Plastic Deformation and Fracture Behavior of Zircaloy-2 Fuel Cladding Tubes under Biaxial Stress

Abstract

Various combinations of biaxial stress were applied on five batches of recrystallized zircaloy-2 fuel cladding tubes with different textures ; elongation in both axial and circumferential directions of the specimen was measured continuously up to 5% plastic deformation.T h e anisotropic theory of plasticity proposed by Hill was applied t o t h e resulting data, and anisotropy constants were obtained through the two media of plastic strain loci and plastic strain ratios. Comparison of t h e results obtained with the two methods proved that t h e plastic strain loci provide d a t a that a r e more effective in predicting quantitatively the plastic deformation behavior of the zircaloy-2 tubes. T h e anisotropy constants change their value with progress of plastic deformation, and judicious application of t h e effective stress and effective strain obtained on anisotropic materials will permit the relationship between stress and strain under various biaxialities of stresses t o be approximated by t h e work hardening law.T h e test specimens used in t h e plastic deformation experiments were then stressed t o fracture under the s a m e combination of biaxial stress as i n the proceeding experiments, and t h e deformation in the fractured part was measured. T h e result proved t h a t t h e tilt angle of the c-axis which serves a s the index of texture is related to fracture ductility under biaxial stress. Based on this relationship, it was concluded that material with a tilt angle ranging from 10" t o 15" is the most suitable for fuel cladding tubes, from t h e viewpoint of fracture ductility, at least in the case of unirradiated material.

Thermomechanical loading applied on the cladding tube during the pellet cladding mechanical interaction phase of a rapid reactivity initiated accident

“…Representative loading biaxialities should be taken into account as the detrimental effect of a high biaxiality level mechanical loading on the ductile fracture is well known [17]. Concerning zirconium alloys, this effect was confirmed on unirradiated recrystallized Zircaloy-2 sheets [18], on unirradiated recrystallized Zircaloy-2 tubes [19], on unirradiated recrystallized Zircaloy-4 [20], on unirradiated and irradiated Zr-1%Nb tubes [21] and on unirradiated CWSR Zircaloy-4 by means of EDC and HB-EDC tests [22].…”

Mechanical behavior of recrystallized Zircaloy-4 under monotonic loading at room temperature: Tests and simplified anisotropic modeling

“…The isotropic Hill coefficients in the shear directions were thus considered (H TR = H RN = H NT = 1.5). As observed by Maki [21], and because of the strong anisotropy of plastic flow, the anisotropic constants changed with plastic strain. A single set of Hill coefficients alone could not represent the change in yield surface and strain hardening with plastic strain.…”

Behavior of Zircaloy Fuel Cladding Tubes

“…where ko: Apparent thermal conductivity of oxide film (24) q, q 0 : Linear heating rates on unoxidized and oxidized specimens Ac: Area of heat transfer surface per unit length t1t, t1t 0 : Temperature differences between inside surface of tube and coolant water on unoxidized and oxidized specimens o : Thickness of oxide film.…”