A cladding tube for a fuel rod for a nuclear reactor, a fuel rod, and a fuel assembly

Abstract

A cladding tube, a fuel rod and a fuel assembly are disclosed. The cladding tube comprises a tubular base component having an outer surface and an inner surface defining an inner space of the cladding tube housing a pile of fuel pellets. The tubular base component is made of a Zr-based alloy. A coating is applied onto the outer surface for protecting the tubular base component from mechanical wear, oxidation and hydriding. The Zr-based alloy has the following composition: Zr=balance, Al=0-2 wt %, Ti=0-20 wt %, Sn=0-6 wt %, Fe=0-0.4 wt %, Nb=0-0.4 wt %, O=200-1800 wtppm, C=0-200 wtppm, Si=0-200 wtppm, and S=0-200 wtppm. The total amount of Al+Ti+Sn>2.5 wt % and ≤28 wt %.

Claims

1-14. (canceled)

15. A cladding tube for a fuel rod for a nuclear reactor, the cladding tube comprising: a tubular base component having an outer surface and an inner surface defining an inner space of the cladding tube housing a pile of fuel pellets, wherein the tubular base component is made of a Zr-based alloy, and a coating applied onto the outer surface of the tubular base component and configured to protect the tubular base component from mechanical wear, oxidation and hydriding, wherein the Zr-based alloy has the following composition: Zr=balance, Al=0-2 wt %, Ti=0-20 wt %, Sn=0-6 wt %, Fe=0-0.4 wt %, Nb=0-0.4 wt %, O=200-1800 wtppm, C=0-200 wtppm, Si=0-200 wtppm, and S=0-200 wtppm, wherein 2.5 wt %<Al+Ti+Sn≤28 wt %.

16. The cladding tube according to claim 15, wherein said coating comprises at least one layer comprising at least one of Cr, a ceramic oxide, a ceramic carbide, a ceramic nitride and Diamond-Like Carbon (DLC), together with possible other alloying elements.

17. The cladding tube according to claim 15, wherein said coating comprises at least one layer forming an outer surface layer configured to be in contact with a cooling and moderating medium of the nuclear reactor.

18. The cladding tube according to claim 15, wherein the coating is physically vapor deposited onto the outer surface of the tubular base component.

19. The cladding tube according to claim 15, wherein the amount of Sn=1-6 wt %.

20. The cladding tube according to claim 15, wherein the amount of Ti=1-20 wt %.

21. The cladding tube according to claim 15, wherein the amount of Ti of the Zr-based alloy is enriched with regard to the isotope Ti-50 and/or depleted with regard to the isotope Ti-48.

22. The cladding tube according to claim 15, wherein the amount of Al=0.3-2 wt %.

23. The cladding tube according to claim 15, wherein the total amount of Al+Ti+Sn>2.7 wt %.

24. The cladding tube according to claim 15, wherein the total amount of Al+Ti+Sn>3.0 wt %.

25. The cladding tube according to claim 15, wherein the total amount of Al+Ti+Sn>3.5 wt %.

26. The cladding tube according to claim 15, wherein the total amount of Al+Ti+Sn>4.0 wt %.

27. The cladding tube according to claim 15, wherein the total amount of Al+Ti+Sn is equal to or less than 24 wt %.

28. The cladding tube according to claim 15, wherein the amount of O>800 wtppm.

29. The cladding tube according to claim 15, wherein the cladding tube comprises an inner liner provided against the inner surface of the tubular base component.

30. A fuel rod comprising a cladding tube according to claim 15.

31. A fuel assembly comprising a bundle of fuel rods according to claim 30.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The present invention is now to be explained more closely through a description of various embodiments and with reference to the drawing attached hereto.

[0049] FIG. 1 discloses schematically a longitudinal sectional view of a fuel assembly for a nuclear reactor according to a first embodiment of the invention.

[0050] FIG. 2 discloses schematically a longitudinal sectional view of a fuel rod of the fuel assembly in FIG. 1.

[0051] FIG. 3 discloses schematically an enlarged longitudinal sectional view of a part of the fuel rod in FIG. 2 comprising a tubular base component and a coating.

[0052] FIG. 4 discloses schematically an enlarged longitudinal sectional view of a part of the fuel rod in FIG. 2 comprising a tubular base component and a coating and according to a second embodiment.

DETAILED DESCRIPTION

[0053] FIG. 1 discloses a fuel assembly 1 configured for being used in a nuclear reactor, especially a Light Water Reactor, LWR, such as a Boiling Water Reactor, BWR, a Pressure Water Reactor, PWR, or a Water-Water Energetic Reactor, VVER.

[0054] The fuel assembly 1 comprises a bottom member 2, a top member 3 and a plurality of elongated fuel rods 4 extending between the bottom member 2 and the top member 3. The fuel rods 4 are maintained in their positions by means of a plurality of spacers 5.

[0055] Furthermore, the fuel assembly 1 may, for instance when configured for use in a BWR, comprise a flow channel or fuel box indicated by dashed lines 6 and surrounding the fuel rods 4.

[0056] FIG. 2 discloses one of the fuel rods 4 of the fuel assembly 1 in FIG. 1. The fuel rod 4 comprises a nuclear fuel, for instance in the form of a plurality of sintered nuclear fuel pellets 10, and a cladding tube 11 enclosing the nuclear fuel, in this case the nuclear fuel pellets 10.

[0057] The fuel rod 4 may comprise a bottom plug 12 sealing a lower end of the cladding tube 11, and a top plug 13 sealing an upper end of the cladding tube 11. The nuclear fuel pellets 10 are arranged in a pile in an inner space 14 of the cladding tube 11. The cladding tube 11 encloses the fuel pellets 10 and a gas in the inner space 14.

[0058] A spring 15 may be arranged in an upper plenum 16 of the inner space 14 between the pile of nuclear fuel pellets 10 and the top plug 13. The spring 15 compresses the pile of nuclear fuel pellets 10 against the bottom plug 12.

[0059] As can be seen in FIG. 3, the cladding tube 11 comprising a tubular base component 20 having an outer surface 21 and an inner surface 22 towards the inner space 14 housing the pile of fuel pellets 10. The tubular base component 20 has a wall thickness extending from the inner surface 22 to the outer surface 21.

[0060] The tubular base component 20 is made of a Zr-based alloy to be described more closely below.

[0061] The cladding tube 11 also comprises a coating 23 applied onto the outer surface 21 of the tubular base component 20. The coating 23 may enclose the whole outer surface 21 of the tubular base component 20. The coating 23 adjoins the tubular base component 20 and is configured to protect the tubular base component 20 from mechanical wear, oxidation and hydriding.

[0062] According to the first embodiment, the coating 23 comprises or consists of one layer 24. The layer 24 may thus form an outer surface layer configured to be in contact with a cooling and moderating medium of the nuclear reactor.

[0063] According to the first embodiment, the layer 24 may comprise Cr. The layer 24 may comprise or consist of elemental Cr together with possible other alloying elements.

[0064] According to a further embodiment, the layer 24 may, as an alternative or a supplement, comprise at least one of a ceramic oxide, a ceramic carbide, a ceramic nitride and Diamond-Like Carbon (DLC), together with possible other alloying elements.

[0065] According to the first embodiment, the coating 23, i.e. the layer 24 may be physically vapor deposited onto the outer surface 21 of the tubular base component 20. Physical vapor deposition, PVD, of the layer 24 may ensure a strong bonding of the coating 23 to the Zr-based alloy of the tubular base component 20.

[0066] It should be noted that also other methods of applying the coating 23 may be employed, for instance chemical vapor deposition, electroplating, cold spraying, etc.

[0067] The coating 23 may have a thickness of at most 0.1 mm. Furthermore, the coating 23 may have a thickness of at least 0.003 mm, at least 0.005 mm or at least 0.01 mm.

[0068] The Zr-based alloy of the tubular base component 20 has the following composition: Zr=balance, Al=0-2 wt %, Ti=0-20 wt %, Sn=0-6 wt %, Fe=0-0.4 wt %, Nb=0-0.4 wt %, O=200-1800 wtppm, C=traces-200 wtppm, Si=traces-200 wtppm, and S=traces-200 wtppm. The total amount of Al+Ti+Sn>2.5 wt % and ≤28 wt %.

[0069] Sn, Al and Ti may be included separately or in combination with each other. In other words, the Zr-based alloy may comprise only one of Sn, Al and Ti, two of Sn, Al and Ti, or all three of Sn, Al and Ti.

[0070] According to a further embodiment, the total amount of Sn+AI+Ti is larger than 2.7 wt %, preferably larger than 3.0 wt %, more preferably larger than 3.5 wt %, and most preferably larger than 4.0 wt %.

[0071] According to a further embodiment, the total amount of Al+Ti+Sn in the Zr-based alloy may be equal to or less than 24 wt %, equal to or less than 20 wt %, equal to or less than 16 wt %, equal to or less than 12 wt %, or equal to or less than 8 wt %.

[0072] The amount of Sn in the Zr-based alloy may be 1-6 wt %, 2-6 wt %, 3-6 wt %, 4-6 wt %, 5-6 wt %, 1-5 wt %, 1-4 wt %, 1-3 wt %, or 1-2 wt %.

[0073] The neutron absorption cross section of natural Sn is 0.626. Natural Sn contains several isotopes, namely Sn-112, Sn-114, Sn-115, Sn-116, Sn-117, Sn-118, Sn-119, Sn-120, Sn-122 and Sn-124. In order to reduce the neutron absorption cross section, Sn may be enriched with regards to some of the even isotopes, such as Sn-114, Sn-116, Sn-118, Sn-120, Sn-122 and Sn-124, which all have a neutron absorption cross section below 0.626 b.

[0074] The amount of Ti in the Zr-based alloy may be 1-20 wt %, 2-20 wt %, 4-20 wt %, 6-20 wt %, 8-20 wt %, 10-20 wt %, 1-18 wt %, 1-16 wt %, 1-14 wt %, 1-12 wt %, or 1-10 wt %.

[0075] The neutron absorption cross-section of natural Ti, containing the isotopes Ti-46, Ti-47, Ti-48, Ti-49 and Ti-50, is 6.09 b. Ti-48 has a high neutron absorption cross section of 7.84 b, whereas Ti-50 has a low neutron absorption cross section of 0.179 b. The amount of Ti in the Zr-based alloy may thus be enriched with regard to the isotope Ti-50 and/or depleted with regard to the isotope Ti-48.

[0076] The amount of Al in the Zr-based alloy may be 0.3-2 wt %, 0.5-2 wt %, 0.8-2 wt %, 1.0-2 wt %, 1.3-2 wt %, 1.6-2 wt %, 0.3-1.6 wt %, 0.3-1.3 wt %, 0.3-1.0 wt %, 0.3-0.8 wt %, or 0.3-0.5 wt %.

[0077] The Zr-based alloy may comprise a higher amount of O, for instance equal to or more than 800 wtppm up to the maximum level of 1800 wtppm.

[0078] The cladding tube 11 may also comprises an inner liner 25 provided against the inner surface 22 of the tubular base component 20. The inner liner 25 may be Zr-based and may include the following alloying elements 0.1-0.4 wt % Sn, 0.04-0.07 wt % Fe, 0-0.07 wt % Cr, and <600 wtppm O. In addition, the Zr-based inner liner 25 may include low or insignificant levels of impurities.

[0079] The amount of the alloying elements in the inner liner 25 is below the levels of the alloying elements in the Zr-based alloy of the tubular base component 20.

[0080] The inner liner 25 may have a thickness that constitutes about 10% of the wall thickness of the tubular base component 20.

[0081] FIG. 4 illustrates a second embodiment that differs from the first embodiment in that the coating 23 is a multilayer coating. In the second embodiment disclosed, the coating 23 comprises three layers 24, wherein the first layer 24a encloses and adjoins the outer surface 21 of the tubular base component 20, the second layer 24b encloses and adjoins the first layer 24a, and the third layer 24c encloses and adjoins the second layer 24b. The third layer 24c forms an outer surface layer configured to be in contact with a cooling and moderating medium of the nuclear reactor.

[0082] The first, second and third layers 24a-24c layers may have different compositions. The thickness of the coating 23 of the second embodiment may be equal to the one of the first embodiment. The first, second and third layers 24 are physically vapor deposited onto the outer surface 21 of the tubular base component 20 and onto each other.

[0083] It should be noted that the coating 23 may alternatively comprise two layers or more than three layers, for instance 4, 5, 6, 7 or even more layers.

[0084] The invention is not limited to the embodiments disclosed but may be varied and modified within the scope of the following claims.