Research Activities on Materials Degradation in Nuclear Power Systems

with Chi Bum Bahn, Pusan National University
Friday, July 21, 2023, 10:10 – 11:30am
440 Goodwin Hall

contact Alida Spalding for Zoom link

Accident-tolerant fuel (ATF) cladding with high oxidation resistance during severe accidents is of critical importance to light water reactor safety and sustainability. The oxidation resistance of an outer FeCrSi layer of a multi-metallic layered composite (MMLC), which is one of ATF concepts, has been studied at 1200 °C steam varying Cr or Si contents, which revealed the role of a thin amorphous Si oxide layer between Cr oxide and metal matrix. As another candidate of ATF cladding materials, we developed (Ti, Mo)C-forming FeCrAlY alloy. The oxidation behavior of this alloy was investigated at 1200 and 1300 °C steam. The test results revealed that Y and Ti could affect the formation of a protective Al oxide layer.

Statistical analysis and modeling research has been conducted on materials degradation data, such as stress corrosion cracking (SCC), environmental fatigue, or irradiation assisted SCC (IASCC) data. A classical approach on lifetime data is to adopt the Weibull model, which can consider not only exact but also right-censored data with covariate effects. Parameters of the Weibull model can be estimated by either maximum likelihood method or Bayesian approach. For the environmental fatigue data, the probabilistic model was able to quantitatively evaluate the conservatism of the current fatigue design limit. Machining learning methods could be a better option when trying to obtain the best-estimate. The comparison study was also conducted between the classical model and a machine learning method.

In order to solve materials degradation issues, surface treatment methods can be considered. Two examples are introduced in this talk: electroless novel metal plating and surface peening. Fouling is a phenomenon in which microparticle suspension such as iron oxide (Fe3O4, magnetite) are deposited on pipe walls and near venture flow meter holes, thereby changing surface roughness, and causes an error in the measurements of the venturi flowmeter. We introduced electroless Ni or Pd plating to reduce the deposition of oxide particles inside the venturi system. Their performance was experimentally verified through relatively short-term lab tests. Improving the surface residual stress condition is considered as one of ways to mitigate SCC, and peening can prevent SCC by creating compressive stress on the surface of finished parts and structures. Various peening techniques were compared from the several perspectives: residual stress conditions, microstructural change near the surface, or SCC resistance.

Chi Bum Bahn earned a Bachelor, Master and Ph.D. in Nuclear Engineering from Seoul National University at South Korea. During the postdoc course with Gary Was of University of Michigan, he studied corrosion and stress corrosion cracking of ferritic/martensitic steels in supercritical water environments. After coming back to Seoul National University, he was actively involved in the design, construction, and operation of a 10-m tall Pb-Bi test loop called HELIOS. Since joining the Argonne National Laboratory on March 2006, he has worked on several projects mainly to support U.S. Nuclear Regulatory Commission, such as the Steam Generator Tube Integrity Program or sump strainer blockage issues related to GSI-191. Bahn has been a member of the faculty member of the School of Mechanical Engineering at Pusan National University since September 2013, focusing on research topics such as accident tolerant fuel cladding materials, statistical analysis and modeling on materials degradation data, and surface treatments to solve materials degradation issues. Bahn is a member of American Society for Testing and Materials International (E08 & G01), Korean Nuclear Society, and Korean Society of Mechanical Engineers. He plans to continue pursuing research activities to overcome materials-related challenges in nuclear power systems through experiments, simulation and modeling.