RU2798478C1 - Integrated nuclear reactor with liquid metal coolant - Google Patents

Abstract

FIELD: nuclear energy.

SUBSTANCE: invention relates to a nuclear reactor of integral type with a liquid metal coolant. The reactor includes a reactor vessel (9) closed by a cover (1) having a lower chamber (16) formed by a separating structure attached to the reactor cover (1), an active zone, at least one circulation pump (21) of the primary circuit with a shell (2) of the circulation pump attached to the cover (1), at least one heat exchanger installed in the shell (20) attached to the cover (1), and a plug (25). The separating structure is made in the form of an annular element (11) attached to the reactor vessel (9), in the guide shell of which the end shell (3) is inserted, connected to the reactor cover (1). Internals (8) are interconnected and attached to the peripheral part of the reactor cover (1), the lower end of the shell (20) of the heat exchanger is located above the annular element (11), and the lower end of the shell (2) of the circulation pump (21) passes through the hole in annular element (11) into the lower chamber (16).

EFFECT: increased safety and reliability of the reactor.

10 cl, 6 dwg

Description

Technical field

The invention relates to nuclear power, in particular, to nuclear reactors with heavy liquid metal coolants (HLMT). More specifically, the present invention relates to the construction of nuclear reactor vessels with integral type heavy liquid metal coolant.

State of the art

A nuclear reactor of an integral type is characterized, first of all, by the fact that it does not have pipelines with a primary coolant. In addition to the core, the reactor vessel houses all the main equipment that ensures heat removal from the core to the secondary coolant. In addition, the integral type reactor includes reactivity control elements necessary for power control, equipment for systems that control the coolant temperature, flow rate, and pressure at various points in the circuit. All of the above equipment is essentially located in the reactor vessel or attached to it. The fission chain reaction maintained in the core and the accompanying transfer of neutrons and radiation both in the core and in the reflector and in the structural elements surrounding them is accompanied by heat release. Removal of heat from the elements of the core and from structural elements located in the nuclear reactor vessel requires such an organization of circulation and distribution of coolant flow rates so that the temperatures of structural elements do not exceed permissible values. To do this, the design of the reactor includes pipes, channels, throttling devices that provide the distribution of coolant flow rates necessary for cooling.

Important devices placed in the reactor vessel also include elements surrounding the core and performing the function of a neutron reflector, radiation protection, which ensures the absorption of neutrons and radiation and reduces their negative impact on other elements of the reactor, for which it is necessary to ensure the integrity of the structure and operability in an integrated impact of all damaging factors.

All internal devices and metal structures must be securely fixed. At the same time, the equipment of a nuclear reactor with HLMC operates under conditions of high temperature gradients, reaching several hundred degrees. The difference in temperature movements associated with different elongation or changes in the dimensions of structural elements at different temperatures can be significant. In the absence of special design solutions that ensure freedom of movement of various elements during heating and cooling, significant stresses may occur that limit the resource or lead to structural failure.

The development of a design that eliminates or reduces the mechanical impact of elements on each other at high temperature gradients is one of the important tasks. An important task is also to exclude uncontrolled or unforeseen coolant leakages through the gaps, which are necessary to ensure the freedom of thermal expansion of structural elements relative to each other. The solution of the latter problem is also complicated by the fact that the reactor equipment is large-sized and, for assembly even in a cold state, it must have the necessary clearances to compensate for manufacturing errors.

An important feature of HLMC reactors is that almost all structural materials and radiation shielding materials have a density lower than that of the coolant. In this regard, when attaching structural elements and associated internal devices and equipment to the bottom of the hull or its side walls, tensile stresses arise due to the effect of buoyancy forces on these elements. Tensile stresses in the structure and welds are the most dangerous in terms of the development of stress corrosion.

Creation of the design of the reactor pressure vessel and the connection of internal devices with the vessel, in which detachable and permanent connections of structural elements would experience mainly compressive stresses, is also an important technical task.

Known nuclear reactor with liquid metal cooling (US10699816, IPC G21C 1/03, G21C 1/32, G21C 5/02, G21C 15/06, publ. 06/30/2020), including a reactor vessel, a hot collector above the core and a cold collector, surrounding the hot manifold and separated by a separating structure, wherein the cold manifold circulates the primary fluid, in particular the HLMC. The reactor contains at least one heat exchanger, in particular a steam generator, to remove heat from the HLMC through a secondary fluid, in particular water. The separating structure contains a lower element located around the active zone and an upper element located above the active zone. The upper element has a reduced radial extent compared to the lower element and is connected to the lower element by means of a connecting element. The connecting element has openings from which vertical channels depart for connection with one or more heat exchangers located between the upper section of the separating structure and the reactor vessel, for supplying hot HLMC leaving the core to the heat exchangers. The connecting element and the upper element of the separating structure form a radial limiter of the active zone, in particular the inactive upper part of the fuel assemblies.

As a separating structure of the known reactor, a complex-shaped shell is provided, which is cantilevered to the reactor lid. In this case, the lower part of the shell is not fixed, which is a significant drawback. Such a constructive solution, with significant dimensions and weight of the core installed in it, leads to increased loads in the area of the cantilever attachment, which is especially dangerous under seismic loads.

Known is a nuclear reactor with a liquid metal coolant (RU2756231, IPC G21C1/00, publ. 09/28/2021), including a reactor vessel with a lower chamber, an active zone, a hot chamber, an upper chamber and heat exchangers. The hot chamber is located above the core and contains a body of the hot chamber of essentially cylindrical shape with branch pipes for removing hot coolant coming from the core to the heat exchangers, and a plug, and said pipes are washed from the outside with cold coolant from the outlet of the heat exchangers. The hot chamber body comprises an inner hot chamber shell and at least one additional hot chamber shell installed with a gap outside and concentric to the inner hot chamber shell and forming at least one hot chamber channel. Each nozzle contains an inner shell of the nozzle and at least one additional shell of the nozzle, installed with a gap outside and concentric to the inner shell of the nozzle and forming at least one channel of the nozzle, and at least one channel of the hot chamber and at least one channel of the nozzle communicate with the outlet of the heat exchangers for directing the flow of cold coolant into these channels.

EFFECT: invention provides reduction of thermal load on the elements of the hot chamber, first of all, the body of the hot chamber and hot coolant outlet pipes, including smoothing and reduction of the temperature gradient arising in these elements, and as a result, increasing their service life. However, this result is achieved by complicating the design and manufacturing technology of the nozzles and the hot chamber.

A known nuclear reactor with a liquid metal coolant (JP2022097583, IPC G21D1/02, G21C1/02, G21C13/00, G21C15/02, publ. a cold header surrounding a hot header separated by a spacer structure and in which primary fluid circulates to cool the core. The reactor is equipped with a heat exchanger having a primary liquid inlet in the lower part and a circumferential outlet window near the free surface of the primary liquid in the cold collector. The exit window is located in an intermediate position with respect to the tube bundle, partially raised with respect to the free surface in the cold collector and filled with primary liquid by means of an auxiliary device for creating a vacuum in the cover gas of the heat exchanger with respect to the cover gas in the vessel. Raising the heat exchanger and positioning the outlet near the free surface of the primary coolant helps to minimize movement of the primary fluid in the event of an accidental release of the secondary fluid inside the heat exchanger.

The known nuclear reactor has low reliability due to the lack of design solutions that ensure freedom of movement of various elements of the reactor during heating and cooling, leading to significant stresses on these elements of the reactor, limiting the resource or leading to destruction of the structure.

Known nuclear reactor with liquid metal coolant (US20180061513, IPC G21C1/03, G21C15/14, G21C1/32, G21C5/02, publ. 06/30/2020), coinciding with the present technical solution for the largest number of essential features and taken as a prototype. The prototype nuclear reactor includes a reactor vessel covered with a lid and containing a core shaft, a hot collector above the core, and a lower chamber separated by a separating structure, with primary fluid circulating in the lower chamber to cool said core. The reactor also contains at least one heat exchanger attached to the lid, in particular a steam generator, for removing heat from the primary fluid via the secondary fluid. The separating structure contains a lower element located around the active zone and an upper element located above the active zone. The upper element has a reduced radial extent compared to the lower element and is connected to the lower element by means of a connecting element made, for example, in the form of a plate. The connecting element has openings from which vertical channels depart for connection with one or more heat exchangers located between the upper section of the separating structure and the reactor vessel, for supplying hot primary fluid leaving the core to the heat exchangers. The connecting element and the upper element of the separating structure form a radial limiter of the active zone, in particular the inactive upper part of the fuel assemblies.

The well-known prototype nuclear reactor has insufficient reliability due to the lack of freedom of movement of various elements of its structure during heating and cooling, due to the occurrence of tensile stresses in structural elements having a density lower than the density of the liquid metal coolant, due to the effect of buoyancy forces on them, and also due to the presence of coolant cavities in the reactor pressure vessel with extremely low velocities, leading to the formation of areas with poor coolant mixing and the occurrence of corrosion damage due to deterioration in coolant quality control.

Disclosure of the essence of the invention

The objective of the present invention was to develop a nuclear reactor, in particular a nuclear reactor with a liquid metal coolant, which would have increased safety and reliability during operation by providing freedom of longitudinal and radial movement of various elements of its design during assembly, heating and cooling relative to each other, increasing corrosion resistance and the necessary antifriction characteristics of the contacting materials; equalization of coolant velocities at the entrance to the lower chamber and further to the core; ensuring the reliability of fixing fuel assemblies (FA) from unauthorized ascent due to a controlled limited preload force that does not prevent thermal expansion.

The technical result of the present invention, achieved when solving the problem, in particular, is:

- ensuring freedom of longitudinal and radial movement of different elements relative to each other during heating and cooling, the absence of which can cause uncontrolled or unforeseen coolant leaks that reduce the reliability of cooling of the reactor equipment, and significant stresses that limit the resource or lead to structural failure;

- increase in corrosion resistance and necessary antifriction characteristics of materials;

- equalization of coolant velocities at the entrance to the lower chamber and further to the core, which is important for ensuring reliable cooling of its elements and safety;

- ensuring the reliability of fixation of fuel assemblies from unauthorized ascent, which does not prevent thermal expansion, which is ensured by limiting the clamping force;

- improving the safety and reliability of reactor operation.

The problem is solved by the fact that a nuclear reactor with a liquid metal coolant includes a reactor vessel closed with a lid, having a lower chamber formed by a separating structure attached to the reactor lid, an active zone, at least one circulation pump of the primary circuit with a circulation pump shell attached to the lid, at least one heat exchanger installed in the shell attached to the lid to remove heat from the liquid metal coolant to the secondary circuit coolant, and a plug. What is new in a nuclear reactor is that the separating structure is made in the form of an annular element attached to the reactor vessel, in the guide shell of which the core shell is inserted, connected to the reactor lid, internal devices (VCU), including channels for organizing the necessary circulation of the coolant, are connected between themselves and are attached to the peripheral part of the reactor cover, the lower end of the heat exchanger shell is located above the annular element, and the lower end of the circulation pump shell passes through the hole in the annular element into the lower chamber.

In the lower part of the core shell, a base plate can be installed, in which fuel assemblies with channels of the control and protection system (CPS) and reflector blocks are fixed.

In the reactor plug, the tips of the CPS channels can be made conical, with internal surfaces in contact with the FA heads.

A baffle can be made in the plug below its upper part, to which the CPS channel is connected by means of an elastic bellows connection, which limits the force transmitted to the fuel assembly head.

Below the annular element, an additional annular element of smaller diameter can be installed, in which at least one hole is made, with the formation of an annular manifold between them, the inlet of which is connected to the outlet of the circulation pump, and the outlet is connected to the lower chamber.

Below the additional annular element, ribs can be attached to the bottom of the reactor vessel to direct the coolant flow from the periphery to the center of the lower chamber. To equalize the distribution of costs in azimuth, it is preferable to provide holes in the ribs that provide azimuthal overflows.

An annular groove can be made in the circulation pump shell, in which at least one piston sealing ring is installed, movable in the radial direction and closing the gap between the circulation pump shell and the annular element during radial movements of the circulation pump shell.

An annular groove can be made in the core shell, in which at least one piston sealing ring is installed, movable in the radial direction and closing the gap between the core shell and the annular element during radial movements of the shell.

The piston seal ring can be made of ductile gray cast iron with lamellar graphite with a silicon content of at least 1% or corrosion resistant stainless steel.

The placement of the most critical equipment in shells rigidly attached to the reactor head using detachable or permanent connections makes it possible to carry out its revision, repair or replacement during reactor operation. In these shells, the necessary holes are provided for organizing the circulation of the coolant. These shells can freely move in the longitudinal direction during heating or cooling, and at the interfaces with other structural elements they have special sliding seals that do not prevent such movements.

So, for example, removable elements of the reactor design can be circulation pumps, steam generators or heat exchangers between the primary and secondary circuits, core support structures, the core and the removable part of the radial reflector, a plug above the core.

The main part of the internal equipment, including pipelines and coolant guide channels, is combined into a single structure and connected to the reactor head. In this case, all efforts from the buoyancy forces of the coolant, which has a higher density than the structural materials, are directed upwards and are ultimately transferred to the reactor head. Taking into account the fact that a significant part of the equipment is placed and fixed on the reactor cover, namely, circulation pumps with a drive, drives of control bodies, inlet and outlet chambers and pipelines of a steam generator or heat exchangers, external radiation protection and other elements, the forces from the action of Archimedes forces are largely compensated by the weight of the specified equipment, which favorably affects the performance of the lid. At the same time, internal elements that are not related to the elements of the core are attached mainly to the peripheral part of the reactor lid, which helps to reduce bending moments and improve the operability of the lid.

Only the minimum necessary coolant flow guiding elements are attached to the bottom of the reactor, in which mates with shells are provided to accommodate the core and pumps. The interface units are provided with seals and provide free longitudinal movement of said shells, as well as necessary and limited radial movements while maintaining tightness or significantly limiting leakage.

The amount of allowable radial movement in the seals is determined by the need to compensate for dimensional tolerances during manufacture and thermal expansion. At the same time, the possibility of large displacements in the radial direction in the present reactor is excluded, since large displacements create a danger in case of significant external influences on the reactor, for example, during earthquakes. The design of seals can be chosen from known solutions in the art, however, the most preferred option is using piston rings. In this case, the preferred material is a material of the class of gray cast irons with lamellar graphite. The presence in the cast irons of this class of silicon on the order of (1-3) wt.% and inclusions of lamellar graphite provide a correspondingly increased corrosion resistance and the necessary antifriction characteristics of the seal material. With small pressure drops, the seals can be labyrinthine. The admissibility of using labyrinth seals is determined by hydraulic calculation according to known methods and the admissibility of the magnitude of the calculated leaks, which must be determined individually in a specific project implementation.

Brief description of the drawings

The present invention is illustrated by drawings, where:

in fig. 1 is a partial sectional perspective view of a real HLMT nuclear reactor;

in fig. 2 shows in section the interface between the CPS channel tip and the fuel assembly head;

in fig. 3 shows in section the attachment point of the CPS channel to the intermediate base plate of the plug;

in fig. 4 is a sectional view of a seal assembly with a self-adjusting seat;

in fig. 5 is an enlarged view of the node D shown in FIG. 4.

in fig. 6 shows the embodiments of the seal assembly in the movable joints of the removable and non-removable housing elements, for example, the D assembly in FIG. 1: Option A - with rectangular O-rings; Option B - with wire sealing rings; Option B - with labyrinth seal.

The following elements are marked in the figures:

1 - reactor cover assembly;

2 - shell of circulation pumps;

3 - end shell;

4 - sealing unit of the shell of circulation pumps;

5 - sealing unit of the core shaft;

6 - scarf;

7 - channel for the coolant;

8 - VKU elements;

9 - reactor vessel;

10 - bottom;

11 - ring element;

12 - core shaft shell;

13 - sealing unit of the core shaft;

14 - connecting shell;

15 - additional ring element;

16 - lower chamber;

17 - guide scarves;

18 - body shell;

19 - support collar;

20 - shell for placement of a steam generator or heat exchanger module between the primary and secondary circuits;

21 - circulation pumps (CPA) of the primary circuit;

22 - base plate of the core shaft;

23 - fuel assembly (FA);

24 - reflector;

25 - reactor plug;

26 - flange;

27 - CPS drive;

28 - CPS channel in traffic jam;

29 - tip of the CPS channel;

30 - fuel assembly head;

31 - intermediate base plate of the plug;

32 - bellows assembly of the CPS channel in the plug;

33 - self-aligning seat of the seal assembly;

34 - assembly connector;

35 - the lower part of the saddle;

36 - landing ring;

37 - pin;

38 - sealing ring;

39 - pressure ring;

40 - holes for coolant flow;

41 - piston sealing ring;

42 - sealing ring made of wire;

43 - CNA drive;

44 - rectangular sealing ring.

Detailed description of embodiments of the invention

A nuclear reactor with a heavy liquid metal coolant assembly is shown schematically in FIG. 1.

The cover 1 of the vessel 9 of the assembled reactor includes shells 2 of the circulation pumps 21 and the shell 12 of the core shaft with the end shell 3, on which the assemblies 4 and 5 of the seals of the shells 2 and 3 are provided. kerchief 6 VKU 8. At the same time, kerchiefs 6 are connected mainly to the peripheral part of the cover 1 of the reactor. VCU elements 8 are located between the reactor cover 1 and the annular element 11 are assembled into a single structure, which may include thermal or radiation protection (conditionally not shown), channels for the coolant flow, for example, channels 7 connecting the collector above the core with shells for accommodating heat exchangers 20 or other elements known in the art. A single cover block 1 with VCU elements 8 assembled into a single block is attached to the reactor vessel 9. The bottom 10 is formed from elements that are designed to organize the supply of coolant from the primary circuit circulation pumps 21 with drives 43 to the core, and is mated with the other elements structures on sliding detachable joints and is mainly loaded only by the weight of the coolant and the pressure drop between different sections of the circuit. An annular element 11 is hermetically attached to the bottom 10. A connecting shell 14 is installed in the annular element 11 along the inner ring, which includes an end shell 3, in which a seal assembly 13 is provided and a connection with the shell of the core shaft 12. The annular element 11 is provided with holes and seal assembly 4 for alignment with the shell 2 of the circulation pumps 21. An additional annular element 15 is attached to the annular element 11 with the help of the connecting shell 14, as a result of which a torus chamber is formed between the elements 11 and 15 into which the flow from the circulation pumps 21 is supplied, which is redistributed and exits into the lower chamber 16 through the peripheral part of said torus chamber. The coolant outlet from the torus chamber can be both through the annular gap, as shown in Fig. 1, for example, and through a system of holes (not shown in the drawing), which will improve the uniformity of the distribution of the coolant flow in azimuth. To equalize the velocity field, guide gussets 17 can be attached to the annular element 15. Thus, an additional technical result of velocities equalization at the entrance to the lower chamber 16 and further to the core is achieved, which is important for ensuring reliable cooling of its elements and safety. Holes 40 can be provided in the gussets 17 to improve the equalization of velocities. A single block of the cover 1 with a single block of the VCU is connected to the shell 18 of the housing 9, which, in turn, is connected to the bottom 10, forming the reactor vessel assembly. In this case, the reactor vessel assembly rests on the supporting structures of the reactor shaft with collar 19 provided on the cover 1 of the reactor. In the reactor vessel assembly, shells 20 are installed to accommodate steam generator modules or heat exchangers between the primary and secondary circuits, circulation pumps 21, which are mounted on the cover 1 of the reactor. The heat exchange surfaces of these heat exchangers and their attachment points to the reactor lid are not conventionally shown and may have various well-known implementations. The weight load and the buoyancy force from their part immersed in the coolant for these elements is transferred to the cover 1 of the reactor and is multidirectional. A support structure (perforated plate) 22 of the active zone is attached to the end shell 3, in which, in turn, fuel assemblies 23 and reflector elements 24 are fixed. Ultimately, multidirectional forces act on these elements 23 and 24. The action of gravity downwards and buoyancy forces upwards largely compensate each other, and the final force is transferred to the shells 3, 12 and the cover 1 of the reactor. The separating structure, assembled from shells 3 and 12, can be either made as a single element or divided in height into additional assembly units while maintaining the tightness of the joints. This solution allows solving an additional technical problem associated with the selection of different materials according to the height of the separating structure, for example, due to a significant difference in the working conditions of the materials. In the lid 1 of the reactor, a plug 25 of the reactor with a flange 26 is installed, on which, in turn, drives of 27 CPS organs are installed. The resulting force is formed similarly to the previous case and is transferred to the cover 1 of the reactor.

Thus, the present invention fundamentally excludes the transfer of forces from the elements of the core, VCU or equipment on the bottom 10 of the vessel 9 of the reactor, respectively, there are no connections of important equipment with the bottom 10 of the reactor, an accident associated with the rupture of such a connection and the uncontrolled ascent of any equipment or reactor element is excluded . The entire weight load from the core, VCU 8, plug 25 and other elements of the reactor is compensated by the action of Archimedes forces and is transferred to cover 1 from bottom to top. In turn, the additional load from the TsNA 21 reactor with drive 43 and CPS drives 27 placed on the cover 1 and plug 25, respectively, is aimed at compensating for the predominant effect of buoyancy forces. Reliable fixation of fuel assemblies 23 from unauthorized ascent in the scheme in which fuel assemblies 23 are fixed by the lower liner in the support structure 22 of the core is important from the point of view of safety and is ensured in the scheme under consideration by preloading the fuel assemblies 23 with CPS channels 28 in plug 25. In this case, the preload force should be limited and not prevent thermal expansion.

CPS channels 28 in plug 25 in the lower part have tips 29 with a conical surface, along which they mate with heads 30 of fuel assembly 23 (Fig. 2). The tips 29 of the CPS channels 28 are fastened to the intermediate base plate 31 of the plug 25 through the bellows assembly 32 so that the CPS channels 28 can move vertically within the mobility of the bellows attached to the intermediate base plate 31 (Fig. 3).

Coolant leaks in the sealing units must be limited to ensure reliable cooling of the core and VCU 8. At the same time, they must provide freedom of thermal expansion and ease of assembly, which, given the large size of the reactor plant, is one of the important tasks. In the case of the highest loads of the seal assembly, associated with a large pressure difference between the pressure chamber of the CNA 21 and the rest of the circuit, the design of the seal assembly with a self-adjusting seat 33 is preferable, as shown in Fig. 4 - fig. 5. The seat 33 has an assembly connector 34 with the lower part 35 of the seat 33, which ensures the assembly and joint operation of the seat 33 with the seat ring 36, which are mated along a spherical surface with a radius R. The center of this spherical surface is located on the axis of the seat ring 36. To limit movements, the ring 36 is fixed by four pins 37 along mutually perpendicular axes. The entire assembly is fixed in the annular element 11 from axial movements and leaks using the sealing ring 38, and the clamping ring 39, which, in turn, is welded to the annular element 11. The gaps δ (Fig. 5) provide an additional possibility of movement in the horizontal direction without violating the sealing of the assembly. The size of the required gaps is related to technological tolerances, the accuracy of manufacturing and assembling large-sized and long reactor elements and is determined by well-known engineering calculations of dimensional chains. Removable shell 2 of the pump shaft is sealed on the inner surface of the seat ring 36 using sealing piston rings 41, preferably made of gray cast iron with lamellar graphite.

For movable connections of large diameter, for example, the connection of the end shell 3 of the core shaft and the corresponding fixed seal assembly, the simplified version shown in FIG. 6 (Option A). In this case, piston rings 44, similar to 41, wire rings 42 (Fig. 6, Option B), or labyrinth seals 43, for example, can be used as sealing elements, for example, as in Fig. 6, Option B.

Ultimately, the metal structures of the reactor cover operate mainly under compressive stresses, the bottom of the reactor pressure vessel is unloaded from the connection with the supporting structures of the core, the internals of the reactor and the removable elements of the reactor are unloaded from thermal expansion and can freely and independently move in the longitudinal direction while maintaining tightness in mating areas, which favorably affects the performance of the structure and safety.

Claims (10)

1. A nuclear reactor of an integral type with a liquid metal coolant, including a reactor vessel closed with a lid, having a lower chamber formed by a separating structure attached to the reactor lid, an active zone, at least one primary circulation pump with a circulation pump shell attached to the lid at least one heat exchanger installed in a shell attached to the cover to remove heat from the liquid metal coolant to the secondary coolant, and a plug, characterized in that the separating structure is made in the form of an annular element attached to the reactor vessel, into the guide shell of which the core shell connected to the reactor lid is inserted, the internal devices, including channels for organizing the necessary circulation of the coolant, are interconnected and attached to the peripheral part of the reactor lid, the lower end of the heat exchanger shell is located above the annular element, and the lower end of the circulation pump shell passes through the hole in the annular element into the lower chamber. 2. Nuclear reactor according to claim 1, characterized in that the separating structure is made of dissimilar materials with detachable joints along the height. 3. Nuclear reactor according to claim 1, characterized in that a base plate is installed in the end element of the separating structure, in which fuel assemblies (FA) with channels of the control and protection system (CPS) and reflector blocks are fixed. 4. Nuclear reactor according to claim 1, characterized in that in the reactor plug the tips of the CPS channels are made conical with internal surfaces in contact with the FA heads. 5. A nuclear reactor according to claim 1, characterized in that a partition is made in the plug below its upper part, to which the CPS channel is connected by means of a bellows connection that limits the force transmitted to the fuel assembly head. 6. Nuclear reactor according to claim 1, characterized in that an additional element of smaller diameter is installed below the annular element, in which at least one hole is made, with the formation of an annular manifold between the annular and additional elements, the inlet of which is connected to the outlet of the circulation pump , and the output is connected to the lower chamber. 7. Nuclear reactor according to claim 5, characterized in that below the additional annular plate, ribs are attached to the bottom of the reactor vessel to direct the coolant flow from the periphery to the center of the lower chamber. 8. A nuclear reactor according to claim 1, characterized in that an annular groove is made in the circulation pump shell, in which at least one piston sealing ring is installed, which is movable in the radial direction and covers the gap between the circulation pump shell and the annular element at radial movements of the circulation pump shell. 9. A nuclear reactor according to claim 1, characterized in that an annular groove is made in the core shell, in which at least one piston sealing ring is installed, movable in the radial direction and closing the gap between the pump shell and the annular element during radial movements shells. 10. Nuclear reactor according to paragraphs. 8 and 9, characterized in that the piston sealing ring is made of high-strength gray cast iron with lamellar graphite with a silicon content of at least (1-3) wt.% or corrosion-resistant stainless steel.

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