Spent fuel assemblies removal facility

Abstract

FIELD: nuclear fuel.SUBSTANCE: invention relates to a unit for removal spent fuel assemblies (SFA) and can be used in the reprocessing of spent nuclear fuel. The SFA removal facility is equipped with separate sealed chambers for cutting fuel element cladding and positioning spent fuel assemblies, connected to each other by a process opening, each of the chambers is equipped with cutting devices. The positioning chamber has a capacity for collecting the uncased spent fuel assembly structure, and the cutting chamber is equipped with a collector of fuel element fragments. Moreover, the outer spacer grid of the spent fuel assembly is used as a disk on the surface of which the fuel element fragments are cut off. The installation is equipped with a system for fixing the outer spacer grid in the process opening between the chambers and the sealing system, as well as a fuel element pusher equipped with a device for positioning and sequential movement to a specified length.EFFECT: increase in radiation safety, as well as a high degree of opening of nuclear fuel without crushing the ends of the fuel element cladding from spent fuel assemblies.1 cl, 3 dwg

Description

[0001] The invention relates to nuclear technology and can be used in the processing of spent nuclear fuel (SNF), and more specifically to the separation of a spent fuel assembly (SFA) into fragments of fuel elements, guaranteeing a high degree of opening of the nuclear fuel without crushing the ends of the fuel element cladding.

[0002] Devices for cutting spent fuel assemblies are known (Radiochemical processing of nuclear fuel from NPPs / V.I. Zemlyanukhin, E.I. Ilyenko, A.N. Kondratyev et al. - 2nd edition, revised and enlarged - M. Energoatomizdat, 1989, pp. 41-51), used in foreign countries, which include, after disassembling the spent fuel assemblies, cutting the fuel elements into individual fuel elements, separating them from all spacer grids, cutting the fuel elements with straight or stepped knives.

[0003] The disadvantage of the devices is the complex procedure for disassembling spent fuel assemblies and the complexity of the design of the devices, the need for additional equipment for individual operations of extracting fuel elements, which affects the duration of the spent fuel assembly cutting cycle.

[0004] A device for shredding spent nuclear fuel is known (RU Patent No. 2145125, IPC G21C 19 / 36, G21C 19 / 37, 27.01.2000). In this device, the separation of spent fuel assemblies into fragments is accomplished by two additional cutting edges of a knife, extended forward in the direction of the knife's movement relative to the main cutting edges, as well as by the main cutting edges of the knife. The knife's configuration ensures the shredding of spent fuel assemblies of hexagonal or round cross-sections with limited dimensions. A clamp crushes the spent fuel assemblies along a thickness and a width equal to the clamp, with a working part repeating the shape of the spent fuel assemblies in a deformed state. The severed fuel elements disintegrate. During the cutting of spent fuel assemblies, when the knife enters the area where the spacer grids are located, the cut pieces of the grid walls are crushed together with the cut pieces of the fuel elements passing through the grids, preventing them from scattering.

[0005] A drawback of this device is that the knife in the grid area cuts simultaneously across the entire width of the spent fuel assembly, and the resulting pieces are not always completely separated from each other. The resulting chains of uncut pieces, connected by bent strips of the spacer grid walls, must be sent for further cutting and separation; otherwise, they could form a blockage in the process chain when sent for spent fuel reprocessing, which would compromise the radiation safety of the process and lead to an accident.

[0006] A plant for processing irradiated nuclear fuel is known (patent GB No. 1314803, IPC G21 C19 / 34, 04 / 26 / 1973), consisting of a device for moving assemblies, a clamping system, a knife (saw) mechanism and auxiliary devices.

[0007] The disadvantages of this device are the complexity of the design and the low degree of grinding of the fuel elements, and the need to perform preliminary operations to cut off the tails of the fuel assemblies.

[0008] A method for cutting fuel elements of nuclear reactor fuel assemblies and a device for performing this method are known (patent DE No. 3723728, G21 C19 / 36, July 17, 1987). The device consists of a mechanism for sequentially ejecting a bundle of fuel elements from the outer cladding of the spent fuel assembly, a transverse plate, a knife, and auxiliary devices.

[0009] The disadvantages of the device are that spent fuel assemblies of a non-separable design and spent fuel assemblies with end parts cannot be subjected to grinding, since in this case it is impossible to ensure guaranteed grinding of the material of the outer shell of the spent fuel assemblies, which creates difficulties in further reprocessing of the spent nuclear fuel.

[0010] The technical objective of the proposed installation is to improve the radiation safety of fuel rod cutting and to refine the design of the device for grinding fuel rods from spent nuclear fuel assemblies, ensuring a reliable increase in the fractionation efficiency of fuel rod cladding during grinding, as well as cutting quality, guaranteeing a high degree of fuel opening. This allows unimpeded solvent access to the spent nuclear fuel pellets contained in the fuel rod fragments during further dissolution of the spent nuclear fuel.

[0011] In the proposed system, radiation safety during spent fuel assembly uncladding is ensured by cutting the end elements of the spent fuel assembly in a sealed positioning chamber, and cutting the fuel rods in a separate sealed cladding cutting chamber. The opening between the chambers is sealed, preventing spent nuclear fuel from entering the positioning chamber during fuel rod cutting. The device is further improved by using the outer surface of the outer spacer grid as the disk along which the fuel rod fragments are cut. Each fuel rod of the fuel assembly can be cut with a knife in a single operation due to the low cutting force, preventing compression of the ends of the fuel rod fragments. To use the spacer grid for fuel rod cutting, one of the spent fuel assembly end elements is cut along the outer surface of the outer spacer grid.To move the spent fuel assemblies, the positioning chamber is equipped with a handling device (crane, manipulator, etc.). A cutting device (guillotine, laser, etc.) is located in the positioning chamber and can move along the chamber's length. After the end elements are cut off, the spent fuel assemblies are moved within the positioning chamber so that the outermost spacer grid is positioned within the process opening. The outermost spacer grid is secured within the process opening by a locking system. Its outer surface must strictly align with the cutting line of the cutting device in the fuel rod cutting chamber. After this, the pusher, using pusher rods and the positioning system, pushes all the fuel assemblies beyond the outer surface of the outermost spacer grid by the required distance. The cutting of the fuel rod fragments is performed in the cutting chamber using a cutting device (guillotine, laser, etc.). The fuel rod fragments are collected in a collector.After uncasing, the spent fuel assembly structure is moved to the collection tank.

[0012] The spent fuel assembly 1 (Fig. 1) is sent to the claimed installation for uncasing. It consists of fuel elements 2, end elements of the spent fuel assembly 1 - head 3 and tail 4, spacer grids 5, central and observation tubes 6. In this case, the central and observation tubes are rigidly fixed in the spacer grids, and the fuel elements are freely located in the openings of the grids. The spent fuel assembly 1 is located in the positioning chamber 8 (Figs. 2-3). In the chamber, the end parts 3,4 of the spent fuel assembly 1 are cut off by means of the cutting device 10. Moreover, the cutting off of one of the end parts 3,4 is performed strictly along the outer surface of the outer spacer grid 12. The end parts 3,4 of the spent fuel assembly 1 are sent by the moving device 21 to the collection tank of the spent fuel assembly structure 20.After this, the device for moving the spent fuel assembly 1 is moved by the device 21 to the technological opening 9 between the positioning chamber 8 and the fuel element cutting chamber 7, and the outermost spacer grid 12 is placed in the technological opening 9 so that its outer surface strictly coincides with the cutting lines of the cutting device of the cutting chamber 11. After this, the outermost spacer grid 12 is fixed in this position by means of the locking system 13. The technological opening 9 together with the spacer grid 12 installed in it is sealed by the sealing system 14. All fuel elements 2 are pushed out beyond the outer surface of the outermost spacer grid 12 by the required amount by means of the pusher rods 17 using the guide grid 19 and the pusher 16 by means of the positioning system 18. The cutting of the fragments of TVEL 2 is performed in the cutting chamber by the cutting device 11. The fragments of TVEL 2 are collected in the collector 15.After uncasing, the spent fuel assembly structure 1 is moved to collection tank 20.

[0013] Advantages of the proposed device:

[0014] - performing all operations for uncasing spent fuel assemblies in one device;

[0015] - increasing the radiation safety of fuel element fragmentation by cutting them in a separate sealed chamber;

[0016] - improving the quality of cutting of fuel element cladding, ensuring a reduction in the wrinkling of fragment ends;

[0017] - rational use of structural elements of spent fuel assemblies during the uncasing process.

[0018] The invention is explained by the following drawings presented in Fig. 1-3: Fig. 1 - design of a fuel assembly; Fig. 2 - design of a device for uncasing spent fuel assemblies; Fig. 3 - design of a device for uncasing spent fuel assemblies when cutting a fuel element.

Claims

A spent fuel assemblies uncasing unit comprising transverse plates, a cutting knife, a mechanism for sequentially pushing a fuel element bundle out of an SFA cladding, characterized in that separate sealed chambers for cutting fuel element claddings and positioning SFAs, interconnected by a process opening, are equipped for SFA uncasing; each chamber is equipped with cutting devices; in the unit, an outer SFA spacer grid is used instead of one of the transverse plates; in addition, the unit is equipped with a system for fixing the outer spacer grid in the process opening between the chambers and the sealing system; the cutting chamber is equipped with a fuel element fragment collector; the fuel element pusher is equipped with pusher rods equal to the number of fuel elements in the SFA, which have a length equal to the length of the SFA assembly; the pusher is equipped with a device for positioning and sequentially moving it to a given length;The positioning chamber has a capacity for collecting the uncased spent fuel assembly structure.

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