Estimated “No-Effect” Radionuclide Concentrations for Non-Human Biota

Abstract

This study further developed a screening methodology to be consistent with Canadian Standards Association (CSA) standard N288.1-14 and N288.6-12, and applied it to derive radiological “No- Effect” Concentrations (NECs) for 45 radionuclides relevant for the disposal of radioactive wastes. This methodology is applicable to used fuel disposal sites in Canadian ecosystems under both present and future hypothetical climate conditions and is useful for conducting screening-level radioecological risk assessments.

Multiple indicator species were evaluated for each ecosystem, representing different trophic levels within the ecosystem. The NEC corresponds to the most limiting biota for each radionuclide in a particular environmental medium (i.e., groundwater, surface water, and soil). A sum-of-fractions rule was used to ensure that total dose does not exceed estimated no effect dose rate values. The conservative nature of the assumptions used to derive the NECs ensures that as long as the NECs are not exceeded, there is confidence that there will be no undue long-term effects on non-human biota. In the event that NECs are exceeded in screening calculations, a site-specific Ecological Risk Assessment would be required.

The NECs were compared to estimated environmental concentrations from a publicly available NWMO postclosure safety assessment case study and the results clearly indicate that there would be no undue long-term impacts on non-human biota.