THERMOMECHANICAL MEASUREMENTS OF ZIRCALOY-4: APPLICATION OF RAMAN THERMOMETRY AND NANO-MECHANCIAL TESTING TECHNIQUES
thesisposted on 17.10.2019, 19:56 by Hao WangHao Wang
Zirconium alloys (zircaloy) have been widely used in light water reactors due to their good thermomechanical properties, corrosion resistance, and low thermal neutron absorption rate. As one of the most important safety barriers, cladding is not only used to encapsulate nuclear fuel, but also to prevent the nuclear fission products from leaking into the coolant. During the operation of nuclear reactors, hydride will form in zircaloy and significantly degrade the tensile strength, ductility, fracture toughness, and creep behavior of the cladding, and eventually leading to the failure of cladding. Therefore, understanding the material properties of zircaloy and its hydrides is crucial to the safety of power plants. In this study, the mechanical Raman spectroscopy and nano-mechancial testing techniques were used to perform thermomechanical measurements and damage analysis of zircaloy-4. The Raman thermometry method was used to measure localized spatially resolved thermal conductivity and establish the potential linkage of microstructure to thermal and mechanical properties of zircaloy-4. The local thermal conductivity values showed to increase with increase in grain size. Nanoindentation and nano-scale impact techniques were used to obtain the viscoplastic constitutive relation of hydrides at elevated temperatures. Based on the obtained viscoplastic model, fracture strength of hydrides was predicted by using finite element method (FEM) simulations. An extended Gurson-Tvergaard-Needleman (GTN) model was used to study the macro-scale fracture behavior of hydrided zircaloy-4 structures. Good agreement between calculated and experimental results was obtained for various boundary conditions.