Influence of Chemical Composition on Uniform Corrosion of Zirconium-Base Alloys in Autoclave Tests

Abstract

The influence of the composition of Zircaloy-type alloys has been evaluated previously with respect to mechanical properties (1973 International Conference Zirconium in the Nuclear Industry, ASTM STP 551) and to nodular corrosion (1985 International ASTM Conference on Zirconium in the Nuclear Industry, ASTM STP 939). The present study extends this previous work to include uniform corrosion, which is of interest for cladding tubes and spacer grids of fuel assemblies. A variety of ingots with compositions both within and outside of the ASTM specification range for Zircaloy-2 and Zircaloy-4 have been tested. The material was fabricated into strips using a conventional fabrication procedure, which incorporated an intermediate beta quench followed by working and annealing in the upper alpha-range. The alloy elements covered the following ranges: tin: 0.2 to 1.7%; iron: 0.05 to 0.53%; chromium: 0.04 to 1.05%; and nickel: 0.003 to 0.046%. In addition, oxygen, carbon, silicon, and phosphorus were varied over the range of standard Zircaloy contents. Uniform corrosion was studied out of pile by long-time autoclave testing in pressurized water at 350°C (380 to 840 days) and in high pressure steam at 400°C (180 to 397 days). These data supplement testing previously reported for these same alloys in steam at 500°C under static and refreshing conditions (Strasbourg, 1985, ASTM STP 939). Electron microscopic examinations (SEM and TEM) have been used to characterize the intermetallic precipitates to clarify the effect of the various elements. The results of the 350 and 400°C testing show that the time to transition from the cubic to linear rate increases and the post transition rate decreases with decreasing tin and carbon and increasing silicon content. Oxygen and phosphorus have not shown an influence in the range studied. The effect of iron and chromium was more complex than for these other elements; the effect was also different in nature between water and steam tests. Markedly accelerated corrosion was seen at Fe + Cr concentrations below the limits of the Zircaloys (⩽0.15%) especially in steam. This composition effect is similar to that previously reported for the same alloys tested at 500°C. High Cr/Fe ratios often resulted in high corrosion even at moderately high levels of both elements. The effect of iron and chromium can be correlated to type, size, and frequency of the intermetallics.

Electrochemical Behavior of Thin Anodic Oxide Films on Zircaloy‐4: Role of the Mobile Defects

“…The oxidation process is usually described in two steps with a transition between a cubic and a linear oxidation rate. '- 4 The first part of the kinetics is classical; it is the result of the oxygen diffusion through a growing oxide layer. 5 7 It is generally accepted that after the transition, * Electrochemical Society Active Member.…”

The formation and stacking faults of Fe and Cr containing Laves phase in Zircaloy-4 alloy

“…The optimized corrosion performance of Zr alloys was achieved when the fine SPPs were uniformly precipitated in α-Zr matrix [6,7] . Meanwhile, the weak anti-radiation ability of precipitates with planar defect makes them prone to amorphization and elemental migration under neutron irradiation, which would change chemical compositions of the matrix as well as the type of precipitates, thereby lowing the corrosion resistance of Zr alloys [8,9] .…”

Microstructure and corrosion characteristics of Zr–1.5Nb–0.4Sn–0.2Fe–0.1Cr alloy with a β-annealing

“…They have reported that the corrosion kinetics of Zr alloy were affected by the alloying element and the precipitates that are formed by various alloying elements. Since the combination of an alloying element such as Nb, Sn, Fe, Cr etc., is very important factor to obtain good corrosion properties in fuel cladding alloys, many researchers have tried to establish the ideal alloying elements and compositions [3,4]. It has been reported that the corrosion properties of the Nb-containing Zr-based alloys were very sensitive to certain factors such as the Nb-content and the second phase characteristics, which could be controlled by heat-treatment [1,3].…”