In-situ Raman spectroscopic analysis of interfaces of Ni-base alloy/LAS dissimilar metal weld

Aging of structural materials in pressurized water reactors (PWRs) has been one of the major issues for plant safety and life extension. While a new alloy (Alloy 690) introduced, some concerns remain unresolved especially deterioration of a dissimilar metal weld. Intergranular stress corrosion cracking (IGSCC) is one of major degradation modes of aging problems that occur in structural materials for steam generators or nozzles in PWRs. The IGSCC of Ni-base alloys in PWR primary water has been extensively studied to establish theoretical and empirical models for predicting the crack initiation in field components. Even though there is no general agreement on the origin of IGSCC, one common assumption of these approaches is that the damage to the alloy substrate can be related to some transport or repair properties of its protective oxide film. Therefore, the oxide film is believed to play a key role in the process of IGSCC on the surface of the Ni-base alloys in the primary water. This study is aimed to characterize the oxide film by in-situ method in order to investigate the effects of aging on the degradation of Ni-base alloy/low alloy steel dissimilar metal weld(DMW). Since the SCC of structural alloys is related to the property of native oxide layers, surface oxides on the aged weld specimens need to be characterized. It is essential to overcome the current limitation of typical ex-situ methods. In this study, therefore, a hydrothermal cell for the in-situ surface oxide analysis using Raman spectroscopy were designed and assembled. It is mainly composed of a water loop for simulated PWR primary water condition, in-situ Raman spectroscopy system, and hydrothermal optical cell for oxide analysis. Using the developed experimental system, the interface region of Ni-base alloy/low alloy steel dissimilar metal weld will be analyzed by acquiring Raman spectrum from DMW specimens exposed to high temperature and high pressure water condition