Note: Descriptions are shown in the official language in which they were submitted.
~03~2~1
Various designs of motor-driven screwing and transporting tools
for tightening or loosening the head bolting of pressure vessels are known.
Such tools are known particularly for nuclear reactor pressure vessels, be-
cause in the case of nuclear reactor pressure vessels the problem arises to
remove and then replace a~d tighten the head of the reactor pressure vessel
quickly and safely, to minimize radiation exposure of the personnel as much
as possible during refueling. In nuclear reactor plants the shutdown time
for refueling is influenced very substantially also by the time required for
opening and closing the reactor pressure vessel. ~lere, the pressure vessel
head is firmly bolted to the vessel proper via threaded studs which are sunk
into the flange of the vessel, and associated tightening nuts on the upper
side of the head.
A motor-driven screwing and transporting tool for loosening, trans-
porting and tightening of individual tightening nuts of threaded studs is
already known (German Offenlegungsschrift 2,061,037). As the loosening of
individual closing or tightening nuts, the transporting and retightening in
a definite order (to avoid asymmetrical stresses of the head and the pres-
sure vessel) still requires relatively much time, thought has been given to
the problem of pretensioning simultaneously several studs arranged in a
pitch circle, to turn the associated vessel nuts up or down and to transport
them forward and away. Thus, one known screw-tightening device (German Of-
fenlegungsschrift 2~243,045) comprises the following elements: A support
body which can be placed on the head flange, adjustably in height; tighten-
ing and loosening units mounted at the support body; means at the studs and
their tightening nuts for coupling the tightening and loosening units and
specifically, external teeth at the tightening nuts for the engagement of
the drive pinion of a nut-rotating drive of the tightening and loosening
units, and teeth arranged at the head end of the threaded stud for engagement
of a gripper unit, w~erein the tightening and loosening units comprise in
turn the following components: A hydraulic tensioning cylinder, supported
.
... . .
103BZ~8
at the support body, for axially elongating the studs by axial action on the
gripping units via a power piston during the loosening or tightening of the
tightening nuts: a drive for coupling and decoupling the gripper body rela-
tive to the studs as well as said nut-turning drive with a drive pinion for
turning the tightening nut in the direction of screwing it on or off via
its external gearing.
Beyond this, it has also been proposed already to improve a motor-
driven screwing and transporting tool of the kind described by loosening or
tightening, as far as possible, all the tightening nuts of a head bolting,
1~ as well as transporting them to and fro, simultaneously. In this older
arrangement, hydraulic plungers are already attached at the screwing and
transporting tool, by means of which the distance of the tool from the sur-
face of the head can be adjusted in accordance with the progress of the un-
screwing and screwing operation.
The present invention is based on the consideration that it is de-
sirable in pressure vessels in general, and in reactor pressure vessels in
particular, to not only loosen, retighten and transport the tightening or
closing nuts of the head bolts, as far as possible, automatically and in
large numbers, but to include also the studs themselves in the operations,
as then a number of important advantages with respect to time and space sa-
vings as well as safety for the operating personnel ar0 obtained.
According to the present invention there is provided a device for
securing or releasing a connector capable of connecting a first member to
a second member, ~he connector comprising a stud having a threaded end region
and a threaded intermediate region, and an adjusting nut on the threaded
intermediate region, the arrangement being such that, during connection, the
stud extends through an aperture in the second member and is located at its
threaded end region in a threaded hole in the first member, with the adjust-
ing nut on that side of the second member remote from the first member and
urging the second member towards the first member; the device comprising:
- 2 -
. .
103B2~1~
a support whicll is intended to be adjustable parallel to the axis of the
stud, and, carried by the support: (1) means for gripping an end region of
the stud remote from the said threaded end region; (2) means for axially
extending the stud; (3) first drive means for rotating the adjusting nut
relative to the stud; (4) second drive means for screwing and unscrewing
the stud (and the adjusting nut carried thereon) relative to the first
member; and (5) lifting means for ~aking up the weight of the stud and ad-
justing nut whilst they are being acted upon by the second drive means.
A preferred embodiment of the invention comprises a device for
unscrewing and screwing nuclear reactor pressure vessel head-retaining nuts
and screw studs, the studs extending upwardly through stud holes in a head
flange of a removable head of a reactor pressure vessel, the studs having
threaded lower ends screwed in~o threaded holes in the pressure vessel's
top and threaded portions on which the nuts are screwed above the head
flange to hold down the head on the pressure vessel with the studs under
pretension between the vessel's top and the nuts, the nuts having external
gear teeth for their rotation and the studs having upper ends spaced above
the nuts; said device comprising a support body and means for supporting
said body at controllable heights on said head flange; and unscrewing and
screwing units for said nuts and studs, mounted on said body and having axial
passages for releasable insertion of the studs and nuts; each of said units
for a stud and nut when inserted in the unit's passage, having a pinion
releasably meshing with the nut's said gear teeth and means for reversingly
driving said pinion for unscrewing and screwing movements of the nut on the
stud, gripping means for releasably gripping the upper end of the stud above :
the nut, and means for applying upward force to said gripping means for
stretching the stud upwardly from the pressure vessel's top to free the nut
from said pretension during said movements; each of said units further
having means for releasably engaging and reversibly rotating the stud so its -
said lower end can be unscrewed and screwed in the threaded hole in the -~
~ _ 3 _
32C18
pressure vessel's top while the nut remains screwed on the stud, and means
for applying a lifting force to both the nut and stud to relieve the stud's
said lower end from the weight of the nut and stud while being unscrewed and
screwed in the pressure vessel's threaded hole.
The advantages attainable with the invention are essentially the
following: The threaded studs of a reactor pressure vessel can now be
screwed out of the lower part of the reactor pressure vessel for each re-
fueling. This permits in-service inspection of the studs at a suitable
storage location away from the reactor pressure vessel as well as in-service
tests of the tapped holes in the lower part of the reactor pressure vessel,
which have become accessible after the studs are removed. Sealing the tapped
holes in the lower part of the reactor pressure vessel is easier than seal-
ing screws which remain in the lower part. The motor-driven screwing and
transporting tool according to the invention requires a minimum of personnel
for moving the studs and nuts, i.e., for unscrewing and screwing. The
transporting of ~he threaded studs with their tightening nuts is possible
in a highly mechanized and therefore, time saving manner. In newly-to-be-
built nuclear
- 3a _
Z~
reactor plants, the level of the llpper edge of tlle reactor room can be low-
ered, as throug~ the removal of the studs, the cross-traveling height for
the refueling machine is reduced. Through such a lowering of the level of
the upper edge of the reactor room, the amount of flooding water required is
reduced.
It is particularly advantageous if the tool is arranged for sim-
ultaneously unscrewing the threaded studs and the tightening nuts mounted
on them, after the latter have been loosened, and for simultaneously screwing-
in the studs and their tightening nuts before the latter are tighten0d, and
that to this end the tightening nut can be secured at the threaded stud in
such a manner that rotation of the tightening nut relative to the stud be-
yond a predeterminable screw-in ready position or a predeterminable readiness
position rotation angle range is prevented in both directions of rotation.
Cne preferred embodiment of the invention provides that the tool for the
simultaneous tightening or loosening of all the bolting positions arranged -
on the pitch circle of the head bolting, comprises one tightening and loosen-
ing unit each for each threaded stud with tightening nut. One thereby avoids
belt or chain drives, and the direct coupling of the drive motors is opera-
tionally reliable and without problems.
According to a further embodiment, the invention provides that the
tool is arranged for transporting to and fro the unscrewed studs together
with the tightening nuts mounted on them and can be brought into engagement
for this purpose by means of support surfaces of its tightening and loosening
units with corresponding counter-support surfaces of the stud. These support
and counter-support surfaces are advantageously identical with the engagement
surfaces by which the power piston of the hydraulic tensioning cylinders and
the gripper body for turning the respective stud are in mutual engagement.
If the tool according to the invention is equipped with a gripper body which
can be screwed on the thread on the head side of the stud and is designed
as a gripping nut with external teeth~ then it is particularly advantageous
-- 4 --
l03sza~
if the lifting and s-~lpport means comprise a lifting cylinder, arranged con-
centrically with the screwed-on gripping nut, with a lifting piston and a
thrust bearing, wherein the lifting piston with an internal shoulder can be
brought into engagement, via the thrust bearing, with an external shoulder
of the gripping nut against the force of gravity. In this manner, the weights
of the studs can be balanced hydraulically or pneumatically in fine dosages,
and the thrust bearing provides advantageous rolling friction for the weight-
compensated stud, so that the rotation drive for the stud has to supply re_
latively small torques. In this connection, a further embodiment of the
tool, which has single-action tensioning pistons, provides that the lifting
cylinder is arranged so as to follow the hydraulic tensioning cylinders in
the axial direction and that the lifting piston is double-acting and can be
brought into contact with the tensioning pistons as the resetting piston
- of the tensioning pistons in the direction opposed to that of its lifting
direction. The multiple, and preferably double arrangement of hydraulic
tensioning cylinders ~nd associated power pistons in tandem is known per se
; from the German Auslegeschrift 1,271,050; this has the advantage that large
lifting and tensioning forces can be obtained with a relatively small dia-
meter.
An example of an embodiment of the invention is illustrated in the
accompanying drawings, in which:
Figure 1 is a vertical cross section of a portion of a reactor
pressure vessel and its removable head and of one of the head-retaining studs
and nuts;
Figure 2 is a vertical cross section on a scale enlarged over Fig-
ure 1, showing a head-retaining stud with the tightening nut which is still
screwed onto the stud, and on which the tightening and loosening unit of the
motor-driven screwing and transporting tool according to this invention is
placed;
Figure 3 is a partial cross section taken on the line III-III in
-- 5 --
Figure 2; 10~8
Figure 4 is a cross section taken on the line IV-IV in Figure 2;
Figure 5 is a top view of the example, showing the annular support
body and three of the series of tightening and loosening units which side-
by-side extend throughout the circumference of the support body; and
Figure 6 is a vertical section of an individual lifting device,
three of which are required to adjust the height of the tool.
The head bolting, shown in a partial view of Figure 1, of a nuclear ~;
reactor pressure vessel (called RPV for short in the following) has a lower
RPV part 1, to which the RPV head 2 is bolted tightly. For this purpose,
two concentric sealing rings 4 are placed in circular slots 3 of the head
2, and threaded studs 6 are screwed by their lower threads 6.1 into the ap-
propriate tapped holes 5; the stud shanks go through the head in appropriate
head holes 2.1 and the head 2 is now clamped to the lower part 1 by the studs
6 and the tightening nuts 6.2 on spherical washers 6.3, in a sealed manner,
as mentioned. To this end, the tightening nut 6.2 holds on the thread 6.4
of the stud 6, the shank of the stud 6 being subjected to an axial preten-
sioning force, which is about 765 ~X 103 kg per stud in the embodiment example
shown. As will be explained later, the studs 6 are axially elongated hydrau-
lically so that this pretensioning force can be attained, and in the elon-
gated condition the tightening nuts 6.2 are then tightened, and for loosening
the head bolting, the studs must also be stretched axially, of course, so
that the tightening nuts 6.2 can be loosened. The maximum hydraulic pre-
tensioning force per screw is about 900 ~ 103 kg. It is ensured by the above-
mentioned large residual pretensioning forces that in the area of the seals
4 the required contact pressure for sealing the RPV is achieved. Even though
only one stud is shown in Figure 1, it is understood that for the head bol-
ting of an RPV a multiplicity of such screws is provided which are arranged
on a so-called pitch circle; in the embodiment example shown, there are 52
studs with the corresponding tightening nuts 6.2, holes 2.1 in the head
-- 6 --
:., ' .,,
~03~Z(~B
flan~e 2.2 and tapped holes 5.
Figure 2 in conjunction with Figure S now shows the details of
the motor-driven screwing and transporting tool for tighteni~g or loosening
the head bolting of a pressure vessel, particularly an RPV, which comprises
the studs 6 and associated tightening nuts 6.2. The tool comprises, first
of all, an annular support body 7 which can be placed, adjustable in height,
on the head flange 1 and has in the case shown a basically circular shape
so as to match the pitch circle of the studs 6. At the support body 7 are
disposed tightening and loosening unit5 8, by means of which the support body
7 can be placed on the respective studs 6 with tightening nuts 6.2; see par-
ticularly Figure 5.
Figure 2 shows one of the tightening and loosening units 8 which is
put over a stud 6 with the tightening nut 6.2. Here, the tightening process
for the stud 6 may have just been completed, or it could be just before the
loosening process is started. The means at the studs 6 and their tighten-
ing nuts 6.2 for coupling the tightening and loosening units 8, comprise
external gear teeth 6.5 on the tightening nuts 6.2 for the engagement of
the drive pinion 9 of a nut-turning drive 10, and a thread 11 at the head
end of the stud (see also Figure 1) for the engagement of a gripper body 12,
designed in the case shown as a gripping nut, In principle, otller suitable
gripping bodies may also be used instead of a gripping nut, e.g., two grip-
per jaws which can be brought into engagement hydraulically or pneumatically
from two opposite sides with teeth or with circular slots and circular shoul-
ders at the upper end of the stud 6, not shown here but as is known per se
from Offenlegungsschrift 2,243,045. The gripping nuts shown, however, are
particularly advantageous, as they fit in with the system of the tightening
and loosening units particularly well, The gripping nuts have an internal
thread 12.1 for the stud thread 11.
Each of the tightening and loosening units 8 comprises the follow-
ing components: Hydraulic tensioning cylinders 13, mounted on the annular
-- 7 --
l03s2a~
support body 7, for axially elongating the studs 6 by axial action on thegripping nuts 12, via power pistons 13.1, during the loosening or tightening
of the tightening nuts 6.2. Two hydraulic tensioning cylinders 13 in tandem
with the respective power pistons 13.1 are shown, whereby twice the tension-
ing force can be obtained with a given diameter, as compared to only one
tensioning cylinder, for a given hydraulic pressure. The annular power pis-
tons 13.1 surround the shank of the studs 6, and the upper power pistons
13.1 attacks via a spherical washer 12.4 at a spherically bevelled shoulder
12.2 of the gripping nut 12, the spherical washer 12.4 being held at the
10 spherical shoulder 12.2 of the gripping nut by means of screws 12.3 distri- ;~
buted over the circumference of the former. It is achieved thereby that
the power pistons exert their pressure forces completely symmetrically on
the gripping nut 12. ~ :
The tightening and loosening units 8 further comprise a drive 14
for coupling and decoupling the gripping nut 12 relative to the stud 6,
with a drive pinion 14.1, which is mounted, secured against rotation, by
means of the key 14.3 and the end thread 14.3', on the shaft 14.2; with a
transmission unit 14.4 and the drive motor 14.5 proper, whose shaft, indi-
cated at 15.5', is coupled with the shaft 14.4' of the transmission unit 14,
for instance, via miter gears (not shown). The transmission unit 14 further
contains a friction clutch, not shownJ so that the drive pinion 14.1 is de-
coupled from the drive motor 14.5 if a maximum torque is exceeded, and the
motor 14.5 idles. This is the case if the gripping nut 12 if fully tight.
Instead of an electric motor 14.5, a hydraulic motor with associated pump
or a pneumatic drive ~not shown) can also be used. The drive pinion 14.1
meshes, as will be seen, with the external teeth 12.5 of the gripping nut 12.
The mounting flange 14.6 of the transmission unit 14 is attached to the lift-
ing piston 15 and is axially movable with the latter, as will be further
explained below.
3~ Part of the tightening and loosening unit 8 is further the nut-
-- 8 --
, ' ~
103~2~B
turning drive 10 with the drive pinion 9 which serves to turn the tightening
nut 6.2 via its external gearing 6.5 in the screw-on and screw-off direction.
The nut drive 10 is designed similar to the drive 14. The drive pinion 9,
whose gear teeth g.1 mesh with the external gear teeth 6.5 of the tightening
nut 6.2, is supported on the shaft 10.1 spring-loaded in the axial direction,
so that the engagement of the teeth 9.1 with the teeth 6.5 is facilitated
when the tightening and loosening unit 8 is put in place, and jamming is
avoided. To this end, there is securely mounted on the shaft 10.1 the washer
10.2, against which the helical compression spring 10.3 is braced and the
drive pinion 9 pushes axially against a snap ring 10.~. The electric motor
is designated with 10.5 and the transmission unit with 10.6. The transmis_
sion unit 10.6 is attached to the support body 7, for instance, via a U-
shaped holder 10.7. 10.8 is a protective sheet-metal cover which is bolted
to the support body 7 and covers the drive pinion 9 at the top.
For screwing the threaded studs 6 into and out of the tapped holes
5 of the lower RPV part 1 (see Figure 1), the tightening and loosening units -~
8 are now provided with lifting and support means 15, 16 which can be switch-
ed into and out of engagement relative to the studs 6, to provide a support
which is rotatable and in the process weight-relieves the screw threads 6.1, -
5 of the stud 6 and the pressure vessel 1, respectively, associated with
each other at the base end, and the tightening and loosening units 8 further
comprise a rotation drive 17 which can be brought into engagement with the
studs 6 in a positively force-transmitting manner. The weight of an indivi-
dual stud 6 with the tightening nut 6.2 and the gripping nut 12 in the RPV
shown, which is laid out for a power of 1200 MWel, is about 2 tons or mega-
ponds (2000 kg). The lifting means 15 are therefore employed for the screw-
ing-in or out of the threaded studs 6 to generate a force compensating this
weight, so that seizing between the screw threads 6.1, 5 is reliably pre-
vented, the support means 16 providing for low friction, preferably rolling
friction.
_ g _
. . ,
~0:182~8
In detail, the lifting an~ support means 15, 16 are comprised of
a lifting cylin~er 15.1, which is arranged concentrically to the screwe~-on
gripping nut 12 and in whicll the annular lifting piston 15.2 is disposed,
and of a thrust bearing 16, where the lif~ing piston 15.2 with an inner
shoulder 15.3 ran be brought into engagement with an outer shoulder 12.6
of the gripping nut 12 via the thrust bearing 16 against the direction of
the force of gravity. As will be seen, the lifting cylinder 15.1 is arran-
ged axially following the hydraulic tensioning cylinder 13, i.e., is flanged
to the upper tensioning cylinder 13, and the lifting piston 15.2 is of double- ~ ~
action design, two hydraulic feed lines being indicated by the dash-dotted ~-
lines 15.21, 15.22. The lifting piston 15.2 can therefore be acted upon due `
to its piston shoulder 15.3, which represents the effective hydraulic area,
deflected upward via the line 15.21, or downward if acted upon via the line -
15.22. rhe upward movement is limited by the stop ring 15.24, which is fas-
tened at the upper circumference of the cylinder 15.1 on its inner side rela-
tive to the annular support 7. Sealing rings placed in slots are designa-
; ted with 15.4 in the arrangement 15. The lower piston shoulder 15.3 can be ~ -
brought to a stop with the upper of the power pistons 13.1, as can be seen,
and can therefore serve as a restoring pressure piston for the power pistons
13.1 in the direction opposed to its lifting direction. The liting piston
15.2 therefore has a dual function; for one, the weight relief of the parts
previously noted, and secondly, the restoring function of these parts.
At the outer circumference of the lifting piston 15.2 there is
fastened in an area left free by the lifting cylinder 15.1, the already men-
tioned drive motor 14 for the gripping nut 12, whose pinion 14.1 goes through
the lifting piston 15.2 in a slot 15.25 to mesh with the gripping nut 12~
Similarly, also the annular support frame 14.7 of the motor 14 is slotted
at this point (slot 14.71). To take up the reaction torque of the drive `~
motor 14, the annular frame 14.7, which is welded to the lifting piston 15.2,
is guided in the axial direction by the guide bar 18, which is attached at
- 10 -
10382~8
the lifting cylinder 15~1 at 18.1 and 18.2. For this purpose, the annular
frame 14.7 has a radially-directed guide bracket 14.8 of U-shaped cross sec-
tion (see Figure 3).
The rotation drive 17 is fastened to the support body 7 and is pre-
ferably a pneumatically energized drive-screw motor, whose drive pinion 17.1
is in engagement with a coupling member 19 which can be engaged and disen-
gaged relative to the stud 6, the teeth 17.2 meshing with the external teeth
19.1 of the coupling member 19. To this end, the drive pinion 17.1 goes
through the support body 7 in a slot 7.1 and the sleeve 20 inserted at the
inside circumference of the support body 7, in a slot 20.1. The drive pin-
ion 17.1 is mounted on the shaft 17.2, secured against rotation, which latter
is supported in bearing elements 17.3 which are arranged at an axial distance
from each other. ~le housing of the drive 17 is designated with 17.5; it
contains the drive-screw motor proper, whose pneumatic feed lines are not
visible.
The coupling member 19 is formed by a hollow cylindrical driving
disk, for instance, which is supported concentrically and rotatably with
respect to the stud 6 and axially spring-loaded in the support body housing,
; i.e., in the sleeve 20, with the external teeth 19.1 and internal teeth 19.2,
which can be engaged with corresponding coupling projections and recesses
21.1, 21.2 of a driving ring 21 which is connected with the stud 6, secure
against rotation, although displaced longitudinally. ~le axially spring
loaded and rotatable support of the driving disk 19 is achieved by the thrust
bearing 19.3 which rests via a support ring 19.4 and a helical compression
spring 19.5 against a counter-support ring 19.6 with a retaining ring 19.7.
If therefore the tightening and loosening units 8 are put over the respec-
tive associated stud 6, then the driving dis~ 19 can give way resiliently
in the axial direction until its teeth 19.2 engage with the mating te~th
21.1, 21.2. A retaining ring for the sleeve 20 is designated with 20.2.
The sleeve is furthermore pinned at 20.3 in the support body 7.
- 11 --
1038Z~E~
~le entire screwing and transporting tool, i.e., its respective
tightening and loosening units 8, are now arranged for simultaneously
screwing-out the studs 6 and the tightening nuts 6.2 sitting on them after
the latter have been loosened, and for simultaneously screwing-in the studs
6 and their tightening screws 6.2 before the latter are tightened. For
this purpose, the tightening nut 6.2 can be locked to the stud 6 in such a
manner that rotation of the tightening nut 6.2 relative to the stud 6 beyond
a preselectable screwing-on readiness position or a preselectable readiness-
position rotation angle range, is prevented in both directions of rotation.
For this purpose, the driving ring 21 has, at its end facing the tightening
nut 6.2, a projection 21.3 with a stop surface pointing in the circumferen-
tial direction, and the tightening nut 6.2 is provided at its upper end face
with a latch 6.8. This latch 6.8 can be attached at the end face of the
tightening nut adjusted in such a manner that the nut 6.2, after traveling
through a screw-off rotation angle which is equal to or larger than the
angle of rotation required for loosening the nut 6.2 during the axial elon-
gation of the stud 6, runs against the stop surface 21.3 with its latch 6.8.
In the case shown in Figure 2, the tightening nut 6.2 is still tight. If
it is, therefore, stretched axially by the tensioning cylinder 13 and piston
13.1, and if the tightening nut 6.2 is turned by the drive pinion 9 counter-
clockwise, then the tight0ning nut 6.2 can travel through a screwing-off
rotation angle which amounts to one full revolution, minus the arc of the
projection 21.3 of the driving ring 21. This means, the pitch of the stud
and tightening nut thread is chosen accordingly. In the present case, the
thread is a metric thread M210 x 8. The pitch of 8 mm per thread is there-
fore sufficient for unscrewing the tightening nut 6.2, from which it is con-
cluded that the axial elongation of the stud 6 in the permanent condition
must be somewhat less than 8 mm. The driving ring 21 is designed as a
separate part, which is, for instance, shrunk onto a corresponding shoulder
3~ 6.9 of the stud. This is advantageous because a certain amount of wear
103~Z~I~
takes place at the part 21. i~owever, the invention is not limited to this;
special threaded stu~s can also ~e used whîch have an integrally formed
driving ring 21.
The engagement between the latch 6.8 and the stop surface 2l.3
as well as between tlle driving disk l9 and the driving ring 21 is illustra-
ted once more in the cross-sectional view according to Figure ~.
As shown particularly in Figure 5> the tool according to the in-
vention for the simultaneous tightening or loosening of all the screw con-
nections arranged in the pitch circle 22 of the pressure vessel's head bol-
ting, is equipped with one tightening and loosening unit 8 for each stud 6
with tightening nut 6.2. The tool is furthermore arranged for transporting
to and fro the loosened studs 6 including the tightening nuts 6.2 sitting
on them, and for this purpose can be brought into engagement, by means of
support surfaces 13.11 of their tightening and loosening units 8, with
corresponding counter support surfaces 12.41 of the stud 6. As will be seen,
the support and countersupport surfaces 13.11, 12.41 are identical with the
contact surfaces with which the power piston 13.1 of the hydraulic tension-
ing cylinders 13 and the gripping nut 12 for stretching the stud 6, are in
mu*ual engagement.
During the hydraulic elongation of the stud 6, the elongation can
be read at a dial gage 22, whose plunger 22.1 rests against the reference
surface 23.1 of a measuring pin 23. This measuring pin 23, with which every
stud 6 is providedJ extends through a hole 23.2 into the interior of the
stud 6 and therefore does not participate in the elongation of the stud 6.
The mounting nuts for holding the dial gage 22 are designated with 22.2 and
22.3.
The bracket 24 serves, as known per se, for the purpose of securing
; against rotation. With its two angled-off ends, which make contact with
the end face of the gripping nut 12, it is secured by the pin 24.1 and the
threaded bolt 24.2. It prevents the gripping nut 12 from being turned off
- 13 -
.... . . .
:
~03~2(~1~
during the movement of the stud 6.
Witll 25 is designated as a whole a high-pressure hydraulic feeding
arrangement. A hydraulic ring line, not visible, leads to the individual
shut-off device 25.1 and from there via the line 25.2 and the distributor
head 25.3 as well as the lines 25.4 to the two tensioning cylinders 13, which
are provided with corresponding hydraulic canals 13.3. Corresponding sealing
rings between the piston 13.1 and the cylinders 13 are designated as a whole
with 13.4. Oil-leak monitoring canals carry the reference symbol 13.5. The
escape of leakage oil can be recognized at transparent, screwed-in caps 13.51.
The mounting frame 25.5 for the hydraulic device 25 is bolted to the support
body 7 at 25.6.
It should be added that the support body 7 with its tightening and
loosening units 8 has hydraulic lifting devices 26 (Figures 5, 6), so that
it can be placed, adjustable in height, on the flange of the RPV head or the
lower part of the RPV. Preferably, three such lifting devices are arranged
at three points uniformly distributed over the circumference of the support
body 7. Each of these lifting devices has a push-off plunger 26.1 with a
foot 26.2 and power pistons 26.3 which are mounted on the plunger and are
arranged in corresponding hydraulic cylinder bodies 26.4. The feed canals
27 for high-pressure oil are associated with the upward movement of the
support body or the downward movement of the power piston 26.3, and the hy-
draulic feed canals 28 are associated with the downward movement of the
support body or the upward movement of the power pistons 26.3. The associa-
ted hydraulic feed lines for the high-pressure oil are not shown, and like-
wise not the specific manner of mounting the lifting device 26, which is
set into corresponding recesses in the support body and are firmly connec-
ted with the latt~r. Through the tandem arrangement of two piston-cylinder
units, as shown, a doubling of the effective pushing-off force is achieved,
which must supply the weight of the entire screwing and transporting tool
of approximately 35 tons plus the weight for the studs with the nuts. ~11
- 14 -
-:
103l9Z08
throe lifting devices 26 must be controlled synchronously in such a manner
that uniform lifting or lowaring of the tDol is possible. In particular,
fine adjustment by millimeters must also be possible.
The operation of the described screwing and transporting tool turns
out as fsllows: It is assumed that the screwing and transporting tool in
Figu~e ~ is placed on the flange of the RPV head 2 for opening the RPV head.
Thereupon, tho high-pressure hydraulic system for the three lifting pistons
26 is switched on and the tool is lifted 3 mm by the three lifting pistons.
Next, the gripping nuts 12 located in the tool are screwed on all 52 studs
(in Figure 2, the already screwed-on position is shown~, and specifically,
on the thread 11, for which purpose the turning drive 14 with its drive pin-
ion 14.1 is switched on. The spherical washer 12.4 at the gripping nut
serves at the same time for guiding the gripping nuts 12 on the chamfered
stud end 11.1, before the threads start to take hold. When the gripping nuts
12 are screwed on, the securing brackets 24 are snapped in place. Now,
the tool is lowered again on the head flange 1 by actuating the lifting de-
vices 26. Now, the studs must be stretched axially by pressurized oil, which
is fed to the tensioning cylinders 13 via the lines 25.4. Then, the power
pistons 13.1 are pushed first 3 mm in an idling stroke and then against the
spherical washer 12.4, and the studs 6 are now stretched in a defined manner
axially by the predetermined amount, which can be read at the dial gago 22.
The gripping nuts therefore serve as the engagement surface for the power
pistons.
Now, the nut-turning drives 10 can be switched on, which screw
up without effort the respoctive tightening nuts 6.2 via the drive pinions
9 by almost a full turn, until the nuts are arrested by means of the locking
device 6.8, 21.3. The hydraulic tensioning device 13, 13.1 is now again
controlled so that the pressure drops slowly and the elongation of the studs
is taken back. As the next step, pressure ~ust be applied to the lifting
cylinder 15, so that the weight of the studs 6 is compensated. When this
- 15 _
2~8
has been accomplished, the drive-screw motors 17 ars switched on and the
studs 6 are screwed out step by s~ep (the mo*ors 17 may be of pulse opera_
tion), the support body 7 with the individual tightening and loosening de-
vices being made to follow by means of the lifting devices 26. The drive-
screw pulsed motors 17 unscrew the studs 6 together with their tightening
nuts 6.2 and their gripping nuts 12, the drives 14 and 10 idling along, of
course. After checking whether all the studs have been screwed out, the
screwing and transporting tool is lifted up, if the finding is positive,
by means of a building crane, not shown, and is run to a set-down location.
Thereby, all the studs with their tightening nuts and gripping nuts are
thus carried off. Through the holes 2.1 in the RPV head, one can now in-
sert plastic plugs for sealing the blind tapped holes 5 in the lower RPV
part, so that subsequently to the lifting of the head, the water-flooding
of the reactor room can be started. The head is then taken off completely
and refueling can begin which, how0ver, is of no significance for the under-
standing of the present invention. It is important, however, that the tool
moved to the set-down location contains all studs and tightening nuts so
that these can now be subjected to a thorough examination. Further, a
close inspection of the blind tapped holes 6.1 can be performed with the RPV
still open, which would not be possible without the removal of the threaded
studs.
After the refueling and the inspection have been completed, the
reactor pressure vessel is closed in the reverse order; after the head bol-
ting has been tightened, the gripping nuts 12 can now be screwed off as the
last step and are then carried with this tool to the set-down location.
'
- 16 -
.
