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Site Selection Study for Radioactive Waste Repository: Study Area of Negeri Sembilan

Che Kamaruddin, A. H.1, Tahar, K. N.2, Wan Mohamad, W. M. N.2

1Malaysian Nuclear Agency (MNA), Selangor, Malaysia 2Universiti Teknologi Mara (UiTM Shah Alam), Selangor, Malaysia

E-mail contact of main author: hadi@nm.gov.my

Abstract. Radioactive materials are used in beneficial ways such as in medical diagnosis and therapy, scientific research and specialized industrial applications, many of these activities generate radioactive waste, which occur either in gas, liquid or solid form. The volume and total amount of radioactive wastes is increasing every year. From 1984 until 2012, there are more than 8000 unit of disused sealed radioactive sources, 445 m³ of solid wastes, 44 m³ of organic waste and 15,000 m³ liquid waste collected and managed by Nuclear Malaysia as recorded in the radioactive waste inventory database Nuclear Malaysia. The government considers that the establishment of a national near-surface repository for low level radioactive waste is a national responsibility and therefore feasible and comprehensive strategies are needed for continuous waste management. A suitable repository site must have long-term stability and attributes that will enable the wastes to be isolated so that there is no unacceptable risk to people or the environment either while it is operating or after closure. Radioactive waste should be disposed of in a controlled and proper manner by considering the fact that the waste contains radionuclides that harmful and can bring danger to any living things. Therefore, the criteria for choosing the suitable or potential sites is very important for an operator who was given responsibility to make sure safety consideration in all aspects is being complied as stipulated by law from regulatory authority. A study for screening the suitable area which covered whole state of Negeri Sembilan has been conducted using ArcGIS software. Two techniques in Multi Criteria Decision Making (MCDM) were considered in the GIS processing by using Boolean Overlay and Weighted Sum Overlay methods.

Key Words: National near-surface repository, ArcGIS software, Multi Criteria Decision Making (MCDM).

1. Introduction

The government considers that the establishment of a national near-surface repository for low level radioactive waste is a national responsibility and therefore feasible and comprehensive strategies are needed for continuous waste management. Nuclear Malaysia has been given the responsibility to develop national repository for low level radioactive waste as a long-term solution for radioactive waste management programme.

A suitable repository site must have long-term stability and attributes that will enable the wastes to be isolated so that there is no unacceptable risk to people or the environment either while it is operating or after closure. Criteria for site selection usually consist of geological factors (which includes soil

properties, lithology, lineament, and geomorphology), meteorological factors such as rainfall distribution, hydrogeological aspects, proximity or distance from road or river, and land-use factors.

Establishment of screening criteria for this study was driven from many references including Chuang, et al., (2006), Huang et al., (2006), and Risoluti, et al., (1999), and some case studies from some countries including Australia, Russia, United Kingdom (U.K) and others as well as understanding on environmental setting of the study area based on researcher’s judgement. According to the International Atomic Energy Agency (IAEA), there are four stages should be recognized in the siting process for a radioactive waste disposal facility consist of conceptual and planning stage, area survey stage, site

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investigation stage and detail site characterization stage.

2. Site Selection

Radioactive waste should be disposed of in a controlled and proper manner by considering the fact that the waste contains radionuclides that harmful and can bring danger to any living things. Therefore, the criteria for choosing the suitable or potential sites is very important for an operator who was given responsibility to make sure safety consideration in all aspects is being complied as stipulated by law from regulatory authority. A study case for implementing this screening process covered for the whole state of Negeri Sembilan area has been conducted. This study case is the first phase of screening process to identify the best suitable sites or location for developing the disposal facility in Malaysia. There are four steps in the site selection processes which consist of conceptual and planning stage, area survey stage, site characterization stage and site confirmation stage (IAEA, 1994).

3. Methodology

Research methodology can be divided into five sections such as spatial data collection and GIS layer preparation, software used, Boolean Overlay and Weighted Overlay, Criteria for site selection and Geographical Information Science (GIS) Modelling using Model Builder in ArcGIS 10.2.

3.1 Data collection and GIS layer preparation

Data collections were obtained from many related agencies which are from Agensi Remote Sensing Malaysia (ARSM), Jabatan Mineral and Geosains (JMG), Jabatan Perangkaan Malaysia. Spatial data collection used to prepare spatial layers in ArcGIS software. The Landsat TM Scene of 126/58 and 127/58 obtained from ARSM were used in this study. The datasets were mosaic and corrected to fit the Rectified Skew Orthomorphic (RSO) Malaysian Projection by applying image-to-image registration technique. The image were already enhanced to improve their appearance by using band combination of red, green, and blue (RGB). Topological and geological features such as lineaments, geomorphology were also interpreted from the images.

Besides, the satellite image Level 1 GeoTIFF Data of The Landsat 8 OLI/TIRS were also obtained and downloaded from USGS Earth Explorer website for this study. Through consideration of all the result, the

RGB natural colour combination of band 4, 3, 2 is the most appropriate combination for visual interpretation for the study area.

Thirteen (13) spatial input data have been used into Model Builder for spatial processing in ArcGIS 10.2 Desktop software. The input data used in this study are consist of lithology, soil properties, rainfall distribution, hydrogeology, land use, geomorphology, lineaments, road, river, town, population, elevation, and slope. Slope was produced from Digital Elevation Model (DEM) which also can give us information about elevation of the study area. Before selecting the suitable sites, input layers need to be categorized and reclassified.

3.2 Software Used

ArcGIS version 10.2 is one of the main software used in this research. This GIS software allows user to edit, update, manipulate and analyze spatial and attributes data explained in the earlier sections. In this research, this software is used to edit and update the spatial data with new information. For example, the main criteria for each parameters can be classified and be determined as represented in the attributes table. The surface analysis or 3D Analyst, Spatial Analyst and the Geoprocessing Tools are the main modules in the ArcGIS software used to manipulate, process and analyze the related data. Suitable areas for radioactive waste repository maps are generated using this software.

3.3 Boolean and Weighted Overlay Method

In this section, all required data for site selection were analyzed and reclassified before appropriate weight value given. A new information layer with a variety of new spatial units from spatial intersection is important to decide which newly created spatial units should be summarized and which must be recorded separately when applying this information to suitability analysis. Boolean algebra is used for this task. Each class in every layer were assigned either as an output value of 0 or 1 for bitmap known as “Boolean Analysis”. It was established by the English mathematician and logician George Boole (1815 – 1864). The value assigned for each class of every parameter was based on their suitability for radioactive waste repository and must followed all criterions fixed in the early study. For the site selection study, the spatial maps produced are at the scale of 1: 600, 000.

Each class in every layer were assigned either as an output or weight value between 1 (lowest) to 10 (highest) according to “Binary

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Evidence Analysis”. The value assigned for each class of every parameter was based on their suitability for radioactive waste repository and must followed all criterions fixed in the early study.

The Weighted Sum tool provides the ability to weight and combine multiple inputs to create an integrated analysis. Basically, there

are four main techniques for the development of weights such as ranking methods, rating methods, pairwise comparison methods and trade-off analysis methods (Malczewski, 1999). However, for this study, ranking and rating methods were used for assessing the importance of weights and estimating of weights on the basis of predetermined scale.

Table 1: This table shows different aspects, parameters, sub-criteria, and score for selecting the potential site of the disposal facility.

No Aspects Parameters Criteria Score (%)

1 Geology

Lithology Igneous rock 8Soil properties Clay 5

Land use Forest, cleared land 15Geomorphology Higher Hills,

mountains10

Elevation 50 - 300 13Slope 5 - 15⁰ 6

2 Hydrogeology

Hydrogeology Low yield 5

3 Meteorology Rainfall 1000 -1500 mm 5

4 Accessibility & Proximity

Lineament 5 km from fault zone

8

Main Road access Within 5 km 5Main River 2.5 km from main

river5

Town 5 km 105 Land cover Area > 100 ha 5

3.4 Criteria for Site Selection

Identifying the criteria for site selection process for developing a radioactive waste facility is the most important part to be discussed. Siting criteria have been selected and determined based on feasibility study, published information and also from “expert opinion” before selecting the best criteria for selection study in order to develop the first National Radioactive Waste Repository facility in Malaysia.

a) Suitable Criteria

There are thirteen (13) criteria are being considered for site selection study of Negeri Sembilan consist of suitable criteria, exclusion criteria and preferred criteria. These criteria influence the site selection decision. Basically, eight (8) parameters related to the suitable criteria are as lithology, soil type, rainfall, hydrogeology, land use, geomorphology, elevation, and slope.

b) Exclusive and Inclusive Criteria

Exclusive criteria can be defined as criteria which lead to an exclusion of unsuitable areas and to the ascertainment of suitable areas within an investigation area. Inclusion criteria means the subject must be included in the study area. There are three (3) exclusive criteria and one (1) inclusive criteria have been defined for the case study as below:-

i. Distance to river: exclusion of all areas within a buffer of 2.5 km from main rivers.

ii. Distance to lineament or fault zone: exclusion of all areas within a buffer of 5 km from lineaments.

iii. Proximity to town: The suitable area should be located at least 5 km from town (buffer 5 km).

iv. Distance to road: considering all areas within a buffer of 5 km from main roads.

c) Preferred Criteria

A preferred criteria for the site selection processes was also be determined. The suitable area for the development of national radioactive waste repository facility shall be more than 100 hectares.

Then, the siting criteria have to be sorted into several categories or classification using ArcGIS after determining it with previous studies and expert opinions from many local and international agencies or companies.

3.5 GIS Modelling

GIS Modelling is used to analyze multi-layer of data spatially and quantitatively. The accuracy and reliability of the result using GIS application could be high depending on the available spatial

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data. All the parameters or layers in every aspect were overlaid to produce an intermediate maps. These maps were overlaid with exclusion map to produce the final suitable area. Then, the most suitable areas were determined.

4. Analysis and Results

For this study, Boolean Overlay were being presented in Model 1(a) and Model 1(b). Analysis using Model 1(a) was not take into account town buffer as one of important criteria for site selection studies. Model 1(b) indicates the area with concerned of buffer from town which should be at least 5 km. Instead of using Boolean Overlay

method, Model 2 was presented with concerned of weighted overlay method in the site selection studies. However, to get the final suitable areas, the Boolean Methods were also used to exclude buffer which related to a specific criteria that have been discussed earlier.

4.1 Boolean Overlay (Model 1a and Model 1b)

To well describe Boolean Overlay Method in the ArcGIS interface, there are some steps and processes which need to be followed before selecting the most potential area for the disposal facility. The result maps produced after geospatial data processing in ArcGIS are shown in Figure 1 as follows:-

Model 1(a) Model 1(b)

Figure 1: Comparison between Model 1(a) and Model 1(b). Model 1(a) before considering buffer 5 km from town and Model 1(b) after considering buffer 5 km from town

4.2 Weighted Overlay (Model 2)

Weighted sum overlay techniques have been applied in order to overlay the map layers. Weighted overlay is a technique for applying a common scale of values to diverse and dissimilar input data to create an integrated

analysis. To produce the final output raster or suitability map, weighted sum overlay of the cell values for each input raster are multiplied by the raster's weight. The maps resulting from this weighted sum overlay for site suitability area is shown in Figure 2.

Figure 2: More potential areas were identified (in white color) by using Model 2 analysis

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5. Discussion

Boolean Overlay and Weighted Sum Overlay techniques have been applied In order to overlay the map layers. Boolean Overlay method are also known as Binary Overlay which is a technique of grid analysis systems using AND function to combine the binary scores of different criteria. This technique also eliminating any cells that did not score “good” in all criteria. An OR function used to allow minimum risk approach where all cells that scored “good” at least one criterion are selected as suitable.

Generally, weighted overlay is a technique that has been used by many scientists or researcher with using a common scale of values to diverse and dissimilar input data for creating an integrated analysis. In this study, different map layers characterizing site suitability of the potential area were weighted using the weights derived from expert opinions and literature review papers. In the weighted sum overlay, the cell values of each input raster are multiplied by the raster's weight criteria weights.

From the results and analysis of Model 1(a), six (6) suitable areas were identified which is located in Mukim Labu, Negeri Sembilan area. After considering town buffer 5 km from town, only one (1) suitable site was identified which is also in Mukim Labu as presented in Model 1(b).

Then, the output results from the process were added in order to produce the output raster. These output raster need to be reclassified again into five (5) classes to show the importance of the layers. Then, the reclassified raster layers were converted into vector maps by using raster to polygon tools. However, weighted sum overlay used in the Model 2 also integrates with Boolean Overlay process to erase the exclusion areas and intersect the inclusion area in order to produce the final output raster or suitable area maps for developing the radioactive waste repository facility.

With using Boolean Overlay and Weighted Overlay methods for Model 2, the identified suitable site areas were scattered into several location in the east, west, and north of Negeri Sembilan.

6. Conclusions

The suitable sites are located at the Mukim Labu area in the district of Seremban from the west of the Negeri Sembilan state. By analyzing the potential area with coverage area of 100 hectares or 1 km2, there are three most

potential sites to be selected for developing radioactive waste disposal facility. This study provides an opportunity to explore a survey method to find potential site for a low level radioactive waste repository in the state of Negeri Sembilan, Malaysia using remote sensing and GIS technologies. Spatial data representing geological, meteorological hydrogeological, and surface process were utilized for assessing and characterizing the suitability of potential sites.

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References

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