51313-02183-Effect of Solution Impurities on the Onset of SCC of Austenitic Stainless Steel in PWR Primary Water

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Product Number: 51313-02183-SG

ISBN: 02183 2013 CP

Author: Florent Bocher

Publication Date: 2013

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There has been a recent growing interest in studying stress corrosion cracking (SCC) of stainless steels in pressurized water reactor (PWR). This is because austenitic stainless steels have long been accepted as being far less susceptible to SCC in PWR primary water than in boiling water reactor. However utilities are becoming more concerned because over 130 SCC events have been reported since the eighties in PWR primary water. As a result SCC of stainless steel in primary water of PWR has been classified as a high priority issue.

The objectives of this program are: (1) to measure the effect of unusual solution chemistries (e.g. chloride boric acid oxygen concentrations) in primary water on the electrochemical properties of austenitic stainless steels (2) to measure the effect of those compounds on the semiconductor properties of the passive film (3) to assess the impact of applied potential on crack initiation and growth and (4) to correlate the changes in electrochemical and semiconductor properties with the measured occurrence of crack initiation and propagation.

This work combined electrochemical and fracture mechanics techniques in high temperature high pressure solution to identify conditions under which SCC in PWR environments may occur. The test setup was designed to accurately replicate the conditions found in the primary water of PWR. Potentiodynamic testing were performed in order to measure the passivity boundaries of austenitic stainless steels AISI 304 and AISI 316. Mott-Schottky electrochemical testing were used to measure the semiconductor properties of the stainless steels. The flat band potential and the density of charge carriers within the passive film can be measured using this technique. Changes in the passive film due to the environment were linked to SCC. The potential drop method was used conjointly with the Mott-Schottky measurements in order to link the semiconductor properties of the film to the crack growth rate.