FR2569490A1 - METHOD FOR DISMANTLING IRRADIATED NUCLEAR COMBUSTIBLE ELEMENTS - Google Patents

Abstract

THE INVENTION RELATES TO THE DISMANTLING OF NUCLEAR FUEL ELEMENTS. IT RELATES TO A PROCESS IN WHICH THE ENCLOSURE 4 OF THE FUEL ELEMENTS IS CUT AT ITS PERIPHERY IN A REGION L OF MAXIMUM SWELLING OF THE COMBUSTIBLE NEEDLES 5, THE UPPER PART OF THE ENCLOSURE BEING REMOVED WITH THE ASSOCIATED GRIDS, THE NEEDLES AND THE GRIDS BEING THEN PUSHED INTO THE REMAINING PART OF THE ENVELOPE SO THAT THE GRIDS 6 STACK ONE AGAINST ANOTHER. THE NEEDLES 5 ARE THEN SEPARATED FROM THE GRIDS, FOR EXAMPLE BY LASER CUTTING. APPLICATION TO NUCLEAR FUEL PROCESSING.

Description

Q9 @ FRENCH REPUBLIC (N e FUlca .: 2 5 '490 {- use only for

  THE NATIONAL INSTITUTE (Reproduction orders) OF INDUSTRIAL PROPERTY N of national registers 85 12542 N of registration: B5 112542 PARIS i) Int CI4: G21 C 19/36,

@ APPLICATION FOR PATENT OF INVENTION A1

  ) Date of deposit: August 20, 1985. Q Applicant (s): Public Institution says: UNITED

  KINGDOM AT TOMIC ENERGY AUTHORITY - GB.

  (Priority: GB, 21 August 1984, No. 8421219: 14 November

1984, No. 8428751.

  ) Inventor (s): Brian Edwin Meredith and James Shaw Burns. Date of the public availability of the

  application: BOPI "Patents" No. 9 of 28 February 1986.

  6 References to other national documents appearing

  paid: 703 Holder (s): () Agent (s): Cabinet Simonnot Process for the dismantling of irradiated nuclear fuel elements.

  The invention relates to the dismantling of com-

nuclear fuels.

  It relates to a method in which the casing 4 of the fuel elements is cut at its periphery in a region L2 of maximum swelling of the fuel needles 5, the upper part of the casing being removed with the grids 8! R, 6 6 associated, the needle beam and the grids being then pushed into the remaining portion of the envelope so that the 6 'grids 6 are stacked against each other. The needles 5 ', <are then separated from the grids, for example by laser cutting.

  I Application to reprocessing nuclear fuel.

  The sale of fascicles NATIONAL PRINTING, 27 rue de la Convention 75732 PARIS CEDEX 15 A 0 Sale of the fascicles at the NATIONAL PRINTING CENTER. The present invention relates to dismantling.

  irradiated nuclear fuel elements and, in particular,

  dismantling a type of fuel element

  nuclear reactor used in a nuclear reactor breeder & zt.

  cooled by a liquid metal, having an outer shell

  hexagonal shape containing several fuel needles

  nuclear power supported by spaced transverse grills. Such a nuclear fuel element is called

  "of the type considered" in the remainder of this memo.

  It is prudent, in every fuel element,

  to separate the hexagonal envelope and the trans-

  of combustible needles so that only the combustible needles, cut into convenient pieces,

  be used as charges to the retirement facility

  the envelope and the gratings being separated and

  used in the form of radioactive waste, so that the quantity of material introduced during the reprocessing of the nuclear fuel is minimal, this reprocessing being the operation in which the uranium and the plutonium of the fuel are extracted for reuse and the

  Fission products are separated before storage.

  It has already been proposed to circumferentially cut the envelope so that it forms a first part that can be removed and a second part containing

  combustible needles which can then be removed

  of the second part. It has also been proposed to remove the grids attached to the first part of the envelope with this first part. The proposed method indicates a central circumferential cut preferably, and the cut had to be performed using cutting tools. There are objections in practice to such proposals because it is difficult to ensure a clamping of the fuel pin bundle in order to separate the

  beam of the part of the envelope that surrounds the

  guilles, in a manner fast enough for the

  flow corresponds to that of an industrial installation.

  The invention relates to a method of dismantling and a device for the implementation of such a method, not having the above disadvantages

or only very little.

  More specifically, the invention relates to a method of dismantling an irradiated nuclear fuel element of the type in question, in which a thrust force is applied to the bundle of combustible needles so that

  the beam is displaced with respect to the outer envelope

pool.

  The invention also relates to a dismantling process

  an irradiated nuclear fuel element comprising cutting the outer casing so that it is separated into two axial portions, at a location between the ends of the bundle of combustible needles, and the thrust of this bundle from one end of the envelope, at least partially in this envelope portion placed from said location and rotated

  towards the first end of the needle beam.

  Preferably, the grids are also pushed

  longitudinally with respect to the first part of

  Veloppe so that they gather together forming a stack near said location. The stacked grates can be separated from the fuel needles by cutting the fuel needles in non-fuel-bearing parts, or while the stacked grates are still in the first envelope portion

  after moving the grids and the beam of

  guilles totally outside the first part of

develops.

  Dismantling can be achieved by cutting the outer casing in the circumferential direction, approximately at its midpoint and, in particular, in the region where the combustible needles have undergone maximum swelling during irradiation in

  the reactor core, by removing the upper part of

  the envelope with the grids associated with it,

:: - :: -. : 2569490

  = 3 and by holding in fixed position the rest of the envelope with application of a cylinder cohrele bundle of fuel needles so that this beam is repulsed at least

  partly out of the rest of the envelope, the grids a.

  The rest of the envelope being simultaneously stacked, the remainder of the envelope being removed from the needles for example by cutting the needles. The de-cutting operation can be: performed by a laser -: - :: :: In an advantageous application, a piston intended to provide the thrust-Pindicatede previously has a plate delimiting a hexagonal face with: cutouts at the corner allowing the passage of branches d. e supports transverse grids and also allows-sliding of the

  plate on the branches, the use during the

  including the tightening of the rest of the envelope, with initial contact with the plate and the lower transverse grid of the beam, then the command

  the cylinder to push the beam: fuel needles

  in the longitudinal direction, in the rest of the

  and, with the first grid, form a stack, this stack of grids being placed near the bottom end of the stack, with the successive breaks of the grids so that they gather at the end of the bundle; The set of grids and needles can be pushed completely out of the rest of the envelope and finally the stack of grids can be removed from the needles by cutting them. Alternatively, the assembly may be pushed back until sections containing no fuel, for example pressurized spaces, formed in the needles, protrude from the upper end of the lower part of the housing. envelope can be cut off at the level of the sections containing no fuel, the stack of grids remaining inside the part

bottom of the envelope. ::: - -

  Other features and advantages of the invention

  will come out of the following description -

  of an embodiment, with reference to the appended drawing in which:

  FIG. 1 is a longitudinal section of an example

  ple of combustible element of the type considered; and FIG. 2 is an enlarged section along the

line II-II of FIG.

  We first refer to Figure 1 which represents

  a nuclear reactor fuel element of the type

  dere, bearing the reference- and having a higher end

  2 for the handling of fuel elements, a lower end 3 to be positioned with many similar fuel elements in the fuel element support device of the reactor (not shown) and allowing the penetration of the liquid coolant metal to the inside of this fuel element and the others, an outer hexagonal envelope 4 containing several combustible needles 5 (only one being represented for clarity) and several remote transverse grids 6 for positioning and supporting the needles 5. The upper and lower grids lower are support grids and have the references 6T and 6B respectively. Each intermediate grid 6 is a spacer and positioning grid, and each grid 6 has branches 6 'ensuring a positioning

angular and axial.

  After irradiation in the nuclear reactor and extraction thereof, the fuel element 1 must be dismantled. More specifically, by remote handling, the outer envelope 4 and the grids 6 are separated from the

  needles which are then cut and

  put in a device for dissolving the reprocessing plant. The separation of the envelope and grids

  fuel needles is now described.

  As shown in Figure 1, a first cut

  cross-section using a laser is carried out in the enve-

  hexagonal loppe 4 and in the branches of the lower grid

  6, at a location L. A second transverse laser cut of the envelope 4 is made at a location L 1: considered to be the approximate position of maximum swelling of the needles as a result of the irradiation. The part of the envelope -: located to the right of location-L (as shown in Figure 1) is maintained and the envelope portion of

  the fuel element on the left of the

  L is pulled out of the maintained part, with driving the upper end 2, the upper grid 6T support, some grids 6 and their branches 6 ', but the fuel needles remain dan`sposition maintained .; Then, the maintained portion of the envelope is cut transversely to the laser at a location L3, this cut also ensuring the release of the lower support grid 6B and the exposure of the ends of the needles and the first gate 6 which is also the grid for holding the fuel needles in the low position. A cylinder having a hexagonal plate and cavities at its corners allowing it to slide on

  the branches 6 'is then placed along the expo-

  Combustible needles 5 and first grid 6 are controlled to break this grid and move it with the needles in the axial direction relative to the lower portion of the envelope. Initially, only the needles and the first grid are displaced as the needles slide relatively freely through the remaining grates because the needle section decreases from the maximum swelling position caused by the irradiation. The operation of the piston then causes the first and second grids to come into contact with each other so that the grids 6 are torn off from their attachment to the envelope 4, one by one, and finally are stacked and collected at the end. lower the needle beam, the cut corners of the hexagonal plate allowing the plate to slide along the branches 6 '. The needles and grids are then e9490 pushed out of the envelope 4, the latter being removed.

  and transmitted to a radioactive waste storage.

  Finally, the stack of grids 6 and removed by a

  transverse cutting by the laser, by the region of the .-

  lower end of the fuel needles, that is to say in the part forming the pressure chamber and which is not occupied by fuel. The needles 5 can then be subjected to the cutting operation then

  the dissolution operation of the retirement facility

ment.

  In a variant, the thrust can be interrupted as soon as the pressure parts of the needles start to emerge from the envelope. The parts of the needles having the fuel can then be separated, the grids and the pressure parts remaining in the envelope

  to be evacuated to a storage.

  In some cases, it may be preferable to avoid breaking the internal integrity of fuel needles, for example, which can occur when they are separated.

  parts under pressure. Various possibilities exist.

  For example, the needles can be removed from the stacked grids by applying a pulling force, the needles being removed one by one or in groups, or they can be pushed back from their position of contact with the grids by displacement relative to the grids using push rods, the grids being still in the lower part of the envelope or after the grids

  have been removed from this lower part of the envelope.

-5S94900

0 00 --- 0-00; =; = ;; 7 - = - - *

Claims (1)

0 0 t = 0 - 40 - 0 0 -REVENDINgS - - - - - d - Method of removing an irradiated nucleation element, of the type which provides a development. : jexagonal-external containing - needles fuel. - =: 05: nuclear supported- es, by distant transverse rilles, characterized in that a -force thrust is applied to the fcc''fuel needle needle (5) so that the beam is moved by -related to envelope-outer- (4). - - Z- 0 ;. Process for the dismantling of an irradiated nuclear fuel element comprising: eenveloppe (4) - so that it is separated in two-parts-axial-in = a: a position between-extreémités- the fa ci cx d-4 fuel needles (5) -characte = ise in -ce- he understands the thrust of the needle from the first end of the eniveloppe to the motor-part in the first part of the envelope from this position to the first end of the beam. needles. <- 3 :. Method according to claim 2, characterized in that the grids (6 - are also pushed): long: = -: 20 of the first part of envelope -afin that theyessent: collected -sub: form -d 4. A method according to claim 3, characterized in that the pushing operation is carried out until the beam (5) extends beyond Stacked grids (6) over a distance such that only parts which do not contain fuel in the needles remain in contact with the stacked grates. 5. Process according to claim 4, characterized in that the fuel needles are substantially separated from the grids. claim 5, characterized in that the separation operation is performed while the stacked grids are within the first portion of envelope n -C t; =, 7.-Preceded according to claim -6-6- caaractérisé in that it -f together-by-the-beam of fuel needles and grids empélees: (6-Y is pushed-out of the first part of the envelope and the separation operation is carried out subsequently. 8. Method according to any one of claims 7, characterized in that the separation operation comprises the cutting of the needles (5) in non-combustible parts and exceeding stacked grids (6). 9. The method of claim 8, characterized in that the parts containing no fuel are pressurized parts of the fuel needles (5). 10. Method according to any one of claims to 8, characterized in that the separation operation is performed without breaking the internal integrity of the fuel needles (5). 11. Method according to any one of claims 7, characterized in that the separation operation comprises the movement of the fuel needles (5) relative to the stacked grids (6) until they separate grids {6). F-ig.1 if "'Fig2. ,,: 2 to ,,,, z,. /.' ::. Jfi5 ... "1 '" I '' -,:, ... '..' .. / z.N   :,! ....... -. ii ..-. j ...... _ ::, ..:.