Corrosion-Resistant Ti-xNb-xZr Alloys for Nitric Acid Applications in Spent Nuclear Fuel Reprocessing Plants

Abstract

This article reports the development, microstructure, and corrosion behavior of two new alloys such as Ti-4Nb-4Zr and Ti-2Nb-2Zr in boiling nitric acid environment. The corrosion test was carried out in the liquid, vapor, and condensate phases of 11.5 M nitric acid, and the potentiodynamic anodic polarization studies were performed at room temperature for both alloys. The samples subjected to three-phase corrosion testing were characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDAX). As Ti-2Nb-2Zr alloy exhibited inferior corrosion behavior in comparison to Ti-4Nb-4Zr in all three phases, weldability and heat treatment studies were carried out only on Ti-4Nb-4Zr alloy. The weldability of the new alloy was evaluated using tungsten inert gas (TIG) welding processes, and the welded specimen was thereafter tested for its corrosion behavior in all three phases. The results of the present investigation revealed that the newly developed near alpha Ti-4Nb-4Zr alloy possessed superior corrosion resistance in all three phases and excellent weldability compared to conventional alloys used for nitric acid application in spent nuclear reprocessing plants. Further, the corrosion resistance of the beta heat-treated Ti-4Nb-4Zr alloy was superior when compared to the sample heat treated in the alpha + beta phase.

Effect of metal ions in a heated nitric acid solution on the corrosion behavior of a titanium–5% tantalum alloy in the hot nitric acid condensate

“…This is because the corrosion of austenitic steels in nitric acid medium is essentially controlled by oxidizing potentials in the transpassive potential regime [5]. Some alternative materials for nitric acid applications, such as Ti base alloys [6,7] and Zr base alloys [8], were developed and have been investigated for utilization in actual plant components. It is well known that Ti and its alloys have superior corrosion resistance in nitric acid solutions due to the passive TiO 2 film that is present on the surface, even at high nitric acid concentrations [9], particularly in the presence of oxidizing ions such as Cr 2 O 2À 7 and Ce 4+ [10,11].…”

Studies on Group IV and V Valve Metal Corrosion in Acidic Fluoride Media

“…3 Acidic fluoride media are encountered in nuclear reprocessing 4,5 and in mud acid treatment of oil-well bores, 6 and valve metals and their alloys are recommended as material of construction in these applications. [7][8][9][10][11] Concentrated nitric acid (11.5 M HNO 3 ) with a small quantity of fluoride ions (0.01 to 0.05 M) is used in fuel dissolver to dissolve spent nuclear fuel rods. 5,12 In other applications, valve metals are deliberately processed in acidic fluoride media, e.g.…”

“…7 Ti-4Nb-4Zr alloy is also reported to offer better corrosion resistance than CP Ti, Ti-Ta, Ti-5Ta-1.8Nb and Ti-2Nb-2Zr in a similar environment. 8 Addition Nb to a Ti-Ta alloy improves the corrosion resistance in concentrated HNO 3 even further. 4 On the other hand, CP Ti offers better corrosion resistance than Zircaloy-4 in boiling nitric acid with 50 mM NaF.…”