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EJAM7-3NT72 A New Mechanical Condition-based Maintenance Technology Using Instrumented Indentation Technique
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Vol.1 No.2 ← GA 6 - 7 - AA 8 - 9 - NT 10 - 11 - 12 - 13 → Vol.1 No.3
Vol.1, No.3, NT13 EJAM (1-3-NT13) - Crack Removing Method for Repair of Reactor Internals

Crack Removing Method for Repair of Reactor Internals
 
Hitachi-GE Nuclear Energy, Ltd.
 

KEYWORDS：
SCC, electric discharge machining, reactor internals, core shroud, shroud support
 
1. Technical summary
 
Classification
(I: Inspection, II: Repair, III: Replacement, IV: Preventive Maintenance, V: Others)
 
This is a repairing method for SCC (stress corrosion cracking) of reactor internals. In this method, existing SCC cracks are completely removed under water by using electric discharge machining (EDM) or grinding,
EJAM1-3-NT13-Fig.1(small)_EDM_method EJAM1-3-NT13-Fig.2(small)_Grinding_method
EDM method (Sheet A) Grinding method (Sheet B)
2. Scope

(1) Components
BWR and PWR core internals. Core shroud, shroud support, for example

(2) Materials
Both base metal and weld of austenitic stainless steel and high nickel alloy

(3) Condition
This method can only be applied to location where the necessary structural strength is ensured by the remaining portion after removal of cracks.
 
3. Features

・Machining head for removing crack is positioned precisely according to the result of eddy current test (ECT) for the crack.

・Crack growth is stopped by removal of cracks completely. In addition, peening treatment or other stress improvement is performed and initiation potential of SCC cracks is reduced.

 
4. Examples of Application
Crack removing equipments for inner and outer surface of core shroud have been developed.

This technique was applied to many BWR core shrouds in Japan.
 
5. Reference
M.Tanaka, T. Itou, T. Yamamoto, A. Mori, M. Makino, “Introduction of repair and Maintenance Technology against SCC in core shroud” Maintenology, Vol.3, No.3, (2004) (in Japanese)
 
6. Contact
Japan Society of Maintenology (ejam@jsm.or.jp)