"Microstructural characterization and density change of 304 stainless steel reflector blocks after long-term irradiation in EBR-II"
Yina Huang, J.M.K. Wiezorek, Frank Garner, Paula Freyer, T. Okita, M. Sagisaka, Y. Isobe, Todd Allen,
Journal of Nuclear Materials
While thin reactor structural components such as cladding and ducts do not experience significant gradients in dpa rate, gamma heating rate, temperature or stress, thick components can develop strong local variations in void swelling and irradiation creep in response to gradients in these variables. In this study we conducted microstructural investigations by transmission electron microscopy of two 52 mm thick 304-type stainless steel hex-blocks irradiated for 12 years in the EBR-II reactor with accumulated doses ranging from ∼0.4 to 33 dpa. Spatial variations in the populations of voids, precipitates, Frank loops and dislocation lines have been determined for 304 stainless steel sections exposed to different temperatures, different dpa levels and at different dpa rates, demonstrating the existence of spatial gradients in the resulting void swelling. The microstructural measurements compare very well with complementary density change measurements regarding void swelling gradients in the 304 stainless steel hex-block components.
The TEM studies revealed that the original cold-worked-state microstructure of the unirradiated blocks was completely erased by irradiation, replaced by high densities of interstitial Frank loops, voids and carbide precipitates at both the lowest and highest doses. At large dose levels the amount of volumetric void swelling correlated directly with the gamma heating gradient-related temperature increase (e.g. for 28 dpa, ∼2% swelling at 418 °C and ∼2.9% swelling at 448 °C). Under approximately iso-thermal local conditions, volumetric void swelling was found to increase with dose level (e.g. ∼0.2% swelling at 0.4 dpa, ∼0.5% swelling at 4 dpa and ∼2% swelling at 28 dpa). Carbide precipitate formation levels were found to be relatively independent of both dpa level and temperature and induced a measurable densification. Void swelling was dominant at the higher dose levels and caused measurable decreases in density. Void swelling at the lowest doses was larger than might be expected based on the dpa level, an observation in agreement with earlier studies showing that the onset of void swelling is accelerated by decreasing dpa rates.
"Measurement of depth-dependent swelling in thick non-uniform irradiated 304 stainless steel blocks using nondestructive ultrasonic techniques"
Frank Garner, Paula Freyer, T. Okita, Y. Isobe, J. Etoh, M. Sagisaka, T. Matsunaga, Yina Huang, J.M.K. Wiezorek, Douglas Porter,
Fontevraud 8 - Contributions of Materials Investigations and Operating Experience to LWR's Safety, Performance and Reliability
September 3-6, (2014)
"Transmission Electron Microscopy of 304-type Stainless Steel after Exposure to Neutron Flux and Irradiation Temperature Gradients"
J.M.K. Wiezorek, Yina Huang, Frank Garner, Paula Freyer, M. Sagisaka, T. Isobe,
Microscopy and Microanalysis 2014
August 3-7, (2014)
"Void swelling and resultant strains in thick 304 stainless steel components in response to spatial gradients in neutron flux-spectra and irradiation temperature"
Frank Garner, Paula Freyer, Douglas Porter, Yina Huang,
Proceedings of 16th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors[unknown]Link
The Nuclear Science User Facilities (NSUF) is the U.S. Department of Energy Office of Nuclear Energy's only designated nuclear energy user facility. Through peer-reviewed proposal processes, the NSUF provides researchers access to neutron, ion, and gamma irradiations, post-irradiation examination and beamline capabilities at Idaho National Laboratory and a diverse mix of university, national laboratory and industry partner institutions.