Filters and fuel assemblies for nuclear power plants

Abstract

A filter (1, 1') for separating debris from coolant in a nuclear power plant is described. The filter (1, 1') has at least one passage (3) with an inner surface (5), an inlet end (2), and an outlet end (4). The at least one passage (3) is arranged to allow coolant to pass therethrough in a main flow direction (MFD) from the inlet end (2) to the outlet end (4) for cooling purposes in the nuclear power plant. The inner surface (5) of the at least one passage (3) has at least one surface portion (7, 7') facing a side flow direction (SFD) of the coolant, the at least one surface portion (7, 7') having at least one surface asperity (9, 9') arranged to capture debris flowing in the coolant in the side flow direction (SFD) opposite the main flow direction (MFD) during lifting or transportation of the filter (1, 1') after the filter (1, 1') has been used to separate debris from the coolant in the nuclear power plant. A fuel assembly (11, 11') for a nuclear power plant having a filter (1, 1') is also described.

Description

[Technical Field]

[0001] The present invention relates to a filter for separating debris from a coolant in a nuclear power plant according to the preamble of claim 1. The present invention also relates to a fuel assembly for a nuclear power plant according to the preamble of claim 15. [Background technology]

[0002] In nuclear power plants, such as BWRs, PWRs, and VVERs, filtering coolant water is important because debris carried by the coolant water can cause defects in the cladding of the fuel rods in the fuel assemblies (FA). Debris can reach the plant from the outside. Debris can consist of objects, metal pieces, or wires, for example, generated during repairs on various components of the plant. Debris can also be particles that can cause defects. For example, defects in the cladding of the fuel rods can result in a fuel leak and the release of uranium into the coolant water. If a larger defect occurs, the reactor must be shut down and the failed fuel replaced. This replacement is not only time-consuming but also costly. Debris can also cause defects in other components of the nuclear power plant, such as pumps. Therefore, debris filters are used to filter the coolant.

[0003] Debris trapped in the debris filter is retained therein by the continuous flow of water through the filter. When the fuel assembly (FA) with the filter is finally removed from the reactor core, the FA is lifted by the fuel handling machine, which reverses the direction of the water flow through the FA and filter. One issue to consider is the risk that during transport of the FA, a downward water flow (relative to the FA) or turbulent water flow could wash away debris trapped in the debris filter, and this loosened debris could fall onto other FAs in the core or spent fuel racks. This risk could lead to fuel-related failures.

[0004] U.S. Patent No. 5,929,999 describes an apparatus and method for handling fuel assemblies. According to the patent, a pump is used to create a water flow through the conduit member and the fuel assembly to retain debris that may be present in the debris filter during the lifting operation. The patent discloses a debris filter having a bent plate.

[0005] While such known solutions have worked well, there is a need for an improved debris filter that prevents debris from falling out of the filter during vertical or horizontal lifting or transport of a fuel assembly having the filter. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] EP Patent No. 2648188 Summary of the Invention

[0007] It is an object of the present invention to provide an improved debris filter for a nuclear power plant that is positioned to prevent debris trapped within the filter from being washed away or falling off the filter during lifting of the fuel assembly with the filter or during vertical or horizontal transport of the fuel assembly with the filter, thereby reducing the risk of debris falling on and causing damage to other fuel assemblies located below or nearby.

[0008] The above object is achieved by a filter as defined in claim 1 and a fuel assembly as defined in claim 15.

[0009] The above objects are therefore achieved by a filter for separating debris from a coolant in a nuclear power plant, the filter having at least one passageway with an inner surface, an inlet end, and an outlet end, the at least one passageway being arranged to allow coolant to pass in a main flow direction MFD from the inlet end to the outlet end for cooling purposes in the nuclear power plant.

[0010] Debris can consist of objects, metal fragments or wires, for example from repairs on various parts of the power plant. Debris can also enter the coolant from the outside. Debris can also be particles that can cause some kind of defect.

[0011] Each of the at least one passage forms a flow path for a coolant, allowing the coolant to flow along the passage from an inlet end to an outlet end during operation of the nuclear power plant for cooling purposes in the nuclear power plant. Thus, the coolant can be conveyed through the at least one passage in a controlled manner, passing through a filter. The main flow direction (MDF) is the direction of the main flow of the coolant passing through the passage from the inlet end to the outlet end of the passage. Therefore, the main flow direction may be defined as a vector along a line that follows the shape of the passage, in a direction toward the outlet end of the passage. Because the shape of the at least one passage may vary, the main flow direction may be simply and accurately defined for different shapes of the at least one passage.

[0012] The inner surface of at least one passage has at least one surface portion facing a sub flow direction SFD of the coolant, the at least one surface portion having at least one surface asperity positioned to capture debris flowing in the sub flow direction SFD within the coolant during lifting or transport of the filter after the filter has been used to separate debris from the coolant in a nuclear power plant. The sub flow direction SFD is opposite the main flow direction MFD.

[0013] The filter may be lifted along with the fuel assembly containing the filter.

[0014] The secondary flow direction SFD is opposite to the primary flow direction MFD and is the direction of the primary flow of coolant through the passage from the outlet end to the inlet end of the passage. Thus, the secondary flow direction SFD may be defined as a vector along a line that follows the geometry of the passage, directed toward the inlet end of the passage. Because the geometry of the at least one passage may vary, the secondary flow direction SFD may be simply and accurately defined for different geometries of the at least one passage.

[0015] The interior surface of at least one passage is oriented such that at least one surface portion faces the secondary flow direction SFD, and thus faces at least one of a plurality of vectors along a line in the passage in a direction toward the inlet end of the passage.

[0016] The at least one surface irregularity is formed on the surface portion for the purpose of capturing debris flowing through the cooling liquid in the secondary flow direction SFD, and the shape and design of the at least one surface irregularity may be different from each other.

[0017] The at least one surface portion may also be defined as a portion or part of the inner surface of the at least one passage. Accordingly, the inner surface of the at least one passage has one or more surface portions, each having at least one surface asperity. The at least one surface portion has a roughened surface due to the at least one surface asperity. The surface portion is characterized by higher frictional properties against debris flowing through the coolant in the secondary flow direction (SFD) compared to other portions of the inner surface of the passage that do not have the surface asperity. The surface asperities of the surface portion are positioned to minimize the effect of flow resistance on the flow in the primary flow direction (MFD).

[0018] As a result, the at least one surface asperity forms an obstacle to debris flowing in the coolant in the secondary flow direction SFD, and therefore debris flowing in the coolant in the secondary flow direction can be stopped by the at least one surface asperity and subsequently captured in the filter.

[0019] In this way, an improved filter for a nuclear power plant is provided that provides for preventing debris trapped within the filter from being washed away or falling off the filter during lifting or transport of the fuel assembly having the filter, thereby at least reducing the risk of debris falling onto or into other fuel assemblies and causing damage. As a result, the above-mentioned objectives are achieved.

[0020] Optionally, at least one surface portion is provided with a plurality of surface irregularities, which constitute an improved obstacle to debris and thus provide conditions for improved capture of debris flowing in the secondary flow direction SFD.

[0021] Optionally, the plurality of surface irregularities are arranged in at least one row.

[0022] By "in a row," it is meant that a plurality of surface irregularities are arranged in a direction extending along the surface portion. The surface irregularities may be arranged in one or more rows. Each row may be arranged at an angle, for example, transversely, to the secondary flow direction SFD. By arranging the surface irregularities in one or more rows, preferably transversely to the secondary flow direction SFD, the likelihood of capturing and retaining debris is increased. Thus, a filter with further improved capture efficiency is provided.

[0023] Optionally, the plurality of surface irregularities are arranged consecutively in the secondary flow direction SFD.

[0024] The plurality of surface asperities may be arranged such that, relative to a reference asperity of the plurality of surface asperities, another surface asperity or a plurality of other surface asperities are arranged upstream and / or downstream of the reference asperity in the secondary flow direction SFD, thereby improving the likelihood of trapping debris in the coolant, as the debris is stopped by the plurality of surface asperities in the secondary flow direction SFD, resulting in an improved filter.

[0025] Optionally, the surface portion has at least one depression forming at least one irregularity. Thus, the surface irregularity can be obtained simply by arranging a depression or recess in the surface portion of the inner surface of the passage.

[0026] Optionally, at least one recess has an elongated groove. By elongated groove is meant a slot or slit extending substantially transversely to the secondary flow direction SFD. The extension of each groove substantially transversely to the secondary flow direction SFD may be greater than the depth of the groove. This allows debris in the cooling liquid to be effectively trapped, for example, along the extension of the groove arranged substantially perpendicular to the secondary flow direction SFD.

[0027] Optionally, at least one depression has a point-like depression. Point-like depression means that the depth of the depression may be equal to or greater than the extension of the depression in a transverse direction relative to the secondary flow direction SFD. When there are multiple point-like depressions, unlike continuous depressions, the point-like depressions are not connected to each other. Therefore, the depressions may be arranged in a point-like manner on the surface portion. This allows for the depressions to be obtained with less energy and material consumption during the process of forming the depressions to manufacture the filter.

[0028] Optionally, the surface portion has at least one protrusion forming at least one unevenness. Thus, the surface portion can be easily obtained by arranging the protrusion, i.e., a unit protruding from the surface of the surface portion and forming a trap for debris flowing into the coolant. Thus, thanks to the protrusion, debris in the coolant can be efficiently stopped.

[0029] Optionally, at least one protrusion comprises an elongated ridge, the elongated ridge extending in a direction oriented transverse to the secondary flow direction SFD. The extension of each ridge substantially transverse to the secondary flow direction SFD may be greater than the height of the ridge, thereby effectively trapping debris in the cooling liquid along the extension of the ridge transverse to the secondary flow direction SFD.

[0030] Optionally, at least one protrusion has a point-like protrusion. Point-like protrusion means that the height of the protrusion may be equal to or greater than the extension of the protrusion in a transverse direction relative to the secondary flow direction SFD. When there are multiple point-like protrusions, unlike continuous protrusions, the point-like protrusions are not connected to each other. Therefore, the protrusions can be arranged in a point-like manner on the surface portion. This allows the protrusions to be obtained with less energy and material consumption during the process of forming the protrusions and manufacturing the filter.

[0031] Optionally, the at least one asperity is disposed at an angle relative to the secondary flow direction SFD. Thus, the at least one asperity can be disposed to have a surface facing the secondary flow direction SFD and inclined at an acute angle α relative to the inner surface of the at least one passage. As a result, conditions can be provided for efficient capture of debris flowing in the secondary flow direction SFD. Furthermore, the at least one asperity disposed at an angle relative to the secondary flow direction SFD contributes to reducing the impact of breakdown on the flow in the primary flow direction MFD.

[0032] Optionally, at least one surface portion has a bend along the secondary flow direction SFD. The surface portion has a portion where the surface portion begins and a portion where the surface portion ends relative to the flow along the secondary flow direction. A bend along the secondary flow direction SFD means that the portion where the surface portion ends is displaced in a direction perpendicular to the secondary flow direction SFD and toward the inside of the passage relative to the portion where the surface portion begins. This can provide conditions for further improved capture of debris flowing in the secondary flow direction SFD.

[0033] Optionally, the features are manufactured by additive manufacturing, sometimes called a 3D printing process, and therefore the features can be manufactured cost and time efficiently.

[0034] Optionally, at least one passage has at least one bend along its length, the bend being arranged such that an inner surface of the at least one passage has a portion that is substantially opposite the secondary flow direction SFD and a portion that is oriented substantially along the secondary flow direction SFD, where the portion that is opposite the secondary flow direction SFD creates some resistance to the flow of the coolant, such that debris in the coolant experiences resistance while passing through the coolant.

[0035] According to a preferred embodiment, the at least one surface portion is advantageously arranged downstream of the at least one bend in the secondary flow direction SFD. The at least one surface portion is arranged on the inner side of the at least one passage, facing the secondary flow direction SFD (as a virtual vector) of the flow immediately upstream of the at least one bend. Thus, the flow passing through the at least one bend in the secondary flow direction SFD encounters the at least one surface portion downstream of the at least one bend. As a result, improved conditions are provided for the at least one surface portion to capture debris flowing in the secondary flow direction SFD, i.e., by utilizing the at least one bend that pushes the debris toward the at least one surface portion, the debris is effectively stopped by the at least one irregularity arranged downstream of the at least one bend.

[0036] A further object of the present invention is to provide an improved fuel assembly. Accordingly, this object is achieved by a fuel assembly for a nuclear power plant, the fuel assembly having a bottom portion, a top portion, and a plurality of fuel rods arranged alongside one another. Spaces are provided between the fuel rods and between the bottom and top portions of the fuel assembly. The bottom portion has a filter according to any one of the embodiments described herein. Since the fuel assembly has the improved filter, an improved fuel assembly is provided. In this way, the above object is achieved.

[0037] Optionally, the filter and the bottom are arranged to direct cooling liquid into the space. [Brief explanation of the drawings]

[0038] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0039] [Figure 1] FIG. 1 is a schematic diagram of a portion of a filter having channels with textured surfaces; [Figure 2] FIG. 2 illustrates the surface texture of the surface portion of FIG. 1 according to an embodiment; [Figure 3] FIG. 3 illustrates a surface texture of the surface portion of FIG. 1 according to yet another embodiment; [Figure 4] FIG. 4 is a schematic cross-sectional view of a fuel assembly for a BWR nuclear reactor having a filter according to an embodiment; [Figure 5] FIG. 5 is a schematic cross-sectional view of a fuel assembly for a PWR reactor having a filter according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0040] FIG. 1 shows a schematic representation of a portion of a filter 1, 1' for separating debris from a coolant in a nuclear power plant. The filter 1, 1' includes a plurality of interconnected plates 8, which form at least one passage 3 between two adjacent plates 8. For simplicity, only some of the plates 8 and some of the passages 3 are shown in FIG. 1. However, the filter 1 may include a plurality of interconnected plates 8. The passages 3 are adjacently arranged and separated from one another by the plates 8. The plates are preferably manufactured as thin sheets of a metallic material interconnected by, for example, welding or additive manufacturing. Other suitable materials, such as ceramic materials, may also be used for the plates 8.

[0041] The entire filter 1, 1' has an outer wall (not shown in FIG. 1) which separates at least one passage 3 on its sides, thereby allowing the coolant to be transported through the passage 3 in a controlled manner.

[0042] As shown in FIG. 1, the plates 8 are arranged parallel to each other with a distance d between adjacent plates 8. The distance d may be equal between all plates of the filters 1, 1′ or may vary between plates 8. Therefore, the distance d between the plates 8 may vary and may be determined during the manufacturing process of the filters 1, 1′. As a result, by adjusting the distance d between the plates 8, the size of the passages 3, i.e., the height or width, can be adjusted to meet various needs.

[0043] As an alternative to the embodiment shown in Figure 1, at least one passage 3 may be formed by tubular units interconnected to form a filter. The tubular units may be, for example, metal pipes connected to each other by welding. Such tubular units may be arranged in one or more levels of interconnected tubular units to form a filter, allowing the coolant to flow through passages arranged in this one or more levels.

[0044] The filter 1, 1' is positioned to separate debris from coolant in a nuclear power plant. The filter 1, 1' has at least one passage 3 with an inner surface 5, an inlet end 2, and an outlet end 4. The at least one passage 3 is positioned to allow coolant to pass therethrough in a main flow direction MFD from the inlet end 2 to the outlet end 4 for cooling purposes in the nuclear power plant. The inner surface 5 of the at least one passage 3 has at least one surface portion 7, 7' facing a secondary flow direction SFD of the coolant, the at least one surface portion 7, 7' having at least one surface asperity 9, 9' positioned to capture debris flowing in the coolant in the secondary flow direction SFD. The secondary flow direction SFD is opposite the primary flow direction MFD.

[0045] In Figure 1, the plates 8 having an inner surface 5 provided with at least one surface portion 7, 7' are similar to one another and the references given apply to all relevant details of the plate 8. To facilitate interpretation of the figure, the references are set in one place for each detail.

[0046] According to the embodiment shown in Figure 1, the surface portion 7, 7' is provided with a plurality of asperities 9, 9' arranged successively in the secondary flow direction SFD. Furthermore, the asperities 9, 9' are formed as depressions formed in the inner surface 5 of at least one passage 3.

[0047] Alternatively, the at least one irregularity 9 , 9 ′ may be formed as at least one protrusion projecting from the inner surface 5 of the at least one passage 3 .

[0048] At least one asperity 9, 9' may be arranged at an angle to the secondary flow direction SFD, i.e., at least one asperity 9, 9' may be arranged to have a surface facing the secondary flow direction SFD and inclined at an acute angle α to the inner surface 5 of the at least one passage 3.

[0049] As shown in FIG. 1 , at least one surface portion 7, 7' may have a bend along the secondary flow direction SFD. The surface portion 7, 7' has a portion 10 where the surface portion 7, 7' begins and a portion 12 where the surface portion 7, 7' ends, relative to the flow along the secondary flow direction SFD. The bend along the secondary flow direction SFD means that the portion 12 where the surface portion 7, 7' ends is displaced in a direction perpendicular to the secondary flow direction SFD and toward the inside of the passage 3 relative to the portion 10 where the surface portion 7, 7' begins. Therefore, the imaginary extension line 1 of the portion 10 where the surface portion 7, 7' begins and the portion 12 where the surface portion 7, 7' ends are separated by a distance s. This provides conditions for further improved capture of debris flowing in the secondary flow direction SFD.

[0050] At least one passage 3 may have at least one bend 6 along the extension of the at least one passage 3. According to the embodiment shown in FIG. 1 , the at least one passage 3 has three bends 6, 6', and 6'', and at least one surface portion 7, 7' is located downstream of the third bend 6'' counting along the secondary flow direction SFD. Therefore, the at least one surface portion 7, 7' is located downstream of the at least one bend 6 in the secondary flow direction SFD, on the side of the inner surface 5 of the at least one passage 3 that faces the secondary flow direction SFD (as a virtual vector) of the flow immediately upstream of the at least one bend 6. Therefore, the flow passing through the at least one bend 6 in the secondary flow direction SFD encounters the at least one surface portion 7, 7' downstream of the at least one bend 6. As a result, improved conditions can be provided for capturing debris flowing in the secondary flow direction SFD by at least one surface portion 7, 7', i.e., by utilizing at least one curved portion that pushes the debris towards at least one surface portion 7, 7', the debris is effectively stopped by at least one irregularity 9, 9' arranged downstream of the at least one curved portion 6.

[0051] FIG. 1 shows an example of debris 14 trapped on at least one surface portion 7 , 7 ′ located downstream of at least one bend 6 .

[0052] As a possible example of a manufacturing process for the indentations 9, 9', the indentations 9, 9' can be manufactured by additive manufacturing, also known as a 3D printing process.

[0053] As shown in FIG. 1, the asperities 9, 9' form small teeth on the inner surface 5 of at least one passageway 3.

[0054] The size of the irregularities 9, 9', ie, the depth and / or height thereof, is in the range of 0.2 to 1.5 mm, for example.

[0055] Figure 2 illustrates, according to one embodiment, the surface textures 9 of the surface portion 7 shown in Figure 1. As shown in Figure 2, the surface textures 9 may be arranged in rows and may be arranged as a series of elongated depressions, e.g., a series of elongated grooves, and / or a series of elongated protrusions, e.g., a series of elongated ridges.

[0056] Figure 3 shows the surface irregularities 9 of the surface portion 7 shown in Figure 1 according to a further embodiment. As shown in Figure 3, the surface irregularities 9' are arranged as spot-like depressions and / or as spot-like protrusions and are arranged in rows.

[0057] 4 is a schematic cross-sectional view of a fuel assembly 11 for a BWR reactor in a nuclear power plant. The fuel assembly 11 has a bottom portion 13′, a top portion 15, and a plurality of fuel rods 17 arranged alongside one another. Spaces 19 are provided between the fuel rods and between the bottom portion 13 and the top portion 15 of the fuel assembly 11. The bottom portions 13, 13′ have a filter 1 according to any one of the embodiments described herein.

[0058] According to this embodiment, the filter 1 and the bottom 13 are arranged to direct the cooling liquid into the space 19 .

[0059] 5 is a schematic cross-sectional view of a fuel assembly 11' for a PWR nuclear reactor having a filter 1' according to an embodiment described herein above. Reference numerals in FIG. 5 indicate the same or similar elements as in FIG.

[0060] Alternatively, the filters 1, 1' may be installed in a VVER reactor.

[0061] The invention is not limited to the described embodiments but can be varied freely within the scope of the claims.

Claims

1. A filter (1, 1') for separating debris from a coolant in a nuclear power plant, the filter (1, 1') having at least one passage (3) with an inner surface (5), an inlet end (2) and an outlet end (4), the at least one passage (3) being arranged to allow the coolant to pass in a main flow direction (MFD) from the inlet end (2) to the outlet end (4) for cooling purposes in the nuclear power plant; The inner surface (5) of the at least one passage (3) has at least one surface portion (7, 7') facing a secondary flow direction (SFD) of the coolant, and the at least one surface portion (7, 7') has at least one surface asperity (9, 9') arranged to capture the debris flowing in the secondary flow direction (SFD) within the coolant during lifting or transportation of the filter (1, 1') after the filter (1, 1') has been used to separate debris from the coolant in the nuclear power plant, the secondary flow direction (SFD) being opposite to the main flow direction (MFD).

2. 2. A filter (1, 1') according to claim 1, wherein said at least one surface portion (7, 7') is provided with a plurality of surface irregularities (9, 9').

3. 3. The filter (1, 1') according to claim 2, wherein the plurality of surface irregularities (9, 9') are arranged in at least one row.

4. 4. The filter (1, 1') according to claim 2 or 3, wherein the plurality of surface irregularities (9, 9') are arranged consecutively in the secondary flow direction (SFD).

5. 5. A filter (1, 1') according to any one of claims 1 to 4, wherein said surface portion (7, 7') comprises at least one depression forming said at least one surface irregularity (9, 9').

6. 6. A filter (1, 1') according to claim 5, wherein said at least one recess comprises an elongated groove (9).

7. 7. A filter (1, 1') according to claim 5 or 6, wherein said at least one depression comprises a punctate depression (9').

8. 8. A filter (1, 1') according to any one of claims 1 to 7, wherein said surface portion (7, 7') has at least one protrusion forming said at least one surface irregularity (9, 9').

9. 9. A filter (1, 1') according to claim 8, wherein said at least one protrusion comprises an elongated ridge (9).

10. 10. The filter (1, 1') according to claim 8 or 9, wherein said at least one projection comprises a point-like projection (9').

11. The filter (1, 1') according to any one of the preceding claims, wherein the at least one surface irregularity (9, 9') is arranged at an angle to the secondary flow direction (SFD).

12. The filter (1, 1') according to any one of the preceding claims, wherein said at least one surface portion (7, 7') has a bend along said secondary flow direction (SFD).

13. The filter (1, 1') according to any one of claims 1 to 10, wherein the plurality of surface irregularities (9, 9') are manufactured by additive manufacturing.

14. 13. A filter (1, 1') according to any one of the preceding claims, wherein said at least one passage (3) has at least one bend (6) along its extension.

15. A fuel assembly (11, 11') for a nuclear power plant, the fuel assembly (11, 11') having a bottom (13, 13'), a top (15, 15'), and a plurality of fuel rods (17, 17') arranged adjacent to one another, with spaces (19, 19') provided between the fuel assemblies (11, 11') and between the bottom (13, 13') and the top (15, 15') of the fuel assembly (11, 11'); A fuel assembly (11, 11') in which the bottom (13, 13') has a filter (1, 1') according to any one of claims 1 to 12.

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