Evaluation of nuclides migration for trench-type disposal by a calculation method taking leaching into consideration

Japan Atomic Energy Agency (JAEA) is planning for the near surface disposal of very low and low level radioactive wastes generated from research, industrial and medical facilities industry in Japan. This document provides the values of radioactivity concentrations equivalent to dose criterion for trench-type disposal and its doses. These values are derived based on the safety assessment for ground water scenarios under generic site conditions by using a mathematical model which is newly developed. The model describes the release of radionuclides from wastes to a cover soil caused by elution having constant rates. These newly derived concentrations are compared with concentrations previously calculated by a model that describe the nuclide release mechanisms as solid-liquid partitioning equilibrium. Additionally, the change in the concentrations and its doses related to the safety assessment for ground water scenarios is evaluated when the amount of water percolating into a disposal facility with impermeable layers varies according to its impermeability performance, because such a disposal facility is under consideration in order to be disposed of cement-solidified waste packages with very low radioactivity concentration. (author)