In-Reactor Corrosion Performance of ZIRLO™ and Zircaloy-4

Abstract

In-reactor and long-term autoclave corrosion data have been obtained on ZIRLO and three variants of Zircaloy-4: conventional (1.5% tin), low-tin, and beta-treated. In-reactor data from demonstration assemblies irradiated in the Virginia Power Company's North Anna Unit 1 reactor demonstrate the superiority of ZIRLO and, to a lesser extent, low-tin Zircaloy-4 over conventional Zircaloy-4. After two cycles of irradiation to an assembly burnup of 37.8 GWD/MTU, the average axial peak corrosion of ZIRLO was 32% that of conventional Zircaloy-4. Low-tin and beta-treated materials displayed average peak oxides 76% and 150% of that formed on conventional Zircaloy-4, respectively. Autoclave corrosion tests of archive tubing have been performed in 633 K water, 672 K, 700 K, and 727 K steam, and in 633 K water containing 70 and 210 ppm lithium as the hydroxide. Correlation of the in-reactor data with the autoclave data indicates that the 633 K pure water test is the best qualitative indicator of in-reactor corrosion performance, and the 672 K steam test the poorest. Differences in in-reactor corrosion between ZIRLO and the Zircaloy-4 materials are consistent with the relative behavior of these materials in lithium hydroxide solutions. The relationships among the in-reactor and autoclave corrosion data, the microstructures, and the processing are discussed. In addition to improved corrosion resistance, ZIRLO exhibits improved dimensional stability over Zircaloy-4. The in-reactor creep of ZIRLO is confirmed to be about 80% of that of Zircaloy-4, and irradiation growth is observed to be about 50% that of Zircaloy-4. These data are also presented and discussed.

Precipitate Stability in a Zr–2.5Nb–0.5Cu Alloy under Heavy Ion Irradiation

“…These changes will affect the material performance in the reactors such as corrosion behavior and irradiation growth. Generally, a finer size and more homogeneous distribution of precipitates benefits the corrosion resistance in Zircaloys [8,9]. In Zr-Nb alloys, the super-saturation of Nb in the matrix was demonstrated to degrade corrosion resistance; thus a full precipitation of β-Nb either from α-Zr or β-Zr is recommended [10][11][12].…”

Effects of precipitation characteristics on the out-of-pile corrosion behavior of niobium-containing zirconium alloys

“…It was reported in Zr-1Nb-1Sn-0.1Fe alloys that the best corrosion performance was obtained for the microstructure containing β-Nb and deviation from this microstructure, such as the presence of β-Zr, tended to degrade corrosion resistance [6,7]. The precipitation of β-Nb was also confirmed to enhance the out-of-pile and in-pile corrosion resistance in Zr-1.0Nb-0.12O alloys [4].…”

“…However, the relationship between the size distribution and the corrosion resistance has not been clarified and explained quantitatively. Moreover, the effect of precipitate size on the corrosion resistance of niobium-containing zirconium alloys [4,6,7] was reported to be contrary to that of Zircaloys [8].…”

“…For the PWR, the corrosion resistance of fuel claddings is one of the main limitations to the extension of fuel rod burnup. From a number of research studies attempting to develop new zirconium alloys, niobium was shown to be the most beneficial alloying element for improving corrosion resistance [2][3][4][5][6]. Many studies were conducted to evaluate the corrosion behavior of niobium-containing zirconium alloys in out-of-pile and inpile conditions.…”

Advanced Proliferation Resistant, Lower Cost, Uranium-Thorium Dioxide Fuels for Light Water Reactors (Progress report for work through June 2002, 12th quarterly report)

“…Zirconium/niobium alloys have long been recognized for their superior corrosion performance and have been used in a wide variety of reactors. ZIRLO from Westinghouse [Westinghouse 1991], DUPLEX from Simmons [Sabol et al 1994, Seibold et al 2000 and M5 from Framatome [Forat and Florentin 1999] represent the innovative claddings and they have been demonstrated to have good in-pile performance. The M5 alloy, in the re-crystallized state for cladding tube material, exhibits better results acquired up to 63 MWd/kgU, when compared to those obtained with any low tin Zircaloy-4 alloy [Forat and Florentin 1999]:…”