Approach for the Prospective Assessment of Radiological Impact to the Population from Decommissioning of "RADON" Type Radioactive Waste Storage Facility in Lithuania

The Maisiagala radioactive waste storage facility in the Republic of Lithuania is of a former Soviet Union "Radon" type facility design and initially was planned for the disposal of institutional waste. It consists of one 200 m(3) sub-surface vault for disposal of solid waste and several auxiliary installations and buildings. The facility started operation in 1963 and was closed in 1989 being partially filled with waste. The waste is of various types: disused sealed radioactive sources, surface and bulk contaminated items from industry, military, and medicine applications. The inventory is estimated to be 7.7x10(13) Bq. The Maisiagala facility cannot be upgraded to a disposal facility that meets the modern environmental and radiation safety standards. Therefore, a decision was taken to retrieve the waste and decommission the site to a "green field" condition. The release of airborne radionuclides to the environment during the decommissioning activities is estimated to be up to 1.8x10(12) Bq in a single year and is governed by release of gaseous Rn-222. The release of aerosols is smaller by several orders, i.e., 3.9x10(7) Bq. The most activity contributing radionuclide is H-3. The release is expected to be irregular and will vary during the year, week, day and the performed activity. The knowledge on the stored waste inventory is uncertain and cautious assumptions are made, especially regarding the emission of gaseous Rn-222. The paper discusses the approach to the assessment of the expected releases of radionuclides into the environment under normal operation conditions and the approach to the consideration of the radiological impact on the population. The increase of external radiation fields in the close proximity to the site and during the waste transport will create additional exposure pathways. The assessment of direct irradiation is discussed only in the context of its significance to the overall impact of the planned activity. Low radiological impact of the decommissioning of the "RADON" type radioactive waste storage facility in Lithuania on the population is expected under normal operation conditions. The assessed annual effective dose to any of the considered representative persons is below 10 mu Sv.