of doing things is particularly simple, reliable and easy to implement with a simple and inexpensive apparatus.

This bath is generally placed in a suitably coated tank, for example Teflon®, and of a sufficient volume so that the object to be treated is completely immersed, immersed in the basic solution, for example the aqueous solution of soda.

The contacting of the object with the basic solution, for example the aqueous sodium hydroxide solution, is generally carried out at a temperature of 25 to 90.degree. C., preferably this contacting is carried out hot, namely at a temperature of generally from 40 to 90 ° C, for example 60 ° C.

The duration of bringing the object into contact with the basic solution, for example the aqueous sodium hydroxide solution, is generally from 10 minutes to 1 hour 20 minutes. This duration corresponds to the duration of the pickling or degreasing desired.

A temperature higher than the ambient temperature, for example a temperature of 60 ° C, has the effect of increasing the rate of degradation of the coating, for example paint, which are provided objects. The choice of such a temperature which is, for example, the temperature of the bath where the object is immersed, is a good compromise between a reasonable pickling time, namely generally from 10 minutes to 1:20 and a bath temperature acceptable from a safety point of view.

When a bath of the mode solution is used, it is preferably stirred, for example with a mechanical stirrer, to ensure homogeneity of the attack.

In addition, the use of a basket to immerse objects, such as bricks, in the bath is wise because it allows easy handling and safety and uniform agitation of the bath.

It is possible to envisage a closed-loop recirculation of the basic aqueous solution, for example of the aqueous solution forming the soda bath, from the bath, with recovery, separation, for example by skimming or by filtration of the waste, residues originating in particular from the degradation, of the possible coating, of which the object was provided, for example the brick.

Indeed, the same basic solution remains effective for a number of treatments, after which the bath must be changed, or the concentration of basic product, for example soda, must be readjusted.

Recirculation of the basic solution, for example of the aqueous sodium hydroxide solution, could also be envisaged, for example, up to a value of radiological activity of the solution resulting in a dose rate in contact with the tanks, which is too great, or up to total carbonation of soda with formation of sodium carbonate and water and consumption of the active hydroxide ion OH ^- .

Following step a), the object is rinsed (step a1)) with water or an aqueous solution.

This rinsing is generally carried out for a period of 5 to 15 minutes.

This rinsing can be carried out by immersing the object in a rinsing bath consisting of water, for example distilled water, or an aqueous solution. The successive operations of basic attack a) and rinsing a1) can be carried out several times.

At the end of the basic treatment, for example with an aqueous solution of sodium hydroxide, as described above, and after rinsing with water or an aqueous solution, the procedure is carried out in accordance with invention to an acid treatment, that is to say that is brought into contact the object from step a), having undergone the basic attack, and having been further rinsed during the step a1) with an acid solution such as an aqueous solution of nitric acid or an aqueous solution of acetic acid.

As with the basic attack, the acid attack has various effects depending on whether uncoated objects are being treated or whether any coating has been completely removed by the basic attack; or to the treatment of objects still comprising in whole or in part a coating such as a coating of one or more layers of paint that has not been completely eliminated by the basic etching treatment.

This treatment makes it possible in both cases to strip the surface of the lead or the alloy of lead, that is to say to eliminate a surface layer on a limited thickness generally of a few microns.

For objects still provided in whole or in part with a coating such as paint, this treatment allows the degradation of the coating and / or the lifting of the coating by solubilization lead or lead alloy located under the coating.

For non-coated objects, for example unpainted, this treatment has the effect of solubilizing contaminants, for example soluble radioelements in the acid phase (it should be noted that the majority of radioelements alpha is soluble in the acid phase) and / or solubilizing lead or lead alloy to remove contaminants such as radioelements therein.

As already indicated above, the contamination is found mainly on the surface of the lead bricks or in the sub-surface, ie in a layer of a limited thickness, generally of a thickness of one to a few microns for example up to 10 microns. By solubilizing the surface of the lead, the contaminants will thus be found in solution in the acid in the form of lead acetate (case of the acetic acid bath) or lead nitrate (case of the nitric acid bath).

If we summarize the different modes of action of the process on coated objects, for example on painted bricks, and on uncoated objects, for example on unpainted bricks, we can say that in the case of coated objects , the first phase basic etching allows to strip partially or completely the coating such as paint and to partially or completely solubilize contaminants such as radioelements present, while the second phase of acid attack can strip coatings, such as non-degraded paints in basic solution, by chemical reaction or uplift due to the dissolution of lead under the paint, and to solubilize all contaminants such as radioelements.

The acid solution in the case of a nitric acid solution generally has a mass concentration of 0.5 to 90%, preferably 30%. It turned out that such concentration was a good compromise, ensuring a reduced soaking time and in particular to achieve the desired decontamination factor.

The acid solution when it is an acetic acid solution generally has a mass concentration of 0.5 to 90%, preferably 30%. It turned out that such concentration was a good compromise, ensuring a reduced soaking time and in particular to achieve the desired decontamination factor.

It should be noted, as already mentioned above, that nitric acid is the preferred acid because it has both acidic and oxidative properties.

The contacting of the object, such as a brick, can be carried out in different ways, for example by spraying, coating the solution or the like. But in a preferred embodiment, this Acid etching step is performed by dipping, immersing, the object in a bath of the acid solution, similar to what has been described for basic attack.

Preferably, this immersion contacting takes place in another container, tray where the basic attack took place. The same container may be used but in this case the container must be rinsed before reuse.

The contacting of the object with the acidic solution, for example of nitric or acetic acid, is generally carried out at ambient temperature, namely from 15 to 30 ° C, preferably from 20 to 25 ° C. Unlike step a), it is not necessary to use heating of the acid solution. Similarly, it is not necessary to use agitation of the nitric or acetic acid solution bath, but the use of a basket to immerse objects, such as bricks in the bath, is wise because it allows easy handling safely.

The total duration of the acid etching step is generally from 15 minutes to 60 minutes, preferably 30 minutes.

As for the basic solution, for example the aqueous solution of sodium hydroxide, it is possible to envisage recirculation of the acid solution from the bath with recovery, separation, for example by skimming or by filtration of the waste, residues coming from the degradation of the possible coating of which the object was provided, for example the brick.

The same acid solution only remains effective for a number of treatments, after which the bath must be changed.

Recirculation of the acid solution could thus be envisaged, for example up to a value of radiological activity of the solution resulting in a dose rate in contact with the tanks too large.

At the end of the acid etching step, the object is rinsed (step b1) with water or an aqueous solution.

Indeed, rinsing agents after the acid treatment is mandatory because otherwise the lead attack reaction continues.

Rinsing is generally carried out for a period of 5 to 15 minutes. The rinsing may be carried out by immersing the object in a rinsing bath consisting of water or an aqueous solution.

The successive acid etching and rinsing operations may be repeated several times until the desired decontamination factor is obtained; each acid attack being carried out with the same acid or successive acid attacks being carried out with different acids. The total duration of acid attacks b) and rinsing steps b1) is as described above.

At the end of the rinsing step b1), a drying step can be carried out, but this step is not mandatory.

After drying, the object can be recovered and reused, this is one of the advantages of method according to the invention, than to allow reuse of the objects at the end of the process without the need to resort to a reflow or other operation.

The effluents generated by the process are treated in various ways, depending on whether they are effluents from the basic treatment stage or effluents resulting from the acid treatment.

After the basic treatment, the bath consists of a solution of sodium hydroxide (NaOH) and for example insoluble paint skins and / or soluble or insoluble phthalates and radioelements. Phthalates are small soluble molecules resulting from the saponification of glycerophthalic paint. It seems that glycerophthalic paint is the most used at nuclear sites.

First, paint "skins" can be separated from the soda solution by filtration or centrifugation. In the case of pickling glycerophthalic paint, it is important to separate as soon as possible the "skins" of contaminated paint from the solution to limit the formation of phthalates and avoid consuming the active product (hydroxide ions).

In the case of the formation of phthalates (saponification of the glycerophthalic paint), they can be precipitated as phthalic acid poorly soluble, after adjustment of the pH (acidic pH). It is also possible to envisage a precipitation of phthalates by addition of calcium.

After the acid treatment, and in the case of the use of an acetic acid bath, the bath consists of acetic acid CH ₃ COOH, soluble or insoluble radioelements and soluble lead acetate ( Pb ²⁺ (CH ₃ COO ^- ) ₂ ).

After the acid treatment, and in the case of the use of a nitric acid bath, the bath consists of nitric acid (HNO ₃ ), soluble or insoluble radioelements and soluble lead nitrate (Pb (NO ₃ ) ₂ ).

• On peut effectuer une dilution pour acceptation dans les unités de traitement des effluents sur les sites nucléaires où la limite en plomb en solution est fixée ;
• On peut réaliser une précipitation du plomb sous forme de sulfure de plomb stable : après ajout de soude jusqu'à un pH neutre et ajout de sulfure de sodium (Na₂S), le plomb (les ions Pb²⁺) est précipité sous forme de sulfure de plomb stable. Par filtration, le précipité est séparé de la solution et cette dernière peut alors être traitée par les unités de traitement des effluents sur les sites nucléaires ;
• On peut enfin faire une précipitation du plomb sous forme d'hydroxyde de plomb Pb(OH)₂, en milieu basique. Il est toutefois préférable de précipiter le plomb sous forme de sulfure plutôt que sous forme d'hydroxyde car le sulfure de plomb est le composé le plus stable ;
• Des traitements séparés par type de solutions (basique, acide) ont été décrits ci-dessus mais on peut aussi mélanger les deux types de solutions acide et basique et ajuster le pH jusqu'à un pH neutre. Les phtalates sont ainsi précipités. Cette précipitation peut être améliorée par ajout de calcium. La précipitation du plomb en solution, sous forme de sulfure de plomb PbS, s'effectue ensuite par ajouts d'ions sulfures S^2- à pH neutre.

The treatments concern the presence of lead in solution.

• Dilution for acceptance can be performed in effluent treatment units at nuclear sites where the lead limit in solution is set;
• Lead can be precipitated in the form of stable lead sulphide: after addition of sodium hydroxide to a neutral pH and addition of sodium sulphide (Na ₂ S), the lead (Pb ²⁺ ions) is precipitated in the form of stable lead sulfide. By filtration, the precipitate is separated from the solution and the latter can then be treated by the effluent treatment units at the nuclear sites;
• Finally, lead can be precipitated in the form of lead hydroxide Pb (OH) ₂ in a basic medium. It is, however, preferable to precipitate lead as a sulphide rather than as a hydroxide since lead sulphide is the most stable compound;
• Separate treatments by type of solution (basic, acidic) have been described above but it is also possible to mix the two types of acidic and basic solutions and adjust the pH to a neutral pH. Phthalates are thus precipitated. This precipitation can be improved by adding calcium. Precipitation of the lead in solution, in the form of lead sulphide PbS, is then carried out by adding ^sodium sulphide ions S ² at neutral pH.

The invention will now be described with reference to the following examples, given by way of nonlimiting illustration.

Examples

• quatre de ces briques sont des « petites » briques peintes de 100 x 100 x 150 mm, la masse estimée d'une brique est de 5,6 kg, ces briques sont numérotées 1, 5, 11 et 12 ;
• deux de ces briques sont des « grandes » briques peintes de 200 x 150 x 60 mm, la masse estimée d'une brique est de 20,4 kg, ces briques sont numérotées 3 et 7 ;
• quatre de ces briques sont des « petites » briques non-peintes de 100 x 100 x 50 mm, la masse estimée d'une brique est de 5,6 kg, ces briques sont numérotées 2, 6, 13 et 14 ;
• deux de ces briques sont des « grandes » briques non-peintes de 200 x 150 x 60 mm, la masse estimée d'une brique est de 20,4 kg, ces briques sont numérotées 4 et 8.

In the following examples, decontamination by the method according to the invention of painted and unpainted lead bricks is carried out with the aim of reducing the level of decontamination of the lead bricks by a mean level of contamination in the order of 300 Bq / cm ² up to 0.4 Bq / cm ² in alpha emitters. The tests are carried out with twelve lead bricks:

• four of these bricks are "small" painted bricks of 100 x 100 x 150 mm, the estimated mass of a brick is 5.6 kg, these bricks are numbered 1, 5, 11 and 12;
• two of these bricks are "large" painted bricks of 200 x 150 x 60 mm, the estimated mass of a brick is 20.4 kg, these bricks are numbered 3 and 7;
• four of these bricks are "small" unpainted bricks of 100 x 100 x 50 mm, the estimated mass of a brick is 5.6 kg, these bricks are numbered 2, 6, 13 and 14;
• two of these bricks are "large" unpainted bricks of 200 x 150 x 60 mm, the estimated mass of a brick is 20.4 kg, these bricks are numbered 4 and 8.

It should be noted that in the examples, as in the remainder of the description, "painted brick" means a brick painted on at least one face.

The thickness of the paint of the bricks of the examples is of some 1/10 ^th of mm to some mm.

These bricks have an average surface activity of 300 Bq / cm ² , essentially due to alpha emitters (U, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu, and Am).

• un bain « téflonisé » chauffant d'un volume de 26 L destiné à recevoir les solutions de soude ou d'acide et muni d'un agitateur mécanique ;
• une cuve en acide inoxydable de 31 L destiné au rinçage des briques.

The tests are carried out in a sealed airlock equipped with a fume cupboard, one deposits in this lock a trolley with roulette on which are placed:

• a heated "teflonized" bath with a volume of 26 L intended to receive the sodium hydroxide or acid solutions and provided with a mechanical stirrer;
• a 31 L stainless steel tank for rinsing bricks.

An effluent recovery tank consisting of used baths is also planned.

The effluents are pumped directly into the tanks to be sent into the carboy by a flexible connection.

40 L of aqueous sodium hydroxide solution at 30% by mass and 30 L of an aqueous solution of nitric acid at 30% by mass are prepared for testing.

The rinsing solution consists of 12 L of distilled water.

Example 1

In this example we describe the first part of the tests devoted to stripping and degreasing bricks by the soda bath.

The bricks are treated in batches of two bricks each comprising a painted brick and an unpainted brick. The same rinsing bath is used for the four lots of two bricks.

The bricks are placed in a stainless steel mesh basket which is introduced into the 26 L Teflon bath. The bricks can be totally immersed in the bath of the soda solution.

The bath is agitated by means of a paddle stirrer and is thermostated at 60 ° C.

When the paint has completely disappeared from the painted brick or the maximum time has elapsed, the wire basket containing the bricks in the rinsing bath is transferred gently by proceeding to a light drainage, for example for 15 minutes.

The wire basket containing the bricks of the rinsing bath is then removed and the bricks are dried with absorbent paper.

• frottis sur chacune des briques ;
• attaque basique des briques pendant une durée de 45 minutes pour les briques 13 et 14, de 1 heure pour les briques 1, 4, 5 et 8, de 1h15 pour les briques 2, 3, 6 et 7 et 1h20 pour les briques 11 et 12 ;
• rinçage des briques pendant une durée de 15 minutes ;
• séchage des briques ;
• frottis sur chacune des briques.

In summary, operations performed by batch of two bricks, namely bricks 1 and 4; bricks 2 and 3; bricks 5 and 8; bricks 6 and 7; bricks 11 and 12; bricks 13 and 14 are as follows:

• smear on each of the bricks;
• basic bricks attack for 45 minutes for bricks 13 and 14, 1 hour for bricks 1, 4, 5 and 8, 1:15 for bricks 2, 3, 6 and 7 and 1:20 for bricks 11 and 12;
• rinsing the bricks for a period of 15 minutes;
• drying bricks;
• smear on each of the bricks.

Example 2

In this example, we describe the second part of the tests, devoted to the study of the attack of bricks, either by a bath of nitric acid, or by an acetic acid bath as prepared above.

The treated bricks are bricks 1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 13 and 14 described above.

The bricks are treated one by one.

The acid attack tests are carried out at room temperature and without agitation.

• on laisse la brique de 15 min à 1 heure dans le bain acide suivant le niveau de décontamination souhaité ;
• on transfère délicatement après égouttage le panier grillagé contenant la brique dans la cuve de rinçage pour la rincer ;
• on attend par exemple 10 minutes ;
• on sèche la brique au moyen de papier absorbant ;
• on réalise un frottis aux fins d'analyse sur la brique ;
• on remet la brique dans le panier grillagé, puis dans le bain « téflonisé » contenant la solution acide si le temps d'attaque n'a pas permis d'atteindre le niveau de décontamination souhaité. Les phases d'attaque acide et de rinçage sont renouvelées tant que le niveau de décontamination n'a pas été atteint.

A brick that has already undergone the basic etching by soda is deposited in the stainless steel mesh basket which is introduced into the teflonized bath of 26 L. The brick must be totally immersed in the bath of the acid solution.

• the brick is left for 15 minutes to 1 hour in the acid bath according to the desired level of decontamination;
• the wire basket containing the brick is carefully transferred after draining to the rinsing tank for rinsing it;
• for example, wait 10 minutes;
• the brick is dried by means of absorbent paper;
• a smear is made for analysis on the brick;
• the brick is put back into the wire basket and then into the "teflonized" bath containing the acid solution if the attack time has not allowed the desired level of decontamination to be reached. The acid etching and rinsing phases are renewed as long as the level of decontamination has not been reached.

• préparation du bain d'acide (nitrique pour les briques 1, 2, 3, 4, 11 et 12 et acétique pour les briques 5, 6, 7, 8, 13 et 14) ;
• attaque acide d'une brique pendant 15 minutes ;
• rinçage d'une brique pendant 10 minutes ;
• séchage ;
• frottis.

In summary, the operations performed on each of the bricks are as follows:

• preparation of the acid bath (nitric for bricks 1, 2, 3, 4, 11 and 12 and acetic for bricks 5, 6, 7, 8, 13 and 14);
• acid attack of a brick for 15 minutes;
• rinsing a brick for 10 minutes;
• drying;
• smear.

The successive stages of smear, acid attack, and rinsing are performed four times, the duration The total acid attack is therefore 1 hour, and the total rinse time is 40 minutes.

Example 3

In this example, the results of the basic etching treatments performed on all the bricks are described. Remember that this treatment was to plunge the bricks in a bath of sodium hydroxide (sodium hydroxide) at 30% by mass at a temperature of 60 ° C until paint stripping and maximum for 1h20.

Visual results on painted bricks

The stripping of the paint on the six painted bricks is effective (because 100% of the paint is removed) and fast (the maximum bath time is 1:20).

At the end of the treatment, the "skins" of paint are recovered in the bath. The "skins" of paints can continue to degrade in the bath if they are not extracted. The only drawback is the consumption of soda which is no longer used for paint stripping but for the degradation of "skins" (formation of soluble degraded compounds).

In conclusion, paints present on lead bricks are etched by the hot basic solution, regardless of the thickness (a few ^1/10 mm to a few mm) and the aging of the paint.

Radiological results

The radiological state of the bricks after basic treatment is determined by performing paper smears on the lead bricks and then analyzing them on a counting bench.

Examples of painted bricks: for painted bricks 1 and 12, the surface activity, after basic treatment, is below the limit of detection (0.027 Bq / cm ² ).

Painted brick 12 was plunged into a "new" soda bath while brick 1 was plunged into a soda bath that had already been used to treat two bricks. However, it is observed that the effectiveness of the treatment is the same in both cases. We can then consider recycling the soda bath and use the same bath to treat several bricks. From a theoretical point of view, it is certain that the concentration of the soda bath is large enough that the consumption of active product is negligible during a single soaking. It may even be thought that the soda bath will be altered more rapidly by air carbonation than by consumption by reaction with the paint.

As for the painted brick 11, the basic treatment has allowed to strip all the paint, but the surface activity remains above the limit of detection. In this case, the residual contamination is embedded in the lead and can not be removed by basic treatment, ie, the radioelements present on the surface of this lead brick are not soluble in the basic phase.

Example of an unpainted brick: the surface activity of the unpainted brick 4, after basic treatment, is lower than the limit of detection. The radioelements present on the surface of the lead brick 4 are soluble in the basic phase, while hot.

It can be concluded from the results of the surface activity of bricks that hot basic bathing is very effective on painted and unpainted bricks, by paint etching and / or by the dissolution of radioelements.

Moreover, the radiological analyzes on the paintings confirm the presence of radioelements on the surface or between the layers of paint.

Example 4

In this example, the results of the acid treatment are described.

Remember that all bricks have undergone the second phase of treatment. Two different baths were tested: nitric acid bath and acetic acid bath. Bricks 1, 2, 3, 4, 11, 12 were immersed in a 30% nitric acid bath at room temperature for a maximum of 1 hour. The bricks 5, 6, 7, 8, 13 and 14 were immersed in a 30% acetic acid bath at ambient temperature for a maximum of 1 hour.

Visual results on bricks

The appearance of the surface of lead bricks before and after acid treatment has not changed.

The acid attack phase is useful for removing contaminants from the lead surface and stripping paint resistant to the basic attack phase.

Radiological results

The radiological state of the bricks after acid treatment is determined by performing paper smears on the lead bricks and then analyzing them on a counting bench.

The surface activity of bricks 1, 2, 3, 4, 5, 6, 8, 12, 13, 14 after basic attack and before acid attack (nitric acid or acetic acid) is below the limit of detection of the counting bench. , ie 0.027 Bq / cm ² . So all contaminants were removed from the lead surface after the basic phase. The acid attack on these bricks only attacks the surface of the lead.

Only bricks 7 and 11 are above the detection limit, after the basic attack.

For example, the brick 11 which was painted was totally etched by the basic bath but the residual surface activity remained important.

The attack with nitric acid had the effect, after a period of between 15 and 30 minutes to lower the surface activity to the limit of detection. In this case, it appears that the dissolution of the lead surface led to the release of contaminants in solution. Given the duration of the bath necessary for the solubilization of the radioelements, one can think that these last ones were not very encrusted in the lead (at most a few microns). It may also be noted that most α-emitting radioelements are more soluble in acid solution than in basic solution, hence the utility of treatment with acid solution.

In principle, nitric acid is more effective than acetic acid in solubilizing radioelements.

Process parameters

The uncertainties of the acid etching process resided in the volume of gas (H ₂ ) generated by the lead attack. However, the treatment with acid is not violent. Given the low gas evolution (no bubbling was observed), the bricks can be treated simultaneously in batches of several bricks.

Summary of results

In the case of painted bricks, the first phase of basic attack can partially strip or completely paint and solubilize partially or totally the radioelements present. The second phase of acid etching makes it possible to strip the non-degraded paints in basic solution (by chemical reaction or uplift due to the dissolution of the lead located under the paint) and to solubilize all the radioelements.

Claims (20)

Method for decontaminating an object made of lead or lead alloy, in which the following successive steps are carried out: a) the object is brought into contact with a basic aqueous solution; a1) the object is brought into contact with water or an aqueous rinsing solution; b) the object is brought into contact with an acidic aqueous solution; b1) the object is brought into contact with water or an aqueous rinsing solution. The method of claim 1, wherein the object is provided with a coating comprising one or more layers. The method of claim 2, wherein said one or more layers are paint layers. A process according to any one of claims 2 and 3, wherein the coating comprises a plurality of layers which differ in composition and / or thickness and / or the nature of the contaminant (s) on and / or in each of the layers. The method of any one of claims 1 to 4, wherein said contaminants are radioactive elements. Process according to any one of the preceding claims, in which the basic aqueous solution of step a) is chosen from aqueous solutions of sodium hydroxide and aqueous potassium hydroxide solutions. Process according to any one of the preceding claims, wherein the basic aqueous solution, for example the aqueous sodium hydroxide solution of step a), has a mass concentration of 0.5 to 90%, preferably 30%. Process according to any one of the preceding claims, in which the contacting of the object with the basic aqueous solution is carried out at a temperature of 25 to 90 ° C, preferably of 40 ° C to 90 ° C, for example 60 ° C. Process according to any one of the preceding claims, in which the duration of bringing the object into contact with the basic solution, for example aqueous sodium hydroxide solution, is from 10 minutes to 1 hour 20 minutes. A process according to any one of the preceding claims wherein the contacting of the object with the basic solution by For example, the aqueous solution of sodium hydroxide is produced by immersing the object in a bath, preferably stirred, of the basic solution. Process according to Claim 10, in which the basic aqueous solution, for example the aqueous sodium hydroxide solution, forming the bath is recirculated in a closed loop. A process according to any one of the preceding claims, wherein the acidic aqueous solution of step b) is selected from aqueous nitric acid solutions and aqueous acetic acid solutions. Process according to any one of the preceding claims, wherein the solution of step b) is a nitric acid solution with a mass concentration of 0.5 to 90%, preferably 30%. Process according to any one of claims 1 to 12, wherein the solution of step b) is a solution of acetic acid in a mass concentration of 0.5 to 90%, preferably 30%. A process according to any one of the preceding claims wherein the contacting of the object with the acidic solution, for example the aqueous solution of nitric acid or acetic acid is carried out at room temperature. A process according to any one of the preceding claims, wherein the duration of contacting the object with the acidic solution, for example the aqueous solution of nitric acid or acetic acid is from 15 minutes to 60 minutes, preferably 30 minutes. Process according to any one of the preceding claims, in which the contacting of the object with the acidic solution, for example the nitric or acetic acid solution, is carried out by immersing the object in a bath of the solution of nitric or acetic acid. Process according to Claim 17, in which the acidic solution, for example the aqueous solution of nitric acid or acetic acid, forming the bath, is recirculated in a closed loop. A process according to any one of the preceding claims, wherein step a1) and step b1) have a duration of 5 to 15 minutes. A process as claimed in any one of the preceding claims wherein step b1) is followed by a drying step.