Assessment of Tritium Activity in Groundwater at the Nuclear Objects Sites in Lithuania

The assessment of nuclear objects sites in Lithuania, including groundwater characterization, took place in the last few years. Tritium activity in groundwater is a very useful tool for determining how groundwater systems function. Natural and artificial tritium was measured in 8 wells in different layers (from 1.5 to 15 meters depth). The results were compared with other regions of Lithuania also. The evaluated tritium activities varied from 1.8 to 6.4？Bq/L at nuclear objects sites in Lithuania and they are coming to background level (1.83？Bq/L) and other places in Lithuania. The data show, that groundwater at the nuclear power objects sites is not contaminated with artificial tritium. In this work, the vertical tritium transfer from soil water to the groundwater well at nuclear objects site was estimated. The data show that the main factor for vertical tritium transfer to the well depends on the depth of wells. 1. Introduction Lithuania is planning to construct a new nuclear power plant (NPP) nearby the closed one. Lithuanian’s obligation to shut down old one was one of the requirements included in the European Union Accession Treaty. Unit 1 of closed NPP was shut down on December 31, 2004, and unit 2 on December 31, 2009. A near surface repository for low and intermediate-level short-lived radioactive waste will be built on the Stabatiskes site in the vicinity of Ignalina NPP during decommissioning works. The disposal capacity can also be used for the waste stored in the temporary repositories of the Ignalina NPP. Engineering barriers are used in the repository for radioactive waste; however, in long-term evolution scenario radionuclides can spread into the environment, extend in the biosphere, and cause (define) the external exposure of the environment due to the natural and premature (prescheduled) degradation of the engineering barriers of the repository [1]. The decommissioning waste, the new NPP sites, and the closed NPP site are located in the north-eastern part of Lithuania on the shore of Lake Druksiai, close to the borders of Latvia and Belarus (Figure 1). Figure 1: The locations of the observation objects sites are Ignalina NPP; Visaginas NPP; Stabatiske; Budiniai; Zarasai; Birzai; Nida. Groundwater characterization is an important issue in the setting process of new NPP and decommissioning of the old NPP’s. Groundwater dating is a very useful tool for determining how groundwater systems function [2, 3]. The radionuclides transport in water systems depends on many factors: the physicochemical condition, pH, salinity, hydrological,