Abstract
Reactor core internal components such as baffle-former bolts (BFBs) are subjected to significant mechanical stress, corrosive environment, and neutron irradiation from the reactor core during the plant operation. Over the long operation period, these conditions lead to potential degradation and of the bolts. In this work, characterization was performed on the oxidized surface of stainless steel BFBs harvested from a commercial pressurized water reactor (PWR) after 40 years of operation. The analysis shows that a complex multilayered surface oxide with six identified layers formed that is different from 2-layer structure commonly observed in model experiments. The oxide varies by composition – predominantly Fe, Cr, and Ni, grain size, and phase, and has features resembling both unirradiated and radiation/ corrosion experiments likely due to the low radiation flux compared to ion-irradiation or the test reactor radiation. In addition, grain boundary oxidative attack featured a pathway for Fe and other elements to move from the metal matrix to the outermost oxide. The results help assess PWR lifetime extension, put into context previous experimental studies, and provide input for designing experiments combining radiation and corrosion effects.
| Original language | English |
|---|---|
| Article number | 113106 |
| Journal | Corrosion Science |
| Volume | 255 |
| DOIs | |
| State | Published - Oct 2025 |
Funding
This research was supported by the US Department of Energy, Office of Nuclear Energy, Light Water Reactor Sustainability Program Materials Research Pathway under contract DE-AC05\u201300OR22725 with UT-Battelle LLC via Oak Ridge National Laboratory. The authors would like to thank Patricia Tedder and Travis Dixon at the Low Activation Materials Development and Analysis (LAMDA) Laboratory at ORNL, where SEM and TEM/STEM evaluation was conducted. Microscopy in LAMDA is a cost recovery center available for users through the US-DOE Nuclear Science User Facilities. The initial handling and cutting of the bolts were done in the hot cells in the Irradiated Materials Examination and Testing (IMET) facility at ORNL. The Thermo Fisher Talos 200X STEM in LAMDA was purchased and funded through the US-DOE Office of Nuclear Energy Advanced Fuel Campaign and Nuclear Science User Facilities. The authors would like to thank the late Mike Burke who was involved in the bolt harvesting and characterization planning and led the sample preparation, machining, and shipping when he was working at Westinghouse Electric Company. Notice: This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05\u201300OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ).
Keywords
- Baffle-former bolt
- Crack initiation
- In-service irradiation and corrosion
- Irradiation assisted stress corrosion cracking (IASCC)
- Multilayered oxide structure
- Radiation-induced segregation (RIS)