Controlled Composition Zircaloy-2 Uniform Corrosion Resistance

The influence of chemical composition and manufacturing variables on the nodular corrosion resistance (determined by 500°C non-refreshed steam autoclave testing) of controlled composition Zircaloy-2 was reported previously (Zirconium in the Nuclear Industry: Eighth International Symposium, ASTM STP 1023, pp. 334–345.). The present study extends the previous work to include uniform corrosion, which is of interest for cladding tubes and spacer strips.

Controlled composition Zircaloy-2 is defined where nickel and iron are adjusted towards the upper ASTM composition limits and tin is adjusted towards the lower limit. To investigate the effects of tin, iron, chromium, and nickel on the uniform corrosion of Zircaloy-2, a special 5500-kg ingot was triple melted. The composition was intentionally varied within a controlled portion of the ASTM B 350 range along the ingot length. Specimens of the ingot with different compositions were hot worked and beta quenched at a common size. Strip specimens (0.7 mm thick) were fabricated using three process schedules spanning the annealing parameter (ςA_i = ςt_i exp (-80 000/RT_i) range applicable to current production practice for either tubeshell or strip material. Corrosion weight gains were obtained from 360 and 420°C static autoclave tests extending to over 500 days exposure.

A statistically significant reduction in 360°C corrosion weight gain was observed as the nickel was increased to the upper ASTM composition limit. An interaction was observed between nickel content and ςA_i. In the 420°C test, increasing nickel decreased the variability in observed weight gains that occurred as the annealing parameter varied. The data are comparable with controlled composition Zircaloy-2 spacer strip manufactured using production equipment and processing. No effect of varying nickel within the upper half of the ASTM Zircaloy-2 composition range (580–750 ppm) on hydrogen uptake was found. Hydrogen uptake depended primarily on corrosion weight gains of the individual specimens.