ICMST-Tohoku 2018
Oct. 23 - 26, 2018
Sendai, Japan
ICMST-Shenzhen 2016
Nov 1 - 4, 2016
Shenzhen, China
ICMST-Kobe 2014
Nov 2(Sun) - 5(Wed), 2014
Kobe, Japan
Nuclear Regulation Authority Outline of the New Safety Standards for Light Water Reactors for Electric Power Generation
For Public Comment
Outline of New Safety Standard (Design Basis)
For Public Comment
New Safety Standards (SA) Outline (Draft)
For Public Comment
Outline of New Safety Standard(Earthquake and Tsunami)(DRAFT)

Vol.10 No.2(Aug)
Vol.10 No.1(May)
Vol.9 No.4(Feb)
Vol.9 No.3(Nov)

< Other Issues


Occasional Topics
OTjapan Measures for Tsunami Striking Nuclear Power Station in Japan
Special Article: The Great Tohoku Earthquake (1)
OTjapan The Tragedy of “To Be” Principle in the Japanese Nuclear Industry
EJAMOT_CN3_Figure1_The_outside_view_of_CEFR OTChinaPlanning and Consideration on SFR R&D Activities in China
< All Occasional Topics

Featured Articles
EJAM7-3NT72 A New Mechanical Condition-based Maintenance Technology Using Instrumented Indentation Technique
EJAM7-3NT73 Survey robots for Fukushima Daiichi Nuclear Power Plant

(in English)

Vol.1 No.1 ← GA 5 - AP 6 - 7 - NT 7 - 7(1) - 7(2) - 8 - 9 Vol.1No.3
Vol.1, No.2, NT8 EJAM (1-2-NT8) - LDT (Laser Desensitization Treatment): Preventive Maintenance Technique for Reactor Internal Piping

LDT (Laser Desensitization Treatment)
Preventive Maintenance Technique for Reactor Internal Piping


SCC, Reactor Internal piping, austenitic stainless steel, sensitized zone, stress improvement, LDT

1. Technical summary
(I: Inspection, II: Repair, III: Replacement, IV: Preventive Maintenance, V: Others)

Laser Desensitization Treatment (LDT) is developed as a preventive maintenance  technique for the reactor internal piping. This technique uses laser irradiation to the inner surface of piping near the weld to recover Chromium carbide segregation at grain boundary in sensitized zone by making surface melt zone and/or solution heat treatment zone. Consequently, sensitized zone due to welding can be improved. Principle of LDT and sample of LDT process tool head is shown in Fig.1.

EJAM1-2-NT8-Fig.1(a)Principle of LDT
(a) Principle of LDT
EJAM1-2-NT8-Fig.1(b)LDT process tool Head
(b) LDT process tool Head
Fig.1 Principle of LDT and LDT process tool Head[1]
2. Scope
(1) Components:Stainless steel piping
  - BWR reactor Internal Piping (ex. Jet pump riser pipe)
(2) Objective Location:SCC Sensitized zone of the base metal near the weld
(3) Material:Austenitic stainless steel
3. Features

(1) Prevent initiation of SCC at the sensitized zone inside the pipe by using LDT process, and also reduce residual stress outside the pipe. Sample of the application result by LDT technique is shown in Fig.2 and Fig.3.
(2) This technique is applied under the air condition.

Fig.2 Test results of LDT to Jet pump riser pipe[2]
EJAM1-2-NT8-Fig.3(b)LDT_processed_surfacepng EJAM1-2-NT8-Fig.3(b)(small)LDT_processed_surfacepng
(a) LDT processed Sample (b) LDT processed surface

Fig.3 Macroscopic view of LDT processed surface of Jet pump riser pipe[3]
4. Examples of Application
LDT technique is adopted as a preventive maintenance at the field work, for the stainless steel piping including Reactor internal piping. Application plan to the Jet pump riser pipe is illustrated in Fig.4.
Fig.4 Concept of field application of LDT to Jet pump riser pipe[3]
5. Reference
(1) Hiroshi Miyano, Yasuhiro Hattori, Akira Sudo, “Refreshment of Nuclear Power Plant”, TOSHIBA review, Vol.53, No.12 (1998)
(2) Osamu Maekawa, Yasuhiro Hattori, Akira Sudo, “State of the Art of Toshiba Maintenance Techniques for Reactor Internals”, TOSHIBA review, Vol.57, No.4 (2002)
(3) Kenji Sato, Masahiro Kobayashi, Yuji Sano, Seiichiro Kimura, “ Maintenance Technologies for Reactor Internals”, TOSHIBA review, Vol.55, No.10 (2000)
6. Contact
Japan Society of Maintenology (