Scoping analyses of the coupled thermal-hydrological-mechanical behaviour of the rock mass around a nuclear fuel waste repository

Scoping calculations were performed in order to assess the influence of radiogenic heat on the performance of the rock mass around a nuclear fuel waste repository. The full coupling between the thermal, mechanical and hydrological processes involved was considered by using the finite element code, FRACON, developed through an extension of Biot's classical theory of soil consolidation. By considering the full T---H---M coupling, several important safety features, which would otherwise be omitted in uncoupled analyses, were detected in the present study. In particular, it was shown that the heat-induced pore pressure increase around the repository has the potential to significantly increase the rate of groundwater flow, and affect the structural integrity of the rock mass.     

亥废料处置概念库近场热-水-应力耦合模型及数值分析

特别考虑了缓冲层中温度梯度水分扩散、水蒸汽扩散对水连续性及能量守恒的影响，进一步完善了所建立的分析饱和-非饱和介质中热-水-应力耦合现象的控制方程，并针对试验资料，使用所开发的有限元程序对一个核废料处置概念库近场的热-水-应力耦合过程进行了数值模拟，考察了缓冲层及岩体中若干点的温度、饱和度、孔隙水压力及主应力的变化、分布情况，并将部分结果与国外类似软件的计算数据作了对比，结果显示，在定性和定量上二者的规律有某种一致性，从而得出了一定的认识。     

核废料处置概念库近场热-水-应力耦合模型及数值分析

特别考虑了缓冲层中温度梯度水分扩散、水蒸汽扩散对水连续性及能量守恒的影响,进一步完善了所建立的分析饱和-非饱和介质中热-水-应力耦合现象的控制方程,并针对试验资料,使用所开发的有限元程序对一个核废料处置概念库近场的热-水-应力耦合过程进行了数值模拟,考察了缓冲层及岩体中若干点的温度、饱和度、孔隙水压力及主应力的变化、分布情况,并将部分结果与国外类似软件的计算数据作了对比,结果显示,在定性和定量上二者的规律有某种一致性,从而得出了一定的认识。     

Ice ages and nuclear waste isolation

The greatest natural threats to the integrity of the geological barriers to nuclear wastes isolated in cavities mined at depths between 400 and 800 m are likely during rapid retreats of future ice sheets. The next major glacial retreat is expected at ca 70 ka, well within the lifetime of high grade nuclear waste, but it is not yet clear how long man's greenhouse effect may delay it.

This contribution discusses the potential problems posed to European waste isolation sites during erosion by ice and over-pressurizing of meltwater and gasses in a lithosphere flexed by major ice sheets. These depend on the target rocks and the location of the site with respect to the ice-streams and margins of future ice sheets of particular size.

No sites are planned under the centres of future ice sheets in Europe where end-glacial earthquakes can be expected to reactivate major faults, nor where ice can be expected to deepen and lengthen fjords along the Atlantic coast. Sites in the Alps may be vulnerable to radical changes in the patterns of glacial troughs. The stability and geohydrology of sites in coastal areas beyond future ice margins are threatened by river gorges when sea level falls ca 125 m or, in enclosed basins like the Mediterranean, ever lower. The greatest problems are likely in lowland regions exposed by the rapid retreat of thick ice fronts where large lakes on or under thick warm-based ice are dammed by more distal cold-based ice. Groundwater in subhorizontal fractures dilated by glacial unloading may reach over-pressures capable of hydraulically lifting megablocks of bedrock with fracture permeability and/or the ice damming them so that less permeable substrates are susceptible to incisions eroded to depths of ca 360 at locations controlled mainly by ice topography, kinematics and history.     

核废料处置概念库开挖及封闭后近场热-水-应力耦合数值分析

考虑了缓冲层中温度梯度水分扩散、水蒸汽扩散对水连续性及能量守恒的影响,进一步完善了饱和-非饱和介质中热-水-应力耦合现象的控制方程。应用缓冲材料的实验资料,对核废料处置概念库开挖及封闭后近场的热-水-应力耦合过程进行了数值模拟,以考察围岩中的位移、塑性区、主应力、孔隙水压力和温度的分布及变化。认为开挖是引起洞室围岩中的变形及应力重新分布的主要原因,但坑道封闭后的热-水-应力耦合过程对变形及应力状态也产生了明显的影响。     

Comparison of vertical and horizontal deposition hole concept for disposal of radioactive waste based on rock mechanical in situ stress-strength analyses

In Finland, a spent fuel repository is being planned in hard, crystalline rock to the depth of 300–800 m. The repository will consist of parallel deposition tunnels which are interconnected by a central tunnel. The spent fuel canisters will be placed in holes drilled according to the tunnel floor—vertical deposition hole concept or in the tunnel wall-horizontal deposition hole concept. Based on the numerical stress-strength analyses, both concepts are found to be feasible. However, when the maximum horizontal stress is perpendicular to the axis of the deposition hole, the rock in the vicinity of the horizontal deposition hole seems to have more stable behavior than in the case of the vertical deposition hole.     

Application of performance data from evaporite mines to salt nuclear waste repository design

Summary Data on the performance of operating mines in rock salt and potash from United States and British sources is reviewed. A design validation scheme for nuclear waste repositories is proposed, based on back analysis of the response of operating evaporite mines.     

A comparative simulation study of coupled THM processes and their effect on fractured rock permeability around nuclear waste repositories

This paper presents an international, multiple-code, simulation study of coupled thermal, hydrological, and mechanical (THM) processes and their effect on permeability and fluid flow in fractured rock around heated underground nuclear waste emplacement drifts. Simulations were conducted considering two types of repository settings (1) open emplacement drifts in relatively shallow unsaturated volcanic rock, and (2) backfilled emplacement drifts in deeper saturated crystalline rock. The results showed that for the two assumed repository settings, the dominant mechanism of changes in rock permeability was thermal–mechanically induced closure (reduced aperture) of vertical fractures, caused by thermal stress resulting from repository-wide heating of the rock mass. The magnitude of thermal–mechanically induced changes in permeability was more substantial in the case of an emplacement drift located in a relatively shallow, low-stress environment where the rock is more compliant, allowing more substantial fracture closure during thermal stressing. However, in both of the assumed repository settings in this study, the thermal–mechanically induced changes in permeability caused relatively small changes in the flow field, with most changes occurring in the vicinity of the emplacement drifts.     

Radionuclides transport at the site of a low- and intermediate-level waste repository,Saligny, Romania

The site of the future Saligny low- and intermediate-level waste repository presents a rather deep unsaturated zone consisting of a pile of loess and clay, underlain by a calcareous aquifer. Van Genuchten parameters were first estimated in laboratory on samples collected from all the horizons, at different depths. In a second kind of test, moisture parameters were estimated from the natural water content profiles, observed in some wells, by inversion of the unsaturated flow equation. Based on the solution of the inverse problem as well as of the sensitivity analyses a simple physical model of the vadose zone was determined, consisting of a layered sequence that was subjected to a constant infiltration flux. Radionuclide migration was simulated in a vertical cross section made along the most probable path from the repository towards the surface water discharge zone. For radionuclide release, a source term was evaluated by ensuring a conservative estimate of cell inventory during the cell-filling operation. According to the simulation results, for the medium half-life nuclides, the unsaturated zone is a perfect barrier, whereas the long half-life isotopes break through in the aquifer at significant concentrations.

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Resumen El sitio del futuro repositorio para desechos de nivel bajo e intermedio, denominado Saligny, presenta una zona no saturada bastante profunda, consistente en un depósito de loess y arcilla, subyacido por un acuífero calcáreo. Los parámetros de Van Genuchten se estimaron por primera vez en laboratorio, a partir de muestras recolectadas de todos los horizontes, a diferentes profundidades. En un segundo tipo de prueba se estimaron los parámetros de humedad a través de la inversión de la ecuación de flujo no saturado, a partir de los perfiles naturales que contienen agua, observados en algunos pozos. Con base en la solución del problema inverso, así como también en análisis de sensibilidad, se determinó un modelo físico simple de la zona vadosa, el cual consiste de una secuencia estratificada sometida a un flujo de infiltración constante. La migración del radioisótopo fue simulada en una sección vertical, hecha a lo largo del camino más probable entre el repositorio y la zona de descarga en el agua superficial. Para la liberación del radioisótopo se evaluó la fuente, asegurando un estimativo conservador del inventario de celdas durante la operación de llenado de celdas. De acuerdo con los resultados de la simulación, para los isótopos con vida media intermedia, la zona no saturada es una barrera perfecta; mientras que los isótopos con vida media larga irrumpen en el acuífero con concentraciones importantes.

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Résumé Le futur stockage de déchets radioactifs de faible et moyenne activité de Saligny est caractérisé par une zone non-saturée assez profonde qui consiste dans des dépôts de loess et dargile qui couvrent un aquifère calcaire. Dans une première étape, les paramètres de van Genuchten ont été déterminés en laboratoires sur des échantillons prélevés de toutes les couches, à des profondeurs différentes. Dans une seconde étape les mêmes paramètres ont été estimés, comme un solution du problème inverse à partir de profils de la saturation en eau, mesurés dans des forages. Les résultats du problème inverse, ainsi que l› analyse de sensibilité ont mené à un modèle multi- couches de la zone non-saturé, rechargé par un flux constant. On a simulé le transport des radionucléides dans une coupe verticale, construite au long du trajet le plus probable entre le stockage et les eaux de surface. Le flux de radionucléides relâchés a été estimé en considérant une valeur consevative pour la masse totale stocké. D› après les résultats de la simulation la zone non saturée forme une barrière presque parfaite pour les radionucléides de période moyenne, denvirons de 30 ans, tendis quelle est traversée avec des concentrations assez importantes par des isotopes à grande période.

     

高放废物处置库预选区新构造运动特征

新构造活动强烈程度是高放废物处置库场址评价的一个重要指标。本文阐述新构造研究的指导思想、方法及其在高放废物处置库选址中的应用。通过东天山地区南、北地段对比研究,选出了在新近纪时期构造环境相对稳定或新构造活动强度相对微弱的东天山南部地区,作为高放废物处置库基地。研究结果表明它对场址评价是有意义的。     

Characterising and modelling the excavation damaged zone in crystalline rock in the context of radioactive waste disposal

This paper describes current knowledge about the nature of and potential for thermo–hydro–mechanical–chemical modelling of the excavation damaged zone (EDZ) around the excavations for an underground radioactive waste repository. In the first part of the paper, the disturbances associated with excavation are explained, together with reviews of Workshops that have been held on the subject. In the second part of the paper, the results of a DECOVALEX [DEmonstration of COupled models and their VALidation against EXperiment: research funded by an international consortium of radioactive waste regulators and implementers (http://www.decovalex.com)] research programme on modelling the EDZ are presented. Four research teams used four different models to simulate the complete stress–strain curve for Avro granite from the Swedish Äspö Hard Rock Laboratory. Subsequent research extended the work to computer simulation of the evolution of the repository using a ‘wall-block model’ and a ‘near-field model’. This included assessing the evolution of stress, failure and permeability and time-dependent effects during repository evolution. As discussed, all the computer models are well suited to sensitivity studies for evaluating the influence of their respective supporting parameters on the complete stress–strain curve for rock and for modelling the EDZ.     

考虑细观等效热学参数的高放废物处置库围岩应力−渗流−温度耦合模拟方法

高放废物处置库中乏燃料持续释放的热量对围岩的应力场和渗流场及其长期稳定性具有重要影响。围岩的热学参数依赖于岩石矿物组成、孔隙率和孔隙流体等因素,准确取值是进行高放废物地质处置库多场耦合分析的前提。通过细观力学分析,建立了围岩等效热学参数（热容、热传导系数、热膨胀系数）取值方法,并基于Biot孔隙介质理论,建立应力?温度?渗流三场耦合模型,进而提出了高放废物处置库围岩应力?渗流?温度耦合数值模拟方法。最后通过COMSOL Multiphysics多场耦合软件,利用瑞士Mont Terri高放废物地下试验室围岩温度?渗流?应力多场耦合现场试验数据对数值模拟方法进行验证,并探讨了温度?渗流?应力耦合过程的演化规律。研究表明,模拟结果和试验值吻合良好。研究结果可为我国高放废物处置库的安全评估和选址提供科学依据。     

花岗岩中高放废物地质处置库系统分析方法研究

首先以甘肃北山预选区花岗岩场址为例,提出该场址中高放废物地质处置库概念设计和结构设计,然后以系统分析方法论为基础,描述处置库的系统功能、结构、环境及其演化过程,并以模拟软件GoldSim为工具,建立该处置库演化过程的计算机模型,最后以该计算机模型为模拟实验平台,模拟处置库中辐射毒性时空分布,分析模型中的参数灵敏度,优化设计参数,并预测和评价处置库性能。其研究成果可为合理配置资源和有效协调各研究项目之间关系提供技术支持。     

核废物地质处置模型试验近场热-水-应力耦合数值模拟

笔者描述了所建立的饱和-非饱和介质中热-水-应力耦合现象的控制方程。针对国际合作项目DECOVALEX II 中Task-2的核废物地质处置轴对称模型试验及计算参数,使用所研制的有限元程序进行了热-水-应力耦合过程模拟。对缓冲层及岩体中若干部位的温度、含水量及接触应力的分布、变化进行了分析, 并将其与量测值和使用THAMES程序的计算结果作了比较,看到了三者的异、同之处,并指出了可能的影响原因。通过与量测值和THAMES程序的计算结果的对比,显示了笔者所研制的有限元程序在热-水-应力耦合数值分析中是可靠和实用的。     

Treatment of uncertainties in the performance assessment of geologic high-level radioactive waste repositories

Federal regulations governing the disposal of high-level radioactive waste in deep, geologic repositories require an assessment of performance over thousands of years. Because of the long regulatory period involved and the complex nature of the events and processes of interest, prediction of the performance of the disposal system will inevitably include uncertainties. These uncertainties come from a variety of sources, and some are quantifiable and others are not. This paper discusses these uncertainties and outlines approaches for their treatment. Recommendations for the potential resolution of current limitations in the treatment of uncertainties in performance assessment are made. Some general issues, as well as a suggested approach for incorporating expert judgment into quantitative performance assessment analysis, are discussed also.This paper was presented (by title) at Emerging Concepts, MGUS-87 Conference, Redwood City, California, 13–15 April 1987.     

Geochemical assessement of actinide isolation in a German salt repository environment

A significant criterion in evaluating disposal strategies for high-level nuclear waste is the assessment of the isolation capacity for the most radiotoxic radionuclides, the actinides. Important processes pertinent to potential mobilization from the waste forms, retention in secondary phases and migration of actinides in the geochemical environment of the near field of disposal locations are summarized. Criteria are formulated for assessing engineered barrier performance as a geochemical barrier for actinide long-term retention.     

Two-phase, partially miscible flow and transport modeling in porous media; application to gas migration in a nuclear waste repository

We derive a compositional compressible two-phase, liquid and gas, flow model for numerical simulations of hydrogen migration in deep geological repository for radioactive waste. This model includes capillary effects and the gas high diffusivity. Moreover, it is written in variables (total hydrogen mass density and liquid pressure) chosen in order to be consistent with gas appearance or disappearance. We discuss the well possedness of this model and give some computational evidences of its adequacy to simulate gas generation in a water-saturated repository.     

高放废物处置北山预选区地表岩体结构与岩体质量相关性及其应用研究

岩体工程质量是影响高放废物地质处置（HLW）工程长期稳定性和安全性的关键因素,也是处置库场址比选的重要依据。在地表岩体节理调查统计的基础上,采用RMR(relative metabolic rate)分级方案,探讨北山高放废物处置预选区内以花岗岩为主体围岩的岩体质量与岩体结构的对应特征,建立结构面间距D与RMR岩体质量总评分值之间的定量关系,对北山预选区芨芨槽地表岩体质量分布进行研究。研究结果表明,RMR与D值的点群分布具有扇形发散的正相关特征,随D值的增大,RMR亦呈增长趋势,但低级序岩体结构与岩体质量比高级序岩体表现出更好的对应关系。研究认为,选用RMR与D的点群中心线对应的线性方程评价花岗岩候选区的岩体质量可达到快速评价岩体质量、查明各级岩体空间分布特征的目的,同时也便于对不同候选场区进行大范围岩体质量对比。分析结果显示,北山芨芨槽预选地段BS16钻孔周边3 km2范围内主要以Ⅰ、Ⅱ级岩体为主,岩体质量总体较好且分布相对较为均匀。     

核废料地质处置概念库锚喷支护坑道热-水-应力耦合效应的二维离散元分析

假定一个核废料地质处置库位于具有一定水头的饱和节理岩体中,开挖完闭施作系统锚杆和喷混凝土支护。对坑道建造和一个50年期的热-水应力（T-H-M）耦合运营过程,使用UDEC程序进行数值模拟,分析无、有支护时近场围岩中的应力、变形、塑性区、温度、渗流的变化状态,以及不同场（温度、渗流、应力）耦合条件下的锚杆和喷混凝土中的承载情况。结果显示,喷混凝土和系统锚杆支护不仅具有常规的支护功能,并且可阻滞地下水从坑道表面的自由渗出,使得围岩中塑性区减小,裂隙水压力和温度升高;相比于应力单场作用的情况,在热-水-力耦合的条件下洞室围岩的稳定性下降,支护结构的受力状况变差。