| The structural material to contain the spallation target during transmutation of spent nuclear fuel (SNF) may develop internal stresses resulting from forming operations including plastic deformation and welding. Techniques such as pair-production, activation and life-time analysis based on classical positron annihilation spectroscopy (PAS) have been used to characterize residual stresses in candidate structural materials subjected to cold-reduction, plastic deformation and welding. Since the PAS techniques can only provide qualitative evaluation of residual stress, calibration curves were developed to estimate the resultant residual stress as a function of PAS line-shape parameters. Since plastic deformation can lead to the generation of defects in structural materials, an extensive effort has also been made to characterize the resultant defects such as dislocations and their densities as a function of the cold-reduction level through utilization of transmission electron microscopy (TEM). An excellent relationship has been established between the dislocation density and a PAS line shape parameter as a function of the cold-reduction level. Further, the metallurgical microstructures and the morphology of failure in the tested specimens has been determined by optical microscopy and scanning electron microscopy. |
