R&D for the Spallation Neutron Source mercury target

An overview of the research and development program for the Spallation Neutron Source (SNS) is presented. The materials-related efforts in target development are emphasized in order to provide a perspective for a number of specialized papers that are included in these proceedings. We give a brief introduction and historical sketch of the SNS project. Part of the materials R&D consists of calculations of radiation damage and of transmutation rates. He and H are considered to be the most important transmutation products. Radiation effects and Hg compatibility investigations make up the major part of the experimental effort. In the former, spallation irradiations are carried out in the LANSCE at Los Alamos National Laboratory and in the SINQ at the Paul Scherrer Institute. Irradiations that simulate aspects of a spallation environment are included to extend the parameter space of the spallation irradiations. The simulations are carried out at the low energy (MeV) accelerators of the TIF facility and at the HFIR reactor, both located at Oak Ridge National Laboratory. Irradiated specimens are tested for changes in mechanical properties and are characterized with respect to microstructural changes by transmission electron microscopy. The compatibility experiments cover both the effects of Hg on behavior in mechanical properties tests, and the effects of flowing Hg on mass transfer in target structural materials. The results of this extensive program of materials work indicate that the target design and materials performance will meet their intended service.