NDLI: Evaluation of retention properties of a semi-synthetic fractured block from modelling at performance assessment time scales (Äspö Hard Rock Laboratory, Sweden)

Content Provider	Springer Nature Link
Author	Grenier, Christophe Bernard Michel, Gilles Benabderrahmane, Hakim
Copyright Year	2008
Abstract	Modelling of radionuclide transport in fractured media is a primary task for safety evaluation of a deep nuclear waste repository. A performance assessment (PA) model has been derived from site characterization data with the aim of improving confidence for quantifying transport of sorbing radionuclides at a safety time scale of 10$^{6}$ y. The study was conducted on a 200 × 200 × 200 m semi-synthetic fractured block, providing a realistic system derived from the Äspö Hard Rock Laboratory (Sweden) dataset. The block includes 5,632 fractures ranging from 0.5 to 100 m in length and a heterogeneous matrix structure (fracture coating, gouge, mylonite, altered and non-altered diorite). The PA model integrates steady-state flow conditions and transport of released radionuclides during the safety time scale. An original simulation method was developed involving Eulerian flow and transport within fracture planes with a mixed hybrid finite element scheme and a semi-analytical source term to account for heterogeneous matrix diffusion. Total mass flux of radionuclides (conservative to strongly sorbing) was computed. A method to simplify the system was demonstrated, leading to a major path of 12 fractures. This is mainly due to the low connectivity of the fracture network. Matrix diffusion and sorption proved to have major impact on block retention properties for PA conditions.La modélisation du transport de radionucléides dans les milieux fracturés est une tâche de première importance dans l’évaluation de la sûreté d’un site d’enfouissement de déchets nucléaires. Un modèle d’évaluation de performances a été développé ici à partir des données de caractérisation de site et en se fixant pour but d’augmenter la confiance dans la quantification du transport de radionucléides sorbants pour des échelles de temps de 10$^{6}$ ans, typiques de l’évaluation de performances. L’étude a été conduite sur un bloc fracturé semi synthétique de 200 mètres de côté, milieu jugé réaliste car ses caractéristiques ont été extraites des données du site du laboratoire souterrain Äspö Hard Rock Laboratory (Suède). Ce bloc contient 5632 fractures dont les extensions varient de 0.5 m à 100 m ainsi qu’une structure de zones matricielles complexe (calcite, remplissages, mylonite, diorite altérée et non altérée). Le modèle d’évaluation de performances prend en compte des conditions d’écoulement permanent pour un transport transitoire de radionucléides relâchés à l’échelle temporelle pertinente pour les analyses de sûreté. Une approche originale de simulation a été développée qui inclut, outre un écoulement Eulérien, un transport Eulérien dans les plans de fractures par schéma aux Eléments Finis Mixtes Hybrides auquel on a adjoint la prise en compte d’une diffusion matricielle hétérogène orthogonale par un terme source semi analytique. Le flux total de radionucléides a été simulé pour un cocktail de traceurs non sorbants à fortement sorbants. Une démarche de simplification des caractéristiques géométriques du système a été mise en œuvre et il a été démontré que le système pouvait être réduit à un chemin principal de 12 fractures. Une telle simplification est en premier lieu due à la faible connectivité du réseau. Il a été démontré que la diffusion matricielle et les phénomènes de sorption ont une influence dominante sur les propriétés de rétention du bloc fracturé étudié.El modelado del transporte de radionucleidos en medios fracturados es una tarea primordial para la evaluación de seguridad de un repositorio profundo de residuos nucleares. Un modelo de evaluación de rendimiento ha sido desarrollado a partir de caracterización de un sitio con el objetivo de mejorar la confianza para cuantificar el transporte de radionucleidos en una escala temporal segura de 10$^{6}$ años. El estudio fue realizado en un bloque fracturado semi sintético de 200 × 200 × 200 m, lo que proveyó un sistema realista derivado de datos del Laboratorio Äspö Hard Rock (Suecia). El bloque incluye 5632 fracturas que van desde 0.5 a 100 m de longitud y una estructura matricial heterogénea (fractura revestida, surco, milonita, diorita alterada y no alterada). El modelo de evaluación de rendimiento integra condiciones de flujo permanente con el transporte de radionucleides liberados durante la escala temporal de seguridad. Se desarrolló un método de simulación original que involucra el flujo Euleriano y el transporte en el interior de los planos fracturados con un esquema de elementos finitos hibridos mixtos y un término fuente semianalítico para determinar la difusión en la matriz heterogénea. Se computó el flujo de masa total de los radionucleidos (conservativos a fuertemente sorbing). Se demostró un método para simplificar el sistema que condujo a una trayectoria principal de 12 fracturas. Esto es debido principalmente a la baja conectividad de la red de fracturas. La difusión y sorción en la matriz ha demostrado tener efectos importantes sobre propiedades de retención del bloque para las condiciones de evaluación del rendimiento.模拟放射性核素在裂隙介质中的运移是深部核废物处置安全评价中的首要任务。从场地描述数据得到了一个性能评价 (PA) 模型, 以提高量化吸附性放射性核素运移在百万年安全尺度上的置信度。研究对象为一个200 × 200 × 200 m的半合成裂隙块体, 为据Äspö硬岩实验室数据建造的实体系统。块体含有5632条长度为0.5到100 m的裂隙, 并具有非均质基质结构 (裂隙表面结垢、断层泥、糜棱岩、蚀变和未蚀变闪长岩)。PA模型集成了安全时间尺度上的稳定流条件和释出核素的运移。通过杂交有限元格式和半解析源项得到了包括欧拉流和裂隙面内运移的原创模拟方法, 以描述非均质基质扩散。计算了放射性核素 (保守至强吸附)的总质量通量。展示了一种简化系统的方法, 生成12条主要裂隙路径。这主要是由于裂隙网络的连通性差。PA条件下, 基质扩散和吸附对块体阻滞性质具有主要影响。A modelação de transporte de radionuclídeos em meios fracturados é uma tarefa essencial para avaliar a segurança de um depósito de resíduos nucleares em profundidade. Um modelo de avaliação de desempenho (performance assessment: PA) foi desenvolvido a partir de dados da caracterização in situ com o objectivo de melhorar os níveis de confiança na quantificação do transporte de radionuclídeos susceptíveis de sorpção à escala do tempo de segurança de 10$^{6}$ anos. O estudo foi desenvolvido num bloco fracturado semi-sintético de dimensões 200 × 200 × 200 m obtendo-se um sistema bastante aproximado da realidade, conseguido a partir da base de dados do Laboratório Äspö Hard Rock (Suécia). O bloco possui 5632 fracturas cujo comprimento varia entre 0.5 e 100 m e uma matriz de estrutura heterogénea (fracturas com revestimento, preenchimento, milonito, diorito alterado e não alterado). O modelo PA integra condições de fluxo em regime permanente e um processo de transporte de radionuclídeos durante a escala de tempo de segurança. Foi desenvolvido um método de simulação original que considera o fluxo e o transporte euleriano através de planos de fractura utilizando um esquema de modelação em elementos finitos do tipo híbrido misto, com um termo de fonte semi-analítico para tomar em conta a difusão matricial heterogénea. Foi calculado o fluxo mássico total dos radionuclídeos (de conservativo a fortemente afectado por sorpção). Foi desenvolvido um método com o objectivo de simplificar o sistema que conduziu a uma rede de caminhos principais constituída por 12 fracturas. Este aspecto deve-se principalmente à baixa conectividade da rede de fracturas. A difusão e a sorpção na matriz rochosa mostraram ter um enorme impacto sobre as propriedades de retenção do bloco para as condições definidas pelo modelo PA.
Starting Page	1051
Ending Page	1066
Page Count	16
File Format	PDF
ISSN	14312174
Journal	Hydrogeology Journal
Volume Number	17
Issue Number	5
e-ISSN	14350157
Language	Portuguese
Publisher	Springer-Verlag
Publisher Date	2008-12-18
Publisher Institution	International Association of Hydrogeologists
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Fractured rocks Matrix diffusion Solute transport Äspö Task Force Sweden Waste Water Technology Water Pollution Control Water Management Aquatic Pollution Geology Hydrogeology
Content Type	Text
Resource Type	Article
Subject	Earth and Planetary Sciences Water Science and Technology

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