RU2602836C1 - Assembly for nuclear reactor containing nuclear fuel and initiation system for input of at least one absorbing neutrons and/or softening consequences of emergency element - Google Patents

Abstract

FIELD: protection means; nuclear technology.

SUBSTANCE: invention relates to nuclear reactor passive protection means. Bearing assembly for a nuclear reactor includes housing (40), fission zone located in the lower part of housing (40), free space, located in the upper part of housing (40), free space (52) located in the fission zone and extending along the height of the fission zone along the longitudinal axis, shell (54), which restricts free space (52), as well as input initiation system (SI) of the absorbent assembly. Input initiation system of the absorbent assembly comprises capsule (10) with a longitudinal axis, absorption and/or softening consequences of emergency assembly (2) suspended in the capsule, and input initiation device (DI) of the absorbing assembly capable of releasing the absorbent assembly at the assembly emergent state, herewith capsule (10) is inserted into shell (54), and the input initiation system of the absorbing assembly is installed in a detachable manner in the bearing assembly.

EFFECT: higher reliability of input of negative reactivity into the active zone.

31 cl, 10 dwg

Description

FIELD OF THE INVENTION

The present invention relates to a mixed assembly for a nuclear reactor containing nuclear fuel and at least one component to be introduced into the core made of neutron-absorbing material and / or a component mitigating the consequences of an emergency in the event of complete core melting . The component mitigating the consequences of an emergency is made of a material that is capable of forming a low-melting eutectic with the sheath material of the rod heat-generating elements of the assembly and, thus, prevents the formation of plugs that impede the removal of molten core or molten core materials.

State of the art

The assembly is intended, in particular, for sodium-cooled fast neutron reactors, hereinafter referred to as SFRs.

In order to regulate the operation of the reactor core or mitigate the consequences of a malfunction of the reactor, components are introduced into the nuclear reactor made of materials that absorb neutrons. These components can be rods that are suspended over the core during normal operation. When it becomes necessary to reduce the reactivity of a reactor, neutron absorbing components are introduced into the core.

A disruption in the operation of a nuclear reactor can be associated, for example, with a problem in the cooling system of the reactor, for example, in the primary circuit, since a plug may form that impedes the circulation of liquid sodium in the reactor with a sodium coolant. Thus, a loss of heat sink can occur, that is, a violation of proper heat removal through the reactor cooling system.

If negative reactivity is not introduced into the core, then the consequences of these malfunctions of the reactor will include an increase in temperature in the core, leading to the melting of one or more assemblies, or even to complete melting of the core, which may cause a violation of the integrity of the reactor.

The purpose of introducing neutron-absorbing components into the core is to suppress the neutron reaction and stabilize the reactor core at a selected temperature that meets the accepted criteria for the alleged malfunction of the reactor.

In addition, several redundant, heterogeneous, and independent reactor shutdown systems are provided to maintain maximum safety during reactor control and to compensate for defects during normal operation.

The shutdown systems previously used in sodium-cooled fast neutron reactors (SFRs), which are considered traditional, are based on active devices, in the sense that the input of neutron-absorbing components is initiated by external electrical control or by the disappearance of an electrical signal. Reactor shutdown systems used so far have a mechanical interface and an upper shell plug.

Next-generation sodium-cooled fast neutron reactors (SFRs) provide an additional reactor shutdown system, which is used when traditional shutdown systems fail; more specifically, the introduction of these "emergency" reactor shutdown systems is carried out only if necessary, namely, after the initiation of traditional reactor shutdown systems. Based on the diversification of equipment, as well as to eliminate the risk of failure of electrical equipment, a regulatory system, and a logical system, the use of passive devices is provided, in the sense that the input of neutron-absorbing components is directly related to a physical phenomenon, and not initiated by electrical control. In this capacity, one can imagine, for example, initiating agents that are sensitive to a change in the flow of a coolant or to an increase in temperature. These passive devices have been studied in detail, but not one of them has ever been used in a reactor.

FR 2230984 discloses a fuel assembly having a housing accommodating rod fuel elements and an emergency reactor shutdown device. The stop device occupies a portion of the space that rod fuel elements typically occupy. The specified stop device has a sealed casing, which is attached to the housing of the assembly. Argon is used in the reactor shutdown device, and oblong components made of boron carbide suspended on a cable are used. The cable is suspended in a sealed enclosure on a temperature sensitive fuse jumper. When the temperature exceeds the threshold value, the fusible link melts and the components of boron carbide are released and fall to the bottom of the capsule in the active zone. Since the casing is attached to the assembly, it is not mechanically isolated from it and therefore can potentially be deformed as a result of applying a mechanical load that violates the periodicity of the lattice, namely, bending and / or creasing the flat plate of the assembly. Thus, an obstacle is created for introducing a component from boron carbide into the core.

Therefore, it is necessary to increase the reliability of the above method of inputting the specified assembly.

There are two reasons for not ensuring the correct operation of the emergency shutdown device of the reactor: the first one is that the system is equipped with a one-time fused jumper, and the second reason is that the emergency shutdown device is attached to the assembly and it is impossible to test for a given operating temperature of the emergency stop device on the carrier fuel assembly.

In addition, since the casing is attached to the carrier fuel assembly, it is not possible to separate the absorbing device and the carrier fuel assembly by the service life. In addition, it is difficult to handle the absorbing material on the manufacturing line of the fuel assembly and during dismantling operations.

FR 2251079 discloses a protective device for a nuclear reactor with absorbing components in the form of cylindrical units. However, the cylindrical shape of the links is not optimal in terms of input reliability, temperature aspects, and neutron absorption efficiency.

FR 2683667 discloses a nuclear fuel installation in which a passive safety device is integrated. The passive protective device contains absorbing components in the form of balls distributed in a fusible matrix. With this design, firstly, there is an effect of bending as a result of the accumulation of balls and, therefore, mechanical blocking, which reduces the reliability of operation of the device and input components. Secondly, the arrangement of the balls within the bundles of fuel elements, especially at the end of the irradiation, when the beam under the action of irradiation can be substantially deformed due to radiation creep and swelling under the action of irradiation, is not regulated. In addition, there is a risk of partial or complete blocking by the balls of the beam of fuel elements, as well as the risk of blocking the gratings located upstream and downstream of the beam, which contradicts the basic rule of designing an additional protective device designed to provide protection in unlikely emergency situations, according to which the use of an additional protective device is not allowed to reduce the level of protection provided by the standard design. However, while in instant sodium-cooled fast reactors (SFRs), instantaneous total blocking (BTI) of the fuel assembly is considered to initiate fuel melting, with a standard core design, it is a residual risk.

US Pat. No. 5,051,229 discloses a thermosensitive triggering device for introducing a neutron absorber into the reactor core, said device being located in a fuel assembly. The reactivity and accuracy of this system is very limited in relation to temperature changes. In addition, during normal operation, this device has a serious impact on the efficiency of neutrons in the core. Since during normal operation the shutdown system of the reactor should have a minimal effect on the efficiency of neutrons in the core, the volume fraction of components whose functioning is related to neutrons (volume fraction of the absorber and fuel) should be maximized per assembly to minimize losses in the volume fraction of fuel in core. As for assemblies intended for control systems, as a rule, the absorber volume per assembly is maximized so that the number of positions in the core is minimized. An attempt to optimize reactivity initiation in a mixed assembly design should result in minimizing the reduction in the volume fraction of fuel compared to a power assembly. According to US Pat. No. 5,051,229, neither is provided, since the maximum volume fraction of fuel (a combination of five fuel capsules with one capsule of the absorber) is much lower than is possible in a standard fuel assembly, and the maximum volume fraction of the absorber (combination of five capsules of a absorber with one fuel capsule) is significantly lower than is possible with control rods.

Disclosure of invention

Thus, the objective of the present invention is to develop a nuclear reactor assembly containing an emergency shutdown system with passive initiation, namely, not mechanically associated with the upper plug of the body and having high accuracy, high response reliability and high input reliability, moreover, adapted to repeated tests for correct functioning, as necessary.

The aforementioned problem is solved by assembling a nuclear reactor containing a housing in which rod fuel elements and an emergency stop system are located, occupying a portion of the space that rod fuel elements usually occupy, and the emergency stop system containing a capsule extending along the geometric axis of the vessel, said capsule being removable is inserted into the shell, which limits the cavity (free space) from the inside of the rod fuel element Comrade, the capsule is suspended subject to entering the assembly, which is a neutron absorbing and / or mitigate the effects of an emergency.

The assembly contains an emergency shutdown system, mechanically separated from the assembly, in which case the system can be placed in the required position and removed from the assembly housing to check for proper functioning, as well as to repair, re-load or replace the assembly to be introduced if negative reactivity is excessively reduced.

Since almost the entire flow of the coolant circulating in the housing passes through the device and is practically equal to the flow in a standard fuel assembly, both the accuracy and the reliability of operation of the assembly input initiation system are optimized. The operation of the system for introducing the indicated assembly is faster and more accurate than for introducing assemblies intended primarily for the absorber, since the power and flow rate of the supplied coolant exclusively for the heat-generating or mixed assemblies is much greater than the power and flow rate of the supplied coolant exclusively for the absorbent assembly.

The release of the assembly to be introduced can be initiated by any of the physical properties that respond to the emergency state of the reactor.

The heat carrier flux or the neutron flux can be used to initiate physical phenomena that depend on the type of emergency condition observed, namely, the losses of the coolant flow in the reactor and the unsteady state when reactivity changes.

Preferably, temperature is used as the initiating physical phenomenon. The initiating device of the rector stop system may be a magnetic type device, and the assembly to be introduced may be released when the Curie temperature is reached. Preferably, the action of said device can be based on relative expansion, increasing the temperature of the heat carrier, causing the assembly to be released, the release device being directly in the heat carrier flow.

Also, preferably, the emergency stop device comprises means to prevent an undesired fall of the assembly to be introduced, which prevents it from being released if the temperature of the coolant does not exceed a predetermined threshold value.

It is highly preferred that the assembly to be introduced contains several approximately spherical components mounted on a cable to form a garland, thereby increasing the reliability of component input.

The subject of the present invention is a carrier assembly for a nuclear reactor, comprising a vessel, the longitudinal axis of which is oriented approximately along the vertical axis of the carrier assembly, a fission zone located in the lower part of the casing, free space located in the upper part of the casing, free space which is in the fission zone and continues, at least partially along the division zone along the longitudinal axis, that is, from the end of the division zone from the upper part, the shell bounding the free space (along ), and also contains a system for initiating input of an absorbent assembly, said system for initiating input of an absorbent assembly comprising a capsule oriented along a longitudinal axis in which the assembly to be input is suspended, and a device for initiating input of an absorbent assembly capable of releasing said assembly to be input in an emergency assembly, and the capsule partially fits into the shell, moreover, the specified system is removable mounted on the carrier assembly, and the capsule contains a grip yu head, which is mounted on the assembly initiation system input located on the shell.

The input initiating device of the absorbent assembly is preferably located in the upper part of the upper zone of the housing.

Preferably, the free space is in the central part of the division zone, while the longitudinal axis of the system for initiating the introduction of the bearing assembly is coaxial to the axis of the assembly.

The assembly to be introduced may comprise a neutron absorbing component and / or a component mitigating the consequences of an emergency.

The longitudinal dimension of the assembly to be introduced may be, for example, half the total longitudinal size of the capsule.

Preferably, the capsule contains means that absorb the fall of the assembly to be introduced at the end of its movement.

In addition, openings for supplying coolant can be made at the end of the capsule portion located in the shell.

The carrier assembly may include guiding means for positioning the input initiation system of the absorbent assembly in the division zone located at the end of the shell on the same side as the free volume of the carrier assembly.

The casing preferably has a hexagonal cross section, the casing preferably has a hexagonal outer cross section and a hexagonal or circular inner cross section, and the capsule has a circular outer cross section.

Preferably, the assembly to be inserted comprises a plurality of absorbent elements pivotally connected to each other, wherein the end absorbent element forms a connecting head cooperating with holding means of the input initiating device of the absorbent assembly. The components preferably slide along the cable. The cable can be made, for example, of braided metal fibers or braided ceramic fibers.

Each of the elements has a spherical shape, which is most preferred.

The carrier assembly may comprise depreciation means located between the elements of at least one pair.

Elements may be formed, for example, from several absorbent materials. At least some of the elements may be made of a first absorbent material, and other elements may be made of a second absorbent material.

A preferred feature of the invention is that the elements may be hollow, or may contain a central core and an outer casing, which are made of different materials.

The input initiation system of the absorbent assembly is preferably sensitive to temperature changes. Preferably, the operation of the input initiation system of the absorbent assembly is based on relative expansion.

For example, the system for initiating input of the absorbent assembly contains blocking means that prevent the assembly from entering at temperatures below the operating temperature of the reactor.

The carrier assembly preferably has means comprising ultrasonic telemetry equipment for detecting input of the absorbent assembly. For example, the input initiating device of the absorbent assembly comprises a part fixed along the capsule and a movable part that is movable in the longitudinal direction, the capsule containing means holding the assembly to be introduced in a suspended position above the division zone, and the assembly to be introduced can be released by the action of the movable parts, the movable part contains blocking means and means holding the assembly to be introduced in a suspended position, as well as means of releasing the subject the input of the assembly from the holding means, said blocking means being formed by at least one first surface called the locking surface, and the release means of the assembly to be introduced are formed by at least one second surface called the releasing surface, the means for moving said locking surface and the release surface are located along the longitudinal axis, while these means of movement are formed by a housing that can expand longitudinally about in relative capsule by increasing the temperature of the coolant, said stop surface and riding surface positioned so that when the coolant temperature increase stop surface is moved axially from the retaining means, and liberating the surface is moved in the axial direction to the retaining means; when the coolant in the reactor has a normal operating temperature, said stopper surface moves away from the holding means, when the coolant temperature exceeds a threshold temperature, the holding means are released and the releasing surface exerts an axial force on the holding means, as a result of which the assembly to be introduced is released.

The detection means may include at least one ultrasonic transducer mounted above the upper part of the capsule, a reflector mounted on the upper part of the capsule and facing the transducer, the longitudinal position of the reflector being adjusted depending on the position of the assembly to be introduced, namely, it is held or the assembly to be entered is not held in by retaining means; said reflector is connected to the assembly to be introduced by means of an elongated element that is able to slide freely along the expanded area, passing through the upper part of the capsule, and holds the reflector in a fixed position, leaning on the assembly to be entered before its introduction.

The carrier assembly may comprise resilient means in a compressed state prior to introducing the assembly and expanding upon entering the assembly, while applying a tensile force to the elongated member to move the reflector.

Between the housing and the capsule, preferably, there is provided a radial clearance defining the channel for the coolant circulating between the housing and the capsule, the housing comprising openings for the coolant circulating in said channel.

For example, the holding means comprise at least two, and preferably three, latches distributed around the longitudinal axis, which are pivotally mounted on the capsule with the ability to move to a position close to the longitudinal axis, in which the assembly to be inserted is held between the latches, and a position remote from the longitudinal axis to release the assembly to be introduced.

The locking surface may be, for example, a surface that is located in the radial direction outside the clamps and counteracts the movement of the clamps from the longitudinal axis, and the releasing surface may be, for example, a surface that is perpendicular to the longitudinal axis, while the clamps have a curved surface, with which interacts with the release surface to move the hinge clips from the longitudinal axis.

As an example, the case is made of austenitic steel, and the capsule is made of tungsten-based alloy, or the case is made of mechanically hardened steel Z10 CNDT 15.15 V, and the fixed part is made of W-5Re alloy.

The carrier assembly, preferably used in a fast reactor, cooled by a liquid metal, preferably sodium, contains a neutron absorber made of a material (s) selected from the following: B ₄ C with a variable enrichment of ¹⁰ V, hafnium metal, refractory materials like borides, for example HfB ₂ and TiB ₂ , europium hexaboride EuB ₆ or Eu ₂ O ₃ . The carrier assembly used in a water-cooled thermal neutron reactor contains a neutron absorber made of material (s) selected from the following: hafnium, Dy ¹¹ B ₆ , Gd ¹¹ B ₆ , Sm ¹¹ B ₆ and Er ¹¹ B ₄ , untreated HfB ₂ and untreated TiB ₂ .

Another subject of the present invention is a nuclear reactor comprising assemblies of fuel elements and a support assembly according to the invention.

Brief Description of the Drawings

The present invention will be better understood after reading the following description with reference to the accompanying drawings.

In FIG. 1 is a perspective view of a carrier assembly according to an exemplary embodiment of the present invention, comprising an input initiation system for an absorbent assembly and a set of suspended absorbent elements.

In FIG. 2 is a view of the assembly of FIG. 1, after entering into the active zone a set of absorbing elements.

In FIG. 3 is a sectional view of the assembly of FIG. 2, wherein the section is made along the absorbing element in the division zone.

In FIG. 4 is a front view of an input initiation system of an absorbent assembly according to a most preferred embodiment of the invention, which can be used in a carrier assembly according to the present invention, wherein an input initiation system of an absorbent assembly is shown, for example, at a positioning temperature.

In FIG. 5A is a partial longitudinal sectional view of the system of FIG. 4, wherein the input initiating device of the absorbent assembly is shown at a positioning temperature.

In FIG. 5B is a partial longitudinal sectional view of the system of FIG. 4, wherein the input initiating device of the absorbent assembly is shown at operating temperature.

In FIG. 5C is a longitudinal sectional view of the system of FIG. 4, wherein the device for initiating input of the absorbent assembly is shown at a response temperature immediately before the input of the absorber into the core.

In FIG. 5D is a longitudinal sectional view of the system of FIG. 4, wherein the input initiating device of the absorbent assembly is shown at the response temperature at the time the absorber enters the core.

In FIG. 6 is a plan view of the system of FIG. four.

In FIG. 7 is a cross-sectional view of the system of FIG. 4, wherein the section is taken along the plane AA shown in FIG. 5C.

As used in the following description, the terms “upper” and “lower” denote component parts located in the upper and lower parts of the drawings in question, corresponding to the arrangement of components in the reactor. The terms “upstream” and “downstream” refer to the direction of circulation of the coolant in the assembly, that is, from the bottom to the top.

The implementation of the invention

In the above description, the term "carrier assembly" refers to an assembly according to the present invention containing both nuclear fuel and absorbent components, and the term "standard assembly" refers to an assembly containing only nuclear fuel.

In addition, the term "normal operation" refers to the operation of the reactor under normal conditions, and the term "emergency state" refers to the state of the reactor, which requires the introduction of absorbers to slow down or even stop the reaction. For example, in this state, the temperature of the reactor increases, leading to an increase in the temperature of the coolant above a given temperature threshold.

In addition, in the following description, the assembly to be introduced is considered to be an assembly containing a set of components made of neutron-absorbing material, however, the invention is also applicable to an assembly to be introduced that contains a set of absorbing elements and / or softening components.

In general, a nuclear reactor comprises a shell in which a plurality of fuel assemblies are arranged adjacent to each other. Fuel assemblies form the core of a nuclear reactor. The coolant circulates in these assemblies and between assemblies to extract heat generated by nuclear fuel, forming a primary circuit. The assemblies contain nuclear fuel, for example, distributed in the rod fuel elements. The assembly area, which contains nuclear fuel, is called the fission zone.

The carrier assembly A of the present invention shown in FIG. 1 and FIG. 2, comprises a housing 40 with a longitudinal axis X1, which has a cylindrical shape and a hexagonal cross section. Typically, in a sodium-cooled fast neutron reactor (SFR), the assemblies have a hexagonal outer cross section. Other types of reactors may use assemblies having an external cross-section of another shape, for example, round or rectangular.

The carrier assembly according to the invention is used instead of one of the standard fuel assemblies. Several support assemblies according to the invention may be used in the reactor.

The housing 40 has a central portion 42, called a division zone, in which the rod fuel elements 41 are located. Housing 40 has a lower portion that holds the assembly in the reactor and is called an assembly holder 44, the assembly holder 44 being designed to be mounted in a support called an end platform . The housing 40 also has an open top 48.

In the holder 44 of the assembly, openings 46 are made for supplying the coolant, which ensure the flow of the supplied coolant into the assembly.

The heat carrier that removes the heat generated by the rod heat-generating elements is pumped and passes in the carrier assembly A from the base to the upper part, as shown by arrow F. The heat carrier also circulates outside the carrier assembly, between standard assemblies and bearing assemblies, in the so-called interassembly zones.

The carrier assembly also contains a cavity (free space) 52, the longitudinal axis of which extends along the entire height of the rod fuel elements 41. The cavity 52 is defined by a shell 54, the outer cross section of which is similar to the cross section of the housing. The shell 54 supports the SI system described below for initiating input of the absorbent assembly in the beam of the fuel elements, giving the beam of the fuel elements a coherent configuration. Thus, in a sodium-cooled fast neutron reactor (SFR), sheath 54 has a hexagonal outer cross section similar to the cross section of the vessel. In the example shown in FIG. 4, the sheath 54 has a circular outer cross section. It should be noted that the inner cross section of the sheath 54 may be hexagonal.

In the presented example, the axis of the cavity 52 is in line with the axis of the assembly, which is preferred and will be described later. Shell 54 occupies the space typically occupied by two rings of rod fuel elements.

At the lower end of the shell 54, one or more openings are provided for supplying a heat transfer medium.

The carrier assembly according to the present invention also comprises a neutron absorber input initiation SI system, said SI system including an emergency shutdown device in the event of an emergency. Said SI system comprises a device DI for initiating input of an absorbent assembly and an absorbent assembly 2 containing a set of absorbers, said set of absorbers in normal operation being kept suspended by a device DI for initiating input of an absorbent assembly, and is released when an emergency occurs.

The SI system for initiating the input of the absorbent assembly is removably mounted in the casing 54. No fixing means are provided between the SI system for initiating the input of the absorbent assembly and the assembly.

In the embodiment of FIG. 4 example, the SI system for initiating the input of the absorbent assembly contains a capsule 10, which is a tubular body with a longitudinal axis X and a circular cross-section. In this example, as already mentioned, the shell 54 has a round inner cross section, and the capsule 10 also has a round inner cross section.

The capsule 10 has an upper zone ZI containing the absorbent assembly 2 suspended in the input assembly initiating device DI, which is located close to the rod fuel elements when the system is installed in the assembly, as shown in FIG. 1. In addition, the capsule 10 has a lower zone ZII, which fits into the shell 54, and is thus located in the division zone, surrounded by rod heat-generating elements. After release, assembly 2 is located in the lower zone ZII (Fig. 2). In order for the lower zone ZII of the capsule 10 to fit into the shell 54, the diameter of the lower zone ZII is slightly smaller than the inner diameter of the shell 54.

While the sheath 54 delimits the cavity for the capsule 10, it also provides improved mechanical isolation of the SI system for initiating the input of the absorbent assembly from the assembly itself, since the rigid structure of the shell protects the SI system of initiating the input of the absorbent assembly from rods swelling by radiation. Thus, mechanical isolation and preservation of the grid pitch are ensured.

The capsule 10 also includes a gripping head 13, which is used to position the capsule 10 and, accordingly, to position the SI system to initiate input of the absorbent assembly. As shown in FIG. 4, the gripping head 13 comprises means for gripping by an external manipulator (not shown). The upper part of the capsule 10 is held in a carrier assembly.

A coolant, such as liquid sodium, circulates in the assembly along the longitudinal axis X from the base to the top.

The inlet openings are used in the lower part of the capsule 10 and are used to fill the capsule 10 with coolant; these inlet openings are equipped with diaphragm valves providing a significant reduction in flow pressure. Thus, regardless of the size of the outlet openings made in the upper part of the capsule 10, the capsule is filled without creating a strong flow. Since assembly 2 preferably has a low mass and liquid sodium has a high viscosity, the flow of coolant in the capsule should be as weak as possible so that the fall of the neutron-absorbing component is not slowed down, that is, the duration of its fall does not increase.

As shown in the presented example, at the top of the shell 54 there is an annular element 61 provided for alignment during installation of the input initiation system of the absorbent assembly, which is preferred; in addition, said annular element 61 provides a thermohydraulic effect when mixing the outlet stream from the shell with the outlet stream from the bundle of rod heat-generating elements, that is, mixing of said flows is ensured, due to which a uniform temperature of the coolant surrounding the expanding body of the system is maintained. The capsule 10 is suspended from the upper part, while the lower end of the capsule is not supported by the body. In FIG. 3 shows a sectional view of the assembly of FIG. 1, wherein the section is made along the absorbent assembly 2 in the division zone. The drawing shows the relative location of the rod fuel elements 41, the shell 54, the capsule 10 and the absorbing element 4 of the assembly 2.

An emergency assembly input initiating device DI is used in an emergency to input a neutron absorber. An emergency, depending on the type, can be detected, for example, by a change in coolant flow or by a change in neutron flux. Preferably, an emergency can be detected by exceeding a predetermined temperature threshold of the coolant inside the assembly, which is directly related to the main factors of the emergency, namely, a decrease in the flow rate of the reactor coolant, a drop in the heat sink in the secondary circuit and an unsteady state when reactivity changes. These three factors of an emergency can cause an increase in the temperature of the coolant, while, for example, only one factor of the emergency can be judged by a change in the flow of the coolant.

In FIG. 2, FIG. 4, FIG. 5A-5D and FIG. 6, the most preferred illustrative embodiment of an input initiation device of an absorbent assembly used in a carrier assembly according to the present invention is shown, the principle of operation of the device based on relative expansion.

The input assembly input device DI of the absorbent assembly is designed so that during normal operation, the absorbent assembly 2 is held above the division zone, and in the event of an emergency, the absorbent assembly 2 is released.

As shown in the presented example, preferably, the absorbent assembly 2 contains a plurality of components 4, which are made of a neutron-absorbing material, have a spherical or approximately spherical shape and slide along the cable 6 (shown by the dashed line), forming a garland. The specified set of absorbing elements is discussed in detail in the rest of the description.

The upper end component 2.1 differs from other components in that it interacts constructively with the input initiation device of the absorbent assembly. The end component 2.1, tapering toward the end relative to the lateral surface, forms a connecting head and has a wide base directed towards the components of a spherical shape.

The shape of the components 4 is in no way restrictive; the use of elongated components such as cylinders of revolution is acceptable. However, in terms of input reliability, components having a cylindrical shape are significantly inferior to components having a spherical shape.

The hinged design of the components forming the garland is also not in any way restrictive; a structure formed, for example, of one or more rods, like control rods and made of absorbent material, is suitable. However, in terms of input reliability, an absorbent assembly containing cylindrical components is significantly inferior to an assembly containing hinged components forming a garland.

A coolant, such as liquid sodium, circulates in the assembly along the longitudinal axis X from the base to the top.

The device DI initiating input of the absorbent assembly is located near the upper zone ZI of the capsule. The DI device comprises means 11 holding the assembly 2, means for locking the holding means 11 and passive activation means releasing the assembly 2 in an emergency.

The input initiation device DI of the absorbent assembly has the shape of a body of revolution with a longitudinal axis X.

The input assembly input device DI of the absorbent assembly has a housing 19, in the lower part of which the upstream end of the capsule 10 is fixed, when viewed in the direction of circulation of the coolant from the base to the upper part, and also has an adjustment head 18 mounted on the upper part of the housing 19 and extending from housing in the axial direction.

The control head 18 is slidably mounted around the capsule 10. A radial clearance is provided between the outer diameter of the capsule and the inner diameter of the control head 18.

The retaining means 11 also comprise locks 20 pivotally mounted on the upper part of the capsule body 10.

The adjusting head 18 and latches 20 are preferably located away from the core, namely, in the region of the upper part of the capsule 10, where the neutron flux is minimal.

Preferably, three clips 20 are provided at an angle of approximately 120 ° relative to each other, thereby providing uniform support for the assembly. However, instead of three clips, only two clips may be provided, or a larger number of clips. In the holding position of the assembly, the latches 20 are inclined to the longitudinal axis X.

Each latch 20 has a first longitudinal end 20.1 pivotally mounted on the capsule body 10 with a possibility of rotation around the Y axis orthogonal to the longitudinal axis X, and a second longitudinal end 20.2 forming a supporting surface in contact with the connecting head 2.1. The capsule 10 contains longitudinal slots into which the second end 20.2 of each retainer 20 enters, thus being located inside the capsule 10.

Preferably, the second end 20.2 of each retainer comprises a groove 22 defined by two surfaces 22.1 and 22.2, which are particularly clearly visible in FIG. 5C. Surface 22.1 makes contact with the wide base of the connecting head 2.1, and surface 22.2 makes contact with the side surface, as shown in FIG. 5A-5C.

The adjusting head 18 supports the locking means of the latches 20 in the locking position of the assembly 2, that is, in the tilt position to the longitudinal axis X.

The locking means include stoppers 24 located radially outside the latches 20 and preventing the latches from moving from their latched position. In the presented example, the end portion 20.3 of each retainer 20 has a spout facing the locking surface 24. Between the spout and locking surface 24, a radial clearance is preferably provided to prevent friction and the risk of jamming.

In the presented example, the locking surfaces 24 are supported by a single annular surface formed inside the control head 18 and having the X axis. In the presented example, this surface is located upstream below the axis of rotation of the clamps on the capsule 10, if viewed in the direction of circulation of the coolant from the base to the upper part.

In addition, the control head 18 supports passive means that trigger the release of assembly 2 in an emergency. Said passive means are formed by release surfaces 26 oriented along the transverse plane, for example, perpendicular to the longitudinal axis, which come into contact with the latches 20 and apply axial force to them, forcing the latches to rotate about the axis of rotation.

The thrust surfaces 26 are in contact with the curved surfaces 28 of the latches 20 located radially inward from the axis of rotation of the latches 20.

In the presented example, the abutment surfaces 26 are located upstream of the axis of rotation of the retainers 20 on the capsule 10, when viewed in the direction of circulation of the coolant from the base to the upper part.

In the presented example, recesses 30 are made on the inner periphery of the adjusting head 18, into which the latches 20 fit.

On the outer surface of the tubular body of the capsule 10 there are three radially protruding supports 32 supporting the axis of rotation of the latches 20.

These passive means are formed using the housing 19 and the regulating head 18. The housing 19 and the regulating head 18 are made of a material with a high coefficient of thermal expansion, exceeding and, preferably, far exceeding, the coefficient of thermal expansion of the material of which the capsule 10 is made.

As shown in FIG. 4-5D, an inner diameter of the housing 19 is provided such that a channel for the passage of coolant is created between the housing and the outer surface of the capsule 10. In the housing 19 and in the parts upstream and downstream, openings 36 are made for supplying and discharging a heat carrier.

For example, the radial distance between the body and the capsule is on the order of one to several centimeters, due to which a significant part of the coolant flow is circulated between the inner surface of the housing 19 and the outer surface of the capsule 10. In this case, the temperature of the system is close to the temperature of the coolant, which contributes to the high accuracy of the system.

It is highly preferable that the axial size of the housing 19 is large enough and a large heat-exchange region with a coolant is created, smoothing out possible local temperature inhomogeneities, as a result of which the system operation reliability can be increased.

In the lower zone of the ZII capsule, means are provided to absorb the fall of the neutron-absorbing material at the end of its movement. For example, the specified depreciation is ensured by reducing the diametrical gap between the absorbent assembly and the lower part of the capsule.

Next will be described the operation of the device DI initiate input of the absorbent assembly according to a preferred, but not restrictive, illustrative embodiment of the invention.

During operation, four main states of the device are distinguished depending on the temperature of the input initiating device of the absorbent assembly according to the present invention:

- the state of installation (SI system in the carrier assembly) at ambient temperature, for example 20 ° C, which is called the "installation temperature";

- the positioning state (matching the carrier assembly with the SI system in the core of a nuclear reactor) at a temperature of about 180 ° C to 250 ° C, which is called the "positioning temperature";

- operating condition at a working temperature reaching about 550 ° C, when the assembly is in the active zone during operation;

- the response state at a threshold temperature, for example of the order of 660 ° C., according to the present invention, in which it is necessary to introduce absorbent material into the core.

The mounting state is not shown, but it is very similar to the state shown in FIG. 5A. In the installation state, thermal expansion of the various components of the input initiation system of the absorbent assembly does not occur; therefore, they are not deformed. The latches 20 support the assembly 2. The locking surfaces 24 are facing the spouts 20.3 of the latches 20, and the thrust surfaces 26 are distant from the curved surfaces 28 of the latches. Thus, the latches 20 are in the locked position, and the assembly 2 cannot be released. The system can be positioned completely safely and there is no risk of unwanted insertion of the assembly into the bundle of rod fuel elements.

In the positioning state, the input initiation system of the absorbent assembly occupies the desired location in the carrier assembly that is installed in the reactor. Under the influence of temperature in the reactor, relative expansion of the capsule 10 and the assembly including the housing 19 and the regulating head 18 occurs, since the material of the capsule 10 and the material from which the housing 19 and the regulating head 18 are made have different coefficients of thermal expansion. Thus, the capsule 10 and the assembly including the housing 19 and the adjusting head 18 are deformed in different ways, as a result of which the locking surfaces 24 and the abutment surfaces 26 supported by the adjusting head 18 are relative to the latches 20.

Thus, in the positioning state shown in FIG. 5A, there is a slight elongation of the elements of the input initiation system of the absorbent assembly. The specified deformation occurs mainly along the longitudinal axis.

However, in the positioning state, compared with the installation state, there is such a relative expansion of the system components that, despite the movement of the locking surfaces 24 relative to the latches 20, the locking surfaces are still partially facing the spouts of the latches 20 and still block the latches, which occupy the holding position of the absorbent assembly 2. Consequently, the latches 20 support assembly 2. Accordingly, assembly 2 cannot be released. Thus, the system can be positioned completely safely, without any risk of unwanted insertion of the assembly into the bundle of rod fuel elements.

The operating state is shown in FIG. 5B. Various elements of the initiation system of the input of the absorbent assembly are immersed in the coolant at the operating temperature. The housing 19 is surrounded by a coolant through a channel formed between the housing 19 and the capsule 10, and, accordingly, is sensitive to the working state of the assembly.

Due to thermal expansion with increasing coolant temperature from the positioning temperature to the operating temperature, the deformation of the elements of the initiation system of the input of the absorbing assembly increases. At operating temperature, there is a relative expansion of the housing 19 and capsule 10 such that the locking surfaces 24 are no longer facing the spouts of the latches 20, as a result of which the latches 20 are unlocked. The thrust surfaces 26 directly come into contact with the curved surfaces 28, as a result of which, the latches 20, which are in the holding position of the assembly 2, are deflected to the longitudinal axis.

With increasing temperature of the coolant from the operating temperature to the response temperature, the elongation of the elements continues. The thrust surfaces 26 exert axially directed longitudinally upward force on the curved surfaces 28 of the latches 20, as a result of which, the latches 20 are deflected outward. The rotation of the latches 20 around the Y axis causes the axial displacement of the assembly 2 up. Due to the specified working movement of the device for initiating input of the absorbent assembly, for example, the connecting part of the assembly 2 relative to the capsule body 10, any adhesion of the moving parts to the stationary parts is violated due to oxidation or accumulation of impurities.

The response state of the device when the temperature threshold is reached, that is, the state in which assembly 2 is released, is shown in FIG. 5C (immediately before release of the assembly) and in FIG. 5D (during assembly input). In FIG. 5C, the latches 20 are shown in the final phase of rotation, with the assembly 2 being substantially released. In FIG. 5D latches are shown in a fully deflected position, as a result of which assembly 2 is released and lowered into the core.

The input of absorbing elements suppresses the neutron chain reaction, due to which, in the near future, core melting is prevented.

Over a sufficiently long period of time, temperature suppression is guaranteed while maintaining the integrity of the main supporting structures of the core, which allows for corrective actions.

As mentioned above, the housing 19 and the adjusting head 18 of the input device for initiating the absorption of the absorbent assembly are made of a material with a high coefficient of thermal expansion, for example, steel, more specifically austenitic steel, which is similar to mechanically hardened steel Z10 CNDT 15.15 V (15/15 Ti) used for the manufacture of the shell of the rod fuel element. A tungsten-based alloy, for example, a W-5Re alloy, that is, containing 5% rhenium, can be selected for the manufacture of capsule 10, since the material used to manufacture the capsule must have a thermal expansion coefficient much lower than the thermal expansion coefficient of the material used to manufacture the housing 19 and control head 18. An alloy such as W with oxide dispersion hardening can be considered as a suitable material. In addition to the low coefficient of thermal expansion, the advantage of tungsten is that it swells slightly under the influence of irradiation at the temperatures considered, due to its heat-resistant properties. Preferably, the W-5Re alloy also has acceptable ductility according to the considered structural standards. Alternatively, Z10 CNDT 15.15 B alloy can be selected for the manufacture of the capsule, and W-5Re alloy can be selected for the manufacture of the housing, respectively, provided that the input initiating device of the absorbent assembly is adapted.

In the presented example, the locking surfaces 24 form a radial surface, and the abutting surface 26 forms a surface perpendicular to the longitudinal axis. However, this configuration is in no way restrictive.

Preferably, means are provided that detect the position of the assembly in the device for initiating input of the absorbent assembly to detect unwanted input of assembly 2. The first detection technology detects the introduction of negative reactivity into the core directly using neutron sensors, or indirectly through “core temperature research” (TRTC ), at which the outlet temperature of the coolant is measured using thermocouples located at the top of the assembly. When the absorbing material is introduced into the active zone, the power of the carrier assembly decreases and the temperature of the coolant at the outlet of the carrier assembly decreases. Therefore, the input of negative reactivity is detected by a drop in the temperature of the coolant.

According to another detection technology, the position of the set of absorbing elements (suspended or not) is detected.

A DT detector device using the latest technology is shown in FIG. 5A-5D. The specified device is an ultrasonic telemetric device designed to measure the distance from one or more transducers 67 installed above the upper part of the assembly to the reflector, the position of which relative to the transducer (s) depends on whether or not the set of absorbing elements of the assembly 2 is introduced into the active zone.

The DT device includes a sensor 64 that slides freely along an expanded area 65 formed in the grip head 13 of the capsule 10. The length of the sensor 64 is such that its lower end is in contact with the connecting head of the absorption assembly 2 and its upper end protrudes from upper end of the gripper head.

The upper end of the sensor 64 contains a reflector 66. The lower end of the sensor is in contact only with the connecting head of the absorption assembly, so the sensor will not prevent the garland of absorbing elements from entering if it is not blocked, since the sensor and the garland are not connected to each other. Since the rod sensor has a small cross section, the upper end portion of the rod sensor forming the reflector is widened so that the section of this section is larger than the section of the rod sensor itself. For example, this section has the shape of a downward-facing cone, the base of which forms a reflector 66. When the sensor is moved downward, the cone is stopped and held in contact with the upper part of the expanded region 65. At the same time, a distance of a few centimeters by which the cone is lowered is sufficient for detecting an absorbent assembly using ultrasound. For example, the indicated distance may be 13 mm.

The reflector 66 is supported by a sensor that passes through the gripping head 13 located as close as possible to the upper part of the assembly (shown schematically in FIGS. 5A-5D), thereby increasing the solid angle of reflection of ultrasound and limiting the echo on the structures surrounding the gripping head.

Transducers 67 (shown schematically) are located above the upper part of the assembly. Due to the axial displacement of the reflectors during insertion of assembly 2, the assembly can be detected and positioned. The transducers can be mounted, for example, on the lattice plug of the core cover.

Preferably, a spring 68 is installed between the rear end of the sensor and the rear end of the expanded area in a compressed state. In normal operation, that is, when the absorbent assembly 2 is not inserted into the active zone and the connecting head is held in place by latches 20, said spring is in a compressed state. When the absorbent assembly 2 containing the coupling head falls, the spring 68 expands and thus forces the sensor 64 to move down. Preferably, said spring 68 does not interfere with the lowering of the sensor 64. Since the sensor 64 has a small mass, corrosion or impurities present can cause it to jam and thus prevent its lowering. The force exerted by the expanding spring 68 overcomes this blocking, so that the sensor is lowered and the DT device thus detects that the garland of the absorbent assembly 2 has fallen. There is little chance of a weakening of the force exerted by the spring due to radiation creep, since the spring is distant from the division zone. Thus, the spring 68 improves the reliability of the telemetry device.

Alternatively, transducers arranged vertically are not in line with the reflector. Several reflectors are mounted on the inner surface in the upper part of the assembly, which direct the ultrasonic beam to the reflector 66. In another case, the reflector 66 supported by the sensor 64 may have a surface with several faces to form a three-plane mirror, for example, to improve beam guidance. Preferably, these reflector options allow the use of a single transducer for multiple assemblies.

Next, the operation of said detection device DT will be briefly described.

When assembly 2 is suspended, as shown in FIG. 5A-5C, the sensor 64 is in contact with the connecting head of the absorbent assembly 2, the spring 68 is compressed, the reflector 66 is located at a distance from the transducer (s), and thus indicates that the absorbent assembly is not inserted.

When the assembly falls (FIG. 5D) because a threshold temperature has been reached or an undesired operation of the device has occurred, the sensor 64 is no longer supported on the connection head and due to the force exerted by the expanding spring 68 and its own gravity, said sensor 64 slides down to the expanded area respectively, moving the reflector 66 to a second position in which it rests on the gripping head 13. The transducer 67 measures the increased distance between the transducer 67 and the reflector 66, and thus, it detects that assembly 2 is introduced.

The specified detector is the most reliable. The sensor 64 has a small cross section and is able to bend, and a large mechanical gap is formed in the expanded region, thereby avoiding all risks of mechanical blocking of the sensor, even if the gripping head 13 is substantially deformed as a result of axial warping and / or compression of the expanded region.

In any case, the specified detector device provides detection (and positioning in the active zone) of the descending absorbing elements, without compromising the reliability of initiating the input of the specified garland formed from the absorbing elements.

The specified detector device can be used in addition to the means of "temperature research in the active zone" (TRTC) and / or to the fission chambers in order to diversify the means of detection of the introduced negative reactivity, or instead of these technologies.

In the present invention, the SI input initiation system SI is integrated in the carrier assembly, and is completely independent of the carrier assembly and, therefore, can be controlled independently of the fuel assembly.

Thus, it is possible to independently carry out operational tests, for example, to test the operation of the device and to test the absorbing assembly 2 for fall, that is, to conduct tests outside the reactor, only in capsule 10. These operational tests can be carried out systematically before installing the specified system in assembly A.

The input initiating device of the absorbent assembly can be checked and replaced if necessary, or if a system malfunction is detected, it can be reloaded independently of other elements of the fuel assembly. The specified replacement or reloading can be made without rejecting the entire assembly.

This is an advantage, since the service life of the input systems of the absorbing assemblies can be adjusted independently of the service life of the fuel assemblies, which reduces production costs and minimizes the amount of activated waste after the cycle.

The absorbent assembly input initiating device DI according to the present invention is particularly suitable for a removable absorbent assembly input initiation system. When using the input initiating device of the absorbent assembly according to the invention and, more specifically, due to the stopper 24, which locks the latches until the positioning temperature is reached, all risks of unlocking the latches are prevented, therefore, the set of absorbing elements cannot fall during the installation of the capsule on the supporting assembly, for example the result of the impact, provided that there is no destruction of the retainers, connecting head or cable. This is an advantage when integrating the assembly into the core (with the previously described positioning state).

When using the fuel assembly proposed in the invention of the design, and when integrating the input system of the input of the absorbing assembly according to the present invention, the volume fraction of fuel is slightly reduced, therefore, the neutron productivity in the core is also slightly reduced. Due to the volume of the central space, the volume fraction of fuel decreases by about 7% in the fuel assembly and about 0.6% in the core.

In addition, the proposed design of the bearing assembly allows with a minimum number of modifications and, therefore, with optimal costs to carry out the fuel cycle using assemblies of the prior art.

In addition, the design of the assembly according to the invention has a negligible effect on the pressure drop in the fuel assembly and, accordingly, on the thermodynamics of the core.

The carrier assembly according to the invention, comprising a device for initiating input of an absorbent assembly according to the invention, makes it possible to optimally use the coolant flow of the fuel assembly, which guarantees maximum speed and accuracy of operation of the device. Due to the central location of the housing in the carrier assembly and its design, the flow of heat carrier in the body has characteristics similar to the flow in a standard fuel assembly, therefore, the expansion of the body characterizes the temperature of the heat carrier and, accordingly, the state of the assembly.

Thanks to the present invention, the reliability of introducing negative reactivity is optimized. The capsule is mechanically isolated from the beam of the rod fuel elements undergoing deformation, since it is protected by a shell with considerable rigidity and due to the fact that after entering the capsule a large radial gap is formed. Since there is a bunch of rod heat-generating elements between the shell and the hexagonal pipe, the capsule is mechanically isolated from the hexagonal pipe undergoing deformation, since the beam of the rod heat-generating elements is able to compensate to some extent for the deformation of the hexagonal pipe (due to the gaps between the rod fuel elements and wire spacers).

Next, the absorbent assembly 2 according to the invention will be described in detail, by using which the input reliability of the set of absorbing elements described below, which can be easily inserted even into the deformed capsule, is further optimized. The assembly 2 contains absorbing components 4 of a spherical shape, sliding on a flexible cable 6. This assembly is very flexible, which facilitates the introduction of absorbing elements into the capsule.

The distribution of absorbing elements along the garland prevents blocking, which is possible in the case of continuous laying due to the effect of freezing and / or due to phenomena such as sintering.

The advantage of the absorbing elements 4 of the spherical shape is that they are highly reliable to enter into the capsule, since the components of the spherical shape are more easily inserted into the deformed structure and / or the structure of small size. In addition, based on the thermal and thermomechanical aspects associated with the absorbing element itself, it should be noted that due to the spherical shape, optimal cooling conditions are provided to minimize the temperature of the component core. For example, the temperature gradient created between the core and the outer surface in the spherical components according to the invention is one third lower than in the cylindrical components according to the prior art.

In this case, thermal stresses are also low, because a low temperature gradient is created between the core and the outer surface of the absorbing element. Thus, the risk of cracking of the absorbent element is reduced.

It should be noted that with the introduction of negative reactivity, the absorbing material is optimally used, since the spherical shape of the absorbing elements minimizes the effect of neutron self-shielding per unit volume.

The spherical components can be solid, and a single absorbent material can be used to make them. Alternatively, to optimize properties, each component can be made of two different materials. For example, the core can be made of metal, which has a lower ability to absorb neutrons, compared with ceramic material (such as B ₄ C), but having better thermal conductivity, so that it is possible to reduce the core temperature and increase the interval to the melting temperature, and the outer surface The component can be made of ceramic material. For the manufacture of the component, two materials are selected whose relative thermal expansion does not lead to a violation of the mechanical integrity of the component. Thus, said component is, for example, a metal ball covered by two hollow hemispheres of ceramic material.

In another embodiment, the spherical absorbent components are hollow. Regarding the thermal effect on the material, this design is preferable, especially in the case of an unexpected input, since the maximum temperature experienced by the absorbing material is reduced. In addition, the magnitude of the secondary stresses caused by the temperature in the components is reduced, since there is no phenomenon of relative thermal expansion of the core and the outer surface. From the point of view of neutron absorption, the core material due to the self-shielding effect is much less effective than the material of the outer surface. Therefore, the absence of core material in hollow spheres is not significant.

Hollow spherical components can be made by assembling two hollow hemispheres or by drilling holes in a solid sphere. In the latter case, a metal insert on each side of the drilled hole may be provided to reduce the diametrical clearance with the garland cable.

The cable 6 may be made of braided metal fibers or bundles of dry ceramic fiber.

The assembly contains a connecting head described above, one of the ends of which interacts with the latches 20.

Preferably, at least one or, preferably three (for example, three) metal elements are provided in the end portion of the assembly opposite the end portion containing the connecting head instead of components made of absorbent material. First, these elements provide emphasis on the absorbing elements. Secondly, these elements provide partial shielding of the absorbing elements from the fission zone, since under the influence of the neutron flux the properties of the absorbing elements may deteriorate. For example, when irradiated, the thermal conductivity decreases, in particular, B ₄ C, which leads to an increase in the temperature of the core of the components. Since metallic elements are installed that create a protective shield, components containing B ₄ C are partially protected from the effects of neutrons.

Finally, these elements can create ballast when the absorbent material of the component has a low density. By creating ballast, the assembly fall time is reduced and the risk of blocking it is reduced. In addition, these metal elements are capable of absorbing the shock load at the base of the capsule, which is especially important regarding B ₄ C, which has low impact strength.

Preferably, mechanical shock absorbing means may be installed between the absorbent components. Disc washers, for example, can be used. These tools do not have to be installed between every two components.

The length of the cable, which determines the flexibility of the garland, is greater than the height of the set of spherical absorbing elements, and the mechanical gap between the components is set taking into account the deformation of the components under the action of irradiation, such as elongation, swelling, creep.

In addition, between the cable and the holes made in the spherical absorbing components, a radial clearance is provided.

Due to the risk of fragmentation of the absorbent material, such as B ₄ C, as a result of relative deformations occurring in the reactor (elongation and radiation swelling), the absorbent components can be enclosed in a casing forming a protective metal shell for the absorbent material.

Absorbing components can be made of any material that absorbs neutrons. For example, boron carbide (B ₄ C), to a greater or lesser extent enriched ¹⁰ V., can serve as the indicated material.

For the manufacture of absorbent elements, hafnium-based materials may be used. These materials have a high density, which reduces the duration of the fall of the components, in addition, during radiation exposure they do not generate gases and do not undergo swelling, and there is no significant decrease in their ability to provide negative reactivity. Therefore, neutron absorption efficiency and detectability of components are stable. Metallic hafnium can be used, which, despite the significantly lower neutron absorption efficiency per unit volume compared to B ₄ C, has the advantage of significantly higher thermal conductivity compared to B ₄ C and stability under irradiation. Hafnium hydride can be used, which has high thermal conductivity in the absence of irradiation and stability when irradiated, like metallic hafnium.

It should be noted that for the manufacture of components, heat-resistant absorbing materials such as borides, for example, HfB ₂ and TiB ₂ , with a melting point of about 3300 ° C, can be used. In addition, you can use europium hexaboride EuB ₆ . You can also use Eu ₂ About ₃ . Under radiation exposure, these materials do not generate gaseous products. These materials also have a high absorption capacity.

Alternatively, the absorbent components, depending on their position along the garland, can be made of different absorbent materials. For example, components from hafnium-based materials can be located at the bottom of the garland, and components from B ₄ C-based materials can be located at the top of the garland. With the indicated distribution of absorbing elements, the main part of the negative reactivity is created by components from materials based on B ₄ C, while components from materials based on hafnium located in the lower part of the garland form a neutron shield that protects components from materials on B ₄ C base located at the top of the garland; in addition, these components from hafnium-based materials make a significant contribution to negative reactivity, both at the beginning and at the end of garland insertion. It should be noted that when entering the active zone there is no risk of melting components containing hafnium, since irradiation of these components in a suspended position did not lead to a decrease in their thermal conductivity.

Hafnium can also be used as a component mitigating the consequences of an emergency in the event of a general core melt.

In a pressurized water reactor, the materials used to make the absorbing elements can be, for example, hafnium, Dy ¹¹ B ₆ , Gd ¹¹ B ₆ , Sm ¹¹ B ₆ Er ¹¹ B ₄ , untreated HfB ₂ and untreated TiB ₂ .

The coolant may be any suitable liquid metal, for example sodium. Lead and lead-bismuth alloy are other liquid metals that can be used as a coolant in a fast neutron reactor. The use of sodium is preferred because it provides good heat transfer. If a boron-containing absorbing element released from ¹⁰ V helium is used, it helps to prevent potential problems with the tightness of shells containing liquid metal medium (rods, capsules, etc.). Finally, since the liquid metal medium has a high viscosity, the fall of the absorbing elements, especially at the end of the movement, is clearly slowed down, as a result, the risk of fragmentation of the absorbing ceramic is significantly reduced.

As an illustrative example, the assembly parameters according to the present invention.

A set of absorbing elements of a spherical shape can have a height of 800 mm. The size and weight of the absorbing elements depend on the material from which they are made:

- when using B ₄ C enriched up to 48% ¹⁰ V, the diameter of the component is 35 mm and the mass is 1.8 kg,

- when using HfB ₂ enriched up to 71% ¹⁰ V, the diameter of the component is 35 mm and the mass is 10.8 kg,

- when using hafnium, the diameter of the component is 67 mm, and the mass is 46.9 kg,

- when using Eu ₂ O _{3, the} diameter of the component is 52 mm, and the mass is 17.6 kg.

The integration of the initiation system for introducing an absorbent assembly containing spherical absorbing elements with a diameter of 35 mm into the bearing assembly eliminates the two rings of the rod fuel elements, which reduces the volume fraction of fuel by 7% in the fuel carrier assembly and by about 0.6% in the core.

Regarding the operation of the system, if it is assumed that the case is made of Z10 CNDT steel 15.15 V, and the capsule is made of W-5Re alloy, the operating temperature is 660 ° C and the case height is approximately 800 mm and the components have selected dimensions, then the estimated relative axial displacement body and capsule is:

- 5.65 mm in the range from ambient temperature to operating temperature,

- 1.44 mm in the range from operating temperature to operating temperature.

The displacement of the connecting head due to the displacement of the latches 20 in the range from the operating temperature to the response temperature can be calculated on the basis of: a linear displacement of the clamp of 5.4 mm and an angular displacement of 7.2 °.

Under these conditions, the axial displacement of the connecting head of assembly 2 in the range from the operating temperature to the operating temperature is 3.5 mm.

The carrier assembly according to the present invention, comprising a set of spherical absorbing elements forming a garland, is particularly suitable for use in sodium-cooled fast neutron reactors. The specified carrier assembly can also be used in other types of nuclear reactors, for example, in fast neutron reactors cooled by other liquid metals, for example, lead or lead-bismuth alloy, as well as in gas-cooled fast neutrons reactors a boiling water reactor or nuclear reactor.

Claims (31)

1. The carrier assembly for a nuclear reactor, comprising a housing (40), the longitudinal axis (X1) of which is oriented approximately along the vertical axis, a fission zone located in the lower part of the housing (40), a free volume located in the upper part of the housing (40), free space (52), which is located in the division zone and extends along at least a part of the division zone along the longitudinal axis (X1) from the end of the division zone located on the upper part of the housing, the shell (54) bounding the free space (52 ), and system (SI) is initiated ia input of the absorbent assembly, said system for initiating input of the absorbent assembly comprising a capsule (10) with a longitudinal axis (X), the assembly (2) to be inserted suspended in the capsule, and an input assembly initiating device (DI) configured to release the the input of the assembly in the emergency state of the assembly, while the capsule (10) is partially inserted into the shell (54), and the initiation system of the input of the absorbing assembly is removably mounted in the carrier assembly, while the capsule contains a gripping head, on A second system (SI) for initiating input of the absorbent assembly is suspended above the shell (54). 2. The carrier assembly according to claim 1, wherein the device for initiating input of the absorbent assembly is located in the upper part of the upper zone of the housing. 3. The carrier assembly according to claim 1 or 2, in which the free space (52) is located in the central part of the division zone so that the longitudinal axis (X) of the input initiation system of the absorbent assembly is coaxial to the assembly axis (X1). 4. The carrier assembly according to claim 1 or 2, in which the assembly to be introduced is neutron-absorbing and / or mitigating the consequences of an emergency. 5. The carrier assembly according to claim 1 or 2, in which the longitudinal dimension of the assembly to be introduced (2) is not more than half the total longitudinal size of the capsule (10). 6. The carrier assembly according to claim 1 or 2, in which the capsule contains means absorbing the fall of the assembly to be introduced at the end of its movement. 7. The carrier assembly according to claim 1 or 2, in which openings for supplying a coolant are made at the end of the capsule portion (10) located in the shell. 8. The carrier assembly according to claim 1 or 2, which contains guiding means for positioning the SI system to initiate the input of the absorbent assembly in the division zone located at the end of the shell on the same side as the free volume of the carrier assembly. 9. The carrier assembly according to claim 1 or 2, in which the housing has a hexagonal cross section, the shell (54) has a hexagonal outer cross section and a hexagonal or circular inner cross section, and the capsule (10) has a circular outer cross section. 10. The carrier assembly according to claim 1, wherein the assembly (2) to be inserted comprises a plurality of absorbing elements (4) pivotally connected to each other, one of the end absorbing elements forming a connecting head (2.1) interacting with means (11) device retention (DI) initiating input of the absorbent assembly. 11. The carrier assembly according to claim 10, in which the absorbing elements (4) are able to slide along the cable (6). 12. The carrier assembly according to claim 11, wherein the cable is made of braided metal fibers or braided ceramic fibers. 13. The carrier assembly according to claim 10, in which each element (4) has a spherical shape. 14. The carrier assembly according to claim 10, which comprises depreciation means located between the elements of at least one pair. 15. The carrier assembly according to claim 10, in which the elements (4) are formed of several absorbent materials 16. The carrier assembly according to claim 10, in which at least some of the elements (4) are made of the first absorbent material, and other elements are made of the second absorbent material. 17. The carrier assembly according to any one of paragraphs. 10-16, in which the absorbent elements are hollow or contain a central core and an outer casing made of different materials. 18. The carrier assembly according to claim 1 or 2, wherein the initiation system of the input of the absorbent assembly is sensitive to temperature changes. 19. The carrier assembly of claim 18, wherein the operation of the input initiation system of the absorbent assembly is based on relative expansion. 20. The carrier assembly according to claim 19, wherein the initiation system for introducing an absorbent assembly comprises blocking means preventing the assembly from entering the core at a temperature below the operating temperature of the reactor. 21. The carrier assembly according to claim 1 or 2, which comprises means for detecting the input of the assembly to be input by ultrasonic telemetry. 22. The carrier assembly according to claim 20, in which the device for initiating input of the absorbent assembly comprises a longitudinally fixed part formed from the capsule (10) and a longitudinally movable part, the capsule containing means (11) for holding the assembly (2) to be introduced in suspension above the division zone, wherein the assembly to be introduced is released under the action of the movable part, the movable part containing locking means and means of holding the assembly to be introduced in a suspended position, as well as release means the assembly to be introduced from the holding means, the locking means being formed by at least one first surface (24) called the locking surface, and the release means of the assembly to be introduced are formed by at least one second surface (26) called the releasing surface and means for moving the locking surface (24) and the releasing surface (26) along the longitudinal axis, while the moving means are formed by a housing (19), which has the possibility of longitudinal expansion relative to psula (10) as a result of increasing the temperature of the coolant, and the locking surface (24) and the releasing surface (26) are positioned so that with increasing temperature of the coolant, the locking surface (24) was able to move in the axial direction from the holding means (11), and releasing the surface (26) had the ability to move in the axial direction to the holding means (11); in this case, when the coolant in the reactor has a normal operating temperature, the locking surface (24) can move away from the holding means so that the holding means are unlocked, and when the temperature of the coolant exceeds the threshold temperature, the releasing surface (26) has the possibility of applying axial force to restraint means so that the assembly to be inserted is released. 23. The carrier assembly according to p. 22, in which the detection means comprise at least one ultrasonic transducer mounted above the upper part of the capsule, a reflector (66) mounted on the upper part of the capsule and facing the transducer, while the longitudinal position of the reflector ( 66) is adjustable depending on whether or not the assembly to be entered is held by retaining means (11); in this case, the reflector (66) is connected to the assembly to be introduced by means of an elongated element (64) that can slide freely along the expanded area, passing through the upper part of the capsule and holding the reflector (66) in the non-inserted position by supporting the assembly to be introduced. 24. The carrier assembly according to claim 23, which comprises an elastic means (68) in a compressed state in the presence of an assembly to be introduced and expandable in the absence of an assembly to be introduced, while the elastic means is capable of applying a tensile force to an elongated element (64) to move the reflector (66). 25. The carrier assembly according to claim 22, wherein a radial clearance is provided between the housing (19) and the capsule (10) defining a channel for circulation of the heat transfer medium between the housing and the capsule (10), the housing (19) having holes for circulation of the heat transfer medium in said channel. 26. The carrier assembly according to claim 22, wherein the holding means (11) comprise at least two locks (20), preferably three locks distributed around the longitudinal axis (X) and pivotally mounted on the capsule (10) with the possibility of movement to a position close to the longitudinal axis (X) to hold the assembly (2) to be inserted between the latches (20), and to a position remote from the longitudinal axis (X) to release the assembly (2) to be entered. 27. The bearing assembly according to claim 26, in which the locking surface (24) is a surface that is located in the radial direction outside the clips (20) and prevents the movement of the clips (20) from the longitudinal axis (X), and the release surface (26) represents a surface that is perpendicular to the longitudinal axis (X), while the latches (20) have a curved surface (28), which interacts with the release surface (26) to rotate the latches from the longitudinal axis. 28. The bearing assembly according to claim 22, in which the housing (19) is made of austenitic steel, and the capsule (10) is made of a tungsten-based alloy or the housing (19) is made of mechanically hardened steel Z10 CNDT 15.15 V, and the capsule (10 ) made of W-5Re alloy. 29. The carrier assembly according to claim 1 or 2, which is designed for a fast neutron reactor cooled by a liquid metal, preferably cooled by sodium, the neutron absorber is made of material (s) selected from the following: B ₄ C with variable enrichment ¹⁰ B, metallic hafnium, refractory materials such as borides, for example HfB ₂ and TiB ₂ , europium hexaboride EuB ₆ or Eu ₂ O ₃ . 30. The carrier assembly according to claim 1 or 2, which is intended for a water-cooled nuclear reactor using thermal neutrons, while the neutron absorber is made of material (s) selected from the following: hafnium, Dy ₁₁ B ₆ , Gd ₁₁ B ₆ , Sm ₁₁ B ₆ and Er ₁₁ B ₄ , untreated HfB ₂ and untreated TiB ₂ . 31. A nuclear reactor containing fuel assemblies and a carrier assembly according to any one of paragraphs. 1-30.

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