Materials Consideration for the National Spallation Neutron Source Target

The National Spallation Neutron Source (NSNS), in which neutrons are generated by bombarding a liquid mercury target with 1 GeV protons, will place extraordinary demands on materials performance. The target structural material will operate in an aggressive environment, subject to intense fluxes of high energy protons, neutrons, and other particles, while exposed to liquid mercury and to water. Components that require special consideration include the Hg liquid target container and protective shroud, beam windows, support structures, moderator containers, and beam tubes. In response to these demands a materials R and D program has been developed for the NSNS that includes: selection of materials; calculations of radiation damage; irradiations, post-irradiation testing, and characterization; compatibility testing and characterization; design and implementation of a plan for monitoring of materials performance in service; and materials engineering and technical support to the project. Irradiations are being carried out in actual and simulated spallation environments. Compatibility experiments in Hg are underway to ascertain whether the phenomena of liquid metal embrittlement and temperature gradient mass transfer will be significant. Results available to date are assessed in terms of the design and operational performance of the facility