FR2596564A1 - Method of installing rails inside steam generators for facilitating remote-control operations without irradiation of personnel - Google Patents

Abstract

Definitive fitting of a rail employed for supporting a remote-control manipulator arm, and method of implementing it semiautomatically. The rail component 901 comprises a lug 902 ending in a tubular boss 903 of the same diameter as the tubular part 904 of the intermediate fastening 905, automatically welded beforehand onto a bearing machined on the bowl. A bore 906 on the lug is used to secure the welding gun thereto. Internal butt-joint welding is performed by manually positioning a welding gun 907. Its nozzle 908, carrying the torch 909, acts as a centering tool. The gun is integrally attached to the rail by a cam 910 passing through the bore 906 and clamping on the lug 902.

Description

METHOD OF INSTALLING A RAIL INSIDE STEAM GENERATORS
AND ATTACHMENTS FOR THE IMPLEMENTATION OF THE PROCESS
The steam generators (steam generators) of nuclear power plants require numerous control and maintenance operations, to maintain them in service, as well as to prolong their lifespan. These interventions are carried out in an ionizing and contaminating medium. They are one of the main factors in the irradiation of personnel.

Currently, among the sixty different operations carried out inside the "bowls" of the steam generators, only a few are carried out at industrial rates, rates which must be respected as soon as one must intervene on a large number tubes, for a very short time, so that these operations have an economic sense.

These rates imply advanced automation in terms of remote manipulators and tools, high speed of movement and high precision.

A remote manipulator that meets these requirements has been described in previous patents (cf. PV 84.01588: remote manipulator for steam generators in nuclear power plants): it has an arm rotating around a rotating base, and which rolls at its end on a rail arranged at the periphery of the bowl of the SG. The rail is temporarily installed inside the SG container, manually by an operator (jumper) entering the container; then the manipulator is installed in turn.

It is very advantageous for interventions that the rail is permanently installed in the bowl, the arm and its base can then be mounted from outside the bowl.

If this presents no particular difficulty during manufacturing in
factory; however, on site and on contaminated steam generators, this operation is not
not easy. I1 should proceed to a grinding of the surface of the bowl,
make a metrology, bring the rail elements, position them with
precision and point them by welding, then weld without deforming the rail
with an acceptable weld quality, and to carry out all
due diligence.

In an irradiating and inaccessible confinement it is difficult work
which, if done manually, would be prohibitively expensive in debit of
dose (irradiation) and duration of execution.

The present invention relates to a design for attaching a rail to the
bowl and a semi-automatic embodiment, thanks to which this work will be
done ~ quickly and with minimal staff radiation. It also relates to an original mechanical arrangement of the rail and of the adapted intervention manipulator.

Figure 1 shows the water boots of the Steam Generators (SGS) of
pressurized water reactors.

The GV water boot is a half sphere formed by two separate 901 chambers
by a vertical plate 904; these rooms are overlooked by the plate
tubular (PT) 902 from where the exchanger tubes 903 start and end
montas hairpin. Each chamber (bowl) has two openings: the hole
of access pipe 905 of diameter 400mm. approximately, and the tubing 906 of the pri circuit.

Figure 2 shows schematically the welding operation of the type of fastener designed for
support the elements of the final rail. This operation, as well as the
grinding and the metrology which precedes it, is carried out starting from a
co-pairing of tools on board the aforementioned remote manipulator.

Recall that the remote manipulator, manually installed in the bowl of the GV,
consists of an arm 910 sliding freely on a rotating base 911 and
running in support on a peripheral rail 912. The base and the rail are
fixed to the tube plate by expansive pins 913 engaged in the
tubes. On the arm circulates a 914 trolley which can receive various tools:
- Flat circular expectations are first ground in cladding
radially at the center of the GV, with reference to the network
tubular plate.

- This operation is followed by a metrology intended to control these positions, their depth and orientation, as well as the profile of the bowl, for the preparation of the rail elements and its attachments.

- Finally, an orbital welding head 915 is mounted on the carriage for pointing and then welding the intermediate fasteners 920 (fig.2).

Figure 3 details the type of fastener that is tele-positioned on the bowl in the ground locations, and welded automatically. On these fasteners are then fixed the rail elements.

The intermediate clip 920 comprises a tubular part 921 with a central housing 922, terminated by a flange 923 which is welded to the ground part.

The orbital welding head 915 is equipped with a central gripping finger 916 which engages in the housing 922 of the fastener, abutting on the tubular part 921. The torch 917, bent at 450, is thus in position by compared to flange 923 for its lap welding on the ground expectation of the bowl.

On the trolley of the manipulator is mounted a plate 924 articulated around a vertical axis 925, carrying a slide plate 926 which supports the welding head 915, and the advance of which is controlled by a jack 927.

The articulation 925 makes it possible to orient the tool radially with respect to the center of the SG, the jack 927 ensuring docking on the cladding of the bowl.

This device, which is applicable to grinding and metrology, also makes it possible to load the fasteners 920 on the finger 916 of the welding head from the outside of the bowl.

FIG. 4 represents the position on the bowl of the fasteners 920 and the arrangement of the rail elements which are attached thereto, relative to the manhole and to the junction of the pipe of the primary circuit.

The rail is composed of five elements 930, each being supported by three fasteners 920. The raceway thus created is interrupted above the manhole 905 to allow the mounting of a manipulator.

Each rail element 930 is manually docked on its fasteners using two temporary fasteners 935, which allow free docking on the central fastener.

Figure 5 shows the provisional method of fixing a rail element on one of the end clips; and Figure 6 the automatic welding of this element on the central attachment.

The rail element 930 comprises a lug 931 terminated by a tubular boss 932 of the same diameter and the same thickness as the tubular part 921 of the clip 920. On the lug is formed a bore 933 serving as a positioning reference for fixing temporary and welding gun.

The temporary fixing 935 (fig. 5) comprises an expandable finger 936 passing through the tubular boss 932 of the rail, which is positioned in the central housing 922 of the clip 920. Its expansion is controlled manually by the lever 937. A finger 938 , integral with the body of the fixing 935, engages in the bore 933 of the rail.

Welding by internal splicing of the tubular boss 932 and the tubular part 921 of the fastener is carried out by manually positioning a welding gun 940 (fiv.6). Its nose 941, carrying the torch 942, acts as a centering device. The gun is secured to the rail by a cam 943 passing through the bore 933, by manual clamping with the lever 944.

The rail element being welded to the central fastener, the temporary fixings are removed to make the additional butt welds.

Figure 7 shows the installation of the intervention remote manipulator carrying with it a removable complementary rail element.

This remote manipulator is identical in principle of operation to that mentioned above. I1 comprises an arm 910 carrying a carriage 914, sliding freely on a rotary base 911 and circulating bearing on the rail 930.

Only the drive system on the rail differs, to allow it to embed the removable element 945 of the rail which completes the raceway above the manhole.

The base 911 can be previously positioned from outside the bowl, the arm is introduced to come into abutment there before being raised and held by the removable element 945 clamped on the adjacent rail elements.

Figure 8 shows the attachment of this removable rail element joining between the rail elements permanently welded to the bowl.

This removable element 945 is equipped with two fixing fingers 946 which engage in two housings 947 arranged in the neighboring rails 930. The locking and unlocking device is ensured by a crown 948 machined in sawtooth, mounted madly on the fingers 946, coming to bear on lugs 948 located in the housings 947 of the rails 930. By simple push, the ring turns to escape the lugs, and present its machined bearing surfaces which come to bear. The reverse operation frees the fingers.

Claims (1)

CLAIMS: Claim 1: The present invention relates to adjustments to be made on site to contaminated steam generators (steam generators), so as to facilitate subsequent maintenance and to reduce the doses of radiation withdrawn by the personnel; it applies to the final installation of a rail formed of elements juxtaposed inside the bowl of the SG, rail used for the support of the remote handling arm; it relates to a process which is characterized in that an intervention sequence is carried out comprising the following main stages: a) grinding of the stainless steel cover of baleen to create flat areas on which will be welded spacers, b) metrology specifies the location of these zones in relation to the tube plate, c) automatic positioning and welding of the intermediate fasteners, d) positioning and hanging of each rail element by temporary mechanisms which are fixed on two of these fasteners, e) welding of each rail element on their central attachment, depositing temporary positioning mechanisms and end of welding on the intermediate attachments thus released, f) control. Claim 2: Intermediate clip 920 for implementing the method according to claim 1, characterized in that it comprises a tubular part 921 with a central housing 922 by which it is carried by the welder 915, and in which the latter is centered; and a flange 923 which is welded to the ground surface. Claim 3: Fastener 920 according to claim 2 characterized in that it comprises a central housing 922 in which is positioned an expandable pin 936 of a provisional fixing device 935 of the rail elements to be welded to the fastener by means of a finger 938 penetrating into the bore of the rail 930. Claim 4: Fastener according to claims 2 and 3, characterized in that it comprises a tube 921 of the same diameter as that 932 carried by a boss of the rail element; by which said rail elements 930 are welded by butt jointing, from the inside, with a welding gun 940. Claim 5: Application of the method according to claim 1, to the final installation by welding of a rail composed of juxtaposed elements 930, forming two continuous paths separated by an interval without rail located above the manhole of the GV. And where this gap without rail is filled during the interventions, by a removable rail element 945 which can be brought by a beam manipulator.