E-Journal of Advanced Maintenance Vol.2 (2010) 77-81
Japan Society of Maintenology

Inspection, Evaluation and Maintenance Guidelines
for Reactor Vessel Internals in JAPANAkihiro SAKASHITA1,*,Tomoya GOTO1 ,Shinro HIRANO2, and Koji DOZAKI3
1Tokyo Electric Power Company, 1-1-3 Uchisaiwai-cho, Chiyoda-ku, Tokyo 100-8560, JapanThe Kansai Electric Power Company, 13-8 Goichi, Mihama-cho, Mikata-gun, Fukui 919-1141, Japan
3
The Japan Atomic Power Company, 1-1 Kanda-Mitoshiro-cho, Chiyoda-ku, Tokyo 101-053, Japan
2ABSTRACT
Inspection and Evaluation Guidelines for reactor internals has been taken into the Rules on Fitness-for–Servicefor Nuclear Power Plants of The Japan Society of Mechanical Engineers. It is a base of the maintenance plan ofeach Nuclear Power Plant. A plant maintenance methodology will have more importance to maintain the plantsafety and stable plant operation. This paper introduces the systematization of the maintenance such as repair,replacement, preventive maintenance in these guidelines. Maintenance methodologies are classified follows.
・Repair : methodology to reinforce degraded parts by some methods or prevent progress of degradation ofwithout replacement of the existing structure when the degradation of structure is actualized.
・Replacement : methodology to replace the existing structure with new one when the degradation of structure isactualized.
・Preventive maintenance : methodology to mitigate the damaged condition.
When the maintenance methodologies are implemented in the actual plant, we have to consider the feedback ofthe inspection program and plant life management.
KEYWORDS

ARTICLE INFORMATION

Inspection and Evaluation, Guideline, reactor vessel internals, repair,preventive maintenance

Article history:
Received 17 May 2010
Accepted 2 August 2010

1. Introduction
In recent years, several SCC (Stress Corrosion Crack) at the austenitic stainless had been foundand reported in domestic and foreign reactor vessel internals and primary boundary piping. [1]In the U.S., the PWR Owners Group (PWROG) and BWR Owners Group (BWROG) have defined
the function and ageing mode for reactor internals, published a guideline of inspection and evaluation for
the reactor vessel internals. Moreover, they have discussed technical and reasonable inspection andevaluation methodology with the US Nuclear Regulatory Commission (NRC) based on these deliverables.
Similarly, Japanese Industry and Academic Committee has discussed and made a guideline ofinspection and flaw evaluation since more than ten years ago in order to make a proposal on theexistence of the reactor vessel internals inspection and evaluation.
These guidelines are classified following sections for each component that consist of the reactor
vessel internals.
-Inspection and Evaluation-Maintenance Methodology-Preventive Maintenance Methodology
This inspection and evaluation guideline had been applied to JSME Fitness-for-Service rules
already, and it has been basis of maintenance plan for the reactor vessel internals of Japanese BWRs
and PWRs. [2] In the future maintenance, inspection for the structures after repair, the replacement
and the preventive maintenance becomes important. This paper mentions inspection and flaw
evaluation guidelines, moreover, introduces the systematization and the idea of the repair, thereplacement and the preventive maintenance in the guidelines.
*

Corresponding author, E-mail: sakashita.a@tepco.co.jp

ISSN – 1883 – 9894/10 © 2010 – JSM and the authors. All rights reserved.

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A.SAKASHITA et al./ Inspection, Evaluation and Maintenance Guidelines
for Reactor Vessel Internals in JAPAN2. Inspection and flaw evaluation
Inspection guidelines consist of “Individual inspection” and “General inspection”. Individual
inspection defines the scope, method and frequency of inspection to maintain each component integrity
considered with the assumed ageing degradation. For more safety, General inspection is required for
all internals even though the specific degradation is not assumed, in addition to Individual inspection.
When any flaw is found in the inspection, the influence for the component integrity has to beevaluated as follows. Detected flaw will be modeled on conservative length and depth. Residual stressand other mechanical stress distribution of the flaw propagate direction will be calculated by FEM
analysis or the mock-up test. Crack propagation will be estimated depending on the K-value withconservative crack growth rate (da/dt). Fracture evaluation will be done to confirm the component
integrity in the plant life duration. If required, the component will be repaired or replaced based on themaintenance guidelines.

3. Comparison conventional with current maintenance
Before the establishment of Fitness-for-service Rules, repair or replacement was required whenflaw is detected on time-based inspection. We have been able to implement flaw evaluation, and makejudgments continuous operation or maintenance activity a result of structural integrity evaluation withflaw growth by using Fitness-for-Service. (Fig.1)
Plant Design andConstruction

Plant Design andConstruction

Plant Operation

Plant Operation
NoIndication

NoIndication

Time-based
Inspection

Not Acceptable(Flaw Found)

Repair orReplacement

Time-based
Inspection
ContinuousOperation

Repair or Replacement was required before theestablishment of Fitness-for-service RulesFlawFound

Flaw Evaluation

Repair orReplacement
as Required

Structural Integulity Evaluation
with Flaw Growth

If required

Definite Rules are necessary for Inspection,
Evaluation and Repair / Replacement

Fig. 1 Conventional and current maintenance flow diagram

4. Position of Repair / Replacement / Preventive maintenance
Under time-frame of nuclear plant management in Japan, the guideline is applied on the step ofmaintenance actions after starting plant operation. The maintenance actions contain repair,replacement, preventive maintenance (Fig 2).

Plant
DesignPlant
Turn / Over
Construction &Plant
Installation
Operation

Operation &MaintenanceManagementInspection
Flaw evaluation【Applied Code and Standard 】【Applied Code andStandard 】

・Design and Construction
Rules of JSME・Fitness-for-service

RepairReplacement
Predictive Maint.

Rules of JSME・Inspection, Evaluation andMaintenance Guidelines

Fig 2 Time-frame of Nuclear Plant Management in Japan78

A.SAKASHITA et al./ Inspection, Evaluation and Maintenance Guidelines
for Reactor Vessel Internals in JAPANFig.3 shows the maintenance activities schematically. Repair is performed when ageing
degradation such as SCC and/or fatigue crack are conformed tangibly. Replacement is performed
regardless of subconscious or tangible of ageing degradation. Preventive maintenance is performed
before ageing degradation is actualized.
Maintenance Activities
Replacement
Preventive Maintenance
Growthof Flaw

RepairTangible
as a Flaw
Limitation ofthe detection

Initiationof flaw

subconscious

tangibleTime

Start of operation

Fig 3 Definition of the maintenance activities

5. Definition and Classification
A repair, replacement and preventive maintenance are defined as follows.
・Repair : methodology to restoration degraded parts by some methods such as welding so on, orto prevent progress of degradation of without replacement of the existing structure when thedegradation of structure is tangible.
・Replacement : methodology to replace the existing degraded structure with a new one orimproved one when the degradation of structure is tangible.
・Preventive maintenance : methodology to mitigate the degradation or damaged condition.
Also, the parts to which it applied the above maintenance methodologies are classified into therequired function (structural strength, sealing function, other safety function).

6. Prescribed Items in the Maintenance GuidelinesThere are several repair and replacement activities for the reactor internals. We clarify the threefundamental methodologies and seven actual controlled items for each maintenance method.
[Three fundamental methodologies]
A. Precondition
To clarify the scope of the portion, environment, material, so on, as the application of theprecondition.
B. Essential Valuables
Prescribe the essential variables based on the precondition. To define the expected effectivenessand secondary effect on certain various condition.
C. Basic Procedure
To confirm the boundary condition of the essential valuables on the operating procedure to
maintain the expected effectiveness.

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A.SAKASHITA et al./ Inspection, Evaluation and Maintenance Guidelines
for Reactor Vessel Internals in JAPAN[Seven actual controlled items]
Effectiveness, Precondition, Applied parts and Equipments, Operating devices, Operatingprocedure, Operator, Others

7. Sample of Maintenance Guideline
In this section, we illustrate two examples of maintenance guideline that developed pursuant toabove prescribed items.
7.1. Seal welding [3][4][5]Seal welding can prevent the crack growth of SCC due to isolation of SCC from corrosion
environment in reactor coolant. Also, seal welded parts have the function to prevent reactor coolant
from leaking out of pressure boundary. (Fig.4)
A. Precondition
Seal welding is applied to the components of BWR and PWR core internals, including pressure
boundary components; core shroud, shroud support, control rod drive housing and stub-tube.
Materials are austenitic stainless steel and nickel based alloy. It required that the necessary structural
strength of parts is ensured by the remaining portion. This welding method does not need machining /grinding for removing cracks, preparing grooves, nor buttering by weld.
B. Essential Valuables
It required to define welding method and condition as the essential valuables. Weld condition
includes heat input and welding wire supply rate and so on.
C. Basic Procedure
Laser welding and TIG welding have been applied as overlaying method. It is necessary toconfirm that welders qualified for each method are selected and trained before the actual operation.

Seal Welding
Seal Welding

SCC Crack
Seal Welding

Fig 4 Pictures of seal welding

7.2. IHSI for pipings [6][7]
IHSI (Induction Heating Stress Improvement) can prevent SCC for piping. Through this process,residual stress in the inner surface is improved for compression by induced thermal stress. The
fundamental methodologies on IHSI are as follow. (Fig.5)
A. Precondition
IHSI is applied to piping and nozzle safe-end such as Primary Loop Recirculation piping of BWR.
Materials are austenitic stainless steel and nickel based alloy. IHSI needs water cooling of innersurface and heating of outer surface using heating coil in order to induce temperature difference inpipe wall thickness direction.
B. Essential Valuables
It required to define minimum requirement such as the specification of objective location and theheating condition by mock up test to ensure the expected effectiveness. The specification of objective
location is outer diameter and base material thickness. The heating condition is maximum heating
temperature and heating time, difference in temperature between outer and inner surface.

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A.SAKASHITA et al./ Inspection, Evaluation and Maintenance Guidelines
for Reactor Vessel Internals in JAPAN

C. Basic Procedure
In management of the essential valuable, it is necessary to confirm the heating condition within
the range among operation. In the actual operations, if you have any concern to disturb the above
operating condition you can control the operating parameter, based on the previous test result such as
duration of the heating time, so on.

Fig 5 Concept of IHSI

8. Conclusion
Inspection, Evaluation and Maintenance Guidelines are extremely useful to manage the nuclear
power plants, and these importance will be increase with the plant ageing. These guidelines have to bedeveloped with the technical and engineering improvement. Especially, the maintenance technologies
are making rapid progress.

Acknowledgement
We would like to express our gratitude to Professor Emeritus, Dr. Toshiharu NOMOTO who isthe chairman of guideline committee and Japan Nuclear Technology Institute that is administration ofguideline committee.

References[1] The Inspection and Evaluation Guidelines for Light Water Reactor Internals (the third edition), Japan
Nuclear Technology Institute[2] Codes for Nuclear Power Generation Facilities –Rules on Fitness-for-Services for Nuclear Power Plants(JSME S NA1-2008), Japan Society Mechanical Engineering[3] Guidelines on repairing methods (seal welding) (JANTI-VIP-01), Japan Nuclear Technology Institute[4] Seal-Welding over Cracks for Preventing SCC Propagation, E-Journal of Advanced Maintenance (EJAM),
Vol.1 No.1 (25 May 2009), NT3. <http://www.jsm.or.jp/ejam/Vol.1.No.1/NT/3/3.html>[5] Seal Welding of PWSCC at J-Weld of Reactor Vessel Head Penetration Nozzle, E-Journal of Advanced
Maintenance (EJAM), Vol.1 No.1 (25 May 2009), NT2. <http://www.jsm.or.jp/ejam/Vol.1.No.1/NT/2/2.html>[6] Guidelines on repairing methods (stress improvement process by heat input from outer surface)(JANTI-VIP-02), Japan Nuclear Technology Institute[7] IHSI (Induction Heating Stress Improvement) Preventive Maintenance Technology for Primary Loop
Recirculation Piping, E-Journal of Advanced Maintenance (EJAM), Vol.1 No.1 (25 May 2009), NT6.
<http://www.jsm.or.jp/ejam/Vol.1.No.1/NT/6/6.html>

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