Note: Descriptions are shown in the official language in which they were submitted.
5~
The present invention relates in general to the
inspection of a pressure tube in a pressure tube type nuclear
reactor, and more particularly to a method and apparatus
for inspecting, for example, flaws or defects of the pressure
tube. In the present invention, an inspection apparatus
is so shaped that it is removably and displaceably inserted
into the pressure tube through remote control by means of a
refueling machine for inspection.
The present invention will be illustrated by way
of the accompanying drawings, in which:-
Figures 1 and 2 are explanatory views of the con-
ventional "external installation system" and "refueling
machine combined system", respectively;
Figures 3A, 3B, 3C and 3D are explanatory views,
showing the steps according to the method of the present
invention; and
Figure 4 is an el.evation of an inspection apparatus
according to the present invention, showing the inspection
apparatus inserted into a pressure tube for inspection.
A pressure tube constituting the core of a pres-
sure tube type nuclear reactor is subjected to an in-service
inspection (ISI) according to the rules. However, since the
pressure tube to be inspected is exposed to a high radiation
environment both internall.y and peripherall.y, the inspection
is carried out on an automatic remote controller so as to
protect the inspection personnel at the time of in-service
inspection.
For structural restriction, the pressure tube
type nuclear reactor cannot have a rail or the like which is
necessary for bringing an inspection apparatus close to the
a~
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pressure tube. ~nder the restriction circumstances as des-
cribed, the pressure tube inspection has been effected on
either of the following two systems according to the prior
art, which will be described with reference to Figures 1 and
2.
The first is a system (hereinafter referred to
as "external
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installation system" for clarification purposes) shown in
Figure 1 wherein an inspection apparatus has a sensor 2
for detecting various defects of a pressure tube 1, a driving
device 3 for the sensor 2, a holder or carriage 4 of the
driving device and a positioning device 6, and is assembled
by hand at the position near the pressure tube 1 before
inspection is carried out. The sensor 2 is mounted on the
top of a supporting rod 5 and inserted within the pressure
tube 1 for inspection through a remote control. After the
inspection is finished, the apparatus is removed out of
the pressure tube and then disassembled by hand. In Figure
1 of the drawing, reference numeral 9 denotes a seal plug
for sealing a reactor coolant in the pressure tube, and
reference numeral 10 a fuel assembly.
The external installation system described above provides
an advantage that inspection personnel is protected from
exposure at the time of inspection only, but has at the
same time serious problems such that an exposure at the
time of assembling and disassembling of the apparatus is
unavoidable, and the assembling/disassembling at each inspec-
tion involves a troublesome and timeconsuming operation.
Moreover, a reactor coolant(water) in the pressure tube
to be inspected must be removed at the time of inspection
unless the inspection apparatus is configured entirely to
have a watertight structure, which however is cost-consuming.
In order to accomplish the removal of the coolant from the
pressure tube, a part of coolant in an inlet pipe and outlet
pipe must be frozen with, for example, liquid nitrogen to
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form an ice plug for working as a valve substitutionally
since there is no valve provided at the inlet and the outlet
of each pressure tube, but provision of ice plug is trouble-
some. Furthermore, it is difficult to install a plurality
of inspection apparatus for space limitation, and thus a
considerably long time will be required for the inspection
of multiple pressure tubes.
The second system in the prior art is a system shown
in Figure 2 (hereinafter referred to as "reflueling machine
combined system" for the purpose of clarification), in which
a driving device 8 of a refueling machine 7 is utilized
not for the purpose of refueling but for the purpose of
insertion of the sensor 2 into the pressure tube for inspection.
Specifically, the sensor 2 is mounted on the supporting
rod 5 thorugh the driving device 8 of ~he refueling machine
7 which is generally provided on a nuclear reactor for loading
and unloading the fuel assembly 10 into and from the pressure
tube. The sensor 2 mounted on the driving device 8 is then
inserted by remote control into the pressure tube for inspec-
tion.
The refueling machine combined system utilizes the
refueling machine as described above, and the operation
for assembling and disassembling the apparatus, which is
required in the first-mentioned external installation system,
is not required.
Thus, the problem of exposure of the inspection personnel
can be settled, and the refueling machine which is of water-
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tight structure requires no removal of water in the pressure
tube. However, the refueling machine is exclusively used
while the pressure tube is subjected to inspection, therefore
a considerably long time also will be required for the
inspection particularly when a number of pressure tubes are
inspected.
The present invention removes the drawbacks pre-
vailing on the prior art systems.
The present invention also provides a system which
can minimize a possibility of exposure of the inspection
personnel in in-service inspection of the reactor pressure
tube and ensure working efficiency with a minimum time for
inspection.
The present invention again provides an inspection
apparatus for a pressure tube of the nuclear reactor, in
which the inspection apparatus has a sensor and a driving
device thereof in a unitary structure adaptable into the
pressure tube.
The invention also provides an inspection method
for pressure tube effective enough to minimize a possibility
of exposure of the inspection personnel at the time of in-
service inspection of the reactor pressure tube and also
to ensure working efficiency with less time for inspection.
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Briefly, the present invention provides a new apparatus
and method for inspecting the pressure tube, utilizing an
inspection apparatus which is a unitary structure of a sensor,
its driving device and a mechanism for securing the sensor
and the driving device. The unitary structure is miniaturized
entirely for ready insertion in the pressure tube to be
inspected. In the present invention, the inspection apparatus
is inserted into the pressure tube by means of a refueling
machine provided generally on a pressure tube type nuclear
reactor for insertion and removal of the fuel assembly into
and out of the pressure tube.
The inspeci~on apparatus according to the present inven-
tion comprises a sensor means, removably and slidably located
within the pressure tube, for detecting defects of the pressure
tube, a driving means for rotational and vertical or longitudi-
nal displacement of the sensor means within the pressure
tube, securing mechanism, releasably connected to an open
end of the pressure tube, for holding the sensor means and
the driving means in position within the pressure tube,
and a sealing device for enclosing a reactor coolant in
the pressure tube.
In the inspection method according to the present inven-
tion, the inspection apparatus of the structure as described
above is inserted into the pressure tube to be inspected
through remote control by means of the refueling machine,
and held in position within the pressure tube, which is
then inspected throuyh remote control. When the inspection
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is finished, the inspection apparatus is removed from the
pressure tube by means of the refueling machine.
Upon analyzing the above-mentioned prior art from various
angles and also examining measures available for settling
defects on the prior art, the inventors have reached the
conslusion that a miniature sensor of the inspecting apparatus
is obtainable hitherto and is ready for inserting within
the pressure tube accordingly, however, the driving device
and holding member of the inspection apparatus are framed
to a larger size, which is problematical in this connection.
Further examinations have obtained the following results:
(1) If the refueling machine 7 is utilized, the positioning
device 6 in the "external installation system" will not
be required, and thus the device 6 can be omitted from the
inspection apparatus.
(2) If the inspection apparatus itself can be inserted
and fixed entirely within the pressure tube 1, then a sensor
driving stroke can be shortened to the same length as an
inspecting range, as a sensor 2 is located near the portion
to be inspected.
(3) The holding member 4 of the inspection apparatus occupies
a considerable area in the external installation system,
however, if the inspeciton apparatus can be inserted full
within the pressure tube, the pressure tube rnay function
as the holding member of the inspection apparatus, therefore
the holding member can be simplified.
(4) The inspection apparatus thus miniaturized and lightweight-
:lZ05589~
ed entirely may entail only a motor of several ten Wattsinstead of several hundred Watts for the driving power
source, and therefore the motor can be replaced by that of
miniature which can be arranged within the pressure tube.
The invention has been contrived according to the
analysis and examinations mentioned above.
A preferred embodiment of the present invention
will be made with reference to the accompanying drawings.
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DETAILED DESCRIPTION OF THE INVENTION
Referring first to Figure 4 which shows the structure
of an inspection apparatus 11 embodying the present invention,
the apparatus 11 is configured to have a shape and size
for insertion completely into the pressure tube 1. The
inspection apparatus 11 has a sensor indicated generally
by reference numeral 15 including, for example, an ultrasonic
test instrument for investigating flaws or defects in the
pressure tube wall, a TV camera for observation of the
state of the pressure tube inner surface, and a bore measuring
apparatus for measuring the inner diameter of the pressure
tube to investigate the "creep" which is an increment in
the inner diameter due to irradiation. Further, the apparatus
11 has a driving mechanism constituted of a vertical driving
device 16 for moving the sensor vertically within and along
the length of the pressure tube and a rotational driving
device 17 for rotationally moving same within the pressure
tube, a securing mechanism 18 for holding the inspection
apparatus in position within the pressure tube 1, and a
sealing unit 20 for sealing a reactor cooling water in the
pressure tube 1.
The securing mechanism 18 is readily releasably engaged
with the pressure tube 1, which may becon5tituted by a combina-
tion of, for example, ball and latch. The driving mec.hanism
16, 17 is firmly held on the securing mechanism 18 to movably
support the sensor 15. The vertical driving device 16 is
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formed of a pinion 25 and rack 26 in the illustrated embodiment,
which however can be modified to a wire driving structure.
Three pieces of rotary ball type guides 19 are provided
on the circumference of a moving part of the inspection
apparatus 11, in which the sensor 15 is received. These
guides 19 are in contact with the inner surface of the pressure
tube 1 to position the moving part at the center at all
times, and thus guide it for a smooth vertical movement
and a rotational operation within the pressure tube 1.
Preferably, one of the three guides 19 is biased outwardly
by a spring (not shown) so as to maintain the three guides
19 in contact with the inner surface of the pressure tube
1 irrespective of any slight change in the inner diameter
of the pressure tube.
The inspection apparatus 11 is handled by the refueling
machine so that it is inserted into and removed from the
pressure tube 1 through remote control. Then, a connector
14 mounted on the end of a signal transmission cable 13
is releasably connected with the inspection apparatus 11
by means of a manipulator 22 of the refueling machine 7,
and the inspection apparatus 11 is operated through remote
control by a control pannel 12 connected to the signal trans-
mission cable 13. The connector 14 may be releasably engaged
with the inspection apparatus 11 by the use of, for example,
a ball and latch mechanism.
Operational steps of the inspection apparatus 11 will
be described with reference to Figures 3A to 3D.
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(i) Withdraw the fuel assembly:
First, the fuel assembly 10 in the pressure tube to
be inspected is withdrawn by means of the refueling machine
7, and the seal plug 9 for sealing the reactor coolant in
the pressure tube l is mounted~
(ii) Install the apparatus in the refueling machine:
The inspection apparatus 11 is then hang down by a
crane 23 and installed in the refueling machine 7 (Fig.
3A)-
(iii) Couple the refueling machine to the pressure tube:
Next, the refueling machine 7 is driven to move underthe pressure tube 1 to be inspected and positioned duly
(Fig. 3B), then an upper end of the refueling machine 7
is coupled to a lower end of the pressure tube 1 so that
the reactor coolant will not leak out of the pressure tube,
and the seal plug 9 is demounted. (A demounting procedure
of the seal plug 9 is not particularly illustrated, however,
its function is included in the refueling machine 7.)
(iv) Insert the apparatus into the pressure tube:
urther the inspection apparatus 11 is inserted within
the pressure tube 1 (Fig. 3C), and the inspection apparatus
11 is fixed in the pressure tube 1 through the securing
mechanism 18 ~Fig. 4) of the inspection apparatus 11. In
this case, the reactor coolant is sealed by the sealing
unit 20 of the inspeciton apparatus 11.
(v) Connect the connector to the apparatus:
Then, the refueling machine 7 is displaced somewhat
to align the manipulator 22 with the pressure tube 1 to
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be inspected, and the connector 14 is connected to the inspec-
tion apparatus 11 by the manipulator 22 (Fig. 3D). The
manipulator 22 and the refueling machine 7 may be removed
from the inspection apparatus after connecting the connector
14 to the inspection apparatus 11. These operations can
be effected all through remote control by the refueling
machine 7 and the manipulator 22.
(vi) Inspection:
Everything is now ready for inspection, and as shown
in Fig. 4, the sensor 15 is moved to the spot for inspection
by operating the vertical driving device 16 and the rotational
driving device 17 through remote control from the control
panel 12. In this case the guides 19 function for operating
the inspection apparatus 11 smoothly in the pressure tube,
as described hereinabove. When the inspection is finished,
the above procedure is reversed to withdraw the inspection
apparatus 11 from the pressure tube.
In the above embodiment a signal is transmitted between
the inspection apparatus 11 and the control panel 12 by
way of the signal transmission cable 13, however, a wi.reless
transmission system can be employed, if desired.
According to the inspection method of the present inven-
tion, the operation fox assembling and removing the inspection
apparatus near the reactor core is not required before and
after inspection, and thus an exposure of the inspection
personnel can be decreased to 1/10 or below as compared
with the conventional "external installation system". Further,
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it is not necessary to withdraw coolant in the pressure
tube to be inspected, which may avoid a troublesome preparation
for the inspection. Furthe, the refueling machine can be
used freely after the inspection apparatus is inserted in
the pressure tube to be inspected, and the other inspection
apparatus, if additionally prepa.red, can be used for inspec-
tion of other pressure tubes simultaneously while one pressure
tube is subjected to inspection, therefore the time required
for inspection can be shortened considerably as compared
with the conventional "refueling machine combined system".
Although the present invention has been described with
reference to the preferred embodiment thereof, many modifica-
tions and alterations can be made within the scope of the
appended claims.
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