Microscopy and neutron diffraction study of a zirconium-8 wt% stainless steel alloy

The electrometallurgical treatment of zirconium-based and Zircaloy-clad spe nt nuclear fuels will yield a metal waste form. The baseline composition fo r the waste form is zirconium-8 wt% stainless steel (Zr-8SS). The microstru cture of the Zr-8SS alloy has been studied by scanning electron microscopy, energy dispersive spectroscopy, and neutron diffraction. The phases presen t in the as-cast alloy include Zr(alpha), Zr-3(Fe,Ni), Zr-2(Fe,Ni), Zr-2(Fe ,Cr), and Zr(Fe,Cr)(2); a solidification sequence has been proposed to expl ain the formation and morphology of these phases. Alloy phase stability has been studied by thermal aging at 780 degreesC for periods up to 30 days. T he phase changes that occur during thermal aging include an increase in Zr- 3(Fe,Ni) and a decrease in Zr-2(Fe,Ni) content; reaction mechanisms have be en proposed to explain these changes. The lattice parameters of alloy phase s have been determined by neutron diffraction and found to be in agreement with those previously reported for similar phases. This study of alloy micr ostructures is the first step towards understanding the actinide and fissio n product distribution and predicting the corrosion behavior of the Zr-8SS metal waste form. (C) 2001 Kluwer Academic Publishers.