EP1520279B1 - Composition, foam and method for surface decontamination - Google Patents

Abstract

The invention relates to a composition which makes it possible to obtain a gelled aqueous foam capable of decontaminating, stripping or degreasing a surface. The composition of the present invention comprises one or more surfactants, one or more acidic or basic reactants and a gelling agent. The decontamination foam obtained from this composition exhibits long lifetimes, generally of between 1 and 10 hours, guaranteeing a prolonged time of action on the surface and a high decontamination effectiveness. These foams can be used to remove the radioactivity from an inaccessible plant, which is large in size and complex in design, by simple filling or by simple spraying over an accessible surface.

Description

The present invention relates to a composition, a solution and a decontamination foam. The composition and the solution of the present invention make it possible to obtain a gelled acidic or basic aqueous foam that can be used for decontaminating surfaces.

The present invention finds for example an application in the decontamination of metal surfaces contaminated for example by grease, by radioactive mineral deposits, by a very adherent oxide layer or in the mass.

It is particularly of great interest in radioactive decontamination, for example nuclear installations of large volumes, complex geometry or inaccessible for which an economy of chemical reagents and liquid effluents used is necessary. For example, decontaminating the interior of tanks of large volumes, for example from 20 to 100 m ³ , spent fuel reprocessing plants containing solutions of fission products is difficult because it is a medium very radiating. In fact, the dose rate can reach up to 40 GyH at the bottom of the tank at a depth of -7.5 m. This level of irradiation virtually prohibits any modification of existing tank equipment. In addition, the presence of numerous cooling coils in the tanks does not allow the introduction of tools for the application of decontamination treatments. Finally, the contaminated fluid can not be extracted from the tanks in order to recycle the foam without very expensive complementary arrangements. The transfer means and the evacuation lines of the existing fluids must therefore be used.

Prior art

Numerous compositions and foams for surface treatments, in particular for cleaning, degreasing and / or radioactive surface decontamination treatments, have been developed. Unfortunately, they all have the same drawbacks: they have lifetimes that are too short and difficult to control. Indeed, the foams of the prior art drain quickly, in minutes, and have a shelf life, defined as the time required for the total transformation of a given volume of foam into liquid, generally ranging from 1 to 10 minutes .

This often leads to the effectiveness of the treatment that it is necessary to repeatedly apply the foam on the surface to be treated. The amount of cleaning effluent and the difficulty of the treatment are thus increased.

In addition, since the contact time of the foam with the surface is limited because of the short life of the foams, the cleaning agents and treatment used must often be chosen so as to be very active in a very short time. Only high concentrations of products or more corrosive products can therefore be used. This results in a limitation of the type of surface that can be treated, greater pollution, increased surface rinsing difficulties, and increased cost of treatment.

There is therefore a real need for a foaming composition that overcomes the disadvantages of the compositions of the prior art, that is to say which allows in particular to extend and control the life of the foam, reduce the amount effluents, to use less corrosive cleaning agents, to use these agents in lower concentrations, as well as to reduce the difficulty, the pollution as well as the cost of treatment.

Presentation of the invention

The present invention is specifically intended to provide a solution to the many problems of the prior art by providing a composition for preparing a foaming aqueous solution for generating a foam that does not have the disadvantages of the prior art.

• un agent tensioactif organique moussant ou un mélange d'agents tensioactifs moussants,
• un agent gélifiant, et
• un agent de décontamination.

The composition used according to the present invention comprises:

• a foaming organic surfactant or a mixture of foaming surfactants,
• a gelling agent, and
• a decontamination agent.

The foams generated from the composition of the present invention thus comprise an agent gelling. Indeed, unexpectedly, the life of this foam is considerably increased compared to the foams of the prior art, and the foam thus prepared has a significantly improved ability, compared to the foams of the prior art, to remain in contact with a surface, even vertical, for several hours thus ensuring the decontamination of said surface in static or spray mode. This unexpected result leads to a greater effectiveness of the surface treatment, where appropriate with lower concentrations of decontamination agents, for example cleaning, degreasing or decontamination, and a decrease in the amount of effluent produced. In addition, it is possible to use active decontamination agents less corrosive than those of the prior art because the contact of the foam of the present invention with the surface to be treated is prolonged.

• 0,2 à 2 % en poids d'un agent tensioactif organique moussant ou d'un mélange d'agents tensioactifs moussants,
• de 0,1 à 1,5 % en poids d'un agent gélifiant, et
• 0,2 à 7 moles d'un agent de décontamination.

The composition of the present invention is an aqueous solution which comprises per liter of solution:

• 0.2 to 2% by weight of a foaming organic surfactant or a mixture of foaming surfactants,
• from 0.1 to 1.5% by weight of a gelling agent, and
• 0.2 to 7 moles of a decontamination agent.

This solution can be prepared very easily, for example at room temperature, by simple mixing, adding in an aqueous solution, for example water, the surfactant (s), the gelling agent and, if it is useful, the decontaminating agent of the composition of the present invention.

According to the present invention, the gelling agent is preferably biodegradable. It is advantageously a thickening organic agent having a pseudo-plastic rheological behavior. According to the invention, the gelling agent may be chosen for example from the group comprising a water-soluble polymer or a hydrocolloid, a heteropolysaccharide chosen, for example, from the family of polyglucoside polymers with trisaccharide branched chains, such as xanthan gum, for example Rhodopol. 23 (trademark) marketed by Rhodia. It may also be chosen from the group comprising cellulose derivatives such as carboxymethylcellulose or a polysaccharide containing glucose as the only monomer, for example Amigel (trademark) marketed by Alban Muller International.

According to the invention, the surfactant may be a foaming nonionic surfactant chosen for example from the family of alkylpolyglucosides or alkylpolyetherglucosides. These surfactants are derived from natural glucose and have the advantage of being biodegradable. As an example, there may be mentioned surfactants "Oramix CG-110" (trademark) sold by the company SEPPIC, the "Glucopon 215" (trademark) marketed by the company AMI.

According to the invention, the surfactant can be an amphoteric surfactant, chosen, for example, from the family of sulfobetaines, the family of alkylamidopropylhydroxysulfobetaines, for example Amonyl 675 SB (trademark) marketed by SEPPIC, or from the family of amine-oxides, for example Aromox MCD-W (trademark), or cocodimethylamine oxide marketed by Akzo Nobel.

The composition of the present invention may comprise a single surfactant or a mixture of surfactants chosen for example from the abovementioned families.

The composition of the present invention is presented primarily as a composition for generating a radioactive decontamination foam of a surface.

The decontamination agent is chosen according to the use for which the composition is intended. When the composition is intended to generate a decontamination foam, the active agent is chosen in particular according to the nature of the contamination and the surface to be decontaminated, for example an acid or a mixture of acids, a base or a mixture base, an oxidizer, for example H ₂ O ₂ , a reducing agent, a disinfectant, etc. The person skilled in the art will know how to choose the decontamination agent according to his needs.

According to the invention, the active decontamination agent may be an acid or a mixture of acids, for example inorganic acids, advantageously chosen from the group comprising hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and oxalic acid. According to the invention, the acid is advantageously present at a concentration of 0.2 to 7 moles, preferably 0.3 to 7 moles, more preferably 1 to 4 moles. These concentration ranges naturally relate to the concentration of H ⁺ ions. In addition, they are given for the preparation of 1 liter of foaming solution. They therefore represent the concentration in mol / l in 1 liter of foaming solution prepared from this composition.

According to the invention, the active decontamination agent may be a base or a mixture of bases, for example inorganic (s), advantageously chosen from the group comprising sodium hydroxide, potassium hydroxide, sodium carbonate, etc. According to the invention, the base is advantageously present at a concentration less than 2 mol.l ^-1 , preferably ranging from 0.5 to 1.5 mol.l ^-1 . These concentration ranges obviously concern the concentration of OH ^- ions. In addition, they are given for the preparation of 1 liter of foaming solution. They therefore represent the concentration in mol / l in 1 liter of foaming solution prepared from this composition.

Thus, according to the above-mentioned composition chosen according to the present invention, an acidic or alkaline foam may have either radiative deposits dissolving properties, for example for the removal of non-fixed contaminations on a surface, or corrosion properties. controlled surface for a contamination fixed on it.

Advantageously, the composition of the present invention has a viscosity at 0.3 rpm (Brookfield LVT, module x) of between 100 and 50,000 cP. This viscosity allows indeed a longer life of the foam, as well as the ability to project this solution by means of a nozzle, or to pass through a porous lining to generate a foam.

The foam can be generated from this foaming solution by any foam generation system of the prior art: mechanical stirring, bubbling, static ball mill or any other device providing the gas-liquid mixture, such as the devices described in FR-A-2,817,170 or a device using a spray or spray nozzle, etc.

The generated foam can act statically, it has a long life, generally between 1 and 10 hours, and allows a duration of action on the controlled surface due to the control of the drainage time with the gelling agent.

The present invention also relates to a process for decontaminating a surface comprising a step of bringing the surface to be decontaminated into contact with a foam prepared from the composition of the present invention, that is to say with a foaming solution according to the present invention.

The invention relates generally to the treatment, in particular to the decontamination, of surfaces of any type, for example glass, plastic, metal, etc., which may be important, which are not necessarily horizontal, but which can be inclined or even vertical. It can be used for example to decontaminate tanks, ventilation ducts, storage pools, glove boxes, steam generators, pipes, floors, etc.

Decontamination foams can be used both in the periodic maintenance of existing industrial installations and in the dismantling of such installations. These installations can be, for example, nuclear installations or industrial chemistry in general.

The contacting of the foam with the surface to be treated can be done by conventional methods of filling, for example a tank, a tank or a pipe, the walls of which are to be decontaminated; spraying or spraying on the surface to be decontaminated; placing the foam into circulation in an installation whose surfaces are to be decontaminated; etc.

For example, the foam may be applied to the surface to be decontaminated by any conventional method of spraying by means of a pump and a nozzle. For spraying, the bursting of the foam jet on the surface to be decontaminated can be obtained for example with a flat jet or round jet nozzle. The short viscosity recovery time of the composition of the present invention allows the spray foam to adhere sufficiently long to the surface on which the foam is projected.

For example, to decontaminate a vessel, the method of the present invention may simply be to fill the vessel with the foam of the present invention so that its surfaces are in contact with the foam. The foam then degrades naturally "in static" under the effect of its gravitational drainage. The term "static" is then opposed to the dynamic application of foams consisting of a circulation or a spray. The foam can also be applied only to the surfaces of the tank without necessarily filling it.

Also, the subject of the invention is also a method of decontaminating an installation which comprises the simple introduction of the foam by simple filling inside the installation, the maintaining "static" this foam within the volume, for example at a temperature between 20 ° C and 50 ° C, during the foam drainage time, usually between 1 and 10 hours, and sufficient to guarantee the decontamination, then finally the elimination of the drained liquid by simple emptying.

The decontamination treatment of the surface may consist of several applications of the same foam or with foams of different nature applied successively. Each of these treatments may comprise a filling of the volume to be decontaminated or a projection of the foam on a surface, a holding for several hours of the foam in static during its drainage and the elimination of the drained liquid by simple emptying. The inventors have however noted that, because of the lifetime of the foam of the present invention, which is longer than that of prior art foams, a small number of applications, see a single application, is sufficient to obtain effective treatment of a surface, where several applications were necessary with the foams of the prior art.

The contact time will depend essentially on the nature of the decontamination, the composition and nature of the foam, and the nature of the surface. Generally, a contact time of from 15 minutes to 10 hours is sufficient for effective treatment. This duration will be adapted according to the needs in the application made of the present invention.

The present invention guarantees a treatment, in particular an effective decontamination, because the lifetime of the foam, and therefore the contact time of the foam with the wall is increased and adjusted by the addition of the gelling agent which delays drainage. Furthermore, on vertical surfaces, or even ceilings, the foams of the present invention, because of the presence of the gelling agent, adhere better than the foams of the prior art, which further increases the effectiveness of treatment or decontamination on these surfaces.

The drained liquid obtained at the end of the life of the foam of the present invention can be evacuated easily by emptying and treated by the conventional decontamination processes of liquid effluents. It can also be regenerated, for example in the manner described in the document FR-A-2,817,170 , to reconstitute a foam.

The method of the present invention may further comprise, after the step of contacting the surface to be decontaminated with the foam, a step of rinsing said surface by means of a foam or a rinsing solution. The foam or rinsing solution may be any foam or solution appropriate to the nature of the decontamination foam and / or the surface to be rinsed. It can be simply a conventional rinsing foam, or a rinsing foam according to the present invention, that is to say simply comprising a surfactant and a gelling agent, and optionally a conventional buffer compound allowing to neutralize the agent of acid or basic decontamination previously used or a surface treatment compound. It may also be an aqueous solution, for example water.

The interest of such a treatment called "gelled foam" according to the present invention compared to existing treatments are numerous.

dans laquelle V représente un volume de liquide, de gaz ou de mousse comme cela est indiqué.First, there are conventional advantages of the foam treatment, that is to say in particular the decrease in the volume of effluents produced. Indeed, the foam consists of a dispersion of air bubbles in liquid and can be characterized by its expansion "F" defined under normal conditions of temperature and pressure by the following relation (1): $$\mathrm{F}\mathrm{=}\left({\mathrm{V}}_{\mathrm{gas}}\mathrm{+}{\mathrm{V}}_{\mathrm{liquid}}\right)\mathrm{/}{\mathrm{V}}_{\mathrm{liquid}}\mathrm{=}{\mathrm{V}}_{\mathrm{foam}}\mathrm{/}{\mathrm{V}}_{\mathrm{liquid}}$$

wherein V represents a volume of liquid, gas or foam as indicated.

The decontamination foams prepared from the composition of the present invention advantageously have an abundance of the order of 10 to 15. They therefore make it possible to decontaminate a large volume, for example 100 m ³ , with less than 10 m ^3. of liquid.

Another advantage, particularly in the case of gelled foam spraying decontamination on radioactive plant surfaces, is that the gelled foam of the present invention produces smaller amounts of radioactive effluents due to its long service life. , whereas projections of aqueous solutions or foams of the prior art produce large quantities of radioactive effluents for limited effectiveness due to the low contact time with the treated surfaces.

Another advantage of the present invention lies in the fact that following the natural drainage of the foam of the present invention, the contaminated drained liquid is recovered, and the surface does not need to be rinsed with very little water. is about 1 liter / m ² . Thus, less liquid effluents to be treated are generated subsequently. This results in a simplification in terms of global treatment of contamination, and a reduction in pollution.

Other features and advantages of the present invention will become apparent on reading the following examples given of course by way of illustration and not limitation with reference to the appended figures.

Brief description of the figures

• The figure 1 is a schematic representation of the device used by the inventors to generate a foam from an aqueous solution of the composition of the present invention, and to measure drainage kinetics of the resulting foam.
• The figure 2 is a graph illustrating drainage kinetics expressed as fractions (F) of recovered liquid (in g) versus time (t) (in minutes), for different foams obtained from different compositions of the present invention.
• The figure 3 is a graph illustrating drainage kinetics expressed in volumes (V) of drained liquid (in ml) as a function of time (t) (in minutes), for different foams obtained on the one hand from different compositions of the present invention and on the other hand from compositions without a gelling agent.

• The figure 4 is a schematic representation of the device used by the inventors to generate a foam from a composition of the present invention, and to implement a method of decontaminating a surface according to the present invention.
• The figure 5 is a graph illustrating the influence of xanthan gum (Xant) quantity (in g / 1) on the drainage delay (foam stability): drained liquid height (H) (in mm) as a function of time (t) (in minutes). In this figure, the legend indicates the various foaming solutions tested, F denotes the expansion of each foam obtained.

EXAMPLES EXAMPLE 1: FOAMS OF THE PRIOR ART

The drainage and effectiveness properties of foams prepared from five foaming solutions each containing a reference mixture of two surfactants were studied: Oramix (trademark) at 8 g / l and Amoyl (trademark) at 3 g / l.

A formulation, called a reference formulation (allowing the generation of a reference foam), did not contain decontamination agent.

• 1^ere formulation : du carbonate de sodium à une concentration de 1 mol.l^-1,
• 2^ème formulation : un mélange d'acide fluorhydrique à une concentration de 0,05 mol.l^-1 et d'acide nitrique à une concentration de 2 mol.l^-1,
• 3^ème formulation : un mélange d'acide oxalique à une concentration de 0,6 mol.l^-1 et d'acide nitrique à une concentration de 0,5 mol.l^-1,
• 4^eme formulation : un mélange d'eau oxygénée à une concentration de 1 mol.l^-1 et d'acide nitrique à une concentration de 3 mol.l^-1.

The other four formulations differed in the nature of the decontamination agent:

• 1 ^st formulation: sodium carbonate at a concentration of 1 mol.l ^-1,
• ^2nd formulation: a mixture of hydrofluoric acid at a concentration of 0.05 mol.l ^-1 and nitric acid at a concentration of 2 mol.l ^-1 ,
• ^3rd formulation: a mixture of oxalic acid at a concentration of 0.6 mol.l ^-1 and nitric acid at a concentration of 0.5 mol.l ^-1,
• 4 ^th formulation: a mixture of hydrogen peroxide at a concentration of 1 mol.l ^-1 and nitric acid at a concentration of 3 mol.l ^-1.

No cloud point was observed between 20 and 50 ° C

These foaming solutions were then used to generate controlled expansion foams using a static glass bead generator (Q1 = foaming solution flow, Qg = air flow, F = (Qg + Q1) / Q1).

• (3) : réservoir de préparation de la solution moussante ; (5) : solution moussante ; (7) : agitateur mécanique ; (9) pompe ; (11) : système d'apport d'air comprimé ; (13) : régulateur de débit ; (15) : générateur de mousse ; (17) conduites ; (19) : réservoir de réception de la mousse ; (21) : mousse ; (23) : vanne manuelle ; et (25) : cuve de récupération du liquide drainé.

An experimental protocol was developed to plot the drainage kinetics of each of the foams in conditions close to industrial reality thanks to the device (I) schematized on the figure 1 . In this figure, the following references indicate the following elements of the device (I):

• (3): preparation tank of the foaming solution; (5): foaming solution; (7): agitator mechanical ; (9) pump; (11): compressed air supply system; (13): flow regulator; (15): foam generator; (17) conduits; (19): foam receiving tank; (21): foam; (23): manual valve; and (25): recovery tank for the drained liquid.

Each of the five formulations exhibited excellent foamability since foaming foams greater than 10 were prepared.

The kinetic studies show that the presence of the decontamination agents does not change the kinetics of drainage compared to the reference foam without a decontamination agent, as shown in Figure 1. figure 2 .

Of all the formulations prepared, more than half of the liquid drains in less than 8 minutes and the lifetimes of each of the formulations remain short (15 to 25 minutes).

EXAMPLE 2: FOAMS OF THE PRESENT INVENTION

The addition of a small amount, that is to say 0.1% by weight or 1 g / l, of xanthan gum, used as gelling agent in the sense of the present invention, to the various formulations of foaming solutions of Example 1 stabilizes all the foams as shown in FIG. figure 3 .

The addition of 1 g / l of xanthan gum has the effect of considerably delaying the drainage of each of the foam formulations and thus increase the life of the foam.

Table 1 below gathers the time t _1/2 necessary so that half of the liquid contained in the foam drains and the service life t ₁ the time for all the liquid of the foam to drain for the different foams studied. <b> Table 1 </ b>: Lifetime t <sub> 1 </ sub> and time t <sub> 1/2 </ sub> for different foam formulations Without xanthan gum 1 g / l of xanthan gum Life time t and half life t _1/2 (in min and s) t _1/2 t ₁ t _1/2 t ₁ Nitric acid foam + hydrogen peroxide 4'30 " 15 ' 18 ' 50 ' Nitric acid foam + hydrofluoric acid 4'30 " 15 ' 24 ' 60 Nitric acid + oxalic acid foam 6 ' 20 ' 36 ' 80 ' Alkaline foam with sodium carbonate 7'30 " 25 '90' > 120 '

With a quantity of 1 g / l of xanthan gum, the time t _1/2 is about 20 minutes for the two acidic formulations containing hydrogen peroxide and hydrofluoric acid. The foam containing oxalic acid is the most stable of acidic foams with a time t _1/2 of nearly 40 minutes. Finally, the alkaline foam drains very slowly since it takes almost an hour and a half to recover half of the liquid.

These results show that the addition of a small amount of xanthan gum, 0.1% by weight or 1 g / l, stabilizes all the formulations of Example 1.

Indeed, very substantial gains on the stability of the formulations are obtained since lifetimes of between 50 and 120 minutes, have been observed from the simple addition of a small amount of xanthan gum.

Tests have been carried out to demonstrate the link between the amount of gelling agent and the lifetime of the foam.

The figure 5 is a graph illustrating the influence of the amount of xanthan gum on the delay in drainage (stability of the foam).

As long as the liquid does not drain, the foam is stable. The foam does not drip for 20 minutes for 1 g / l of xanthan gum, 60 minutes for 2 g / l xanthan gum and 120 minutes for 3 g / l xanthan gum. It also appears on this graph that foaming solutions without a gelling agent drain immediately (t = 0 minutes).

EXAMPLE 3: TREATMENT OF A SURFACE WITH FOAMS OF THE PRESENT INVENTION

The effectiveness of the foams of Example 2 has moreover been tested for the decontamination of surfaces.

The objective is indeed to demonstrate that the foams prepared with the foaming solutions of the present invention can for example solubilize a deposit of reconstituted insoluble simulating a real deposit radiating adhering to a wall.

• (40) : colonne en plexiglas ; (42) : plaques en acier suspendues ; (44) : vanne ; (46) générateur de mousse à lit de billes de verre ; (48) : système d'apport d'air comprimé ; (50) : conduite d'amenée de la mousse générée dans la colonne (40) ; (52) : conduite de récupération du liquide de drainage ; (54) vanne ; (56) : pompe ; (58) : amortisseur de pulsation ; (60) : filtre ; (62) : tube de prélèvement ; (64) : réacteur de préparation de la solution moussante ; (66) solution moussante ; (68) : agitateur mécanique ; (70) : thermomètre ; (72) : conduite d'alimentation en eau ; (74) : conduite d'alimentation en composés de la solution moussante ; (76) : conduite d'alimentation du générateur de mousse (46) en solution moussante ; (78) réservoir d'alcool ; (80) pompe doseuse d'alcool ; (82) conduite de récupération de la mousse.

Stainless steel plates coated with adherent deposits are suspended in a 30 liter plexiglass column in the device (II) shown schematically on the figure 4 . In this figure, the following references indicate the following elements of the device (II):

• (40): plexiglass column; (42): suspended steel plates; (44): valve; (46) foam generator with a glass bead bed; (48): compressed air supply system; (50): feeding duct of the foam generated in the column (40); (52): drainage fluid recovery line; (54) valve; (56): pump; (58): pulsation damper; (60): filter; (62): sampling tube; (64): reactor for preparing the foaming solution; (66) foaming solution; (68): mechanical stirrer; (70): thermometer; (72): water supply pipe; (74): supply line of compounds of the foaming solution; (76): supply line of the foam generator (46) in foaming solution; (78) alcohol tank; (80) alcohol dosing pump; (82) foam recovery pipe.

The two plates (42) covered with the deposit to be solubilized are voluntarily placed in the center of the column. The column is filled until the samples are completely immersed and the generation is stopped when the highest edge of each of the two plates is at a depth of 10 cm in the foam. This level of foam corresponds to 20 liters of foam and is voluntarily limited to quantify the efficiency of the upper part of the foam.

The low immersion of the plates is penalizing since the foam dries upwards under the effect of gravitational drainage. The foam / deposition contact times are then shorter and may be insufficient to ensure effective dissolution. However, if the dissolution is important in the upper part of the foam, it will be even more in the foam.

The stopwatch is started when the column has been filled with 20 liters of foam and the foam is allowed to act statically. The sample is removed after a given time to weigh the dissolution of the deposit. If two samples have been placed, one may be removed after one hour of immersion, for example, the other after two hours.

To carry out these deposition dissolution experiments, the foams are obtained successively in the following manner. 4 liters of a solution containing one of the three reagents, the surfactants and the xanthan gum are prepared. The solution is placed under stirring in the reactor (64) thermostated between 20 and 50 ° C. Then, a gas-liquid mixture of known proportion is then generated through a bed of glass beads: about 12 liters per hour of acid solution are mixed with a controlled gas flow rate of 180 liters per hour of air to generate a relatively wet foam of known overrun close to 14.

Foam phase tests were conducted for example with the carbonated foaming formulation containing 1.5 g / l of xanthan gum, of the brand Rhodopol 23. The lifetime of the foam is then of the order of 2 to 3 hours.

A first adherent deposit, sample 1, a thickness of 0.5 mm, or 1 g per 25 cm ² , is placed within the column. The objective of the test is to let a carbonated foam act statically and recover the sample once the foam has returned to the liquid state. The test is carried out by preheating the foaming solution at 50 ° C., which makes it possible to obtain a temperature within the foam of 33 ° C. After one hour, the temperature of the foam is 30 ° C, and after two hours of 28 ° C. After 3 hours, the temperature is that of the laboratory (27 ° C) and the carbonated foam, obtained from a 1M solution, drained completely.

The sample, invisible at first because immersed in the foam, appears completely free of the deposit.

This qualitative result, very positive, motivated the introduction of two deposits of MoZr thicker about 1.2 mm thick so as to quantify the rate of dissolution on the first two hours of treatment. A deposit is removed after one hour of contact with the foam, the other after two hours. The results are summarized in Table 2 on the following page.

It appears that the mass dissolved in two hours, that is to say 0.74 g or 0.71 g, is practically double that dissolved in the first hour, ie 0.42 g (slightly lower since the average temperature on the second hour is lower than 3 ° C).

At an average temperature of the foam of 30 ° C, the dissolution rate of a deposit of 25 cm ² in contact with the foam is of the order of 0.4 g / h, that is still 0.2 mm / h compared to the 0.8 g / h obtained in the liquid phase at 30 ° C. This dissolution rate, almost constant over the first two hours, shows, as in the case of the liquid phase, that the dissolution is regular and homogeneous on the surface. It advantageously makes it possible to completely solubilize an irradiating deposit of 0.5 mm in 3 hours at 30 ° C.

This result makes it possible to envisage using, rather than a rinsing with sodium carbonate in the liquid phase, a rinsing in the foam phase according to the invention which makes it possible to reduce the amount of sodium used which is penalizing for the ultimate formation of the conditioning glasses. . <b> Table 2 </ b>: Mass Losses of a MoZr Deposition in Contact with a Static Foam Containing Sodium Carbonate (1 M) Sample Immersion time in the foam Temperature Initial deposition mass (25 cm ² ) in (g) Loss of mass during immersion time (g) 2 1 hour 1h from 33 ° C to 30 ° C 2.4 0.42 3 2 hours 1h from 33 ° C to 1h of 30 ° C
1h from 30 ° C to 28 ° C 2.49 0.74 3 1 hour extra (48 hours later) 1h from 36 ° C to 30 ° C 1.75 0.49 3 2 additional hours 2h from 35 ° C to 28 ° C 1.26 0.71

Claims (17)

1. Use of a foam prepared with an aqueous solution which comprises, per litre of solution:

   - 0.2 to 2% by weight of a foaming organic surface-active agent or of a mixture of foaming surface-active agents,

   - from 0.1 to 1.5% by weight of gelling agent and,

   - 0.2 to 7 mol of an inorganic acid or base for radioactive decontamination or of a mixture of inorganic acids or bases for radioactive decontamination,

   in a process for the radioactive decontamination of a surface.
2. Use according to Claim 1, in which the surface-active agent is a foaming non-ionic surfactant.
3. Use according to Claim 1, in which the surface-active agent is a foaming non-ionic surfactant chosen from the family of the alkylpolyglucosides or alkylpolyetherglucosides.
4. Use according to Claim 1, in which the surface-active agent is an amphoteric surfactant.
5. Use according to Claim 1, in which the surface-active agent is an amphoteric surfactant chosen from the family of the sulphobetaines, from the family of the alkyl amidopropyl hydroxysulphobetaines or from the family of the amine oxides.
6. Use according to Claim 1, in which the acid is chosen from the group consisting of hydrochloric acid, nitric acid, sulphuric acid, phosphoric acid and oxalic acid or is a mixture of acids from this group.
7. Use according to Claim 1, in which the acid is in an amount of 0.3 to 7 mol.
8. Use according to Claim 1, in which the acid is in an amount of 1 to 4 mol.
9. Use according to Claim 1, in which the base is chosen from the group consisting of sodium hydroxide, potassium hydroxide and sodium carbonate or is a mixture of bases from this group.
10. Use according to Claim 1, in which the base is in an amount of less than 2 mol.
11. Use according to Claim 1, in which the base is in an amount of 0.5 to 1.5 mol.
12. Use according to Claim 1, in which the gelling agent is a thickening organic agent exhibiting a rheological behaviour of pseudoplastic type.
13. Use according to Claim 1, in which the gelling agent is chosen from the group consisting of a water-soluble polymer, a hydrocolloid and a heteropolysaccharide or from the group consisting of cellulose derivatives.
14. Use according to Claim 1, in which the gelling agent is chosen from the group consisting of heteropolysaccharides chosen from the family of the polyglucoside polymers comprising trisaccharide branched chains; and cellulose derivatives, such as carboxymethylcellulose or a polysaccharide comprising glucose as sole monomer.
15. Use according to Claim 1, in which the gelling agent is xanthan gum.
16. Use according to Claim 1, in which the surface to be decontaminated is brought into contact with the foam for 1 to 10 hours.
17. Use according to Claim 16, additionally comprising, after the operation of bringing the surface to be decontaminated into contact with the foam, rinsing said surface using a rinsing solution.

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