FR2717709A1 - Gel capable of retaining radioactive contamination and its use for protecting or decontaminating a surface. - Google Patents

Abstract

The invention relates to a gel capable of retaining radioactive contamination and its use for protecting or decontaminating surfaces. This gel consists of a colloidal aqueous solution comprising 2.5 to 15% by weight of a gelling agent and 5 to 15% by weight of a film-forming agent optionally with one or more additives chosen from preservatives (0.2 at 1%), antistatic agents (0.5 to 1.5%), acrylic copolymers (0.1 to 8%), dyes (0.001 to 1%) and adsorbents (1 to 5%). These gels can be easily applied to the surface to be protected or decontaminated and then eliminated with the radioactivity which they have fixed, by simply rinsing with water.

Description

GEL CAPABLE OF RETAINING RADIOACTIVE CONTAMINATION AND

  ITS USE TO PROTECT OR DECONTAMINATE A

AREA

DESCRIPTION

  The subject of the present invention is a gel capable of retaining a radioactive contamination, which can be used in particular for interventions in the dry process in nuclear installations such as

  dismantling facilities.

  During a dismantling operation of a nuclear installation, it is often necessary to dismantle and / or cut the equipment present in the installation. However, these operations can cause a general radioactive contamination of the installation due to the projection of filings or the production of aerosols. This is often the case during the maintenance of these facilities where radioactive contamination is often caused by the repair or

replacement of equipment.

  In order to avoid radioactive dissemination during such operations, it is advantageous, before any intervention, to fix the radioactivity on the already contaminated surfaces and to protect the surfaces

not contaminated.

  One of the techniques used is to cover the contaminated surfaces with a polyvinyl chloride film capable of fixing the contamination and then mechanically removing the

  contaminated polyvinylchloride film.

  This technique is difficult to apply when it comes to intervening on large surfaces,

  because it produces a large volume of waste.

  Also, it has been envisaged to replace these films with varnishes or peelable paints, applicable to the surface to be protected or decontaminated, which is then removed mechanically, but this causes problems because the film partially tears. It is also possible to deposit on the contaminated surface a polymer such as polyurethane, which remains fixed on the surface, but this technique, which is used mainly to confine the radioactivity during dismantling, does not

  does not eliminate radioactive contamination.

  The present invention specifically relates to gels capable of retaining radioactive contamination, which can be used to protect or decontaminate a surface and then be easily removed. According to the invention, the gel capable of retaining a radioactive contamination consists of a colloidal aqueous solution comprising: from 2.5 to 15% by weight of a gelling agent, and

  from 5 to 15% by weight of a film-forming agent.

  Preferably, the aqueous solution further comprises 0.2 to 1% by weight of a preservative with a bacteriostatic effect and optionally one or more additives chosen from antistatic agents, acrylic copolymers and dyes. In this case, the amount of antistatic agent is generally 0.5 to 1.5% by weight, the amount of acrylic copolymer is generally 0.1 to 8% by weight and the

  The amount of dye may be from 0.001 to 1% by weight.

  More preferably, the gels additionally comprise particles of an adsorbent agent dispersed in the aqueous solution, the quantity of particles

  representing 1 to 5% of the aqueous solution.

  It is recalled that a gel is a colloidal solution whose phases are difficult to define because of the molecular weight of the colloid and its state

  significant dispersion in solution.

  This gel structure is obtained by adding to an aqueous solution, with slow and continuous stirring, a gelling agent to obtain the

optimum swelling.

  In the gel of the invention, the gelling agent used is preferably an organic gelling agent consisting of a synthetic polymer or an ether

cellulose.

  By way of examples of such gelling agents, mention may be made of the product sold by Scott Bader SA under the reference Texipol 63 508 which consists of a dispersion in an organic solvent of an aqueous solution of synthetic polymer, and the product marketed by Dow Chemical Company under the trademark Methocel which is a hydroxypropylated methylcellulose

in the form of granules.

  The content of gelling agent is chosen so as to obtain a viscosity sufficient to be able to

  keep the gel layered on the surface of a room.

  Generally, it is preferred that the gel has a viscosity of at least 800 CPs at the time of use in order to easily apply it to

  surfaces, for example by spraying.

  To obtain these characteristics with the organic gelling agents used in the invention, the contents of gelling agent represent from 5 to 15% by weight of the solution, and the choice of this content

  depends in particular on the gelling agent used.

  According to the invention, the gel also comprises a film-forming agent which is preferably an inorganic agent. As an example of a film-forming agent which is very effective in the invention, mention may be made of products comprising SiO 2, Al 2 O 3, MgO, FeO and K 2 O such as the product sold under the reference Plastorit Naintsch, which is a product with three mineral components. , having a unique interweaving of mica, quartz and chlorite (magnesium and aluminum hydrosilicate). This product contains, for example, 52% of SiO 2, 22% of Al 2 O 3, 12.6% of MgO, 3.6% of FeO and 2.8% of K 2 O. It is practically inert and has a good wetting attitude in an aqueous environment and

  oily. Moreover, it increases the adhesion of the gel.

  The aqueous solution of the gel of the invention may furthermore comprise a preserving agent, an antistatic agent, an acrylic copolymer, a dye and

optionally an adsorbent.

  The preservatives that can be used are products with bacteriostatic effect avoiding bacterial fermentation. As examples of preservatives that may be used, mention may be made of phenoxyethanol, the product sold by Rhône Poulenc.

under the reference IGEPAL OD 410.

  It is also possible to add an antistatic agent to the solution, especially when the gel is intended to be applied to plastic surfaces such as polymethyl methacrylate surfaces, for example Plexiglas, or to ferritic steel surfaces. The antistatic agents that may be used may be chosen from surfactants of the cationic, anionic or nonionic type. By way of examples of such cationic surfactants, mention may be made of ethoxylated amines, such as the product marketed by Rhône-Poulenc under

reference Cemulcat 020.

  The addition to the aqueous colloidal solution of an acrylic copolymer is advantageous in cases where the gel is intended to be applied to metal surfaces. This acrylic copolymer increases the cohesion and mechanical strength of the applied gel film. This copolymer can be added in the form of an aqueous dispersion free of styrene. By way of example of a copolymer which may be used, mention may be made of the product sold by Luzzato & Figlio under the reference

Luzamul AC.

  Advantageously, the gel further comprises a coloring agent. This makes it possible to visualize, first of all, the good gel recovery of the surface to be treated, and then the complete removal of the contaminated gel at the end of the operation. As examples of dyes that may be used, mention may be made of Red

Lumina 2B and E 127 dye.

  Advantageously, the gel of the invention further comprises a powdered adsorbent agent for adsorbing and retaining the radioactive elements responsible for the contamination. This adsorbent agent can be constituted by a zeolite since the zeolites are capable of fixing many cations. Activated charcoal can also be used. The adsorbent used is chosen according to the radioactive element responsible for the contamination. The gels of the invention can be prepared in a simple manner, at room temperature, by mixing with demineralized water, with slow stirring, the optional additives such as the preserving agent, the antistatic agent and / or the colorant. then gradually adding to this solution, with slow stirring, the gelling agent until optimum swelling is obtained, then the film-forming agent, and finally, if necessary, the acrylic copolymer and / or the adsorbent agent. The gels of the invention can be used to protect a surface from contamination or to

  decontaminate a contaminated surface.

  In the first case, a gel according to the invention is applied to the surface to be protected before it has been contaminated; after contamination of

  the surface, the gel is removed by rinsing with water.

  In the second case, a gel according to the invention is applied to the contaminated surface, the gel is maintained on this surface for a time sufficient for it to fix the radioactivity, and then

remove it by rinsing with water.

  The gel can be applied to the surface by any conventional method, for example by spraying, spraying, dipping and dripping, or by means of a brush. It can then be easily removed from the surface by detaching it by a simple rinsing with water, for example by means of a jet of water. For rinsing, demineralised water or an aqueous solution is usually used in which the gels can be dissolved or

  detachable film and entrainable by water.

  When an adsorbent is incorporated in the gel such as a zeolite or activated carbon, the radioactivity can be concentrated on this adsorbent; this avoids the production

  of aqueous effluents heavily loaded with radioactivity.

  Surfaces capable of being protected or decontaminated by means of the gel of the invention may be of different types. It may be plastic surfaces, for example Plexiglas, that is to say polymethylmethacrylate, or metal surfaces, for example ferritic steel

or stainless steel.

  Other features and advantages of the invention will appear better on reading the

  following description of examples of realization given

  of course for illustrative and not limiting.

  EXAMPLE 1 Preparation of Gel No. 1 Gel No. 1, the composition of which is given in Table 1, is prepared by mixing with demineralized water, neutralized with sodium hydroxide, with slow stirring, the preserving agent (Igepal OD 410). and the coloring agent (E 127), and the gelling agent (Texipol 63508) is then gradually added to this solution with slow and continuous stirring until the optimum swelling is obtained. The agent is then gradually incorporated with slow stirring.

film forming (Plastorit S).

  EXAMPLE 2 Preparation of gel No. 2 The bare gel 2, the composition of which is given in Table 1, is prepared by following the same procedure as in Example 1, but adding in addition to the demineralized starting water 0, 5% by weight of antistatic agent consisting of Cemulcat 020 and

  replacing the E 127 dye with Rouge Lumina 2B.

  EXAMPLE 3 Preparation of gel No. 3 To prepare this gel, the composition of which is given in Table 1, starting from 80 parts by weight of gel No. 1 prepared in Example 1 and adding 20 parts by weight of acrylic copolymer. (Luzamul AC) and 1.4 parts by weight of gelling agent

Texipol 63 508.

  EXAMPLE 4 Preparation of gel No. 4 To prepare gel No. 4, the composition of which is given in the attached Table 1, starting from 80 parts by weight of gel No. 2 prepared in Example 2 and adding 20 parts by weight. acrylic copolymer

  (Luzamul AC) and 1.5 parts by weight of Texipol 63 508.

  Examples 5 to 7: Protection of Plexiglas Surfaces In these examples, No. 1, No. 2 or No. 4 gels are applied to Plexiglas supports to study the properties of the gel with regard to scratch resistance, adhesion and adhesion. on the support and the

easy rinsing with water.

  The results obtained are given in the

table 2.

TABLE 2

  SUPPORT IN PLEXIGLAS Ex. GEL HELD TO THE ADHESION FACILITY OF

SCRATCHES ON RINSING WITH WATER

SUPPORT

  No1 very very good very good bad 6 Ne 2 good very good very good 7 N 4 very good very good bad Based on these results, we notice that the gel n '2 which includes an antistatic agent and no acrylic copolymer is best adapted to the

  protection of Plexiglas surfaces.

  Examples 8 to 11: Protection of ferritic steel surfaces In these examples, the properties of the various gels for the protection of a ferritic steel support are also studied. The gels used and the results obtained are given in

table 3.

TABLE 3

FERRITIC STEEL SUPPORT

  Ex. GEL AT THE FACILITY OF ADHERENCE

  SCRATCHES ON THE RINSE SUPPORT WITH WATER

  8 N "1 bad bad good good enough with 9 N '2 very good very good good enough with pressurized water N' 3 good bad good good enough jave 11 N 4 very good very good good enough with pressurized water Given these results, it is found that the gels that are best suited in this case are gels n 2 and n 4 which also contain an agent

  antistatic and optionally an acrylic copolymer.

  Examples 12 to 15: 304 L Stainless Steel Surface Protection In these examples, the protective properties of the gels with respect to a 304 L stainless steel support are studied as in the previous examples. The gels used and the results obtained are

given in Table 4.

TABLE 4

STAINLESS STEEL SUPPORT (304 L)

  Ex. GEL AT THE FACILITY OF ADHERENCE

  SCRATCHES ON THE RINSE SUPPORT WITH WATER

  12 No 1 very good average bad 13 N / A 2 very good average bad quite good with 14 Ne 3 good very good good enough with pressurized water quite good with N 4 good very good good enough with pressurized water In view of this table, we note that the best results are obtained with the gels n 3 and 4 which contain an acrylic copolymer and

  possibly an antistatic agent.

  Example 16: Protection of a Plexiglass Surface

  against contamination by cesium-137.

  In this example, gel No. 2 is used, to which 5% by weight of IE 96 zeolite is added as cesium-137 adsorbent. Zeolite IE 96 is an aluminosilicate

  sodium sold by Union Carbide.

  The gel is spray-applied onto Plexiglas specimens by means of a spray gun, the gel is allowed to dry for 24 hours and deposited on cesium-137 gel coated specimens. The gel is then removed by rinsing with demineralised water. We filter the rinsing water and we count

  the activity retained by the gel and the filtrate.

  The results obtained are given in the

Table 5.

BOARD

PROTECTIVE AND RETENTION GEL

  Activity Retained Activity Activity Ex Initial gel of the sample by gel 1 'sample on Bq / ech Bq / ech Fraction of Bq / ech. the activity initi.en% 16 no 2 zeolite IE 96 2.47.104 2 2.33.104 94.3 17 no 2 zeolite IE 96 2.45 × 10 94 2.22 × 10 90.6 18 n 2 without zeolite 1.45 × 10 4 48, 43. 103 58.1 This test confirms the effectiveness of qel protection. Indeed, after rinsing with demineralised water, almost all the radioactivity (94.3%) was

driven and retained by the gel.

  Example 17: Decontamination of a surface in

Plexiglas -

  In this example, the same procedure as in Example 16 is followed, but the deposition of the gel is carried out on Plexiglas test pieces which have already undergone radioactive contamination with cesium-137. We also use the gel n 2 which we

added 5% IE 96 zeolite.

  The results obtained are given in the

table 5.

  In view of these results, it is noted that the gel has a high retention capacity with respect to cesium,

  even when it has already been deposited on the support.

  Example 18: Protection of a Plexiglas Surface.

  In this example, the same procedure as in Example 16 is followed, but gel No. 2 is used without addition of zeolite. The results

  obtained are given in Table 5.

  These results highlight the protective power of the gel, since the residual radioactivity of the support after removal of the gel is very low. On the other hand, the retention capacity of the gel without zeolite is lower than in Example 16, because, without the presence of adsorbent, a significant fraction of the

  radioactivity is entrained in the rinsing water.

  Example 19: Protection of an austenitic steel surface. In this example, the procedure of Example 16 is followed to protect the austenitic steel surface from cesium-137 contamination. Gel No. 3, which contains 5% of IE 96 zeolite, is used in this case. The protected surface is then contaminated with cesium-137, and the gel is then removed by rinsing with water. The results obtained are

given in Table 6.

  These results confirm the effectiveness of gel protection against cesium-137 contamination. Example 20: Decontamination of an austenitic steel surface. In this example, the same procedure as in Example 17 is followed to decontaminate a cesium-137 contaminated austenitic steel surface using gel No. 3 containing 5% by weight of IE 96 zeolite. The results obtained are given in Table 6. These results confirm the high retention of the gel, even when the

  radioactivity is deposited beforehand on the support.

TABLE 6

PROTECTIVE AND RETENTION GEL

  Activity retained Activity Activity by the gel EX Initial gel of the sample the sample Bq / ech Fraction of Bq / ech Bq / ech. the initial activity in 19% zeolite IE 96 2.4.104 38 2.2.104 92.3 2 zeolite IE 96 3, 38.104 1.76.103 2.90.104 85.8 21 n 3 without zeolite 2.32.104 2, 92.102 1.35.104 58.2 Example 21: Protection of an austenitic steel surface. In this example, the same procedure as in Example 18 is followed using gel n 3 without zeolite to protect the surface. The results obtained are given in Table 6 and they also confirm the protective power of the gel, but its lower power retention of radioactivity. Examples 22 to 24: In these examples, the protective effect of gels n 1 and 2 with respect to plutonium-239 contamination of steel surfaces is studied.

  stainless steel, ferritic steel or Plexiglas.

  The supports and the results obtained are

given in Table 7.

  The results of this table highlight the interest of the protection of the support by a gel in the case of contamination with Pu-239. Indeed, by protecting the support in this way, almost the entire Pu-239 can be removed from the support by simple

rinsing with water.

  In this table, the results obtained in the case of a contamination of the same supports by Pu-239 without protection by a gel, by carrying out only a rinsing with water, were given by way of comparison. In this case, the rinsing with water is inefficient, the major

  part of the Pu-239 remaining on the support.

  These results confirm the interest of the

gels of the invention.

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TABLE 7

  Ex Support Protection with Frost Free

,, ..:, .. '

  . ::: ....... ........................:

  Activity Pu-239 initial Activity Pu-239 after Activity Pu-239 Activity Pu-239 (Bq / ech) rinsing with water (Bq / ech) initial (Bq / ech) after rinsing & water (Bq / ech) 22 Stainless steel 1.29. 105 <103 7.75.104 2.10 Gel n1 (detection threshold) 23 Steel 1.04.105 <103 1.14.105 1.3.104 Ferritic n2 gel (detection threshold) 24 Plexiglas 3.5.105 <103 2.4.105 2.7.104 Gel n2 (detection threshold) Gel n'2j

Claims (17)

  1. Gel capable of retaining a radioactive contamination, characterized in that it consists of a colloidal aqueous solution comprising: - from 2.5 to 15% by weight of a gelling agent, and   from 5 to 15% by weight of a film-forming agent.   2. Gel according to claim 1, characterized in that the aqueous solution further comprises 0.2 to 1% by weight of a preservative with bacteriostatic effect. 3. Gel according to any one of   claims 1 and 2, characterized in that the   aqueous solution further comprises 0.5 to 1.5% by weight an antistatic agent. 4. Gel according to any one of   1 o 3, characterized in that the solution   aqueous composition further comprises 0.1 to 8% by weight of a acrylic copolymer. 5. Gel according to any one of   Claims 1 to 4, characterized in that the solution   The aqueous composition further comprises 0.001 to 1% of a dye. 6. Gel according to any one of   Claims 1 to 5, characterized in that it comprises   in addition, particles of an adsorbent agent dispersed in the aqueous solution, the quantity of particles   representing 1 to 5% of the aqueous solution. 7. Gel according to any of   Claims 1 to 5, characterized in that the agent   gelling agent is constituted by a synthetic polymer. 8. Gel according to any one of   Claims 1 to 7, characterized in that the agent   film-forming is a three-component charge   inorganic compounds comprising SiO2, Al2O3, MgO, FeO and K2O. 9. Gel according to any one of   Claims 1 to 8, characterized in that the agent   preservative is phenoxyethanol. 10. Gel according to any one of   Claims 1 to 9, characterized in that the agent   antistatic is an ethoxylated amine. 11. Gel according to any one of   Claims 1 to 10, characterized in that the agent   adsorbent is a zeolite or activated carbon.   Method for protecting a surface from contamination, characterized in that, prior to contamination, a gel is applied to the surface   any one of claims 1 to 11, and in that   that, after contamination of the surface, the gel by rinsing with water.   13. A method for decontaminating a contaminated surface, characterized in that a gel is applied to the contaminated surface according to any one of   1 to 11, and in that it eliminates   then the gel by rinsing with water.   14. Process according to any one of   claims 12 and 13, characterized in that the   surface is of polymethylmethacrylate or ferritic steel and that the gel comprises a gelling agent, a film-forming agent, an antistatic agent and a preservative.   15. Process according to any one of   claims 12 and 13, characterized in that the   surface is a ferritic steel surface and in that the gel comprises a gelling agent, a film-forming agent, an antistatic agent, a preservative and an acrylic copolymer.   16. Process according to any one of   claims 12 and 13, characterized in that the   surface is made of stainless steel and in that the gel comprises a gelling agent, a film-forming agent, a   acrylic copolymer, a preservative and optionally an antistatic agent.   17. Process according to any one of   Claims 14 to 16, characterized in that the gel further comprises an adsorbent agent consisting of a zeolite and a dye.