DE3330357A1 - METHOD FOR REPAIRING A CORE REACTOR FUEL - Google Patents

Description

Dipl. Ing. R. WOODS

DIPL. ING. (FH) W. GALLO PHIUPPINE-WELSER-STRASSE 14

8900 AUGSBURG

TELEPHONE 516475 TELEX 533202 paiol d

Augsburg, August 18, 1983 Application file: W.1156

Vv'estinghouse Electric Corporation,

Westinghouse Building, Gateway Center, Pittsburgh,

Pennsylvania 15,222, V.St.A.

PATENT LAWYERS | -Jf- J

Method of repairing a nuclear reactor fuel assembly j

The invention relates to a method for repairing a nuclear reactor fuel assembly according to the preamble of Claim 1.

As is known, fuel assemblies of nuclear reactors consist of a multiplicity of fuel rods and a number of control rod guide tubes, which by means of means along the fuel | element length of distributed elements can be kept in a certain geometric arrangement. The ■ Ilaltegitter are attached to the steamer support tubes. At the two upper and lower ends of the fuel assembly, a head piece or a foot piece is attached to the control rod guide tubes, which b:?. V /. something protrudes downwards over the fuel rod ends. At the upper end of the fuel assembly, the control rod guide tubes are fastened in corresponding openings formed in the head piece. The control rod guide tubes jeuoils can be enclosed by a sleeve which is used to attach the i-lead tube a: a head piece and ara top holding grille.

BATH ORIGINAL. COPY

During the operation of such fuel elements in a nuclear reactor, they can occasionally stick to the fuel rods Form longitudinal cracks in the fuel rod cladding, which are mainly due to internal stresses and due to there is a possibility that radioactive fission products from the fuel rod cladding out into the primary coolant the reactor can get. Such fission products can also enter the flooding water of the flooded reactor chamber or in Case of spent fuel elements in the storage basin circulated through for the spent fuel Cooling water get in.

Since the fuel rods are part of an integrated 3aueinheit welded to the head and foot Control rod guide tubes are, it is difficult to find and replace defective fuel rods. To the defective To make fuel rods accessible at all, it is necessary to first remove the affected fuel element from the reactor core take out and then cut the weld seams, which connect the head piece to the control rod fixing rollers, in order to gain access to the defective fuel assembly from above in this way. With this work, however, it will Fuel element often for multiple use in the reactor unusable, as both on the control rod guide tubes when cutting how damage also occurs on the head piece that prevent subsequent re-welding.

In view of the high cost, the .axt exchange connected by fuel assemblies, the need for serviceable fuel assemblies has developed, both their operating and maintenance costs to keep it minimal.

COPY

Conventional repairable fuel assemblies v / iron already intended for the second time that it was first manufactured Design features that allow rapid expansion defective Brennetabe, the possibility of exchange these defective fuel rods through good racing rods and the subsequent further advance in the reactor and / or the normal handling and storage of the affected £> racing - .. element allow. The repair of the fuel assembly is made possible by the fuel assembly with a removable head piece. This removable head piece v / iru usually using Very hard connections with the upper Unuen of the control rod guide tubes mechanically attached to these guide tubes such that the headpiece is remotely operated; from an irradiated one Fuel assembly can be augeoaut while this in a neutron absorbing liquid remains submerged. After removal or the Exchange of the defective dipstick and after it has been put back on of the head piece onto the control rod guide tubes can then put the thus repaired fuel assembly back into place the keactor is used and until the end of its service life further users and / or in the usual way in one Storage basins for used Bronnstoff or at other storage locations securely v / grounded.

The aim of this known design is more repairable Fuel assemblies consists in having all fuel assemblies already at the time of their production with the one fast Construction features that enable repair, but are costly equip. The various screw connections or other detachable connections to the removable Attachment of the head piece to each of the control rod guide tubes requires a great deal of time and money for the additional fuel assembly compared to the production of the simple, welded fuel assembly

Manufacturing steps, while only with one very small percentage of all fuel assemblies later actually a fuel rod leak and consequently the need a repair of the relevant fuel assembly occurs.

The invention is therefore based on the object of providing a method for repairing normal fuel assemblies create, which enables the re-use of the refurbished fuel assembly in a nuclear reactor.

This object is achieved according to the invention by the procedure indicated in the characterizing part of claim 1.
15th

The invention also relates to a fuel assembly with a connection made according to the invention of the head piece with the control rod guide tubes.

The invention is described in more detail below with reference to the accompanying drawings, for example. In the drawings:

Fig. 1

In a partially cut-away view of a fuel element with according to the invention formed attachment between head piece and control tab guide tubes,

30th

Fig. 2

a top view of the fuel assembly shown in Fig. 1,

Fig. 3

the conventional type of attachment in an enlarged longitudinal section of the head piece to the control rod inlet holes by welding,

-χ-

starting from v / elcher that

repair according to the invention

can be used

Fig. 4 in a corresponding representation

type of fastening according to the invention between head piece and control rod guide tubes, as in the repair process according to the invention, starting from

an arrangement according to FIG. 3, is produced, and

5 shows a modified embodiment

that shown in Fig. 4 according to the invention Fastening, as it is based on a possibly necessary second repair from the state according to FIG. 4,. can be produced.

Figures 1 and 2 of the drawings, in which the same reference numerals denote the same or corresponding parts, show a nuclear reactor fuel assembly. 10 with 'an arrangement of fuel rods 12, which by means of retaining grids 14, 15, 17, of which only three are shown in Fig. 1 and those with mutual Ali stands along the length of the fuel assembly are arranged distributed, held at mutual distances in their intended geometric arrangement v / earth. Each fuel rod contains a plurality of nuclear fuel pellets 16 and one in the empty space of the fuel rod arranged spring 10, which the fuel tray column pushes down, and the two ends of each fuel rod are closed by end caps 20 in the usual manner.

COPY

To control the splitting process, the number of control rods 21 is up and down in control rod guide tubes movable, which at certain positions in each focal element of the reactor are arranged. The control rod guide tubes are attached to the holding grids 14, 15, 17. The fuel assembly also has a head piece 24 and a Foot piece 26 to which the upper and lower ends of the control rod guide tube c are attached, so that an in solid framework is formed, which transport and handling of the fuel assembly without risk of damage made possible by its individual components.

Typically, the control rod guide tubes uii Sleeves provided, Ji ^: ait the upper and lower grids 14, 17 and the head piece 24 and the foot piece are compatible with sweat. Such a sleeve 53 is in the Figures 1 and 4 for connecting a control rod guide tube 50 to the upper holding grid 17 on the head piece shown. Each control rod guide tube 50 extends the entire length of the fuel assembly 10 between the head piece 24 and the foot piece 26. The sleeve 53 extends extends only from the head piece 24 to the upper retaining grid 14, while a corresponding sleeve 54 is on The lower end of the fuel assembly extends only from the foot piece 26 to the lower holding grid 17. The control rod guide tube 50 is attached to the sleeve 53 by a "bead connection, the bead connection typically of three with mutual.ii axially spaced apart Bead groups 55 consists, with two groups between dor Head piece connecting plate 32 and the upper holding grid 14 are arranged and a bead group 17 is located below the upper Ilaltegitter 14. Jado 5ickor.grappe for its part consists of four rotationally symmetrical ones Single sickness in the form of bulges. In appropriate In the same way, the control panel can be attached to the sleeve 54 be attached.

BAD ORIGINAL ^ " _Copy

As shown in Figures 1 and 2, the head piece 24 has a square shape in plan view and v / e is a frame 23 with an upper plate 30 and a lower connection plate 32 arranged at a distance therefrom on. On opposite edges of the upper plate 30, hold-down springs 34 are attached by means of screws 36, when the upper core support plate is placed on the fuel assembly installed in the reactor core, for the purpose of Holding down the fuel assembly compressed v / ground.

Furthermore, the head piece has a control rod bundle actuating mechanism 37 with an internally threaded cylindrical component 3 2 and arms protruding radially therefrom. The individual control rods 21 are each connected to the arm 40 in question by means of a coupling 42, and the arrangement is such that the control rod bundle actuation mechanism can move all the control rods of the fuel assembly vertically in the control rod guide tubes to prevent the fission process in the fuel assembly ζ α steer.

A preferred embodiment of the invention The method for repairing a nuclear reactor fuel assembly 10 will be described next year with reference to FIG State of a conventional fuel assembly before repair shows, and äer Fig. ■! described the Su- ~~ stood after the repair according to the invention. the Control rod guide tubes 50, of which in Figures 3 and only one is shown in each case, are with their upper sleeves 52 coaxially in the control rod bushing bores 60; the head piece connection plate 62 is used. The sleeves 52 are preferably by welding or another material connection in the area of the top side 64 of the head piece connection plate 62 attached to this. This common type of attachment is less time consuming and costly than the use of screw fastenings in the course of manufacturing the known repairable fuel assemblies.

ORIGINAL COPY

AO

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If a fuel assembly 10 of the type shown in Fig. 3 has to be repaired, which is actually only the case with a very small percentage of all fuel assemblies, according to the inventive method

b move the sleeves 52 separated from the connecting plate 62, indera the sleeve wall is severed along its circumference below the fastening area. This The separation process can be carried out, for example, using a conventional inner pipe cutter, the inside the control rod through-hole 60 of the connection plate cuts through the sleeve wall from the inside below the weld seam. Alternatively, the separation process using a conventional hole saw-like cutting tool from the top G4 of the connection plate 62 with the cutting diameter required to cut the weld seam and the corresponding cutting depth. So-Jann is the head piece with the connection plate 62 in the usual V / s removed from the sleeves. Separating the welded joints and "removing the head piece from the irradiated fuel assemblies 10 are carried out remotely, while the fuel assembly is in a neutron-absorbing Liquid, such as \ / as scr, is submerged. Then the fuel assembly is to be fixed at its upper end and accessible for exchanging defective racing rods.

For the repair of the fuel assembly, a modified head piece 24 is used, which is preferably basically with the abcjenoiaiaonen. Head piece is identical, with the exception that the control rod through holes of the connection plate 32 preferably all with one in their Soffit formed llingaut 74 are spared. This ring groove 74 is located axially below the dor separating groove of the sleeves 52 from the original connection place 62 corresponding üoröicheü. The jut 74 can be used as any designed wall recess or formed by a group of arbitrarily shaped individual wall recesses

COPV % * BAD ORIGINAL

of any dimensions, but it is preferably around a coaxial, continuous circumferential groove. The modified head back 2-i is preferred a noues, unbostrahltas headjoint, however, can if desired just as well the removed headjoint naca corresponding Ilachbearbcibuiig visor used in front of. The production the grooves 74 in dun individual bores 72 can can be done with conventional vision cutting tools.

The severed sleeves 53 with the control rod guide tubes 50 are inserted into the implementation bores 72 of the connection plate of the modified head piece 24 in such a way that they protrude axially beyond the IJuts 74. The separated sleeves 53 are preferably introduced from below into the feed-through bores 72, specifically in an axial position corresponding to their axial position in the original head piece. In practice, this process is of course carried out by placing the new head piece on the submerged fuel assembly. Then the sleeves by pressing in in di <: i-Juben fixed 74 engaging annular beads in the AnschluiJplatte. Conventional tools are used for this. For example, the beads can be pressed in hydraulically by forcing pressure fluid into the feed-through bore through a supply pipe with seals arranged above and below the groove to enclose: 1 hydraulic fluid in the feed-through bore, so that the bead, which rests on the ilubwand, enters the sleeve through the fluid is pushed in. Another possibility is the use of a piston with a piston rod in the through-hole, v / whether the piston is pulled upwards closer to the out by means of the piston rod, if the piston is more courageous than it is, in order to get a Ti material introduced into the through-hole, such as polyurethane, to press against a seal located above the rage, through which the piston is bange passed, so that again through ..las compressed material

BAD ORiGIiSiAL _Copy

Al

in the through hole one engaging in the groove Bead is imprinted in the sleeve. All these Ilaßnahivien can in turn be carried out remotely.

The ancestors of the present invention described above is also the possibility, only partially spent Brei'instäbe from a fuel assembly: remove with besonadigtei.i frame and insert into another Brennelenentengestell completely burn the fuel to reach the vorgeselienen Abbrandpegels on then. In addition, the method according to the invention enables the removal and / or the removal of the racing rods for the purpose of better liranuusnut'iuiig in the reactor.

The invented ancestor is in the same "," used for the repair of fuel assemblies, other tax discharge tubes are attached directly to the back of the head by welding, without the use of any Zv / iscut_nnQlsen In this case, the corrugations are cut off and pressed in, and the top part is placed directly on the control rod guide tubes instead of sleeves ^ ri <-ang, jj-ei maxien already in the 2uge of the original production or also during a previous installation the sockets or control tube through a safety connection with corresponding holes or depressions aor a head piece connection plate can be attached ^ .ent, from ^ c-hcn ¹ · of the Zuataa · !, instruiugc ^ et :: t ^T .- / · -raeii, \. ^r ob i_: i the repaired condition in? ig. ^r > ciar ^^ represents is. Fi'j. 5 the state, nacxi cuior r .'.- 'eic-aalijeii IristanJ-setting of the Ureimoleiuont. D-; nje..i: i ^ is n: i rig. D.

3AD ORIGINAL

the sleeve OO of the control rod guide tube 50, which has been separated from the second shark, as well as a 3 C control rod guide tube bO itself by pressing a bead into contact ^{with the T} attached. The left DO lies below the area of the hat 74 in the head piece connection plate 32 shown in FIG. 4, from which the sleeve 53 is separated at the beginning of the installation process. As a result of the lower position of the groove 90, not only the sleeve SO, but also the stacking guide tube 50 which overlaps it, must be pressed into the anger 90.

from the above explanation it can be seen that the invention also relates to a new type of fastening operated between J era head piece of a fuel assembly and a control rod guide tube. This type of attachment can already during the original production of the fuel assembly, but preferably only when it is used for a repair Find. The use of this type of fastening only in the case of repairs, while in the case of the original Fuel element production, for example, a traditional one Welded connection between control rod guide tube and Head piece / application leads to lower overall time and costs compared to a general application the orfinduiigsgemäße type of attachment already in the course of the original manufacture of the fuel element. This is due to the fact that only a very small percentage the fuel elements actually need to be repaired later. . .

A preferred embodiment of the attachment of the Head piece 3; it on the control rod guide tube, as shown in Fig. 4 is shown using a head piece,

BA3 ORIGINAL _οοργ

.. ■ - 3J3UJb7

at its connection plate ΎΙ a number (at least two

and preferably all) of the control rod through-hole j

Gen 72 is stranding with a fury 74. for fastening the;

rait sleeves 53 fitted gteaor bar support pipes i3ü;

the sleeves are inserted coaxially into the guide bores

leads, the sleeves in aen with a wat 74 provided j

Implementation constraints this mat. overlap axially and in

this groove has been pressed into it. - I.

Alternatively, you can use tax stowage agencies, what is not shown, also onne sleeves directly pushed into the grooves of the legal function j weraen. at the ßefesr.iyungsarc shown in Fig. 5 weraun both the sleeves and the control runner.

roiire pressed into the angry 90. :

If necessary, rliccel can be used for positioning uülsen or the Fünrungsronre with. specified axial distance are used in the implementation judgments.

Preferably, as shown, for example, in FIG. 5, a lower section of the upper section of the passage unij-sboiiruiiCjun serves for this purpose, as a result of which a shoulder 9 6 is formed which serves as an axial bearing for the sleeve bzv /. the guide tube serves as a jleiciimiijiije liüac-nlaje Cac headrest -on the gesanteix Bronnelo.icnt ensures v / whether the previously separated length of the sleeve iiechnan ··; rjotra ^ n will. Alternatively, lcönnta tue sleeve OO r-; it oinei-i Kragon or a .lanschette vorse.ien seiii, -: lie sicii an uio rear side of the attachment ^^ latte yl cuilejt.

Sugfesti-jjieitcunteariuichanyoK b.abcn ge-eijt, aa.il the firmness oiner liiilso, the r.iictel :: a nic]: _- nverbindany with a complete ring groove in the leadthroughaljolirung of a head piece _{connector is y} greener than the firmness of the Sleeve itself is.

ÖAD ORIGINAL

Claims (5)

Patentans; rücno Ί. Method for repairing a nuclear reactor fuel assembly, the "Steuerstaufünrungsrolire" or attached sleeves are inserted coaxially into the control rod diameter guide tubes of a head piece connection plate and attached to this, characterized in that the guide tubes or the sleeves are separated below their attachment point on the connector, platto along their circumference are, according to which, the head piece with the connection plate of the separated control rod guide tubes "or Sleeves from _d enor.uaen, so then the fuel rods are accessible, and that a head piece is used to replace the head piece, in the connection plate of which a plurality of the control rod feed-through bores are provided axially below the separating point of the control rod guide tubes or sleeves with preferably groove-shaped depressions in the bore wall , and that by pressing the control rod guide tubes or sleeves, which protrude axially up to above these depressions into the through bores of the connection plate, into the depressions, the control rod guide tubes or sleeves are fastened to the connection plate by means of beaded connections. 2. The method according to claim 1, characterized in that between the Steucrstabführungrohron or thereon fastened sleeves and the head piece connection plate ring-thickness connections by pressing the guide tube or sleeve wall into the oinu Uufangsnut of the passage bore wall manufactured in. BAD ORIGINAL COPY 3. Nuclear reactor fuel assembly with control rod guide tubes attached to a connection plate of a head piece, the guide tubes bz \ i. Sleeves attached to it are inserted coaxially into control rod feed-through bores of the connection plate, characterized in that the fastening of the control rod guide roller or the fastened sleeves of the head piece connection plate (32) are each formed as a bead connection by pressing the guide tube or sleeve wall into depressions in the feed-through bore wall, whereby the guide tubes or sleeves each extend axially above the depressions. 4. fire element according to claim 3, characterized in that the fastening as a ring pre-binding by pressing in the guide tube Lr: w. Sleeve wall in an annular groove-shaped recess (74) in the wall of the bore is trained. 5. Fuel element according to claim 3 or 4, characterized in that that linschlaginittel (9G) for axial positioning of the guide tube or the sleeve in the control rod feed-through bore (9 2) are provided. BATH ORIGINAL