WO2023018350A1 - Nuclear reactor with a heavy liquid metal coolant - Google Patents

Abstract

The invention relates to nuclear engineering, and more particularly to ensuring the safety of nuclear reactors, primarily reactors with a heavy liquid metal coolant based on lead or on alloys based on lead and bismuth. The claimed nuclear reactor has, at the inlet to the core, a filter (5) with openings (11, 12), arranged at different heights on the filter (5), for allowing the passage of a coolant and catching particulate impurities. The size of openings (11) does not exceed the typical size of the minimum flow cross section in the core, and openings (11, 12) are spaced apart heightwise on the filter (5) so that none of the particulate impurities can simultaneously block openings at different heights. The technical result consists in more thoroughly purifying coolant of particulate impurities, with a negligible decrease in the level of natural circulation of the coolant.

Description

NUCLEAR REACTOR WITH HEAVY LIQUID METAL COOLANT

Technical field

The invention relates to nuclear power, in particular, to ensuring the safety of nuclear reactors (NR), primarily with a heavy liquid metal coolant (HLMC) based on lead or alloys based on lead and bismuth.

A feature of all liquid-metal coolants used in reactor plants is the potential for the formation of insoluble impurities as a result of malfunctions in the operation of systems that maintain the required quality of the coolant, or the ingress of other working media into the coolant. For example, the ingress of oil from the bearings of circulation pumps leads to its cracking and the formation of solid particles that are insoluble both in HLMC and in alkali metals. The ingress of air into the gas system of HLMC circuits leads to the formation of an excess amount of lead oxides, which can either be deposited on surfaces or be present in the coolant in the form of solid particles.

The appearance of solid particles in the coolant and on surfaces with the potential for surface contaminants to be torn off by the coolant flow is an extremely dangerous phenomenon that can lead to blocking of the coolant flow section at the core inlet. The result of such events can be a loss or a significant decrease in heat removal from fuel elements (fuel rods) in the reactor core, dangerous overheating of fuel rods with their subsequent destruction.

A possible solution to the problem described above is to install a full-flow filter at the core inlet, which cleans the entire coolant flow going to cool the core from insoluble impurities. However, the problem does not have a simple solution, since clogging of the filter can also cause an accident with loss of core cooling. At the same time, traditional filter designs, as a rule, have a sufficiently large hydraulic resistance, which leads to an increase in the cost of pumping the coolant and can significantly reduce the level of natural circulation, worsening safety characteristics.

State of the art

From the prior art, there are various approaches to solving the problem of cleaning a liquid metal coolant from impurities and particles, which, however, are mostly based on the use of chemical reagents or heating of the coolant. So, according to a number of patents of the Russian Federation RU2226723, RU2247435, RU44414, RU120275 and others, it is proposed to apply the supply of a reducing gas mixture to the lead coolant to clean the coolant. In US patent US3854933, sodium coolant is purified by dissolving impurities at a temperature of 450 to 850 degrees Celsius and then cooling to a temperature just above the melting point of the coolant. In another US patent US4928497, a cold trap is used to clean a liquid metal coolant from oxygen and hydrogen dissolved in it, which can lead to the formation of particles. The German patent DE1813822 discloses the purification of a heat transfer medium, including one containing lead, by heating it slightly above the saturation point in a recuperative heat exchanger. Next, the coolant enters the cooler, in which, in addition (in addition to the deposition of impurities on the walls), a cyclone separator is installed.

RF patent RU2632814 mentions the possibility of using mechanical filters for the coolant. The use of porous membranes for mechanical cleaning of the coolant is proposed in German patents DE1583891 and DE1758953. And in the Chinese patent application CN111739671, it is proposed to use a magnetic separator to clean lead-based coolant from impurities.

As a prototype of the present invention, a fast neutron nuclear reactor with a liquid metal coolant can be selected according to RF patent RU2608596. Hot traps are placed in the core of a nuclear reactor formed by fuel assemblies (FA). The body of the hot trap is made identical to the body of the fuel assembly, and inside the body there is a cartridge with a material (getter) designed to absorb impurities in the sodium liquid metal coolant. This well-known technical solution makes it possible to simplify the design of the reactor and its operation, improve the reliability of the reactor pressure vessel, and eliminate the need for additional process equipment.

The disadvantages of the known technical solutions aimed at cleaning the coolant, including the prototype, is their complexity, leading to a decrease in the reliability of the nuclear reactor, the need for constant maintenance, as well as the low efficiency of cleaning the coolant from particles.

The objective of the invention is to eliminate the noted disadvantages of analogues and improve the safety of the nuclear reactor. The technical result of the invention is to increase the degree of purification of the coolant from particles with a slight decrease in the level of natural circulation of the coolant.

Brief summary of the invention

In order to solve the problem and achieve the indicated technical results, it is proposed to install a filter with holes located at different heights of the filter in a nuclear reactor at the entrance to the core to allow the coolant to pass through them and trap impurity particles. The size of the holes does not exceed the characteristic size of the minimum flow area in the core. In this case, the holes are spaced along the height of the filter in such a way that none of the impurity particles can simultaneously cover the holes located at different heights.

To eliminate the problem of clogging or a significant deterioration in the permeability of the filter by the coolant, the size of the particles trapped by the filter must be greater than the minimum size of the flow area between the fuel rods and must be a structure with holes of the above characteristic sizes. Then the particles that can potentially block the flow area through the coolant between the fuel rods will be trapped, and the particles that do not pose a threat of blocking the flow area in the core will be passed through the filter. In other words, the filter only traps those particles that pose an immediate threat to core cooling.

In this way, two important technical problems are solved: firstly, the prevention of loss of core cooling due to the blocking of the passage section along the coolant in the fuel grid; secondly, preventing loss of core cooling due to clogging of the filter with small particles that do not pose a danger to heat removal in the core. Between the filter and the active zone, in which the elements of the active zone are fixed, a chamber is formed. In this case, even when part of the flow sections of the filter are clogged in the specified chamber, the coolant flows are redistributed, so that the flow rate at the core inlet is equalized in all channels. The presence of this chamber provides increased reliability of the core cooling.

In addition, due to the use of at least two levels along the height of the openings in the filter, large conglomerates of particles or large parts of sediments torn from the surface overlap the passageways to a minimum extent. cross section of such a trap filter without significantly affecting the coolant flow.

The problem is solved, and the claimed technical result is also achieved in possible embodiments of the invention, to which, however, it is not limited.

Thus, the filter can be made in the form of a first plate with holes and contain a plurality of cups with bottoms placed essentially perpendicular to the first plate and protruding from the first plate with their bottoms downstream of the coolant flow. At the same time, holes are made in the bottoms. In such a filter design, the coolant flow is divided into two: one part passes through the holes downstream through the glasses with bottoms, in which there are holes; the second part of the flow passes through the holes in the upstream first plate, and the holes in the first plate preferably have a larger diameter than the holes in the bottoms. In this case, large particles carried by the flow are either separated into smaller ones as a result of collisions with the glasses, or pass above the second level of holes through holes of a larger diameter, or are pressed by the flow against the first plate and do not create obstacles for the flow of the coolant through the glasses. Thus, large particles or deposits cannot simultaneously cover large areas, and the protruding elements of the filter design create conditions for crushing large particles of contaminants.

It is preferable if the filter contains a second plate located on the side of the first plate opposite to the location of the bottoms. The coolant flow with larger particles, passing through the first plate, enters the chamber formed between the first plate and the second plate and the glasses passing through them. The glasses can be provided with holes in the area between the first plate and the second plate, located mainly in the lower part of the glasses, closer to the first plate. The size of these holes, as well as the size of the holes in the bottoms of the cups, preferably not more than the minimum flow area in the core. Then the larger particles that have fallen into the cavity of the specified chamber between the first and second plates and glasses, either crushed as a result of collisions with structural elements, or get stuck in this chamber. Since the holes for the outlet of the coolant are located in the lower part of the chamber, the accumulation of particles in the upper part of the chamber does not create obstacles for the flow of the coolant until these holes are blocked. The shape of the holes in the first plate and the glasses may be round. Alternatively, all or part of the holes of the minimum characteristic size can be made in the form of longitudinal slots, in which the characteristic minimum dimension is the width of the slit. In this case, the slotted holes, obviously, provide the achievement of the above technical results, but due to the increase in flow sections, they further reduce the hydraulic resistance of the filter.

In another embodiment of the invention, the filter of which contains a second plate, air vents can be placed in the second plate to remove gas when a removable block is installed in a nuclear reactor.

In addition, the nuclear reactor may contain a means for mixing the coolant placed before the filter downstream of the coolant.

Further, with reference to the attached drawings, the claimed device of a nuclear reactor, as well as possible options for its implementation, to which the present invention is not limited, are explained in more detail.

Brief description of the drawings

In FIG. 1 schematically shows a block of a removable nuclear reactor with a filter.

In FIG. 2 shows an embodiment of the filter with a first plate and a second plate.

In FIG. 3 is an enlarged view of area A of the filter embodiment of FIG. 2.

In FIG. 4a shows a cross section of 1-1 cups from FIG. 3.

In FIG. 4b shows a cross section of 2-2 cups from FIG. 3.

The following elements are marked on the figures:

1 - support grid;

2 - fuel assembly (FA);

3 - CPS cover;

4 - element of the side reflector;

5 - filter;

6 - filter housing;

7.1 - the first plate;

7.2 - second plate;

8 - glass;

9 - air vent;

10 - the bottom of the glass; 11 - hole in the bottom of the glass;

12 - hole in the first plate;

13 - hole in the body of the glass.

The arrows conditionally show the movement of the coolant.

Detailed description of embodiments of the invention

In general, a nuclear reactor (NR) contains a reactor vessel, a core, a control and protection system, at least one circulation pump, at least one heat exchanger, and other components well known to a person skilled in the art. Since these components are not the subject of the protection of the present invention, they are not explained in detail.

The active zone of the NR is determined by a removable block, which is also a well-known component of the NR and is schematically shown in Fig. 1. In particular, the removable block contains a support grid 1, TVS 2, covers 3 of the control and protection system (CPS), elements 4 of the side reflector and other components.

A design feature of a nuclear reactor according to the invention is the placement under the active zone, in particular, under the support grid 1, of a filter 5 designed to filter particles in the liquid metal coolant flow. Filter 5 is a mechanical filter in which particles are filtered through holes made in filter 5 design elements: when the coolant passes through the holes, particles whose characteristic size exceeds the characteristic size of the holes are retained in filter 5 and do not enter the nuclear reactor core.

Since the filter 5, on the one hand, must provide effective filtration of particles, and on the other hand, provide low resistance to the flow of the coolant, in the present invention it is proposed to make the filter 5 in such a way that the holes are located at different heights, at least at two different heights. The holes are spaced along the height of the filter in such a way that none of the impurity particles can simultaneously cover the holes located at different heights. In this case, the size of the holes (or the characteristic size of the holes, if they are made of a complex shape, for example, elongated) should not exceed the characteristic size of the minimum flow area in the core, for example, the distance between adjacent fuel elements in the fuel assembly 2. In particular, the filter 5 is designed to protect the core from mechanical particles larger than 2.5 mm, which is smaller than the size of the inter-fuel cell, as well as to equalize the coolant flow at the core inlet.

A possible embodiment of the filter 5 is shown in detail in FIG. 2. The filter 5 is an assembly unit consisting of a cylindrical filter housing 6, inside of which the first plate 7.1 is fixed by welding. Additionally, but not necessarily, a second plate 7.2 can also be fixed inside the body 6, spaced from the first plate 7.1.

Filter cups 8 are fixed (for example, by welding) on the first plate 7.1.

If the filter 5 also contains a second plate 7.2, it is preferable that part of the cups 8 is welded to only one of these plates, for example, to the second plate 7.2, and the other part of the cups 8 is welded to both the first plate 7.1 and the second plate 7.2 for ensuring sufficient rigidity of the filter design 5.

In addition, in the second plate 7.2, if it is included in the filter 5, air vents 9 can be installed to remove gas when installing the removable block in the NR.

Cups 8 have cup bottoms 10 with bottom holes 11 made in them (FIGS. 3, 4a). The coolant flow towards the active zone is filtered, passing through these holes 11, as well as holes 12 made in the first plate 7.1 (Fig. 3). In this case, holes 11 and holes 12 are located at different heights of the filter 5, as shown in FIG. 3. The coolant flow is divided into two parts: one part of the coolant flow passes through the holes 11 downstream through the cups 8 with bottoms 10. The second part of the coolant flow passes through the holes 12 in the upstream first plate 7.1.

The size of the holes 11 (or the characteristic size of the holes 11, if they are of complex shape, for example, elongated) should not exceed the characteristic size of the minimum flow area in the core, for example, the distance between adjacent fuel elements in the fuel assembly 2. In this case, it is preferable if the diameter the holes 12 in the first plate 7.1 are larger than the diameter of the holes 11 in the bottoms 10.

Large particles carried by the flow are either separated into smaller ones as a result of collisions with glasses 8, or pass above the second level of holes through holes 12 of a larger diameter, or are pressed by the flow against the first plate 7.1 and do not create obstacles for the flow of the coolant. Thus, large particles or deposits cannot simultaneously cover large areas, and the protruding elements of the filter 5 design create conditions for crushing large particles of contaminants. If the filter 5 also includes the second plate 7.2, in the middle part of the cup 8, holes 13 of the cup (see Fig. 3, 4b) are preferably made for the passage of the coolant through the filter 5 in case of blocking the passage section in the lower part of the cups 8. The filtered particles can linger between the first plate 7.1 and the second plate 7.2.

The size of the holes 13, as well as the size of the holes 11 in the bottoms of the cups 8, preferably not more than the minimum flow area in the core. Then larger particles that have fallen into the cavity between the first plate 7.1 and the second plate 7.2 and cups 8 are either crushed as a result of collisions with structural elements or get stuck in this cavity.

The shape of the holes 11, 12, 13 in the first plate 7.1 and/or cups 8 may be round. Alternatively, all or part of these holes can be made in the form of longitudinal slots, in which the characteristic (minimum) size is the width of the slot. At the same time, the slotted holes reduce the hydraulic resistance of the filter 5 due to the increase in flow sections.

Thus, the claimed invention provides an increase in the safety of the operation of a nuclear reactor, as well as an increase in the degree of purification of the coolant from particles with an insignificant decrease in the level of natural circulation of the coolant.

Claims

CLAIM 1. A nuclear reactor with a heavy liquid metal coolant containing a reactor vessel, an active zone, a control and protection system, at least one circulation pump and at least one heat exchanger, characterized in that at the inlet of the active zone it contains a filter with holes located at different height of the filter, for the passage of the coolant through them and trapping particles of impurities, while the characteristic size of the holes does not exceed the characteristic size of the minimum flow area in the core and the holes are spaced along the height of the filter in such a way that none of the particles of impurities can simultaneously block the holes located on different height. 2. The nuclear reactor according to claim 1, in which the filter is made in the form of a first plate with holes and contains a plurality of cups with bottoms placed essentially perpendicular to the first plate and protruding from the first plate with their bottoms downstream of the coolant flow, and holes are made in the bottoms. 3. Nuclear reactor according to claim. 2, in which the filter contains a second plate located on the side of the first plate, opposite the location of the bottoms. 4. Nuclear reactor according to claim 3, in which holes are made in the glasses in the area between the first plate and the second plate. 5. Nuclear reactor according to any one of paragraphs. 1-4, in which the cross section of at least part of the holes has a substantially circular shape. 6. Nuclear reactor according to any one of paragraphs. 1-4, in which the cross section of at least a portion of the holes has a substantially elongated shape. 7. Nuclear reactor according to claim 3 or 4, in which air vents are placed in the second plate. 9