Study of sub-surface disposal concepts for uranium waste, 2

Tsujimura, Seiichi; Funabashi, Hideyuki ; Ishibashi, Makoto*; Takase, Toshio*; Kurosawa, Mitsuru*

Uranium waste has characteristics that it is rarely expected to decay its radioactivities and it is not almost necessary to consider external exposure to radiation from waste package. We studied reasonable sub-surface disposal concepts for uranium waste in 2004 and 2005 considering the characteristics. In 2005, we studied necessity of engineered barrier for the disposal of uranium waste, considering change of chemical condition around disposal facilities over long periods of time. Safety assessment was made to analyze effect of difference in sorption parameters at reduction and oxidation conditions. The assessment showed that change from reduction to oxidation around disposal facilities did not lead to increase dose to the public. The assessment with realistic sorption parameters showed that dose to the public was not more than 10 Sv/y. The results proved that it was not necessary to keep reduction conditions around disposal facilities. This two-year- study showed that there was possibility of sub-surface disposal system without engineered barrier for uranium waste.