GB2064853A

GB2064853A - Disassembly of irradiated fuel rods

Info

Publication number: GB2064853A
Application number: GB8035699A
Authority: GB
Original assignee: Interatom Internationale Atomreaktorbau GmbH
Current assignee: Interatom Internationale Atomreaktorbau GmbH
Priority date: 1979-11-17
Filing date: 1980-11-06
Publication date: 1981-06-17
Also published as: DE2946464A1; GB2064853B; DE2946464C2

Abstract

In disassembling an irradiated nuclear fuel or breeder element, which consists of individual rods arranged in a casing 1 and held in grid-type spacers, a first cut I is made at the point of the greatest neutron-induced swelling of the fuel rods and a first part of the casing 1 is removed with the spacer grids attached thereto. Thus the spacers need only be drawn over rod portions of smaller diameter thereby avoiding a greater force expenditure and damage to the individual rod casing tubes resulting from this. <IMAGE>

Description

SPECIFICATION Disassembly of irradiated fuel or breeder elements This invention relates to the disassembly of fuel or breeder element.

This invention more particularly, but not exclusively, relates to a method of disassembling fuel or breeder elements from nuclear reactors which is part of a recycling process for irradiated elements.

Known methods, by means of which the fission material formed in irradiated fuel, in particular in breeder elements, is extracted and intended for re-use, operate by mechanically breaking up the elements or the individual rods composing them and then dissolving them in an acid. The amount of structural material unavoidably introduced into the process should be kept as low as possible in order to reduce the proportion of high-activity waste produced at the end of the recycling process. It is therefore advantageous if, instead of treating the entire elements, only the individual rods are treated, so that only the relatively thin breeder rod casings are introduced into the recycling process.

According to the present invention there is provided a method of disassembling an irradiated fuel or breeder element comprising a plurality of rods within a casing, the method comprising the steps of: (a) dividing the casing into a first part and a second part by means of a first circumferential cut; (b) removing the first part of the casing; and (c) withdrawing one or more of the fuel or breeder rods from the second part of the casing.

When the method is effected on elements in which the rods are located by spacers, secured to the casing, the spacers secured to the first part of the casing can be removed with the first part.

Preferably the circumferential cut is made at the centre of an element.

In use of a nuclear reactor, the element is exposed to a neutron dose which varies along the length of the element; as a result there is a varying degree of expansion in regions of high and low radiation exposure. Depending on the configuration of the reactor and on the position of the element in the nuclear structure, the region of the highest radiation exposure frequently will be approximately half way up the element. If, as is preferred, the casing is cut through at this point, its upper part can be removed using relatively little force, as the expanded spacers or spacer grids from the central region have only to be drawn over areas of the rods where the cross section is not so greatly expanded. Therefore, there is little likelihood of rod casings being damaged.By cutting the element casing circumferentially, as opposed to cutting it longitudinally for example, the danger of damaging the fuel rods should be reduced. The individual fuel rods may be fixed at their lower ends in a rod holding device or plate, the purpose of which is to prevent the rods being moved or vibrated by the coolant flow. If the rods are secured to the holding plate by an interference fit (as suggested, for example, in German Offenlegunsschrift 2520 233), the subsequent removal of individual rods or groups of rods from the rod holding plate presents no particular difficulties.

However, if they are connected in a form-locking manner, i.e. they engage the rod holding device (as described for example, in German Offenlegunsschrift 27 21 869) the method is completed by the additional steps of: (i) removing a base piece from the casing by a second circumferential cut; and (ii) disengaging the rods from the rod holding device.

The first circumferential cut is preferably made in a region of the casing in which a spacer is located in order to provide greater protection against the possibility of damaging a casing of a rod.

For a better understanding of the present invention and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a complete fuel or breeder element; Figure 2 shows the element of Figure 1 with part of the casing removed; Figure 3 shows the element of Figure 2 with a base piece removed; Figure 4 shows on an enlarged scale a detail of the fuel or breeder element; and Figure 5shows on an enlarged scale and in partial cut-away section a perspective view of a further detail of the fuel or breeder element.

Viewed from the outside, the element essentially comprises a casing 1 in the form of hexagonal section, a base piece 2 (by means of which the element is held in a nuclear supporting grid, not shown here) and a head piece 3 which is designed for the handling of the element and has surfaces corresponding to surfaces of handling devices (see Figure 4). After use in a nuclear reactor, the element has been expanded by neutron-induced swelling, and this swelling or expansion is approximately at its greatest in the centre as the highest neutron flux is present at the centre.

In order to disassemble the fuel element, a first circumferential cut 1 is made as shown in Figure 1, by means of cutting tools (not shown here), dividing the casing 1 into two parts. By pulling on the head-piece 3, designed expressly for this purpose, the upper or first part of the casing 1 is removed together with the spacer grids fixed thereto (see Figure 2). If necessary, a second circumferential cut II is then made, to enable the base piece 2 to be separated in order to make a rod holding device 7 accessible (see Figure 3). The rod holding device 7 holds lower ends of the individual rods 4. The individual fuel or breeder rods 4 in this device are then detached from the device 7 and they may then be withdrawn from the device 7 singly or in groups and conveyed to, for example, a crushing machine not represented here. The arrangement of spacer grids 5 is shown in Figure 5, which also shows how the spacer grids 5 are fixed to the casing 1 by strips of sheet metal 6 attached by spot welding. The rods 4 are omitted from Figure 5 for the sake of clarity.

Claims

1. A method of disassembling an irradiated fuel or breeder element comprising a plurality of rods within a casing, the method comprising the steps of: (a) dividing the casing into a first part and a second part by means of a first circumferential cut; (b) removing the first part of the casing; and (c) withdrawing one or more of the fuel or breeder rods from the second part of the casing.

2. A method as claimed in claim 1, when effected on elements in which the rods are located by spacers secured to the casing, wherein, when step (b) is carried out the spacer(s) secured to said first part are removed with said one part.

3. A method as claimed in claim 1 or 2, wherein the first circumferential cut of the step (a) is made at the centre of the element.

4. A method as claimed in any preceding claim, when effected on an element in which ends of the rods are engaged in a rod holding device in the second part of the element, wherein between the steps (a) and (c) the following additional steps are carried out: (i) a base piece is removed from the second part of the casing by a second circumferential cut; and (ii) the rods are disengaged from the rod holding device.

5. A method as claimed in claim 2, or claim 3 or 4 when appendant to claim 2, wherein the first circumferential cut is made in a region of the casing, in which a spacer is located.

6. A method of disassembling an irradiated fuel or breeder element substantially as hereinbefore described with reference to the accompanying drawing.