Basic Study on Transmutation Method of Long-Iived Radioactive Waste

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In order to drastically decrease a risk of radioactivity in long future, we have investigated several methods of nuclear transmutation of long-lived nuclides in high level radwastes from nuclear fuel cycle and obtained many important data as follows :(1) Novel methods of the transmutation have been searched, however the use of neutrons is shown to be superior to other particles and photons for this purpose at present.(2) Conceming fission physics, multi-mode analysis and prompt neutron analysis have been actively carried out. Fission cross sections for three americium isotopes (Am-241,242m and 243) from thermal to several tens keV have been measured using a lead spectrometer.(3) Experimental works on spallation physics have been perfomed by making use of GeV proton beams at KEK,and the result has been analyzed. Furthermore, we have taken a large number of nuclear data in several tens and hundreds MeV.(4) Several transmutation systems have been proposed, and their characteristics have been investigated. An experiment of the fission ratio of Np-237 to U-235 in a core of Kyoto University Critical Assemblies, KUCA,has been done.(5) Feasiblity study of high temperature chemical separation for partitioning of radioactive elements has been experimentally performed.(6) Metallic and hydride fuels of minor actinide elements for the transmutation have been investigated.(7) Assessment of the transmutation in the nuclear fuel cycle has been carried out, not only from the technical viewpoint, but also from the standpoints of economics and environmental ethics.