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The addition of oversized solutes has the potential to reduce the effects of radiation-induced segregation (RIS) in austenitic alloys. This RIS has been implicated as one of several factors in enhancing stress corrosion cracking (SCC) under irradiation, so oversized solute additions could promote SCC resistance. Either Zr or Hf was added to 316-type stainless steel, at levels between 0.05 and 0.37 at. pct. Samples were irradiated with 3 MeV protons to 3 dpa at 400 °C and analyzed using high-resolution–scanning transmission electron microscopy (HR-STEM) with energy-dispersive X-ray spectroscopy (EDS), to measure the grain-boundary (GB) composition. The Zr additions substantially reduced the amount of RIS, while the Hf was much less effective. Despite similar sizes, first-principles calculations using the Vienna Ab Initio Simulation Package (VASP) demonstrate that solute-vacancy binding for Zr is 1.05 eV vs 0.69 eV for Hf. This difference results in the greater effectiveness of Zr in reducing RIS, as determined by kinetic rate theory calculations, in agreement with experimentally-measured results. [ABSTRACT FROM AUTHOR]

Nuclear powered spacecraft will enable missions well beyond the capabilities of current chemical, radioisotope thermoelectric generator and solar technologies. The use of fission reactors for space applications has been studied for over 50 years. Structural material performance has often limited the potential performance of space reactors. Space fission reactors are an extremely harsh environment for structural materials with high temperatures, high neutron fields, potential contact with liquid metals, and the need for up to 15-20 year reliability with no inspection or preventative maintenance. Many different structural materials have been proposed. While all of those proposed meet many of the requirements for space reactor service, none satisfy all of them. However, continued development and testing may resolve these issues and provide qualified materials for fission reactors for space power. [ABSTRACT FROM AUTHOR]