REMOTE VISUAL INSPECTIONS OF RPV AND REACTOR INTERNALS ... · PDF file657 REMOTE VISUAL...

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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 4 th 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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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