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

Mudali

2009

Trans Indian Inst Met

Self Cite

Zircaloy-4 has been considered as a candidate material for dissolver and evaporators in nuclear fuel reprocessing plants involving nitric acid of high concentrations at high temperatures. The present work deals with the electrochemical studies and surface analysis of passive films on zircaloy-4 and its welds in 11.5 M nitric acid medium. Potentiodynamic polarization technique was employed to study the corrosion behaviour of the alloy in both base and welded (Manual TIG and electron beam (EB) welding) conditions. The polarization curves for zircaloy-4 and its welds exhibited a distinct breakdown of passivity at 1.5 V (SCE) and repassivation, after showing a region of stable passivation. The characterization of passive films by SEM, XRD and LRS, grown at different potentials in 11.5 M nitric acid are presented. The surface morphology and phase analysis of passive films grown at higher potentials showed the presence of monoclinic ZrO 2 . The phases present in the passive film grown electrochemically in 11.5 M nitric acid at 2.0 V and by autoclaving are found to be similar. The presence of characteristic 1040 cm -1 Raman peak from the sample passivated at 1.2 V indicate that the oxide present consist of nanometer size grains of monoclinic zirconia.

Section: Potentiodynamic Polarization Studiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Electrochemical and surface studies on zircaloy-4 exposed to concentrated nitric acid medium

Mudali

2009

Trans Indian Inst Met

Self Cite

“…Ti-based alloys such as Ti-5Ta ( Ref 3,4), Ti-5Ta-1.8Nb (Ref 4,5) have shown better corrosion resistance than Ti. The weldability of new developmental Ti-5Ta-1.8Nb alloy was also excellent (Ref 6); however, corrosion behavior of titanium welds with different heat inputs was not known.…”

Section: Introductionmentioning

confidence: 99%

Effect of Heat Input on Microstructural Changes and Corrosion Behavior of Commercially Pure Titanium Welds in Nitric Acid Medium

J. of Materi Eng and Perform

Gopalakrishnan²,

Balusamy³

et al. 2009

Self Cite

Commercially pure titanium (Ti) has been selected for the fabrication of dissolver for the proposed fast reactor fuel reprocessing plant at Kalpakkam, India. In the present investigation, microstructural changes and corrosion behavior of tungsten inert gas (TIG) welds of Ti grade-1 and grade-2 with different heat inputs were carried out. A wider heat affected zone was observed with higher heat inputs and coarse grains were observed from base metal toward the weld zone with increasing heat input. Fine and more equiaxed prior b grains were observed at lower heat input and the grain size increased toward fusion zone. The results indicated that Ti grade-1 and grade-2 with different heat inputs and different microstructures were insensitive to corrosion in liquid, vapor, and condensate phases of 11.5 M nitric acid tested up to 240 h. The corrosion rate in boiling liquid phase (0.60-0.76 mm/year) was higher than that in vapor (0.012-0.039 mm/ year) and condensate phases (0.04-0.12 mm/year) of nitric acid for Ti grade-1 and grade-2, as well as for base metal for all heat inputs. Potentiodynamic polarization experiment carried out at room temperature indicated higher current densities and better passivation in 11.5 M nitric acid. SEM examination of Ti grade-1 welds for all heat inputs exposed to liquid phase after 240 h showed corrosion attack on the surface, exposing Widmanstatten microstructure containing acicular alpha. The continuous dissolution of the liquid-exposed samples was attributed to the heterogeneous microstructure and non-protective passive film formation.

“…Thermal plasma sprayed yttria stabilized zirconia (PSZ) coatings onto 316L SS rod samples have shown better corrosion resistance in molten LiCl-KCl medium [6]. Laser surface modification of the as-coated plasma sprayed PSZ on type 316L SS was carried out at varying laser powers using a CO 2 Continuous Wave (CW) laser to close the pores in order to improve the corrosion resistance [7]. The present paper discusses the corrosion behaviour of uncoated 316L SS in the molten LiCl-KCl eutectic salt at 873 K and the results were compared with PSZ-coated 316L SS.…”

Section: Introductionmentioning

confidence: 99%

Corrosion of type 316L stainless steel in molten LiCl–KCl salt

Mudali

2008

Materials & Corrosion

Pyrochemical reprocessing in molten chloride salt medium has been considered as one of the best options for the reprocessing of spent metallic fuels. The AISI 316L stainless steel (SS) is envisaged as a candidate material for the fabrication of components for various unit operations like salt preparation vessel, electro-refiner and cathode processor, on which ceramic coatings with metallic bond coat will be applied by the thermal plasma spraying. The unit operation like electro-refining is carried out in the molten lithium chloride-potassium chloride (LiCl-KCl) eutectic salt at 773 K in argon atmosphere. The corrosion behaviour of the container vessel in molten chloride salts is therefore important, hence corrosion tests were carried out in a molten salt test assembly under argon gas atmosphere. The present paper discusses the corrosion behaviour of 316L SS in the molten LiCl-KCl eutectic salt at 873 K. The 316L SS samples were immersed in the molten LiCl-KCl eutectic for 25, 100 and 250 h, while 316L SS with yttria stabilized zirconia coating was exposed for 1000 h. The exposed samples were examined by optical and scanning electron microscope for corrosion attack. The X-ray mappings of the cross-section of the degraded layer onto the 316L SS indicated that the mechanism of corrosion corresponds to the selective diffusion of Cr to the surface with the formation of voids below, and the formation of chromium compounds at the surface. The results of the present study indicated that the yttria stabilized zirconia coating onto the 316L SS exhibits a better corrosion resistance in molten chloride salt than with uncoated 316L SS.