CZ281979B6 - Detachable nuclear fuel element - Google Patents

Abstract

The reactor fuel-cooled, light-water-cooled nuclear fuel cell comprises a support frame with two extensions (12, 14) connected by guide tubes (16) and bars (20, 22). Each lattice has three sets of plates that cross each other to define cells. The plates are provided with means for clamping the rods that hold the rods in the meshes of a regular triangular mesh. The top extension (12) includes a bottom portion with a transition bell (34) of hexagonal cross section per cylindrical piece provided with a removable adapter plate (32) and an upper portion having a cylindrical sleeve (40) slidably mounted on the cylindrical piece and retaining plate (42) . The tubular spacers (44) limit the distance between the adapter plate (32) and the retaining plate (42). The springs (46) exert a force on the plates that tries to move them apart

Description

Technical field

The present invention relates to a nuclear fuel cell reactor cooled and attenuated by light water. The cell consists of a carcass with two attachments connected by guide tubes and lattices distributed along the assembly. Each lattice has three sets of plates intersecting each other defining 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 grid and are attached to at least some guide tubes.

BACKGROUND OF THE INVENTION

To date, fuel cells 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 central grids are of a zirconium-based alloy (whose neutron absorption is much less than grids and are provided with such means 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 constructed in such a way that it transmits the anti-rotation force exerted by the upper core plate and allows different dilatations between assemblies, kits and between the cell and reactor structure. outlet of water towards the passages formed in the upper core plate between the abutments of the upper extensions.

SUMMARY OF THE INVENTION

In particular, the fuel cell according to the invention satisfies this requirement in that the upper extension comprises a lower part with a hexagonal-to-cylindrical transitional bell having a transverse adapter plate which is detachably connected to some of the guide tubes; and an upper portion with a cylindrical sleeve slidably mounted on the cylindrical piece of the lower portion 35, 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 mounted between the force plates, trying to move these plates apart.

The guide tubes located opposite the spacers can simply be supported against these spacers, while the other, more numerous, guide tubes 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. The bolts and plugs may be provided with a central opening to allow cooling of the bars of the control beam 45, or to alter 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.

Overview of the drawings

Figure 1 schematically illustrates the principle of cell lift showing a single fuel rod and a single guide tube; Figure 2 is a detailed large-scale view showing the top of the cell. This is a section through the axial plane. Giant. 3 is a detailed view in the raised position showing a method of securing a major portion of the guide tubes to the upper and lower extension as well as a portion of the lower

End grilles. Giant. Fig. 4 is a bottom view of a portion of one of the cell bars of Fig. 1; Figs. 5A, 5B and 5C schematically show several possible connections between the inner plates of the lattice. Giant. 6 is a bottom view of the portion of FIG. 4 showing a method of making grilles that allows guide tubes of a diameter slightly greater than the diameter of the fuel rods to be admitted. Giant. Fig. 7 is a bottom view and Fig. 8 is a section along line VIII-VIII of Fig. 7, showing a possible construction of elastic means of transverse grip and support in the end grille; Fig. 9 is similar to Fig. 8; 6. FIG. 10 is a close-up view showing a portion of the plate adjoined by the fixing tab on the guide tube. Giant. 11 is a bottom view on a large scale of a portion of the lattice showing the curvature of the inner pads when they are joined 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 lattices 20 and 22 regularly spaced along the guide tubes 16. The lattices 20, 22 define cells distributed into meshes of the regular mesh, some of which run through the guide tubes 16 or the auxiliary center tube (not shown), and the others pass through the fuel rods 24. These rods may rest on the lower extension 14. They are axially held and held in the mesh by the grids 20. 22 as shown below. The grids 20, 22 are themselves attached to at least some guide tubes 16.

In operation of the reactor, the lower extension 14 is placed on the core support plate 26, perforated by the coolant inlet passages into the cells. The upper extension 12 receives the pressure of the core core plate 28, perforated by the refrigerant outlet openings 30 between the extensions.

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 picked up and put back in place, for example, to replace the bars 24.

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 core core plate 28 from one part to the other.

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

For example, the bell 34 is made of stainless steel sheet welded to plates 32 and 36. The wide slots 38 in each front side allow the refrigerant to exit into the gap located 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 a holding plate 42 is welded laterally and provided with a coolant passage in its center.

The retaining means consist of several sets of span springs, for example 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 plates 32 and 42. In the embodiment shown in Fig. 2, each set comprises two springs 46 of different radius placed concentrically to each other.

Each tubular strut 44 is terminated by a flange attached to the adapter plate 32. At the top of the strut 44 a thread for a nut 48 is cut to adjust the maximum spacing between the plates 32 and 42 and hence the biasing of the springs 46. as guide tubes 16 to allow the insertion of control grape rods 24 or spectrum change 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 the spacers. The other guide tubes 16 are each fixed to the first adapter plate 32 by detachable connection means. In the exemplary embodiment illustrated in FIG. 3, these means comprise threaded sleeves 50 having an internal diameter such as to permit passage of the command grapes bars or spectrum changes. These sleeves 50 are screwed into threaded sleeves 52 welded to the ends of the guide tubes 16. Once the threaded sleeves 50 are screwed on, they are locked against rotation by deformation of the thin jacket they are provided with. 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 attachment 14, generally made of stainless steel, comprises a second adapter plate 54, attached to a body of hexagonal cross-section and provided with openings for the passage of coolant.

This plate serves as 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 provided with a calibrated hole 56a for supplying cooling water of the guide tubes 16, control rods 24 or rods. the spectrum changes that are inserted into the guide tubes 16.

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

In the embodiment of the invention shown in FIG. 4, each grid 20, 22 consists of sixty inner plates and six outer plates. The outer plates may be extended by curved guide tabs 60 (see FIG. 3), thereby eliminating 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 Inconel 718. Thus, the plates may be soldered two and two together. 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 second adapter plate 54 of the lower extension 14 by means of a threaded rod 56 are inserted into these guards. The upper grille 20 can similarly carry welded sleeves, each intended to enclose the guide tube 16. The upper end grille 20 so armed may either be loose once inserted on the guide tubes 16 or may be axially held by zirconium-alloy alloy rings welded to at least some guide tubes 16 from both sides of the sleeves. One set can be modified to prevent stress.

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

The inserts 64, 66 may 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.

- j GB 281979 B6

In the exemplary embodiment illustrated in Fig. 5A, the joining grooves of the plate 64 to the plate 66 are arranged at an angle of 120 ° at an angle with alternating inclination. The advantage of this solution is that while cutting is complex, it facilitates welding.

In a similar solution illustrated in FIG. 5B, the grooves are perpendicular, which facilitates the production of the inserts, but sows less advantageously in terms of welding.

Fig. 5 is a compromise of the two previous solutions: the grooves of one plate are straight but provided with a supporting bevel of the plates of the other sets.

The bars of the lattice are provided with means for clamping the bars, 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 support lugs 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 °. Two of the plates 64 and 66 (see Figures 5-7) 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 slotted and deformed spring 72. The grooves 68 close to the grooves are often advantageously formed by slotted 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 semicircle, as described in French Patent Application No. 90 09446.

As indicated earlier, the plates 64, 66 must be locally deformed 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 extend 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 6 and 9, and the rod 24 is held at four points, two being formed by bending the plates 74 and two further by springs 72.

When the inner grilles are made of a zirconium-based alloy as guide tubes 16, they can be fixed to the tubes by welding. To this end, the plates 64, 66 can be drawn around the guide tubes by bending 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 provide 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 indicated in Fig. 11 or at the front faces. This attachment can be done by joining the inner plates to each other, by electron beam welding or laser welding.

As pointed out above, it is also possible to use intermediate grids 22 formed from plates of an alloy that retains its irradiation properties, such as Inconel alloy. In this case, the plates 64, 66 may have a somewhat smaller thickness than when using a Zircaloy alloy. Thus, the plates 64, 66 may be brazed to each other at the locations where they fit together.

In a preferred embodiment, the cell 10 was designed for thirteen twelve bars 24 located in the mesh meshes of a 12.75 mm step. The supporting structure consisted of fifteen guide tubes 16 mounted

Detachable 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 Zircaloy. These parameters led to the use of a common width of 108 mm for the protrusions 68 and the compression spring 72. The height of the inserts 64, 66 was the same for the intermediate grilles 22 and the end grilles 20. The thickness of the inner inserts of the order of 0.4 mm proved to be satisfactory; advantageous for external inserts when the bars are made of Zircaloy alloy.

Claims (10)

PATENT CLAIMS A removable, light water cooled and attenuated nuclear fuel cell reactor comprising a support frame with two extensions (12, 14) connected by guide tubes (16) and having grids (20, 22) distributed along the assembly, each lattice having three sets plates (64, 66, 70) intersecting each other defining cells, one of which is guided by the guide tubes (16) and the other by the fuel rods (24), the plates (64, 66) having clamping means (68, 72) rods (24) that hold the rods (24) in the eyes of a regular triangular grid, and wherein the plates (64, 66 70) are attached to at least some guide tubes (16) characterized in that the upper extension (12) consists of a lower part comprising a hexagonal cross-sectional transition bell (34) into a cylindrical piece provided with a first adapter plate (32) releasably connected to the first guide tubes (16); and a top portion comprising a cylindrical housing (40) slidably mounted on a cylindrical piece of the bottom portion and a retaining plate (42) of tubular spacers (44) to define a distance between the first adapter plate (32) and the retaining plate (42) that is connected to second guide tubes (16) and springs (46) disposed between these plates (32, 42). 2. The reactor nuclear fuel cell of claim 1, wherein the springs (46) are disposed around the spacers (44). 3. The nuclear reactor fuel cell of claim 1 or 2, wherein the second guide tubes (16) are also those. which are located in connection with the tubular spacers (44) and in that the spacers (44) have the same inner diameter as the guide tubes (16) to allow the introduction of the bars (24) belonging to the command beam or spectrum change. 4. The nuclear reactor fuel cell of claim 3, wherein the second guide tubes (16) are supported on spacers (44) and in that the spacers form a support bridge on the first adapter plate (32) and the end portion is threaded for. a maximum distance regulating nut (48) between the first adapter plate (32) and the holding plate (42). A nuclear 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). guide tubes (16). 6. The reactor nuclear fuel cell according to any one of the preceding claims, characterized in that the plates (64, 66) are each two and two crossed and joined and in that the means for clamping the rods (24) comprise protrusions (68) disposed. at the cell partitions gripping 120 ° 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 partition (64, 66) and provide to the rods (24). Five points of support. A nuclear reactor fuel cell according to any one of the preceding claims, characterized in that if the guide tubes (16) have a larger diameter than the fuel rods (24), they are: 5, the plates (64, 66) around the insertion cells (16) are deformed and this deformation extends to adjacent cells. 9. A nuclear fuel cell according to any one of claims 1 to 8, wherein the inner plates (64, 66) of each lattice (20, 22) have cut-outs at their ends. 10 (79) to achieve their intersection with the outer plates at 90 °. A nuclear reactor fuel cell according to any one of claims 1 to 10, wherein the plates (64, 66) are provided with straight bevelled grooves at the crossing points. 3 drawings