ENIQ-Qualified Visual Examinations by Means of a Remote

O P E R AT I O N A N D N E W B U I L D
452
atw Vol. 60 (2015) | Issue 7 ı July
ENIQ-Qualified Visual Examinations by
Means of a Remote Controlled Submarine
Elenko Tsvetkov and Jan Heinsius
Introduction The ENIQ “European Network for Inspection and Qualification” is a European network developing
methods for the qualification of non-destructive examination methods for nuclear power plants. The network is driven
by nuclear plant operators, inspection companies, nuclear component and system suppliers, regulation bodies and
non-destructive institutes. The network deals with the reliability and effectiveness of non-destructive examination
methods for nuclear power plants. The main objective of this network is to harmonize the different national standards
and codes related to qualifications of inspection personnel, equipment and methods. The network publishes recommendations for an objective assessment of the technical capability of non-destructive examination systems.
ENIQ-qualified remote visual
examination
Remote visual examination is one of
the most important methods for
non-destructive in-service inspections
of primary components at nuclear
power plants. It features two main advantages, short examination duration
and fast interpretation of results. It
does not require extensive preparation
and the examination is relatively
short. The results are clear and explicit, without any undetermined indications.
Many European countries are considering the ENIQ-methodology and
its recommended practices. An
ENIQ-qualification establishes the essential parameters for a non-destructive testing method. For the remote
visual examination, some of the essential parameters are: illumination,
examination distance, viewing angle,
scanning speed, positioning accuracy
and sizing of indications. An ENIQqualified visual examination requires
fulfillment of all essential parameters
during the entire examination.
ENIQ-qualified remote visual
examination presented by
the example of the reactor
pressure vessel
The inner surface of the reactor pressure vessel (RPV) has to be visually
examined after a period of time according to codes and standards. The
time lag between the periods is established by the national regulation body
and implemented through the inspection manual of the nuclear power
plant operator.
The remote visual examination is
the most effective method to perform
a qualified visual examination.
Prior to the remote visual examination of the inner surface of the RPV,
the inspection system and personnel
have to pass a qualification process.
The main steps of the qualification
process are:
ƒƒ Preparation of the TJ “Technical
Justification” that defines all the
essential parameters. The TJ serves
as justification that the inspection
system is capable of meeting the
technical requirements for the remote visual examination.
ƒƒ Preparation of the Examination
Procedure that describes the inspection system and specifies the
requirements for the inspection
personnel certification, the inspection sequences, the inspection
area, the inspection method VT-1/
VT-3 for each inspection area, the
calibration/verification process for
the inspection system, the process
for the evaluation of findings, the
documentation and the presentation of the inspection results.
Both documents, the Technical Justification and the Examination Procedure, have to be reviewed and approved
by the nuclear power plant operator
and the regulation body. After the approval of the documents, the inspection company must demonstrate the
capability of the inspection system in
front of an accredited qualification
body, the regulation body and the
nuclear power plant operator. After
the successful demonstration, the inspection system is qualified and the
qualification will be documented with
a qualification dossier issued by the
accredited qualification body. After
the inspection system qualification,
the inspection personnel of the accredited testing laboratory has to
demonstrate its capabilities on test
blocks with natural indications with
the qualified inspection system in
front of an accredited qualification
body, the regulation body and the
nuclear power plant operator. The
demonstration consists of the correct
use of the inspection system, the de-
Operation and New Build
ENIQ-Qualified Visual Examinations by Means of a Remote Controlled Submarine ı Elenko Tsvetkov and Jan Heinsius
tection and the evaluation of indications according to the examination
procedure. After the successful demonstration the inspection personnel
is qualified and the qualification will
be documented with a qualification
certificate issued by the accredited
qualification body.
For the inspection on site the approved examination procedure, the
certificate of the qualified inspection
system and certificates of the qualified
inspection personnel must be present.
The right choice of
manipulator for the visual
examination inside the RPV
How can an ENIQ-qualified remote
visual examination be performed at the
inner surface of the reactor pressure
vessel of pressurized water reactors?
Possibilities that come to mind are
to use the same stable manipulator
used for the ultrasonic testing (UT) of
the reactor pressure vessel from inside
or to use a camera system mounted to
poles and operated from the refueling
auxiliary bridge.
The advantage of fixing a video
camera instead or in addition to the
UT probe is the possibility to perform
the examination within the essential
parameters by using the encoder system of the UT manipulator. The disadvantages of using the UT manipulator
or a camera system mounted to poles
are the time needed for such an examination and the use of reactor floor
equipment such as the polar crane, the
refueling machine or the auxiliary
bridge. The reactor floor equipment is
elementary necessary on the critical
path for an outage for different work
scope. Therefore, it is not the best solution to use this kind of manipulator for
ENIQ-qualified visual examinations.
Hence, the question rises whether
there is another possibility to perform
ENIQ-qualified visual examinations
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without working on the critical path
and causing any delay in the time
schedule. AREVA presents the answer
to this question with “SUSI 420 HD“.
“SUSI” stands for SUbmarine System for Inspection. With 20 years of
experience in the field of underwater
visual examination and the development of inspection manipulators,
AREVA can provide state of the art underwater submarine systems and
highly certified and experienced personnel to meet all criteria for passing
the qualification process of an ENIQQualified remote visual examination.
“SUSI 420 HD” one
submarine out of AREVA´s
submarine family
Equipped with a high definition camera
with a resolution of more than 750
lines (pixels 1920 x 1080) , “SUSI 420
HD” is the most flexible remotely operated manipulator for visual examinations of reactor pressure vessels of pressurized water reactors. It weighs only
25 kg, so there is not even need for a
crane to put the submarine into water.
Moreover, visual examinations with
“SUSI 420 HD” require neither the use
of the refueling machine nor the use of
the auxiliary bridge. In this way the
visual examination can be performed
in parallel to other activities which are
on the critical path, for example UT of
the reactor pressure vessel from inside
or in parallel to the assembling and disassembling of the UT manipulator.
In addition to the high quality, the
easy assembling, the independent operation, the time efficiency and the
flexibility, “SUSI 420 HD” can be operated from any place at the reactor pool
floor. The distance to the reactor cavity reduces the personnel dose exposure to a minimum compared to camera systems operated from the refueling machine or the auxiliary bridge. By
using “SUSI 420 HD” the personnel
dose ALARA (As low as reasonably
achievable) requirements are supported at its best.
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Fig. 1.
Crawler mounted to the submarine.
Beside ENIQ-qualified remote
visual examination, “SUSI 420 HD”
can support other activities during the
entire outage such as “FOSAR” (Foreign Object Search and Retrieval), observation of component handling under water, core mapping, fast and flexible under water image support of detected problems and non-qualified
visual examinations.
In the following, we take a closer
look at the essential parameters such
as: illumination, examination distance,
viewing angle, scanning speed and positioning accuracy. We will describe how
“SUSI 420 HD” can fulfill these parameters through some adaptations.
Illumination
One essential parameter is the illumination of the component surface.
Nowadays, it is very common to replace Halogen lighting by LED lighting. For the development of “SUSI 420
HD”, AREVA compared Halogen light
and LED light for the detection of
cracks. The laboratory trials have
shown that it is very important to perform the visual inspection with a combination of Halogen and LED lighting
that can be varied in brightness and
incidence angle. “SUSI 420 HD” is
equipped with (2) two 80 Watt LED
bars that can be turned on and off separately. The main purpose of the LED
lighting is to provide a very bright and
diffuse illumination for the inspection, especially the VT-3 inspections.
The HD camera is equipped with (4)
four 35 Watt Halogen lights around
the lens. The (4) Halogen lights are
following the camera and can be
dimmed stepless from 0 to 100 %. For
VT-1 examinations the surface illumination with Halogen light is the
best solution for crack detection. The
combination of the two different light
sources allows the most flexible illumination of the object surface.
Examination distance and
scanning speed
The determination of the
examination distance is
realized in two different
ways. If the object is fully
accessible and the surface
is flat and without any
obstacles like the cylindrical part of the Reactor Pressure Vessel, the
inspection distance will be
realized by using a crawler
mounted to “SUSI 420
HD” (Figure 1).
The crawler (1) is fixed
to the submarine (2) at the
Operation and New Build
ENIQ-Qualified Visual Examinations by Means of a Remote Controlled Submarine ı Elenko Tsvetkov and Jan Heinsius
necessary inspection distance by four
screws (3). By using the horizontal
thrusters of the submarine, the crawler
is pressed to the reactor pressure vessel
surface. The two drive motors (4) that
are connected to the two belts (5) enable the horizontal movement of the
crawler over the examination surface.
The scanning speed can be adjusted
stepless by using the remote control of
the submarine in order to fulfill the required scanning speed for a VT-1 and
for a VT-3 inspection. The adaptation
of a crawler to “SUSI 420 HD” allows
keeping a constant inspection distance
and scanning speed during the entire
examination.
If the examination object is not
fully accessible or the surface is not
flat like the calotte of the reactor pressure vessel, the determination of the
inspection distance will be realized by
using a transit time sensor (Figure 2).
The two transit time sensors (1)
and (2) are fixed on the camera head.
The high definition camera can be
moved up and down (tilt) and rotated
(pan). The distance meter follows
each movement of the camera and allows the proper measurement of the
examination distance during the entire examination.
Viewing angle
Practical investigations have shown
that VT-1 inspections must be carried
out at as straight as possible viewing
angles. This applies for the vertical (λ)
and horizontal (β) viewing angle (Figure 3).
The vertical viewing angle is determined through the camera coordinate tilt. The tilt is displayed on the monitor during the entire examination.
The horizontal viewing angle is
determined either by the crawler
(Figure 1) or by the transit time
sensors (Figure 2).
If the crawler is mounted to the
submarine and pressed to the examination surface, the horizontal viewing
angle is absolutely straight.
If the two transit time sensors are
mounted the horizontal viewing angle
will be measured as trigonometric
function. For a straight viewing angle,
the difference between the two distances should be close to zero. The
higher the difference, the larger the
deviation from the horizontal straight
angle.
Positioning accuracy
Another essential parameter is the positioning accuracy. In case that an indication is detected, the position of
the indication must be determined as
atw Vol. 60 (2015) | Issue 7 ı July
“SUSI 420 HD” not only for
reactor pressure vessel
examinations
Apart from the visual examination of
the reactor pressure vessel, the “SUSI
420 HD” submarine can be used for
the visual examination of the upper
and lower internals and the main
coolant lines.
A carriage mounted on the submarine ensures that the camera will
be positioned in the middle of the
main coolant lines during the entire
inspection. The carriage can be moved
up to pass nozzles located inside the
main coolant lines (Figure 6) and
O P E R AT I O N A N D N E W B U I L D
Sizing
The detection target is defined at the
beginning of an ENIQ-Qualification.
The detection target is an indication
with certain length and width. The
width for VT-1 examination is given
almost in micrometer (µm). Even
though the high definition camera
has a 36 x optical zoom, practically a
precise measurement of the width is
not possible. Proper width measurement can only be performed in laboratory conditions by using a microscope.
Therefore, the sizing of indications
is limited to the length measurement.
Length measurement will be performed by means of two laser lines
(Figure 4).
The two separate lasers (1) and (2)
that are integrated in the camera head
produce two laser lines which are parallel to each other (Figure 5).
The distance between the two laser
lines amounts to 20.5 mm. The distance will be calibrated before the
length measurement. A verification of
the distance between the laser lines
will be carried out in order to ensure
that the measurement will be performed accurately.
By using computer software, the
distance of 20.5 mm is set on the picture. Thereafter, the length measurement is performed on the basis of the
calibration. The length of the indication in Figure 5 amounts to 4.83 mm.
455
accurately as possible. The position of
an indication in the reactor pressure
vessel is defined through its axial and
circumferential position. Mounting a
depth sensor on the submarine allows
the determination of the axial position of an indication. The circumferential position will be established by
means of an overview camera. The
pan value of the camera corresponds
to the position of the indication in circumferential position.
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Fig. 2.
Two transit time sensors fixed on the camera.
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Fig. 3.
Definition of the vertical and horizontal viewing angle.
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Fig. 4.
Position of the line lasers.
down to position the camera in the
middle.
Long-time experience in ENIQ
qualified visual examinations
The accreted testing laboratory of
AREVA GmbH, IBOO-G (D-PL-1115304-00) is specialized in visual examinations of pressurized and boiling water reactors.
The testing laboratory has done
different qualifications and examinations in accordance with ENIQ. The
variety of qualifications carried out in
different European countries has
shown that the testing laboratory is
able to carry out qualifications and
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Fig. 5.
Laser lines shown on the surface.
visual examinations due to the requirements of the domestic qualification bodies and nuclear power plant
operators. Realizing the increasing of
the importance of ENIQ, the testing
laboratory is continuously carrying
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ENIQ-Qualified Visual Examinations by Means of a Remote Controlled Submarine ı Elenko Tsvetkov and Jan Heinsius
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main coolant lines. The
state of the art equipment
allows the fulfillment of
all essential parameters.
The long time experience
of the testing laboratory in
the field of ENIQ qualifications ensures that the
qualification will be completed on time. Due to the
flexibility of the submarine, the examination can
be implemented within a
reasonable time frame
and without work on the
critical path.
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Fig. 6.
Carriage mounted on “SUSI 420 HD“, on the left – carriage down, on the
right – carriage up.
out practical trials and improving its
visual examination technique and is
able to cope with any customer requirements.
||
Authors
Fig. 7.
“SUSI 420 HD”.
Conclusion
for an ENIQ-qualified remote visual
The article concludes that “SUSI 420 examination of the reactor pressure
HD” (Figure 7) is the right solution vessel, upper and lower internals and
Elenko Tsvetkov and
Jan Heinsius
AREVA GmbH
Paul-Gossen-Straße 100
91058 Erlangen,
Germany
Imprint
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