Evaluationm of Hoop direction tensile properties of 9cr-ODS and T91 steel nuclear fuel clad tubes using ring tensile test

Abstract

Nuclear power plants are powered by nuclear fuel pellets stacked inside fuel clad tubes. These tubes act as housing for the fuel pellets and remain as the first barrier for the radioactive material. The present focus of nuclear power plants is to increase the efficiency of the power plants by increasing the fuel burn up. However, this enhances cladding degradation which may increase the chances of cladding failure. During operation the fuel clad tubes experience maximum value of stress in the hoop or transverse direction which results in failure of the tubes. Hence, it is very important to determine the mechanical properties in hoop direction of the clad tubes. Ring Tensile Test is used for measuring the mechanical properties of tubular specimens along hoop direction. The testing method consists of loading the ring along the transverse direction by applying double D inserts inside the ring. However there are some limitations in this procedure which includes bending of sample during loading and the friction between the inner surface of ring and outer surface of the loading pin. Like in conventional tensile test there are no standards available for the specimen geometries and test procedure. The present work focuses on the selection of suitable combination of specimen geometries for ring tensile test, mitigation of bending of sample during loading and to reduce friction between the inner surface of ring and outer surface of loading pin. The optimized specimen geometries and testing parameters were used to measure the hoop direction tensile properties T91 and 9Cr-ODS steel clad tubes. To understand the effect of temperature on mechanical properties of T91 and 9Cr-ODS steel clad tube ring tensile tests were carried out both at room temperature and elevated temperatures. Fractography studies were also performed on the fractured specimens to understand the fracture behavior at different temperatures by using scanning electron microscopy.