Methodological Proposal for the Site Selection of a borehole Repository in Brazil

Pereira1, P. Rodrigues1, S. Cota1

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

3. Fissural Aproach

• 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