Nuclear reactors using heavy liquid metal coolants

Abstract

The present invention relates to nuclear power engineering, and in particular to ensuring the safety of nuclear reactors mainly using heavy liquid metal coolants based on lead or lead-bismuth alloy. The nuclear reactor comprises a filter (5) at the core inlet, wherein the filter (5) has a plurality of holes (11, 12) located at different heights of the filter 5 for the passage of coolant and for capturing foreign particles. The size of the hole (11) does not exceed the characteristic size of the minimum flow area in the core, and the holes (11, 12) are spaced apart along the height of the filter 5 so that no foreign particles can block holes located at different heights at the same time. The technical effect is to improve the degree of purification of particles in the coolant without significantly reducing the natural circulation level of the coolant.

Description

Technical Field

[0001] The present invention relates to nuclear power engineering, in particular to ensuring the safety of nuclear reactors (NRs), mainly using heavy liquid metal coolant (HLMC) based on lead or lead-bismuth alloy. Background Art

[0002] A characteristic of all liquid metal coolants used in reactor installations is that insoluble impurities may form due to interruptions in the operation of the system for maintaining the required coolant quality or due to the ingress of other working media into the coolant. For example, the ingress of oil from the bearings of the circulation pump can lead to their rupture and the formation of solid particles that are insoluble in the heavy liquid metal coolant and alkali metals. The ingress of air into the gas system of the heavy liquid metal coolant circuit can lead to the formation of excess lead oxide, which can be deposited on the surface or can also be present in the coolant in the form of solid particles.

[0003] Solid particles present in the coolant and on the surface have the potential to be removed by the coolant flow, an extremely dangerous phenomenon that may lead to an overlap with the coolant flow area at the core inlet. The consequence of such an event could be a loss or significant reduction in the heat of the fuel elements (FEs) in the reactor core, as well as a dangerous overheating of the fuel elements and their subsequent damage.

[0004] One possibility to solve the above problem is to install a full-flow filter at the core inlet to remove insoluble impurities from the entire coolant flow that cools the core. However, there is no simple solution to this problem, because filter clogging can also lead to accidents of core cooling loss. At the same time, conventional filter designs usually have sufficiently high hydraulic resistance, which leads to increased costs for pumping coolant and significantly reduces the level of natural circulation, thereby deteriorating safety characteristics.

[0005] The prior art discloses a variety of methods to solve the problem of purifying impurities and particles in liquid metal coolants, however, most of these methods are based on using chemical reagents or heating the coolant.

[0006] Therefore, according to some Russian patents, RU2226723, RU2247435, RU44414, RU120275, etc., for coolant purification, it is recommended to apply a reducing gas mixture to a lead coolant. U.S. Patent No. 3,854,933 discloses a sodium coolant that is purified by dissolving impurities at a temperature of 450 to 850 degrees Celsius and then cooling to a temperature slightly above the melting point of the coolant. Another U.S. Patent No. 4,928,497 discloses a cooled trap for purifying liquid metal coolant by removing oxygen and hydrogen dissolved in the coolant, which leads to the formation of particles. German Patent DE1813822 discloses purifying (lead-containing) coolant by heating the coolant to slightly above the saturation point in a recuperative heat exchanger. The coolant then enters the cooler, in which a cyclone separator is additionally installed in addition to the impurities deposited on the wall.

[0007] Russian patent RU2632814 mentions the possibility of using a mechanical filter to purify the coolant. German patents DE1583891 and DE1758953 propose the use of porous membranes to mechanically purify the coolant. In addition, Chinese patent application CN111739671 proposes the use of a magnetic separator to remove impurities from lead coolant.

[0008] As a prototype of the present invention, a fast neutron reactor with liquid metal coolant can be selected according to Russian patent RU2608596. A hot trap is located in the core of a nuclear reactor formed by a fuel assembly (FA). The hot trap body is made the same as the fuel assembly body and has a filter cartridge filled with a material (getter) inside the body, which is intended to absorb impurities in the sodium liquid metal coolant. This prior art solution makes it possible to simplify the reactor design and operation, improve the reliability of the reactor vessel and eliminate the need to use additional process equipment.

[0009] Disadvantages of known prior art techniques (including prototypes) aimed at purifying the coolant are their complexity, resulting in reduced reliability of the nuclear reactor, the need for frequent maintenance and low efficiency of coolant purification particles. Summary of the invention

[0010] The problem to be solved by the present invention is to eliminate the above-mentioned disadvantages of the same family of patents and to improve the operational safety of the nuclear reactor.

[0011] The technical result of the proposed invention is an increased degree of purification of particles from the coolant without significantly reducing the level of natural coolant circulation.

[0012] In order to solve the above problems and achieve a specific technical effect, it is proposed to install a filter with holes at different heights in the filter at the inlet of the nuclear reactor core, so that the coolant can pass through these holes and capture foreign particles. The size of these holes does not exceed the characteristic size of the minimum flow area in the core. At the same time, these holes are spaced apart along the height of the filter so that any foreign particle cannot block holes at different heights at the same time.

[0013] To avoid problems with coolant clogging or significant deterioration of filter permeability, the filter should capture particles larger than the minimum size of the flow area between the fuel elements, and a design with holes of the above characteristic size should be used. Then, particles that could clog the coolant flow section between the fuel elements will be captured, while particles that do not pose a threat of clogging the flow area in the core will pass through the filter. In other words, the filter captures only those particles that pose a direct threat to core cooling.

[0014] Thus, two important technical problems are solved: first, to prevent waste of core cooling due to overlapping coolant flow areas within the fuel element grid; second, to prevent waste of core cooling due to clogging of the filter by small particles, which does not pose a danger to heat dissipation in the core. A chamber is formed between the filter and the core, and the core elements are fixed in the chamber. In this case, even if part of the flow area of ​​the filter is blocked, the coolant flow in the chamber is redistributed so that the flow at the core inlet is equal in all channels. The presence of the chamber ensures an improvement in the reliability of core cooling.

[0015] Additionally, due to the use of at least two highly level filter holes, large particle aggregates or most of the deposits removed from the surface minimally block the flow area of ​​such a filter trap without significantly affecting the coolant flow.

[0016] The given problems are also solved and the claimed technical results are also achieved in possible embodiments of the present invention, however, the present invention is not limited thereto.

[0017] Thus, the filter can be made in the form of a first plate with holes and comprises a plurality of cups, whose bottoms are placed substantially perpendicular to the first plate and protrude from the first plate, the bottoms being oriented downstream of the coolant flow. At the same time, the bottom comprises a plurality of holes. In such a filter design, the coolant flow is divided into two parts: one part passes through the holes downstream, through the cups with the bottom, and the bottom comprises holes; the second part of the water flow passes through the holes on the first plate located upstream, and the diameter of the holes in the first plate is preferably greater than the diameter of the holes in the bottom. In this case, the large particles carried by the water flow are either divided into smaller particles due to collision with the cups, or they pass through the holes of the larger diameter above the second height level holes, or are pressed by the water flow to the first plate without hindering the coolant flow through the cups. Thus, large particles or sediments cannot block a large area at the same time, and the protruding structural elements of the filter form a means for crushing large pollutant particles.

[0018] Preferably, the filter includes a second plate, which is located on the side of the first plate opposite to the bottom position. The coolant flow with larger particles passes through the first plate, enters the chamber formed between the first plate and the second plate, and the cup passes through the first plate and the second plate. The holes in the cup can be formed in the area between the first plate and the second plate, and are preferably located in the lower part of the cup, closer to the first plate. The size of these holes and the size of the holes in the bottom of the cup preferably do not exceed the minimum flow area in the core. Therefore, larger particles that have entered the cavity of the chamber between the first plate, the second plate and the cup are crushed due to collision with structural elements, or are stuck in the chamber. Since the holes for the coolant outlet are located at the bottom of the chamber, the agglomeration of particles in the upper part of the chamber will not hinder the flow of coolant before these holes are blocked.

[0019] The shape of the holes in the first plate and the cup can be circular. Alternatively, all or part of the holes of minimum characteristic dimension can be made in the form of longitudinal slots, where the characteristic minimum dimension is the slot width. While the slots obviously ensure the achievement of the above technical results, they also reduce the flow resistance of the filter by increasing the flow area.

[0020] In another embodiment of the invention, the filter comprises a second plate in which exhaust ports may be provided to remove gases when the removable unit is installed in a nuclear reactor.

[0021] Additionally, the nuclear reactor may include a coolant agitator located upstream of the filter and downstream of the coolant flow.

[0022] In the following, the claimed design of a nuclear reactor and possible embodiments thereof are explained in more detail with reference to the accompanying drawings, without the invention being restricted thereto. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A removable unit of a nuclear reactor with filters is schematically shown.

[0024] Figure 2 An embodiment of a filter having a first plate and a second plate is shown.

[0025] Figure 3 Shown according to Figure 2 Magnified view of area A of a filter embodiment.

[0026] Figure 4a Shows Figure 3 1-1 part of the middle cup.

[0027] Figure 4b Shows Figure 3 2-2 parts of the middle cup.

[0028] The following elements are labeled in the figure and arrows in the figure generally show the movement of coolant.

[0029] 1: Support grid;

[0030] 2: fuel assembly;

[0031] 3: Sheath;

[0032] 4: Side reactor element;

[0033] 5: Filter;

[0034] 6: Filter body;

[0035] 7.1: First board;

[0036] 7.2: Second board;

[0037] 8: cup body;

[0038] 9: vent hole;

[0039] 10: bottom;

[0040] 11: Bottom hole;

[0041] 12: Holes on the first plate;

[0042] 13: Hole on the cup body. DETAILED DESCRIPTION

[0043] Generally speaking, a nuclear reactor (NR) comprises a reactor vessel, a core, a control and protection system, at least one circulating pump, at least one heat exchanger and other components well known to those skilled in the art. Since these components are not the protection objects of the present invention, they are not explained in detail.

[0044] The core of the nuclear reactor is defined by detachable units, which are also well-known nuclear reactor elements, schematically shown as Figure 1 In particular, the detachable unit includes a support grid 1, a plurality of fuel assemblies 2, a plurality of jackets 3 of a control and protection system (CPS), a side reactor element 4 and other elements.

[0045] The design of the nuclear reactor according to the invention is characterized in that a filter 5 is placed below the core, in particular below the support grid 1, which filter 5 is designed to filter particles in the liquid metal coolant flow. The filter 5 is a mechanical filter, in which particles are filtered through holes formed in the structural elements of the filter 5: when the coolant passes through these holes, particles whose characteristic size exceeds the characteristic size of these holes are retained in the structural elements of the filter 5 and do not enter the core of the nuclear reactor.

[0046] Since the filter 5 must firstly ensure effective filtering of particles and secondly ensure low resistance to the coolant flow, the present invention proposes that the filter 5 comprises a plurality of holes located at different heights, at least holes located at two different heights. These holes are spaced apart along the height of the filter so that no foreign particle can simultaneously block holes located at different heights. In this case, the size of these holes (or the characteristic size of these holes, if they are made into complex shapes, such as elongated shapes) should not exceed the characteristic size of the smallest flow area in the core, such as the distance between adjacent fuel elements in the fuel assembly 2.

[0047] Specifically, the filter 5 is designed to protect the core from the ingress of mechanical particles larger than 2.5 mm (smaller than the cell size between fuel elements) and to balance the coolant flow at the core inlet.

[0048] Figure 2 A possible embodiment of the filter 5 is shown in detail. The filter 5 is an assembled unit comprising a cylindrical filter body 6, in which a first plate 7.1 is fixed by welding. Additionally, but not necessarily, a second plate 7.2 may also be fixed inside the body 6, spaced apart from the first plate 7.1.

[0049] A plurality of filter cups 8 are fixed to the first plate 7 . 1 (eg by welding).

[0050] If the filter 5 also includes the second plate 7.2, it is preferred that a portion of the cup body 8 is welded to only one of the plates (for example, the second plate 7.2), while the other portion of the cup body 8 is welded to both the first plate 7.1 and the second plate 7.2 to ensure that the filter 5 has sufficient structural rigidity.

[0051] Furthermore, if the filter 5 comprises the second plate 7.2, vent holes 9 may be installed in the second plate 7.2 to remove gas when installing the removable unit in the nuclear reactor.

[0052] The cup body 8 includes a bottom 10, in which a bottom hole 11 ( Figure 3 , Figure 4a The coolant flowing to the core is filtered through the holes 11 and the through holes 12 formed in the first plate 7.1 ( Figure 3 ). At this time, the hole 11 and the hole 12 are located at different heights of the filter 5, such as Figure 3 The coolant flow is divided into two parts: one part of the coolant flow passes through the hole 11 downstream through the cup 8 with the bottom 10. The second part of the coolant flow passes through the hole 12 in the first plate 7.1 located upstream.

[0053] The size of the holes 11 (or the characteristic size of the holes 11 if they are made in a complex shape, such as an elongated shape) should not exceed the characteristic size of the smallest flow area in the core, for example the distance between adjacent fuel elements in the fuel assembly 2. In this case, preferably, the diameter of the holes 12 in the first plate 7.1 is larger than the diameter of the holes 11 in the bottom 10.

[0054] The large particles carried by the water flow are divided into smaller particles due to the collision with the cup body 8, or they pass above the second height hole and through the larger diameter hole 12, or are pressed by the water flow toward the first plate 7.1 without hindering the coolant flow. Therefore, large particles or sediments cannot block a large area at the same time, and the protruding structural elements of the filter 5 can crush large pollutant particles.

[0055] If the filter 5 also comprises the second plate 7.2, a hole 13 may preferably be made in the middle portion of the cup 8 (see Figure 3 , Figure 4b ) for the coolant to pass through the filter 5 to prevent the lower flow portion of the cup 8 from being blocked. The filtered particles can be retained between the first plate 7.1 and the second plate 7.2.

[0056] The size of the holes 13 and the size of the holes 11 in the bottom of the cup 8 preferably do not exceed the minimum flow area in the core. Thus, larger particles that have entered the cavity between the first plate 7.1, the second plate 7.2 and the cup 8 are either crushed due to collision with structural elements or become stuck in the cavity.

[0057] The shape of the holes 11, 12 and 13 in the first plate 7.1 and / or the cup 8 can be circular. Alternatively, all or part of the holes can be made in the form of longitudinal grooves, where the characteristic (minimum) dimension is the groove width. At the same time, the grooves reduce the hydraulic resistance of the filter 5 by increasing the flow area.

[0058] Thus, the claimed invention improves the operational safety of nuclear reactors and increases the extent of coolant purification from particles without significantly reducing the level of natural coolant circulation.

Claims

1. A nuclear reactor using a heavy liquid metal coolant, the nuclear reactor comprising a reactor vessel, a core, a control and protection system, at least one circulation pump and at least one heat exchanger, characterized in that: A filter is included at the inlet of the core, the filter includes a first plate and a plurality of cups, wherein the first plate has a plurality of holes, and the cups are substantially perpendicular to and protrude from the first plate, each cup has a bottom and the bottom extends downward into the coolant flow, wherein a plurality of holes are provided at the bottom of each cup, and the plurality of holes of the first plate and the plurality of holes of the bottom are located at different heights of the filter, serving as channels for the coolant and for capturing foreign particles, wherein the characteristic dimensions of the plurality of holes of the first plate and the plurality of holes of the bottom do not exceed the characteristic dimensions of the minimum flow area in the core, and the plurality of holes of the first plate and the plurality of holes of the bottom are spaced apart along the height of the filter, so that foreign particles cannot simultaneously block the plurality of holes of the first plate and the plurality of holes of the bottom located at different heights, wherein the filter includes a second plate located on a side of the first plate opposite to the bottom position, and the second plate is provided with a plurality of ventilation holes.

2. The nuclear reactor according to claim 1, characterized in that: The cup also has a plurality of holes in the area between the first plate and the second plate.

3. The nuclear reactor according to claim 1 or 2, characterized in that: At least some of the plurality of apertures are substantially circular in cross-section.

4. The nuclear reactor according to claim 1 or 2, characterized in that: At least some of the plurality of holes are substantially elongated in cross-section.

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