1. PAPER NUMBER 98
Disposal project for LLW and VLLW generated from research facilities in Japan: A feasibility study for the near surface disposal of VLLW that includes uranium
Sakai1, M. Hasegawa1, Y. Sakamoto1, T. Nakatani1
Japan Atomic Energy Agency
Japan Atomic Energy Agency plans to implement the near surface disposal of LLW and VLLW in Japan.
Approximately 25% of the volume of VLLW is uranium-bearing waste.
The calculated dose due to uranium and its progeny is estimated to reach its peak value beyond 10,000 years. The peak dose is a relatively larger value.
Two safety measures to deal with this issue are discussed.
First, dose assessment in the very conservative assumptions for long periods of time is performed. The implementer confirms that the calculated dose does not exceed 0.3mSv/y, (dose constraint), or 1 mSv/y (lower reference level for existing exposure).
Second, the amount of uranium radioactivity disposed in a trench section is controlled to reduce the average uranium concentration in the section to lower than 1 Bq/g. The result considers the situation as an existing exposure situation. The possibility of a non-acceptable exposure situation is reduced, even if an extreme long-term exposure situation is assumed.
Dose constraint
Control period
(50 years)
Annual Radiation Dose (mSv/y)
Conservative condition
Likely condition
*A section composed of VLL uranium-bearing waste, VLLW, and soil fill.
Fig.2 Management concept for the average uranium radioactivity concentration for each section of waste layer.
Time of scenario occurrence (year)
Average concentration of total Uranium in waste is 10 Bq/g.
The composition condition is the enriched uranium containing 5 wt% U-235
These results show that it is possible to safely implement the trench disposal of VLL uranium-bearing waste by adequately controlling the disposed radioactivity of uranium.
Fig.1 Evaluated dose due to uranium from a residence scenario that assumes a different site situation.