RU2754136C2 - Iron-oxide portland cement for core catcher of nuclear reactor - Google Patents

Abstract

FIELD: cements.

SUBSTANCE: invention relates to systems for ensuring localisation of the core melt of water-cooled tank reactors in the event of a beyond design basis accident. The composition of an iron oxide Portland cement contains pre-made Portland cement of a class no lower than 42.5 as a binding substance, iron oxide III is used as an active mineral additive and C-3 superplasticiser is used as a surface-active agent at the following ratio of components, % wt.: Portland cement 30 to 50, iron oxide III 50 to 70, C-3 superplasticiser 1 to 2 over 100% of the rest of the components. The method for preparing an iron oxide cement consists in dry grinding of the components to reach a specific surface area of 7000 to 10000 cm²/g, then gauging the resulting mixture with water at a water/cement ratio of 0.16 to 0.25, followed by hardening for 28 days with a compressive strength of at least 20 MPa and apparent density 2.40 to 2.85 g/cm³.

EFFECT: producing a composition with the maximum possible iron oxide content, the minimum possible content of physically and chemically bound water, reduced water requirement, increased apparent density and a specified compressive strength of no less than 20 MPa.

4 cl, 1 tbl

Description

The technical field to which the invention relates

The invention relates to one of the varieties of functional materials, called "sacrificial materials used to ensure passive safety of water-cooled nuclear reactors (VVER) [Udalov Y. P., Fedorov NF, Soloveichik E. Ya., Pavlova E .А., New functional oxide materials for nuclear reactor building. Chemical industry, v. 80, no. 12, p. 3-9, 2003]. These materials are used in a melt localization device (MLC) of a nuclear reactor of the VVER type, in which binders fill free structural volumes, fix structural elements from mechanical displacements under mechanical impacts on the MRL, in the event of a severe accident with the release of molten corium beyond the reactor walls, they reduce the enthalpy ( temperature) of the melt and oxidize elemental zirconium corium. ULR is essentially a water-cooled heat exchanger and is designed to collect and cool down high-temperature reactive metal and oxide melts formed after the destruction of a nuclear reactor due to ceramic and concrete sacrificial materials. To perform all these functions, sacrificial materials must contain the maximum possible amount of iron oxide III (Fe ₂ O ₃ ) [Asmolov V.G. The concept of management of severe accidents at PVPP with VVER “Safety Issues of NPP with VVER. Investigation of the process in case of beyond design basis accidents with the destruction of the core ”. Tr. scientific. pr. seminar, St. Petersburg, September 12-14, 2000 St. Petersburg: Publishing house. AEP, 2000, p. 1-22].

State of the art

The main sacrificial material that fills the HRM are ceramic elements made of a mixture of iron and aluminum oxides [Asmolov VG, Zagryazkin VN, Udalov Yu.P. et al. Choice of a sacrificial material for a trap to contain the melt of a VVER-1000 core. - Atomic Energy, 2002, vol. 92, no. 1, p. 7-18]. These ceramic elements must be bonded to each other and the steel walls of the ULR into a monolithic mass with a special spatial configuration and a sufficiently high mechanical strength (the design requirement is a compressive strength of at least 20 MPa) when heated up to melt. To meet this requirement, masonry cement is used, which makes the seams between ceramic products, connecting them to the steel structural element of the ULR.

Known masonry cement that meets these requirements [RF patent No. 2215340 from 08/01/2002, G21C 9/016, C04B 7/52, Cement for trapping the melt of the core of a nuclear reactor, publ. 27.10.2003], which consists of a mixture of Portland cement clinker, iron oxide and gypsum. This masonry cement has been used by the industry for the installation of URM for almost 20 years in the construction of nuclear reactors of the VVER type with an increased degree of protection against the consequences of potential severe accidents (nuclear reactors of the Tianwan NPP - 1, 2, 3, 4 (China), Kudankulam NPP - 1, 2, 3, 4 (India), Novovoronezh NPP - 1, 2 (Russia), Leningradskaya NPP - 1, 2 (Russia), Belarusian NPP - 1, 2 (Republic of Belarus), Rooppur NPP - (Bangladesh). cement according to patent No. 2215340 showed that this material has a number of disadvantages:

- high water demand when receiving a masonry mobile mortar (45-55%);

- low bulk density of cement stone (1.9-2.3 g / cm);

- low rate of strength gain at the initial stage of hardening (7-10 MPa 3 days after mixing);

- high content of physically and chemically bound water in the hardened stone (up to 10.2 wt.%).

The listed disadvantages significantly reduce the effectiveness of the implementation of the functional properties of masonry cement. The most significant disadvantage is the high content of physically and chemically bound water in the cement stone. In the event of a severe accident, the interaction of this water with zirconium contained in molten corium will result in a vapor-zirconium reaction with the release of a significant amount of gaseous hydrogen:

Zr + 2H ₂ O = ZrO ₂ + 2H ₂ ↑

Thus, reducing the water demand of the cement masonry mortar is an urgent task, and its solution will improve the safety of a nuclear reactor by reducing the amount of gaseous hydrogen in the containment.

In the cement industry, the compositions of binders and methods for their preparation are known, which ensure a decrease in water demand when they are mixed. This type of binders is called "binders of low water demand" [Batrakov V.G., Babaev Sh.G., Bashlykov NF, Falikman V.R. Binder-based concretes with low water resistance // Concrete and reinforced concrete. 1988. - No. 11. - S. 4-6], [Bikbau M.Ya. Nanotechnology in the production of cement / M.Ya. Bikbau - M .: JSC Mosk. in-t material science and effect, tekhn., 2008, 768 p.].

Binder of low water demand (VNV) is a high-strength hydraulic binder obtained by joint grinding of Portland cement clinker, gypsum stone and water-reducing additive of superplasticizer S-3. As a result of mechanochemical activation (cement grinding with a superplasticizer), the cement acquires unique, specific properties that distinguish it from standard Portland cement. VNV is characterized by:

- high dispersion (specific surface 4000-5000 cm / g);

- low water demand - normal cement paste density is on average 18.0-20.0%, while Portland cement of class 42.5 has a normal cement paste density of 24.5% -27.0%);

- activity in terms of strength up to 10 MPa.

According to the material composition, VNV is subdivided into purely clinker (VNV-100) and multicomponent with various mineral additives: a combination of active and inert additives. Blast-furnace slags and fly ash are used as active mineral additives; inert additives: building sand, waste from mining and processing plants, carbonate materials (limestone, dolomite, marble). An example of the technical implementation of such a solution is the patent [RF No. 2029749 dated 01.22.1992, С04В 7/52, Method for manufacturing a binder with low water demand, published in BI 27.02.1995]. This patent claims a method for manufacturing a binder of low water demand by mechanical treatment by joint grinding of Portland cement clinker, mineral additives, calcium sulfate and a dry modifier including a hardening accelerator and an organic water-reducing agent, up to a specific surface area of 4000-7000 cm / g, the dry modifier contains a hardening accelerator and organic dehydrating agent in a ratio by weight from 3: 7 to 7: 3, while sodium or potassium sulfate is used as a hardening accelerator, superplasticizer C-3 based on the sodium salt of the condensation product of naphthalenesulfonic acid with formaldehyde or technical lingosulfonates ... Another example of using the VNV technology to obtain the technical effect of reducing water demand is a method for producing cement with low water demand, including grinding Portland cement, a mineral filler and an organic dewatering agent to a specific surface area of 4000-7000 cm / g, characterized in that a carbonate-containing material is used as a mineral filler. the proportion of calcium carbonate not less than 60 wt. %, and the specified grinding is carried out by joint grinding of Portland cement with an organic dewatering agent to the specified specific surface area, and then grinding them with the addition of the specified carbonate-containing material [RF patent No. water demand and method of its production, published on 20.01.2010].

The essence of the invention

The objective of the invention is to achieve a technical result, including obtaining a binder sacrificial material with the maximum possible content of iron oxide, the minimum content of physically and chemically bound water and a design compressive strength of at least 20 MPa. The technical result is achieved by the fact that the iron oxide Portland cement for trapping the melt of a nuclear reactor, in contrast to the prototype [RF patent No. 2215340 - Cement for trapping the melt of the nuclear reactor core, published 10/27/2003] has the composition:

Portland cement 30-50 mass. % iron oxide III 50-70 masses. % superplasticizer S-3 1-2 mass. % over 100%

Such a composition provides the preparation of cement stone with a low content of physically and chemically bound water, which makes it possible to achieve the following results when the core melt interacts with the cement stone in the LRM:

- to reduce the formation of hydrogen due to the vapor-zirconium reaction and surface high-temperature decomposition of water vapor and, thereby, to reduce the likelihood of hydrogen explosions in the rooms surrounding the nuclear reactor, and in the hermetically sealed NPP envelope during the outflow of hydrogen from the ULR;

- to reduce the formation of aerosols and their removal into the rooms surrounding the nuclear reactor, and into the sealed enclosure of the nuclear power plant of radioactive substances from the core melt;

- to reduce the volumetric vaporization in the near-surface layers of the cement stone during its heating by the core melt, which makes it possible to slow down the rate of decrease in the strength of the cement stone during the heating process and to prevent its volumetric destruction by the pressure of water vapor;

- to exclude the impact destruction of the cement stone by the internal pressure of water vapor during thermal shock from the side of the core melt. The preparation of iron oxide Portland cement consists in joint grinding of a mixture of the above composition in intensive grinding mills until the powder mixture reaches a specific surface area of 7000-10000 cm ² / g. The possibility and efficiency of using such a composition and the method of its preparation using the VNV technology are confirmed by the data of experimental studies presented in the table.

Analysis of technological parameters and properties of iron oxide cements obtained from the selected components and prepared by joint grinding to values of 6000-10000 cm ² / g, showed that, in comparison with the prototype, the obtained compositions have the following advantages:

- decrease in water demand during mixing by 2-3 times (W / T = 0.54 for the prototype, and for the best compositions of iron oxide cements (0.16-0.17%).

- reduction of physically and chemically bound water in cement stone by almost two times (from 8.3% for the prototype composition to 4.6 / 4.7%) of the stone mass for the best compositions of iron oxide cements),

- an increase in apparent density by 1.3 times (from 2.0 g / cm for the prototype to 2.6-2.7 g / cm ³ ),

- an increase in the rate of strength gain almost twofold (the compressive strength of the prototype at 3 days of age is 12 MPa, and for a stone made of iron oxide cement at the same age up to 30 MPa).

Information confirming the possibility of carrying out the invention.

Example 1 (prototype)

Using the initial raw materials: iron oxide (Fe ₂ O ₃ ) grade "h" according to TU 14-106-340-89 in the amount of 50 wt. % loading, gypsum - 1.5%, the rest is Portland cement clinker. The listed components were loaded into a vibrating mill and the mixture was ground to a Blaine specific surface area of 6500 cm ² / g. Next, in a paddle mixer, a solution of normal density was prepared in accordance with GOST 310.6-76. Technological parameters and characteristics of the stone are shown in the table sample 1. Obviously, this sample meets the requirements for sacrificial materials in terms of iron oxide content and strength at 28 days of age, but has a number of disadvantages (high water-cement ratio, low rate of strength gain and a significant amount of bound water in the stone.

Example 2 (in accordance with the proposed composition and method of preparation of iron oxide cement)

We use raw materials: iron oxide (Fe ₂ O ₃ ) grade "h" according to TU 14-106-340-89, Portland cement of class 42.5 according to GOST 31108-2016 and dry superplasticizer C-3 according to TU 5870-002-58042865- 03. These materials were loaded into a vibrating mill in the ratio of iron oxide 50 wt%, Portland cement 50% and, in addition, 1.5% of the superplasticizer C-3. This composition corresponds to No. 4 of the table. We grind until the specific surface area of the mixture is 7450 cm ² / g. After that, in a paddle mixer, we plug the mixture with water. The water-cement ratio for obtaining a dough of normal density is 0.17. At the age of 3 days, a stone made of iron oxide cement obtained by the above described method had a strength of 30 MPa. After hardening for 28 days, the compressive strength (equal to 34 MPa), apparent density (equal to 2.85 g / cm) and loss on ignition at 700 ° and 1000 ° were measured. The total weight loss was 7.4%, and the loss due to physically and chemically bound water was 5.6%.

Example 3

We use the same raw materials: iron oxide (Fe ₂ O ₃ ) grade "h" according to TU 14-106-340-89, Portland cement of class 42.5 according to GOST 31108-2016 and dry superplasticizer C-3 according to TU 5870-002- 58042865-03. These materials were loaded into a vibrating mill in the ratio of iron oxide 60 wt. %, Portland cement 40% and over this amount 2.0% superplasticizer C-3. This composition corresponds to No. 9 of the table. The grinding was carried out until the specific surface area of the mixture was 8200 cm ² / g. After that, mixing with water was carried out in a paddle mixer. The water-cement ratio for obtaining a dough of normal density is 0.16. At the age of 3 days, a stone made of iron oxide cement obtained by the above method had a strength of 18 MPa. After hardening for 28 days, the compressive strength (equal to 22.5 MPa), apparent density (equal to 2.65 g / cm ³ ) and loss on ignition at 700 ° and 1000 ° were measured. The total weight loss was 8.4%, and the loss due to physically and chemically bound water was 5.8%. Example 4

We use the same raw materials: iron oxide (Fe ₂ O ₃ ) grade "h" according to TU 14-106-340-89, Portland cement of class 42.5 according to GOST 31108-2016 and dry superplasticizer C-3 according to TU 5870-002- 58042865-03. These materials were loaded into a vibrating mill in the ratio of iron oxide 70 wt. %, Portland cement 30% and over this amount 0.5% superplasticizer C-3. This composition corresponds to No. 10 of the table. The grinding was carried out until the specific surface area of the mixture was 9100 cm ³ / g. After that, mixing with water was carried out in a paddle mixer. The water-cement (W / T) ratio for obtaining a dough of normal density is 0.16. At the age of 3 days, a stone made of iron oxide cement obtained by the above method had a strength of 13 MPa. After hardening for 28 days, the compressive strength (equal to 17.5 MPa), apparent density (equal to 2.60 g / cm ³ ) and loss on ignition at 700 ° and 1000 ° were measured. The total weight loss was 5.7%, and the loss due to physically and chemically bound water was 4.6%. Analysis of the characteristics of the obtained cement stone shows that this composition does not provide the design compressive strength of 20 MPa.

The proposed composition of iron oxide cement and the method of its manufacture solve the problem of optimizing the technology of sacrificial materials and reduce the danger of a steam-hydrogen reaction in the containment in the event of a severe accident.

Claims (5)

1. The composition of the iron oxide Portland cement of low water demand for the production of cement stone used in the trap of the melt of a nuclear reactor, made by dry grinding of the components, characterized in that a ready-made Portland cement of a class of at least 42.5 is used as a binder, and iron oxide is used as an active mineral additive III, and as a surfactant - superplasticizer C-3 with the following ratio of components, wt%: Portland cement 30-50 iron oxide III 50-70 superplasticizer S-3 1-2, in excess of 100% of other components 2. A method of preparing portland iron oxide cement, characterized in that during its implementation, a mixture of components according to claim 1 is ground in an intensive grinding mill until the specific surface of the powder reaches 7000-10000 cm ² / g, the resulting dry mixture of iron oxide Portland cement is mixed with water in a paddle mixer to obtain test of normal plasticity with a water-cement ratio in the range of 0.16-0.25, the dough after hardening for 28 days has a compressive strength of at least 20 MPa. 3. The method according to claim 2, characterized in that the cement stone after 28 days of hardening has an apparent density of 2.40-2.85 g / cm ³ . 4. The method according to claim 2, characterized in that the losses during the calcination of the cement stone at a temperature of 700 ° C are equal to 4.7-6.1 wt.% (Losses of physical and chemically bound water), and at a temperature of 1000 ° C are equal to 5 , 7-8.9% (total losses due to the removal of volatile substances - water and carbon dioxide).