Ceramic nuclear fuel having UB2 enriched in 11B

Abstract

A fuel assembly for a nuclear reactor, a fuel rod of the fuel assembly, and a ceramic nuclear fuel pellet of the fuel rod are disclosed. The fuel pellet includes a first fissile material of UB.sub.2, The boron of the UB.sub.2 is enriched to have a concentration of the isotope .sup.11B that is higher than for natural B.

Claims

1. A ceramic nuclear fuel pellet for a nuclear reactor, wherein the nuclear fuel pellet comprises a first fissile material of UB.sub.2, wherein the boron of the UB.sub.2 is enriched to have a concentration of the isotope .sup.11B that is higher than for natural B, wherein the concentration of the isotope .sup.11B is at least 85% by weight, wherein the nuclear fuel pellet further comprises at least one second fissile material, the at least one second fissile material comprises UN.

2. The ceramic nuclear fuel pellet according to claim 1, wherein the concentration of the isotope .sup.11B is at least 90% by weight.

3. The ceramic nuclear fuel pellet according to claim 1, wherein the concentration of the isotope .sup.11B is at least 95% by weight.

4. The ceramic nuclear fuel pellet according to claim 1, wherein the concentration of the isotope .sup.11B is at approximately 100% by weight.

5. The ceramic nuclear fuel pellet according to claim 1, wherein the nuclear fuel pellet consists of UB.sub.2.

6. The ceramic nuclear fuel pellet according to claim 1, wherein the at least one second fissile material comprises one of an actinide nitride, an actinide silicide and an actinide oxide.

7. The ceramic nuclear fuel pellet according to claim 1, wherein the first fissile material and the at least one second fissile material are mixed in the nuclear fuel pellet.

8. The ceramic nuclear fuel pellet according to claim 1, wherein the nuclear fuel pellet is a sintered nuclear fuel pellet.

9. A fuel rod comprising a cladding tube and a plurality of nuclear fuel pellets according to claim 1.

10. The fuel rod according to claim 9, wherein the fuel rod comprises a plurality of absorbing pellets comprising UB.sub.2, in which the boron of the UB.sub.2 has a concentration of the isotope .sup.10B that is higher than in the UB.sub.2 of the first fissile material of the nuclear fuel pellets.

11. The fuel rod according to claim 10, wherein the concentration of the isotope .sup.10B in the UB.sub.2 of the absorbing pellets is at least 25, 30, 40, 50, 60, 70, 80, 90 or 100% by weight.

12. A fuel assembly comprising a plurality of fuel rods according to claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The 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 schematically a longitudinal sectional view of a fuel assembly for a nuclear reactor.

(3) FIG. 2 discloses schematically a longitudinal sectional view of a fuel rod of the fuel assembly in FIG. 1.

(4) FIG. 3 discloses longitudinal sectional view of a nuclear fuel pellet according to a first embodiment and suitable for being contained the fuel rod in FIG. 2.

(5) FIG. 4 discloses longitudinal sectional view of a nuclear fuel pellet according to a second embodiment and suitable for being contained the fuel rod in FIG. 2.

(6) FIG. 5 discloses schematically a longitudinal sectional view of another fuel rod suitable for the fuel assembly shown in FIG. 1.

DETAILED DESCRIPTION

(7) FIG. 1 discloses a fuel assembly 1 configured to be introduced into a core of a nuclear reactor, in particular in a water cooled light water reactors, LWR, such as a Boiling Water Reactor, BWR, or a Pressurized Water reactor, PWR. The core may comprise or consist of high burnup areas and low burnup areas.

(8) 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.

(9) Furthermore, the fuel assembly 1 may, for instance when to be used in a BWR, comprise a flow channel or fuel box indicated by dashed lines 6 and surrounding the fuel rods 4.

(10) FIG. 2 discloses one of the fuel rods 4 of the fuel assembly 1 of FIG. 1. The fuel rod 4 comprises a nuclear fuel in the form of a plurality of nuclear fuel pellets 10, and a cladding tube 11 enclosing the nuclear fuel pellets 10. The fuel rod 4 comprises a bottom plug 12 sealing a lower end of the cladding tube 11, and a top plug 13 sealing an upper end of the fuel rod 4. The nuclear fuel pellets 10 are arranged in a pile in the cladding tube 11. The cladding tube 11 thus encloses the fuel pellets 10 and a gas.

(11) A spring 14 is arranged in an upper plenum 15 between the pile of nuclear fuel pellets 10 and the top plug 13. The spring 14 compresses the pile of nuclear fuel pellets 10 against the bottom plug 12.

(12) A first embodiment of one of the nuclear fuel pellets 10 is disclosed in FIG. 3. The nuclear fuel pellet 10 is a ceramic nuclear fuel pellet 10 and comprises, or consists of, a first fissile material of UB.sub.2.

(13) A second embodiment of one of the nuclear fuel pellets 10 is disclosed in FIG. 4, according to which the ceramic nuclear fuel pellet 10, in addition to the first fissile material 20, may comprise at least one second fissile material 21. The concentration of the second fissile material 21 may vary depending on the position of the nuclear fuel pellet in the fuel rod, or in the fuel assembly.

(14) In low burnup areas, for instance in the lower region of the core of the nuclear reactor, the concentration of the second fissile material may be relatively high and in high burnup areas of the core, where the temperature is expected to be higher, the concentration of the second fissile material may be relatively low.

(15) For instance, the concentration of the second fissile material may be 99.9%, at least 90%, at least 80%, at least 70%, at least 60%, at least 50% or at least 40% by volume in low burnup areas. In high burnup areas, the concentration of the second fissile material 21 may be at most 40%, at most 30%, at most 20%, at most 10% or at most 5% by volume.

(16) At least in high burnup areas, the first fissile material 20 may thus constitute the main fissile material, and the second fissile material 21 the minor fissile material.

(17) The at least one second fissile material 21 comprises one of an actinide nitride, an actinide silicide and an actinide oxide. In the embodiments disclosed, the second fissile material 21 comprises no boron.

(18) For instance, the at least one second fissile material 21 may comprise one of UN, U.sub.3Si.sub.2, UO.sub.2, U.sub.3Si, USi, PuN, Pu.sub.3Si.sub.2, PuO.sub.2, Pu.sub.3Si, PuSi, ThN, Th.sub.3Si.sub.2, ThO.sub.2, Th.sub.3Si and ThSi.

(19) Furthermore, the at least one second fissile material 21 may comprise UB.sub.x, wherein x is larger than 2, for instance UB.sub.4. Such a UB.sub.x compound offers a possibility to increase the neutron absorbing capability of all or some of the nuclear fuel pellets 10 in the fuel rod 4.

(20) The first fissile material 20 and the at least one second fissile material 21, or second fissile materials 21, may be intimately mixed in the nuclear fuel pellet 10.

(21) In the nuclear fuel pellet 10 of the first and second embodiments, the boron of the UB.sub.2 is enriched to contain a concentration of the isotope .sup.11B that is higher than for natural B. The concentration of the isotope .sup.11B may be at least 85% by weight, preferably at least 90% by weight, more preferably at least 95% by weight or most preferably approximately 100%, or 100%, by weight.

(22) These concentrations constitute an enrichment compared to the natural concentration of the isotope .sup.11B, which is approximately 80% by weight.

(23) The ceramic nuclear fuel pellet 10 may be a sintered nuclear fuel pellet. A powder of the first fissile material, and possible a powder of the second fissile material or materials, may be mixed to form a mixture. The mixture is compressed to a green body, which is then sintered in suitable oven to the nuclear fuel pellet 10.

(24) The nuclear fuel pellet 10 may also as an alternative be manufactured in other ways, for instance through casting or extrusion.

(25) FIG. 5 discloses another fuel rod 4, which differs from the fuel rod 4 in FIG. 2 in that it in addition to the nuclear fuel pellets 10 also comprises a plurality of absorbing pellets 17, for instance 20, 40, 60, 80 or 100% absorbing pellets 17, the remaining pellets being nuclear fuel pellets 10.

(26) Also the absorbing pellets 17 comprises UB.sub.2. However, in the absorbing pellets 17, the boron of the UB.sub.2 has a concentration of the isotope .sup.10B that is higher than in the UB.sub.2 of the first fissile material of the nuclear pellets 10.

(27) The concentration of the isotope .sup.10B in the UB.sub.2 of the absorbing pellets 17 may be at least 25, 30, 40, 50, 60, 70, 80, 90 or 100% by weight.

(28) The absorbing pellets 17 may also comprise UB.sub.2 as a first fissile material and possibly at least one second fissile material as described above.

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