RU2699229C1 - Low-power fast neutron modular nuclear reactor with liquid metal heat carrier and reactor core (versions) - Google Patents

Abstract

FIELD: nuclear equipment.

SUBSTANCE: invention relates to modular nuclear reactor of fast neutrons with liquid metal heat carrier. Reactor comprises housing with cover, core zone located inside it, intermediate circuit heat exchangers, circulation pumps with pressure manifold, CPS system, wherein housing is made with double walls with inner gas cavity, with inserts installed in upper part of housing inner wall by fusions, and external wall of housing is made with finning. There are versions of the reactor core design formed by vertically installed canless fuel assemblies (FA), including heterogeneous canless fuel assemblies, in which fuel elements with MOFC fuel are used and reproducing fuel elements with reproducing material of U-Zr alloy or uranium metal oxide with oxide coating. Reproducing fuel elements are evenly distributed between fuel elements and their amount is in ratio 1 to 2, respectively, and diameter of reproducing fuel elements is more than diameter of fuel elements.

EFFECT: high radiation and fire safety of the reactor in severe accident conditions with loss of core cooling, internal self-protection, possibility of flexible control of the value of core characteristics and operation with a wide range of isotopic composition and types of fuel and reproducing materials.

9 cl, 3 tbl, 9 dwg

Description

The invention relates to the field of atomic energy and can be used in projects of nuclear power plants with fast low-power reactors - by which in modern energy we mean values less than 300 MW (e), according to the IAEA classification.

List of abbreviations used in this text:

TVS - fuel assembly;

TVEL - fuel element;

CPS - reactor control and protection system;

KB - reproduction rate;

KVA - fuel reproduction coefficient in the core;

RAO - radioactive waste;

VKG - intracassette heterogeneity;

SNF - spent nuclear fuel;

AZ - active zone;

BR - fast reactor;

OR - regulatory authorities;

NES - nuclear power system;

VVER - water-water power reactor;

VTGR - a high-temperature gas-cooled reactor;

ALMR PRISM - fast neutron reactor with sodium coolant.

State of the art

Known nuclear reactor ALMR PRISM (DC WADE and YI CHANG, "The Integral Fast Reactor Concept: Physics of Operation and Safety", Nucl. Sci. Eng., 100, 507 ~ 1988., LN SALERNO, RC BERGLUND, GL GYOREY, FE TIPPETS, and PM TSCHAMPER "PRISM Concept, Modular LMR Reactors", Nucl. Eng. Des., 109, 79 ~ 1988., General Electric ML082880369. GEFR-00793, "PRISM - Preliminary Safety Information Document, Volume 1, Chapters 1- 4 "., 401 page (s), 12/31/1987., General Electric ML082880396 - Submittal of PRISM - Preliminary Safety Information Document, Volume III, Chapters 9-14, 519 page (s), 5/26/1993) with an integrated layout, with a fast neutron spectrum, with a sodium coolant, with an active zone with dense mixed fuel and with an electric power of 145 MW. U-Pu-Zr metal alloy with several variants of isotopic composition and plutonium fraction is used as fuel in the core. Liquid sodium acts as a coolant of the I and II circuits, its temperature at the inlet to the active zone is 360 ° С, at the outlet 499 ° С (General Electric ML082880369. GEFR-00793, “PRISM - Preliminary Safety Information Document, Volume 1, Chapters 1 -4 ", 401 page (s), 12/31/1987). The active zone consists of fuel-filled sheath assemblies (FAs) and reproducing cassettes, which are used to equalize heat generation, and surround the active zone to provide enhanced fuel reproduction. To control the reactivity, 9 regulatory bodies are used; 3 rods of large weight are used as emergency protection. Also, 6 gas expansion modules are used for passive protection in accidents with loss of flow. The reactor design provides for an additional emergency cooling system, which operates due to the influx of atmospheric air along the outer casing of the unit. The air itself is delivered using concentric intake pipes, the heat between the inner reactor vessel and the safety casing is carried by convection and radiation. A nuclear plant based on such a modular reactor provides for the installation of several units on one turbine to obtain electric power of 290 MW or more (DC WADE and YI CHANG, “The Integral Fast Reactor Concept: Physics of Operation and Safety”, Nucl. Sci. Eng. 100, 507 ~ 1988).

The disadvantages of the known reactor are the low efficiency of the expanded reproduction of nuclear fuel (KV = 1.12) due to the lack of lower and upper end reproduction screens, its general configuration and the small thickness of the side reproduction screens and, associated with this, a large neutron leak from the core, leading to additional activation of materials (increase in the amount of radioactive waste) and reduction of the service life of primary equipment. According to the system requirements established for the sustainable development of nuclear energy (On the strategy of nuclear energy in Russia until 2050 // P.N. Alekseev, V.G. Asmolov, A.Yu. Gagarinsky, N.E. Kukharkin, Yu.M. Semchenkov, V.A. Sidorenko, S.A. Subbotin, V.F. Tsibulsky, Ya.I. Shtrombakh, M., SIC KI, 2012, 143 s, “Energy Strategy of Russia for the Period until 2030”, approved by order of the Russian Government Federation of November 13, 2009), a fast reactor should have a certain level of initial loading and excess fuel production. The active zone of a small-sized fast reactor has a large leakage and a hard neutron spectrum, which is why it has a high potential for expanded reproduction of fissile isotopes, but it is not fully implemented in the ALMR PRISM prototype.

In the reactor core of the known reactor, the traditional core arrangement with large flattening (D / H = 2) is used, which, combined with the small size, leads to a large specific loading of fissile isotopes, which is 8000 kg / GW (e). This value exceeds the recommended value in (On the Strategy of Nuclear Energy of Russia until 2050 // P.N. Alekseev, V.G. Asmolov, A.Yu. Gagarinsky, N.E. Kukharkin, Yu.M. Semchenkov, V.A. Sidorenko, S. A. Subbotin, V. F. Tsibulsky, Ya. I. Shtrombakh, M., SIC KI, 2012, 143 pp., “Energy Strategy of Russia for the Period until 2030”, approved by order of the Government of the Russian Federation of 13 November 2009) a restriction on the initial fuel load of a fast reactor.

In total, the regulatory, protective, and neutron sources account for 19 core cells (the remaining core cells are occupied by fuel assemblies). This occupies more than 10% of the area of the core core. Such an arrangement of the active zone leads to the fact that a large number of cells in the active zone of low fuel content (enrichment) are replaced by technological channels, which affects the neutron balance and also increases the specific load. Also, this increases the neutron leakage and the number of additional radioactive waste due to the activation of materials in the core.

As fuel assemblies, traditional hexagonal cassette tapes with a triangular lattice of rod fuel rods (relative pitch of fuel rods ~ 1.20) are used, in which metal wire winding on the fuel rods is used for spacing fuel rods. Such a lattice, taking into account the method of spacing the fuel rods, has a high hydraulic resistance of the core, which complicates the establishment of natural circulation and worsens the cooling conditions of the core in emergency situations associated with pump failure. Also, such a design increases the proportion of steel in the core to (~ 25%), which affects the neutron balance.

U-Pu-10% Zr metal alloy is used as fuel in the core; U-10% Zr glory from depleted uranium is used as a reproducing material. Such a fuel has a number of advantages, first of all, it is high (taking into account the specified porosity in the core) mass density ~ 13.0 g / cm ^{3 of} heavy nuclei (with a theoretical density of metallic fuel ~ 17.0 g / cm ^{3 of} heavy nuclei), which increases the intensity of interactions in the core, the absence of light nuclei - neutron moderators, high thermal conductivity and the possibility of efficient processing by pyrometallurgy methods. The main disadvantage of this fuel is the possible interaction with the shell and the formation of a eutectic at high temperatures. In operating conditions, the fuel-shell contact temperature should not exceed 704 ° С (General Electric ML082880369. GEFR-00793, “PRISM - Preliminary Safety Information Document, Volume 1, Chapters 1-4”, 401 page (s), 12/31 / 1987 and Status and Trends of Nuclear Fuels Technology for Sodium Cooled Fast Reactors, IAEA Technical Reports, Nuclear Energy Series, No. NF-T-4.1, 113 pp, 76 figures, Vienna, 2011). For cases of short transients, this limit on the contact temperature can be exceeded, since the interaction process itself with the formation of a eutectic has a low speed.

The practical operation of such fuel was carried out in the EBR-II reactor (General Electric ML082880369. GEFR-00793, "PRISM - Preliminary Safety Information Document, Volume 1, Chapters 1-4.", 401 page (s), 12/31/1987., General Electric ML082880396 - Submittal of PRISM - Preliminary Safety Information Document, Volume III, Chapters 9-14, 519 page (s), 5/26/1993). As a result of the irradiation of several thousand fuel rods, depressurization was not noticed, and more than 800 fuel rods burned out above 10%, i.e., burnup of ~ 18.5% so obtained for 30 fuel rods. Also, the fabrication and processing of zirconium alloy was mastered.

Operating temperatures of the heat carrier are selected below possible (Th / Th. = 360 ° С / 499 ° С). Selecting an inlet temperature of less than 400 ° C leads to the development of cold radiation embrittlement of steels in the lower part of the core, and lowering the outlet temperature reduces the overall cycle efficiency.

The disadvantage of the sodium coolant used is its high chemical activity when interacting with water and air, which makes it necessary to introduce additional measures to ensure safety, reliable control and tightness of the sodium circuit (High Security Nuclear Reactors (analysis of conceptual developments) // V.M. Novikov , I.S.Slesarev, P.N. Alekseev, V.V. Ignatiev, S.A. Subbotin, M., Energoatomizdat, 1993, 384 p.).

The proposed passive emergency cooling system is primarily aimed at preserving the integrity of the protective casing, while during transient processes in severe accidents the temperatures of internal components can exceed permissible values (LN SALERNO, RC BERGLUND, GL GYOREY, FE TIPPETS, and PM TSCHAMPER “PRISM Concept, Modular LMR Reactors ", Nucl. Eng. Des. 109, 79 ~ 1988).

A BN-800 nuclear reactor with a fast spectrum, a sodium coolant, an active zone with uranium dioxide and uranium-plutonium fuel and an electric power of 880 MW is also known (Boris Vasiliev, “Mastering MOX fuel in BN-800” by ROSENERGOATOM, No. 11, 2014, p. 18-23 and Technical Physics of Fast Reactors with Sodium Fluid: A Training Manual / V.I. Matveev, Yu.S. Khomyakov; Edited by Corresponding Member of the Russian Academy of Sciences V.I. Rachkov - M .: MEI Publishing House, 2012 .-- 356 s., Ill.). Its core is composed of case-type fuel assemblies with three options for fuel enrichment (content) to even out the radial distribution of energy release, and is surrounded by reproducing screens on the sides and bottom. The upper reproduction zone was removed in BN-800 to reduce the risk of the possible realization of a positive void reactivity effect. Liquid sodium acts as a coolant, its inlet temperature is 350 ° C, at the outlet 540 ° C. To control reactivity and protection, 12 regulatory bodies are used. The BN-800 reactor has an emergency cooling system, which is based on additional built-in emergency heat exchangers.

A disadvantage of the known reactor is the low level of excessive reproduction of nuclear fuel due to the use of dioxide fuel in the active zone, which also contains light oxygen nuclei, and the absence of an upper reproduction zone. In BN-800, the nuclear fuel reproduction rate in the core is less than 1.0, which increases the required burnup reactivity margin.

As in the case of ALMR PRISM, in the BN-800, traditional heat-insulated hexagonal cartridges with a triangular lattice of rod fuel elements are used as fuel assemblies, for the spacing of which a metal wire is used. The disadvantages of this design of fuel assemblies are indicated above.

Disclosure of the invention

The technical result of the invention is:

- improving the safety of a fast neutron reactor in severe accident conditions with loss of core cooling;

- meeting the system requirements for the sustainable development of nuclear energy in terms of specific initial loading and excess fuel production;

- increasing internal self-protection and reducing the cost of building nuclear power plants with given (and) modular reactors;

- increasing the radiation and fire safety of a fast neutron reactor in severe accident modes with coolant leaks;

- a significant improvement in fuel use and fuel cycle parameters;

- the ability to flexibly control the magnitude of the characteristics of the active zone and work with a wide range of isotopic composition and types of fuel and reproducing materials;

- expansion of the scope of the power unit.

To achieve this result, a modular low-power fast neutron nuclear reactor with a liquid metal coolant is proposed, comprising a housing with a lid, an active zone located inside it, intermediate circuit heat exchangers, circulation pumps with a pressure header, and a CPS system, while the housing is made with double walls with internal gas cavity, with inserts installed in the upper part of the inner wall of the casing, and the outer wall of the casing is made with fins.

In addition, sodium or eutectic Na-Tl 92.9 and 7.1 atomic%, respectively, are used as the liquid metal coolant.

Also, to achieve this result, a core of a modular fast neutron nuclear reactor with a liquid metal coolant is proposed, formed by vertically mounted case-free fuel assemblies (FAs) with power elements and spacing belts located in the upper part, with a triangular lattice of cylindrical fuel elements with spacer grids with mixed U -Pu-Zr fuels, with lower and upper end areas of reproduction formed by placed I am above and below U-Pu-Zr fuel in the fuel elements of the reproducing material from depleted uranium / thorium metal or depleted uranium / thorium dioxide, and the lateral reproduction zone with fuel case assemblies (FAs) with large diameter cylindrical fuel elements, in which the reproducing depleted uranium / thorium dioxide material or depleted uranium / thorium metal material.

Besides:

- power elements are six steel rods located in the corners of the fuel assemblies attached to the shanks and heads of the fuel assemblies.

- part of the fuel assembly is made with a central cavity for the placement of the CPS regulation bodies with a power element installed in it in the form of a steel cover

Also, to achieve this result, a core of a modular fast neutron nuclear reactor with a liquid metal coolant is proposed, formed by vertically mounted heterogeneous caseless fuel assemblies (fuel assemblies) with power elements and spacing belts located in the upper part, with a triangular lattice of cylindrical fuel elements (fuel rods) with distance lattices, while the fuel rods in heterogeneous fuel assemblies are made in the form of fuel fuel rods with MOX fuel and producing fuel rods with reproducing material from an U-Zr alloy or an oxide-coated metal uranium, while the reproducing fuel rods are evenly distributed between the fuel rods and their number is in the ratio of 1 to 2, respectively, and the diameter of the reproducing fuel rods is larger than the diameter of the fuel rods, and the lower and upper reproduction end zones are formed from depleted uranium / thorium metal or depleted uranium / thorium dioxide, and the lateral reproduction zone is formed by sheath fuel assemblies (FA) with cylindrical fuel element of large diameter, in which is placed a reproducing material dioxide depleted uranium / thorium metal or depleted uranium / thorium.

In this active zone, the power elements are six steel rods located in the corners of the fuel assemblies attached to the shanks and heads of the fuel assemblies,

and a part of the fuel assembly is made with a central cavity for accommodating the CPS regulatory bodies with a power element installed in it in the form of a steel cover

The inventive modular nuclear fast-neutron reactor with liquid metal coolant is made with an electric power of (180-250) MW. The design of the unit provides a flow of cold coolant after the heat exchanger along the wall of the housing into the pool of cold coolant. Between the double walls of the reactor vessel is a cavity filled with inert gas. Compared to the ALMR PRISM reactor, fuses are located in the upper part of the vessel above the coolant level. This scheme allows the loss of heat removal to organize the filling of liquid metal into the cavity on passive principles due to thermal expansion of the coolant with increasing temperature. At the same time, effective heat transfer from the fuel rods of the core to the reactor vessel is organized during the operation of the pumps or through the natural circulation of the coolant.

Compared with the ALMR PRISM reactor, fins were added to intensify heat transfer on the side wall of the reactor vessel, and its surface was blackened. The side wall with ribbing is surrounded by a blackened metal sheet of a shield-like shape. To this design, an influx of atmospheric air is provided, which is passively supplied through the pipe system to the base of the reactor, after which it is transmitted through the channel system to the outlet pipe 5-15 meters high, depending on the configuration.

This system makes it possible to efficiently remove heat from a block body using emergency convection and thermal radiation. At the same time, when the power unit is operating at full power, in case of accidents with the loss of forced standard heat removal, the permissible temperatures of structural elements, including the reactor vessel, are ensured, and the further operability of the main reactor systems is maintained.

The active zone is formed by case-free fuel assemblies (FAs) with mixed uranium-plutonium metal fuel for the active zone and sheathed fuel assemblies with reproducing material for the lateral reproduction zone. The geometry of the core differs from the traditional geometry used for fast reactors: less flattening is used compared to ALMR PRISM, BN-800 reactors, its effective diameter is 140 cm at a height of 80 cm, which is closer to the optimal value in terms of minimizing leakage neutrons.

In the basic version of core loading, fuel assemblies with a triangular lattice of fuel rods of the same diameter with a relative pitch of (1.16) are used with mixed fuel from the U-Pu-Zr alloy, which has a high mass density and thermal conductivity, with an initial porosity of 25%. The plutonium isotopic composition corresponds to the energy plutonium released during the processing of spent nuclear fuel (SNF) from thermal reactors. The share of fuel, structural materials and coolant in the core is 51.5%; 12.4%; 36.1% respectively. The diameter of the fuel rods in the core (8.100 mm) is increased compared to the ALMR PRISM reactor, in which the diameter of the fuel rods in the core (7.366 mm) (General Electric ML082880369. GEFR-00793, "PRISM-Preliminary Safety Information Document, Volume 1, Chapters 1 -4. "401 page (s), 12/31/1987), and spacers are used for spacing. There is no cover for the fuel assemblies, belts have been added to span the fuel assemblies along its edges, 6 steel rods with corners that replace part of the fuel rods located in the corners of the fuel assemblies take the load. They are attached to the shanks and heads of the fuel assemblies; spacer grids and spacer belts are held on them.

These changes compared to ALMR PRISM and BN-800 allowed to reduce neutron leakage from the core, increase fuel density and the intensity of interactions in it, reduce neutron absorption by structural materials, and also tighten the neutron spectrum. This led to a decrease in the specific initial charge for fissile materials in the core to a value (~ 3990 kg / GW (e)) that satisfies the system requirements. At the same time, despite the small size of the AZ, it achieves a high reproduction rate up to 1.0 when using energy plutonium, starting with a certain proportion of Pu-240 in the isotopic composition, or when using a heterogeneous arrangement of the core, and accordingly, the reactivity margin is minimized burnout.

As an alternative, in our embodiment, it is possible to form an active zone based on fuel assemblies with intasset heterogeneity, in which there are fuel rods (of a regular or smaller diameter) with MOX fuel, as well as reproducing fuel rods (of a larger diameter) with U-Zr alloy or metal uranium with oxide coating. Reproducing fuel rods are evenly distributed among the fuel rods and are in a triangular lattice in a ratio of 1 to 2, respectively.

This combined arrangement of fuel assemblies allows you to save the number of heavy nuclei in the core without using U-Pu-Zr fuel, but using only spent MOX fuel and U-Zr alloy or spent on blanks of fast uranium metal reactors, which also increases the core reproduction rate up to 1 when using plutonium from SNF with low burnup or from blanks of the BR. When fuel is irradiated in the replicating fuel rods, enough plutonium is generated to maintain criticality of the reactor, and when the spent heterogeneous fuel assemblies are removed from the holding pool, the replicating fuel rods can be sorted, for example, by weight, and processed with a short exposure cycle due to their low burnup .

To minimize the burnup reactivity margin (to obtain the optimal reproduction coefficient in AZ), in the case of using fuel assemblies with intasset heterogeneity, the diameter of the reproducing fuel element can be varied to a small extent. Such a measure does not have a noticeable effect on the remaining characteristics of the unit and can be easily implemented, in contrast to alternative methods of controlling fuel parameters, for example, by varying the height of the fuel column in the fuel rods.

One of the main advantages of fuel assemblies with cassette heterogeneity is the distribution of power between the types of fuel elements over the campaign. At the beginning of the MOX campaign, fuel in a fuel rod has good fuel pellet properties, which makes it possible to increase their linear load while maintaining acceptable temperatures in it. As it burns out, along with the degradation of the thermal properties of the dioxide fuel pellets, their linear power decreases. This provides the possibility of choosing a higher linear load for fresh fuel than in the case of using a traditional homogeneous assembly of fuel assemblies.

To control reactivity and emergency protection, combined fuel assemblies with CPS bodies (TVS-CPS) are used, in which instead of 4 central rows of fuel elements in a standard fuel assembly, a six-sided cover is placed. Through the drives in the reactor cover in these covers of the TVS-CPS, the movement of hexagonal or circular neutron absorbers from shell-coated boron carbide is ensured. The bulk of the fuel assembly-control system is concentrated closer to the center of the core.

Such an arrangement allows one CPS rod to extract almost 4 times less fuel from the core than in the BN-800 core, thereby maintaining it in the core, thereby reducing plutonium content and increasing nuclear fuel reproduction in the core. The location of the TVS-CPS along the radius of the active zone is additionally used to align the energy release field.

The active zone is surrounded by reproducing cover assemblies with large-diameter fuel rods in which tablets can be placed, for example, with depleted metal uranium or thorium, or with depleted uranium or thorium dioxide. Reproducing fuel assemblies form a lateral zone of reproduction. Also, tablets with depleted uranium / thorium metal or with depleted uranium / thorium dioxide are placed in the fuel cladding under and above the core fuel pellets. They form the lower and upper end zones of nuclear fuel reproduction.

The use of thorium in blankets makes it possible to efficiently run U-233 for fueling thermal reactors. With this arrangement of thorium, the negative effect of the protactinium reactivity effect is practically absent, and due to the high leakage of neutrons from the core and their hard spectrum, the rate of excessive reproduction corresponds to system requirements. If plutonium is not enough for the formation of a reactor core, then partial or complete replacement of thorium screens with uranium screens is possible to increase the reproduction of plutonium.

To increase the internal self-protection of the reactor, it is proposed to use the Na-Tl eutectic (92.9 and 7.1 atomic%, respectively) as a coolant.

Wherein:

- significantly reduces the chemical activity of the coolant;

- excludes violent reaction with water, steam and atmospheric air, accompanied by fire or explosion;

- significantly reduces the formation of radioactive aerosols in accidents with a coolant leak;

- the boiling point of the coolant rises;

- decreases the melting temperature of the coolant;

- the technology of purification of the modified heat carrier from oxygen is simplified and the exclusion of a cold trap is potentially allowed.

In order to increase the neutron-physical characteristics of the reactor, thallium isotope enrichment using the T1-205 isotope can be applied.

In the event of technical or economic limitations using sodium thallium coolant, it is possible to maintain the use of pure sodium in the intermediate circuit.

Brief Description of the Drawings

The invention is illustrated by the drawings shown in FIG. 1-9.

In FIG. 1 shows the basic design of the reactor vessel with a passive heat sink system.

In FIG. 2 shows the basic design of the emergency cooling system using natural air convection.

In FIG. Figure 3 shows the calculated area of permissible dimensions of a modular reactor, in which the set requirements for its characteristics are satisfied.

In FIG. 4 shows a cartogram of a modular reactor.

In FIG. Figure 5 shows the change in burnup of a fuel rod of a linear load of fuel and reproducing fuel rods in fuel assemblies with intasset heterogeneity.

In FIG. Figure 6 shows the phase diagram of the state of the sodium-thallium alloy.

In FIG. Figure 7 shows changes in the temperature of the coolant and structural materials in an accident with the loss of forced heat removal.

In FIG. 8 shows the design of the standard fuel assemblies of the core and fuel assemblies-CPS.

In FIG. Figure 9 shows the design of a standard fuel assembly of an active zone with cassette heterogeneity and a fuel assembly-control system.

The positions in the figures indicated

1 - active zone

2 - pressure header

3 - cold coolant pool

4 - intermediate circuit heat exchanger

5 - pool of hot heat carrier

6 - circulation pump

7 - fusible inserts

8 - gas cavity between the walls of the housing

9 - the influx of atmospheric air

10 - heated air outlet

11 - ribbing on the side wall of the housing

12 - screen-shaped sheet - heat shield

13 - thermal insulation

14- shank with spiral seal

15 - holes for the coolant inlet

16 - support grid

17 - a bunch of fuel rods

18 - spacer grids

19 - belts for spacing fuel assemblies

20 - upper support grill

21 - head

22 - grip

23 - six thickened steel rods

24 - fuel rods

25 - inner steel cover - channel OR SUZ

26 - thickened steel rods for heterogeneous fuel assemblies

27 - reproducing fuel elements

28 - fuel rods

29 - internal steel cover - channel OR CPS for heterogeneous fuel assemblies

The implementation of the invention

Figure 1 presents the organization diagram of the passive emergency cooling system in the housing without additional heat exchangers. It is based on passive principles, is technological and not difficult to implement. To eliminate the negative effect on energy conversion (Efficiency) in the nominal operating mode, the reactor vessel is made with double walls, between which there is a gas cavity 8. In normal mode, it is filled with argon (or other inert gas). If you lose the possibility of heat removal through heat exchangers 4, the average temperature of the internal sodium in pools 3 and 5 increases, which leads to its expansion. Thus, it becomes possible to organize a level, upon rising to which, sodium will come into contact with the fusible inserts 7 and fall into this inter-shell gas cavity, while its thermal resistance sharply decreases. After troubleshooting, the sodium from the cavity can be drained or displaced by gas under pressure. In the nominal mode, with a block thermal power of 400 MW, constant heat loss through the inter-shell space filled with gas, according to preliminary calculations, is less than 100 kW, which may be acceptable for passive heat removal. In the course of the study of the scattering ability of the body wall, it was found that it is not enough to maintain the temperatures of the components of the primary circuit within acceptable limits.

In FIG. 2 shows the installation diagram of the reactor vessel and the shaft for organizing a passive cooling system through the vessel. On the side wall of the reactor, along which the possibility of air flow is created, ribbing 11 is added, and the surface is blackened. At a certain distance from the wall, around it there is a heat shield 12 — a screen-type metal sheet. This form allows you to achieve a larger surface area, effectively absorb thermal radiation from the wall of the reactor, and scatter it using natural convection. Behind the heat shield is a sheet of thermal insulation 13, which reflects thermal radiation, and also serves as the thermal protection of the reactor shaft. Through a network of pipes, atmospheric air is drawn, which is lowered along communications 9 along the sheet of the heat shield 12, then distributed into 3 streams: along the ribbed wall of the reactor 11 and on each side of the screen sheet 12 and exits through the network of exhaust channels of heated air 10. They are provided radiation monitoring system and dampers in case of sodium leakage. Also, the dimensions of the shaft are selected in such a way that in case of depressurization of the housing and the formation of a leak, the active zone was under a layer of coolant.

The configuration of the reactor core can be changed by moving from a three-zone alignment along the radius of the active zone of the energy release field to a two-zone when placing the fuel assembly-control system in the central part of the reactor. A cartogram with two-band radial alignment of the energy release field in the core is shown in FIG. four.

The general characteristics of the reactor and the initial data for the calculation are presented in the table

To reduce the share of structural materials in the core, increase the share of fuel and obtain other advantages, case-free fuel assemblies are used. The design of such an assembly is shown in FIG. 8. It is a shank 14 with a spiral seal and openings 15 for the coolant inlet, then comes the support grid 16, a bunch of fuel rods 17, which are held in place by the spacer grids 18. The spacing belts 19 are located above, the upper support grid 20 and the head 21 through which the heat carrier leaves. In the upper part of the fuel assembly there is a grip 22 for its installation and movement.

The cross section of the fuel rods of a standard cartridge is shown in FIG. 8 b Among the lattice of the fuel rods there are six thickened steel rods 23, which act as a power structure, and to which the spacer grids 18 are fastened holding the fuel rods 24.

In the embodiment of the fuel assembly with a cavity under the regulatory bodies, the overall design is similar. Differences in the cross section of the fuel elements are shown in FIG. 8 c. The central 4 rows of fuel rods with fuel 24 are removed, and instead of them a steel cover 25 is installed. It acts as a power element instead of rods.

When using cassette heterogeneity of the VKG, the design of the fuel assembly is shown in FIG. 9. The main elements repeat the standard cassette described above, the differences are present in the fuel rods. The cross section of the fuel rods of the VKG cassette is shown in FIG. 9 b Among the lattice of the fuel rods, there are six thickened steel rods 26, which act as a power structure, and to which spacer grids 18 are mounted that hold the fuel rods 24. Two types of rods are used - fuel 28, which contain mixed oxide fuel, and reproducing 27, containing metallic fuel from dump uranium and having large diameter.

In the embodiment of a fuel assembly with a VKG with a hollow under the regulatory bodies, the general design is similar. Differences in the cross section of the fuel elements are shown in FIG. 9 c. The central 4 rows of fuel rods with fuel 27-28 are removed, and instead of them a steel cover 29 is installed. It acts as a power element instead of rods.

Examples of specific calculation

, J., et al. (2015) «The Serpent Monte Carlo code: Status, development and applications in 2013». Ann. Nucl. Energy, 82 (2015) 142-150) на основе метода Монте-Карло.To calculate the neutron-physical characteristics, the JARFR programs were used (Yaroslavtseva L.N. The JARB program package for calculating the neutron-physical characteristics of nuclear reactors. diffusion approximation and SERPENT 2 (

, J., et al. (2015) “The Serpent Monte Carlo code: Status, development and applications in 2013”. Ann. Nucl. Energy, 82 (2015) 142-150) based on the Monte Carlo method.

An example of a multivariate calculation with varying block power and core flattening is shown in FIG. 3. It can be seen that the flattening, which ensures the minimum loading of fissile isotopes, differs from that used in the ALMR PRISM reactor. In the proposed reactor, it is closer to the optimal value for neutron leakage, which provides more favorable neutron-physical characteristics.

In FIG. 4 presents a cartogram of the core. Table 1 presents the general characteristics of the module and the initial data for the calculation. The results of the neutron-physical calculation of the block for options for loading the core with plutonium with different isotopic composition are presented in table 2.

As you can see, almost all of the options presented satisfy the system requirements for specific initial loading and excess operating time of nuclear fuel. The specific load for fissile isotopes does not exceed 4.0 t / GW (e), the specific reproduction in the reproduction zones is above 250 kg / GW (e) * year. The use of plutonium with a high proportion of Pu240 is more preferable, since it increases the KB in the core and reduces the burnup reactivity margin. The addition of the upper and lower reproducing end screens did not lead to a significant increase in the void effect of reactivity in comparison with ALMR PRISM, which contains a lower core height. In the case of using fuel assemblies with intracassette heterogeneity, it is possible to obtain a small burnup reactivity margin with virtually any composition of plutonium, providing the required parameters with a small variation in the diameter of the reproducing fuel element.

In FIG. 5 shows the change in the linear power of the fuel and reproducing fuel rods depending on the burnup of the fuel rod. It can be seen that during the fuel campaign the power of the fuel rod decreases and the maximum load on it occurs only at the beginning of the campaign, when the thermophysical parameters of the fuel pellet are the best. Also, importantly, this arrangement of cassettes, in addition to fuel production in the reproduction areas, allows producing more than 400 kg / GW (el) * year Pu with high Pu-239 content in the reproducing fuel rods. Reproducing fuel rods have low burnup, can be separated from fuel rods and processed with less exposure by existing methods for reprocessing spent fuel from VVER reactors.

In FIG. 6 is a phase diagram of the state of the Na-Tl system. A stable eutectic is formed at a point with an atomic fraction of thallium of 7.1% (Alekseev PN, Shimkevich AL. Expediency of eutectic modification of liquid metal coolants. Atomic energy. 2015. Vol. 119. No. 3. P. 178-179). Using the described software, the effect of the addition of thallium on the neutron-physical characteristics of the reactor was calculated. The results of the effect of thallium addition on the main characteristics of the reactor in relative units are presented in table 3. Table 3 shows the differences between the characteristics of the reactor with the Na + Tl coolant and the characteristics of the reactor with the sodium coolant for different variants of the isotopic composition of thallium in the Na + Tl coolant.

The results are presented in various columns: for a natural mixture of T1 isotopes; for a mixture of T1 isotopes with enrichment in the T1-205 isotope to 90% and for a mixture of T1 isotopes with enrichment in the T1-205 isotope to 99%, respectively. The ρ _{Dopler value} corresponds to the Doppler coefficient, ρ _void1 is the void effect reactivity, which is realized when the upper part of the active zone and the end shield are _empty , ρ _void2 is the reactivity, which is realized when the region of the active zone is empty, which has the maximum positive local void reactivity effect and ρ _void3 - reactivity, which is realized when the entire core and the upper end shield are emptied, respectively.

It can be seen that the overall effect of the addition of thallium on the neutron-physical characteristics of the reactor is small and also allows satisfying the system requirements for the sustainable development of nuclear energy. Isotope enrichment of T1 by the isotope T1-205 allows to reduce the negative impact of thallium and is suitable for use in the case of economic justification. As for the activation of the coolant and the radiation load from it, very small amounts of gamma-active thallium isotopes are formed under irradiation, and it makes an insignificant contribution to the total intensity of gamma sources in the coolant. Together with the greater self-shielding effect of NaTl compared to pure Na, this leads to a decrease in the equivalent dose from the irradiated coolant.

To assess the efficiency of heat removal of residual heat through the casing, a quasi-dynamic model of the reactor and the surrounding space was created, which takes into account the nature of the heat exchange between its elements, their heat capacity and the nature of the heat released from the fuel after the unit is stopped. The results of modeling the temperatures of the elements as a function of time for the case of complete loss of heat removal and resetting of emergency protection when operating at full power are presented in FIG. 7. T _Na is the temperature of sodium, T _st1 is the temperature of the inner wall of the body, T _st2 is the temperature of the outer wall of the body with fins. The temperatures of the claddings of fuel rods and fuel differ slightly from the temperature of the primary circuit sodium and therefore are not represented. As you can see, after the loss of heat removal and shutdown of the reactor, the temperature of the elements increases, and the transition process is smoothed due to the heat capacity of the coolant. Further, after 50 minutes, the fusibles melt and the coolant overflows into the cavity between the parts of the body. This leads to the intensification of heat transfer between the walls of the housing and the heating of all other parts. Then, the primary coolant temperature rises to 680 ° C, after which the residual heat from the fuel is compared with the power taken off, and the temperature drops. Such a system can work for an unlimited time, and during the transition process the temperature of the elements did not exceed the critical values for the permissible shell temperature and for the formation of the eutectic between steel and fuel.

Thus, a modular fast neutron reactor with a liquid metal coolant is proposed, the design of which provides high internal self-protection, in which a minimum burnup reactivity margin is realized, a special choice of the ratio of the maximum void and Doppler reactivity effects eliminates instantaneous neutron acceleration of the reactor with an emergency decrease in coolant density , to reduce chemical activity when interacting with water and air, sodium heat the carrier is replaced with a Na-Tl eutectic (92.9 and 7.1 atomic%, respectively), to ensure safety in case of accidents with loss of heat sink, a passive air emergency emergency cooling system is organized through the reactor vessel without additional heat exchangers. It is based on passive principles, is technological and not difficult to implement. It is shown that, despite the small size of the proposed modular fast reactor and high neutron leakage, due to the choice of fuel, minimization of the fraction of structural materials in the core, the presence of end and side reproduction screens, its characteristics satisfy the system requirements for the development of a nuclear energy system (NES) by the value of the specific initial load and the excess operating time of nuclear fuel.

The relevance of the proposal is due to the fact that, according to the energy strategy in Russian nuclear energy, along with increasing the number of power units with promising VVER (and VTGR) thermal reactors and the transition to a closed fuel cycle, fast reactors (BR) with high internal self-protection, with expanded reproduction of fuels intended for the effective involvement of U-238 and Th-232 in energy production, minimizing the amount of spent fuel and fuel supply for new and existing reactors, as well as small units and average power.

Claims (9)

1. A modular fast neutron nuclear reactor with a liquid metal coolant, comprising a casing with a lid, an active zone located inside it, intermediate-circuit heat exchangers, circulation pumps with a pressure header, CPS system, and the casing is made of double walls with an internal gas cavity, with inserts installed in the upper part of the inner wall of the housing, and the outer wall of the housing is made with fins. 2. A nuclear reactor according to claim 1, characterized in that sodium is used as the liquid metal coolant. 3. A nuclear reactor according to claim 1, characterized in that a Na-Tl eutectic of 92.9 and 7.1 atomic%, respectively, is used as the liquid metal coolant. 4. The active zone of a modular fast neutron nuclear reactor with a liquid metal coolant, formed by vertically mounted case-free fuel assemblies (FAs) with power elements and spacing belts located in the upper part, with a triangular lattice of cylindrical fuel elements with spacer grids with mixed U-Pu-Zr fuel, with the lower and upper end zones of reproduction, formed by placing above and below the U-Pu-Zr fuel in the fuel elements material producing depleted uranium / thorium metal or depleted uranium / thorium dioxide, and a lateral reproduction zone with case fuel assemblies (FAs) with large diameter cylindrical fuel elements in which reproduction material is made of depleted uranium / thorium dioxide or depleted uranium / thorium metal . 5. The active zone according to claim 4, characterized in that the power elements are six steel rods located in the corners of the fuel assemblies attached to the shanks and heads of the fuel assemblies. 6. The active zone according to claim 4, characterized in that a part of the fuel assembly is made with a central cavity for accommodating the CPS regulation bodies with a power element installed in it in the form of a steel cover. 7. The active zone of a modular fast neutron nuclear reactor with a liquid metal coolant is formed by vertically mounted heterogeneous caseless fuel assemblies (fuel assemblies) with power elements and spacing belts located in the upper part, with a triangular lattice of cylindrical fuel elements (fuel rods) with spacer grids, in heterogeneous fuel assemblies made in the form of fuel rods with MOX fuel and reproducing fuel rods with reproducing material from sp Ava U-Zr or oxide-coated metal uranium, while the reproducing fuel rods are evenly distributed between the fuel rods and their number is 1 to 2, respectively, and the diameter of the reproducing fuel rods is larger than the diameter of the fuel rods, and the lower and upper end zones of reproduction are formed of metal depleted uranium / thorium or depleted uranium / thorium dioxide, and the lateral reproduction zone is formed by sheath fuel assemblies (FAs) with cylindrical fuel elements b lshogo diameter, which is placed in a reproducing material dioxide depleted uranium / thorium metal or depleted uranium / thorium. 8. The active zone according to claim 7, characterized in that the power elements are six steel rods located in the corners of the fuel assemblies attached to the shanks and heads of the fuel assemblies. 9. The active zone according to claim 7, characterized in that a part of the fuel assembly is made with a central cavity for accommodating the CPS regulation bodies with a power element installed in it in the form of a steel cover.

Images