RU2569315C1 - Method of shotcreting of external surface of radiation protecting package - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: on external surface of the enclosure the reinforcement grid is secured, and shotcrete layer is applied under compressed air, the layer covers the grid and includes portland cement, fillers, chemical and mineral additives, and water. At that grid with cell at least 110×110 mm is used, it is made out of nanomodified basalt-plastic reinforcement rods with sand external coating, the grid is installed with clearance 8 mm maximum from the shotcreted surface, and shotcrete is applied with definite ratio of components. Under particular case of specified method of shotcreting of the enclosure external surfaces to reduce its weight and dimensions the maximum layer of the shotcrete with thickness 25 mm is applied.

EFFECT: increased storage life of the enclosure.

2 dwg

Description

The invention relates to nuclear engineering and technology, in particular to the integrated disposal, conservation, temporary and long-term storage of radiation hazardous reactor compartments (RO), large floating and other objects, such as large surface ships (NK), cargo transport vessels, icebreakers and floating power plants with nuclear power plants (NPP).

A known method of installation for long-term storage of radiation-hazardous large-sized objects according to the patent of the Russian Federation No. 2390063.

According to this method of installation for long-term storage and storage of radiation-hazardous large-sized objects installed in rows on a long-term storage site, the object is pre-formed into a block package on which supporting surfaces are made and transported to a storage location at a long-term storage point (MP). After installing the package at the place of technological maintenance, an external protective coating is applied to its surface.

There is also known a method according to RF patent No. 2293386 "Method for the formation of radiation-protective block packaging for installation on shore storage."

This method includes conducting a comprehensive engineering survey of the RO, removing spent fuel assemblies, dismantling the equipment from the RO, forming the RO packaging and transferring it to the shore, applying a radiation-protective sprayed concrete layer up to 30 mm thick on the outer surface of the packaging, and installing formed radiation-protective block packaging for onshore storage.

However, during long-term storage of block packages according to the above analogues, the external immobilization barrier that prevents the release of radioactivity and radionuclides into the surrounding environment is corroded and destroyed, therefore, it is necessary to periodically restore the outer protective coating of the block packages.

A known method of shotcrete for corrosion protection of steel structures is described in the document of the Central Research Institute of Industrial Buildings OJSC “Guidelines for the use of shotcrete in the construction, repair and restoration of building structures, buildings and structures” code M 10. 1/06 and technical specifications TU 5745- 001-16216892 "Shotcrete". This method is closest in technical essence to the claimed and adopted as a prototype.

The method extends to the use of shotcrete, applied to the outer surface of the object, on which metal reinforcement with a diameter of 3 ÷ 6 mm is preliminarily fixed in the form of a mesh with a square side of 25 mm to 100 mm and then a layer of shotcrete is applied under pressure of compressed air including binder - Portland cement, aggregates, chemical and mineral additives, and water as a hardener.

A monolith of such shotcrete has satisfactory strength, fire safety, good frost resistance, and has a water resistance mark of no more than W12. When laying concrete mortar by this method, the rebound of the mortar from the outer surface reaches 20%.

However, according to the data of FSUE TsNII KM Prometey, the corrosion rate of the outer surfaces of block packages during storage in atmospheric conditions at the storage facilities of the Far North and the Far East is 0.1 mm per year, which leads to a limited service life of the shotcrete concrete monolith. The limited service life of reinforced concrete structures is associated primarily with the corrosion of steel reinforcement. The impact on the metal reinforcement of moist air and water with aggressive chemical compounds that penetrate the helium pores of concrete, cause corrosion of the metal. The result of this process is the appearance of corrosion products, the volume of which is up to 2.5 times the volume of the corroded metal. Such a significant increase in internal volume contributes to the appearance of stresses in reinforced concrete structures and, as a result, cracks in concrete, which lead to its constant destruction. Therefore, the estimated service life of the outer surface of the block packaging made in this way under storage conditions at the MP will be no more than 25 years, which will lead to high operational costs of storage of block packaging and this is a disadvantage of this method.

The objective of the invention is to develop a reliable and inexpensive technology for the formation of the outer surface of the radiation-protective block packaging for installation on long-term storage on the foundation supports of the MPC without any movements.

The main technical result, due to which the task is achieved, is a significant increase (by an order of magnitude) in the shelf life of the block package due to the construction of a protective barrier when forming the outer protective surface of the block package using modern materials for reinforcing mesh and the composition of shotcrete .

The specified technical result is obtained due to the fact that according to the proposed method, a reinforcing mesh is fixed on the outer surface of the block package and a layer of shotcrete concrete is applied under compressed air pressure, covering the mesh and including Portland cement, aggregates, chemical and mineral additives, as well as water. In this case, a mesh with a cell side of at least 110 × 110 mm made of nanomodified basalt-plastic reinforcement with a sandy outer coating is used, the mesh is installed with a gap of not more than 8 mm from the shotcrete surface, and shotcrete is applied in the following ratio of components, wt.%:

Portland cement brand 500 37.0 ÷ 39.2 Thick sand (at least 2 density modulus) 29.8 ÷ 32.7 Silica fume 5.8 ÷ 6.0 Additive "Relamix SP-2" by TU-5870-002-14153664-04 1,1 ÷ 1,5 Ash 4,5 ÷ 5,2 Water 17.7 ÷ 18.8

In the particular case of the claimed method of shotcreting the outer surfaces of the block package in order to reduce its weight and dimensions, the maximum layer of shotcrete is applied with a thickness of not more than 25 mm.

The combination of reinforcing mesh made of basalt-plastic rods with an external sand coating and modified with nano-clay, with shotcrete makes it possible to create a monolithic outer coating with the following properties compared to a monolith of shotcrete with a metal reinforcing mesh:

- absolute corrosion resistance;

- absolute fire safety;

- increased strength characteristics;

- increased resistance to aggressive environments;

- ensuring increased environmental and radiation safety.

Minimizing rebound shotcrete, as well as reducing the cost of the mesh, depend on the optimum mesh cell sizes and the distance of the mesh from the empirically found during testing.

The outer monolithic coating of the block packaging with such properties will ensure its safe storage on the foundation supports of the MP for several hundred years.

The production of basalt-plastic reinforcement (BPA) in the form of rods modified with nanoclay began in Russia in 2007. BPA is ANK-B-6 fittings (designation of the manufacturer of the fittings when ordering), manufactured by Galen LLC (Cheboksary, Russia), passed various tests not only in Russia (JSC "TsTSS", LLC "Galen"), but also in the UK. Durability tests were performed at the Faculty of Structural Engineering at the University of Sheffield (The University of Sheffield, UK). The studies consisted of holding the samples in an alkaline medium of ph 9 and determining the tensile, bending and compression strengths, followed by extrapolation of the results obtained in terms of durability. According to the results of studies, the preservation of strength from environmental influences for a period of 100 years in wet concrete at a temperature of 20 ° C is 94%.

According to the results of studies conducted in Russia (OJSC "TsTSS", LLC "Galen"), the following results were obtained:

- a monolithic concrete outer coating reinforced with a mesh of basalt-plastic rods modified with nano-clay has increased strength characteristics (17% more compared to a reinforced metal mesh);

- a monolithic concrete outer coating reinforced with a mesh of basalt-plastic rods modified with nano-clay is an absolutely corrosion-resistant and non-combustible material;

- the bond strength of concrete with BPA with a diameter of 5 ÷ 6 mm with a sand coating applied to the surface of the rods is 2.7 times greater compared to a reinforcing mesh of metal wire ⌀ 5 ÷ 6 mm with a embedment depth of 30 mm;

- the smallest rebound of the concrete mixture from the outer shotcrete surface is not more than 5% by weight of the dry mixture (up to 20% shotcrete with a metal mesh) was determined when applied to the outer surface, with a reinforced mesh fixed, with a mesh size of 110 × 110 mm, made of basalt-plastic rods modified with nanoclay with a diameter of 5 ÷ 6 mm with a sandy outer coating, while the reinforcing mesh was installed at a distance of 8 mm from the outer surface;

- the ratio of the components of the concrete mixture using the additive "Relamix SP-2" according to TU-5870-002-14153664-04 allows you to increase the design brand of concrete by 15 ÷ 25%, to obtain the mobility of the concrete mixture to P5, while increasing the strength of concrete in the first two days of normal hardening by 15 ÷ 20%. The additive "Relamix SP-2" compacts the structure of concrete, provides an increase in its frost resistance to F> 500 and water resistance W> 16, and has inhibitory properties with respect to reinforcement.

The rods made of basalt-plastic materials modified with nanoclay allow to produce a reinforcing mesh with absolute corrosion resistance and fire safety, increased strength characteristics and resistance to aggressive environments. Nanoclay is based on smectite clays, such as montmorillonite — hydrated hydroxide of sodium silicate, calcium, aluminum, magnesium (Na, Ca) (Al Mg) 6 (Si ₄ O ₁₀ ) 3 (OH) 6nH ₂ O hydroxide. Montmorillonite is found in smectite clay strata in a natural geological state.

The selected materials and the procedure for constructing a monolithic concrete outer coating of the block packaging allow:

- create reliable and long-term biological protection of the environment and maintenance personnel of the MP;

- significantly reduce operating costs for the maintenance of block packages at the PDH due to an increase by an order of magnitude of the time for long-term storage of the package at the foundation supports of the PDH without any movements;

- significantly reduce the rebound of the concrete mixture from the outer shotcrete surface;

to reduce the complexity of the technological process of shotcreting the outer surface in comparison with shotcrete when using a metal reinforcing mesh and, accordingly, reduce dose loads on personnel.

The invention is illustrated by the following graphic drawings:

FIG. 1. The layout of technological equipment and block packaging for the performance of shotcrete work.

FIG. 2. Section AA. Section of a monolithic concrete outer coating of a block package.

The proposed method is as follows.

The outer surface of the package 1 must be sandblasted, i.e. prepared for laying shotcrete 2.

A reinforcing mesh 4 made of basalt-plastic rods ⌀ 5 ÷ 6 mm with a sandy outer coating 5 and using a nanomodifier - nanoclay is hung on the outer surfaces of the packaging unit 1, which is located on the supporting foundations 3 of the MPC.

The reinforcing mesh 4 has a mesh size of 110 × 110 mm and is fixed at a distance of 8 mm from the outer surface of the package 1 by any known method. In the working area of shotcrete, the following equipment is located and connected in the technological sequence (Fig. 1) for performing shotcrete work:

- compressor 6;

- cement gun 7;

- nozzle 8;

- water tank 9;

- air distributor 10.

In the cement gun 7 load the dry mixture in the following ratio of components, wt.%:

Portland cement brand 500 37.0 ÷ 39.2 Thick sand (at least 2 density modulus) 29.8 ÷ 32.7 Silica fume 5.8 ÷ 6.0 Additive "Remix SP-2" 1,1 ÷ 1,5 Ash 4,5 ÷ 5,2

This dry mixture in the indicated mass% is prepared in a standard mixer (the mixer is not shown in FIG. 1). Water in an amount corresponding to 17.7 ÷ 18.8 wt.%, Is poured into a water tank 9.

After the compressor 6 is turned on, compressed air through the air distributor 10 enters the water tank 9 and the cement gun 7. From the cement gun 7 the dry mixture and from the water tank 9 enter water under the pressure of compressed air into the nozzle 8, where water is mixed with the dry mixture in the ratio of mass%: dry mixture 82.3 ÷ 83.4, water 17.7 ÷ 18.8.

From the nozzle 8, a shotcrete-concrete solution 2 is ejected onto the outer surface of the package 1 under pressure of compressed air, while the nozzle 8 must be 500 to 1000 mm from the outer surface of the package 1. This distance is manually adjusted by the shotcaster. Further, the shotcrete process continues until a shotcrete layer is formed on the outer surface of the package 1 with a thickness of not more than 25 mm using a typical shotcrete technology.

Sprayed concrete applied by the proposed method and using the specified materials on the entire outer surface of the block packaging allows you to create a strong external protective immobilization barrier that provides radiation and environmental protection for the environment and personnel in accordance with the IAEA requirements and increase the shelf life of block packages by an order of years without any movement from the foundation supports of the MPC.

Claims (1)

A method of shotcrete of the outer surfaces of a radiation-protective block packaging, according to which a reinforcing mesh is fixed to the surface of the block packaging and a layer of shotcrete concrete is applied under compressed air pressure, covering the mesh and including Portland cement, aggregates, chemical and mineral additives, as well as water, characterized the fact that
use a mesh with a cell side of at least 110 × 110 mm made of basalt-plastic reinforcement with a sandy outer coating, the rods of which are modified with nanoclay, based on montmorillonite - hydrated hydroxide of sodium silicate, calcium, aluminum, magnesium (Na, Ca) (Al Mg) 6 (Si ₄ O ₁₀ ) 3 (OH) 6nH ₂ O, the mesh is installed with a gap of not more than 8 mm from the shotcrete surface, and shotcrete is applied in the following ratio of components, wt.%:
Portland cement brand 500 37.0-39.2 Thick sand (at least 2 density modulus) 29.8-32.7 Silica fume 5.8 ÷ 6.0 Additive Relamix SP-2 1.1 ÷ 1.5 Ash 4,5 ÷ 5,2 Water 17.7-18.8

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