RU219060U1 - MELT LOCALIZATION DEVICE - Google Patents

Abstract

The utility model relates to a melt localization device. The device includes a cooled body and a guide element for organizing the movement of the melt, on which an outer layer of protective enamel is applied, made in the form of a suspension of finely dispersed thermally activated silicates, titanium dioxide and chromium (III) oxide in a toluene solution of polydimethylsiloxane containing silanol groups and a hardener. In a preferred embodiment of the utility model, the protective coating can be made from the OS-51-03 organosilicate composition. The technical result is to increase the safety of the melt localization device of a nuclear power plant through the use of a guide device coating with increased resistance to temperature and radiation effects. 1 z.p. f-ly, 6 ill.

Description

Technical field

The melt localization device relates to nuclear engineering, in particular to systems for localizing the melt of the active zone of a nuclear reactor and can be used to prevent the melt from leaving the nuclear power plant (NPP) in case of a severe accident.

Prior Art

In a severe accident at a nuclear power plant, it is possible for the reactor vessel to melt through the melt formed during the accident and consisting of the melted components of the reactor core and their fragments. In order to counteract the ingress of melt into the environment, in recent decades, various types of melt localization devices (MLCs) have been developed, the purpose of which is to trap the core melt with its further cooling inside the MLC, while cooling occurs through the walls of the MLC due to contact with the coolant that fills the mine in which the HR is located, in case of a severe accident. An important element of the CLR is the guide element (plate) located directly under the bottom of the reactor and installed on the truss-console, which, in turn, is fixed in the walls of the concrete shaft of the CLR.

The guide element is made in the form of a funnel and organizes the flow of molten corium into the body of the ULR in its central axial zone. Thus, the strength characteristics of the guide element are of great importance for the safety of the operation of the ULR in severe accidents.

One of the important requirements for HRM is the requirement in terms of aging management of both equipment and materials used in the design and construction of nuclear power plants.

The ULR is located in the under-reactor shaft. It provides for the use of specialized concretes such as OKA, OKA-M, TsKS and TsKS-M as protective and sacrificial material, which perform their functions during severe accidents.

Materials used in CRM are subject to special requirements in terms of composition, thermal conductivity, porosity, strength, moisture absorption and other properties, including those under aging and operation conditions, as well as under conditions of thermal and radiation load. At the same time, it should be taken into account that, since the CLR is located in the under-reactor space, the concretes used in it are subjected to high radiation and thermal effects during the entire period of NPP operation. This can lead to the loss of strength of the guide element of the ULR and its destruction in a severe accident, which can cause corium to hit the walls of the ULR instead of its central part. As a result, when falling into the body of the CLR, the corium can touch the thermal protection of the elements of the CLR, and the zone of maximum energy release shifts from the center of the CLR body, which can lead to the penetration of the CLR body.

There are a number of technical solutions that disclose the melt localization device.

A known system for localization and cooling of the corium of an emergency nuclear pressurized water reactor (RF patent No. 2253914, publ. 27.02.2005), containing a trap located in the sub-reactor space of a concrete mine, the cooled shell of which is made in the form of a vessel and filled with sacrificial materials. This system also includes a funnel-shaped corium guide located between the bottom of the reactor and the upper edge of the trap, with the walls of the guide device covered with heat-resistant concrete, over which a coating of fusible concrete is applied.

The closest in technical essence to the claimed utility model is a melt localization device (RF patent No. 100327, publ. 12/10/2010), including a cooled double-walled housing filled with a filler, a guide element for organizing the movement of the melt, a passive system for supplying water to the melt surface , the filler is arranged into blocks, each of which is divided into segments by attachment points installed radially relative to the vertical axis of the device, while filling the segments with filler is carried out with the formation of free zones communicating with the central through hole for the passage of the melt, while the cooling of the body is made in the form of a passive system that has the ability to operate with natural circulation of cooling water for an unlimited time, using water from the containment volume and sump tanks, the guiding element is made with a three-layer protective coating consisting successively of TsKS-M masonry cement, OKA-M refractory concrete, into which granules are introduced Fe ₂ O ₃ , and OKA.

The disadvantage of both of the above technical solutions is the lack of coating of the guide element, which provides increased resistance to temperature and radiation effects, which, as shown above, adversely affects the safety of nuclear power plants.

Utility Model Disclosure

The objective of this utility model is to develop a device for localizing the melt of a nuclear power plant, which has increased safety due to the use of a guide device coating with increased resistance to temperature and radiation effects.

The technical result of this utility model is to improve the safety of the device for localizing the melt of a nuclear power plant through the use of a coating of the guide device with increased resistance to temperature and radiation effects.

The technical result is achieved by the fact that in the known melt localization device, which includes a housing and a guide element for organizing the movement of the melt, an outer layer of protective enamel is additionally applied to the surface of the guide element, made in the form of a suspension of finely dispersed thermally activated silicates, titanium dioxide and chromium (III) oxide in toluene solution of polydimethylsiloxane containing silanol groups.

It is preferable to make the outer layer of protective enamel with a thickness in the range of 100-200 µm.

Brief description of the figures of the drawings.

In FIG. 1 shows the dependence of the compressive strength of concrete TsKS and TsKS-M on the heating temperature.

In FIG. Figure 2 shows the dependence of the compressive strength of OKA and OKA-M concretes on the heating temperature.

In FIG. Figure 3 shows a comparison of the compressive strength of CKS concrete specimens with coated specimens (P) based on OS-51-03 composition.

In FIG. Figure 4 compares the compressive strength of TsKS-M concrete specimens with coated specimens (P) based on OS-51-03 composition.

In FIG. Figure 5 compares the compressive strength of OKA concrete samples with coated samples (P) based on OS-51-03 composition.

In FIG. Figure 6 compares the compressive strength of OKA-M concrete specimens with coated specimens (P) based on OS-51-03 composition.

Organosilicate compositions are suspensions of fine layered silicates and metal oxides in toluene solutions of branched polyorganosiloxanes - organosilicon varnishes. In some cases, special additives are introduced into the composition of organosilicate compositions (OS) to impart special properties. In this case, the main components that determine the complex and the level of properties are organosilicon polymers, the main chains of which are built from alternating silicon and oxygen atoms, and the organic components are represented by hydrocarbon radicals combined with silicon.

After evaporation of the solvent and curing OS form a polymer composite material with a polyorganosiloxane matrix. At the same time, hydrophobicity and such physicochemical properties as resistance to temperature loads are provided by the nature of the organic radical at the silicon atom, the molecular and supramolecular structure of the film former.

The composition of the OS gives the coating high performance: weather resistance, i.e. the ability to resist the absorption of water from a humid environment, chemical resistance, and also allows for operation in a wide temperature range from -60 to +700 ° C.

In the process of OS manufacturing, the mechanochemical grafting of polyorganosiloxane molecules on the surface of filler silicon particles takes place. As a result of this process, zones of the compacted structure of the film former are formed near the surface of the filler. With a high volume content of the filler, the entire film former will be involved in this zone. This leads to a maximum of mechanical and adhesive strength, as well as the insulating ability of the coating.

In a preferred embodiment of the utility model, the protective coating can be made from the OS-51-03 organosilicate composition.

Coatings made of OS-51-03 weather-resistant organosilicate compositions of various colors have high weather resistance, and are also vapor-permeable and hydrophobic; The advantage is also a high maintainability in case of any violations of the coatings.

The composition of the organosilicate composition in the preferred embodiment is as follows:

Hardener:

tetrabutoxytitanium 0.1-0.3%

Main cast:

polyorganosiloxanes with end silanol groups,

layered hydrosilicates,

transition metal oxides.

The conducted experimental studies have shown that specialized concretes such as OKA, OKA-M, TsKS and TsKS-M under thermal loading conditions when treated with an organosilicate coating demonstrate increased compressive strength, as shown in Fig. 1-6.

For the study, samples of the same volume and shape were made from concrete of the indicated grades. After holding for 28 days, their physical properties were determined, such as water distribution, water absorption, density and compressive strength.

In order to provide reliable anticorrosion protection in the lining of the inner containment containment, a combined protective coating is widely used, including metallization of the steel surface of the shell with aluminum and subsequent application of the organosilicate composition OS-51-03 to it. This protective coating has shown itself well on metal surfaces, including thermal exposure. In connection with this, the determination of the compressive strength of samples coated with OS-51-03 organosilicate composition was singled out as a separate series of experiments. The organosilicate coating was applied in accordance with TU 84-725-78 "Organosilicate compositions", in one layer no more than 200 microns until completely dry. After drying in air, the samples coated with composition OS-51-03 were heated in a muffle furnace in the temperature range from 100 to 1000°C with a step of 100°C. After heat treatment, the samples were also tested for compressive strength.

Results

For OKA samples, with an increase in hardening time up to 14 days, an increase in the density and strength of concrete occurs. Further, during hardening, the structure loosens due to recrystallization of the hydration products of high-alumina cement, which leads to a slight decrease in density, but the strength of concrete samples is constantly increasing. The strength determined on the 28th day is 32.7 MPa, which meets the requirements for compressive strength specified in TU 1569-386-02068474-2008 for OKA concrete - at least 20 MPa.

The behavior of concrete based on the OKA-M mixture is similar to concrete based on the OKA mixture. The strength determined on the 28th day is 38.5 MPa, which is also higher than the regulatory requirements (at least 20 MPa) according to TU 1569-417-02068474-2008 for OKA-M concretes.

The strength of TsKS-M samples at 28 days of age is 25.1 MPa, which corresponds to the lower limit of compliance with the requirements of TU 1569-415-02068474-2008 [8] for TsKS-M concretes.

With an increase in the hardening time, an increase in the strength of CFB concrete occurs, which by the 28th day of hardening reaches a value of 22.75 MPa. According to TU 1569-385-02068474-2008 [9], the strength of CFB concrete should be within 25-30 MPa. The obtained experimental values of compressive strength are 9% lower than those indicated in the specifications, which may be due to the large amount of mixing water and the use of highly dispersed inert materials as a filler (aggregate), which take a significant amount of water for their wetting, excluding it from the hydration process . This is also evidenced by the high value of free water (from 4.32 to 4.69 wt.%) in the hardened composition and the low (from 1.66 to 1.99 wt.%), practically unchanged amount of bound water. The total water content is in the range from 5.98 to 6.68 wt.%

The results obtained as a result of heat treatment are shown in Table 1.

The data in Table 1 show that the amount of bound water in concretes of the OKA type increases during hardening (from 1.88 to 5.3 wt.%), which is associated with the ongoing process of formation of new hydrated phases and their recrystallization. This process determines the increase in the strength of the samples. The total amount of water varies from 4.90 to 6.78 wt.%.

In concrete samples based on OKA-M, the amount of bound water increases (from 1.75 to 4.14 wt.%), with an increase in the hardening period, which indicates an increase in the number of hydrate neoplasms in the process of hardening and thereby strengthening the structure. The total amount of water varies from 3.59 to 7.63 wt.%. The amount of free water in the process of hardening slightly increases, which is associated with the greater hygroscopicity of the modifying component of the OKA-M mixture - iron ore pellets, which can take water from the environment in small quantities.

The amount of bound water for concrete TsKS-M does not increase significantly (from 1.70 to 1.97 wt.%) due to the low content of the cement component. At the same time, the amount of free water is practically constant (4.44-4.45 wt.%), which indicates the water-retaining capacity of the finely dispersed filler. The total water content is in the range from 6.14 to 6.42 wt.%.

Water absorption determined on OKA and OKA-M samples characterizes the open porosity of the samples, so for compositions based on a mixture of OKA and OKA-M, water absorption is 19 vol.% and 20.1 vol.%, respectively.

The water absorption of compositions based on a mixture of TsKS and TsKS-M is 42 vol.% and 40 vol.%, respectively. The high value of water absorption is associated with a high content of inert finely dispersed filler (50%), which does not allow creating a strong impermeable hardening structure of the composition.

Thermal impact has a significant impact on the structure and properties of concrete, in many cases leading to a change in their properties.

The change in properties during heat treatment can be significant, which should be taken into account, in particular, when designing nuclear power plants.

Studies of the strength characteristics of concrete under thermal exposure conditions were carried out in a muffle furnace by heating the samples after reaching the design age.

As a result of heat treatment, various physical and chemical processes occur in concrete, which determine the behavior of concrete.

Studies have shown that during the heat treatment of concretes based on mixtures of TsKS and TsKS-M, with an increase in the treatment temperature, the compressive strength of the samples decreases. The decrease occurs stepwise, in the temperature range from room temperature to 400°C, after that, in the range of 400-600°C, there is some slowdown in the decrease in compressive strength, and after 600°C, the density decreases again (Fig. 1).

This behavior of concrete reflects the processes that take place in it in different temperature ranges:

200-400°C - water is removed from calcium hydrosilicates (dehydration);

405-480°C - calcium hydroxide decomposes;

700-800°C - complete dehydration of hydrosilicates and hydroaluminates occurs;

1000°C - there is a polymorphic transition of calcium silicate (C ₂ S in β-C ₂ S).

In FIG. Figure 2 shows the dependence of the compressive strength for concretes of the composition OKA and OKA-M. When the samples of concrete of the OKA composition are heated to a temperature of 200°C, the strength drops by 40%. The drop in strength is associated with the phase transition of concrete from the hexagonal phase to the cubic form. With further heat treatment up to 400°C, the process of decomposition and dehydration of Al(OH) ₃ occurs. In the same temperature range, a significant amount of crystallization water is removed, the strength is reduced by 57.5%. In this area, the sample is compacted due to the developing sintering process, which slows down the rate of strength loss. At a temperature of 1000°C there is a sharp drop in strength.

The change in the strength of the samples treated and not treated with the organic composition is shown in Figs. 3-6.

The appearance of the curves in different figures of the drawings is similar to each other, while 3 main areas can be distinguished. The first region - 200-400°C: in this area there is a significant increase in the strength of the samples treated with the organic composition. This is probably due to the sealing of the surface of the samples during the drying of the organic composition and the creation under the impermeable crust of conditions close to those of heat and moisture treatment, which significantly intensifies the synthesis of the main phases, which provide an increase in strength. Further, with an increase in temperature, the organics completely burn out from the organic composition, a white powder of the filler remains on the surface, according to X-ray fluorescence analysis, it is represented by the CaCO ₃ phase. In the area from 600 to 800°C, the process of decomposition of calcium carbonate occurs, which is used as a filler in OS-51-03. The resulting active calcium oxide reacts with concrete components to form the main calcium-containing phases, and also leads to the healing of defects on the surface. The course of these processes provides an increase in the strength of concrete samples coated with OS-51-03 relative to those not coated with an organic composition.

Based on the data obtained, the following conclusions can be drawn. Heating of concrete at all temperatures above 200°C leads to a decrease in strength characteristics. The curves of the dependences of the change in strength on the heating temperature for all concretes are similar. Concretes based on Portland cement (PCC) lose strength faster than concretes based on high alumina cement (HCA), as concretes based on high alumina cement have a more refractory base.

A comparative analysis of the obtained data on the properties of samples of specialized concretes with samples coated with organosilicate composition OS-51-03 was carried out.

It was found that the coating of samples of all concrete grades with composition OS-51-03 had a positive effect on the strength of coated samples in comparison with uncoated samples when heated to 800°C. Processing organic composition OS-51-03 samples of concrete, and their subsequent heat treatment leads to a significant increase in compressive strength for all compositions of concrete in the temperature range from 200 to 800°C. In the temperature range of 400 to 800°C, the increase in strength is from 15 to 30%, which is a significant advantage in the course of a severe accident.

Industrial Applicability

The melt localization device can be used in the nuclear industry and ensures the safety of the use of nuclear power plants in severe accidents.

Claims (2)

1. A melt localization device, including a cooled body and a guide element for organizing the movement of the melt, characterized in that the guide element is coated with an outer layer of protective enamel, made in the form of a suspension of finely dispersed thermally activated silicates, titanium dioxide and chromium (III) oxide in a toluene solution of polydimethylsiloxane containing silanol groups, and a hardener. 2. The melt localization device according to claim 1, characterized in that the protective enamel layer has a thickness in the range of 100-200 microns.

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