Experience in radiological risk assessment of a surface waste disposal facility in Chişinău, Moldova

The long-term condition and potential radiological consequences of legacy radioactive waste stored in a RADON-type of near-surface disposal facility outside the city of Chişinău is of concern to the central government and health protection authorities of the Republic of Moldova. A 'zero alternative scenario' risk assessment has been undertaken in order to evaluate the potential radiological impact on humans and the environment of the facility, were it to be left in its current state with no remediation. The results have been used as a basis for regulatory decision making regarding remediation and decommissioning of the legacy radioactive waste facility. The aim of this study was two-fold: first to demonstrate a complete radiological risk assessment of a real site using a combination of methodologies developed by the IAEA (ISAM and BIOMASS), the second to illustrate the current state-of-the-art in respect of extracting site-specific information from site-descriptive material. We illustrate the practicality of employing geographic information systems techniques on site-specific topographic data to identify relevant biosphere dose objects, thereby allowing customisation of the generic ISAM model framework to site-specific conditions. As a result, a simple method is suggested to bound activity concentrations in well water based on an understanding of water balance in the local catchment area in which the biosphere dose object is embedded. With conservative assumptions, estimated doses from the calculation cases of the design scenario remain lower than the IAEA's dose criteria and environmental screening values. However, the results also indicate that human intrusion activities after the institutional control period could lead to radiological exposures above the IAEA's criteria for a period up to 100 000 years. The long-lived radionuclide²³⁹Pu dominates doses for the on-site residence scenario. Remediation measures should be implemented were the waste to remain at its present place of disposal.

Implementation of graded approach in ensuring safety in management of emergency and legacy radioactive waste in Ukraine

Ukraine has accumulated large amounts of Chernobyl-origin emergency radioactive waste stored in the Chernobyl Exclusion Zone and beyond, as well as legacy radioactive waste in the Radon-type facilities and military sites of the former Soviet Union. Management of such radioactive waste requires the application of a graded approach, in particular, ranking of sites with such radioactive waste by the degree of hazard. Based on the results of ranking, a decision is made on one of the three options: urgent removal of radioactive waste from the site, delayed removal of radioactive waste from the site, and absence of necessity to remove radioactive waste from the site. If it is decided to leave radioactive waste at the site, the graded approach determines the scope of measures to maintain the safety level of that site. This paper presents methodological aspects and experience of the practical application of the graded approach to ensure the safe management of emergency and legacy radioactive waste. In particular, it includes the experience of the Ukrainian State Scientific and Technical Center for Nuclear and Radiation Safety in expert reviews of safety assessments of such sites with emergency and legacy radioactive waste, results of their ranking by degree of hazard, designs for removal of radioactive waste from sites, and establishment of levels for the remediation of territories.