Methodological Proposal for the Site Selection of a borehole Repository in Brazil Pereira 1 , P. Rodrigues 1 , S. Cota 1 1 Centro de Desenvolvimento da Tecnologia Nuclear (CDTN), Belo Horizonte, Brazil Abstract According to the Brazilian regulation for site selection for low level waste repositories, areas of interest and preliminary areas steps must encompass a bibliographic review, followed by a systematic study of natural characteristics and infrastructure. Using a GIS platform, a methodology based on spatial and geochemical/hydrochemical databases for porous and fissural domains, along with selection/exclusion criteria, were proposed to select possible sites of a borehole repository for sealed sources. After this selection, technical, logistical and juridical features were also considered. Applying this methodology for Brazil, 209 counties were selected as preliminary areas. The lack of necessary databases can be a difficult for applying this approach. • Developed to meet the requeriments of the Brazilian Standards [1] and the ISAM methodology [2, 3]. • The site selection is a key component for assuring the safety of the repository design. • Main goal is to select Areas of Interest and Preliminary Areas. • The methodology uses a systematic process proposed by [4], including the Conceptual and Planning Stage and the Area Survey Stage. • Site selection process: indentification of the desirable features and data evaluation (FIG 1) [4,5,6] • Databases were divided in Spatial data (Terrain and Technical, Logistical and Juridical Features) (TABLE 1 and 2) and Geochemical/Hydrochemical Data (Water analysis). • Spatial data evaluation divided in each round, • Desirable features for each group ( TABLE 1 e 2) TABLE 1: Desirable Terrain Features Terrain Features Desirable Characteristics Terrain Features Desirable Characteristics Geology (Geodiversidade and Levantamento Geológico/Litológico database) (1:2.500.000 scale) Uniform stratigraphy, lithology and mineralogy, both in thickness and mineral composition Meteorology (Atlas Pluviométrico do Brasil) (1:5.000.000 scale) Low rainfall index (<1400 mm/year) Simple structural characteristics High temperatures Argillaceous and massive crystalline geologic terrains. Arenaceus in conjunction with favorable climatic conditions. Geochemistry/hydro chemistry (Rede Integrada de Monitoramento das Águas Subterrâneas database) Low sulphide/sulphates and chloride content Older rocks, with seismological stability and not disturbed by fractures pH is a dynamic propriety, having different impacts on the engineered barriers depending of the geochemical characteristics. Higher pH solutions (pH>8.5) are desirable Hydrogeology (Mapa Hidrogeológico do Brasil ao Milionésimo database) (1:1.000.000 scale) Low hydraulic conductivity and low porosity values Eh redox >200 mV (NECSA.2004) Regions with deep seated groundwater table or deep geological confining units (aquicludes) - below of drinking water zones Tectonic and seismicity: (Sismos database) Low tectonic and seismic activity Apart from recharge zones or poor recharge No foresee uses Surface processes (Mapa Hidrogeológico do Brasil ao Milionésimo database) (1:1.100.000 scale) Stable and not steeply relief, easy access by road Underdeveloped, young soil No presence of water bodies Far from coastal and marine features No. Criterion Cutt -off values Numerical parameters (in km) Method Scale Level (*) 1 Source Cities none 720 Inclusion 1:100.000 1 2 Indigenous Criterion none 10 and 20¹ Exclusion ~1:5.500.000 1 3 Demographic density (municipal) <57,39 inhab/km² 0 Inclusion ~1:500.000 2 4 Main Drainage none 1 Exclusion 1:1.000.000 2 5 Environmental Conservation Units none 10 Exclusion ~1:500.000 2 6 Mining Areas none 0 Exclusion 1:100.000 3 7 Altitude aspect (over 1.800 m) none 1 Exclusion 1,000,000 3 8 Highways + main roads none 15 Inclusion 1:50.000 3 (*)Selection Levels defined on CNEN 6.06: Region of Interest 2: Preliminary Areas 3: Potential Areas 1: Aprox. mean area of all indian reservations in Brazil. Adopted for areas in study TABLE 2: Desirable TLJ Features FIGURE 2: Workflow of the methodology • The evaluation lead to 209 counties containing areas that met the requirements proposed on the methodology • Possibility of correlating different variables and parameters • Tendency of rejecting sites based on false premises due the lack of appropriated databases, heterogeneous scales, data inconsistencies and subjectivity of some criteria. • As well established in the literature [3], only few requirements of the site must be satisfied, mainly related to hydrological and geochemical conditions Results of fissural and porous approach Bibliography: [1] COMISSÃO NACIONAL DE ENERGIA NUCLEAR, Seleção e escolha de locais para depósitos de rejeitos radioativos, CNEN- NE-6.06, Brazil (1989). [2] INTERNATIONAL ATOMIC ENERGY AGENCY, Safety Assessment Methodologies for Near Surface Disposal Facilities, Vol1 , Austria (2004). [3] INTERNATIONAL ATOMIC ENERGY AGENCY, BOSS: Borehole Disposal of Disused Sealed Sources, IAEA-TECDOC-1644, Vienna (2011). [4] SOUTH AFRICAN NUCLEAR ENERGY CORPORATION, Borehole Disposal Concept: Generic Site Selection and Characterisation, GEA-1622, Pretoria (2004). [5] INTERNATIONAL ATOMIC ENERGY AGENCY, Siting of Near-Surface Disposal Facilities, IAEA Safety Guide, Vienna (1990). [6] INTERNATIONAL ATOMIC ENERGY AGENCY, Borehole Disposal Facilities for Radioactive Waste, SSG-1, Vienna (2009). 1.Introduction 2.Methodology 3.Fissural approach 4. Porous approach 5. TLJ Features and potential hydrogeoeochemicical associated sites 6.Conclusions