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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

 
TOSHIBA CORPORATION
 

KEYWORDS:
Laser, peening, stress improvement, SCC, reactor internals

 
1. Technical summary
 
Classification
(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.

EJAM1-3-NT12-Fig.1_Fundamental_Process_of_Laser_Peening(LP)

Fig.1 Fundamental Process of Laser Peening(LP)

EJAM1-3-NT12-Fig.2_LP_Scan_Method

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.

EJAM1-3-NT12-Fig.3_Scope_of_LP_for_BWR_reactor_internals

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.

EJAM1-3-NT12-Fig.4_Depth_profile_of_residual_stress

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

EJAM1-3-NT12-Fig.5_Depth_profile_of_residual_stress

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

EJAM1-3-NT12-Fig.6_Creviced_Bent_Beam_Test_Result

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.

EJAM1-3-NT12-Fig.7_Experience(1)Core_Shroud_of_BWR_plant

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

EJAM1-3-NT12-Fig.8_Experience-(2)RPV_Bottom_of_BWR_plant

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

EJAM1-3-NT12-Fig.9_Portable_LP_System

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 (http://www.toshiba.co.jp/nuclearenergy/me/laser/l_01.htm)
 
6. Contact
Japan Society of Maintenology (ejam@jsm.or.jp)