Influence of technetium on the microstructure of a stainless steel-zirconium alloy

Stainless steel-zirconium alloys are being developed for the disposal of me tallic waste generated during the electrometallurgical treatment of spent E xperimental Breeder Reactor (EBR-II) fuel. The metallic waste contains the fission product technetium, which must be incorporated into a stable waste form matrix to prevent its release into the environment. The baseline waste form for metallic waste from EBR-II fuels is a stainless steel-15 wt% zirc onium (SS-15Zr) alloy. The microstructure of SS-15Zr alloys containing 2 wt % technetium was characterized using a combination of microscopy, spectrosc opy, diffraction, and chemical analysis techniques. Peaks corresponding to the iron solid solutions ferrite and austenite, ZrFe2-type Laves polytypes C36 and C15, and an Fe23Zr6-type intermetallic were identified in diffracti on patterns of the alloy. Discrete technetium-rich phases were not observed either in diffraction patterns or in the microstructure; the element parti tioned into various phases of the SS-15Zr alloy. Technetium favors ferrite and austenite over the Zr-based intermetallics. The lattice parameters of t he Zr-based intermetallics are smaller than those in an alloy without techn etium, which appears to substitute at the zirconium sites of the intermetal lic lattice. (C) 2000 Elsevier Science B.V. All rights reserved.