Transverse holding device for a steam generator of a pressurized water nuclear reactor, and for its adjustment

An adjusting and positioning assembly for a bearing element (55), constituted by a nut (52) carried by a base plate, (40) fixed on a wall of a concrete structure in which the component is arranged, and a screw-jack (54) engaged with and blockable with respect to the nut (52). The transverse holding of the lower part of a steam generator pressurized-water nuclear reactor is provided by an assembly of supports each constituted by an adjustable transverse holding device (24) according to the invention. The position of the bearing element is adjusted in such a manner as to maintain play allowing movement of the steam generator as a result of thermal effects or in the event of an earthquake.

FIELD OF THE INVENTION 
The invention relates to a transverse holding device for a component of 
large dimensions of a nuclear reactor, such as a steam generator, and to a 
method for adjusting a holding assembly of the component. 
BACKGROUND OF THE INVENTION 
Steam generators of nuclear reactors cooled by pressurized water are 
components of large dimensions comprising an enclosure of general 
cylindrical shape, placed with its axis vertical, in a lateral arrangement 
with respect to the vessel of the nuclear reactor enclosing the core, 
within a stationary concrete structure comprising vertical walls, called a 
bunker. 
Each of the steam generators is placed on a loop of the primary circuit of 
the nuclear reactor constituted by pipelines of large diameter connecting 
the vessel to the primary part of the steam generator. One of these 
pipelines, called hot leg, ensures a direct connection between the vessel 
and the inlet part to the water box of the steam generator ensuring the 
distribution of pressurized water for cooling the reactor in the tubes of 
the bundle of the steam generator, which tubes are contained within the 
enclosure. 
A second pipeline or intermediate leg connects the outlet part of the water 
box of the steam generator to a primary pump ensuring the circulation of 
the cooling water in the loop of the primary circuit. 
The primary pump is connected to the vessel of the steam generator, in such 
a manner as to return the cooled cooling water into the steam generator 
within the vessel, via a third pipeline, called a cold leg. 
The steam generator rests, within the concrete bunker, on vertically 
articulated support columns connected at their lower part to support 
plates embedded in a concrete slab constituting the bottom of the bunker. 
Moreover, the steam generator is held within the bunker by an assembly of 
tie rods and dampers interposed between the vertical walls of the bunker 
and a ring for holding the wrapper of the steam generator situated in the 
vicinity of the middle part of the steam generator, between its lower end 
constituting the wall of the water box and its upper end from where the 
steam produced within the generator exits. 
The steam generator also comprises transverse holding devices or supports 
ensuring the guiding of the steam generator and holding it in the event of 
an accident. These devices or supports are arranged in the vicinity of the 
primary bottom of the steam generator constituting the wall of the water 
box. 
The transverse holding assembly of the steam generator generally comprises 
two lateral supports placed in symmetric positions with respect to the 
vertical plane containing the axis of the hot leg and a front support of 
which the contact zone with the steam generator is situated in the 
vicinity of the vertical plane containing the axis of the hot leg and in 
an opposite position with respect to the hot leg connected to the water 
box. 
Holding supports for the Steam generator comprise a bearing element 
intended to come into contact with or into the vicinity of a bearing 
surface of the steam generator which can be constituted either by the 
primary bottom of the generator, i.e. the external surface of the water 
box, or by the outer lateral surface of the tube plate upon which the 
bundle of tubes for the steam generator is fixed and which provides the 
junction between the water box and the wrapper of the steam generator, or 
alternatively by a welded ring surrounding the lower part of the steam 
generator. 
The holding devices each comprise a base plate anchored in the concrete of 
one of the walls of the bunker to which the bearing element of the support 
is connected, which can be constituted by a second base plate fixed on the 
first in a parallel arrangement with a certain spacing. 
Generally, an energy absorbing system is interposed between the two base 
plates, in such a manner as to damp out impacts or energy connected with 
movement of the steam generator in the event of an accident. 
These energy absorbers can be constituted by "cushions" made of stainless 
steel wires. 
In the case of the front support, the energy absorption system is generally 
constituted by several rows of steel bars arranged parallel to each other 
in each of the rows and in arrangements perpendicular from one row to the 
next and staggered, in such a manner as to absorb the energy by 
deformation or bending, in the event of an accidental movement of the 
steam generator in the direction of the corresponding wall of the bunker. 
When the steam generator is installed in the bunker, the supports which 
ensure transverse holding of its lower part must be adjusted, in such a 
manner that a perfectly defined play remains between the bearing element 
of each of the supports and the corresponding bearing surface of the steam 
generator. 
The play is defined as a function of the foreseeable movements of the steam 
generator, in normal operation and during an accident due to a cause 
internal to the nuclear reactor, for example due to rupture of a primary 
pipe or to steam or due to a cause which is totally external to the 
nuclear reactor, such as an earthquake. 
The play can be variable as a function of the supports, in that the 
movements of the steam generator are not identical in all directions. 
The bearing element of the front support is thus generally arranged at a 
significant distance, of the order of 50 mm from the surface of the steam 
generator, the movements of the steam generator in the axis of the hot leg 
having a relatively significant amplitude. Due to this significant play, 
the front supports do not come into contact with the steam generator and 
do not participate in holding the steam generator in the event of an 
earthquake. 
The lateral supports arranged on the side of the plane of symmetry of the 
hot leg on which are situated the intermediate leg and the primary 
motor-driven pump group must be arranged with zero play with respect to 
the bearing surface of the steam generator. Thus, the guiding of the steam 
generator with respect to this reference is assured, both during normal 
operation of the steam generator and in the event of an accident. 
The other lateral supports situated in a symmetric position with respect to 
an axial plane of the hot leg comprise bearing elements arranged with a 
certain play with respect to the surface of the steam generator. 
The adjustment of the supports constituting the shimming operation of the 
steam generator must be carried out during the mounting of any new 
generator in a nuclear power station, whether it concerns a generator 
intended for a new power station before it is put into service or a 
replacement steam generator intended for a nuclear reactor which has 
operated for a longer or shorter period of time. 
The adjustment of the play of the various supports is carried out by fixing 
shims of appropriate thickness on an external base plate of the support 
directed towards the steam generator and connected to the fixed base plate 
anchored in the concrete of the wall of the bunker. The external base 
plate and the shims in this case constitute the bearing element of the 
support intended to come into contact with the bearing surface of the 
steam generator. 
The shimming of the steam generator is carried out in several phases. 
During hot testing of the nuclear reactor, the primary fluid being at 155 
bar and 286.degree. C. during these tests, which corresponds to the 
nominal operational conditions of the reactor, the lower lateral and front 
supports of the steam generator are installed and preadjusted, and the 
play between the steam generator and the external base plates of the 
supports which do not comprise any shims in this phase is measured. 
The measured values of the play during the hot testing of the steam 
generator are communicated to the research department of the constructor 
of the nuclear reactor. 
The necessary shim thicknesses are calculated as a function of the play 
measured and the movements of thermal origin of the steam generator which 
are calculated. 
Prefabricated shims are labelled as a function of their destination and 
equipped with lifting means to enable them to be handled. 
The shims are then pierced, machined to their final dimensions, checked and 
delivered to the site of the nuclear reactor. The shims which are 
identified on site are installed and fixed either by screws, or by 
welding, in the bunker of the steam generator, the primary circuit being 
at a low temperature. 
It is necessary to carry out the operations described above on an assembly 
of about thirty shims, in order to provide the shimming of a steam 
generator, each of the lateral supports and the front support requiring 
the presence of ten shims to ensure its adjustment. 
These operations are thus long and complex, which has drawbacks, especially 
in replacing a worn steam generator. In fact, in this case, it is 
necessary to reduce to a minimum the amount of time needed to replace the 
steam generator and the total shut-down time of the nuclear reactor. 
SUMMARY OF THE INVENTION 
An object of the invention is thus to propose a transverse holding device 
for a component of large dimensions of a nuclear reactor, such as a steam 
generator of a pressurized-water nuclear reactor, arranged in a stationary 
concrete structure having vertical walls surrounding the component, 
comprising at least one base plate fixed on one wall of the concrete 
structure and a bearing element carried by the base plate and arranged in 
contact with or in the vicinity of a bearing surface of the component, 
this device allowing the adjustment of the bearing element without using 
shims of adjusted dimensions. 
To this end, the device comprises an assembly for adjusting and positioning 
the bearing element constituted by: 
a nut carried by the stationary base plate passed through along its axis by 
a tapped orifice, 
a screw-jack engaged with the nut and arranged in the axial direction, and 
a means for blocking the screw with respect to the nut, in a specified 
position of the screw in the axial direction, 
the bearing element being constituted by a pad carried by one end of the 
screw directed towards the bearing surface of the component. 
The invention also relates to a transverse holding assembly for a component 
of large dimensions of a nuclear reactor and to its method of adjustment.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a steam generator of a pressurized-water nuclear reactor 1, of 
generally cylindrical form and arranged within a bunker 2 comprising 
lateral walls and constituting a part of the building of the nuclear 
reactor, which part is placed laterally with respect to the vessel well of 
the reactor in which the vessel enclosing the core constituted by fuel 
assemblies is arranged. 
The steam generator 1 comprises an enclosure constituted by an assembly of 
cylindrical shells and of a frustoconical shell which are butt welded, the 
enclosure being closed at its ends by two domed bottoms 3 and 4 of 
substantially hemispherical shape. 
The lower domed bottom 3 constitutes the water box of the steam generator, 
through the intermediary of which the pressurized cooling water of the 
nuclear reactor is distributed and caused to circulate within the tubes of 
the bundle arranged within the cylindrical enclosure; this water is then 
recovered after having circulated in the tubes of the bundle. 
The water box 3 is connected to the cylindrical wrapper of the steam 
generator, through the intermediary of a tube plate of great thickness in 
which the tubes of the bundle are fixed by their ends. 
In the region of the tube plate, a welded ring 5 is fixed in a coaxial 
arrangement around the outer surface of the steam generator 1. The outer 
peripheral surface of the welded ring 5 constitutes the bearing surface of 
the transverse holding devices such as 6 and 7 of the lower part of the 
steam generator. 
The water box 3 of the steam generator is directly connected to the vessel 
of the reactor, by a pipeline 8 constituting the hot leg of the loop of 
the primary circuit on which the steam generator 1 is arranged. The 
pressurized water for cooling the reactor penetrates into the water box 3 
via the hot leg 8, after having been heated in contact with the core 
assemblies, within the vessel. 
The water box 3 is also connected to a pipeline 10 constituting the 
intermediary branch of the loop of the primary circuit on which is placed 
the primary pump (not shown) for circulating the cooling fluid. 
The steam generator 1 rests on articulated support columns 11, through 
intermediary of supporting clevises bolted on a ring 5 securely attached 
to the tube plate. 
The articulated support columns 11 arranged vertically are each connected 
at their lower part to a bearing plate 12 embedded into a slab 13 
constituting the bottom of the bunker 2 resting on the base slab of the 
nuclear reactor. 
The steam generator 1 is held transversely, i.e., in horizontal directions, 
by holding assemblies 15 comprising tie rods and dampers connected to a 
welded ring 16 fixed around the enclosure of the steam generator. 
The transverse holding of the steam generator is provided at its lower 
part, by transverse holding devices or supports 6 and 7 which are fixed on 
the vertical walls of the bunker 2, in the region of the ring 5. 
The support 6 or front support comprises a bearing part 6a placed opposite 
a zone of the bearing surface of the ring 5 arranged in the vicinity of a 
vertical plane containing the axis of the hot leg 8 and in a location 
situated opposite the hot leg 8, with respect to the axis of the steam 
generator. 
Lateral supports such as the support 7 are arranged on either side of the 
vertical plane containing the axis of the hot leg 8, substantially 
symmetrically with respect to this plane. 
In the case of a lower transverse holding device of the steam generator 
according to the prior art, such as that shown in FIG. 1, a significant 
play is left, on adjusting the holding assembly during the mounting of the 
steam generator, between the bearing part 6a of the front support 6 and 
the bearing surface of the ring 5. 
The bearing part 7a of the lateral support 7 arranged on the side of the 
intermediary leg 10 and of the primary motor-driven pump group, with 
respect to the plane containing the axis of the hot leg, is arranged, 
during adjustment, in contact with the bearing surface of the ring 5, in 
such a manner as to provide the guiding of the steam generator 1, during 
movements thereof under the effect of expansions. 
The second lateral support (not visible in FIG. 1) is placed with a certain 
play with respect to the bearing surface of the ring 5. 
The adjustment of the play of the lateral and front supports is carried 
out, as indicated previously, during hot testing of the nuclear reactor, 
by machining an assembly of shims whose dimensions are defined by 
measurements of the residual play made when the steam generator is at its 
service temperature. 
Such a method for adjusting the transverse holding devices according to the 
prior art requires numerous successive operations in order to manufacture 
and install the shims; this increases the time needed for mounting a steam 
generator in the containment of the reactor. This time is particularly 
critical when mounting a replacement steam generator. 
FIG. 2 illustrates a transverse holding assembly for the lower part of a 
steam generator comprising adjustable holding devices according to the 
invention. 
In FIG. 2 can be seen the lower part of the steam generator 21 within the 
bunker 20 which comprises the lateral vertical walls 20a and 20b and a 
front wall 20c in the shape of a portion of a cylinder. 
The transverse holding assembly for the lower part of the steam generator 1 
comprises two lateral supports 22 and 22' situated on a first side of the 
vertical plane of symmetry 23 containing the axis of the hot leg of the 
steam generator 21 and two lateral supports 24 and 24' situated in a 
position which is substantially symmetrical with the supports 22 and 22' 
with respect to the plane 23. 
The pairs of supports 22, 22' and 24, 24' are fixed by the intermediary of 
a support plate 25 and embedding elements 26, onto the internal surface of 
the wall 20a of the bunker 20. 
The transverse holding assembly for the lower part of the steam generator 
21 also comprises three front supports 28, 28' and 28" fixed through the 
intermediary of a support plate 27 and embedding tie rods 29, onto a 
bearing block 20d attached against the wall 20c of the bunker 20. 
The supports 22, 22', 24, 24', 28, 28' and 28" are all identical and 
constituted by adjustable holding devices according to the invention, to 
be described below. 
The lateral and front supports 22, 22', 24, 24', 28, 28', 28" are arranged 
in the proximity of or in contact with bearing blocks, respectively 30, 
30', 31, 31', 32, 32', 32" fixed against the external surface of the 
wrapper of the steam generator 21. 
The bearing blocks 30 and 30' are fixed on the enclosure of the steam 
generator through the intermediary of a base plate in the shape of a 
portion of a cylinder 33. In the same way, the bearing blocks 31 and 31' 
are fixed on the wrapper of the steam generator by the intermediary of a 
base plate 34 and the blocks 32, 32' and 32" through the intermediary of a 
base plate 35. 
The transverse holding of the lower part of the steam generator 21 is 
provided by an assembly of seven identical adjustable holding devices 
which will be described in more detail with reference to FIGS. 3 and 4, 
and with reference to the lateral holding device 24. However, the 
description which follows is applicable to the set of holding devices 
constituting the lateral and front supports represented in FIG. 2. 
The transverse holding device 24 is fixed on a flat support structure 25 
fixed through the intermediary of embedding tie rods 26 onto the wall 20b 
of the bunker of the steam generator 21. 
The support assembly 25 comprises an outer metal plate attached against a 
flat concrete plate, the assembly constituting the support block being 
itself embedded by the tie rods 26 into the wall 20b. 
The transverse holding device 24 comprises a first base plate 40 fixed by 
screws 41 onto the metal plate constituting the external part of the 
support assembly 25. 
The device 24 also comprises a second base plate 42 which is connected, by 
of screws 43 to the first base plate 40. 
A deformable structure for energy absorption 45 is interposed between the 
base plates 40 and 42. 
The assembling screws 43 are engaged with a certain play in smooth holes in 
the plate 42 on which they come to bear by the screw heads and are screwed 
within the tapped holes in the plate 40. 
Moreover guiding columns 44 are fixed on the plate 40 at one of their ends 
and engage slidingly in sleeves fixed within the orifices passing through 
the plate 42. 
The screws 43 and the columns 44 allow the base plate 42 to be held against 
the deformable assembly 45 and to guide the plate 42, which is likely to 
move in the transverse direction 47 constituting the axial direction of 
the support 24 when the steam generator 21 is brought to bear against the 
support 24; this may result in a deformation of the assembly 45. 
The deformable assembly 45 is held on the base plate 40, by feet 49 fixed 
by screws. The assembly 45 is manufactured in the shape of an 
elasto-plastic cushion of parallelepipedal shape constituted by crossed 
metal bars arranged in several layers, in directions at 90.degree. from 
each other and staggered. 
Such a deformable assembly with crossed bars is known in the prior art and 
used for absorbing, by deformation, the energy transmitted to the front 
supports, situated in the axis of the hot leg, of a steam generator. 
On the outer face of the second base plate 42 directed towards the steam 
generator 21, a load distribution block 50, of parallelepipedal shape and 
comprising a cylindrical central orifice, is fixed by the screws 51. 
The central orifice 50a of the distribution block 50 comprises a 
diametrically widened part 50b in which is engaged a part of a nut 52, in 
such a manner that the tapped orifice 52a of the nut 52 is arranged along 
the axis 47 extending in the transverse direction of movement of the 
support. The nut 52 is fixed by screws 53 onto the distribution block 50. 
One screw 54 is engaged by screwing in the tapped orifice 52a of the nut 
52. 
The screw 54 comprises a head 54a having one part in the shape of a 
spherical cap upon which is attached a bearing pad 55 having an internal 
cavity 55a in the shape of a spherical cap coming into contact with the 
surface of the end part 54a of the screw. 
The bearing pad 55 is fixed on the end part of the screw 54 by a fixing 
screw 56 and a spring washer 58, in such a way that the pad 55 has a 
slight latitude of orientation with respect to the screw 54. 
The bearing pad 55 is arranged opposite the surface of the bearing block or 
shoe 31 fixed on the wrapper of the steam generator through the 
intermediary of the cylindrical base plate 33. 
The nut 52 comprises a slot 57 in a plane perpendicular to the axis 47 of 
the nut, the slot 57 opening into the tipped bore 52a of the nut 52 and 
having a circumferential extension slightly greater than the 
half-circumference of the nut. 
The slot 57 which is arranged at a short distance from the outer face of 
the nut 52 delimits a deformable part 52b of the nut 52 which can be 
brought closer to the remaining part of the nut by press-screws such as 
59. 
The deformable part of the nut comprises a part of the tapped orifice 52a 
of the nut, so that this tapped part can be moved by tightening the screws 
59 so as to block the screw 54 in a predetermined axial position within 
the tapped orifice 52a. 
The screw 54, which can be moved by screwing in one direction or the other 
within the nut 52, when the press-screws 59 are in the untightened 
position constitutes a screw-jack, the position in the axial direction of 
which can be fixed by tightening the screws 59. 
During hot testing of the steam generator 21, it is thus possible to fix 
the position of the bearing surface of the pad 55 with respect to the 
external surface of the bearing block or shoe 31. 
For example, the screw 54 can be placed in a position such that a play 60 
remains between the bearing surface of the pad 55 and the outer surface of 
the shoe 31. The play 60 is determined as a function of movements of the 
steam generator which are of thermal origin and can be calculated. 
The position of the screw allowing the play 60 to be obtained is fixed by 
tightening the screws 59. 
There will now be described an operation for adjusting the supports of a 
transverse holding assembly for the lower part of a steam generator, these 
supports being constituted by holding devices according to the invention 
such as represented in FIGS. 3 and 4. 
The transverse holding of the steam generator is provided by four lateral 
supports and three front supports arranged as represented in FIG. 2. 
The adjustment is carried out during hot testing of the nuclear reactor, 
the cooling water of the nuclear reactor circulating in the steam 
generator being at a temperature of 28620 C. and at a pressure of 155 
bar. 
The screws 54 of the support assembly are unscrewed into a position such 
that the bearing pad securely attached to the end of the screw comes into 
contact with the corresponding shoe fixed on the wrapper of the steam 
generator, at the height of the tube plate. 
The screws 54 of the supports 22 and 22' arranged on the side of the 
intermediate leg of the primary circuit and of the motor-driven pump group 
are blocked in position by tightening the screws 59, so as to retain the 
position leading to zero play at the service temperature and under the 
service conditions of the steam generator. 
The lateral supports 24 and 24' situated opposite the supports 22 and 22' 
with respect to the plane 23 are moved, so as to introduce a certain play 
between their bearing pad and the corresponding shoes 31 and 31' fixed on 
the wrapper of the steam generator. To this end, the screws 54 of the 
supports 24 and 24' are moved in the axial direction, by screwing by a 
number of turns corresponding to the desired play. The screws 54 are then 
blocked in position by tightening the screws 59 providing the deformation 
of the nut. 
The play between the supports 24 and 24' and the bearing parts of the steam 
generator is provided in order to allow accidental movements or movements 
of thermal origin of the steam generator between the lateral supports 
which ensure its guiding. 
The front supports 28, 28' and 28" are adjusted by their screws 54, so that 
a play 61 (FIG. 2) which is relatively significant is maintained between 
the bearing pad of the support and the corresponding shoe 32, 32', 32". 
The play 61 can be of the order of 50 mm, so as to allow significant 
movement of the steam generator in the axis of the hot leg corresponding 
to the trace of the plane 23 in FIG. 2. 
The adjustment of the assembly of the transverse holding device for the 
lower part of the steam generator is provided by adjusting an assembly of 
seven supports, each of the supports being adjusted by a screw placed in 
the desired axial position and then blocked in position. 
These operations which are carried out during hot testing of the nuclear 
reactor are carried out much more easily and more rapidly than the 
adjusting operations according to the prior art, which required 
measurement and machining and installation of shims. 
Moreover, the adjustment of the play can be carried out in a very precise 
manner, the position of the screw-jack being able to be fixed with very 
great precision by counting the number of turns or fractions of turns 
necessary in the direction of screwing, from the reference position 
corresponding to placing the bearing pad in contact with the shoe which is 
securely attached to the wrapper of the steam generator. 
The simplicity of the operations and the reduction in the time required for 
adjustment constitute very considerable advantages, in particular when 
replacing a steam generator. 
The means for blocking the screw in its adjusting position can be carried 
out by means other than a screw for tightening a deformable part of the 
nut, for example in a more conventional manner, by a lock nut, a split 
lock nut, or by locking screws. 
The bearing pad of the support and the bearing blocks securely attached to 
the steam generator can have shapes other than those which have been 
described. 
The second base plate of the support on which the nut is fixed, could be 
fixed directly onto a stationary concrete wall instead of being attached 
to a first base plate with the interposition of a deformable element. 
The support according to the embodiment which has been described has the 
advantage of comprising an assembly constituted by the bearing pad, the 
screw, the nut, the distribution block and the second base plate which is 
able to move in the axial direction of the support, being perfectly guided 
by the columns which are securely attached to the first base plate. 
In the event of movement of the support under the effect of a deformation 
or a movement of the steam generator, the mobile assembly of the support 
remains perfectly aligned along the axial direction, despite a deformation 
which could be irreversible of the deformable assembly 45 which ensures 
the absorption of part of the energy brought into play during a movement 
of the steam generator. 
The deformable assembly can be of a different type other than that which 
has been described which comprises successive layers of crossed bars. 
The invention applies to the transverse holding of any component of large 
dimensions of a nuclear reactor arranged in a locality and able to move 
with respect to the walls of the locality, as a result of heat or through 
accidental causes such as an earthquake.