Speaker
Charles Henager
(Pacific Northwest National Laboratory, Richland, WA, United States)
Description
Iron-base alloys are the leading candidate structural material for first-wall and blanket applications in near-term fusion devices, but their long-term viability to reliably function in the harsh fusion nuclear environment remains to be established. Helium produced by transmutation reactions interacts with microstructural features such as pre-existing dislocations, martensite lath boundaries, precipitate interfaces, and vacancy clusters. Helium accumulation can lead to hardening and embrittlement, bubble formation that may exacerbate swelling, and premature creep-rupture due to cavity formation at grain boundaries.
An investigation of helium on damage evolution under neutron irradiation of PM2000, an oxide dispersion strengthened (ODS) ferritic alloy, was performed. While the aluminum content of PM2000 precludes it for fusion first-wall applications, the different grain structure and ODS size distribution provides a useful basis for comparing helium and dpa effects in ODS steels with nanostructured ferritic alloys. The study was done in the High Flux Isotope Reactor using the in situ helium injection (ISHI) technique. Under mixed spectrum neutron irradiation, one ISHI approach is to use a thin nickel-bearing layer applied to the surface of a TEM disc to produce high-energy alpha particles via a two-step thermal neutron reaction sequence. Helium is injected to a uniform depth of several microns. ISHI enables exploring the effects of helium on microstructure development at fusion relevant helium-to-displacement damage ratios.
Microstructural and micro-chemical evolution was characterized using a suite of transmission electron microscopy techniques. The ISHI technique allows direct comparisons of neutron-damaged regions with and without high concentrations of helium. The microstructure evolution observed includes formation of dislocation loops and associated helium bubbles, precipitation of a variety of phases, amorphization of the Al2YO3 oxides, which also variously contained internal voids, and several manifestations of solute segregation. High concentrations of helium had a significant effect on many of these diverse phenomena.
Co-authors
Charles Henager
(Pacific Northwest National Laboratory, Richland, WA, United States)
Dan J. Edwards
(Pacific Northwest National Laboratory, Richland, WA, United States)
G. Robert Odette
(University of California, Santa Barbara, Santa Barbara, CA, United States)
Hee Joon Jung
(Pacific Northwest National Laboratory, Richland, WA, United States)
Richard J Kurtz
(Pacific Northwest National Laboratory, Richland, WA, United States)
Takuya Yamamoto
(University of California, Santa Barbara, Santa Barbara, CA, United States)
Yuan Wu
(University of California, Santa Barbara, Santa Barbara, CA, United States)
