SK208892A3 - Disassembleable nuclear fuel element - Google Patents

Description

In particular, a fuel element according to the invention is satisfied in that the upper extension comprises a lower part with a transition bell from a hexagonal cross-section into a cylindrical piece, provided with a transverse adapter plate which is detachably connected to some of the guide tubes; and an upper part with a cylindrical sleeve slidably mounted on a cylindrical piece of the lower part and a retaining plate, tubular spacers limiting the distance between the adapter plate and the retaining plate, to be coupled to other guide tubes and springs disposed between the force generating plates attempting the plates apart.

The guide tubes located opposite the spacers can simply be supported against these spacers, while the other guide tubes, much more numerous, are extensively connected to the adapter plate. The apertures in the bell may be approximately semicircular in shape and each may open on a greater 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. The bolts and plugs may be provided with a central hole to allow the control beam bars to be cooled or to change the spectrum when the 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.

An overview of the figures in the drawings

In FIG. 1 schematically illustrates the principle of lifting the cell, showing a single fuel rod and a single guide tube; FIG. 2 is a large scale detail view showing the top of the cell. This is an axial plane rust. Fig. 3 is a detailed view in the raised position showing a method of securing a larger portion of the guide tubes to the upper and lower extension as well as a portion of the lower end grille. Fig. 5 is a bottom view of a portion of one of the cell bars of Fig. 1, Figs. 5A, 5B and 5C schematically illustrate several possible methods of connection between

- And lattice plates. Fig. 6 is a bottom view of a portion of Fig. 4 showing a method of making grilles that allows the guide tubes of a diameter slightly larger than the diameter of the fuel rods. Fig. 7 is a bottom view and Fig. 8 is a section along line VIII-VIII in Fig. 7, showing a possible construction of elastic means of transverse gripping and support in the end grating; 6 in FIG. Fig. 10 is a detail view showing a portion of the plate adjacent the fixation tab on the tube guide. Fig. 11 is a bottom scale view of a portion of a grid showing the curvature of the inner pads at their connection with the belt.

The fuel cell 10 shown in FIG. 1 consists of a carcass 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. The grids define the cells laid out in regular mesh meshes, some of which pass through the conductors of the tube 16 or the auxiliary center tube (not shown) and the other pass through the fuel rods 24. These bars may rest on the lower extension 14. They are axially held and held in the mesh of the grid as shown below. The grilles are themselves attached to at least some guide tubes.

In operation of the reactor, the lower extension 14 is placed on the core support plate 26, perforated by coolant inlet passages. The upper extension 12 has a pressure of the core core plate 28, perforated by the refrigerant outlet openings 30 therebetween. extension.

2 and 3, one suitable construction of the upper extension and a suitable method of detachable connection of the extension allowing it to be picked up and put back into place, for example for bar replacement.

The extension 12 comprises two portions which can be vertically displaced relative to one another and retaining means designed to limit the spacing of the two components and to transfer the pressure of the plate 29 from one to the other.

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

For example, the bell 34 is made of stainless steel sheet welded to the plates 32 and 36. The wide slots 38 in each front side allow the refrigerant to exit into the gap located between the flaps.

The top of the slide is mounted on the cylindrical wall formed by the periphery of the adapter plate 32 and the upper piece 34 ^{does not} select · it includes a cylindrical casing 4 0, which is welded PNIC retaining plate 42, provided in its center a sleeve for passage of coolant.

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

Each tubular spacer is terminated by a flange attached to the adapter plate 32. At the top of the spacer is threaded for a nut 4 ', which adjusts the maximum spacing between the plates 32 and 42 and thus the biasing of the springs 41. The central opening of the spacer 44 has the same diameter as the guide tubes 16 to allow insertion of control grape bars or spectrum changes into the guide tubes associated with the tubular spacer.

The guide tubes 16 mounted in connection with the spacers 44 are simply supported on the flange of these spacers. The other guide tubes are each attached to the adapter plate by other means of connection. In the exemplary embodiment illustrated in FIG. 3, these means comprise a threaded sleeve 50 having an internal diameter that allows the flow of bars of the command bunch or spectrum change. These sleeves are screwed into threaded sleeves 52 welded to the ends of the guide tubes 16. Once the sleeves 50 are screwed on, they are locked against rotation by deformation of the thin jacket with which they are provided. This deformation occurs in the matrices formed in the adapter plate 32.

All guide tubes 16 are fastened in the same way to the bottom extension. This lower attachment 14, generally made of stainless steel, comprises an adapter plate 54 fixed to the hexagonal body and provided with openings for the coolant flow.

This plate serves as support for the fuel rods 14. It is provided with auxiliary holes for the passage of threaded cartridges 56 to be screwed into the end plugs 58 of the guide tubes 16. The lamps are provided with a calibrated orifice 56a for supplying cooling water to the guide tubes, control bars, or spectrum change bars that are inserted into the guide tubes.

The lattices may be of the construction shown in FIG. 4 and may consist of three sets of inserts provided with connecting grooves, wherein the bars of one of the sets are parallel to each other and form an angle of 1 120 ° with the plates of the other two sets.

As can be seen from FIG. 4, the plates may be two and two crossed and joined together as legs.

In the exemplary embodiment of the invention illustrated in FIG. 4, each plate consists of sixty inner plates and six outer plates. The outer plates may be extended by the curved guide tabs 60 (see FIG. 3), thereby avoiding the risk of hooking between the assembly during handling.

The at least two end gratings 20 are formed by alloy plates that retain mechanical irradiation properties, for example, from Iconel 718. Thus, the plates may be soldered two and two to one another. Other materials such as martensitic steel may also be used.

In the embodiment of FIG. 3, stainless steel protective covers 62 are welded to the lower end grille plates. The lower ends of the guide tubes 16 attached to the lower extension plate 5A by means of a screw 56 are inserted into these guards. The upper grille 20 can similarly carry welded sleeves, each designed to enclose the guide tube. The upper end grille, so armed, may either be free once inserted on the tube guide, or it may be axially held by zirconium-based alloy rings welded to at least some of the tube guides from both sides of the sleeves. One set may be adapted to prevent loading.

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

The inserts can be assembled in various ways, depending on whether the ease of manufacture of the inserts 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 of one set at an angle of 120 ° are aligned obliquely. This solution has the disadvantage that it makes the cutting difficult, but facilitates welding.

In a similar solution shown in FIG. 5B, the grooves are straight, perpendicular, which facilitates the manufacture of the inserts, but is less preferred in terms of welding.

Fig. 5 shows the compromise of the two previous solutions: the grooves of one plate are straight but provided with an operational bevel of the plates of the other sets.

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

In conventional cells, the rods can be supported at five points, divided in three directions by 120 °. 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 projections 68 close to the grooves are often advantageous to make cut-out bridge-shaped portions of small width, the openings below the bridge being in the longitudinal sense of the plates. The projections and springs may have the same width. However, other types of protrusions may be utilized, for example in the form of a window window as described in French patent application no. 90 09446.

As previously indicated, the plates must be serially defended to define cells of sufficient size to accommodate the guide tubes 16 (see FIG. 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 are inserted. In this case, the deformation of the plate is replaced in one set by two projections connected in the longitudinal sense of the rods, as shown in FIG. 6 and 9 and the rod is held at four points, two being formed by folding the plates 74 and two further by springs 72.

When the internal bars are made of a zirconium-based alloy, such as guide tubes 16, welding may be attached to these tubes. To this end, the plates may be elongated by a guide tube guide by means of bent tabs 76 (FIG. 10) which are resistively welded to the guide tubes.

To facilitate assembly between the inner plates and the outer wafer-forming plates, it is preferable to bend the end portions 79 of the inner wafering in such a way that they cross at 90 ° the outer wafer forming the waistband 78 (see FIG. 11). This arrangement makes it possible to provide the inner plates with pins that west into the grooves prepared in the strip before welding.

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

As noted above, it is also possible to use intermediate grids formed of alloy plates that retain their irradiation properties, for example, Inconel alloy. In this case, the plates may have a somewhat smaller thickness than when using a Zircaloy alloy. Thus, the plates may be soldered to each other at the locations where they fit together.

In a particular embodiment, the article was designed for three twelve bars placed in mesh sieves of 12.75 mm increments. The supporting structure consisted of fifteen guide tubes fixed to the disassembled rate In another way to the extensions and three guide tubes placed in connection with the spacers. The end bars were made of Inconel 718 and the middle bars were made of Zircaloy. These parameters led to the use of a common width of 108 mm for protrusions and compression springs. The height of the plates was the same for the middle lower and end grids. The thickness of the internal 0.4 mm plates has been shown to be satisfactory, a slightly higher thickness is preferred for the outer plates if the bars are of Zircaloy.

Claims (10)

Contain 1 / K ^ light water-cooled reactor fuel cell! a supporting frame with two extensions connected by guide tubes and having lattices distributed along the assembly, each lattice having three sets of plates intersecting each other defining cells, one passing through the guide tubes and the other fuel rods, the plates being provided with means for the grip of the bars you maintain! the bars in the meshes of a regular mesh and wherein the plates are attached to at least some guide tubes characterized in that the upper extension (12) consists of a lower part comprising a transition bell (34) of disassembling the cross section into a cylindrical piece provided with the adapter plate (32) disassembled 1 not connected to the first guide tubes (16); and from the top, comprising a cylindrical sleeve (40) slidably mounted on the cylindrical piece of the bottom, and a retaining plate (42), tubular spacers (44) to define a distance between the adapter plate (32) and the retaining plate (42) that is connected to the second guide tubes and springs (46) mounted within the same plates for applying a force thereon to try to pull them away from each other. 2. The nuclear fuel cell of claim 1, wherein the springs are disposed around the spacers (44). 3. The nuclear reactor fuel cell of claim 1 or 2, wherein the second conduit tubes are straight and positioned. The spacers have the same inner diameter as the guide tubes to allow the insertion of the bars belonging to the command beam or the spectrum change. 4. The nuclear fuel cell of claim 3, wherein the second guide tubes are supported by spacers and in that the spacers form a support bridge on the adapter plate and the end portion is provided with a thread for a nut (48) to control the maximum distance between the adapter plate. 32) and a retaining plate (42). A nuclear reactor fuel cell according to any one of the preceding claims, characterized in that the adapter plate fasteners with at least some of the conductors. the tubes comprise screws locked against rotation upon clamping on the end sleeves (52) of the guide tubes. 6. A nuclear reactor fuel cell according to any one of the preceding claims, wherein the plates are always two and two crossed and joined together, and wherein the rod clamping means comprises protrusions positioned on the bulkheads of the 120 [deg.] Cell with a spring arranged for further. rung. 7. The nuclear reactor fuel cell of claim 6, wherein the springs and projections are cut out in the plate septum and provide a plurality of plates. I support five points. 8. A nuclear reactor fuel cell according to any one of the preceding claims, wherein if the tube guides have a larger diameter than the fuel rods, the platelets around the tube insertion cells are deformed and this deformation extends to adjacent cells. 9. The nuclear fuel cell of any of the preceding claims, wherein the inner plates of each lattice have at their ends a cutout (79) to achieve their intersection with the outer plates at an angle of 90 [deg.]. 10. The nuclear fuel cell of any of the preceding claims wherein the plates are provided with straight bevel grooves in the crossing points.