Irradiation Assisted Degradation of LWR Vessel Internal Materials: Brief Review

Hosted by Dr. Andreas Enqvist

Nuclear Engineering Program Seminar Series

Thursday, October 27, 2016                 2:00 – 3:00 p.m.                Rhines Hall, 125



Dr. Appajosula S. Rao

Division of Engineering

Office of Nuclear Regulatory Research

US Nuclear Regulatory Commission



Irradiation Assisted Degradation of LWR Vessel Internal Materials: Brief Review



Austenitic stainless steels (SSs) are used extensively as structural alloys in the internal components of light water reactor (LWR) pressure vessels. It was shown that a continued exposure to neutron irradiation for extended periods changes the microstructure (radiation damage) and microchemistry (radiation-induced segregation or RIS), and degrades the fracture properties of the steels. In addition, while addressing nuclear plant aging and license renewal issues, the loss of fracture toughness due to radiation embrittlement of the austenitic SSs LWR vessel internal components has to be considered in the design. The United States Nuclear Regulatory Commission is actively conducting confirmatory research to determine (a) the threshold neutron dose (fluence) for the irradiation assisted stress corrosion cracking (IASCC) and (b) the disposition curves for SCC growth rates for irradiated SSs in LWR environments.


In this present talk some of the concerns arising from irradiation-induced materials issues will be discussed.  Later a brief review of the NRC test results as a function of steel chemistry and irradiation conditions will be presented.



Dr. Appajosula S. Rao is a Technical Team Leader and Program Manager for the Irradiation Assisted Degradation of Nuclear Reactor Core Internals at the US Nuclear Regulatory Commission (USNRC) in Washington, DC. Dr. Rao’s expertise are in the area of irradiation assisted degradation of reactor core internals, physical metallurgy and corrosion.  Dr. Rao has published more than 250 Journal papers, conference proceedings and Govt. Technical reports.  He gave more than 300 technical presentations all over the world and he has received more than 30 awards.