JPS6157896A - Method of overhauling irradiated nuclear fuel element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the disassembly of irradiated nuclear fuel elements, more particularly for use in liquid metal cooled fast breeder reactors;
The present invention relates to the disassembly of a hollow nuclear fuel element having a hexagonal outer casing containing a number of nuclear fuel pins supported by a spaced apart transverse grid. Such a nuclear fuel element will be referred to hereinafter as a specific type of nuclear fuel.

for each fuel element to minimize the amount of structural material introduced into nuclear fuel reprocessing, such as extracting the uranium and plutonium in the fuel for reuse and separating the fission products for storage. , separate the hexagonal casing and transverse grid from the fuel pin, cut into convenient pieces, use only the fuel pin as raw material in a reprocessing plant, and dispose and store the casing and grid as radioactive waste. It is preferable to do so.

It has already been proposed to cut the casing circumferentially in such a way as to produce a first part that can be taken out and a second part that accommodates the fuel pin that can then be taken out. It was also proposed by M that it would be advantageous to include a grid such as that fixed to the first part of the casing together with the first part. In this plan, a central circumferential cut was better, and this cut was made with a cutting tool.

Practical drawbacks to such proposals include gripping and drilling the fuel pin bundle in order to separate it from the casing portion surrounding the pins quickly enough to accommodate the processing requirements of commercial plants.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a disassembly method and an apparatus for carrying out such disassembly without or with fewer of the above-mentioned disadvantages.

According to seven aspects of the invention, a method of dismantling certain types of irradiated nuclear fuel elements is provided that applies a pushing force to a fuel pin bundle to displace the fuel pin bundle relative to an outer casing.

According to a second aspect of the invention, the step of cutting the outer casing and separating it into two axial portions at a position intermediate between the ends of the fuel pin bundle, and the step of cutting the outer casing to separate it into two axial parts at a position intermediate between the ends of the fuel pin bundle; There is provided a method for dismantling an irradiated nuclear fuel element, comprising the step of pushing out one casing portion extending from the position toward the one end of the pin bundle.

Preferably, the grids are also pushed along the length of one of the casing sections so that these grids converge in an S stack adjacent to the casing section. cutting the fuel pins at the fuel-free portion while the stacked grid remains in the one casing section, or after displacing the grid and pin bundle completely from the one casing section; It is best to separate the stacked grid from the fuel pins by

The outer casing is cut circumferentially at approximately its midpoint, more specifically at the area where the fuel pins have undergone maximum bulging during irradiation in the core, and the upper part of the casing with its associated grid is cut. ejecting and then holding the remainder of the casing stationary and applying a ram device to the fuel pin bundle to at least partially push this pin bundle out of said remainder and stacking of the grid associated with said remainder. Disassembly is preferably carried out by, for example, removing the grids by cutting the pins. The cutting operation is preferably carried out with a laser.

In a clever application, the pushing ram as described above has a hexagonal face plate with corner cut-outs for receiving the support legs of the tangential grid, so that the face plate slides over said legs. In disassembly use, the fuel pin bundle can be gripped by the remainder of the casing, first bringing the lower transverse grid of the fuel pin bundle into contact with the faceplate, and then actuating the ram to move the fuel pin bundle a length within the remainder. Release the grids one after another by pressing in the direction 7, so these grids? f'l converges on the end of the pin bundle and forms a stack with the first grid, the stack of grids being positioned adjacent the lower end of the pin bundle. The grid/pin assembly may be pushed completely out of the remainder, and finally the stack of grids may be removed from the pins by cutting the pins. As an example of a change,
It is best to push the assembly until the unfueled part of the pin, e.g. the plenum space, protrudes beyond one end of the bottom of the casing, in which case the pin should be pushed in such a way as to leave the grid stack within the bottom of the casing. It can be cut in areas where there is no fuel.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

Referring first to FIG. 1, a particular type of reactor fuel element l is positioned in a fuel element handling upper end 2 and a fuel element support arrangement of a reactor (not shown) for a number of similar fuel elements; and a lower end 8 for admitting liquid gold coolant into the interior of that fuel element and other fuel elements, and a six-piece housing a number of fuel pins 5 (seven of which are shown for clarity). It has a square casing 4 and spaced lateral support/positioning grids 6 for pins 5. The upper and lower grids are support grids and are designated 6T and 6B, respectively. Each intermediate grid 6 is a spacer and positioning grid and has legs 6 for diagonal and axial positioning.

For irradiation and removal from the reactor, it is necessary to dismantle the fuel elements. In one, with remote control, the outer casing 4 and the grid 6 are separated from the fuel pin 5, which is then cut and fed to the melting stage of the reprocessing plant. The separation of the casing and grid from the fuel pin will be described below.

Referring to FIG. 1, a first lateral laser cut is made in the hexagonal outer casing 4 and the leg of the lower support grid 6B at position iL1. A third lateral laser cut is made in the casing 4 at position [L2, which is the position where the pin bulges maximum as a result of irradiation. The part of the casing on the right side of position L2 (as seen in FIG. 1) is held, and the part of the casing of the fuel element on the left side of position L2 is injected from the held part to the upper end part 2, upper support grid 6, Some of the grids 6 and their grid legs 61
with it, leaving the fuel pin in the retained part.

The retained portion of the casing is then cut laterally by the laser at position #L8 (this cut is done by releasing the lower support grid 6B at 411F and cutting the pin ends and the first grid 6 (which also happens to be the fuel Bring the ram, which has a hexagonal faceplate with corner recesses, to the exposed end of the fuel pin 5 and the first grid 6. The hexagonal face plate can slide on the grid legs 6'. The ram is actuated to move the grid apart and displace it and the pin axially relative to the lower part of the casing. Initially the pin and the Only one grid is displaced because the taper of the pin cross-section away from the maximum bulge position caused by maximum radiation allows the pin to slide relatively freely through the transition grid. .Successive action of the ram brings the first grid into contact with the next and releases the grids 6 from their attachment to the casing 4 one in seven times, until these grids are stacked at the lower end of the pin bundle. The corners of the hexagonal face plate are cut off to allow the face plate to slide along the grid legs 6'.The pins and grid are thus pushed out of the casing 4 and the casing removed to remove the radioactive material. Send to waste storage.

Finally, the stack of grids 6 is extracted by performing a coffin laser cut in the lower end region of the fuel pin, ie, in the part without fuel, called the plenum part. Thus, 8
The 1P pin 5 is now ready to proceed to the cutting stage and then to the melting stage of the reprocessing plant.

Alternatively, the pushing may be stopped as soon as the plenum portion of the pin begins to emerge from the casing.

Next, k! The fuel loading portion of the tube may be separated and the grid and plenum portions may be left in the casing for disposal to waste storage.

In some circumstances, it is desirable to avoid destroying the internal integrity of the fuel pins, such as would occur if the fuel pins were cut at their plenum portions. There are various possibilities. For example, the pins may be removed from a stack of grids by pulling them out of the stack in sevens or groups, or the pins may be removed from a stack of grids by leaving them in the lower part of the casing or The pin may be forced out of engagement with the grid by displacing the pin relative to the grid by a bushing rod after it has been pushed out of the lower casing.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional side view of a typical glare element of the specified class 287, and FIG. 1 is an enlarged cross-sectional plan view taken along the line It--U in FIG. ■・・・Specific type of nuclear reactor science element, 2...
...Top end, 8.Bottom end, 4.Bent, outer casing, 5.Fuel pin, 6.Tap, grid, 64.Leg, 61.・・・・・・
・Upper autopsy/Rip top, ・6. S, , , inner lower grid.

Claims (1)

Claims: 1. A method for dismantling certain types of irradiated nuclear fuel elements, characterized by applying a pushing force to the fuel pin bundle in order to displace the fuel pin bundle relative to the outer casing. 2. Cutting the outer casing and separating it into two axial parts at a position midway between the ends of the fuel pin bundle, and directing the pin bundle from one end of the casing, at least in part, from said position to said one end of the pin bundle. 1. A method of dismantling an irradiated nuclear fuel element, the method comprising extruding it through one casing portion extending over the casing. 3. A method according to claim 2, characterized in that the grids are pushed along the length of said one casing part so that they come together in a stack adjacent said location. 4. carrying out the pushing step until the pin bundle projects beyond the stacked grid to such an extent that only the fuel-free portions of the fuel pins remain engaged within the stacked grid; The method according to claim 3. 5. The method of claim 4, further comprising separating the fuel pins from the stacked grid. 6. A method as claimed in claim 5, characterized in that the separation step is carried out while the stacked grid remains in one of the casing parts. 7. A method according to claim 6, characterized in that the fuel pin bundle/stacked grid assembly is extruded from said one casing section, followed by a separation step. 8. Any one of claims 5 to 7, characterized in that the separating step comprises cutting the pin at its fuel-free portion that projects beyond the stack. The method described in. 9. The method of claim 8, wherein the fuel-free portion comprises a plenum portion of a fuel pin. 10. A method as claimed in any one of claims 5 to 8, characterized in that said separating step is carried out without destroying the internal integrity of said fuel pin. 11. The separating step includes displacing the fuel pins relative to the stacked grids until the fuel pins are disengaged from the stacked grids. The method described in section.