LDRD Seminar Series: ‘Ensuring the Safety of Aging Nuclear Reactors: Understand the Embrittlement in Cast Austenitic Stainless Steels and Stainless Steel Welds’
Principal Metallurgical Engineer Yiren Chen (NE) will discuss his Laboratory-Directed Research and Development (LDRD) sponsored work at the LDRD Seminar Series presentation Tuesday, April 18, 2017.
“Ensuring the Safety of Aging Nuclear Reactors: Understand the Embrittlement in Cast Austenitic Stainless Steels and Stainless Steel Welds” will begin at 12:30 p.m. in the Bldg. 203 Auditorium. All are welcome to attend.
Nuclear power generates about 20 percent of the United States’ electricity without carbon emission. This critical role of nuclear power is essential for the nation’s baseload energy infrastructure and must be sustained for long-term energy stability and security. With the aging of the existing nuclear power plants in the U.S., long-term service performance of reactor materials has become an important issue. In-depth understandings of degradation mechanisms and new technical solutions for mitigation strategy are crucial for the prolonged operation of aging nuclear power plants.
In this project, we worked with the U.S. Department of Energy Light Water Reactor Sustainability (LWRS) Program and the U.S. Nuclear Regulatory Commission (NRC) to study the embrittlement of reactor core internal materials, a subject critical for long-term operation and subsequent license renewal. Consisting of a dual-phase microstructure of delta ferrite and austenite, cast austenitic stainless steels (CASS) and stainless steel (SS) welds are vulnerable to thermal aging embrittlement and neutron irradiation damage. The service performance of CASS alloys and SS welds can be deteriorated considerably after long-term service exposure to reactor core environments, resulting in a significant decline in fracture resistance.
While the effects of thermal aging and neutron irradiation have been studied separately, it is difficult to predict if these two degradation mechanisms will interact with each other, leading to unexpected failures of reactor core components. With increasing neutron doses and thermal aging time in the extended operating period, the potential risk of reduced safety margin must be evaluated and addressed adequately by aging management and license renewal. To explore the potential synergy between two degradation processes, we investigated the embrittlement mechanisms of CASS alloys and SS welds subject to both neutron irradiation and thermal aging. Using advanced microstructural characterization techniques and X-ray in situ mechanical testing, we studied (1) the combined effect of thermal aging and neutron irradiation on the microstructural evolution, and (2) the deformation behavior of the dual-phase microstructure responsible for the embrittlement. The outcome of this study helps answer the fundamental questions regarding the degradation of LWR core components, and provides a scientific basis for assessing and managing the embrittlement of CASS alloys and SS welds.
Yiren Chen is a principal metallurgical engineer in the Nuclear Engineering Division. He received his Ph.D. from University of Illinois at Urbana-Champaign and joined Argonne in 2005. Chen has broad experience in radiation damage and irradiation effects, welding and environmental degradations of structural materials for nuclear applications. He is a key member of the environmentally assisted cracking program at Argonne sponsored by the U.S. Nuclear Regulatory Commission
Chen leads several research programs of post-irradiation examinations on highly radioactive reactor materials. He also provides technical support to the U.S. NRC on various material aging issues concerning light water reactors. Chen’s research topics cover irradiation-assisted stress corrosion cracking, fatigue, corrosion fatigue, radiation damage, irradiation embrittlement and environmental degradations of reactor core internal materials. Prior to joining Argonne, he also worked in China Institute Atomic Energy and Paul Scherrer Institute in Switzerland on various projects on heavy-ion irradiations and high-energy proton irradiations. His research focused on the development of structural and first-wall materials for fusion applications.