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	A New Mechanical Condition-based Maintenance Technology Using Instrumented Indentation Technique
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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, NT7(1) EJAM (1-2-NT7(1)) - The Water Jet Peening for Reactor Internals Technology for Preventing Stress Corrosion Cracking by Using Cavitations

The Water Jet Peening for Reactor Internals
Technology for Preventing Stress Corrosion Cracking by Using Cavitations

Hitachi-GE Nuclear Energy, Ltd.

KEYWORDS：
water jet, peening, stress improvement, SCC, reactor internals

1. Technical summary

Classification
(I: Inspection, II: Repair, III: Replacement, IV: Preventive Maintenance, V: Others)

When highly pressurized water is injected into water through a nozzle, the high-speed water jet generates cavitations. The intensive pressure wave at collapsing of cavitations, generates compressive stress on surrounding metal surface, which is effective for preventing stress corrosion cracking (SCC).

2. Scope

	Fig.1 Water jet peening to the BWR reactor internal
(1) Components Reactor internals of BWR and PWR Core shroud, shroud support, control rod drive (CRD) housing and stub-tube for example. (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.

3. Features

Features are

(1)In the optimum condition, the WJP improves stress condition on a metal surface in a wide and deep area with only one or a few travel paths as shown in Figure 2.

Fig. 2 Typical stress relief profile after the WJP

	Fig.3 Typical WJP system configuration in BWR
(2)Since only water is used for treatment, no foreign material is delivered into the reactor and no heat influence is developed to the materials.
(3)As WJP tooling (Figure 3 Typical WJP system configuration in BWR) has a simple water transfer line, the WJP is easily implemented with equipment that can be controlled simply. This simple structure contributes short period of application in actual plants and robust schedule management.
(4)As process parameters can cover a wide range, the WJP is applicable to complicated/narrow structures (See Figure 4 (a)-(d) below) and has robust execution characteristics. Fig.4 (figure show as mouseover headlings below) (a) Effect at corner portion (b) Effect on pipe inner surface (c) Effect on pipe outer surface (d) Effect on 3D shaped surface
	Fig. 4(a), (b), (c) and (d)

4. Examples of Application

Reactor vessel head of Ohi nuclear power plant No.3 in 2004

Fig. 5 WJP experiences in BWR

5. Reference

Guideline for Preventive Maintenance Method “Peening Method”, JANTI-VIP-03-rev.2, JANTI (Japan Nuclear Technology Institute) (in Japanese)

6. Contact

Japan Society of Maintenology (ejam@jsm.or.jp)


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