Water Jet Peening (WJP) has been widely applied to Japanese nuclear power plants since 1999 in order to mitigate stress corrosion cracking (SCC) generation on SCC susceptible material used their reactors as an approved mechanical mitigation technique against SCC [1].

Laboratory data shows that WJP has an effect to mitigate or suppress shallow crack propagation if the achieved compression depth is deeper than the crack, and that WJP has no adverse effect on pre-existing cracks on the mitigated surface, such as crack propagation during WJP treatment or acceleration effect after its treatment [2]. However, there was no field experience of applying WJP on cracked surfaces of operating reactor internals since we removed the crack(s) as the practice in Japan was to remove the crack prior to WJP implementation.

When observed crack can be left as is according to its profile, it is required to perform the crack sizing periodically by Ultrasonic Testing in order to monitor its propagation. In order to apply WJP on the cracked surface, additional testing was needed to clarify that no adverse effect on UT sizing capability after WJP will be observed. The Japan Atomic Power Company (JAPC) and Hitachi-GE Nuclear Energy, Ltd. (HGNE) have performed several tests about this UT crack sizing test before and after WJP treatment and other related test before its field application.

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