Basic Study on Transmutation Method of Long-Iived Radioactive Waste

为了在今后很长一段时间内大幅度降低放射性危险，我们对核燃料循环产生的高放放射性废物中长寿命核素的几种核嬗变方法进行了研究，获得了以下重要数据：(1)探索了新的嬗变方法，但目前使用中子比其他粒子和光子更优越。(2)在裂变物理方面，积极开展了多模分析和提示中子分析。用铅谱仪测量了三种镅同位素（Am-241,242m和243）从热到几十keV的裂变截面。(3)利用GeV质子束在KEK进行了散裂物理实验，并对实验结果进行了分析。此外，我们还采集了大量几十、几百兆电子伏特的核数据。(4)提出了几种嬗变系统，并对其特征进行了研究。在京都大学临界组件堆芯中进行了镎-237与铀-235裂变比的实验。(5)对放射性元素高温化学分离分配的可行性进行了实验研究。(6)研究了用于嬗变的少量锕系元素的金属燃料和氢化物燃料。(7)不仅从技术角度，而且从经济和环境伦理的角度对核燃料循环中的嬗变进行了评价。

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.