Fig. 4-15 Underground Research Laboratory arrangement, Canada A rock sample and groundwater for experiments were taken from a fracture zone at a depth of about 250 m. Groundwater from the fracture zone was introduced into the experimental system without air contact.

Fig. 4-16 Distribution of TRU elements in the columns Columns 2.54 cm in diameter and 20 cm in length were used in the experiments. Radionuclides, such as neptunium, plutonium, americium were injected into each column individually. Most of the injected nuclides were retained within the first few centimeters of the column. These results show the behavior of nuclides under deep geological conditions. 110 ml of each radionuclide solution was injected into a column at a flow rate of 2.2 ml/h. Following the injection of the radionuclide solution, groundwater was passed through the column. After 2000 hours of column operation, the column was retrieved and the nuclide distribution in the column was measured.

High-level radioactive wastes are planned to be disposed of in the deep, stable underground. Transportation of radionuclides by groundwater from the storage vault to the biosphere through geological media is the most important concern to be considered. It is necessary to understand radionuclide migration behavior at the depth where the vault would be constructed. For the investigation of nuclide migration under deep geological conditions, Japan and Canada opened an experimental room in the Underground Research Laboratory located near Whiteshell Laboratories, eastern Manitoba, Canada. This project was carried out under the JAERI/AECL agreement. Column experiments were performed in the experimental room for these migration tests. A rock sample was taken from a fracture zone at a depth of about 250 m and plated in a column. Groundwater from the fracture zone was introduced into the column without air contact. Technetium and Neptunium were injected individually into columns with ground water. Although these elements show very small sorption onto rocks under atmospheric conditions, they were strongly retained in the column. Results suggest that these elements were reduced under the deep geological conditions present and sorbed onto the rock. Technetium and neptunium have long radioactive decay half-lives. Accordingly, they are among the most important nuclides that are contained in high-level radioactive waste.

Reference M. Kumata et al., Technetium Behavior under Deep Geological Conditions, Radioactive Waste Manag. and Nucl. Fuel Cycle, 17(2), 107 (1993).

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