SK279650B6 - A detachable nuclear fuel element - Google Patents

Abstract

The invented nuclear fuel element (10) of a light water cooled and attenuated reactor comprises a supporting frame with two extensions (12, 14) and grids (20, 22), whereby said extensions (12, 14) are connected by means of guide tubes (16). Each grid is provided with three sets of plates (64, 66, 70) crossing each other and defining individual cells. The plates (64, 66, 70) are provided with means for gripping rods (24), which means hold said rods (24) in eyes of the regular triangle-shaped network. The upper extension (12) comprises a lower section with a transient bell (34) from a hexagonal cross-section to a cylindrical piece being provided with a dismountable first adjustment plate (32), and an upper section which has a cylindrical jacket (40) slidably mounted on the cylindrical piece and a holding plate (42). Tubular spacers (44) restrict mutual distance of the first adjustment plate (32) and the holding plate (42). Springs (46) impart on said plates a force, trying to pull the plates from each other.

Description

The invention relates to a nuclear fuel cell of a reactor, cooled and buffered with light water, which consists of a carrier frame with two extensions connected by guide tubes and of gratings distributed along the assembly. Each lattice has three sets of plates intersecting each other that define transverse cells, with one cell passing through the guide tubes and the other through the fuel rods. The plates are provided with means for clamping the bars which hold the bars in the eyes of a regular triangular net and are attached to at least some guide tubes.

BACKGROUND OF THE INVENTION

To date, fuel rods are known which have at least one end grating of a material retaining its mechanical irradiation properties and this grating contributes to the vertical holding of the rods, while the center grids are of zirconium-based alloy (whose neutron absorption is much less than and are equipped with means, such as protrusions and springs cut in the plates, exerting on the rods a transverse holding and support force which can be reduced during radiation.

In particular, it is an object of the present invention to provide a fuel cell in which the upper adapter is designed to transmit the anti-rotation force exerted by the upper core plate and allow different dilatation between the assemblies and between the cell and reactor structure and allow water to flow towards in the upper core plate between the supports of the upper extensions.

SUMMARY OF THE INVENTION

In particular, the fuel element according to the invention satisfies this requirement, the essence of which is that the upper attachment also comprises a lower part to which the upper part is provided with a transverse bell from hexagonal cross-section into a cylindrical piece provided with a first adapter plate. The tubular spacers define a spacing between the first adapter plate and the retaining plate connected to the second guide tubes and the springs disposed between the plates.

The guide tubes placed opposite the spacers can simply be supported on these spacers, while the other guide tubes, far more numerous, are detachably connected to the adapter plate. The apertures in the bell may be approximately semicircular in shape, and each may open on a larger portion of the hexagonal surface. For example, the guide tubes are secured to the lower extension by means of a screw locked against rotation upon clamping on the end sleeves of the guide tubes. Screws and plugs may be provided with a guide hole to allow cooling of the control beam bars or spectrum change when these bars are inserted into the cell.

The invention will be better understood from the description of an exemplary embodiment of the invention, to which the accompanying drawings also refer.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1 is a schematic representation of the principle of cell lift showing a single fuel rod and a single guide tube; FIG. 2 is a detailed, large-scale view showing the top of the cell. It is a cross-section through the axial plane. Fig. 3 is a detailed view in the raised position showing a method of attaching a major portion of the guide tubes to the upper and lower extensions as well as a portion of the lower end grille. Fig. 4 is a bottom view of a portion of one of the cell bars of FIG. 1, FIG. 5A, 5B and 5C schematically show several possible methods of connection between the inner plates of the lattice. Fig. 6 is a bottom view of the portion of FIG. 4, illustrating a method of making grilles that allows guide tubes with a diameter slightly greater than the diameter of the fuel rods to be admitted. Fig. 7 is a bottom view and FIG. 8 shows a section along line VIII-VIII in FIG. 7 and show a possible construction of elastic means of lateral gripping and support in the end grille, FIG. 9 is similar to FIG. 8 and is a section along line IX-IX of FIG. 6; FIG. 10 is a detail view showing a portion of a plate to which a fixing tab on a guide tube abuts. Fig. 11 is a bottom view to a large extent of a portion of the lattice, showing the curvature of the inner plates when coupled to the belt.

DETAILED DESCRIPTION OF THE INVENTION

The fuel cell 10 shown in FIG. 1 consists of a skeleton having an upper extension 12 and a lower extension 14 connected by guide tubes 16 and having grids 20 and 22 regularly spaced along the guide tubes 16. The grids 20, 22 define the cells staggered in the meshes of the regular network from which some guide tubes 16 or the auxiliary central tube (not shown) and the fuel rods 24 pass through the other rods. These rods may rest on the lower extension 14. They are axially held and held in the mesh by the grids 20, 22, as will be shown below. The grids 20, 22 are themselves attached to at least some guide tubes 16.

In operation of the reactor, the bottom extension 14 is placed on the core support plate 26, perforated by the coolant inlets into the cells. The upper adapter 12 receives the pressure of the core core plate 28, perforated by the coolant inlets 30 between the extensions.

First, the embodiment shown in FIG. 2 and 3, one suitable construction of the top extension 12 and a suitable method of detachably connecting the top extension 12, allowing it to be lifted up and put in place again, for example for replacing the bars 24.

The extension 12 comprises two parts which can be vertically displaced relative to one another and retaining means intended to limit the spacing of the two parts and to transfer the pressure of the core core plate 28 from one part to the other.

The lower part is the one which is attached to the guide tubes 16. It consists of a first disc-shaped adapter plate 32 attached to the upper cylindrical part of the transition bell 34. The lower part of the bell 34 is attached to a support plate 36 of hexagonal cross section provided with through holes 16 and coolant passage openings. The support plate 36 is sufficient over the distances of the fuel rods 24 to allow the extension of these ends (FIG. 1) and forms a stop limiting the stroke of the rods 24.

SK 279650 Β6

For example, the bell 34 is made of stainless steel sheet welded to plates 32 and 36. The wide slots 38 at each front allow the refrigerant to exit into the gap between the upper extensions 12.

The upper portion is displaceably mounted on a cylindrical wall formed by the periphery of the first adapter plate 32 and the upper portion of the bell 34. It comprises a cylindrical shell 40 in which the holding plate 42 is welded transversely, provided with a coolant passage at its center.

The retaining means consist of several sets of spacer springs, for example of three. Each assembly comprises a tubular spacer 44 connected to a guide tube 16 and at least one helical spring 46 surrounding the spacer 44 and compressed between the plates 32 and 42. In the embodiment shown in FIG. 2, each assembly comprises two springs 46 of different radius, disposed concentrically to each other.

Each tubular spacer 44 is terminated by a flange attached to the adapter plate 32. At the top of the spacer 44 a thread is cut into a nut 48, which adjusts the maximum spacing between the plates 32 and 42 and hence the biasing of the springs 46. a diameter such as guide tubes 16 to allow insertion of the control bands bars 24 or change of spectrum into guide tubes 16 associated with the tubular spacer 44.

The guide tubes 16 mounted in connection with the spacers 44 are simply supported on the flange of these spacers. The other guide tubes 16 are each attached to the first adapter plate 32 by removable fasteners. In the embodiment shown in FIG. 3, these means comprise threaded sleeves 50 having an internal diameter such as to allow passage of the command strap bars or spectrum change. These sleeves 50 are screwed into threaded sleeves 52 welded to the ends of the guide tubes 16. Once the sleeves 50 are threaded screwed, they are locked against rotation by deformation of the thin jacket with which they are equipped. This deformation occurs in the matrices formed in the first adapter plate 32.

All guide tubes 16 are fixed in the same way to the lower extension 14. This lower extension 14, generally made of stainless steel, comprises a second adapter plate 54 attached to a hexagonal body and equipped with coolant passage openings.

This plate serves as a support for the fuel rods 24. It is provided with auxiliary holes for the passage of threaded rods 56 to be screwed into the end plugs 58 of the guide tubes 16. The rods are equipped with a calibrated hole 56a for supplying cooling water of the guide tubes 16, control rods 24 or rods. spectrum changes to be inserted into guide tubes 16.

The grids 20, 22 may be of the construction as shown in FIG. 4 and may consist of three sets of plates 64, 66 which are provided with connecting grooves, the lattices of one of the sets being parallel to each other and forming an angle of 120 ° C with the plates of the other two sets. As can be seen from FIG. 4, the plates 64, 66 may be two and two crossed and joined together as scissors.

In the embodiment of the invention illustrated in FIG. 4, each lattice 20, 22 consists of sixty inner plates and six outer plates. The outer plates may be elongated by curved guide tabs 60 (see FIG. 3), thereby eliminating the risk of twisting between the assembly during handling.

At least two end gratings 20 are formed by alloy plates that retain mechanical irradiation properties, such as zleonel 718. Thus, the plates may be joined two and two together. It is also possible to use other materials, such as martensitic steel.

In the embodiment of FIG. 3, stainless steel protective covers 62 are welded to the lower end grid plates. The lower ends of the guide tubes 16 secured to the second adapter plate 54 of the lower extension 14 by means of a threaded rod 56 are inserted into these protective covers. The upper grille 20 can similarly carry welded sleeves, each intended to enclose the guide tube 16. The upper end grille 20 so armed can either be loose once inserted on the guide tubes 16, or it can be axially held by zirconium-based alloy rings welded to at least some guide tubes 16 from both sides of the sleeves. One kit can be adapted to prevent stress.

The intermediate grids 22 may be made of either a zirconium-based alloy, or may be (if observed maintaining mechanical properties during irradiation) a stainless steel alloy, such as Inconel 718. The outer plates may still be provided with a deflector (guiding). plate) to prevent trapping between adjacent cells during handling.

The plates 64, 66 can be assembled in various ways, depending on whether the ease of manufacturing the plates or the reliability of the welds at the crossing points is monitored.

In the embodiment shown in FIG. 5A, the joining grooves of the plate 64 with the plate 66 at an angle of 120 ° C are arranged obliquely with alternating inclination. The disadvantage of this solution is that cutting out is difficult but makes welding easier.

In a similar solution illustrated in FIG. 5B, the grooves are perpendicular, which facilitates the production of the plates, but in turn is less preferred in terms of welding.

In FIG. 5 is a compromise of the two previous solutions: the grooves of one plate are straight but equipped with the opposite bevel of the plates of the other sets.

The lattice plates are provided with means for clamping the rods, which comprise support lugs arranged on the outer plates and spring lugs on the inner plates. In the particular embodiment shown in FIG. 6, where the guide tubes 16 have a larger diameter than the bars 24, the abutment protrusions must be removed near the cells containing the guide bars, as will be explained below.

In conventional cells, the bars 24 may be supported at five points, divided by three directions of 120 ° C. Two of the plates 64 and 66 (see Figures 5 to 7) that define the cell are provided with protrusions 68 located at two different levels. One of the plates 70 of the third set comprises a slit and deformed spring 72. The grooves 68 close to the grooves are often advantageously formed by cut-out portions in the form of a bridge of small width, the openings below the bridge being in the longitudinal sense of the plates. The projections 68 and springs 72 may have the same width. However, other types of protrusions 68 may be utilized, for example in the shape of a hemobomb, as described in French patent application no. 90 09446.

As previously indicated, the plates 64, 66 must be locally deformed to define cells of the following dimension to accommodate the guide tubes 16 (see Figure 6). When the diameter difference between the guide tubes 16 and the fuel rods 24 is significant, this deformation must be extended to those adjacent cells into which the guide tubes 16 are inserted. In this case, the plate deformation is replaced in one set by two projections 68 connected in the longitudinal direction of the rods. 24 as shown in FIG. 6 and 9 and the rod 24 is held at four points, two being formed by folding the plates 74 and two further by springs 72.

When the inner grids are made of zirconium-based alloy, such as guide tubes 16, they may be welded to these tubes. To this end, the plates 64, 66 can be drawn around the guide tubes by folding tabs 76 (see FIG. 10), which are resistively welded to the guide tubes 16.

To facilitate assembly between the inner plates and the outer plates forming the belt, it is preferable to bend the end portions 79 of the inner plates in such a way as to cross at 90 ° the outer plates forming the belt 78 (see Fig. 11). This arrangement makes it possible to fit the inner plates with pins which fit into the grooves prepared in the strip before welding.

The outer plates may be attached at the corners of the strip as shown in FIG. 11, or on the faces. This attachment can take place as a connection of the inner plates to each other, by electron beam welding or by laser.

As pointed out, it is possible to use intermediate grids 22 made of alloy plates that retain their irradiation properties, for example, the Inconel alloy. In this case, the plates 64, 66 may have a slightly smaller thickness than when using a Zircaloy alloy. Thus, the plates 64, 66 may mate with each other at the locations where they fit together.

In a preferred embodiment, the cell 10 has been designed for three hundred and twelve bars 24 positioned in the mesh meshes with a pitch of 12.75 mm. The support structure consisted of fifteen guide tubes 16 detachably attached to extensions 16, 14, and three guide tubes 16 positioned in connection with spacers 44. End bars 20 were of Inconel 718 and middle bars 22 of zirconium alloy (Zircaloy). These parameters led to the use of a common 108 mm width for the protrusions 68 and the compression springs 72. The height of the plates 64, 66 was the same for the intermediate grids 22 and the end grids 20. The thickness of the inner row plates 0.4 mm proved to be satisfactory; it is advantageous for external inserts when the bars are made of Zircaloy.

Claims (10)

PATENT CLAIMS A removable nuclear fuel cell, cooled and buffered with light water, comprising a support structure with two extensions connected by guide tubes and having gratings distributed along the assembly, each grating having three sets of plates intersecting each other defining the cells from which they pass through one the guide tubes and second fuel rods, wherein the plates are provided with means for clamping the bars which hold the bars in the eyes of a regular triangular net and wherein the plates are attached to at least some guide tubes and the upper attachment comprises an upper part provided with a cylindrical shell to a holding plate, characterized in that the upper extension (12) also comprises a lower part to which the upper part provided with a transverse bell (34) from a hexagonal cross-section to a cylindrical piece provided with a first adapter plate is slidably mounted a pipe (32) releasably connected to only some of the first guide tubes (16), the tubular spacers (44) defining a spacing between the first adapter plate (32) and the retaining plate (42) connected to the second guide tubes (16) and the springs (46) positioned between these plates (32, 42). 2. The nuclear reactor fuel cell of claim 1, wherein the springs (46) are disposed around the spacers (44). 3. The nuclear reactor fuel cell according to claim 1, wherein the second guide tubes (16) are also located in connection with the tubular spacers (44) and in that the spacers (44) have the same internal spacers. clearance as guide tubes (16). 4. The nuclear reactor fuel cell of claim 4, wherein the second guide tubes (16) are supported by spacers (44) and in that the spacers form a support bridge on the first adapter plate (32) and the end portion is supported by a thread on a maximum distance regulating nut (48) between the first adapter plate (32) and the retaining plate (42). The nuclear reactor fuel cell according to any one of the preceding claims, characterized in that the fastening means of the first adapter plate (32) with at least some guide tubes (16) comprise sleeves (50) locked against rotation upon clamping on the end sleeves (52). ) of guide tubes (16). 6. The nuclear fuel element of any of the preceding claims, wherein the plates (64, 66) are each crossed and joined and in that the means for clamping the rods (24) comprise protrusions (68) disposed. at 120 ° cell compartments with a spring (72) arranged on another partition. A reactor nuclear fuel cell according to claim 6, characterized in that the springs (72) and the projections (68) are cut in the plate compartment (64, 66). A reactor nuclear fuel cell according to any one of the preceding claims, characterized in that the guide tubes (16) have a larger diameter than the fuel rods (24) and the plates (64, 66) are deformed around the cells for receiving the tubes (16). and neighboring cells are distorted as well. 9. The nuclear reactor fuel cell of any one of claims 1 to 8, wherein the inner plates (64, 66) of each lattice (20, 22) have a cutout (79) at their ends to achieve their intersection with the outer plates. at 90 °. A nuclear reactor fuel cell according to any one of claims 1 to 10, characterized in that the plates (64, 66) are provided with straight bevelled grooves at the crossing points.