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EJAM7-3NT72 A New Mechanical Condition-based Maintenance Technology Using Instrumented Indentation Technique
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(in English)

Vol.1 No.2 ← GA 6 - 7 - AA 8 - 9 - NT 10 - 11 - 12 - 13Vol.1 No.3
Vol.1, No.3, NT12 EJAM (1-3-NT12) - Laser Peening Technology for Preventing Stress Corrosion Cracking for BWR reactor internals

Laser Peening Technology for Preventing Stress Corrosion Cracking for BWR reactor internals


Laser, peening, stress improvement, SCC, reactor internals

1. Technical summary
(I: Inspection, II: Repair, III: Replacement, IV: Preventive Maintenance, V: Others)
Laser Peening (LP) is a method of SCC mitigation that eliminates surface tensile stress using the impulsive effect of high-pressure plasma induced by irradiation with high-power laser pulses in water.

Its effects for stress improvement and SCC-mitigation of laser-peened materials were confirmed through SCC tests for austenitic stainless steels and nickel-based alloys.


Fig.1 Fundamental Process of Laser Peening(LP)


Fig.2 LP Scan Method

2. Scope

(1) Components
BWR reactor internals
(Core shroud, shroud support, control rod drive (CRD) housing, CRD stub-tube, In-Core monitor (ICM) housing, for example.(See Fig.3))

(2) Materials
Both base metal and weld of austenitic stainless steel / nickel-based alloy.

(3) Condition
This method can be applied to components under water.


Fig.3 Scope of LP for BWR reactor internals

3. Features

(1) LP is a fully-controlled process for each pulse under predetermined conditions (pulse energy, spot diameter, etc.).

(2) LP has excellent accessibility due to the flexible optical fiber delivery and the reaction force-less process. So implementation in complicated form is possible.

(3) There is no influence on surrounding equipments due to the vibration, etc.

(4) It is easy to confirm the peened area visually. (See Fig.2)

(5) Effects of SCC susceptibility have been verified for the following materials: Type 304 stainless steel, Type 316L stainless steel, Alloy 600, Alloy 182. (Fig.4,5,6 for example)

(6) There is no requirement for any surface preparation (protective coating, etc.) before and after laser irradiation.

(7) Using only laser for treatment, no foreign materials is delivered into the reactor.


Fig.4 Depth profile of residual stress
(Type 304 Stainless Steel (20%CW), which simulates irradiation hardening)


Fig.5 Depth rofile of residual stress
(Alloy 600, Alloy 182)


Fig.6 Creviced Bent Beam Test Result (cross section)

4. Examples of Application
(1) Core Shroud of BWR plant (5 plants) (Fig.7)

(2) RPV Bottom of BWR plant (4 plants) (Fig.8)

(3) Portable LP System (Fig.9,10)
New smaller and robust LP system, called Portable LP(PLP),has been developed and ready for field application.


Fig.7 Experience(1) Core Shroud of BWR plant (H2 inside)


Fig.8 Experience (2)RPV Bottom of BWR plant (CRD Stub Tube)


Fig.9 Portable LP System

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Fig.10 Portable LP System Mockup (Underwater)
5. Reference
(1) Guideline for Preventive Maintenance Method “Peening Method”, JANTI-VIP-03-rev.2, JANTI(Japan Nuclear Technology Institute)(in Japanese)
(2) “Underwater Laser Peening”, M.Yoda, B.Newton, Welding and Repair Technology for Power Plants Eighth International EPRI Conference June 18-20,2008 Fort Myers, Florida
(3) “Development of Portable Laser Peening Systems for Nuclear Power Reactors”, I.Chida, T.Uehara, M.Yoda, h.Miyasaka, H.Kato, Proceedings of ICAPP(2009)
(4) TOSHIBA Corporation Home Page (
6. Contact
Japan Society of Maintenology (