Fuel bundle for a liquid metal cooled nuclear reactor

In one embodiment, the fuel bundle for a liquid metal cooled reactor includes a channel, a nose assembly secured to a lower end of the channel, and a plurality of fuel rods disposed within the channel. At least one of the fuel rods has at least one guard ring surround the fuel rod and spacing the fuel rod from adjacent fuel rods.

BACKGROUND OF THE INVENTION

Field of the Invention

Example embodiments relate generally to liquid metal cooled nuclear reactors, and more particularly, to a fuel bundle for a liquid metal cooled nuclear reactor.

Related Art

Liquid metal cooled nuclear reactors such as sodium cooled fast reactors may suffer from thermal striping. Thermal striping occurs when hot and cold spots develop in the sodium flow exiting the fuel bundles. These hot and cold spots cause thermal stresses in the upper part of the primary vessel that can be damaging over time.

SUMMARY OF INVENTION

In one embodiment, the fuel bundle for a liquid metal cooled reactor includes a channel, a nose assembly secured to a lower end of the channel, and a plurality of fuel rods disposed within the channel. At least one of the fuel rods has at least one guard ring surrounding the fuel rod and spacing the fuel rod from adjacent fuel rods.

In another embodiment, the fuel bundle for a liquid metal cooled reactor includes a channel, a nose assembly secured to a lower end of the channel, and a plurality of fuel rods disposed within the channel. At least one of the plurality of fuel rods is a wrapped rod. The wrapped rod is helically wrapped with a wire, and at least one of the plurality of fuel rods is not a wrapped rod.

DETAILED DESCRIPTION

The fuel bundle or assembly is the major heat generating component of the reactor core in a nuclear power plant. The fuel bundle design in a liquid metal cooled reactor such as a liquid metal fast breeder reactor produces energy by means of a high integrity assembly of fissionable material that can be arranged in a critical array in the reactor core and can be readily cooled by liquid metal such as sodium at the reactor design conditions.

FIG. 1illustrates a fuel bundle for a liquid metal cooled nuclear reactor according to an example embodiment. In particular, the fuel bundle ofFIG. 1will be described with respect to a sodium cooled nuclear reactor. As shown, the fuel bundle includes a hexagonal channel or casing10having a plurality of lateral load pads11on the upper external surface and containing therein a plurality of fuel rods12in the upper region and an orifice/shield section13in the lower region. The fuel rods12are secured at the lower ends thereof in a fuel rod support14. The lateral load pads11function to space the fuel assemblies in the reactor core to allow for fuel assembly insertion and distortion, and minimize friction due to surface contact in sodium coolant. A nose subassembly16is secured to the lower end of channel10and includes a plurality of sodium inlets17for directing sodium coolant into channel10and having seals18on opposite ends of inlets17for preventing leakage of the sodium between the nose subassembly16and an opening19in associated support structure20within which subassembly16is located. Fuel assembly support points on structure20are indicated at21and22. A top end subassembly23is secured to the upper end of channel10, with the sodium coolant having passed upwardly around fuel rods12, passing through an internal mixer24in the upper end of channel10and exhausting through an outlet indicated at25in the top end subassembly23.

Each fuel rod12is a long, hollow, stainless steel or stainless type alloy (e.g., HT9) tube with a central region containing, for example, plutonium-uranium metal fuel slugs bordered above and below by a region of uranium axial blanket pellets, and can, of course, be used in a radial blanket arrangement. It will be understood, that many variations of fuel exist and the embodiments are not limited to this example. A welded stainless steel plug seals the tube at the bottom. The region above the upper blanket contains a fission gas plenum section and a fuel column hold-down device and is sealed at the top by a similar plug. The duct channel assembly (components10,16and23) is constructed of stainless steel or stainless-type alloy and thus compatible with the liquid sodium coolant.

FIG. 2Aillustrates an example of a fuel rod according to one embodiment. In this embodiment, instead of having a spacer wire wrapped there around to space the fuel rods12from adjacent rods and the interior surface of channel10, at least one of the fuel rods12includes at least one guard ring205. While four guard rings205are shown inFIG. 2A, it will be understood the fuel rod12may include any number of guards rings.

FIG. 2Billustrates a fuel rod adjacent to the fuel rod shown inFIG. 2A. As shown, the adjacent fuel rod may have one or more guard rings disposed at different positions along a longitudinal length thereof than the positions of the guard rings on the fuel rod ofFIG. 2A.

In one embodiment, the fuel rods12of the reactor may be divided into two or more sets. The fuel rods12in each set may have the same pattern of guard rings205along the longitudinal length thereof, and the different sets may have different guard ring patterns. Still further, one or more fuel rods12may be included in more than one set.FIGS. 3A and 3Billustrate an example embodiment of such an arrangement.FIG. 3Aillustrates a top down cross-section view of the fuel rods at 1 meter from the bottom of the fuel rods, and shows the guard rings205of fuel rods in a first set305and second set310at 1 meter from the bottom of the fuel rods12.FIG. 3Billustrates a top down cross-section view of the fuel rods at 2 meters from the bottom of the fuel rods, and shows the guard rings205of fuel rods in the first set305and the second set310at 2 meters from the bottom of the fuel rods. As shown, the center fuel rod12-C belongs to both sets. The pattern shown inFIG. 3Amay be repeated at each odd meter interval, and the pattern shown inFIG. 3Bmay be repeated at each even meter interval. As will be appreciated fromFIGS. 3A and 3Bsome of the fuel rods may not include any guard rings205. It will also be understood, that the more than two sets and more than two patterns may be employed. It will further be understood that the embodiments are not limited to the disclosed intervals, instead any interval (e.g., 0.5 meters) may be used.

Eliminating the use of wire wraps as the spacing element, reduces bulk sodium rotation within a bundle and promotes good mixing of the sodium flow inside the core region, reducing thermal striping.

FIG. 4illustrates a top down cross section view of the fuel rods according to another embodiment. In this embodiment, some of the fuel rods12, but not all of the fuel rods12are helically wrapped by wires405. Namely, according to one embodiment, at least one fuel rod is a wrapped rod (i.e., is helically wrapped by a wire), and at least one fuel rod12is not a wrapped rod. In the embodiment shown inFIG. 4, each of the wrapped rods400has unwrapped fuel rods410adjacent thereto. Still further,FIG. 4shows that tabs420may be attached to interior walls of the channel10to space unwrapped rods410away from the walls of the channel10.

FIG. 5illustrates a wrapped rod400, and shows the helical wrapping of the wire405along the longitudinal length of the fuel rod.FIG. 6illustrates the tabs420projecting from a wall of the channel10along the longitudinal length of a two adjacent unwrapped rods410. In one embodiment, the wires405are constructed of material such as 304 stainless steel (SS), 316 SS, and PE-16. In one embodiment, the tabs420are constructed of material such as 304 SS, 316 SS, and PE-16.

FIG. 7illustrates another embodiment of the tabs. In this embodiment, the tabs820are formed having a desired angle or orientation. The orientation of the tabs820may be the opposite of the orientation of the wires205,405of the wrapped rods.

FIG. 8illustrates a top down cross-section view of the fuel rods according to another embodiment. In this embodiment, the wrapped rods400are divided into a first set400-1and a second set400-2. The wrapped rods400of the first set400-1are helically wrapped according to a same first orientation. The wrapped rods400of the second set400-2are helically wrapped according to a same second orientation, where the second orientation is different from the first orientation. For example, as shown inFIG. 9, the second orientation may be opposite to the first orientation.

Reducing the number of wrapped rods, and/or changing the orientation of the wire wrapping the wrapped rods, reduces bulk sodium rotation within a bundle and promotes good mixing of the sodium flow inside the core region, reducing thermal striping.

By reducing thermal striping, thermal stresses on the fuel bundle internal components are reduced, thereby extending the lifetime of the equipment.