NSUF 17-950: SEM, EBSD, and TEM Investigation of Irradiated Austenitic Stainless Steel Weldment

As the existing light water reactor (LWR) fleet ages, the weldability of structural austenitic materials used to construct reactor internals is diminished. This decrease in weldability is primarily attributed to the formation of helium from neutron transmutation reactions of boron and nickel. A collaborative research program supported by the EPRI Long Term Operations (LTO) and DOE Light Water Reactor Sustainability Programs (LWRSP) is currently underway to perform extensive weldability investigations on highly irradiated materials. The materials being used for this research are 304L and 316L austenitic stainless steels irradiated at the ORNL High Flux Isotope Reactor (HFIR) facility. Boron levels of these stainless steel materials were precisely controlled to produce a range of post-irradiation helium levels representative of LWR internals. However, the nature in which the irradiations were conducted on these materials are not expected to produce void swelling typically found in highly irradiated PWR reactor components. The post-weld characterization proposed herein will address this research gap by investigating the effects of welding on the mechanical and microstructural properties of highly activated 304L stainless steel irradiated in the INL Experimental Breeder Reactor-II (EBR-II). A series of welds were recently performed on this material at Westinghouse, which contains both considerable void swelling and helium levels in the microstructure. SEM-EBSD analysis will be performed at ORNL on these welds to characterize grain structure, texture, and the helium-void interaction on cracking, if any, in the HAZ. EBSD and back-scatter electron imaging will also allow for identifying areas of interest for further FIB lift-outs (high- or low-angle or special grain boundaries, cracks, if they appear, and presence of second phases such as delta-ferrite or martensite). TEM foils will be extracted from several locations of interest in the weldment, HAZ, and base material to investigate helium distribution within the microstructure. Furthermore, nano-hardness measurements will be taken in these same areas of interest to measure the effects of irradiation on hardness. The period of performance for this study is expected to be four to six months.

Additional Info

Field	Value
Abstract	As the existing light water reactor (LWR) fleet ages, the weldability of structural austenitic materials used to construct reactor internals is diminished. This decrease in weldability is primarily attributed to the formation of helium from neutron transmutation reactions of boron and nickel. A collaborative research program supported by the EPRI Long Term Operations (LTO) and DOE Light Water Reactor Sustainability Programs (LWRSP) is currently underway to perform extensive weldability investigations on highly irradiated materials. The materials being used for this research are 304L and 316L austenitic stainless steels irradiated at the ORNL High Flux Isotope Reactor (HFIR) facility. Boron levels of these stainless steel materials were precisely controlled to produce a range of post-irradiation helium levels representative of LWR internals. However, the nature in which the irradiations were conducted on these materials are not expected to produce void swelling typically found in highly irradiated PWR reactor components. The post-weld characterization proposed herein will address this research gap by investigating the effects of welding on the mechanical and microstructural properties of highly activated 304L stainless steel irradiated in the INL Experimental Breeder Reactor-II (EBR-II). A series of welds were recently performed on this material at Westinghouse, which contains both considerable void swelling and helium levels in the microstructure. SEM-EBSD analysis will be performed at ORNL on these welds to characterize grain structure, texture, and the helium-void interaction on cracking, if any, in the HAZ. EBSD and back-scatter electron imaging will also allow for identifying areas of interest for further FIB lift-outs (high- or low-angle or special grain boundaries, cracks, if they appear, and presence of second phases such as delta-ferrite or martensite). TEM foils will be extracted from several locations of interest in the weldment, HAZ, and base material to investigate helium distribution within the microstructure. Furthermore, nano-hardness measurements will be taken in these same areas of interest to measure the effects of irradiation on hardness. The period of performance for this study is expected to be four to six months.
Award Announced Date	2017-04-26T10:06:34.447
Awarded Institution	None
Facility	None
Facility Tech Lead	Kory Linton
Irradiation Facility	None
PI	Jonathan Tatman
PI Email	[email protected]
Project Type	RTE
RTE Number	950