EP0727243A1 - Ozone containing decontamination foam and decontamination methid using this foam - Google Patents

Abstract

A foam for decontamination with O3 comprises (a) a liq. phase comprising a soln. of (i) a tenside and (ii) an oxidn.-redn. couple forming the decontamination agent, and (b) a gas phase dispersed in the liq. phase and comprising air enriched in O3 or O2 enriched in O3.

Description

The invention relates to an ozone decontamination foam, which can be used in particular to decontaminate or rinse the surface of objects, in particular relatively large objects or of complex shapes, more particularly hollow volumes. The invention also relates to a decontamination process using this foam.

The foam according to the invention is particularly applicable to the decontamination of devices or circuits of the nuclear industry, the chemical industry, the food industry or health. It applies more particularly to the decontamination of circuits or devices made of copper, copper alloy, ordinary steel, or an alloy of iron, chromium and nickel, such as stainless steel in particular. Austenitic stainless steel, for example 304 L stainless steel, or the alloy known under the brand name Inconel.

Chemical or radioactive decontamination of the surface of objects is generally carried out by wet chemical processes, using solutions containing decontamination reagents and generally having a pickling power.

The decontamination techniques used with solutions can consist of washing, spraying or soaking, but when the parts to be decontaminated have large dimensions, these techniques are unsuitable because they have the disadvantage of requiring large volumes of reagents and by consequently leading to the formation of very large quantities of active liquid effluents.

To decontaminate such objects using smaller volumes of reagent, foams containing decontamination solutions can be used.

• d'une phase liquide constituant le milieu de dispersion, qui renferme le(s) réactif(s) de décontamintion et le(s) additif(s) nécessaire(s) pour former la mousse, et
• d'une phase gazeuse constituant la phase dispersée, qui est généralement formée d'air, d'azote ou d'un gaz neutre tel que l'argon.

Thus, a decontamination foam is a microdispersion or a gas-liquid emulsion consisting of:

• a liquid phase constituting the dispersion medium, which contains the decontamination reagent (s) and the additive (s) necessary to form the foam, and
• a gas phase constituting the dispersed phase, which is generally formed of air, nitrogen or a neutral gas such as argon.

In such a foam, the volume of the liquid phase can be small because the foam generally contains 5 to 50 times more gas than liquid. Consequently, the liquid active effluents obtained after decontamination are significantly reduced.

In the particular case of radioactive decontamination of elements of the nuclear industry, it should be noted that radioactive contamination falls into two types, whether they are fission products, activation products or actinides.

• une contamination radioactive de surface due à des éléments radioactifs qui se déposent sur les surfaces des appareils et des tuyauteries et qui sont piégés par les oxydes métalliques également présents sur ces surfaces, et
• une contamination radioactive en profondeur due à une petite fraction des éléments radioactifs qui pénètrent dans le métal des appareils et des tuyauteries, c'est-à-dire dans les microfissures et les joints intergranulaires.

These two types of contamination are:

• radioactive surface contamination due to radioactive elements which deposit on the surfaces of devices and pipes and which are trapped by the metal oxides also present on these surfaces, and
• radioactive contamination in depth due to a small fraction of the radioactive elements which penetrate into the metal of the apparatus and pipes, that is to say into the microcracks and intergranular seals.

As part of the maintenance of nuclear facilities, it is generally sufficient to proceed with the elimination of surface radioactive contamination. However, there remains a certain residual dose which irradiates the intervening personnel. In the context of the dismantling of nuclear installations, it is however necessary to eliminate not only the metal surface oxides and their contaminants but also to erode by a few microns the metal (generally steel) forming the apparatus and piping , in order to eliminate radioactive contamination which has entered the metal microcracks. Thus, the dose received by the intervening personnel is reduced practically to nil and, in addition, the reuse and recycling of the steel is authorized, after fusion in a specialized steelworks.

A process for decontamination and elimination of corrosion products deposited on the contaminated surfaces of a nuclear reactor is already known from French patent application FR 2 454 159. According to this process, the surfaces to be treated are brought into contact with ozone in the form of water saturated with ozone or of water mist containing ozone. Ozone dissolves the chromium oxides in the treated steels and makes them sensitive to further treatment with acid reagents.

This process is therefore selective in dissolving the surface oxide but gives very minimal, or even zero, dissolution of the metal surface. In addition, it generates a large amount of liquid effluents.

We also know from the article by JR COSTES and JP GAUCHON, entitled: "Foam Decontamination of Large Nuclear Components before Desmantling", Waste Management'92, Meeting in Tucson, 1992, 738-743, a decontamination foam used to decontaminate hollow objects of the nuclear industry, in particular those made of steel and having complex shapes, such as valves or exchangers. This foam has a liquid phase comprising at least one foaming agent and a mixture of decontamination acids or bases and a gas phase comprising air, nitrogen or argon. The application referred to in this document only concerns ferritic steels.

Also known from patent application WO 85/04279 is a process for decontaminating the surfaces of the primary circuit of pressurized water reactors, in particular surfaces made of chromium-nickel-iron alloy. This process involves contacting the surfaces to be treated with an acidic decontamination solution containing cerium (IV) nitrate and chromic acid, in the presence of ozone as an oxidizing agent. Ozone is preferably present in the form of a saturated solution. It can also be used in the form of a two-phase gas / water mixture in which the ozone is in gaseous form, or also in the form of oxygen enriched in ozone.

However, here again, the attack of the metal is very slow and very weak, (of the order of a few micrometers in 48 hours), but it is precisely the erosion of the surface surface of the metal which makes it possible to obtain a good decontamination. In addition, the volumes of reagent involved represent several times the volume of the circuit of the device to be decontaminated.

There is also known a process similar to that described in WO 85/04279 but not using ozone and which consists in adding Ce (IV) as and when it is consumed in Ce (III). However, in addition to being expensive, this leads to accumulation in the final solution of the ions which increase the volume of the dry residue. However, it is precisely this dry residue, which after treatment contains all the initial contamination and which is intended to be packaged and stored over very long periods. Consequently, the more the volume of the dry residue is increased, the higher the cost of storage.

Finally, a process is known which is similar to that described in WO 85/04279 but which does not use ozone and which also consists in electrolytically regenerating the cerium (III) into cerium (IV). This solution is however difficult to apply during the treatment of alloys containing iron, because it is then the regeneration reactions from Fe ²⁺ to Fe ³⁺ which predominate at the electrodes.

Consequently, the object of the invention is to remedy the drawbacks of the above-mentioned prior art.

To this end, the invention relates to a decontamination foam.

• a) une phase liquide comprenant une solution d'au moins un agent tensio-actif et d'un couple oxydo-réducteur formant agent de décontamination, et
• b) une phase gazeuse dispersée dans la phase liquide et comprenant de l'air enrichi en ozone ou de l'oxygène enrichi en ozone, (de préférence entre 1 et 1000 g d'ozone/Nm³ d'oxygène, ou mieux entre 10 et 200 g d'ozone/Nm³ d'oxygène).

According to the characteristics of the invention, this foam comprises:

• a) a liquid phase comprising a solution of at least one surfactant and of an oxidation-reduction couple forming a decontamination agent, and
• b) a gaseous phase dispersed in the liquid phase and comprising air enriched in ozone or oxygen enriched in ozone, (preferably between 1 and 1000 g of ozone / Nm ³ of oxygen, or better still between 10 and 200 g of ozone / Nm ³ of oxygen).

/SO $\genfrac{}{}{0ex}{}{\text{2-}\hfill }{\text{4}\hfill }$

, V²⁺/V³⁺ ou Cr⁴⁺/Cr³⁺ et il est associé à au moins un acide. Cet acide permet la solubilisation du couple oxydo-réducteur. Il peut être choisi parmi HCl, HNO₃, H₂SO₄, H₃PO₄ ou leurs mélanges ou être un acide faible Ce couple oxydo-réducteur peut également être MnO $\genfrac{}{}{0ex}{}{\text{-}\hfill }{\text{4}\hfill }$

/MnO₂ associé à au moins une base, notamment une base forte.Advantageously, the redox couple forming decontamination agent is chosen from the pairs Ce ⁴⁺ / Ce ³⁺ , Co ³⁺ / Co ²⁺ , Ag ²⁺ / Ag ⁺ , S ₂ O $\genfrac{}{}{0ex}{}{\text{2-}\hfill }{\text{3}\hfill }$

/ N / A $\genfrac{}{}{0ex}{}{\text{2-}\hfill }{\text{4}\hfill }$

, V ²⁺ / V ³⁺ or Cr ⁴⁺ / Cr ³⁺ and it is associated with at least one acid. This acid allows the solubilization of the redox couple. It can be chosen from HCl, HNO ₃ , H ₂ SO ₄ , H ₃ PO ₄ or their mixtures or be a weak acid This redox couple can also be MnO $\genfrac{}{}{0ex}{}{\text{-}\hfill }{\text{4}\hfill }$

/ MnO ₂ associated with at least one base, in particular a strong base.

Thanks to the characteristics of the invention, the oxidizing action of ozone is increased, due to the enormous increase in the liquid surface (in the form of thin strips), encountered in foam bubbles and due to the significant dissolution of ozone inside this foam, while ozone also has very limited solubility in water.

The action of ozone foam is particularly remarkable for the decontamination of the first oxide layer which is deposited on the surface of copper alloys or alloys of iron, chromium and nickel, in particular austenitic stainless steels. Indeed, the layers of liquid in contact with the metal surfaces to be treated are rapidly renewed due to the coalescence (degradation) of the bubbles and the drainage of the liquid phase on the surfaces, whereas if a liquid solution of decontamination and not foam, the boundary layers prevent the deep action of the liquid phase. In addition, the use of a foam makes it possible to evacuate deposits and metallic particles of several mm ³ which is not possible with a conventional liquid decontamination solution. Therefore, the foam of the present invention is particularly suitable in the case where a strong and rapid action is necessary, for example for dismantling and to "decategorize" the waste.

Furthermore, this decontamination foam is also particularly suitable for decontamination of the surface layer of a metal substrate. Indeed, cerium (IV) (for example) brought initially in the foam tends to degrade into cerium (III), but it can then be transformed back into cerium (IV) by the action of ozone and can thus oxidize the chromium and make it soluble which facilitates decontamination. Therefore, the invention is very economical in cerium (respectively in another redox element) and it is not necessary to add cerium during the use of the foam.

The surfactant used in the liquid phase of the foam is preferably a betaine, in particular a sulfobetaine or an alkyl oligosaccharide ether which have the advantage of being biodegradable. These two surfactants can also be used as a mixture.

One can in particular use a sulfobetaine such as that sold by the company Seppic under the trade name Amonyl®.

By way of example of alkyl ethers of oligosaccharides, mention may be made of that sold by the company Seppic under the trade name Oramix CG 110® and that sold by the company Rohm and Hass under the name Triton CG60®.

The combination of the two surface-active agents is also interesting because it remains surface-active whatever the pH and is therefore suitable both in neutral medium and in acidic or basic medium.

Unexpectedly, it has been discovered that the surfactant used in the decontamination foam according to the invention destroys very slowly in contact with ozone. Therefore, it is sometimes necessary to add a little surfactant in the decontamination foam during the use thereof. On the other hand, ozone has the great advantage of destroying surfactants in the longer term, especially during the intermediate storage of the liquid effluent obtained at the end of the decontamination, before the discharge of this liquid effluent to the treatment station. The foaming power of this liquid effluent is then considerably weakened.

Generally, the liquid phase consists of an aqueous solution comprising 0.1 to 3 mol / l of H ₂ SO ₄ (or better 1 mol / l), 0.1 to 3 mol / l of HNO ₃ ( or better 1 mol / l), 0.001 to 0.1 mol / l of ceric sulphate (or better 0.005 mol / l) and 0.2 to 1% by weight of surfactant (or better 0.5%) .

The invention also relates to a decontamination process consisting in bringing contaminated surfaces into contact with the above-mentioned foam. This operation is generally carried out at ambient pressure and at a temperature between 10 and 70 ° C., preferably between 20 and 30 ° C. Indeed, the reactivity of the foam increases with temperature, but beyond 70 ° C, the foam tends to coalesce.

Advantageously, before the decontamination step, at least one degreasing step is carried out using a degreasing foam, the gaseous phase of which is air and the liquid phase of which is an aqueous solution of at least at least one surfactant, a base and a viscosifier, and after having carried out the decontamination step, a rinsing step is carried out at least once using a rinsing foam, the gas phase is air and the liquid phase of which is an aqueous solution of at least one surfactant.

Furthermore, after decontamination and when the aqueous phase of the decontamination foam contains an acid, the degreasing, decontamination and rinsing foams can be mixed to form a neutral effluent in which the residual ozone oxidizes the surfactant.

Finally, preferably, after decontamination, each decontamination foam used is recovered, filtered and recycled in the decontamination process and the gas phase of the decontamination foam is treated on a catalyst to destroy the residual ozone before the discharge of the gas phase in the atmosphere.

The invention will be better understood on reading the following description of an embodiment of the invention, given by way of illustrative and nonlimiting example, this description being made with reference to the single attached figure representing an installation manufacturing the foam used during the implementation of the decontamination process according to the examples described below.

In the figure, it can be seen that the installation comprises a tank of decontamination solution 1 connected to a foam generator 3 by a pipe 5 provided with a filter 7 and a circulation pump 9.

The foam generator 3 is supplied in gaseous phase from an ozone generator 11 via a pipe 13. A pipe 15 connects the foam generator 3 to the exchanger 17 to be cleaned. This will be described in more detail later.

In this generator, the foam is in contact with the walls to be decontaminated, then this foam leaves the exchanger through an upper orifice 19 while the liquid (coalesced foam) flows to the bottom 21 of the exchanger and is evacuated by a pipe 23 provided with a filter 25 and a recycling pump 27, towards the solution tank 1.

The upper orifice 19 is connected by a line 29 to the solution tank 1. The gaseous phase separated in the solution tank 1 is filtered through high efficiency filters 31 then treated on a catalyst 32 before being discharged into the atmosphere by means an extractor fan 33.

The following examples illustrate the preparation and use of a foam according to the invention.

• matériau : acier inoxydable 304L,
• dimensions de la virole : longueur 6,5 m, diamètre 0,5 m,
• surface des tubes : 214 m²
• le fluide primaire circulait du côté de la calandre, sans chicanes. C'est donc l'espace entre les tubes qui a été contaminé en radio-éléments béta et gamma et qui fait l'objet de la décontamination
• le fluide secondaire circulait côté tube en trois passes.

The decontamination tests were carried out respectively on two disused tubular exchangers 17I and 17II, coming from the nuclear industry. These exchangers have the following characteristics:

• material: 304L stainless steel,
• shell dimensions: length 6.5 m, diameter 0.5 m,
• tube area: 214 m ²
• the primary fluid circulated on the side of the grille, without baffles. It is therefore the space between the tubes which has been contaminated with beta and gamma radio-elements and which is the subject of decontamination.
• the secondary fluid circulated on the tube side in three passes.

To carry out these tests, the isolation plates for the inlet and outlet of the primary fluid were replaced by plates provided with a foam introduction valve and a liquid suction valve. The two exchangers were placed on slightly inclined planes.

• première phase : il s'agit d'une phase de dégraissage réalisée à l'aide d'une mousse de dégraissage basique dont la phase liquide contient 250 l d'eau, 40 kg d'NaOH et 0,5% en poids d'agents tensio-actifs.
• deuxième phase : il s'agit d'une phase de dissolution des oxydes et d'attaque du métal, réalisée à l'aide d'une mousse acide dont la phase liquide comprend 250 l d'eau, 16 kg d'acide sulfurique à 92%, 46 kg d'acide nitrique à 62%, 6 kg de sulfate cérique et 0,5% en poids d'agents tensio-actifs ;
• troisième phase : elle est identique à la deuxième ;
• quatrième phase : il s'agit d'une phase de rinçage à l'aide d'une mousse de rinçage formée de 250 l d'eau et de 0,5% en poids d'agents tensio-actifs.

In the following two examples, the decontamination process consisted in carrying out four phases of approximately 4 hours each:

• first phase : this is a degreasing phase carried out using a foam of basic degreasing whose liquid phase contains 250 l of water, 40 kg of NaOH and 0.5% by weight of surfactants.
• second phase : this is a phase of dissolution of the oxides and attack of the metal, carried out using an acid foam whose liquid phase comprises 250 l of water, 16 kg of sulfuric acid 92%, 46 kg of 62% nitric acid, 6 kg of ceric sulphate and 0.5% by weight of surfactants;
• third phase : it is identical to the second;
• fourth phase : this is a rinsing phase using a rinsing foam formed from 250 l of water and 0.5% by weight of surfactants.

In the two aforementioned examples, the foam was formed in a mixer 3 using a hydropneumatic pump simultaneously injecting the liquid phase at the rate of 500 l / h and the gas phase, at the rate of 3 to 4 Nm ³ / h . The pressure of the gas allows the foam to fill the exchanger from the bottom. This foam has a humidity close to 15% by volume. Furthermore, the pressure of this foam also causes the foam to overflow at the top of the exchanger through the return connection to the tank of decontamination solution 1. The return foam is partially destroyed in the tank 1 by spraying with liquid and by centrifugation. Furthermore, the liquid from this foam after coalescence again serves to recreate a foam in the mixer 3. A portion of the foam can even be recycled as it is through the hydropneumatic pump. Liquids are kept at a temperature of 20 ° C.

EXAMPLE 1

In this example, decontamination of exchanger No. 17 I is carried out, using air foam.

EXAMPLE 2

Decontamination of exchanger No. 17 II is carried out using oxygen foam enriched with ozone (100 g of O ³ / Nm ³ of O ₂ ), in the presence of cerium (IV).

During the basic and acidic phases, the dose rate is measured at the bottom, in the middle and at the top of the exchanger at the start and at the end of the process (4 hours after). In addition, 50 ml liquid samples are taken, either from the foam return (line 29) or from the liquid return (line 1, 2 hours and 3 hours respectively after the start of the process). In order to follow the progress of the decontamination, the dose rate of these samples is measured, as well as their total iron content, which testifies to the dissolution of the metallic layer. Finally, the contamination removed and the quantities of ozone and cerium consumed are calculated.

The results are illustrated in Table 1 below.

In Example 1, the quantities of cerium (IV) added are regularly consumed by the oxidation of metals, which requires permanent additions, up to 16 kg. Decontamination is good to judge by the lower dose rates (16 µGy / h), and the radioactivity extracted. The quantity of liquid effluent is small: 1.2 m ³ . The decontamination factor is 40.

In Example 2, better results are obtained than in Example 1. In fact, a smaller quantity of cerium (IV) is used (6 kg), but this product is expensive. Each of the two acid phases goes further in decontamination. The quantity of dissolved iron can exceed by 100% that dissolved in example 1. Finally, which is the most important result, the residual dose rate of the exchanger is low (<6 μGy / h). The quantity of liquid effluent is also low: 1.2 m ³ . The decontamination factor is 160.

Claims (16)

Ozone decontamination foam, characterized in that it comprises: a) a liquid phase comprising a solution of at least one surfactant and an oxidation-reduction couple forming a decontamination agent, and b) a gaseous phase dispersed in the liquid phase and comprising air enriched in ozone or oxygen enriched in ozone. Decontamination foam according to claim 1, characterized in that the gas phase comprises between 1 and 1000 g of ozone / Nm ³ of oxygen, preferably between 10 and 200 g of ozone / Nm ³ of oxygen. Decontamination foam according to claim 1, characterized in that the redox couple forming decontamination agent is chosen from the pairs Ce ⁴⁺ / Ce ³⁺ , Co ³⁺ / Co ²⁺ , V ²⁺ / V ³⁺ , Ag ²⁺ / Ag ⁺ , S ₂ O $\genfrac{}{}{0ex}{}{\text{2-}\hfill }{\text{3}\hfill }$

/ N / A $\genfrac{}{}{0ex}{}{\text{2-}\hfill }{\text{4}\hfill }$

or Cr ⁴⁺ / Cr ³⁺ and in that it is associated with at least one acid. Decontamination foam according to claim 3, characterized in that the acid is chosen from HCl, HNO ₃ , H ₂ SO ₄ , H ₃ PO ₄ or their mixtures. Decontamination foam according to claim 1, characterized in that the redox couple forming a decontamination agent is MnO $\genfrac{}{}{0ex}{}{\text{-}\hfill }{\text{4}\hfill }$

/ MnO ₂ and in that it is associated with at least one strong base. Decontamination foam according to claim 1, characterized in that the surfactant is chosen from betaine, an alkyl ether of oligosaccharide or their mixtures. Decontamination foam according to claim 3, characterized in that the phase liquid consists of an aqueous solution comprising: - 0.1 to 3 mol / l of sulfuric acid, - 0.1 to 3 mol / l of nitric acid, - 0.001 to 0.1 mol / l of ceric sulfate, - 0.2 to 1% by weight of surfactant. Decontamination foam according to claim 7, characterized in that the liquid phase consists of an aqueous solution comprising approximately 1 mol / l of sulfuric acid, 1 mol / l of nitric acid, 0.005 mol / l of ceric sulfate and 0 , 5% by weight of surfactant. Decontamination process characterized in that it consists in bringing a surface to be decontaminated into contact with the decontamination foam according to any one of the preceding claims. Decontamination process according to claim 9, characterized in that the decontamination temperature is between 10 and 70 ° C, preferably between 20 and 30 ° C. Decontamination process according to claim 9, characterized in that after having carried out the decontamination step, a rinsing step is carried out at least once using a rinsing foam, the gaseous phase of which is air and whose liquid phase is an aqueous solution of at least one surfactant. Decontamination process according to claim 9 or 11, characterized in that before the decontamination step, at least one degreasing step is carried out using a degreasing foam whose gaseous phase is air and the liquid phase of which is an aqueous solution of at least one surfactant, of a base and of a viscosifying agent. Decontamination process according to claim 12, characterized in that after decontamination and when the aqueous phase of the decontamination foam contains an acid, the degreasing, decontamination and rinsing foams are mixed to form a neutral effluent in which the residual ozone oxidizes the surfactant. Decontamination method according to claim 9, 11 or 12, characterized in that after decontamination, each decontamination foam used is recovered and recycled in the decontamination process. Decontamination method according to claim 9, 11 or 12, characterized in that after the decontamination step, the gas phase of the decontamination foam is treated on a catalyst to destroy the residual ozone before the discharge of the gas phase in the air. Decontamination method according to any one of the preceding claims, characterized in that it is applied to the cleaning of contaminated surfaces made of copper, copper alloy, steel, or an alloy of iron, chromium and nickel such as stainless steel.

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