京都大学 / 新制・課程博士 / 博士(工学) / 甲第23498号 / 工博第4910号 / 新制||工||1767(附属図書館) / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 米田 稔, 教授 高岡 昌輝, 教授 平井 康宏 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Thesis (M.Sc.)--Memorial University of Newfoundland. / Typescript. Restricted until May 1997. Bibliography: leaves 100-104. Also available online.

The UK has a large and growing inventory of higher activity radioactive waste awaiting safe long term disposal. The international consensus is to dispose of this radioactive and toxic waste within a deep geological repository, situated 200-1,000 metres beneath the ground surface. The deep geological disposal facility is designed to be a series of engineered and natural barriers. Groundwater forms an integral component of the natural barrier because it 1) controls the flux of reactive components towards the engineered repository, and 2) forms one of the primary transport mechanism through which released radionuclides can be transported away from the repository. The timescale of protection provided by the natural barrier exceeds those provided by the engineered barriers. Knowledge of the regional hydrogeology is a vital step towards predicting the long term performance of any potential repository site. Topically, a UK government decision in 2017 to re-open a nation-wide repository location search has now created a renewed mandate for site exploration. This research aims to determine the regional groundwater characteristics of three UK settings, selected to be hydrogeologically distinct, in order to determine which, if any, offers natural long term hydrogeological containment potential. The settings selected for analysis include Sellafield in West Cumbria, the Tynwald Basin within the East Irish Sea Basin, and Thetford within East Anglia. Site selection is based on diverse groundwater characteristics, and on previous research suggesting potential hydrogeological suitability at these locations. This research is novel in that it provides, for the first time, a direct comparison between the characteristics and qualities of different regional groundwater settings to contain and isolate radioactive waste, based on UK site specific data. Large and detailed numerical models for the three sites, covering areas of 30 km length by 2- 4 km depth have been developed using the open source finite element code 'OpenGeoSys'. The models couple the physical processes of liquid flow and heat transport, in order to replicate regional scale groundwater flow patterns. Models are calibrated to measured rock properties, and predict groundwater behaviour 10,000 years into the future. Uncertain parameter ranges of lithological and fault permeabilities, and peak repository temperatures are tested to determine the possible range of groundwater outcomes. Geochemical retention is assessed separately and validated using the finite difference modelling software 'GoldSim'. Worst case groundwater characteristics for containment and isolation at each site are compared to an 'ideal' benchmark far-field hydrogeological outflow scenario, and scored accordingly using a newly proposed method of assessment. Results show that the Tynwald Basin offers the best potential of the three sites for natural radionuclide containment, performing between 3.5 and 4 times better than Sellafield, and between 1.7 and 4 times better than Thetford. The Tynwald Basin is characterised by 1) long and deep groundwater pathways, and 2) slow local and regional groundwater movement. Furthermore, the Tynwald Basin is located at a feasible tunnelling distance from the coast, adjacent to the UK's current nuclear stockpile at Sellafield, and thus could provide a simple solution to the current waste legacy problem. Results from the Sellafield model indicate that this location cannot be considered to exhibit beneficial characteristics due to short and predictable groundwater pathways which ascend, from the repository, towards surface aquifers. Finally, Thetford within East Anglia has never been drilled to depth so that sub-surface rock properties of basement, located beneath layered sediments, are based on evidence inferred from around the UK. Uncertainties in rock properties has produced a wide range of groundwater characteristic possibilities, with results indicting prospective performance to range from 0 to 2.4 times better than Sellafield. As such, the hydrogeological suitability to host a potential deep geological repository is promising when modelled with most-likely permeability values, but cannot be accurately determined at present. Consideration of decaying heat from the heat emitting waste packages at the three sites reveal that the natural groundwater flow patterns can be distorted up to as much as 7 km away from the theoretical repository, depending on setting. This thus changes the use of the term 'near-field' for safety assessments, as implying an area within the immediate vicinity of the excavated repository site. The overarching findings from this research are that: 1) some locations have greater long term radionuclide containment and isolation prospectivity than others, due to variable quality far-field geological and hydrogeological characteristics; 2) the effect of radiogenic heat emission on the natural groundwater flow pattern is dependent on the site specific geological and hydrogeological characteristics, and therefore so is the area defined as the 'near-field'; and 3) a simple method of site comparison is possible for regional groundwater system under steadystate conditions. Recommendations are for scoping models of regional groundwater settings to be used as a comparative tool, such as undertaken as part of this research, to differentiate between potential sites at an early stage of the current UK site selection programme.

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No. of bitstreams: 2 Dissertação - Roberta Vieira Nunes Pinheiro - 2017.pdf: 3792860 bytes, checksum: 7c88e98986a260c816ea80a305ce962a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-02-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Vulnerability models are important tools in the study of water contamination by different soil usage activities. The goal of this research is to evaluate the risk of contamination by the presence of an urban solid waste disposal site (UWDS) within the surface water catchment basins (SWCB) used in the State of Goiás public water supply. An identification and characterization of the SWCBs and UWDSs has been carried out in a geographical identification system using the QGis 2.12.0 – Lyon software. Afterwards the overlapping of this information allowed the identification of all SWCBs which had an UWDS within its limits. A Susceptibility Index (SI) was applied to these SWCBs. The SI was formed by intrinsic characteristics such as the depth of a non-saturated zone, net recharge, aquifer material and topography. Also contributing to the SI was an extrinsic characteristic, soil usage. The comparison and identification of the dominant classes of the SI was done through the calculation of the average vulnerability of each SWCB. The SWCBs, which had the highest risk of water contamination were selected and had the UWDSs in its areas analyzed by six technical parameters: type of UWDS, estimate of waste generation, surface area, slope, SI of the UWDS and its distance to the nearest body of water. Each parameter was classified according to its risk to water contamination and given a scale from 1 to 7. The given values were correlated evaluating the interdependence of the parameters. The use of this method led to the identification of 204 catchment points and its SWCBs and 228 UWDS, out of which 93% were irregular dumping sites. The SI for each of the 43 SWCBs identified in the State in which there was the presence of 69 UWDSs, was then calculated. The average vulnerability for each SWCB allowed the selection of the 9 most vulnerable ones. These were distributed in the high-to-moderate and moderate-to-low classes (SI > 50), which had 18 UWDSs within its limits. A Spearman analysis was done using the coefficients attributed to each parameter of the UWDSs. The analysis permitted the identification of only 2 parameter with significant correlation (surface area and estimate of waste generation). This confirmed the interdependence of the selected characteristics. It also allowed for a risk calculation through the addition of the parameters, which ranged from 15 to 27. These were distributed into three classes (low, medium and high). The high risk UWDS identified were in the cities of: Bom Jesus de Goiás, Itumbiara, Jataí e Rio Verde. The surface area, waste generation and slope were the parameter which most influenced this classification. In conclusion, the vulnerability evaluation proved effective, and of great relevance in the identification of the SWCBs most susceptible to water contamination. It can also be applied to other study areas. In Goiás, the analysis allowed the existing risk calculation for each of the 18 UWDSs out of which 4 were classified as high risk. These were considered priority adequate and remediation sites. / Modelos de vulnerabilidade são importantes ferramentas no estudo de contaminação da qualidade das águas por diferentes atividades de uso do solo. O objetivo desta pesquisa foi avaliar o risco de contaminação pela presença de disposição final de resíduos sólidos urbanos (DRS) em bacias de captação superficial de água (BCS) para abastecimento público no estado de Goiás. Foi realizada a identificação e caracterização das BCS e das DRS em um sistema de informações geográficas utilizando o software QGis 2.12.0 - Lyon. Posteriormente essas informações foram sobrepostas permitindo identificar as BCS com DRS em suas delimitações. Para esse grupo foi aplicado o Índice de Susceptibilidade (IS), composto por características intrínsecas das BCS (profundidade da zona não saturada, recarga, material do aquífero e topografia) e por uma extrínseca, o uso e ocupação do solo. A realização do comparativo e a identificação das classes predominantes do IS foi realizado pelo cálculo da vulnerabilidade média de cada BCS. Desta forma, foram selecionadas as BCS com maior risco de contaminação de suas águas e as DRS presentes em suas áreas, que foram analisadas por seis parâmetros técnicos: tipo de DRS, estimativa de geração de resíduos, área superficial, declividade, IS da DRS e distância da DRS até o corpo d’água. Cada parâmetro foi classificado, de acordo com o risco de contaminação das águas, e valorado em uma escala de um a sete. Posteriormente, os valores atribuídos foram correlacionados avaliando a interdependência dos parâmetros. A aplicação desse método permitiu a identificação de 204 pontos de captação com suas respectivas BCS e de 228 DRS, sendo 93% classificadas como lixões. Foi calculado o IS para as 43 BCS identificadas no Estado com presença de DRS (69) em suas áreas. A vulnerabilidade média calculada para cada BCS permitiu a seleção das nove BCS mais vulneráveis, estando distribuídas nas classes moderada a alta e moderada a baixa (IS>50), e possuindo 18 DRS em suas delimitações. Foi realizada uma análise de componentes principais de Spearman com os coeficientes atribuídos para cada parâmetro das DRS o que permitiu a identificação de apenas dois parâmetros com correlação significativa (área superficial e estimativa de geração de resíduos), confirmando a interdependência das características selecionadas. Desta forma foi possível o cálculo do risco, pelo somatório dos parâmetros, que variou de 15 a 27 e foi discretizado em três classes (baixo, médio e alto). As DRS de risco alto foram as dos municípios de Bom Jesus de Goiás, Itumbiara, Jataí e Rio Verde sendo que a área superficial, geração de resíduos e declividade foram os parâmetros que mais influenciaram nessa classificação. Conclui-se que a avaliação da vulnerabilidade mostrou-se eficaz e de grande relevância para a identificação das BCS mais susceptíveis à contaminação de suas águas podendo ser aplicado em outras áreas de estudo. Em Goiás, a análise permitiu o cálculo do risco existente em cada uma das 18 DRS, onde quatro DRS foram classificadas como de risco alto, sendo consideradas prioritárias para adequação ou remediação.