On the Embrittlement of Zircaloy-4 Under RIA-Relevant Conditions

The extended use of Zircaloy cladding in light water reactors degrades its mechanical properties by a combination of irradiation embrittlement, coolant-side oxidation, hydrogen pickup, and hydride formation. The hydrides are usually concentrated in the form of a dense layer or rim near the cooler outer surface of the cladding. Utilizing plane-strain ring-stretch tests to approximate the loading path in a reactivity-initiated accident (RIA) transient, we examined the influence of a hydride rim on the fracture behavior of unirradiated Zircaloy-4 cladding at room temperature and 300 C. Failure is sensitive to hydride-rim thickness such that cladding tubes with a hydride-rim thickness >100 {micro}m ({approx}700 wppm total hydrogen) exhibit brittle behavior, while those with a thickness <90 {micro}m ({approx}600 wppm) remain ductile. The mechanism of failure is identified as strain-induced crack initiation within the hydride rim and failure within the uncracked ligament due to either a shear instability or damage-induced fracture. We also report some preliminary results of the uniaxial tensile behavior of low-Sn Zircaloy-4 cladding tubes in a cold-worked, stress-relieved condition in the transverse (hoop) direction at strain rates of 0.001/s and 0.2/s and temperatures of 26-400 C.

[1]  Saurin Majumdar,et al.  Mechanical property testing of irradiated Zircaloy cladding under reactor transient conditions , 2001 .

[2]  A. Motta,et al.  Strain localization in sheet metal containing a geometric defect , 2000 .

[3]  E. Andrieu,et al.  Anisotropic behavior and rupture of hydrided ZIRCALOY-4 sheets , 2000 .

[4]  S. Majumdar,et al.  Influence of specimen design on the deformation and failure of zircaloy cladding , 2000 .

[5]  Arthur T. Motta,et al.  Failure of Zircaloy cladding under transverse plane-strain deformation , 1998 .

[6]  R. O. Meyer,et al.  A regulatory assessment of test data for reactivity accidents , 1997 .

[7]  C. Prioul,et al.  Hydride embrittlement in ZIRCALOY-4 plate: Part I. Influence of microstructure on the hydride embrittlement in ZIRCALOY-4 at 20 °C and 350 °C , 1994 .

[8]  Fan Yunchang,et al.  The influence of multiaxial states of stress on the hydrogen embrittlement of zirconium alloy sheet , 1985 .

[9]  L. A. Simpson.  Criteria for Fracture Initiation at Hydrides in Zirconium-2.5 Pct Niobium Alloy , 1981 .

[10]  C. Ells.  Hydride precipitates in zirconium alloys (A review) , 1968 .

[11]  D. Hardie,et al.  The hydrogen embrittlement of α-zirconium—A review , 1966 .

[12]  T. Fuketa,et al.  Progress of the RIA experiments with high burnup fuels and their evaluation in JAERI , 1997 .

[13]  Gp Smith,et al.  Effects of Hydride Precipitate Localization and Neutron Fluence on the Ductility of Irradiated Zircaloy-4 , 1996 .

[14]  Z. Marciniak,et al.  The mechanics of sheet metal forming , 1992 .

[15]  H. Chung,et al.  Fracture behavior and microstructural characteristics of irradiated Zircaloy cladding , 1987 .

[16]  J. H. Schemel,et al.  Zirconium in nuclear applications : a symposium co-sponsored by the American Society for Testing and Materials and the American Institute of Mining, Metallurgical, and Petroleum Engineers, 21-24 August 1973, Portland, Ore. , 1974 .