Research and Development of Long-life Target for Spallation Neutron Source

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This research has been made by selecting tungsten as a candidate of target materials having a high neutron performance and a long life for MW-class high power spallation neutron source in the wide field covering from material production to optimum target system development. The main results are as follows :(1) Target material production : New heavy metal composed of tungsten and stainless steel was developed by means of powder metallurgical technique, aiming at developing a high tough and corrosion-resistant tungsten alloy. Its thermal property was not as expected but the technique will be much instructive for powder metallurgy.(2) Cladding technique : Tantalum clad gives a corrosion-resistance to tungsten target. Three kinds methods such as hot-isostatic press method, brazing technique and molten-salt electro chemical method were developed. The development of HIP method has been established and successfully applied to fabrication of the tungsten target block for renewal of target-mode … More rator-reflector assembly of KENS at High Energy Accelerator Research Organization. The latter two methods were examined and their applicability was confirmed.(3) Measurement of material properties : Material properties of various tungsten alloys and target materials were investigated. Especially, corrosion tests gave a lot of scientifically interesting data : parameter dependence on temperature and water flow and data for interpretation of corrosion mechanism.(4) Nuclear and Thermo-hydraulic study of solid target : Neutron and Thermo-hydraulic performance was studied by applying computer simulation. The solid target system for MW-class spallation neutron source was designed and its performance was clarified to be superior to that of liquid target system up to 2 MW. As a complemented study, thermo-hydraulic experiments were made to evaluate the correlation formula to have been used for designs.(5) Study on material irradiation effects : Target is heavily exposed by high-energy protons and neutrons, and radiation damage will determine the target life. We have participated in the international collaboration experiments (STIP Experiments) to irradiate the target materials put in the spallation target of SINQ facility at PSI (Polly-Sheller Institute in Switzerland) and send the many specimen of tungsten alloys, platinum and structural materials to there. Now, the specimens are under irradiation.The irradiated specimen of the STIP Experiments will be returned in 2005 and 2007. Therefore, we have to continue the research to make post irradiation experiments even after this Grant-in-Aid for Scientific Research (A) (1). Additionally, new irradiation-resistant material is urgently needed for higher power spallation sources for the Accelerator-Driven System to transmute long-lived nuclear waste isotopes to shorter nuclides and for fusion reactor. Further research is planed to establish the techniques to develop new materials, cladding technique and so on. Less