Scenario options to calculation of Derived Concentration Guideline Levels for a multi-unit decommissioning site

Abstract

To release a site after nuclear power plant decommissioning, it is necessary to demonstrate compliance with a radiological requirement that the residual radioactivity in a decommissioned site does not result in dose in excess of the site release criteria applicable. This is generally accomplished by ensuring that the residual concentrations of radionuclides are below Derived Concentration Guideline Levels (DCGLs) which are derived, using RESRAD dose modeling code, from the site release criteria under a site reuse scenario assumed for the site. In this paper, we propose a methodology to calculate the preliminary DCGLs for a multi-unit decommissioning site. For this, five site reuse scenario options were applied taking into account the most foreseeable and practical future site reuse conditions at Kori site, especially the operation and decommissioning schedules of other units: Option 1 of a single residential farmer scenario with unrestricted condition, Option 2 of a single industrial worker scenario with unrestricted condition, Option 3 of a hybrid industrial worker plus residential farmer scenario with unrestricted condition, Option 4 of a single nuclear facility scenario with restricted condition, and Option 5 of a hybrid nuclear facility plus residential farmer scenario with restricted condition. For restricted cases (Options 4 and 5), a case where institutional controls of the original scenario fail is also considered by applying residential farmer scenario instead. We hope that the approach to applying multiple site reuse scenario options to calculate DCGLs, proposed in this paper, will give a valuable insight to other related researcher who need to calculate DCGLs, especially for a multi-units site.