RU2263984C2 - Method for preventing formation of radioactive pollutants and their spreading in dismounting of building structures when decommissioning primary nuclear projects - Google Patents

Abstract

FIELD: environment control engineering.

SUBSTANCE: proposed method includes coating building structure outer surfaces with localizing foam and filling their inner space with this foam. For the purpose use is made of localizing foam incorporating film-forming material. Dismounting of building structures is followed by destruction of localizing foam and formation of localizing films reducing residual pollution when removing dismounting wastes.

EFFECT: reduced spread of radioactive pollutants.

1 cl, 2 tbl, 2 ex

Description

The invention relates primarily to nuclear energy and the radiochemical industry, in particular to methods for reducing emissions of radioactive aerosols during the dismantling of contaminated building structures, which is an inevitable element of the decommissioning of nuclear facilities.

Any nuclear and radiation hazardous facility has a service life limit, after which its operation for its intended purpose ceases and decommissioning work begins. To date, the nuclear industry in Russia already has several dozen stopped nuclear hazardous facilities to be decommissioned.

When decommissioning nuclear facilities, the following options can be implemented: storage under surveillance, partial or complete dismantling of equipment and facilities [Poluektova GB, Kovalchuk OV, Kruglov AK Decommissioning of NPPs. / Nuclear Technology Abroad, 1990, No. 8, pp. 3-8]. In most cases, regardless of the decommissioning option, dismantling of building structures having radioactive contamination and not amenable to decontamination is necessary. The destruction of building structures by known methods (explosion, mechanical impact, etc.) is inevitably associated with the formation of radioactively contaminated dust settling in the adjacent territories. When carrying out dismantling, measures must be taken to prevent the formation and spread of radioactive dust.

There is a method of preventing the spread of dust, in particular when mining opencast, which uses irrigation methods of destructible rocks with water or special solutions [Saranchuk VI, Zhuravlev VP, Veisenberg IV et al. Chemicals for dust control. Kiev, Naukova Dumka, 1987, p.105-110].

The achievement of the technical result indicated below is impeded by the fact that the method has a rather low dust suppression efficiency and a large number of solutions are used for irrigation, which under the conditions of processing of radioactive contaminated objects will lead to the washing off of radionuclides and their transfer to the soil, as well as to a significant increase in the volume of liquid radioactive waste, which will require additional processing.

The closest way to the same purpose of the claimed invention in terms of features is a method of reducing aerosol emissions of radioactive substances during the dismantling of structures using foam-filled pools [US Patent No. 4529449, cl. 08 V 7/00. Method for reducing the amount of particles which become airborne during either or both the dismantling and moving of structures / Steve Baustert, Ivan L. Denny (USA); Kerr-McGee Chemical Corporation (USA). Publ. 07/16/1985], in which are placed the dismantled fragments, adopted as a prototype.

The reasons that impede the achievement of the following technical result when using the known method include the fact that large volumes of foam and foaming liquid are necessary for the formation of foam pools, as well as the fact that foams based on water and a surfactant after their destruction do not create surface protective films that prevent the formation of radioactive aerosols during further handling of dismantled fragments.

The objective of the invention is to provide a method for preventing the formation and spread of radioactive contamination during the dismantling of building structures of nuclear power plants, industrial reactors and radiochemical plants.

The technical result in the implementation of the invention is that in the claimed method, before carrying out work on the destruction of the structure, the latter is filled from the inside and coated on the outside with a foaming agent (for example, 7-10% polyvinyl alcohol, 1% OP-10, the rest is water). Foaming solutions containing a foaming agent have an increased viscosity of ~ 50-70 mPa · s, foams based on them are stable, able to fill all the voids of the premises and have good wettability and high adhesion to many materials. When a structure is destroyed under a layer of foam, the resulting dust is absorbed by the foam, not spreading to the adjacent territories. After the destruction of the foam, protective films are formed on the surfaces that prevent aerosol entrainment of contaminants during subsequent handling of fragments of structures. Obtaining foams with the necessary properties is possible using existing means of foam generation.

The method is as follows:

A structure contaminated with radioactive substances prepared for dismantling using existing foam generation means (GVP-500 foam generators and others) is filled from the inside and covered with foam from the outside containing a film-forming substance (7-10% polyvinyl alcohol, 1% OP-10, the rest is water) having a low rate of destruction. Then, the structure under the foam layer is destroyed using local explosions, mechanical impact, or other methods. The foam layer on the surfaces prevents the formation of dust and its entry into the environment. Subsequent destruction of the foam and the formation on the surfaces of the localizing films based on polyvinyl alcohol allows safe handling and disposal of waste dismantling structures.

Upon contact of localizing foams with non-porous surfaces, liquid, subsequently hardening protective films are formed on the latter. When foams interact with porous materials (concrete, brick, plaster), they are additionally impregnated with a foaming liquid, which prevents the formation of dust during destruction. At high levels of contamination, the dismantling of building structures is also advisable to carry out under a layer of foam, but after one-two-time localization of surface contamination with foams.

Example 1. To assess the consequences of the interaction of building materials with localizing foams based on a foam-forming solution of the composition: polyvinyl alcohol - 7%, preparation OP-10 - 1%, water - 92%, in a glass with a capacity of 0.6 l at a height of 10 cm from the top the edges were hung with plaster samples (size - 25 × 25 × 8 mm, density - 1.5 g / cm ³ , free porosity - 0.17 cm ³ / g) and bricks (size - 30 × 30 × 10 mm, density - 1 , 93 g / cm ³ , free porosity - 0.117 cm ³ / g), contaminated with fission products (Sr-90, Cs-137, Ru-106) and pre-weighed. The glass was filled using a foam-type foam generator with a foam with a multiplicity of 100. After the foam was destroyed for 10-15 minutes, the amount of foam-absorbing liquid absorbed by the samples was recorded, and based on the data obtained, the specific gravity of the absorbed liquid and the fraction of free porosity filled, characterizing the process of impregnation of foam-forming materials, were calculated. liquid in contact with foam. After drying of the samples, to assess the effectiveness of preventing the formation and spread of contaminants, the residual non-fixed contamination was determined by the dry smear method. The average test results are shown in table 1.

Table 1
The parameters of the interaction of localizing foam with a multiplicity of 100 with building materials Material The specific gravity of the absorbed liquid, mg / cm ² The percentage of free porosity,% The initial pollution, Bq / cm ² Residual pollution, Bq / cm ² Plaster 30,2 52.1 1600 92 Brick 24.4 36.3 1000 96

Example 2. To assess the effectiveness of the repeated processing of building materials with foams, the samples used in example 1 were treated with foam with a multiplicity of 65 under the same conditions as in example 1. The results of the experiments are shown in table 2.

table 2
The results of the re-treatment with foam of building materials. Material The specific gravity of the absorbed liquid, mg / cm ² Residual pollution, Bq / cm ² Plaster 20,0 7 Brick 18.0 5

From the above data it follows that when building materials come in contact with localizing foam, they are intensively impregnated with a foaming liquid. Wetting the external and internal surfaces of materials with a foaming liquid will significantly reduce the formation of dust during destruction. The forming protective film of polyvinyl alcohol significantly reduces residual contamination, which simplifies subsequent work to remove dismantling waste. Under real conditions, the foam layers will have a significantly greater thickness and, therefore, greater dust suppression efficiency due to the higher specific gravity of the absorbed liquid and increased localization efficiency.

Claims (1)

A method for preventing the formation and spread of radioactive contamination during the dismantling of building structures during the decommissioning of predominantly nuclear facilities, comprising coating localizing foam from the outside and filling inside the building structures, dismantling them under a layer of localizing foam, characterized in that they use localizing foam containing a film-forming substance, and carry out the dismantling of building structures with the subsequent destruction of the localizing foam and with the formation of localizing captives to reducing residual pollution at work on the removal of dismantling waste.