Remediation criteria for radioactively contaminated nuclear sites

The paper presents new methods for estimating operational criteria for remediation of radioactively contaminated nuclear sites in compliance with current environmental and radiation-hygiene requirements. Reference levels of radionuclide content in soils were calculated using numerical modeling based on exposure limits set for humans and non-human biota species. Operational levels of a variety of radionuclides content in soil calculated with respect to environmental and radiation-hygiene criteria for remediation of specific areas within contaminated sites were compared with specific activity limits (SCL) set for solid radioactive waste categorization. The findings suggest that each of these three criteria can be considered as a limiting factor. More strict values of reference levels estimated with regard to ecological criterion were set for 90Sr and 99Tc. The results indicate that SCL can be considered as the prime criterion if contaminants are natural isotopes 232Th and 238U, as well as the majority of transuranium elements. Radiation-hygiene criteria play a key role for the majority of g-emitting isotopes (60Co, 137Cs and etc.). Relatively high impact of the environmental factors in remediation of contaminated nuclear sites is attributable to the fact that radiation exposure pathways to biota differ from those to a man, non-human biota species are continuously exposed to radiation and receive higher doses. People being at a nuclear site are not involved in its intrinsic food chains. Thus, for g-emitting isotopes human exposure pathways are reduced to external exposure coming from contaminated ground surface and inhalation, as for α- and b-emitting radionuclides, inhalation is the only possible pathway. The findings suggest that all three criteria shall be considered in the development of remediation criteria for radioactively contaminated nuclear sites. The remaining issue requiring regulatory clarification is the potential application of SCL levels in the decision making process when it comes to demonstrating that remedial efforts are required at specific industrial sites.