GB1604065A

GB1604065A - Method and tool for producing a control assembly guide for nuclear reactors

Info

Publication number: GB1604065A
Application number: GB22786/78A
Authority: GB
Original assignee: Leleu SA Marcel
Current assignee: Leleu SA Marcel
Priority date: 1977-12-06
Filing date: 1978-05-25
Publication date: 1981-12-02
Also published as: IT1108033B; CH623425A5; BE866082A; IT7868202A0; DE2815315A1

Abstract

The cluster guide comprises a lower part consisting of a subassembly defined by conduits placed around and parallel to the axis of the cluster guide and held together by positioning plates, and an upper part consisting of guide plates which with the conduits define aligned paths for descent of the neutron-absorber rods, the whole being retained inside a casing made up of two half-covers which on their periphery have openings through which points of the positioning and guide plates pass. According to the process the half-covers enclosing the subassembly and the guide plates are placed inside a cage (110) made up of two half-shells (111, 112) and which has flanges (119, 120) placed facing the cluster guide plates and whose inner edges act as support for the positioning and guide plates. Expandable mandrels are introduced into the positioning and guide plates in order to press the sides of the said plates against the corresponding periphery of the flanges (119, 120) of the cage (110) and the operation of welding the plates to the half-covers is performed. <IMAGE>

Description

(54) METHOD AND TOOL FOR PRODUCING A CONTROL ASSEMBLY GUIDE FOR NUCLEAR REACTORS (71) We, MARCEL LELEM S.A., a French company of 152, Boulevard Haussmann, 75008 Paris, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The object of the invention is a method and tool for producing a control assembly guide or guide tube for nuclear reactors.

A control assembly guide or guide tube is part of the internals of a PWR (pressurised water reactor) nuclear reactor. As its name indicates, it is intended to act as a guide unit for an assembly of control rods carrying neutron absorber rods, which are lowered and introduced into the reactor via the control assembly guide for the purpose of slowing down the nuclear reaction.

Control assembly guides for nuclear reactors, such as are known in Europe, comprise a lower part consisting of a sub-assembly defined by sheaths placed in a stellate arrangement around the axis of the control assembly guide and parallel to said axis, the sheaths being kept together by positioning plates or boards, and an upper part consisting of guide plates that define, together with the sheaths, aligned paths for lowering of the neutron absorber rods carried by a control assembly or a head, the upper and lower parts of the control assembly guide being held within a casing formed by two casing members bent longitudinally at 90' and assembled, the casing presenting over its circumference at the location of each positioning and guide plate openings designed to receive with a clearance projections provided on the circumference of the said positioning and guide plates.

As mentioned above, the guide paths defined by the sheaths and by the guide plates should be perfectly aligned so as not to restrain the neutron absorber rods and so that the latter can descend in the guide tube and be withdrawn in a frictionless manner and without being obstructed during these operations. Since the control assembly guide is an article some four metres long, the fit of the guide surfaces of the rods of the control assembly within the control assembly guide poses extremely complex manufacturing problems.

The object of the invention is thus to provide a method of manufacture as well as the complex equipment that will enable the pieces constituting the control assembly guide to be assembled and welded, the control assembly guides produced according to the method and with the equipment of the invention exhibiting only such minimal divergences in the adjustment of the guide paths for the rods (a few hundredths of a millimetre) that they eliminate any friction that may arise between the rods and the guide surfaces.

The method according to the invention comprises placing the casing members enclosing a previously assembled and welded sub-assembly, together with the guide plates, within a jig formed by two jig halves and having ribs placed opposite the positioning and guide plates and whose interior edges are configured to engage the projections provided on the circumference of the positioning and guide plates so as to act as a support therefor, applying a stress to the plates outwardly away from the axis so as to press the projections against the ribs, and welding the plates to the casing members by making a weld between each projection on the plate and its corresponding opening in the casing.

Preferably the welds are made in accordance with a satisfactory welding programme designed so as to avoid the effects of stress in the control assembly guide.

Preferably the sub-assembly is itself fabricated by placing the positioning plates of the sub-assembly in a cylindrical jig formed by two jig halves and having ribs spaced apart and perpendicular to the axis of the housing, the positioning plates being placed opposite the ribs whose interior edges are configured to engage the projections on the circumference of the plates so as to serve as a support therefor, wherein the sheaths are introduced into slots provided for this purpose in the positioning plates and the sheaths are maintained in their appropriate positions with the aid of clamping means integral with the housing and/or with the aid of autonomous clamping means assembling the sheaths two by two, introducing expansion tools within the sub-assembly thus formed at the location of each positioning plate so as to press each sheath against its corresponding slot on the said positioning plate, the latter being retained by the interior edge of each rib, and welding each intersection of a sheath and its slot in accordance with a satisfactory welding programme designed so as to prevent the effects of stress in the sub-assembly.

The basic equipment for carrying out the method comprises a cylindrical jig for assembling the subassembly and the upper part of the control assembly guide between the two half-members forming the casing, the jig comprising two assembled jig halves, the jig being rotatably mounted about its axis in a support and having ribs made in two parts, each integral with one of the jig halves, the said ribs being placed one after the other perpendicular to the axis and along the jib, and each having a central hollowed-out part whose edge is configured to engage the projections on the circumference of the positioning and guide plates of the control assembly guide to be assembled.

Each jig half may comprise two longitudinal stiffening tubes integral with a serniannular end plate, the assembled end plates having a circular configuration enabling the jig to turn on rollers secured to a frame.

A plurality of expanders are used to stress the positioning and guide plates so as to press their projections against the edge of the ribs of the housing.

Each expander may have four jaw members expandable by engagement with a cone and operating in directions at 90 with respect to one another, the expansion of the jaws being controlled by means of a rod sufficiently long to enable the expander to be introduced into the interior of the control assembly guide placed in the housing.

Preferably the equipment also comprises a second cylindrical jig for assembling the subassembly forming the lower part of the control assembly guide, the jig comprising two assembled jig halves and being mounted for rotation around its axis in a roller support, the support being pivotally fixed to a shaft integral with a base, the jig having ribs made in two parts, each being integral with one of the jig halves, and the ribs being placed after one another perpendicular to the axis along the jig and each having a hollowed-out central part whose edge is configured to engage the projections on the circumference of the positioning plates of the sheaths of the lower sub-assembly.

In the jig for assembling the lower subassembly, each jig half may comprise two longitudinal stiffening tubes integral with a semi-annular end plate, the assembled end plates having a circular configuration that enables the jig to turn between the rollers fixed to the frame. Longitudinal bars may be inserted between the stiffening tubes and parallel thereto, two adjacent bars being provided at the point of separation of the two jig halves. The jig may have securement means for holding the sheaths of the subassembly.

The equipment for assembling the subassembly preferably also comprises expansion tools each having a central body provided with a plurality of oblique milled cavities regularly distributed around the axis of the body from opposite ends thereof and opening onto lateral faces of the central body, fingers in the milled cavities, springs biasing the fingers against a respective one of two discs disposed one at each end of the central body and connected by a threaded rod carrying a tightening nut, the tightening of the discs against the body causing the fingers to project laterally so as to bear against the sheaths and press them against slots made within the positioning plates. The projecting lateral surface of each finger is a fiat bevelled surface corresponding to the configuration of the polygonal line traversed by following the bearing surface of all the sheaths placed in a stellate arrangement around the axis of the sub-assembly of the control assembly guide. A tightening rod is provided to engage with the nut and position the mandrel.

The invention also extends to a control assembly guide or guide tube obtained by carrying out the method.

The accompanying drawings show by way of example one embodiment of guide tube or control assembly guide as well as the successive steps in a method for producing the guide tube with the equipment used in the production. In the drawings: Fig. 1 is a part-sectional side view of one embodiment of a guide tube, the guide tube casing being shown partially removed so as to provide a view of a lower part forming a sub-assembly and an upper part formed by guide plates, Fig. 2 is a perspective view of a jig tool enabling the various constituent parts to be positioned and the sub-assembly of the guide tube to be effected, Fig. 3 is a perspective view ofthejig in Fig.

2, one of the jig halves having been removed so as to show the sub-assembly within the tool, Fig. 4 is an end view of the jig of Figs. 2 and 3, showing the positioning of the constituent parts of the sub-assembly and a compensator expansion tool located at the centre of the constituent parts of said sub-assembly and enabling them to be held in place under tension against the jig tool, Fig. 5 is a view taken from above of the expansion tool visible in the centre of Fig. 4, Fig. 6 is a section through the expansion tool along the line VI-VI of Fig. 5, Fig. 7 is a view of the end of the jig according to Figs. 2 and 3, similar to the view of Fig. 4, positioned ties having been placed at the ends of the sub-assembly, Fig. 8 is a perspective view of a second jig tool for positioning the guide tube in its entirety, that is to say the sub-assembly and an upper part, in the casing members, Fig. 9 is a partial view of the jig of Fig. 8, one of the two jig halves having been removed, the other showing in its interior the positioning of the guide plates situated above the sub-assembly within the guide tube casing, Fig. 10 is a longitudinal section through an expansion tool with remote control means designed for positioning the guide plates of the upper part of the guide tube, Fig. 11 is a front view of the part in front of the tool of Fig. 10, and Fig. 12 is a section along line XII-XII of Fig. 11.

The control assembly guide or guide tube shown in Fig. 1 is intended, as its name indicates, to serve as a guide element for a control rod assembly carrying neutron absorber rods. The control assembly guide of Fig. 1 is thus employed in the nuclear industry and, together with a plurality of other identical guides, comprises part of the internals of a reactor. It serves as a guide element for rods that are lowered into the reactor to slow down nuclear reactions. It is thus essential that the control assembly carrying the neutron absorber rods can descend in the guide tube and be withdrawn in a frictionless manner and without obstruction. Since the control assembly guide is an element some 4 metres long, the "fit" of the guide surfaces of the rods within the guide presents very complex manufacturing problems.

The guide tube of Fig. I comprises a lower part 2 forming a compact guide sub-assembly and an upper part 3 comprising guide plates 4 regularly spaced along the upper part 3. The sub-assembly 2 comprises positioning plates 5 also regularly spaced along the sub-assembly 2, the positioning plates 5 maintaining sheaths 6 placed in a stellate arrangement around the central axis 7 of the control assembly guide 1, each sheath defining two circular guide paths 8, 9 parallel to the axis 7.

The sub-assembly 2 forming the lower part of the control assembly guide 1 and comprising the sheaths 6 previously assembled and welded to the positioning plates 5, as well as the upper part 3 formed by the guide plates 4, are placed within two casing-half members bent by 90 and assembled so as to form a casing 10 of square cross-section. As shown in Fig. 1, the guide plates 4 and the positioning plates 5 have on their square-shaped circumference corresponding to the crosssection of the casing 10, projections or points arranged so as to pass through correspondingly rectangular holes 12 provided in the casing. When the two casing members have been welded to form the casing 10, the sub assembly 2 forming the lower part and the guide plates 4 should be positioned and adjusted within the casing 10 so as to align the axes 13, 14 and 15, 16 of the lowering paths of the rods defined by the sheaths 6 by means of the guide plates 4 before carrying out the operation of welding the projections 11 to the edges of the holes 12 of the casing 10. On account of the length of the control assembly guides 1 (about 4 metres), and the accuracy with which the axes ofthe lowering paths for the rods should be aligned (not more than a few hundredths of a millimetre between the top and bottom of the control assembly guide 1), those skilled in the art will understand the filling and adjustment problems that can arise. Furthermore, everyone knows that each welding point tends to deform the assembly and create distortions and displacements between the various elements constituting the whole control assembly guide. In the description that follows, there will be disclosed a method of production and a tool enabling the required accuracy for the lowering paths of the rods to be obtained, and this despite the contractions and distortions due to the stress effects of the welding.

When the various constituent elements are welded to the casing 10, a crown 17 for securing the control assembly guide to the internals (not shown) of the reactor is placed against the upper guide plate 4. The crown 17 has boreholes 18 designed to receive fixing rods, also not shown. In the same way, a spacing plate 19 placed at the base of the control assembly guide I has fixing means 20, 21 for securement to the internals of the reactor.

The tool shown in Figs. 2, 3, 4, 5, 6 and 7 enables the constituent parts of the subassembly of the control assembly guide to be assembled, the subassembly consisting of sheaths 6 and positioning plates 5 (see Fig.

1). As shown in Fig. 2, a cylindrical jig 25 is mounted so as to be able to turn about its own axis in a frame 26 comprising two main bars 27 having two forks 28 at their ends.

Each fork has a fixed branch 29 carrying two friction rollers 30 and 31, and a removable branch 32 situated on the fork 28 by means of two screws 33 and carrying a friction roller 34. The frame 26 is pivotally mounted on a head 35 bv means of a shaft 36, and the head 35 is secured to the top of four substantially vertical beams 37 and an oblique beam 38 integral with a frame 39 placed on the floor.

The frame 26 must thus turn around the shaft 36 and be brought into any position so that all the constituent parts of the subassembly are accessible to the operator carrying out the welding of the sub-assembly.

As also shown in Fig. 3, the jig 25 consists of two halfjigs 40, each of the two halfjigs having a semi-annular plate 41 at their ends.

When the halves are assembled, the two plates 41 form a circular external circumference which can roll between the friction rollers 30, 31 and 34 mounted on the forks 28 of the frame 26. The jig 25 may thus turn about its own axis.

Stiffening tubes 42, visible in Fig. 2, are provided between the semi-annular plates 41.

Bars 43 of rectangular cross-section are provided between the stiffening tubes, two adjacent bars 44 (see Fig. 3) being placed at the point of separation of the two halves 40 on each side of the halfjigs. Securing screws 45 are provided on each side on the bars 44 of one half, while in the corresponding bars of the other half are provided holes that will accept the screws 45. It will thus be possible to assemble the two halves of the jig by means of ordinary nuts, not shown.

The rectangular bars 43 and 44 have securement tie members 46 that will enable sheaths 47, 48, 49 and 50, disposed at 90 with respect to one another, to be held in place. As shown in Fig. 4, the sub-assembly of the control assembly guide also comprises four sheaths 51, 52, 53 and 54 disposed at an angle of 454 to the sheaths 47, 48, 49 and 50.

These four latter sheaths 51, 52, 53 and 54 are held together by means of independent clamp means, as described hereinafter. The assembly formed by the eight sheaths 47 to 54 is placed within the positioning plates 55, also shown in Fig. 3, the positioning plates 55 being placed opposite ribs 56. The internal edges of the ribs 56 are configured to engage the projections or points 57 of the positioning plates when the latter are pressed against the ribs as subsequently described. It should also be noted that each of the sheaths 47 to 54 defines two slide paths, that is to say two neutron absorber rods may descent in each of the sheaths. As also shown in Fig. 1 and in Fig. 4, the description of which follows hereinafter, the sheaths 51, 52, 53 and 54 have a part 58 cut off at right angles, which slightly shortens the path closest to the axis of these four sheaths. When the eight sheaths 47 to 54 are introduced into the positioning plates and held in place, the housing is closed by assembling the two half-jigs 40. If the assembly is examined from one of the ends of the jig 25, the configuration shown in Fig. 4 will be seen, with the internal truncation of a positioning plate 55, the sheaths 47, 48, 49 and 50 held by the clamp means 46, and the sheaths 51, 52, 53 and 54 with their truncated parts 58. In order to tension the sheaths against the interior circumference of the positioning plates 55, expansion tools 61 are introduced opposite each of the plates 55 within the sub-assembly represented by the sheaths and the positioning plates.

An expansion tool 61 is shown in detail in Figs. 5 and 6. The expansion tool 61 of Figs.

5 and 6 is a relatively simple apparatus enabling the eight sheaths 47 to 54 to be tensioned from within against the internal edge of the positioning plates 55. The mandrel 61 thus enables forces to be exerted from a centre point along eight directions represented in Fig. 1 by arrows 62, 63, 64, 65, 66, 67, 68 and 69. The stresses are exerted in the directions 62, 64, 66 and 68 from faces 70, 71, 72 and 73, and stresses along the directions 63, 65, 67 and 69 from faces 74, 75, 76 and 77.

Consequently, the forces exerted on the faces 70 to 73 can be applied at points closer to the centre of the tool than the forces exerted by the faces 74 to 77. If Fig. 4 is examined, it can be seen that the faces 70, 71, 72 and 73, and 74, 75, 76 and 77 respectively of the tool 61 are designed so as to come into contact with the sheaths 53, 52, 51 and 54, and 48, 47, 50 and 49 respectively.

The expansion mandrel 61 comprises a housing 78 having a central bore 79 through which passes a rod 80 having a threaded end 81 and a tightening nut 82 at the other end. A disc 83 whose surface adjacent to the housing 18 has a rounded part 84 is screwed on to the threaded end 81 of the rod 80. At the other end of the rod 80, a second disc 85 of smaller diameter than the disc 84 and having a central bore 86 is traversed by said rod 80, the disc 85 having a shoulder 87 against which the nut 82 bears. The surface of the disc 85 adjacent to the housing 78 has, like the corresponding surface of the disc 83, a rounded part 88. The circumference of the housing 78 has slots defining the faces 70; 71, 72, 73 and 74, 75, 76, 77, which engage with the sheaths 47 to 54 (Fig. 4).

A milled cavity shown at 90 is machined along an oblique axis 91 between an end of the housing 18 and each of the faces 70, 71, 72 and 73 so as to open onto the respective faces. The milled cavities shown at 90 terminate before completely passing through the housing 78, so as to form stop surfaces 92 that will serve as a bearing for springs 93 exerting a force on fingers 94 introduced into the bores 90. The fingers 94 have rounded heads 95 to engage the rounded part 88 of the disc 85, and bevelled lateral surfaces 96 parallel to the faces 70, 71, 72 and 73 of each slot.

In the same way, a milled cavity 97 is machined along an oblique axis 98 from the other end of the housing 78 to each of the surfaces 74, 75, 76 and 77. The milled cavities 97 again terminate before passing completely through the housing 78 so as to form stop surfaces 99 that will act as a bearing for springs 100 exerting a force against fingers 101 introduced into the cavities 97, the fingers 101 being identical to the fingers 94 and having rounded heads 102 to engage the rounded part 84 of the disc 83, and bevelled lateral surfaces 103 parallel to the surfaces 74, 75, 76 and 77.

The tool that has just been described is used as follows: Before introducing the tool into the subassembly shown in Figs. 1 to 4, the nut 82 will be turned in an anti-clockwise direction to cause the bevelled surfaces 96 and 103 to enter the housing 78. A positioning and control rod (not shown) is inserted in the nut 82 and the tool 61 is then positioned by means of the said rod. When the tool 61 has been positioned within the subassembly and corresponding to the height of a positioning plate 55, the sheaths 47 to 54 being adjacent to the faces 70 to 77, the nut 82 is turned in a clockwise direction with the aid of the rod, not shown. The discs 83 and 85 come closer to the housing 78 and press the fingers 94 and 101 against the action of the springs 93 and 100, thereby causing the lateral advance of the bevelled surfaces 96 and 103, which, in their turn, stress the eight sheaths 47 to 54 (Fig. 4) by pressing them against the slots in the positioning plate 55. The mandrel 61 allows the fingers to slide to some extent relative to the rounded surfaces 84 and 88 of the discs 83 and 85, this being permitted by the degree of play in the whole assembly.

This sliding enables differences between two bearing surfaces at 90 to be compensated.

A tool 61 is placed within the subassembly formed by the sheaths and the positioning plates, opposite each of the positioning plates 55. As shown in Fig. 7, the sheaths 47, 48, 49 and 50 are maintained within the housing in clamp means 46 formed by tie members. The ends of the sheaths 51, 52, 53 and 54 are held by means of two bars 105 assembled by means of two screws 106. The sub-assembly formed by the sheaths 47 to 54 and by the positioned plates 55 is thus held within the housing 25 by the clamp means 46, the clamp means 105, 106, the ribs 56 serving as a bearing for the positioning plates 55, and the mandrels 61 which stress the sub-assembly from within by pressing it against the jig 25.

The workman carrying out the welding may then make his welds at each intersection of a sheath and its slot in accordance with a suitable welding programme designed so as to prevent the effects of stress in the subassembly. The assembly formed by the jig 25, which turns about its own axis (see Fig. 2), and the frame 26 which turns about the shaft 36, enables the operator to position the subassembly and its housing so that each point is easily accessible.

Figs. 8 to 12 show the tool used to carry out the final assembly of the control assembly guide or guide tube, this final assembly consisting of positioning within the two casing members the sub-assembly previously assembled and welded as described with regard to Figs. 2 and 7 and the guide plates forming the upper part of the control assembly guide. In order to carry out this final assembly, a jig 110 formed from two jig halves 111 and 112 is provided, in the same manner as for the sub-assembly, and the end of the two jig halves Ill and 112 forming the jig 110 has two semi-annular plates 113, 114 which, when assembled, have a circular configuration able to roll on the friction rollers 115 of a carriage 116 in contact with the ground through rollers 117. Stiffening tubes 118 are welded between the semiannular plate ends 113, 114, and ribs 119 are placed perpendicular to the axis along the stiffening tubes 118. A rib 120 of circular circumference is provided substantially in the centre of the jig 110, the said rib 120 having the same internal circumference as the other ribs 119. The ribs 119 and 120 are intended to act as a support for positioning and guide plates, in an identical manner to the support provided by the ribs 56 of the jig 25 (see Figs. 2 to 4). Rectangular-shaped bars 121 and 122 are provided at the connection point between the two jig halves 111 and 112 respectively. These bars 121 and 122 comprise fixing means for the two jig halves 111 and 112, these means not being shown in Fig.

8 however.

In order to cary out the assembly of the guide tube, the jig half 112 is removed and a casing member is placed in the jig half 111, the guide plates 124 with their projections 125 engaging with the corresponding openings in the casing member as well as with the subassembly previously assembled and welded as described in connection with Figs.

2 to 7. Two bars 126 are then introduced into slits opposite the guide plates 124, and the second casing member, not shown in Fig. 9, is then positioned. It is then sufficient to replace the jig half 112 and secured it by means of the screws 127 shown in Fig. 9.

When the guide plates 124 hsve been positioned, the precaution is taken of arranging them opposite the ribs 119, 120 so that these ribs will serve as a bearing for the projections 125 on the circumference of the plates 124 when the latter are stressed before the welding.

The guide plates 124 are stressed by means of an expander 128 shown in detail in Figs. 9, 10, 11 and 12.

The expander 128 comprises four jaw members 129 arranged at 90 with respect to one another around a cone 130. A screw 131 having a threaded part 132 pushes the bearing surfaces 129 against the cone to expand the jaw members of means of a member or piece 133 when it is turned in a clockwise direction. The screw 131 has, at its end opposite the threaded part 132, a nut 134 that bears against a collar piece 135 within the cone 130. The rear end of the cone 130 has a chamber 136 designed to receive a drive device 137 having at its end a rod 138 that comes into engagement with the nut 134.

The drive device 137 has a pin 139 introduced into the chamber 136 by means of two grooves 140 provided in the rear part of the cone 130 (see Fig. 12). The drive device 137 is secured to a rod 141 which enables the expander 128 to be introduced into the control assembly guide and to control the jaw members 129. The expander 128 is guided by a member 142 placed on the rod and shown in Fig. 9. The member 142 is mounted so as to be able to turn freely on a cylindrical sleeve 143 (see Fig. 10) integral with the drive device 137 and secured to the rod 141 by means of a pin 144.

Those skilled in the art will easily understand that by means of the rod 141 and the member 142 (Fig. 9), which slides on the bars 126, it is possible to position an expander 128 within each of the guide plates 124 so as to stress the latter in order to press the projections 125 against the ribs 119, 120 of the housing 110.

When the two jig halves 111 and 112 are closed and all the guide plates are stressed and their projections urged against the ribs of the housing 110, the operator may then weld the plates to the casing members by making welds between each projection 125 of the plates 124 and its corresponding opening on the casing in accordance with a satisfactory welding programme designed so as to avoid the effects of stress in the control assembly guide. It is clear to those skilled in the art that during the final assembly the sub-assembly will also be stressed by means of the expanders 128 in the housing 110, the welding of the sub-assembly and the casing members being effected in the same manner and according to the same programme developed for welding the guide plates to the casing members.

WHAT WE CLAIM IS:- 1. A method for producing a control assembly guide for nuclear reactors and comprising a lower part consisting of a subassembly defined by sheaths placed in a stellate arrangement around the axis of the control assembly guide and parallel to said axis, the sheaths being held together by positioning plates or boards, and an upper part consisting of guide plates defining, together with the sheaths, aligned paths for the lowering of neutron absorber rods carried by a control assembly, the upper and lower parts of the control assembly guide being retained within a casing formed by two casing-half members bent longitudinally by 90 and assembled, the casing having over its circumference at the site of each positioning and guide plate openings designed to accommodate with clearance projections provided on the circumference of the positioning and gu

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

125 on the circumference of the plates 124 when the latter are stressed before the welding.

The guide plates 124 are stressed by means of an expander 128 shown in detail in Figs. 9, 10, 11 and 12.

The expander 128 comprises four jaw members 129 arranged at 90 with respect to one another around a cone 130. A screw 131 having a threaded part 132 pushes the bearing surfaces 129 against the cone to expand the jaw members of means of a member or piece 133 when it is turned in a clockwise direction. The screw 131 has, at its end opposite the threaded part 132, a nut 134 that bears against a collar piece 135 within the cone 130. The rear end of the cone 130 has a chamber 136 designed to receive a drive device 137 having at its end a rod 138 that comes into engagement with the nut 134.

The drive device 137 has a pin 139 introduced into the chamber 136 by means of two grooves 140 provided in the rear part of the cone 130 (see Fig. 12). The drive device 137 is secured to a rod 141 which enables the expander 128 to be introduced into the control assembly guide and to control the jaw members 129. The expander 128 is guided by a member 142 placed on the rod and shown in Fig. 9. The member 142 is mounted so as to be able to turn freely on a cylindrical sleeve 143 (see Fig. 10) integral with the drive device 137 and secured to the rod 141 by means of a pin 144.

Those skilled in the art will easily understand that by means of the rod 141 and the member 142 (Fig. 9), which slides on the bars 126, it is possible to position an expander 128 within each of the guide plates 124 so as to stress the latter in order to press the projections 125 against the ribs 119, 120 of the housing 110.

When the two jig halves 111 and 112 are closed and all the guide plates are stressed and their projections urged against the ribs of the housing 110, the operator may then weld the plates to the casing members by making welds between each projection 125 of the plates 124 and its corresponding opening on the casing in accordance with a satisfactory welding programme designed so as to avoid the effects of stress in the control assembly guide. It is clear to those skilled in the art that during the final assembly the sub-assembly will also be stressed by means of the expanders 128 in the housing 110, the welding of the sub-assembly and the casing members being effected in the same manner and according to the same programme developed for welding the guide plates to the casing members.

WHAT WE CLAIM IS:- 1. A method for producing a control assembly guide for nuclear reactors and comprising a lower part consisting of a subassembly defined by sheaths placed in a stellate arrangement around the axis of the control assembly guide and parallel to said axis, the sheaths being held together by positioning plates or boards, and an upper part consisting of guide plates defining, together with the sheaths, aligned paths for the lowering of neutron absorber rods carried by a control assembly, the upper and lower parts of the control assembly guide being retained within a casing formed by two casing-half members bent longitudinally by 90 and assembled, the casing having over its circumference at the site of each positioning and guide plate openings designed to accommodate with clearance projections provided on the circumference of the positioning and guide plates, the method comprising placing the casing members enclosing a previously assembled and welded subassembly, together with the guide plates, within a jig formed by two jig halves and having ribs placed opposite the positioning and guide plates and whose interior edges are configured to engage the projections provided on the circumference of the positioning and guide plates so as to act as a support therefor, applying a stress to the plates outwardly away from the axis so as to press the projections against the ribs, and welding the plates to the casing members by making a weld between each projection on the plate and its corresponding opening in the casing.
2. A method according to Claim 1, wherein the sub-assembly is fabricated by placing positioning plates in a cylindrical jig formed by two jig halves and having ribs spaced apart and perpendicular to the axis of the housing, the positioning plates being placed opposite the ribs whose interior edges are configured to engage the projections on the circumference of the plates so as to serve as a support therefor, introducing the sheaths into slots provided for this purpose in the positioning plates and maintaining the sheaths in their appropriate positions with the aid of clamping means integral with the housing and/or with the aid of autonomous clamping means assembling the sheaths two by two, introducing expansion tools within the sub-assembly thus formed at the location of each positioning plate so as to press each sheath against its corresponding slot on the said positioning plate, the latter being retained by the interior edge of each rib, and welding each intersection of a sheath and its slot in accordance with a satisfactory welding programme designed so as to prevent the effects of stress in the sub-assembly.
3. A tool for carrying out the method according to Claim 1, which comprises a cylindrical jig for assembling the sub-assembly and the upper part of the control assembly guide between the two half-mem

bers forming the casing, the jig comprising two assembled jig halves, the jig being rotatably mounted about its axis in a support and having ribs made in two parts, each integral with one of the jig halves, the said ribs being placed one after the other perpendicular to the axis and along the jig, and each having a central hollowed-out part whose edge is configured to engage the projections on the circumference of the positioning and guide plates of the control assembly guide to be assembled.
4. A tool according to Claim 3, wherein each jig half comprises two longitudinal stiffening tubes integral with a semi-annular end plate, the assembled end plates having a circular configuration enabling the jig to turn on rollers secured to a frame.
5. A tool according to Claim 3, comprising a plurality of expanders for stressing the positioning and guide plates so as to press their projections against the edge of the ribs of the housing.
6. A tool according to Claim 5, wherein each expander has four jaw members expandable by engagement with a cone and operating in directions at 90 with respect to one another, expansion of the jaws being controlled by means of a rod sufficiently long to enable the expander to be introduced into the interior of the control assembly guide placed in the housing.
7. A tool according to Claim 3 further comprising a second cylindrical jig for assembling the sub-assembly forming the lower part of the control assembly guide, the jig comprising two assembled jig halves, and being mounted for rotation around its axis in a roller support, the support being pivotally fixed to a shaft integral with a base, the jig having ribs made in two parts, each being integral with one of the jib halves, and the ribs being placed after one another perpendicular to the axis along the jig and each having a hollowed-out central part whose edge is configured to engage the projections on the circumference to the positioning plates of the sheaths of the lower subassembly.
8. A tool according to claim 7, wherein each jig half comprises two longitudinal stiffening tubes integral with a semi-annular end plate, the assembled end plates having a circular configuration that enables the jig to turn between the rollers fixed to the frame.
9. A tool according to claim 8, wherein longitudinal bars are inserted between the stiffening tubes and parallel thereto, two adjacent bars being provided at the point of separation of the two jig halves.
10. A tool according to claim 7, wherein the jig carries securement means for holding the sheaths of the sub-assembly.
11. A tool according to claim 10, wherein the securement means are clamp means formed by two tie members tightened by means of a screw.
12. A tool according to claim 7, further comprising expansion tools each having a central body provided with a plurality of oblique milled cavities regularly distributed around the axis of the body from opposite ends thereof and opening into lateral faces of the central body, fingers in the milled cavities, springs, biasing the fingers against a respective one of two discs disposed one at each end of the central body and connected by a threaded rod carrying a tightening nut, the tightening of the discs against the body causing the fingers to project laterally so as to bear against the sheaths and press them against slots made within the positioning plates.
13. A tool according to claim 12, wherein the projecting lateral surface of each finger is a flat bevelled surface corresponding to the configuration of the polygonal line traversed by following the bearing surface of all the sheaths placed in a stellate arrangement around the axis of the sub-assembly of the control assembly guide.
14. A tool according to claim 12, including a tightening rod to engage with the nut and position the mandrel.
15. A control assembly guide or guide tube obtained by carrying out the method according to claim 1 or 2.
16. A method for producing a control assembly guide for nuclear reactors substantially as hereinbefore described with reference to the accompanying drawings.
17. A jig tool for producing a control assembly guide for nuclear reactors, substantially as hereinbefore described with reference to the accompanying drawings.