Experimental creep behaviour determination of cladding tube materials under multi-axial loadings

Abstract

Cladding tubes are structural parts of nuclear plants, submitted to complex thermomechanical loadings. Thus, it is necessary to know and predict their behaviour to preserve their integrity and to enhance their lifetime. Therefore, a new experimental device has been developed to control the load path under multi-axial load conditions. The apparatus is designed to determine the thermomechanical behaviour of zirconium alloys used for cladding tubes. First results are presented. Creep tests with different biaxial loadings were performed. Results are analysed in terms of thermal expansion and of creep strain. The anisotropy of the material is revealed and iso-creep strain curves are given.

Microstructural characterization of creep anisotropy at 673 K in the M5® alloy

“…Recently, a critical analysis of the influence of complex loading paths was made to point out their effects on strain [10,11,22] and strain rate [15]. It was shown that, in comparison with uniaxial tests, zirconium alloys can exhibit either overstrengthening or oversoftening under multiaxial loading paths.…”

“…where A and n are constants having different values for each a [15]. A comparison of the isocreep curve with the von Mises yield locus for 0°< a < 90°leads to an illustration of the macroscopic creep anisotropy (Fig.…”

“…The dimensional measurements and temperature regulation were made on a gauge of 20 mm long, centered on the middle of the specimens. Specimens are sealed by a clamping set before being subjected to creep tests with a specific device [15]. A constant temperature of 673 ± 2 K is maintained on the gauge using a radiative furnace.…”

Thermal isocreep curves obtained during multi-axial creep tests on recrystallized Zircaloy-4 and M5™ alloy

“…This cold-working form ing process induces anisotropie crystallographic textures which are comparable for both investigated alloys. C-axes of the grains are mainly orientated around ±30° of the radial direction resulting in a mechanical anisotropy (Grosjean et al, 2009b;Priser et al, 2011 ). Ail the tests were realized at a temperature of 673 K. Creep tests were stopped when stationary creep strain rate was stabilized.…”

Multiaxial Creep Testing Device for Nuclear Fuel Claddings

“…Zircaloys, which are hexagonal close packed materials, exhibit anisotropy in the creep properties, especially in cold-worked condition. Several studies indicate that the creep strength of such materials is different in the hoop and axial directions of the internally pressurized tube, because they form preferred orientations or texture during the manufacturing process (Yutaka, 1987;Murty and Charit, 2006;Li and Holt, 2007;Grosjean et al, 2009). Austenitic stainless steels are candidate materials for fuel claddings in e.g.…”