Rock Mechanical Characterization of an Argillaceous Host Rock of a Potential Radioactive Waste Repository

Summary The physical properties of foliated marls and shales from the Swiss Central Alps were investigated in the laboratory as part of the site characterization of a potential low and intermediate level radioactive waste repository. The rocks were first characterized by density, porosity and water content, then P-wave velocity measurements and uniaxial compression tests were conducted on samples oriented parallel, perpendicular and ∼45° inclined to the foliation. Correlations between P-wave velocities, Young's moduli, and uniaxial strengths and directional dependence of compressibility and permeability (determined at elevated hydrostatic pressures) revealed that two distinct families of microcracks cause the significant anisotropy. The pressure and time dependence of strength was then measured in triaxial compression, creep, and relaxation tests. In triaxial compression at room temperature, confining pressures up to 90 MPa and strain-rates as low as 10⁻⁸ s⁻¹ failure occured after small inelastic strains. Failure strength exhibits a strong pressure and a weak strain-rate dependence. The low friction coefficient of clay minerals appears to dominate the bulk frictional properties. Micromechanical modeling of triaxial compression, creep, and relaxation tests suggests that inelastic deformation is accommodated by subcritical crack growth.     

Analysis of the Excavation Deviations Impact on Geological Radioactive Waste Repository Performance

Numerical simulations of the transport of radionuclide from high-level radioactive waste stored in geological repositories often do not take into account construction defects in the repository. The potential impact of drilling and excavation deviation from the engineer planned design is a priori considered negligible. We conducted computations on repository geometries that contain deviations from horizontal of a few degrees. The analysis of the results shows that the impact of deviation defects varies from 9 to 16%. A perfect control of the galleries and waste repository cell orientations is then of concern for radioactive waste repository construction, failing which numerical simulations must be conducted on the worst geometric configuration or margin errors added. On the other hand, if the orientation control is precise enough, a modification of the repository design including controlled deviations from the horizontal may be of interest.     

Selection and Basic Properties of the Buffer Material for High-Level Radioactive Waste Repository in China

Radioactive wastes arising from a wide range of human activities are in many different physical and chemical forms, contaminated with varying radioactivity. Their common features are the potential hazard associated with their radioactivity and the need to manage them in such a way as to protect the human environment. The geological disposal is regarded as the most reasonable and effective way to safely disposing high-level radioactive wastes in the world. The conceptual model of geological disposal in China is based on a multi-barrier system that combines an isolating geological environment with an engineered barrier system. The buffer is one of the main engineered barriers for HLW repository. It is expected to maintain its low water permeability, self-sealing property, radio nuclides adsorption and retardation properties, thermal conductivity, chemical buffering property, canister supporting property, and stress buffering property over a long period of time. Bentonite is selected as the main content of buffer material that can satisfy the above requirements. The Gaomiaozi deposit is selected as the candidate supplier for China＇s buffer material of high level radioactive waste repository. This paper presents the geological features of the GMZ deposit and basic properties of the GMZ Na-bentonite. It is a super-large deposit with a high content of montmorillonite （about 75 %）, and GMZ-1, which is Na-bentonite produced from GMZ deposit is selected as the reference material for China＇s buffer material study.     

高放废物处置库甘肃北山预选区地下水的形成

在高放废物处置库场地选择和性能评价中,水文地质特征是最重要的因素之一,地下水的形成则是水文地质研究中的首要问题。在水文地质、地下水化学、同位素、CFC、地下水动态等资料综合分析的基础上,探讨了高放废物处置库甘肃北山预选区地下水的形成问题。研究结果表明,北山地区地下水以赋存于变质岩、岩浆岩、碎屑岩、碳酸岩节理、裂隙中的基岩裂隙潜水为主,地下水化学成分具有明显的水平分带性特征,地下水动态类型主要为入渗—蒸发—径流型,结合地下水同位素和CFC 特征,认为区内地下水主要由当地大气降水入渗补给形成。浅部地下水主要由现代区内降水补给形成,而深部地下水则可能由地质历史时期降水补给形成。     

Consequences of the Thermal Transient on the Evolution of the Damaged Zone Around a Repository for Heat-Emitting High-Level Radioactive Waste in a Clay Formation: a Performance Assessment Perspective

A proper evaluation of the perturbations of the host rock induced by the excavation and the emplacement of exothermic wastes is essential for the assessment of the long-term safety of high-level radioactive waste disposals in clay formations. The impact of the thermal transient on the evolution of the damaged zone (DZ) has been explored in the European Commission project TIMODAZ (thermal impact on the damaged zone around a radioactive waste disposal in clay host rocks, 2006–2010). This paper integrates the scientific results of the TIMODAZ project from a performance assessment (PA) point of view, showing how these results support and justify key PA assumptions and the values of PA model parameters. This paper also contextualises the significance of the thermal impact on the DZ from a safety case perspective, highlighting how the project outcomes result into an improved understanding of the thermo–hydro–mechanical behaviour of the clay host rocks. The results obtained in the TIMODAZ project strengthen the assessment basis of the safety evaluation of the current repository designs. There was no evidence throughout the TIMODAZ experimental observations of a temperature-induced additional opening of fractures nor of a significant permeability increase of the DZ. Instead, thermally induced plasticity, swelling and creep seem to be beneficial to the sealing of fractures and to the recovery of a very low permeability in the DZ, close to that of an undisturbed clay host rock. Results from the TIMODAZ project indicate that the favourable properties of the clay host rock, which guarantee the effectiveness of the safety functions of the repository system, are expected to be maintained after the heating–cooling cycle. Hence, the basic assumptions usually made in PA calculations so far are expected to remain valid, and the performance of the system should not be affected in a negative way by the thermal evolution of the DZ around a radioactive waste repository in clay host rock.     

CFC在中国高放废物处置库预选区地下水研究中的应用

本文介绍了地下水测年的CFC方法及其原理,并将这种方法实际应用于我国高放废物处置库预选区--甘肃北山地区的水文地质研究,结果表明,研究区内沟谷洼地浅部地下水的CFC年龄在15~26 a,基岩裂隙浅部地下水多为不含CFC的老水与含CFC的新水的混合水.在描述了确定混合比方法的基础上,根据样品CFC含量计算了研究区地下水的混合比.与氚相比,CFC是目前年轻地下水测年更好的工具,具有更多的优越性.     

高放废物处置库芨芨槽预选场址深部地下水同位素研究

深地质处置是目前国际上普遍接受的高放废物安全处置方案.对于这种方案而言,安全处置高放废物的前提是选择适宜的场址,而场址的适宜性在很大程度上取决于其水文地质条件.高放废物处置库场址需要低渗透岩体作为处置库围岩,对于低渗透岩体而言,经典和传统的水文地质研究方法受到了很大的限制,而同位素技术与其他水文地质方法结合时,却能发挥出良好的作用.本文以目前我国高放废物处置库预选场址之一的芨芨槽场址为例,重点讨论了同位素方法在花岗岩体场址水文地质研究中的应用.根据钻孔不同深度的地下水环境同位素(δD、δ18O、3H和14C)组成特征,结合场址水文地质条件,识别了区内地下水的来源,揭示了控制地下水运移交替速率的主要因素.结果表明,该区深部地下水14C年龄高达8000 a左右,说明其交替、运移十分缓慢,但同时也含有少量的氚,说明地下水以侧向补给的“老水”为主,接受当地大气降水入渗补给的“新水”所占比例很小.此外,通过地下水14C年龄与取样段岩芯采取率的对比,认识到对于区内的花岗岩体而言,决定地下水交替、运移速率的主要因素是裂隙的发育程度,而不是深度.     

高放废物处置库北山预选区地下水同位素组成特征及其意义

在高放废物处置库选址中,场地水文地质条件的认识极为重要,因为任何从处置库释放出来的放射性物质都将通过地下水搬运向人类生存环境或生物圈迁移.甘肃北山地区是我国高放废物处置库的重要预选区之一,位于我国西北甘肃省西北部.为了认识预选区的水文地质条件,从水文地质角度评价其作为高放废物处置库场地的适宜性,在过去的10 a,在该区开展了同位素水文地质调查工作.野外调查和氢、氧稳定同位素分析结果表明,研究区地下水主要源自大气降水补给.浅部地下水主要由现代区内降水补给形成,而深部地下水则可能由地质历史时期降水补给形成;浅部地下水系统具有相对开放性特征,水循环交替能力较强,而深部地下水系统具有相对封闭性特征,水循环交替能力较弱.     

Thermo-mechanical Stability Analysis for a Multi-level Radioactive Waste Disposal Concept

To dispose of the spent fuels generated from the Korean nuclear power plants in an underground repository, a large area of about 4 km² is required. This could be a constraint for selecting an adequate repository site and it is required to investigate the possibility of a multi-level repository design. In this study different parameters related to the multi-level repository design such as the level distance, waste type disposed of at each level, and the time interval between the operations at the levels, were investigated using the three-dimensional code, FLAC3D. For obtaining more reliable results, rock properties measured from deep boreholes were used. From the analysis, it was possible to conclude that a multi-level repository concept could be an attractive alternative to reduce the underground area as well as to dispose of the spent fuels from Pressurized Water Reactors (PWR) and Canadian Deuterium Uranium (CANDU) reactors at different levels with different time schedules.     

放射性废物处置研究进展

放射性废物的处置是制约核能可持续发展的关键因素,目前已成为国际社会关注的热点问题之一.针对处置场地核素运移污染的风险问题,对放射性废物的处置及其选址、核素运移试验和核素运移模型进行了回顾和论述.指出采用多重屏障系统进行放射性废物的处置,其安全性是可以得到保障的;处置场的选址应遵循就近原则,并应从环境水文地质的角度来构建...     

高放废物地质处置研究中的矿物学问题

在高放废物地质处置研究中的一些矿物学问题应引起矿物学家的注意 。高放废物地 质处置库的缓冲/回填材料是选择以钠质蒙脱石为主要成分的钠基膨润土,还是以钙质蒙脱 石为主的钙基膨润土?怎样选择对99Tc、129I有较好吸附能力的硒汞矿、脆 硫锑铅矿和辉锑矿的替代物来作缓冲/回填材料中的添加剂,以能阻滞99Tc和129 I的迁移?沸石对某些放射性核素的吸附特征也需进一步研究。     

粤北下庄铀矿田中铀酰矿物的成分特征——对核废料处置库中UO2氧化行为的启示

下庄铀矿为一花岗岩型铀矿，矿田地处湿热气候条件下，沥青铀矿普遍产于破碎带中，这种特定的产出环境致使该区沥青铀矿经受了强烈的风化，形成种类繁多、数量丰富的铀酰矿物；而我国高放废物地质处置库拟建在花岗岩体中。因此，下庄铀矿田是开展核废料氧化的天然类比研究的理想地区，并对我国的高放废物地质处置库的安全性评价有重要的指导作用。下庄铀矿田的铀酰矿物组合为铀酰氢氧化物、铀酰硅酸盐和铀酰磷酸盐，包括柱铀矿、黄钙铀矿、calciouranoite、红铀矿、富硅铀酰相、硅钙铀矿、钙铀云母和盈江铀矿等。根据它们的空间分布特征可划分成两个风化系列，即硅酸盐风化系列和磷酸盐风化系列，其共生次序分别为：沥青铀矿→铀酰氢氧化物（氧化物）→富硅铀酰相→硅钙铀矿和沥青铀矿→铀酰氢氧化物（氧化物）→钙铀云母→盈江铀矿。在该矿田中，铀酰氢氧化物是亚稳定相矿物，常常被铀酰硅酸盐或磷酸盐取代，因此，铀酰氢氧化物仅出现在少数样品中，而铀酰硅酸盐和铀酰磷酸盐矿物则非常普遍。矿田中的铀酰矿物在化学成分上以富钙为其显著特征，由于核废料地质处置库近场地下水中的Ca^2＋含量应该明显比下庄矿田地下水中的高，因此，我们预测含Ca的铀酰硅酸盐和铀酰磷酸盐矿物等热力学上的稳定物相很可能是地质处置系统中最主要的铀酰矿物，处置库内放射性核素的迁移主要是由这些矿物控制的。     

高放废物处置系统地下水同位素特征

在高放废物处置库场地特性评价中,对于深地质处置方案而言,最有可能使放射性核素进入生物圈的机制是地下水的迁移,因此,水文地质研究是场址预选和评价中的一个重要内容.本文以甘肃北山预选区旧井地段为例,根据地下水同位素数据,结合所获得的地质、水文数据和信息,分析研究了研究区基岩地下水的起源、形成、演化和循环特征.研究表明,北山预选区旧井地段,深部地下水和浅部地下水均源自大气降水的补给,弱含水、低渗透、低流速是该区的主要水文地质特征.     

高放废物地质处置战略讨论

概述了全球核电开发情况，介绍了高放废物地质处置国际态势及发展动向，对我国有关工作提出了意见和建议。     

震前卫星热红外环形应力场特征

本文包括两部分内容:①描述了1996年2月3日云南丽江Ms 7.0级地震,震前几天的卫星热红外图像呈现圆形,它的NNW、NW、SN、及NE向的热旋扭面往S收敛.该地震地表破裂由一系列张扭性裂缝组成,呈左旋左列,水平位错不明显,垂直断距数厘米.垂直力对构造变动的作用较为明显;而丽江地震震源机制解破裂面II的走向NNE6o,倾向W,倾角44o,P 轴方位为NNE3o、仰角75o,近于直立,综合热旋扭面展布、地震地表破裂特征及震源机制解,得出该旋扭椭圆为地幔外侧右旋上涌所造成;②菲律宾萨马岛Ms7.0~7.5强震群及青海共和Ms7.0地震前热应力环椭圆的推进路径.根据这一特征得出交变潮汐力的地球动力学解释.卫星热红外图像震前应力热场的方法是临震预测地震的有效方法,卫星热红外技术辅以震源机制解和地表破裂带力学分析是研究地球动力学有力工具.地球自转速度变化,交变潮汐力和地幔旋扭上涌力是地球动力学的主因.     

高放废物处置库北山预选区岩体筛选定量研究

以北山预选岩体的地学数据集成为基础、GIS技术为支撑,开展预选区众多岩体筛选特征分析,针对预选区岩体规模、形态与完整性开展定性及定量研究,为北山预选区岩体筛选和评价提供方法与依据。     

根据地球物理场特征评价核废物处置场址——对疏勒河断裂带稳定性评价

以疏勒河断裂带中段及其以北的北山地区遥感地质图象特征为基础，从该地区地球物理场（包括磁场、电磁场、射气场和地温场）特征的角度，对建造高放废物处置库的稳定性进行评价，得出结论：疏勒河断裂带中段及其北山地区的地质稳定性较好，是高放废物处置库选址的有利地区。     

高放废物处置库甘肃北山预选区同位素水文学研究及设想

甘肃省北山地区是我国高放废物处置库场址重要预选区之一,花岗岩是处置库候选围岩。10余年来,在北山地区开展了水文地质和同位素水文学调查、研究工作,为场址评价提供了重要的水文地质依据。今后,在深入开展预选区水文地质研究工作中,应进一步开展同位素水文学研究,示踪地下水的补给来源,揭示水循环过程,测定地下水滞留时间和流速等,以获得高放废物处置场址特性评价所需的水文地质参数资料。