JPS6239913B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has a large number of elongated fuel rods having a circular cross section and are arranged parallel to each other, and the fuel rods run in a spiral shape over the entire length thereof. The present invention relates to fuel assemblies of a nuclear reactor which are mutually supported by spacer ribs projecting from the cross section and are further clamped by an outer enclosure.

A fuel assembly of this type is shown in the document "Kerntechnik", published by BG Teubner Verlag, Schmidtgarz, West Germany, 1958, page 146, 1462, a, FIG. The outer enclosure therein is constructed as a very strong, solid, splittable part, since it has to adapt with a concave curve to the contour of the enclosed fuel rod.

In contrast, the present invention aims to provide a fuel assembly for use in a breeder reactor or a converter reactor that is lightweight, that is, has a stable structure using less material. In the case of breeder reactors and converter reactors, the spacing between fuel rods is desired to be so small that it is difficult to maintain spacing using conventional spacers. That is, the small spacing must be maintained with great precision.

According to the invention, this object is achieved in a fuel assembly of the type mentioned at the outset, in which the enclosure has a plurality of bands each covering only a small fraction of the length of the fuel rods, which bands are placed in place of the fuel rods. This solution can be achieved by connecting the elements to each other by means of at least one skeleton pin.

In the case of the fuel assembly according to the invention, the fuel rods are in direct contact with each other, particularly within a predetermined area delimited by the band. The contact support and enclosure may be such that tolerances are not exceeded, taking into account possible deformation of the fuel rods. Thus, for example, 14 contact support points may be provided over a fuel assembly having a length of, for example, approximately 2 m. Considerable material savings result thereby, which is also good in terms of neutron savings. In that case, the fuel assembly box, which would otherwise be provided as an enclosure, i.e., as a closed shape extending over the entire length of the fuel assembly, has a pressure difference between the inside and the outside, i.e. at least the inlet of the coolant. It shall be designed for the differential pressure between the This increases the wall thickness so that the spacing between the fuel assemblies becomes too large. Furthermore, the present invention allows for a good equilibrium of the coolant temperature across the cross-section of the core, which is desirable in heterogeneous nuclear reactors with special breeder fuel elements.

The present invention is applicable to various cross-sectional shapes of fuel assemblies. However, in the case of polygonal cross-sections, preferably hexagonal cross-sections, a skeleton pin is placed at each corner, which screw-like connection of the substantially flat individual parts to a band surrounding the fuel assembly. That's good.
This allows simple manufacture and easy assembly. Moreover, this construction allows for subsequent repairs such that the fuel assembly inclusions can be lifted without damaging the material. It is best to make all parts of the van the same shape. Furthermore, it is advantageous for each part to have a support projection projecting into the cross-section of the fuel assembly. As a result, the fuel rods to be held can be spaced particularly precisely from one another.

The frame pin can have a uniform cross-section, in particular a circular cross-section, over the entire length of the fuel assembly. Moreover, this skeleton pin can also be provided with projections that are used to determine the position of the band, so that metallurgical connections are avoided. The bands are also spaced apart along the length of the fuel assembly by tubes inserted over the framework pins and screwed together at their ends. The projections mentioned above also include spacing projections that allow mutual support of adjacent fuel assemblies.

It is particularly advantageous if the band consists of sheet metal having the same thickness as the spacing rib at least in the region of the framework pin. The frame pin then acts like a spacing rib over its entire circumference.

The present invention will be described in detail below based on embodiments shown in the drawings.

The fuel assembly 1 has a leg member 2 and a head member 3, and within the fuel assembly 1, 217 fuel rods 4 of the same shape are arranged to form a fuel assembly with a regular hexagonal cross section. ing. The fuel rod 4 has a circular cross section with a diameter of 9.5 mm, for example, as shown in FIG. This fuel rod 4 has spaced ribs 6 distributed evenly around its circle and having a width of 1 mm and a height of 0.5 mm. This spacing rib 6 is made integral with the cladding tube (not shown) of the fuel rod 4, or is brazed or welded thereto, and runs in a spiral over the entire length of the fuel rod. The pitch of this spiral is, for example, 1/3 of the length of the fuel rod. This ensures that when the fuel rods 4 are correctly aligned, the spirals always assume the same position with respect to one another in the region of the band 8, thereby ensuring that the fuel rods 4 are clamped as an enclosure.

The band 8 mainly has screw protrusions 11 and 12 on both ends.
It has a flat sheet metal 10 made of steel plate with a .
This sheet metal 10 includes spacing ribs 6 of the outer fuel rods 4.
An extrusion molding section is provided for forming a support protrusion 14 that becomes a contact surface for the support (see FIG. 4).

At the corners of the hexagonal cross-section there are frame pins 16 which extend over the entire length of the fuel assembly 1 instead of the fuel rods. This frame pin 16 is, for example, solid and made of steel and acts as a hinge pin for the metal plates 10 which are connected to each other in a spiral manner. In this case, the thickness of the sheet metal 10 of 0.5 mm is the same as the height of the spacing rib 6.

Furthermore, the framework pin 16 has a spacing projection 18, which allows support of adjacent fuel assemblies 1, as shown in FIG. Therefore, a predetermined distance exists between the fuel rods 4 of adjacent fuel assemblies 1. The spacing protrusions 18 can be sloped to facilitate the insertion and withdrawal of individual fuel assemblies 1 from the core, allowing the fuel assemblies 1 to slide relative to each other.

FIG. 1 shows that the skeleton pin 16 is screwed into the leg member 2 with a threaded shank portion 20. A nut 21 is screwed into the threaded shaft portion 22 at the other end of the skeleton pin 16, and the skeleton pin 16 is fixed to the head member 3 by this nut 21. Between the leg part 2 and the head part 3 there is a spacing tube 23 whose diameter of 0.5 mm is the same as the height of the spacing rib 6.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional side view of a fuel assembly of a light water-cooled high conversion reactor, FIGS. 2 and 3 are partial perspective views of a band according to the present invention, and FIG.
FIG. 3 is a partial plan view of one fuel assembly. DESCRIPTION OF SYMBOLS 1... Fuel assembly, 2... Leg member, 3... Head member, 4... Fuel rod, 6... Spacing rib, 8...
Band, 10... Planar portion of band, 16... Skeleton pin, 18... Interval protrusion.

Claims (1)

[Scope of Claims] 1. A fuel rod having a large number of long fuel rods with a circular cross section arranged in parallel to each other, the fuel rods running in a spiral shape over the entire length and protruding from the cross section of the fuel rods. In a nuclear reactor fuel assembly in which a plurality of fuel rods are supported on each other by spacer ribs and further clamped by an outer shroud, said shroud comprises a plurality of Fuel assembly for a nuclear reactor, characterized in that it has bands 8 which are interconnected by at least one skeletal pin 16 placed in place of a fuel rod 4. 2. In a fuel assembly having a polygonal cross-section, preferably a hexagonal cross-section, a frame pin 16 is placed at each corner,
2. A fuel assembly according to claim 1, characterized in that said skeletal pins (16) hingely connect the substantially planar individual parts (10) to a band (8) surrounding the circumference of the fuel assembly. 3. The fuel assembly according to claim 2, characterized in that all parts 10 of the band 8 have the same shape. 4. Fuel assembly according to claim 2 or 3, characterized in that the parts 10 of the band 8 have support projections 14 projecting into the cross section of the fuel assembly. 5. A fuel assembly according to any one of claims 1 to 4, characterized in that the framework pin 16 has a spacing projection 18 projecting from the cross section of the fuel assembly. 6. According to any one of claims 1 to 5, the band 8 is made of a sheet metal having the same thickness as the spacing rib 6 at least in the region of the frame pin 16. fuel assembly.