The Study on the conceptual design of uranium waste repository (Phase3)

Saito, Shigeyuki*; Ikuse, Hiroyuki*

(1)study on disposal condition of uranium-bearing waste. Possibility of approximately-100m-depth disposal of various uranium-bearing waste (4.5% enrichment and uranium concentration of 1000 Bq/g) has been studied in order to clear the disposal condition. While exposure rate to the public is over 0.01 mSv/y if all of interested parameters are the worst case, it is less than 0.01 mSv/y only if flow rate in the river is not less than 1E9 m/y, independent of other parameters. In this study, there is no case that exposure rate is less than 0.01 mSv/y for the limit of only one parameter except 1E9 m/y of flow rate in the river. However, less than 0.01 mSv/y is possibly expected in the following case : one is that both inhalation rate and flow rate in the river take reference values, another is that inhalation rate takes reference value and media have good adsorptivity. (2)study on concentration and flux of natural radioactive elements. A literature survey on natural elemental concentrations has been conducted. The collective state of elemental concentration data in Japan is reporterd. To construct methodology of the assessment of natural safety indicators (including flux and concentration), studies on natural geological environments and geological processes in Japan were examined. The methodology of natural safety indicators is divided into the following 6 parts; (a)Geological modeling of assessment area, (b)Gathering of concentraion (,density and radioactivity) data, (c)Research and selection of geological processes (including prosess rate data), (d)Elemental circulation modelling at assessment area, (e)Research of geological repository system and outlines of safety assessment, (f)Setting up of purpose of natural safety indicators, and presentation of the indicators. The international researches of guidelines and laws concerned with natural safety indicators and the review of reserches on the latest natural safety indicators were also examined.