Irradiation Assisted Stress Corrosion Cracking of Reactor Internals of Light Water Reactors

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The objective of this research is to develop a nondestructive evaluation method for detection of radiation induced segregation such as Cr-depletion with very narrow width and impurities segregation. These changes in grain boundary chemistries are possible causes of Irradiation Assisted Stress Corrosion Cracking. Several heats of Type 304 Stainless Steels including high purity, commercial purity, nuclear grade, low sulfur materials. In addition to grain boundary chemical analysis, slow strain rate tests were performed in oxygenated high temperature water at 288ﾟC. Results can be summarized as follows,1. Modified EPR can detect irradiation induced narrow Cr depletion.2. RIS was strongly affected by carbon content and nuclear grade material showed the highest resistance to IGSCC.3. Impurity segregation can be quantitatively evaluated by total charge density measured at-1050mv for one hours in 5N-H_2SO_44. These NDE technique can be applied to TEM disc specimens by RIS detector.5. IGSCC region can be mapped in terms of Cr-depletion and impurity segregation.6. Further research is needed to evaluate the segregation of B and N which can transmute to form He and H and results in grain boundary weakening.Taking account of those grain boundary analysis and it relation to IGSCC, IASCC mechanisms can be made clear.