An innovative approach for public dose apportionment at multi-facility sites

The atmospheric and aquatic releases of radioactive effluents from nuclear facilities in India are governed by the Technical Specification limits for discharges. These are based on the ICRP effective dose limit of 1mSv/y. At any multi-facility site in India, this dose is apportioned amongst various facilities and among the various radionuclides discharged by each facility. The existing dose apportionments and the corresponding Technical Specification limits were established when the nuclear power industry was at its initial stages. Now, with the nuclear industry poised for a substantial growth, it was felt necessary to evolve a new approach for arriving at dose apportionments and the radioactive effluent release limits taking into account the considerable operating experience in respect of effluent releases. This paper presents the methodology of arriving at the radioactive effluent release limits based on extreme value analysis of the effluent release data of Indian Nuclear Power Plants (NPPs) and then arriving at the dose apportionment. Ten years data of gaseous and liquid effluent discharges of some typical NPPs were subjected to extreme value analysis. The extreme value of release computed with a return period of twenty years formed the basis for arriving at Technical Specification limits. This discharge limit was then applied to other NPPs, which belong to the same category as the typical plant in respect of design and vintage. The dose apportionment for each of the radionuclides and subsequently for the facility is then calculated from the Technical Specification limit of discharges using site-specific environmental dose assessment parameters such as dietary intake, environmental transfer factors and meteorological data. For facilities under construction of existing design, the Technical Specification limits based on that of operating plants can be used. For a facility of new design, the theoretical estimates of releases during normal and anticipated operational occurrences could form the inputs for arriving at Technical Specification limits of discharges and the dose apportionment. (author)