Study of "Inadvertent Human Intrusion or Rare Natural Event Scenarios" for sub-surface disposal of radioactive waste

Nakatani, Takayoshi ; Ishitoya, Kimihide; Funabashi, Hideyuki ; Sugaya, Toshikatsu; Sone, Tomoyuki ; Shimada, Hidemitsu*; Nakai, Kunihiro*

The purpose of this study was to assess exposure dose of "Inadvertent Human Intrusion or Rare Natural Event Scenarios" on sub-surface disposal. It was one of "Classification of three types scenarios" in "Basic Policy for Safety Regulation Concerning Land Disposal of Low-Level Radioactive Waste (Interim Report)" formulated by the Nuclear Safety Commission of Japan. Selection of the assessed scenarios, development of the assessment tool and preliminary exposure dose assessment were conducted. Exposure dose of "Well water drinking scenario" was the highest in the assessed scenarios. This scenario assumed that the groundwater in Excavation Disturbed Zone (EDZ) was directly used as drinking water without any dilution. Although this was very conservative condition and the result exceeded 10 mSv/y, it was under the upper limit of standard dose value (10100 mSv/y) in the Interim Report for "Inadvertent Human Intrusion or Rare Natural Event Scenarios".