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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

 
TOSHIBA CORPORATION
 

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

 
1. Technical summary
 
Classification
(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.

EJAM1-2-NT8-Fig.2_Test_results_of_LDT_to_Jet_pump_riser_pipe
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.
EJAM1-2-NT8-Fig.4_Concept_of_field_application_of_LDT_to_Jet_pump_riser_pipe
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 (ejam@jsm.or.jp)