Filter zones with different filtering efficiencies for a fuel assembly of a nuclear water reactor

Abstract

A fuel assembly for a nuclear water reactor having an upstream end, a downstream end, and a flow interspace between the upstream and downstream ends. Fuel rods are provided in the flow interspace between the upstream and downstream ends. The flow interspace permits a flow of coolant through the fuel assembly along a flow direction from the upstream end to the downstream end. A filter device is provided to catch debris particles in the flow of coolant. The filter device has a first filter zone for a major part of the flow of coolant, and a second filter zone for a minor part of the flow of coolant. The first filter zone has a first filtering efficiency and the second filter zone has a second filtering efficiency. The second filtering efficiency is higher than the first filtering efficiency.

Claims

1. A fuel assembly configured to be positioned in a nuclear water reactor, wherein the fuel assembly comprises: an upstream end, a downstream end, a flow interspace between the upstream end and the downstream end, a plurality of fuel rods provided in the flow interspace between the upstream end and the downstream end, the flow interspace being configured to permit a flow of coolant through the fuel assembly along a flow direction from the upstream end to the downstream end in contact with the fuel rods, a filter device configured to catch debris particles in the flow of coolant, wherein the filter device comprises a first filter zone provided in the flow of coolant between the upstream end and the fuel rods, and a second filter zone, wherein the first filter zone comprises a plurality of passages arranged to guide at least a part of the flow of coolant to pass the first filter zone through the passages towards the downstream end, wherein the second filter zone comprises a plurality of passages arranged to guide at most a part of the flow of coolant to pass the second filter zone through the passages towards the downstream end, wherein the first filter zone has a first filtering efficiency and the second filter zone has a second filtering efficiency, wherein the second filtering efficiency is higher than the first filtering efficiency, and wherein the passages of the first filter zone and the second filter zone are formed by a plurality of sheets, which are arranged beside each other and oriented along the flow direction, and wherein adjacent sheets of the first filter zone are provided at a larger distance from each other than adjacent sheets of the second filter zone.

2. The fuel assembly according to claim 1, wherein the second filter zone is dimensioned to permit the second filter zone to be clogged and wherein the first filter zone is configured to secure a sufficient flow of coolant through the first filter zone even if no coolant passes the second filter zone.

3. The fuel assembly according to claim 1, wherein the first filter zone comprises an inlet end turned towards the upstream end, and an outlet end, and is arranged to guide said at least a part of the flow of coolant to pass the first filter zone through the passages from the inlet end to the outlet end, and wherein the second filter zone comprises an inlet end turned towards the upstream end, and an outlet end, and is arranged to guide said at most a part of the flow of coolant to pass the second filter zone through the passages from the inlet end to the outlet end.

4. The fuel assembly according to claim 1, wherein the first filter zone and the second filter zone are provided beside each other.

5. The fuel assembly according to claim 1, wherein each of the passages of the first filter zone defines a first flow area and each of the passages of the second filter zone defines a second flow area, which is smaller than the first filter area.

6. The fuel assembly according to claim 1, wherein each of the passages of the first filter zone defines a first passage length from an inlet end to an outlet end, and each of the passages of the second filter zone defines a second passage length from an inlet end to an outlet end, which second passage length is longer than the first passage length.

7. The fuel assembly according to claim 1, wherein the first filter zone has a first pressure loss coefficient ξ.sub.1 and the second filter zone a second pressure loss coefficient ξ.sub.2 and wherein the second pressure loss coefficient ξ.sub.2 is greater than the first pressure loss coefficient ξ.sub.1.

8. The fuel assembly according to claim 1, wherein the first filter zone has a first flow area A.sub.1 and the second filter zone a second flow area A.sub.2 and wherein the first flow area A.sub.1 is greater than the second flow area A.sub.2.

9. The fuel assembly according to claim 1, wherein the filter device comprises a magnetic member provided to create a magnetic field on at least some of the passages of the second filter zone to attract debris particles flowing through the passages of the second filter zone.

10. The fuel assembly according to claim 1, wherein the filter device is provided in the flow interspace to guide at most a minor part of the flow of coolant through the second filter zone.

11. The fuel assembly according to claim 10, wherein the filter device is provided in the flow interspace to guide at least a major part of the flow of coolant through the first filter zone.

12. The fuel assembly according to claim 1, wherein the filter device is provided in the flow interspace to guide the entire flow of coolant through the first filter zone.

13. The fuel assembly according to claim 12, wherein the second filter zone is provided at a distance from the first filter zone.

14. The fuel assembly according to claim 13, wherein the second filter zone is provided downstream the first filter zone.

15. The fuel assembly according to claim 13, wherein the second filter zone is provided upstream the first filter zone.

16. The fuel assembly according to claim 1, wherein each sheet comprises a first portion, which extends from the inlet end, a second portion, which extends from the outlet end, and a third portion, which extends between the first portion and the second portion, and wherein each sheet along the first portion has a wave-shape extending in a direction transversally to the flow direction and along the third portion has a wave-shape extending in the flow direction.

17. The fuel assembly according to claim 16, wherein each sheet along the second portion has a wave-shape in the direction transversally to the flow direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is now to be explained more closely through a description of various embodiments and with reference to the drawings attached hereto.

(2) FIG. 1 discloses a longitudinal section through a fuel assembly according to a first embodiment of the invention.

(3) FIG. 2 discloses a longitudinal section through a filter device of the fuel assembly in FIG. 1.

(4) FIG. 3 discloses a plan view of the filter device in FIG. 2.

(5) FIG. 4 discloses a longitudinal section through a filter device of a fuel assembly according to a second embodiment of the invention.

(6) FIG. 5 discloses a longitudinal section through a filter device of a fuel assembly according to a third embodiment of the invention.

(7) FIG. 6 discloses a longitudinal section through a lower portion of a fuel assembly according to a fourth embodiment of the invention.

(8) FIG. 7 discloses a longitudinal section through a lower portion of a fuel assembly according to a fifth embodiment of the invention.

(9) FIG. 8 discloses a longitudinal section through a lower portion of a fuel assembly according to a sixth embodiment of the invention.

(10) FIG. 9 discloses a longitudinal section through a filter device of a fuel assembly according to a seventh embodiment of the invention.

(11) FIG. 10 discloses a plan view of the filter device in FIG. 9.

(12) FIG. 11 discloses a longitudinal section through a fuel assembly according to an eighth embodiment of the present invention.

(13) FIG. 12 discloses a longitudinal section through a lower portion of a fuel assembly according to a ninth embodiment of the invention.

(14) FIG. 13 discloses a longitudinal section through a lower portion of a fuel assembly according to a tenth embodiment of the invention.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

(15) FIGS. 1 to 3 disclose a first embodiment of a fuel assembly 1 configured to be positioned in a nuclear water reactor, and more precisely a boiling water reactor, BWR. The fuel assembly 1 has an elongated shape and extends along a longitudinal axis x between an upstream end 1a and a downstream end 1b. During use of the fuel assembly 1 in the reactor, the upstream end 1a forms a lower end and the downstream end 1b forms an upper end of the fuel assembly 1. A flow interspace 2 is provided in the fuel assembly 1 between the upstream end 1a and the downstream end 1b.

(16) A plurality of fuel rods 3 is provided in the flow interspace 2 between the upstream end 1a and the downstream end 1b. The fuel rods 3 are held by means of spacers 4. In the first embodiment, the spacers 4 are attached to a number of water rods 5, two of which are shown in FIG. 1.

(17) The fuel assembly 1 also comprises a casing 6 enclosing the fuel rods 3, the spacers 4 and the flow interspace 2, which is configured to permit a flow of coolant through the fuel assembly 1 along a flow direction F from an inlet 7 at the upstream end 1a to the downstream end 1b in contact with the fuel rods 3.

(18) The water rods 5 are attached to a bottom plate 8 provided beneath the fuel rods 3.

(19) Furthermore, the water rods 5 may also be attached to a top plate 9 at the downstream end 1a. The top plate 9 comprises a handle 10. The bottom plate 8, the water rods 5, the top plate 9 and the spacers 4 form a support structure which may be lifted via the handle 10 and carry the weight of the fuel rods 3.

(20) The fuel assembly 1 also comprises a bottom piece 11, frequently designated as a transition piece. The bottom piece 11 extends to the upstream end 1a and defines the inlet 7 for the flow of coolant. The bottom piece 11 may be attached to the bottom plate 8 or to the casing 6.

(21) The fuel assembly 1 also comprises a filter device 19 configured to catch debris particles in the flow of coolant. The filter device 19 is provided between the upstream end 1a and the fuel rods 3. In the first embodiment, the filter device is provided between the upstream end 1a and the bottom plate 8. The filter device 20 may be supported by or attached to the bottom piece 11.

(22) The filter device 19 comprises a first filter zone 20 and a second filter zone 30.

(23) In the first embodiment, the first filter zone 20 and the second filter zone 30 are both provided in the flow of coolant between the upstream end 1a and the fuel rods 3, and more precisely between the upstream end 1a and the bottom plate 8. Furthermore, the first filter zone 20 and the second filter zone 30 are provided beside each other. As can be seen in FIG. 3, the second filter zone 30 is located in the center of the filter device 19 and thus surrounded by the first filter zone 20. It should be noted that the second filter zone 30 may be located anywhere on the filter device 19, for instance along a side edge as indicated by the dashed line. As also appears, the shape of the contour of the second filter zone 30 may vary.

(24) The first filter zone 20 is greater than the second filter zone 30, i.e. the first filter zone 20 covers at least a major part of the total area of filter device 19 or of the total flow area of the flow interspace 2 at the level of the filter device 19. The second filter zone 30 covers at most a minor part of the total area of the filter device 29 or of the total flow area of the flow interspace 2 at the level of the filter device 19. For instance, the second filter zone 30 may cover at most 40%, 30%, 20%, 10% or 5% of the total area of the filter device 19.

(25) As can be seen more clearly in FIG. 2, the first filter zone 20 comprises an inlet end 21 turned towards the upstream end 1b, an outlet end 22 turned towards the downstream end 1b and a plurality of passages 23 extending between the inlet end 21 and the outlet end 22. The first filter zone 20 is arranged to guide at least a major part of the flow of coolant to pass the first filter zone 20 through the passages 23 from the inlet end 21 to the outlet end 22 towards the downstream end. The first filter zone 20 has a first filtering efficiency.

(26) The second filter zone 30 comprises an inlet end 31 turned towards the upstream end 1b, an outlet end 32 turned towards the downstream end 1b and a plurality of passages 33 extending between the inlet end 31 and the outlet end 32. The second filter zone 30 is arranged to guide at most a minor part of the flow of coolant to pass the second filter zone 30 through the passages 33 from the inlet end 31 to the outlet end 32 towards the downstream end 1b. The second filter zone 22 has a second filtering efficiency.

(27) The second filtering efficiency is higher than the first filtering efficiency. In the first embodiment, the differing filtering efficiency has been accomplished by each of the passages 23 of the first filter zone 20 defining a first flow area and each of the passages 33 of the second filter zone 30 defining a second flow area, wherein the second flow area is smaller than the first filter area. In other words, the passages 33 of the second filter zone 30 are thinner than the passages 23 of the first filter zone 20 as can be seen in FIG. 2.

(28) In the first embodiment, the passages 23 of the first filter zone 20 are formed by a plurality of sheets 24 arranged beside each other and oriented along the flow direction F. Also the passages 33 of the second filter zone 30 are formed by a plurality of sheets 34 arranged beside each other and oriented along the flow direction F. Adjacent sheets 24 of the first filter zone 20 are provided at a larger distance from each other than adjacent sheets 34 of the second filter zone 30.

(29) It is to be noted, that the passages 23, 33 may be configured in other ways, for instance through holes in a plate, wherein the holes may have a circular or elongated shape seen in the flow direction.

(30) FIG. 4 discloses a second embodiment, which differs from the first embodiment only with regard to how the differing filtering efficiency is accomplished. In the second embodiment, each of the passages 23 of the first filter zone 20 defines a first passage length L2 from the inlet end 21 to the outlet end 22, and each of the passages 33 of the second filter zone 30 defines a second passage length L3 from the inlet end 31 to the outlet end 32, wherein the second passage length L3 is longer than the first passage length L2.

(31) It should be noted that the differing filtering efficiency may be accomplished also by a combination of a varying flow area, as in the first embodiment, and a varying passage length, as in the second embodiment.

(32) FIG. 5 discloses a third embodiment, which differs from the first and second embodiments in that the second filter zone 30 has a differing geometrical configuration than the first filter zone 20. In the fourth embodiment the passages 33 of the second filter zone 30 extend along a curved or bent path whereas the passages 23 of the first filter zone 20 are straight. The passages 33 of the second filter zone 30 may thus be formed by bent sheets 34.

(33) FIG. 6 discloses a fourth embodiment, which differs from the first embodiment in that the second filter zone 30 is provided at a distance from the first filter zone 20 along the flow direction F, and more precisely the second filter zone 30 is provided upstream the first filter zone 20. In the third embodiment, the filter device 19 is thus provided in the flow interspace 2 to guide the entire flow of coolant through the first filter zone 20. A minor part of the flow of coolant will be guided through the second filter zone 30, and the first filter zone 20.

(34) FIG. 7 discloses a fifth embodiment, which differs from the fourth embodiment only in that the second filter zone 30 is provided downstream the first filter zone 20.

(35) It should be noted, that the filter devices 19 shown in FIGS. 6 and 7 may be provided with filter zones 20 and 30 as shown in FIGS. 2 to 4.

(36) FIG. 8 discloses a sixth embodiment of a fuel assembly 1, with a filter device 19 comprising a magnetic member 35 attached to the second filter zone 30. The magnetic member 35 will create a magnetic field on at least some of the passages 33 of the second filter zone 30 to attract debris particles flowing through the passages 33 of the second filter zone 30. The magnetic field will provide the second filtering efficiency. For the rest, the configuration of the first and second filter zones 20, 30 may be identical.

(37) FIGS. 9 and 10 disclose a filter device 19 of a fuel assembly a according to a seventh embodiment, in which the sheets 24, 34 forming the passages 23, 33 of the first filter zone 20 and the second filter zone 30 have a curved configuration. FIG. 10 illustrates the filter device 19 in a plan view seen from the inlet end 21, 31 along the flow direction F.

(38) Each sheet 24, 34 comprises a first portion 26, 36 which extends from the inlet end 21, a second portion 27, 37 which extends from the outlet end 22, and a third portion 28, 38 which extends between the first portion 26, 36 and the second portion 27, 37.

(39) Each sheet 24, 34 has a first wave-shape along the first portion 26, 36 in a direction transversally to the flow direction F, a second wave-shape along the second portion 27, 37 in a direction transversally to the flow direction F, and a third wave-shape along the third portion 28, 38 in the flow direction F. The wave-shapes are continuous, i.e. there are no sharp transitions.

(40) The sheets 24, 34 are arranged beside each other along the first portion 26, 36 in such a way that substantially each pair of adjacent sheets 24, 34 abuts each other at valleys and ridges, respectively, of said wave-shape to permit each passage 23, 33 between two adjacent sheets 24, 34 to form a plurality of inlet channels arranged beside each other.

(41) In the same way, the sheets 24, 34 are arranged beside each other along the second portion 27, 37 in such a way that substantially each pair of adjacent sheets 24, 34 abuts each other at valleys and ridges, respectively, of said wave-shape to permit each passage 23, 33 between two adjacent sheets 24, 34 to form a plurality of outlet channels arranged beside each other. Each inlet channel may have the same, or substantially the same, flow area as each outlet channel. A centre line of substantially each inlet channel may be concentric, or substantially concentric, with a centre line of a respective corresponding outlet channel.

(42) The sheets 24, 34 may be connected to each other said valleys and ridges, respectively. The sheets 24, 34 may then be connected to each other by means of a fuse weld or a spot weld where the sheets 24, 34 abut each other.

(43) Substantially each wave of said wave-shape of the first portion 26, 36 and of the second portion 27, 37 may have a maximum amplitude, wherein the maximum amplitude decreases continuously in the direction towards the third portion 28, 38. The maximum amplitude may be zero, or substantially zero, at the transition to the third portion 28, 38.

(44) Each passage 23, 24 of the third portion 28, 38 forms an intermediate channel between two adjacent sheets. The sheets along the third portion 28, 38 may at least include a part portion extending in parallel, or substantially in parallel, with a direction transversally to the flow direction F.

(45) The third portion 28, 38 may include projections 29, 39 extending into the intermediate channel. The projections 29, 39 may be arranged along a line extending in parallel, or substantially in parallel, with a direction transversally to the flow direction F, wherein one such part portion is arranged on each side of the projections 29, 39.

(46) According to a twelfth embodiment of the invention, the third portion 38 of the second filter zone 30 may have such projections 39, whereas the third portion 28 of the second filter zone 20 has no such projection 29. Thus the projections 39 may provide the second filtering efficiency.

(47) FIG. 11 discloses an eighth embodiment of a fuel assembly 1 configured to be positioned in a nuclear water reactor, and more precisely in pressure water reactor, PWR.

(48) It should be noted, that the same reference signs have been used for similar or corresponding elements in all the embodiments disclosed.

(49) Also the fuel assembly 1 according to the eighth embodiment has an elongated shape and extends along a longitudinal axis x between an upstream end 1a and a downstream end 1b. During use of the fuel assembly 1 in the reactor, the upstream end 1a forms a lower end and the downstream end 1b forms an upper end of the fuel assembly 1. A flow interspace 2 is provided between the upstream end 1a and the downstream end 1b.

(50) A plurality of fuel rods 3 is provided in the flow interspace 2 between the upstream end 1a and the downstream end 1b. The fuel rods 3 are held by means of spacers 4. In the eighth embodiment, the spacers 4 are attached to a number of guide tubes 13, two of which are shown in FIG. 11. The guide tubes 13 contains coolant during normal operation and are configured to receive a respective control rod when the operation of the PWR is to be interrupted.

(51) In contrast to a fuel assembly 1 for a BWR, the fuel assembly 1 according to the eighth embodiment has no casing, but still comprises a flow interspace 2 for a flow of coolant from the upstream end 1a to the downstream end 1b in contact with the fuel rods 3.

(52) The guide tubes 13 are attached to a bottom plate 8 provided beneath the fuel rods 3, and to a top plate 9 at the downstream end 1a. The bottom plate 8, the guide tubes 13, the top plate 9 and the spacers 4 form a support structure which carries the weight of the fuel rods 3.

(53) The fuel assembly 1 also comprises a bottom piece 11. The bottom piece 11 extends to the upstream end 1a and defines the inlet 7 for the flow of coolant. The bottom piece 11 may be attached to the bottom plate 8.

(54) The fuel assembly 1 also comprises a filter device 19 configured to catch debris particles in the flow of coolant. The filter device 20 is provided between the upstream end 1a and the fuel rods 3. In the eighth embodiment, the filter device 19 is provided between the upstream end 1a and the bottom plate 8. Also the filter device 19 of the eighth embodiment comprises a first filter zone 20 and a second filter zone 30.

(55) In the eighth embodiment, the first filter zone 20 and the second filter zone 30 are both provided in the flow of coolant between the upstream end 1a and the fuel rods 3, and more precisely between the upstream end 1a and the bottom plate 8. Furthermore, the first filter zone 20 and the second filter 30 zone are provided beside each other. The first filter zone 20 is greater than the second filter zone 30, i.e. the first filter zone 20 constitutes major part of the total flow area of the flow interspace 2 and the second filter zone 30 constitutes a minor part of the total flow area of the flow interspace 2.

(56) The filter device 19 may thus be configured in the same way as in the first embodiments. Especially, the first filter zone 20 and the second filter zone 30 may be configured as in the second and third embodiments.

(57) FIG. 12 discloses a ninth embodiment with a filter device 19 for a fuel assembly 1 of a PWR. The filter device 19 corresponds to the one of the fourth embodiment, i.e. the second filter zone 30 is provided at a distance from the first filter zone 20 along the flow direction F, and more precisely, the second filter zone 30 is provided upstream the first filter zone 20. In the ninth embodiment, the filter device 19 is thus provided in the flow interspace 2 to guide the entire flow of coolant through the first filter zone 20. A minor part of the flow of coolant will be guided through the second filter zone 30.

(58) FIG. 13 discloses a tenth embodiment, which differs from the ninth embodiment only in that the second filter zone 30 is provided downstream the first filter zone 20.

(59) It is to be noted that all the variants of the filter devices 19 disclosed above for the first to seventh embodiments concerning a BWR are applicable also to fuel assemblies for a PWR.

(60) The present invention is not limited to the embodiments disclosed but may be varied and modified within the scope of the following claims.