A Practical Approach to Evaluate Stress-Strain Behavior of Remotely Handled Pressure Tubes of Nuclear Reactors Using Ring Tension Test

Determination of transverse mechanical properties of nuclear reactor pressure tubes is important to perform integrity assessment of these components, especially for those which have been subjected to extended duration of reactor operation. Machining of standard tensile specimens is difficult in case the specimens are to be obtained from these thin tubular components. However, the more practicable option would be to fabricate the ring tensile type of specimens by directly machining them from the tube as it is a less cumbersome option in comparison to that of machining of the miniature plate tensile specimens especially when the component has been discharged from the nuclear reactor and are to be handled remotely due to activity. But, adopting this approach requires certain specific standardization work to be done to make the technique fully acceptable, adaptable and reliable when compared to the conventional techniques. In this work, we have developed a practical approach to evaluate the transverse mechanical properties and the stress-strain behavior of tubular components using ring tensile test. Different types of mandrel design and gauge length orientations of the specimens with respect to loading axis have been explored and the dependence of the results on the above parameters has been discussed. Two different types of Zirconium based alloys as used in Indian nuclear reactors have been tested with this technique and the material stress-strain behavior have been evaluated. Finally, the advantages of this method to evaluate the transverse mechanical properties of remotely-operated tubular components have been highlighted and use of appropriate loading and mandrel geometry for the ring tensile test have been recommended. The paper elucidates the methodology followed in validating the ring tensile test results in order to make the test suitable for the estimation of the irradiation-induced alteration in mechanical properties of nuclear reactor pressure tubes.