EP0928489B1 - Organomineral decontamination gel and use thereof for surface decontamination - Google Patents

Description

The present invention relates to a gel organomineral decontamination usable for radioactive decontamination of surfaces, in particular of metal surfaces.

Decontamination of parts soiled by radioactive elements can be carried out either by mechanical treatments, either by treatments chemical.

Methods using mechanical treatments have the disadvantage to cause a more or less significant modification from the surface of the room and to be, moreover, difficult to implement on shaped parts complicated.

Soaking treatment methods which basically consist of training the elements radioactive attached to the workpiece surface using solutions of active decontamination agents suitable, in particular Ce (IV) stabilized in strong concentrated acid medium such as nitric acid or sulfuric, have the disadvantage of leading to the production of large volumes of effluent including further treatment, in particular by concentration, is very expensive.

Furthermore, dipping methods implementing solutions pose some problems for handling large parts dimensions that are difficult to immerse and soak completely in the reagent solution.

Decontamination solutions do not allow soaking treatment only removable metal parts of limited sizes, that is to say that these solutions cannot in practice only be used for dismantling radioactive installations.

On the other hand, on-site decontamination of radioactive installation by projection of solutions water produces large amounts of effluent radioactive for limited effectiveness due to the low contact time with parts.

It has therefore been proposed to viscose the decontamination solutions comprising an active agent by viscosifying / gelling agents, in particular by divided solids of large specific surface, small elementary particle sizes and chemically inert.

Among the solids meeting these requirements, mineral supports such as aluminas and commercially available silicas which also present a wide variety of their characteristics such as hydrophilicity, hydrophobic, pH ..... appear to be the best means of viscosing / gelling these solutions.

Spraying such gels, on the contrary solutions, can allow decontamination on large metal surfaces that are not not necessarily horizontal, but which can be also inclined or even vertical.

Decontamination gels can therefore be described as colloidal solutions comprising a generally mineral viscous agent such as alumina or silica and an active agent of decontamination, for example an acid, a base, a oxidizing agent, reducing agent or mixture of these, which is chosen notably according to the nature of contamination and surface.

Thus an alkaline gel for stainless steels and ferritics will have degreasing properties for the removal of unbound contamination.

An oxidizing gel for stainless steels will allow elimination of hot fix contamination and cold. A reducing gel will preferably be used in supplement of the oxidizing gel and alternately for dissolution of hot formed oxides for example in the primary circuit of water reactors pressurized (REP).

Finally an acid gel for ferritic steels will eliminate cold-set contamination.

The use of gels for radioactive decontamination of parts is described in particular in document FR-A-2 380 624.

In this document, we use a gel decontaminant consisting of a colloidal solution an organic or mineral compound to which we add possibly a decontaminating product such as acid hydrochloric acid, stannous chloride, oxine and / or sodium fluoride.

Although these gels work satisfactory, however they have the disadvantage to be able to remove the encrusted radioactivity only over a small thickness of the workpiece surface, for example example over a thickness of around 1µm.

Document FR-A-2 656 949 describes a gel oxidizing decontaminant which eliminates radioactive elements deposited on the part as well as the radioactive elements encrusted on its surface.

a) 8 à 25 % en poids d'un agent gélifiant minéral, de préférence à base de silice, de préférence de silice pyrogénée ou d'alumine,

b) 3 à 10 mol/l d'une base minérale ou d'un acide minéral, et

c) 0,1 à 1 mol/l d'un agent oxydant tel que Ce^IV, Co^III ou Ag^II ayant un potentiel normal d'oxydoréduction E₀ supérieur à 1400 mV/ENH (électrode normale à hydrogène) en milieu acide fort (pH<1) ou de la forme réduite de cet agent oxydant.

This decontaminating gel consists of a colloidal solution comprising:

a) 8 to 25% by weight of a mineral gelling agent, preferably based on silica, preferably fumed silica or alumina,

b) 3 to 10 mol / l of a mineral base or of a mineral acid, and

c) 0.1 to 1 mol / l of an oxidizing agent such as Ce ^IV , Co ^III or Ag ^II having a normal redox potential E ₀ greater than 1400 mV / ENH (normal hydrogen electrode) in a strong acid medium (pH <1) or the reduced form of this oxidizing agent.

In the latter case, the gel includes plus 0.1 to 1 mol / l of a compound d) capable of oxidizing the reduced form of this oxidizing agent.

In the decontaminating gel described above, the presence of components b) and c) ensures respectively the elimination of radioactive deposits formed on the workpiece surface and removing embedded radioactivity, by controlled erosion of the surface to be decontaminated.

This oxidizing gel does not, however, sufficient effectiveness with regard to the layers adherent metal oxides deposited on the surface alloys such as austenitic steels, Inconel 600 and the Incoloy.

a) 20 à 30 % en poids d'un agent gélifiant minéral, de préférence à base d'alumine,

b) 0,1 à 14 mol/l d'une base minérale, telle que NaOH ou KOH, et

c) 0,1 à 4,5 mol/l d'un agent réducteur ayant un potentiel d'oxydoréduction E₀ inférieur à -600 mV/ENH en milieu base forte (pH≥13) choisi parmi les borohydrures, les sulfites, les hydrosulfites, les sulfures, les hypophosphites, le zinc et l'hydrazine.

Document FR-A-2 695 839 therefore describes a reducing decontaminating gel which makes it possible to remove these adherent metal oxide layers and which comprises:

a) 20 to 30% by weight of a mineral gelling agent, preferably based on alumina,

b) 0.1 to 14 mol / l of a mineral base, such as NaOH or KOH, and

c) 0.1 to 4.5 mol / l of a reducing agent having a redox potential E _{0 of} less than -600 mV / ENH in a strong base medium (pH≥13) chosen from borohydrides, sulfites, hydrosulfites, sulfides, hypophosphites, zinc and hydrazine.

Applying gels to the surface, for example example the metal surface, to be decontaminated preferably by spraying, for example under a pressure which can range from 50 up to 160 bars and even beyond, the gel being agitated before spraying to make the gel homogeneous. After an adequate duration of action, the gel is rinsed with water spray, then the effluents generated are treated for example by neutralization, decantation and filtration.

The document EP-A-0 674 323 relates to a gel for radioactive decontamination of surfaces consisting of a colloidal solution comprising a gelling agent and a fibrogenic agent based on silica. This document also mentions that an acrylic copolymer can be added to the colloidal aqueous solution.

All of the gels described above, whether are alkaline, acidic, reducing or oxidizing, have the advantages already mentioned more top, like the ability to process parts of complex form, the advantages notably of easy work, of a small quantity of reagents chemicals sprayed per unit area, therefore low quantity of effluents produced by rinsing the applied gels, perfectly contact time controlled with the surface to be treated and therefore erosion control during decontamination. In furthermore, it is possible to spray the gel from a distance, the doses absorbed by the agents responsible radioactive remediation are highly decreased.

Typical gels of the prior art are marketed by FEVDI under the name of "FEVDIRAD"

All of the above gels, whether they're acids, alkalis, oxidants or reducers present also, especially with regard to gels oxidants, good corrosive power.

Unfortunately, they do not support high shear speeds imposed by the spraying which is the most classic process for applying these gels.

Indeed, all these gels containing an agent viscous mineral, in particular silica, that it is hydrophilic, hydrophobic, basic or acidic have rheological properties characterized by a thixotropic behavior; viscosity decreases under shear during the projection, then we witness a restructuring of the freeze after cessation of shear with adhesion to the surface. A rheogram in hysteresis characterizes the behavior of such fluid.

Control of this thixotropy is fundamental to allow projection and optimal adhesion of the gel to the surface to be treated. The speed of resumption of freezes, or restructuring partial or total, constitutes the primordial concept for their projection.

Indeed, restructuring means a back to gelation, therefore adhesion to the surface, and a short recovery time characterizes a gel quickly recovering sufficient viscosity after projection to avoid any sagging.

Whatever the agent charge mineral viscosity of the gels described above or currently on the market, recovery times are too long. For example, for various charges in Cab-O-Sil® M5 which is a hydrophilic fumed silica and acid marketed by the company DEGUSSA, the recovery times are always greater than 5 seconds, which is notoriously excessive.

The time to return to viscosity sufficient for the gel to adhere to the wall can be certainly decreased, but this then requires increasing significantly the mineral load.

The viscosity with stirring before projection is large and the spray becomes difficult. In addition, this increasing mineral load generates large amounts of effluent on rinsing and solid waste to be treated.

For example, at present 20 kg of gel gives, after filtration treatment of the rinsing effluents, a volume of radioactive waste corresponding to a barrel of 200 l .

There is therefore a need to improve the rheological properties of existing gels, including a gelling / viscous agent, solely based on silica or alumina, especially for obtaining shorter recovery times, thus increasing the ability of the gel to restructure while retaining systems which, under agitation, are sufficiently liquids to allow projection.

These improvements must be obtained with a reduced mineral load, preferably significantly lower than the mineral load of the gels the prior art in order to generate a volume of waste minimal solids.

Finally, these property improvements rheological must be obtained without being affected the corrosive and other qualities of these decontamination gels.

In particular, the factors of decontamination obtained must be at least identical to those of existing gels.

The object of the present invention is therefore to provide a decontamination gel that meets between others to all of the needs mentioned above.

a) un agent viscosant

b) un agent actif de décontamination

caractérisé en ce que l'agent viscosant a) comprend la combinaison d'un agent viscosant minéral et d'un agent viscosant organique (coviscosant) choisi parmi les les Ethers polyoxyéthyléniques de formule;

où n est un entier de 6 à 18 et m est un entier de 1 à 23. .According to the invention, this object and others still are achieved by an organomineral decontamination gel consisting of a colloidal solution comprising:

a) a viscous agent

b) an active decontamination agent

characterized in that the viscosity agent a) comprises the combination of an inorganic viscosity agent and of an organic viscosity agent (coviscosant) chosen from among the polyoxyethylene ethers of formula;

where n is an integer from 6 to 18 and m is an integer from 1 to 23..

According to the invention, the incorporation into viscosity agent a) decontamination gel, in addition mineral viscosity agent, viscosity agent specific organic (called coviscosant) allows so surprising, in particular, to greatly improve rheological properties of gels, and decrease significantly the mineral load of these gels without that the corrosive properties and other qualities of these gels are not affected.

Reduction in mineral load leads to a concomitant reduction in waste solid.

Decontamination factors obtained with the gels according to the invention are completely comparable or even superior to those of gels analogs of the prior art, i.e. gels comprising the same decontamination agent but without coviscosant.

The effectiveness of the decontamination agent implemented is absolutely not affected by the presence of a coviscosant in the gel according to the invention.

For example, the corrosive properties of gels called "acid oxidizing gels" according to the invention described below are in no way degraded by the addition of a coviscosant.

In addition, these gels keep their structure feature much longer and so are much easier to remove for example by rinsing, again reducing the volume of rinsing effluents.

Finally, the price of the reagents used, which are readily available, is weak, and gels according to the invention can thus be implemented at large scale and on an industrial level.

The gel according to the invention is obtained in adding component a) to an aqueous solution, that is to say a viscosifying / gelling agent which comprises the combination of a mineral viscosity agent and a organic viscosifier.

The mineral viscosity agent is generally an mineral viscosity agent which is insensitive to oxidation, resists the active decontamination constituents b), and preferably has a high specific surface, for example greater than 100 m ² / g.

Incorporation into the viscosity agent a) of an organic viscosifier according to the invention allows, thanks to a synergistic effect between the two viscosants (mineral viscosifier and coviscosant), dramatically reduce the agent content mineral viscosant necessary for training a gel with sufficient viscosity to ability to maintain a layer on the surface of a part which is not necessarily horizontal and which can be optionally vertical or tilted.

Generally, it is preferred that the gel has a viscosity of 10 ^-3 to 10 ^-1 Pa.sec, preferably 10 ^-2 Pa.sec at the time of use, that is to say under high shear to be able easily apply it to the surface of a part, for example by spraying with a spray gun.

According to the invention and unlike gels of the prior art whose viscosity agent comprises only a mineral viscosifier, the content of this mineral viscosity agent can generally be lowered for example to less than 20% by weight, for example still from 1 to 15% by weight, preferably from 1 to 8% by weight, more preferably from 1 to 7% by weight, for example from 4 to 6% by weight, in particular 5% in weight.

In the case of alumina, the content of mineral viscosity agent can be lowered for example up to 1 to 15% by weight, preferably 1 to 8% by weight, more preferably from 1 to 7% by weight, per example from 4 to 6% by weight, in particular 5% by weight of the solution.

In the case of silica, the content of mineral viscosity agent can represent for example less than 8%, for example from 1 to 7% and generally 4 to 6%, for example 5% by weight of the solution.

This content is given only for indicative and depends in particular on the viscosity agent mineral and the active decontamination agent used.

For an analogous gel, the mineral load of gel according to the invention is always greatly reduced compared to the equivalent gel comprising only one agent viscous mineral.

The mineral viscosifier / gelling agent can be based on alumina Al ₂ O ₃ and it can be obtained by hydrolysis at high temperature. By way of example of a viscous / gelling mineral agent which can be used, mention may be made of the product sold under the trade designation "Alumina C".

The mineral viscosifier / gelling agent can also be based on silica; this silica can be hydrophilic, hydrophobic, basic like silica marketed under the name "Tixosil 73" by the Company RHONE-POULENC or acid such as silicas marketed under the names of "TIXOSIL 331" and "TIXOSIL 38AB" by the company RHÔNE-POULENC.

Among the acidic silicas, mention may be made of silicas in liquid form sold under the names of "SNOWTEX O" and "SNOWTEX OL" by the Company Nissan Chemical Industries, and silicas marketed under the general name of "Cab-O-Sil" by Degussa Company such as "Cab-O-Sil" silicas M5 "Cab-O-Sil" H5 and "Cab-O-Sil" EH5.

Among these silicas, pyrogenic silica "Cab-O-Sil" hydrophilic and acidic M5 with a specific surface of 200 m ² / g, is preferred and gives the best results: that is to say maximum viscous properties for a minimum mineral charge, in particular when it is used in so-called "oxidizing gels".

According to an essential characteristic of the invention, the viscosity agent a) further comprises the mineral viscosity agent described above an agent specific organic viscosant.

This organic viscosity agent, again called "coviscosant" is chosen from among polyoxyethyethylene ethers responding to the formula given above.

This coviscosant must meet a number of conditions related in particular to its use in nuclear installations.

It must not contain sulfur or halogen, it must participate at least in the charge overall organic, good resistance in the presence of active decontamination agents a): for example a good resistance in acid and / or oxidizing medium. he must also be insensitive to the ionic strength of the medium, be thermally stable in the range of temperature generally from 0 to 50 ° C. Finally, he must have a good affinity for the viscosity agent mineral, in particular for silica.

Specific surfactants included in the agent viscosant a) according to the invention meet the conditions mentioned above.

According to the invention, it has also been demonstrated that, surprisingly, the surfactants of the family of polyoxyethylene ethers of formula: CH ₃ - (CH ₂ ) _n-1 - (O - CH ₂ - CH ₂ ) _m - OH also called C _n E _m , fulfilled the required criteria, that is to say among other things a great affinity for mineral particles, in particular silica, and a great chemical inertness and sufficient stability in particular in very acidic environments, very oxidizing and electrolytically strong like decontamination gels.

Even in very small quantities, these surfactants are capable of building the three-dimensional network of a thixotropic gel.

Without wishing to be bound by any theory, it seems that could be involved simultaneously interactions between silica particles and head polar on the one hand and aliphatic chains hydrophobic between them on the other hand.

In the above formula, n defines the length of the aliphatic chain and is an integer which can vary from 6 to 18, preferably from 6 to 12, m controls the size of the polar head and is an integer which can vary from 1 to 23, preferably from 2 to 6.

Among these surfactants, the compounds C ₆ E ₂ (hexyl ether of di (ethylene glycol)), C ₁₀ E ₃ and C ₁₂ E ₄ are preferred.

Such compounds C _n E _m are available from the companies ALDRICH and SEPPIC.

The nature of the surfactant depends on the type of decontamination gel used, i.e. the nature and content of the active agent decontamination b) and the nature and content of the mineral viscosity agent.

Thus, the compounds C _n E _m are particularly suitable for use in acid oxidizing gels comprising silica.

Likewise, the surfactant content depends on the nature of the decontamination gel as well as the concentration and nature of the viscosity agent mineral.

This surfactant content will be generally between 0.1 and 5% by weight, preferably between 0.2 and 2% by weight, preferably still between 0.5 and 1% by weight.

The viscosity agent a) according to the invention can be used in any decontamination gel whatever either the type of it, that is to say whatever the active decontamination agent b) used in decontamination gel.

It can, in particular, be used at the place of the exclusively mineral viscous agent used works in any of the decontamination gels of the prior art such as those described for example in documents FR-A-2 380 624; FR-A-2 656 949 and FR-A 2 695 839.

We have seen that decontamination gels are of different natures depending on the active agent of decontamination b) they contain; we distinguish in general so-called alkaline gels, acid gels, reducing gels and oxidizing salts.

Thus, the decontamination gel according to the invention may contain as active agent decontamination b) an acid, preferably an acid mineral preferably chosen from acid hydrochloric, nitric acid, sulfuric acid, phosphoric acid and their mixtures.

The acid is usually present at a concentration from 1 to 10 mol / l, preferably from 3 to 10 mol / l.

Such a gel called "acid gel" is particularly suitable for eliminating contamination cold-set on ferritic steels.

In this type of acid gel, the agent mineral viscosity is preferably silica and coviscosant is an ether polyoxyethylene.

The decontamination gel according to the invention may also contain as an active agent decontamination b), a base preferably a base mineral preferably chosen from soda, potash and their mixtures.

The base is usually present at a concentration from 0.1 to 14 mol / l.

Such a gel called "alkaline gel" presents interesting degreasing properties and is particularly suitable for eliminating contamination not fixed on stainless and ferritic acids.

In this type of alkaline gel, the agent mineral viscosity is preferably alumina.

The decontamination gel according to the invention may also contain as active decontamination agent b) a reducing agent, this reducing agent may for example be a reducing agent such as that described in document FR-A-2 695 839 in which the reducing agent used is a reducing agent having a normal redox potential E ₀ less than -600 mV / ENH (normal hydrogen electrode) in a strong base medium (pH≥13).

As an example of such agents reducing agents, there may be mentioned borohydrides, sulfites, hydrosulfites, sulfides, hypophosphites, zinc, hydrazine and their mixtures.

When using borohydrides, sulfites, sulfides, hydrosulfites or hypophosphites, these are usually in the form of salts metallic, for example of alkali metal salts such as sodium.

When the reducing agent is used sodium borohydride, the pH of the colloidal solution is preferably greater than or equal to 14 so that the borohydride remains stable.

Reducing agents as described in document FR-A-2 695 839 are generally associated with a mineral base such as NaOH or KOH to a concentration generally between 0.1 and 14 mol / l, the concentration of reducing agent being, as to it, generally between 0.1 and 4.5 mol / l.

In such a reducing gel the viscosity agent mineral is rather based on alumina.

Such a gel called "reducing gel" is in general used in addition to and alternating with a gel oxidant as described below.

Such a gel makes it possible in particular to weaken and move the metal oxide layers adherent superficies which have been deposited hot on the surface of alloys such as steels austenitic stainless steels, the Inconel and the Incoloy which form the primary circuits of water reactors pressurized (REP) that are not sensitive to action oxidizing decontaminating gels.

The decontamination gel according to the invention may still contain, as an active agent of decontamination b), an oxidizing agent.

This oxidizing agent can for example be a oxidizing agent such as that described in document FR-A-2 659,949 in which the oxidizing agent used is a oxidizing agent which must have normal potential oxidation-reduction higher than 1400 mV / ENH in medium strong acid (pH <1), i.e. an oxidizing power higher than that of permanganate.

By way of example of such oxidizing agents, mention may be made of Ce ^IV , Co ^III and Ag ^II and their mixtures.

In fact, the potentials of the redox couples corresponding to these oxidizing agents have the following values: Ce ^III / Ce ^IV Eo / ENH = 1610 mV Co ^II / Co ^III Eo / ENH = 1820 mV Ag ^{I /} Ag ^II Eo / ENH = 1920 mV

The use of these oxidizing agents powerful particularly suitable when the surface to be decontaminate is a metallic surface, for example by noble alloy, such as stainless steel 304 and 316L, the Inconel and the Incolloy.

In addition, these oxidizing agents can also oxidize certain poorly soluble colloidal oxides such as PuO ₂ to transform them into a soluble form such as PuO ₂ ²⁺ .

In the decontaminating gel of the invention, one can also use the oxidizing agent in its reduced form, for example one can use Ce ^III , Co ^II , Ag ^I , on condition of adding to the gel a compound capable of oxidizing this reduced form, or on condition that the gel is combined with another gel or with another colloidal solution containing a compound capable of oxidizing this reduced form of the oxidizing agent.

The compound capable of oxidizing the form reduced oxidizing agent can consist of for example with an alkali metal persulfate.

Oxidizing agents, of which Cerium (IV) is preferred, are generally associated, with a mineral base, or for stabilization purposes, with a mineral acid such as HCl, H ₃ PO ₄ , H ₂ SO ₄ and preferably HNO ₃ at a concentration generally between 1 and 10 mol / l, preferably from 3 to 10 mol / l, more preferably from 2 to 3 mol / l, for example 2.88 mol / l, the concentration of oxidizing agent being, for its part, generally between 0.1 and 2 mol / l, preferably between 0.6 and 1.5 mol / l, more preferably this concentration is 1 mol / l.

When an oxidizing cation such as Ce ^IV , Ag ^II or Co ^{III is} used as the oxidizing agent, this can be introduced in the form of one of its salts such as nitrate, sulfate or the like, but it can also be electrogenerated .

Preferred oxidizing gels contain cerium (IV) in the form of electrogenerated cerium (IV) nitrate Ce (NO ₃ ) ₄ or hexanitrato diammonium cerate (NH ₄ ) ₂ Ce (NO ₃ ) ₆ , the latter being preferred due to the relative instability of cerium (IV) nitrate in concentrated nitric medium.

Nitric acid stabilizes the cerium at oxidation state IV, participates in corrosion and ensures, among other things, the maintenance in solution of corroded species, namely complex oxo-nitrato transition metals constituting the alloy metallic.

Such gels contain, for example, the mineral viscous agent, preferably silica such as "Cab-O-Sil" M5 at a concentration preferably of between 4 and 6% by weight, for example 5% by weight, and l organic viscosifying agent, which is a polyoxyethylene ether, for example of the C ₆ E ₂ , C ₁₀ E ₃ or C ₁₂ E _{4 type} at a concentration preferably between 0.2 and 2% by weight, for example 1% by weight .

• 0,6 à 1,5 mol/l de préférence 1 mol/l de (NH₄)₂ Ce(NO₃)₆ ou de Ce(NO₃)₄,
• 2 à 3 mol/l, de préférence 2,88 mol/l de HNO₃,
• 4 à 6 % en poids, de préférence 5 % en poids de silice,
• 0,2 à 2 % en poids, de préférence 1 % en poids d'un éther polyoxyéthylénique.

Thus a typical example of an oxidizing decontamination gel according to the invention consists of a colloidal solution comprising:

• 0.6 to 1.5 mol / l preferably 1 mol / l of (NH ₄ ) ₂ Ce (NO ₃ ) ₆ or Ce (NO ₃ ) ₄ ,
• 2 to 3 mol / l, preferably 2.88 mol / l of HNO ₃ ,
• 4 to 6% by weight, preferably 5% by weight of silica,
• 0.2 to 2% by weight, preferably 1% by weight of a polyoxyethylene ether.

The decontaminating gels described above can be used especially for the decontamination of metal surfaces and this, too well as part of periodic maintenance existing installations, only dismantling nuclear facilities.

The gels according to the invention can be used for example to decontaminate tanks, fuel storage pools, glove boxes etc.

The subject of the invention is also a method for decontaminating a metal surface, which includes applying it to the surface to decontaminate a decontaminating gel according to the invention, maintaining this gel on the surface for a period sufficient to carry out the decontamination, this duration ranging for example from 10 min. at 24 hrs, from preferably from 30 min to 10 h, and more preferably from 2 to 5 hours, and removing this gel from the surface metallic thus treated for example by rinsing or by mechanical action.

The amounts of gel deposited on the surface to be decontaminated are generally from 100 to 2000 g / m ² , preferably from 100 to 1000 g / m ² , more preferably from 200 to 800 g / m ² .

Obviously we can repeat the treatment several times each time using the same gel or gels of different natures during different successive stages, each of these stages including applying a gel, maintaining the gel on the surface and removing the gel from the surface, for example by rinsing or mechanical action.

Similarly, the treatment can be repeated on the entire surface to be treated or on a part only of it having for example a form complex, or depending on the activity of the surface (mRad / h) at certain particular points thereof requiring intensive treatment.

One can also perform, in particular before the first application of the gel, one or more rinsing of surfaces to be decontaminated with water or an aqueous solution, preferably under strong pressure, to sanitize and / or degrease the surface to be treated.

1) appliquer sur la surface à décontaminer un gel décontaminant réducteur conforme à l'invention, maintenir ce gel sur la surface pendant une durée allant de 10 min à 5 h et rincer la surface métallique pour éliminer ce gel réducteur, et

2) appliquer sur la surface ainsi traitée, un gel oxydant en milieu acide, maintenir ce gel sur la surface pendant une durée allant de 30 min à 5 h et rincer la surface métallique ainsi traitée pour éliminer ce gel oxydant.

For example, the decontamination process may include the following successive steps as described in document FR-A-2 695 839:

1) apply a reducing decontaminating gel according to the invention to the surface to be decontaminated, maintain this gel on the surface for a period ranging from 10 min to 5 h and rinse the metal surface to remove this reducing gel, and

2) apply to the surface thus treated, an oxidizing gel in an acid medium, maintain this gel on the surface for a period ranging from 30 min to 5 h and rinse the metal surface thus treated to remove this oxidizing gel.

• projection sur la surface à décontaminer d'une solution de soude pendant une durée, par exemple de 30 minutes,
• rinçage à l'eau,
• application sur la surface ainsi traitée d'un gel oxydant en milieu acide et son maintien sur la surface pendant une durée de 30 minutes à 5 heures, de préférence pendant deux heures,
• rinçage à l'eau.

Or the decontamination process may include the following steps:

• spraying onto the surface to be decontaminated with a sodium hydroxide solution for a period of time, for example 30 minutes,
• rinsing with water,
• application to the surface thus treated of an oxidizing gel in an acid medium and its maintenance on the surface for a period of 30 minutes to 5 hours, preferably for two hours,
• rinse with water.

Contact time can vary between wide limits and also depends on the nature of the active decontamination agent and the nature of the "coviscosing" agent. As an example for a gel acid oxidant comprising a surfactant such as co-occurring, the contact time is preferably 30 min to 5 hours, more preferably 2 to 5 hours.

For a reducing gel, the contact time will preferably be 10 minutes to 5 hours.

The application of the gel to the metal surface to be decontaminated can be carried out by conventional methods, for example by spraying with a spray gun, by soaking and draining, by packaging or even by means of a brush. Preferably, the gel is applied by spraying / spraying with a spray gun, for example under a pressure (Airless compressor) at the level of the injector ranging from 10 to 200 kg / cm ² for example, from 10 to 160 kg / cm ² , again for example from 50 to 100 kg / cm ² .

The gel can be removed, preferably by rinsing of the treated surface, you can also eliminate it by other means, for example mechanical or by a jet of gas, for example compressed air.

To carry out the rinsing, we use usually demineralized water or a solution aqueous in which the gel used can be dissolved or in which it can form a film detachable and drivable by water.

The rinsing can be carried out under pressure, that is to say at a pressure for example from 10 to 160 kg / cm ² .

According to a particularly advantageous characteristic of the invention, and of the fact that the gels according to the invention, comprising the combination of an inorganic viscous agent such as silica, and an organic viscous agent described above, keep for a period prolonged, up to 48 hours or more, their gel texture, rinsing the surface is much easier, can be done at low pressure for example 15 kg / cm ² , or even without pressure and requires a reduced amount demineralized or other water, for example less than 10 liters / m ² .

The number of rinsing treatments (or passes) during a decontamination operation, after which defined contents of the mineral load of the effluents (for example the contents of SiO ₂ and Al ₂ O ₃ in. fuel storage during decontamination) are reached, is reduced, since the gel according to the invention contains less mineral filler.

Again, thanks to the invention, the quantity of effluent generated defined in particular by the volume of rinsing effluents is greatly reduced.

On the contrary, gels without coviscosants organic, without surfactant, art including only for example silica, become after application, and in a while relatively short, dry and cracked, their rinsing is very difficult and requires a high amount of water under strong pressure. Therefore large quantities liquid effluents are generated.

The rinsing effluents are then treated adequately for example they can be neutralized, for example by soda in the case where an acid gel has been used.

The effluents are then generally subjected to solid-liquid separation, for example by filtration with a cartridge filter to give on the one hand liquid effluents, and on the other hand solid waste of which the quantity is extremely reduced due to the low mineral load of the gels according to the invention.

So the mineral load of gels according to the invention, being reduced for example by a factor of 3 to 4 compared to the gels of the prior art comprising only a mineral viscous agent, waste solids retained for example on filters are also reduced by a similar factor, for example 3 to 4.

In some cases, the amount of charge mineral in the gel according to the invention is even if low, that it makes it possible to transfer the effluents from rinsing to an evaporator without any treatment prior.

The decontaminating gels of the invention can be prepared in a simple way, for example by adding to an aqueous solution of component b), that is to say the active decontamination agent, viscosity agent a). Generally, we add the agent mineral viscosity agent such as silica before the agent organic viscosant (coviscosant).

The gels according to the invention generally have a very long storage period, however the inertia chemical of some surfactants although good is limited in time, for example in the presence of a oxidant such as Ce (IV).

The high solubility of these surfactants induces rapid homogenization during their incorporation into the gel. Their introduction into the solution should preferably be done shortly before using gels for efficiency optimal.

• la figure 1 illustre la viscosité (exprimée en Pa.sec.) en fonction du temps de reprise (en sec.) de divers gels représentant l'art antérieur, dont l'agent viscosant comprend uniquement du "Cab-O-Sil" M5 à des teneurs respectives en poids de 6 % (courbe en trait plein), de 8 % (courbe en trait pointille), de 10 % (courbe en tirets) et enfin de 12 % (courbe en trait mixte),
• la figure 2 illustre la viscosité (exprimée en Pa.sec) en fonction du temps de reprise (en sec.) de divers gels dont l'agent viscosant comprend respectivement la combinaison de "Cab-O-Sil" à 6 % en poids et de Texipol (1 %) (courbe en trait pointillé), selon l'invention de "Cab-O-Sil" à 5 % en poids et de C₁₂E₄ (1 %) (courbe en tirets), selon l'invention de "Cab-O-Sil" à 5 % en poids et de C₁₀E₃ (1 %) (courbe en trait mixte), et selon l'invention de "Cab-O-Sil" à 5 % en poids et de C₆E₂ (1 %) (courbe du haut en trait plein).

Other characteristics and advantages of the invention will appear better on reading the following examples given, of course, by way of illustration and not limitation with reference to the accompanying drawings in which:

• FIG. 1 illustrates the viscosity (expressed in Pa.sec.) as a function of the recovery time (in sec.) of various gels representing the prior art, the viscosity agent of which comprises only "Cab-O-Sil" M5 at respective contents by weight of 6% (solid line curve), 8% (dotted line curve), 10% (dashed curve) and finally 12% (dashed line curve),
• FIG. 2 illustrates the viscosity (expressed in Pa.sec) as a function of the recovery time (in sec.) of various gels whose viscosity agent comprises respectively the combination of "Cab-O-Sil" at 6% by weight and Texipol (1%) (dashed line curve), according to the invention of "Cab-O-Sil" at 5% by weight and C ₁₂ E ₄ (1%) (dashed curve), according to the invention of "Cab-O-Sil" at 5% by weight and of C ₁₀ E ₃ (1%) (dashed line curve), and according to the invention of "Cab-O-Sil" at 5% by weight and of C ₆ E ₂ (1%) (top curve in solid line).

We also represented the curve giving the viscosity as a function of the gel recovery time including only 10% of "Cab-O-Sil" as viscosity agent (bottom curve in solid line).

EXAMPLE 1

The rheological properties of aqueous gels representing the prior art by measuring their viscosity at different times, time 0 corresponding to the moment when the gel is sprayed.

The results are shown in the figure 1 which represents the curves giving the viscosity in function of recovery time for gels whose agent viscosant includes only a viscosifier mineral: namely "Cab-O-Sil" M5 silica, at contents of 6%, 8%, 10% and 12% respectively.

We notice that whatever the load in "Cab-O-Sil" M5 of these gels, recovery times always exceed 5 seconds and are therefore many too long, even with high concentrations of silica.

EXAMPLE 2

The rheological properties of gels according to the invention by measuring their viscosity at different times, time 0 corresponding to the moment the frost is projected.

The results have been plotted in FIG. 2 which represents the curves giving the viscosity as a function of the recovery time for gels of which the viscosity agent comprises the combination of an inorganic viscosity agent (silica "Cab-O-Sil") and a surfactant according to the invention ("C ₆ E ₂ ", "C ₁₀ E ₃ " or "C ₁₂ E ₄ "); or of a polymer ("Texipol") each time at 1% by weight.

We have also shown in FIG. 2, for comparison, the curve already plotted on the Figure 1 and giving the viscosity as a function of time resumption of a gel comprising only 10% of "Cab-O-Sil" as viscosity agent.

The curves in Figure 2 show the spectacular evolution of the characteristics rheological of the different gels prepared according to the invention. Low viscosity under high shear (t = 0) of the gels according to the invention remains below the gels of the prior art of FIG. 1 and less than 0.1 Pa.sec.

Gels prepared with combinations viscosifiers according to the invention are therefore, under agitation, and like the gels of the prior art, sufficiently liquid to allow projection.

But, moreover, all the gels prepared with the combination of viscosifiers according to the invention have an ability to restructure which is increased in spectacular, surprising proportions, and totally unexpected.

The viscosity at rest of all gels prepared according to the invention with a combination of agent viscous silica type and "coviscosing" agent surfactant is greatly increased even for very low concentrations (1%) by surfacting.

Thus, the viscosity at rest of a gel according to the invention such as the gel, prepared with a viscosifying agent comprising 5% by weight of "Cab-O-Sil" and 1% by weight of surfactant C ₆ E ₂ is multiplied by up to 50 to reach 20 to 25 Pa.s.

The curves in Figure 2 show also that the gel recovery times according to the invention are extremely reduced and that the restructuring of the gels according to the invention is almost instantaneous ensuring almost grip immediate to the treated surface.

Improvement of rheological properties gels according to the invention due to the incorporation into the gel of a specific organic viscosity agent (co-viscosity) in addition to the mineral viscosity agent will along with a significant decrease in the concentration of mineral viscosity agent. Gels according to the invention incorporating quantities also low than 5% by weight of silica have rheological properties greatly improved by compared to prior art gels incorporating the same amount of silica, but without organic coviscosant.

We can therefore speak of a real effect synergistic between, on the one hand, the mineral viscous agent and on the other hand the coviscosant.

If you want to prepare gels according to the invention having properties analogous to those of gels of the prior art without coviscosant, one could actually lower the viscosity agent concentration mineral such as silica up to less than 1%, or even "even less than 0.1% by weight.

The gels according to the invention therefore generate makes their mineral load significantly less large, less waste.

EXAMPLE 3

This example relates to the implementation oxidizing gels which include title of active decontamination agent, an agent oxidant which is Cerium (IV) and as an agent organic viscosant (coviscosant) of ethers polyoxyethylene according to the invention; or a water-soluble polymer.

Corrosion tests were carried out, inactive, i.e. in the absence of contamination radioactive on metallic steel plates austenitic stainless type 316L: This is a iron-based stainless steel (70%), chromium (17%), nickel (11%) and molybdenum (2%).

• 370 g d'hexanitrato cérate de diammonium (NH₄)₂ Ce(NO₃)₆ fourni par la Société Aldrich), soit une concentration de 1 mol/l.
• 105 ml d'acide nitrique à 65 % fourni par la Société Aldrich, soit une concentration en HNO₃ de 2,88 mol/l,
• 50 g ou 60 g de "Cab-O-Sil" M5 fournis par la Société Degussa soit une concentration en silice de 5 % ou 6 % en poids selon les gels.
• 10 g de TEXIPOL 63-510 fourni par la Société SCOTT BADER, soit une concentration de 1 % en poids,

ou bien, conformément à l'invention, selon les gels 10 g d'éther polyoxyéthylénique de type C₆E₂ éther hexylique du diéthylène glycol fourni par la Société Aldrich, ou C₁₀E₃ fourni par la Société SEPPIC, ou C₁₂E₄ (appelé "BRIJ 30") fourni par la Société Aldrich. La concentration en surfactant est donc de 1 % en poids.The gels tested are prepared by adding to demineralized water, to prepare one kg of gel:

• 370 g of diammonium hexanitrato cerate (NH ₄ ) ₂ Ce (NO ₃ ) ₆ supplied by the company Aldrich), ie a concentration of 1 mol / l.
• 105 ml of 65% nitric acid supplied by the Aldrich Company, i.e. an HNO ₃ concentration of 2.88 mol / l,
• 50 g or 60 g of "Cab-O-Sil" M5 supplied by the Degussa Company, ie a silica concentration of 5% or 6% by weight depending on the gels.
• 10 g of TEXIPOL 63-510 supplied by the company SCOTT BADER, ie a concentration of 1% by weight,

or, in accordance with the invention, according to the gels 10 g of polyoxyethylene ether of type C ₆ E ₂ hexyl ether of diethylene glycol supplied by the company Aldrich, or C ₁₀ E ₃ supplied by the company SEPPIC, or C ₁₂ E ₄ (called "BRIJ 30") supplied by the Aldrich Company. The surfactant concentration is therefore 1% by weight.

The gels prepared are applied to the steel plates to be treated over a thickness of 1 mm, ie 1 kg of gel per m ² of surface to be treated.

The effect of corrosion is checked by weighing.

The amount of cerium used in this example, i.e. 1 mol / liter, removes steel plate on average 1 micron in one hour for a gel thickness of approximately 1 mm.

The following table I specifies the quantities of material removed from a new stainless steel plate of type 316L with different gels for a concentration of cerium (IV) 1M.

The amount of alloy corroded depends essentially the amount of cerium (IV) in the frost, so it's completely normal that all of these values are comparable.

These results show that the presence of a specific surfactant in the oxidizing gel in accordance with the invention does not hinder the diffusion species dissolved in these gelled media.

EXAMPLE 4

• (NH₄)₂Ce(NO₃)₆1M,
• HNO₃ 2,88M,
• SiO₂ "Cab-O-Sil" M5 5% en poids,
• Ethers Polyoxyéthyléniques de type C₆E₂, C₁₀E₃ ou C₁₂E₄ à 1% en poids.

Corrosion tests are carried out under the same conditions as Example 3 on metal plates of type 316L. The gels tested have the following formulation:

• (NH ₄ ) ₂ Ce (NO ₃ ) ₆ 1M,
• HNO ₃ 2.88M,
• SiO ₂ "Cab-O-Sil" M5 5% by weight,
• Polyoxyethylenic ethers of type C ₆ E ₂ , C ₁₀ E ₃ or C ₁₂ E ₄ at 1% by weight.

For comparison, a weakly oxidizing gel viscous comprising as active agent hexanitrato 1M diammonium cerate, 2.88M nitric acid and as viscosity agent 8% by weight of "Cab-O-Sil" M5, and without coviscosant was tested in parallel.

Note that the bad properties rheological of this gel of the prior art make it improjetable.

The thickness of gel applied is approximately 1mm, i.e. 1kg of gel per m ² of surface to be treated. The effect of corrosion is checked by weighing.

The following Table II specifies the quantities of material removed from a naturally passivated commercial type 316L stainless steel plate.

• 0,4 µm en 1 heure,
• 0,9 µm en 2 heures,
• 1,2 µm en 5 et 24 heures.

The corrosion data indicated in Table II show that whatever the type of gel used, the generalized erosion is, for 1.1 kg of gel per m ² , almost identical and on average:

• 0.4 µm in 1 hour,
• 0.9 µm in 2 hours,
• 1.2 µm in 5 and 24 hours.

• Ech. 4, sans surfactant : après 5 comme 24 heures de contact, le "gel" a conservé sa couleur orange, caractéristique de la présence d'espèces Ce(IV). Au bout de 24 heures, il est complètement sec et craquelé, le rinçage de la plaque est difficile : elle présente une surface d'aspect "marbrée".
• Ech. 8, C₆E₂ 1% : Après 5 heures de contact, le gel a perdu toute coloration, si ce n'est une légère teinte bleue, certainement due à la présence d'oxydes ou d'oxonitrato complexes de métaux de transition. Après 24 heures et malgré une perte de 25 % de son poids, il conserve la texture d'un gel, et le nettoyage de la plaque est beaucoup plus facile que pour le gel sans surfactant et nécessite moins de 10 litres d'eau/m² à faible pression.
• Ech. 12, C₁₀E₃ 1% et éch. 16, C₁₂E₄ 1% : Au bout de 24 heures, les gels présentent quelques résidus de coloration jaune, ils ne sont pas craquelés malgré une perte de 27% de leur poids. Ils conservent la texture d'un gel, et leur rinçage demeure aisé.

The following remarks can be made about the state of the gels after 5 and 24 hours of contact:

• Ech. 4, without surfactant : after 5 as 24 hours of contact, the "gel" has retained its orange color, characteristic of the presence of Ce (IV) species. After 24 hours, it is completely dry and cracked, rinsing the plate is difficult: it has a "marbled" appearance surface.
• Ech. 8, C ₆ E ₂ 1% : After 5 hours of contact, the gel has lost all color, if not a slight blue tint, certainly due to the presence of oxides or oxonitrato complexes of transition metals. After 24 hours and despite a loss of 25% of its weight, it retains the texture of a gel, and the cleaning of the plate is much easier than for the gel without surfactant and requires less than 10 liters of water / m ² at low pressure.
• Ech. 12, C ₁₀ E ₃ 1% and ec. 16, C ₁₂ E ₄ 1% : After 24 hours, the gels have some residues of yellow coloring, they are not cracked despite a loss of 27% of their weight. They retain the texture of a gel, and rinsing remains easy.

• dans le gel sans surfactant, 24 heures de contact ne permettent pas la consommation totale de Ce(IV) même si les valeurs de corrosion sont importantes. De plus, des problèmes de rinçage apparaissent.
• dès 5 heures, la perte de la couleur orange du gel avec surfactant indique la réduction "totale" de Ce(IV) en Ce(III).

It follows from all of these results that:

• in the gel without surfactant, 24 hours of contact do not allow the total consumption of Ce (IV) even if the corrosion values are high. In addition, flushing problems appear.
• after 5 hours, the loss of the orange color of the gel with surfactant indicates the "total" reduction of Ce (IV) to Ce (III).

The corrosion stop, after this time of application, is moreover confirmed by the values generalized erosion. It therefore seems pointless to extend contact beyond 5 hours.

• la différence de couleur après 5 heures d'attaque entre les gels avec (incolore) et sans surfactant (orange) pour une corrosion identique, nous indique qu'une partie du Ce(IV) oxyde le surfactant. Cela est un avantage pour limiter la DCO des effluents par dégradation du surfactant. Ce point particulier est développé plus loin.

In addition, the gels with surfactants are all easily rinsable with a lesser amount of water, that is to say less than 10 liters / m ² at low pressure,

• the difference in color after 5 hours of attack between the gels with (colorless) and without surfactant (orange) for identical corrosion, indicates that part of the Ce (IV) oxidizes the surfactant. This is an advantage for limiting the COD of the effluents by degradation of the surfactant. This particular point is developed further.

Note: A second attack on sample # 5 with the same amount of gel showed corrosion of 0.9 µm, while 0.4 µm had been removed within an hour during the first application. So, once the passivation layer due to natural oxidation, widespread erosion occurs around 1 µm in one hour, in accordance with Example 3 above.

Four successive attacks, on the same plate then showed corrosion of: 0.9 - 1-1.1 and 0.9 µm. The same results are obtained whether the type of gel, with or without surfactant.

EXAMPLE 5

This example relates to the use of oxidizing gels according to the invention comprising, as mineral viscosifying agent, silica "Cab-O-Sil" at 5 or 6% by weight; as an organic viscosifying agent (coviscosant) of C ₆ E ₂ at 0.7 or 1% by weight, and as an oxidizing agent for hexa nitrato diammonium cerate at 1 mol / l and HNO ₃ to 2 , 88 mol / l.

Conditions for applying gels are the same as for examples 3 and 4 above, but the corrosion tests are carried out on oxidized 316L type plates.

Samples were prepared by heating in the oven at 600 ° C under air flow, plates similar to those of Examples 3 and 4, according to the method described W.N. Rankin in "Decontamination processes for waste glass canisters. Nuclear technology, vol. 59, 1982 ".

This heat treatment generates on the surface stainless alloys a layer of oxide of composition, thickness and morphology comparable to that likely to be on the surface of steels to decontaminate.

Table III below specifies the quantities of material removed from 316L stainless steel plates with different gels. The plates having been oxidized by 4 days of heating at 600 ° C. (the oxide layer is uniform). Ech. coviscosant Cab-O-Sil mineral filler
% in weight Amount of gel kg / m ² duration
h Corrosion
microns 20 without surfactant 8 1.11 2 1.6 21 without surfactant 8 1.11 5 2.2 22 without surfactant 8 1.11 24 2.6 23 C ₆ E ₂ 1% 5 1.07 2 0.6 24 C ₆ E ₂ 1% 5 1.09 5 1.4 25 C ₆ E ₂ 1% 5 1.11 24 2.3

The following Table IV specifies the quantities of material removed from 316L stainless steel plates. The plates having been oxidized by 2 days of heating at 600 ° C., the oxide layer is not uniform on the surface of the plate:

Examples 3 to 5 above show that besides the unexpected improvement of .properties rheological and the reduction of the mineral load obtained by using a co-viscous agent in a gel oxidant according to the invention, the presence of surfactant does not very moderately limits the corrosive power of gels, only a small part of Ce (IV) is indeed consumed by the surfactant.

During corrosion, unlike frost without surfactant, the gel structure is preserved, ensuring better dissemination of species both corrosive than corroded. In addition, rinsing is ease.

In addition, gel corrosion changes little the condition and surface composition of the plates.

The following examples show examples of application of the gels according to the invention and of the gels existing.

EXAMPLE 6

In this example, decontamination is carried out by the method according to the invention of a 316 m stainless steel tank of 50 m ³ , that is to say which has a surface to be decontaminated of 120 m ² .

• "Cab-O-Sil" M5 :   5 %
• coviscosant (étherpolyéthylénique "C₆E₂") :   1 %
• CeIV :   0,5 M
• HNO₃ :   10 M

An acid oxidizing gel according to the invention is used having the following composition:

• "Cab-O-Sil" M5: 5%
• coviscosant (polyethylene ether "C ₆ E ₂ "): 1%
• CeIV: 0.5 M
• HNO ₃ : 10 M

• projection sur la surface de la cuve d'une solution de soude maintenue sur la surface pendant une durée de 2 heures,
• rinçage à l'eau,
• projection au pistolet à une pression de 15 kg/cm² du gel oxydant acide selon l'invention décrit plus haut de façon à en déposer 1 kg/m² de surface, et maintien de ce gel sur la surface pendant une durée de 12 heures,
• rinçage à l'eau à basse pression à savoir environ 15 kg/cm²,
• projection d'une deuxième passe du gel dans les mêmes conditions que ci-dessus, à savoir 1 kg/m² de surface et une durée d'application de 2 heures,
• rinçage à l'eau à basse pression à savoir environ 15 kg/cm².

The decontamination treatment includes the following stages:

• spraying onto the surface of the tank of a sodium hydroxide solution maintained on the surface for a period of 2 hours,
• rinsing with water,
• spraying with a spray gun at a pressure of 15 kg / cm ² of the acid oxidizing gel according to the invention described above so as to deposit 1 kg / m ² of surface, and maintaining this gel on the surface for a period of 12 hours ,
• rinsing with water at low pressure, namely around 15 kg / cm ² ,
• spraying of a second pass of the gel under the same conditions as above, namely 1 kg / m ² of surface and a duration of application of 2 hours,
• rinsing with water at low pressure, i.e. approximately 15 kg / cm ² .

We determined before and after the treatment, the dose rate of the surface.

The initial dose rate of the surface was 557 mRad / h and its final dose rate was 4 mRad / h.

We also determined the FD decontamination which corresponds to the flow ratio of initial dose over the final dose rate and which is about 140.

EXAMPLE 7 (COMPARATIVE)

• "Cab-O-Sil" M5 :   15 %
• CeIV :   0,5 M
• HNO₃ :   10 M

The decontamination of a stainless steel tank identical to that of Example 6 was studied, but using a commercial oxidizing gel of the "FEVDIRAD OX" type available from the company FEVDI and which has the following composition:

• "Cab-O-Sil" M5: 15%
• CeIV: 0.5 M
• HNO ₃ : 10 M

The steps and conditions of the decontamination treatment are the same as in Example 6, except that it was necessary during the rinses for the removal of the gel, to implement a very high pressure 150 to 300 kg / cm ² at place of low pressure.

We get a decontamination factor of 140.

But besides the fact that the elimination of gel by rinsing was much more difficult than in the previous example and required pressure much stronger, and that the volume of effluents from rinsing was much more important; load mineral reduced by a factor of 3 of organomineral gel according to the invention of the previous example, gave when subsequent filtration of the rinsing effluents solid waste three times less than that generated by filtration of the rinsing effluents of the gel of this representative example of art prior.

EXAMPLE 8 :

In this example, we realize the decontamination by the process according to the invention of three glove boxes in contaminated 316L stainless steel essentially by Uranium, Cesium, Plutonium and Strontium.

These glove boxes have an overall surface to be decontaminated of 26 m ² .

• "Cab-O-Sil" M5 :   5 %
• coviscosant (étherpolyéthylénique "C₆E₂") :   1 %
• CeIV :   0,5 M
• HNO₃ :   10 M

An acid oxidizing gel according to the invention having the same composition as the gel is used in Example 6, namely:

• "Cab-O-Sil" M5: 5%
• coviscosant (polyethylene ether "C ₆ E ₂ "): 1%
• CeIV: 0.5 M
• HNO ₃ : 10 M

• pulvérisation d'une solution de soude pendant une durée de 15 minutes,
• rinçage à l'eau,
• projection au pistolet sous une pression de 15 kg/cm² du gel oxydant acide selon l'invention décrit plus haut, de façon à déposer au total 80 kg de gel oxydant, et maintien de ce gel sur la surface pendant une durée de 2 heures,
• rinçage à l'eau à basse pression,
• mesure du débit de dose de la surface,
• projection d'une deuxième passe de gel oxydant, soit 10 kg au total, réalisée uniquement sur quelques points particuliers en fonction du débit de dose mesuré précédemment. Le gel est maintenu sur ces parties de la surface pendant une durée de deux heures.
• rinçage à l'eau à basse pression.

The decontamination treatment includes the following stages:

• spraying with a sodium hydroxide solution for 15 minutes,
• rinsing with water,
• spraying with a spray gun at a pressure of 15 kg / cm ² of the acid oxidizing gel according to the invention described above, so as to deposit a total of 80 kg of oxidizing gel, and maintaining this gel on the surface for a period of 2 hours ,
• low pressure water rinsing,
• measurement of the dose rate of the surface,
• projection of a second pass of oxidizing gel, ie 10 kg in total, carried out only on a few specific points depending on the dose rate measured previously. The gel is maintained on these parts of the surface for a period of two hours.
• rinse with water at low pressure.

We determined before and after the treatment, the dose rate of the surface.

The initial dose rate of the surface was 3 rad / h and its final dose rate was 2 to 20 mRad / h.

The decontamination factor is approximately 150.

EXAMPLE 9 (COMPARATIVE)

• "Cab-O-Sil" M5 :   15 %
• CeIV :   0,5 M
• HNO₃ :   10 M

The decontamination of stainless steel glove boxes identical to that of Example 8 was carried out, but using a commercial oxidizing gel of the "FEVDIRAD OX" type available from the company FEVDI, the composition of which is as follows:

• "Cab-O-Sil" M5: 15%
• CeIV: 0.5 M
• HNO ₃ : 10 M

The steps and conditions of the decontamination treatment are the same as in Example 8, except that it was necessary during the rinses for the removal of the gel, to apply a very high pressure (150 to 300 kg / cm ² instead of low pressure.

We get a decontamination factor of 150.

But besides the fact that the elimination of gel by rinsing was much more difficult than in the previous example and required pressure much stronger, and that the volume of effluents from rinsing was much more important; load mineral reduced by a factor of 3 of organomineral gel according to the invention of the previous example, gave when subsequent filtration of the rinsing effluents solid waste three times less than that generated by filtration of the rinsing effluents of the gel of this representative example of art prior.

Claims (32)

1. Organomineral decontamination gel constituted by a colloid solution comprising:

   a) a viscosing agent

   b) an active decontamination agent

   characterized in that viscosing agent a) comprises the combination of a mineral viscosing agent with an organic viscosing agent (coviscosant) chosen from among polyoxyethylene ethers of formula: CH₃-(CH₂)_n-1-(O-CH₂-CH₂)_m-OH, in which n is an integer from 6 to 18 and m is an integer from 1 to 23.
2. Gel in accordance with claim 1, characterized in that the mineral viscosing agent is chosen from among silicas and aluminas.
3. Gel in accordance with claim 1, characterized in that the mineral viscosing agent used is a silica in the proportion of 1 to 7% by weight.
4. Gel in accordance with claim 2, characterized in that the mineral viscosing agent used is an alumina in the proportion of 1 to 15% by weight.
5. Gel in accordance with claim 1, characterized in that the coviscosant content is 0.1 to 5% by weight.
6. Gel in accordance with claim 1, called an "acid gel", characterized in that active decontamination agent b) comprises a mineral acid.
7. Gel in accordance with claim 6, characterized in that the mineral acid is chosen from among hydrochloric acid, nitric acid, sulphuric acid, phosphoric acid and their mixtures.
8. Gel in accordance with claim 6, characterized in that the mineral acid is present at a concentration of 1 to 10 mol/l.
9. Gel in accordance with claim 1, characterized in that active decontamination agent b) comprises a mineral base.
10. Gel in accordance with claim 9, characterized in that the mineral base is chosen from among soda, potash and their mixtures.
11. Gel in accordance with claim 9, characterized in that the mineral base is present at a concentration of 0.1 to 14 mol/l.
12. Gel in accordance with claim 1, called "reducing gel", characterized in that active decontamination agent b) comprises a reducing agent.
13. Gel in accordance with claim 12, characterized in that the reducing agent has a standard redox potential Eo of less than -600 mV/SHE (standard hydrogen electrode) in a strong base medium (pH ≥ 13).
14. Gel in accordance with claim 12, characterized in that the reducing agent is present at a concentration of 0.1 to 4.5 mol/l.
15. Gel in accordance with claim 13, characterized in that the reducing agent is chosen from among borohydrides, sulphites, hydrosulphites, sulphides, hypophosphites, zinc, hydrazine and their mixtures.
16. Gel in accordance with claim 13, characterized in that active agent b) also comprises a mineral base at a concentration of 0.1 to 14 mol/l.
17. Gel in accordance with claim 1, called an "oxidizing gel", characterized in that active decontamination agent b) comprises an oxidizing agent or the reduced form of this oxidizing agent.
18. Gel in accordance with claim 17, characterized in that the oxidizing agent has a standard redox potential E_o of more than 1400 mV/SHE (standard hydrogen electrode) in a strong acid medium (pH < 1).
19. Gel in accordance with claim 17, characterized in that the oxidizing agent is present at a concentration of 0.1 to 2 mol/l.
20. Gel in accordance with claim 18, characterized in that the oxidizing agent is chosen from among Ce^IV, Ag^II, Co^III and their mixtures.
21. Gel in accordance with claim 20, characterized in that the Ce^IV is in the form of cerium nitrate, cerium sulphate or hexanitrato cerate of diammonium.
22. Gel in accordance with claim 18, characterized in that the oxidizing gel, in addition to the reduced form of the oxidizing agent, also comprises a compound able to oxidize the reduced form of this oxidizing agent.
23. Gel in accordance with claim 22, characterized in that the compound able to oxidize the reduced form of the oxidizing agent is a persulphate of an alkali metal.
24. Gel in accordance with claim 18, characterized in that active agent b), in addition to the oxidizing agent, also comprises a mineral acid or a mineral base at a concentration of 1 to 10 mol/l.
25. Gel in accordance with claim 24, characterized in that the mineral acid is chosen from among HNO₃, HCl, H₃PO₄, H₂SO₄ and their mixtures.
26. Oxidizing decontaminant gel in accordance with claim 18, characterized in that it is constituted by colloid solution comprising:

    0.6 to 1 mol/l, preferably 1 mol/l, of (NH₄)₂ Ce(NO₃)₆ or of Ce (NO₃)₄,

    2 to 3 mol/l, preferably 2.88 mol/l, of HNO₃,

    4 to 6% weight, preferably 5% by weight, of silica,

    0.2 to 2% by weight, preferably 1% by weight, of a polyoxyethylene ether.
27. Decontamination process for a metal surface, characterized in that it comprises the application onto the surface to be decontaminated of a gel in accordance with any of claims 1 to 26, maintaining this gel on the surface for a period that is sufficient to carry out decontamination, and removing the gel from the metal surface treated in this way.
28. Process in accordance with claim 27, characterized in that the gel is applied by gun spraying.
29. Decontamination process in accordance with claim 27, characterized in that the gel is maintained on the surface for a period of 10 minutes to 24 hours.
30. Decontamination process in accordance with claim 27, characterized in that the gel is an acid oxidizing gel and that it is applied to the surface for a time of between 2 and 5 hours.
31. Process in accordance with claim 27, characterized in that the gel is removed from the surface by rinsing.
32. Process in accordance with claim 27, characterized in that the gel is applied to the surface to a thickness of 100 g to 2000 g/m².

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