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657
REMOTE VISUAL INSPECTIONS OF RPV AND REACTOR INTERNALS
Author: Jani Pirinen, Fortum Power and Heat Oy, Finland
Co authors: Petri Seppälä, Fortum power and Heat Oy, Finland, Raimo Paussu, Fortum Power and
Heat Oy, Finland
ABSTRACT
Fortum operates two VVER-440 Nuclear Power Plant units in Loviisa, Finland. The in-service inspection
of components is closely following ASME Section XI requirements. Inspection interval of RPV inside
inspection is 8 years and reactor internals are removed from reactor every 4th year and the protective tube
unit every year.
Fortum uses both own staff and camera systems for ISI of reactor internals as well as services and
equipment of inspection companies, depending on the inspection object.
Fortum plans inspection programs for 10 years period and prepares the inspection procedures,
actions and schedules for each outage. Remote VT inspection has an important role to ensure and verify
the structural integrity of the components. Inspection objects at high radiation areas are inspected using
black and white camera. Color cameras are used whenever the dose levels are low enough.
Remote VT inspection of RPV and internals includes special inspection objects at both Loviisa NPP
units. The most challenging objects are determined to be in the core basket due to high radiation levels and
the complex geometry. Remote VT inspection of RPV internal cladding surface has an important role in 4
years interval outage, because other NDT methods such as ET and UT are not performed, due to their 8
years interval. The qualification of remote visual inspection may be required in the future. This paper
presents overview and the present status of VT inspections at Loviisa power plant.
INTRODUCTION
Fortum operates two VVER 440 Nuclear Power plants in Loviisa, Finland. Visual inspections are done
directly (with e.g. by eyes or binocular) or indirectly (remote visual inspection with e.g. camera). Main
purpose for inspections is to ensure and verify the structural integrity of the components.
Remote visual inspections for reactor pressure vessel (RPV) and its internals belong to 10-year
interval component inspection program. Also other main components belong into the same program, such
as steam generators, main circulation pumps, pressurizer and RPV head. The program shall full fill the
Finnish YVL (Regulatory Guides for nuclear safety) guideline 3.8 [1] and it follows closely ASME
section XI [2] requirements completed with Finnish pressure law. STUK (the Radiation and Nuclear
Safety Authority Finland) approves inspection programs and procedures, results of inspections as well as
supervises inspections.
Reactor pressure vessels are inspected visually every 4th year. During long outage in every 8-year
reactor pressure vessels are inspected with eddy current and ultrasonic inspection with supplementary
visual inspection. Remote visual inspections are also done for RPV and internals in the middle of the 8-
year interval, in so called 4-year inspection. Remote visual inspections and methods have belonged to
component program since 1982. Since then remote visual techniques have been development to keep the
inspection quality in high level. Mainly work have been done by following technological development and
latest solutions.
The aim of this paper is to present current status of the inspections objects and challenges related to
selected inspection objects inspected with remote visual inspection system. These challenges are mostly
related to environment and geometry aspects. There are also presented documentation methods with the
way of comparison to previous inspection.
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Inspection objects, methods and guidelines
Remote visual inspection objects of internals are intermediate rods, protective tube unit, core basket, pit
and pit bottom. Visual inspection objects of the RPV are welds related to instrumentation (pipes, supports
and cover box), Flow separator area, nozzle areas (main circulation and emergency coolant nozzles),
circumferential core area weld, radial support areas, material sample areas and bottom segment of a
sphere. Over view of visually inspected components are presented in Figure 1
Figure 1. Over view of visually inspected components
Remote visual inspections in Loviisa Nuclear Power Plants are performed by Fortum employees
under supervision of the third part as well as external suppliers. External suppliers are mainly used for
objects where advanced technologies in manipulator techniques are assessed to be used in time consuming
and economically point of view.
Reactor pressure vessels are inspected visually during the ultrasonic and eddy current inspection.
Current 8 year interval inspections are performed by external supplier. Supplementary internal visual
inspections of RPV for external UT inspection of core weld as well as internals are carried out in the
middle of the 8 year interval. The shortest inspection interval is for protective tube unit (upper structures)
with binocular and one set (9-10 pieces) of intermediate rods with color camera. Those inspection objects
are inspected every year at both units.
Remote visual inspections are performed with black and white or color camera. Cameras are
connected to manipulator and control unit. Inspection system includes also lighting unit and monitors.
Linear and/or rotating type manipulators are used in inspections operated by Fortum employees. Refueling
machine is also used in some inspections e.g. in inspection of intermediate rod objects.
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Color cameras are supplied by Swedish company Ahlberg Electronics [3]and when Black and white
cameras are needed for inspection, Russian Diakont company's cameras [4] are assembled to manipulator.
Used techniques are presented
Figure 2
Figure 2. Examples of used techniques. Diakont camera [5]on left and Ahlber electronics [6] on right.
External suppliers use their own designed manipulators or submarine system. Any special requirements
are not set for manipulator systems e.g. positioning of indication. View angle requirements are according
to the AMSE code. Viewing angles less than 30° between the surface and the direction of viewing must be
avoided, when physically possible; therefore, the viewing angle may vary by ± 60° from the perpendicular
line. Camera systems shall full fill the resolution requirements (450 lines/500 lines) tested with EIA 1956
Resolution chart or underwater table. Used test charts are presented
Figure 3.
Figure 3. Underwater tables upper part on left and lower in the middle and EIA 1956 Resolution chart on
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most right.
For inspections of the internals and RPV have several separate inspection procedures. Amount of
procedures for a component depends for a complexity of geometry and inspection method (direct or
indirect visual inspection). Usually there are at least procedures for internal and external inspection and for
some components has also a procedure for direct inspection. Internal inspections of reactor pressure vessel
inspection objects have inspection procedures for direct and indirect inspections.
Challenges of the inspection objects
Challenges for inspections are caused by environment and geometry of component. Environment
challenges during the inspection mainly consist from radiation levels. Surface conditions effect also for the
quality of inspection. In some cases amount of scrud in surface limits inspection scope. When necessary
and possible, the scrud and other similar particles are removed before inspection
Another factor increasing the challenge level is the geometry of the component. In complex
geometry components have several angles, linear and needs for rotation movements of manipulator.
Because of the complex geometry there are some inspection objects when it is not always possible to
perform inspections in optimum angle. These cases are handled with optimizing manipulator movement
and avoiding angles less than 30 degree.
Intermediate rods are assessed as simple geometry object. Inspections of intermediate rods are performed
by using refueling machine. Totally there are 4 inspection objects to be inspected. Inspection objects of
intermediate rods are categorized according to ASME XI to class B-N-3 with inspection requirement VT-
1. All items are inspected with rotating movement. See
Figure 4 and more detail view on
Figure 5.
Figure 4. Example from geometrically simply inspection objects. Marked support bush on left and
locking washer and bayonet on right
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Figure 5. Support bush on left and locking washer and bayonet (below of the measurement) on right
Most challenging inspection objects are assumed to be in the core basket (see
Figure 6 and
Figure 7), due to complex geometry and high radiation level. In core basket there are totally 10
inspection objects during the internal inspection and in external inspection there are totally 4 objects to be
inspected. Inspection objects are categorized as B-N-3 according to ASME XI and for VT-1 class visual
inspection method.
Figure 6. Example from geometrically complex inspection objects, the core basket
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Figure 7. Detail view from upper inspection object of core basket on left and lover objects on right
RPV challenges are mainly environment challenges. The cleanliness of the bored water effects to the
picture quality. Visibility in the water decreases whit the amount of scrud in the water. Scrud also affects
to defectiveness when it have been stuck to surface. Possible crack opened to surface under scrud layer is
assumed to be the worst case thus the possibility miss indication increases. There are totally 17 objects to
be inspected with remote visual inspection. Inspection objects are presented in
Figure 8. Items are categorized according to ASME as B-N-1 or either B-N-2. Requirement for all
inspection objects is VT-1 class visual inspection.
Figure 8. Inspection objects of external inspection of the reactor pressure vessel
Goals of the inspections
The goal of the remote visual inspection of the RPV and reactor internals is to verify the structural
integrity. The fault types to be searched in the inspection have small differences between component and
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the inspection object. Typical fault types to be search are integrity of welds and structure, cleanliness of
the structure and possible leaking marks. Also important targets in inspections are to evaluate possible
abrasion wears, scratches, impact marks on surface and cutting marks. Visual inspections should also give
information if other NDE inspections should be added for inspected component.
Reportable findings will be documented to record (log sheet) with comparison to previous inspection and
evaluation of its acceptability. Impacts to utilization needs for addition inspections are evaluated in the
cases of the new indication. For example, according to visual hologram inspection results from baffle bolts
of core basket condition additional UT inspection was performed, see
Figure 9. With UT inspections more accurate information was get from the structural integrity of
the baffle bolts.
Figure 9. Comparison of the hologram inspection (on left) and visual inspection on right
Typical findings in the intermediate rods are scrud and slight erosion. The intermediate rods can be
changed based on the inspection results. One reason for change is wearing of the support bush to its
minimum, body pipe (see
Figure 10).
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Figure 10. Change limit to intermediate rod (marked to picture)
The goal of reactor pressure vessel inspection is to determinate the integrity of the component. Special
focus is set on inspection to verify the integrity of cladding and core area circumferential weld. There are
also searched cracks, scratch, cutting marks on sealing and glide surfaces and marks of water flow through
sealing surfaces. Typical followed indications are presented in
Figure 11.
Figure 11. Typical followed and detected indications of RPV. Scratches on flow separator ring is
presented on left and wear marks on radial support on right
There are also differences between NPP units RPV inspection objects. One of the interests is in the
construction of the flow guides. From fatigue point of view in unit 2 has been done improvements
compared to unit 1. Differences like drillings at the end of cuttings are presented in
Figure 12
Figure 12. Differences between flow guides in unit 1 (on left) and unit 2 (On right)
The geometry of the core basket is more complex and as mentioned previously it has assumed to be most
challenging inspection object. Radiation level is high and it affects to picture quality and set high
requirements for camera technique. Difference between color and black and white camera pictures in
radiation environment is presented in
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Figure 13.
Figure 13. Difference between color and black and white camera picture in radiation environment
Indications which have set to be searched are similar as in RPV inspection. Special focus for inspection is
in the baffle bolts and their integrity and position. The inspection verifies that the screws are at the liner
plate level. Cracks have been found from the linear plate, caused by assembly technique (see
Figure 14).
Figure 14. Example from cracks which has found from linear plate
FUTURE ACTIONS
Inspections have been and will be under constant development. Development of the new techniques and
methods are closely followed and own research has been done. Every year a new inspection program has
been done following the 10 year program and if necessary changes are added to component program.
Changes are made if e.g. something important has been found in other nuclear power plants. The results
are evaluated from the point of view if it is possible in Loviisa as well as should a new inspection object
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add to program. Also needs for additional inspections and/or alternative focused inspection object of the
component are evaluated.
So far the visual inspection program as a part of yearly component program has been quiet similar,
following the 4 year interval. Resent years has been done probabilistic based in-service-inspection
program for all piping system in Loviisa NPP according to ASME XI. At the moment component
inspection program is based to the deterministic method. Evaluating total risk of the nuclear power plant,
both programs (component and pipe) are contained to calculations. One big effect for total risk arises from
heavy lifting of the internals. It has been evaluated that the total risk on one year can be decreased even
17% if remote visual inspections interval of the internals decrease from 4 year to 8 year.
At the moment there have been discussion concerning qualification of the visual inspections. So far
only eddy current and ultrasonic inspection procedures have been under qualification. Qualifications of the
VT inspections are not considered to follow similar procedure as UT and ET. The qualification has been
planned to carry out more flexible by evaluating the inspection procedures by utility 3dr party and
regulator.
SUMMARY
Visual and especially remote visual inspections have an important role in ISI for complementing other
NDE inspection to ensure and verify the structural integrity of the components. With the visual inspections
other NDE inspections are added to program, like ultrasonic inspection of the baffle bolts. Constant
development of the techniques, methods and inspection procedures are required to get high quality results
from inspections.
In this paper were presented the general remote visual inspection procedure concentrated to reactor
pressure vessel with example from simple and complex internal component. Selected component
represents both extremities. All internals have similar challenges by reason of environment (especially
radiation level and clearness of the water), component geometry and fault types to be searched.
Challenges are solved by optimizing manipulator tracks and camera angles. Used cameras are
selected to get sufficient resolution for high quality picture. Also external suppliers are used when
advanced technologies in manipulator techniques are assessed to be used in time consuming and
economically point of view.
REFERENCES
1) YVL 3.8, Nuclear power plant pressure equipment 22 September 2003,
http://www.edilex.fi/stuklex/en/lainsaadanto/saannosto/YVL3-8
2) ASME Boiler and Pressure Vessel Code, an international Code, XI Rules for In service Inspection of
Nuclear Power Plant Components, 2011a addenda
3) Website http://www.ahlberg-electronics.com/
4) Website http://www.diakont.com/
5) Camera information from website
http://www.diakont.com/solutions/nuclear-energy/camera/visual-inspection-d40-camera/
6) Camera information from web site
http://www.ahlberg-electronics.com/products/product/id/33?cat=12
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