Corrosion of Zircaloy-4 and its welds in nitric acid medium

Abstract

Zirconium and its alloys are considered as candidate materials for various applications in spent nuclear fuel reprocessing plants involving nitric acid of various concentrations at different temperatures. In the present work an attempt was made to study the corrosion behaviour of Zircaloy-4 (Zr-with Sn-1.5%, Fe-0.22%, Cr-0.1%) in wrought and welded forms in comparison with other candidate materials like commercially pure Titanium (CP-Ti), Ti-5%Ta and Ti-5%Ta-2%Nb. Manual TIG welding and electron beam welding was carried out with Zircaloy-4 pipes of 5 mm thick and 120 mm diameter, and radiography was made for choosing defect-free regions for making samples for corrosion investigations. Three phase corrosion testing in liquid, vapour and condensate regions was conducted in boiling 11.5 M nitric acid medium using a specially designed experimental set up. The results indicated that Zircaloy-4 exhibit superior corrosion resistance in both wrought and welded conditions in comparison with other materials. The electron beam welded samples did not show any deterioration and performed similar to wrought alloy. The detailed results of microstructure, microhardness, corrosion rate, morphology of attack and nature of surface film formed are presented in this paper. The results of the present investigation indicated that Zircaloy-4 could be a candidate material for nitric acid medium of high concentration and temperature in reprocessing plants and other industries.