Main outcomes from in situ thermo-hydro-mechanical experiments programme to demonstrate feasibility of radioactive high-level waste disposal in the Callovo-Oxfordian claystone

In the context of radioactive waste disposal,an underground research laboratory(URL)is a facility in which experiments are conducted to demonstrate the feasibility of constructing and operating a radioactive waste disposal facility within a geological formation.The Meuse/Haute-Marne URL is a sitespecific facility planned to study the feasibility of a radioactive waste disposal in the Callovo-Oxfordian(COx)claystone.The thermo-hydro-mechanical(THM)behaviour of the host rock is significant for the design of the underground nuclear waste disposal facility and for its long-term safety.The French National Radioactive Waste Management Agency(Andra)has begun a research programme aiming to demonstrate the relevancy of the French high-level waste(HLW)concept.This paper presents the programme implemented from small-scale(small diameter)boreholes to full-scale demonstration experiments to study the THM effects of the thermal transient on the COx claystone and the strategy implemented in this new programme to demonstrate and optimise current disposal facility components for HLW.It shows that the French high-level waste concept is feasible and working in the COx claystone.It also exhibits that,as for other plastic clay or claystone,heating-induced pore pressure increases and that the THM behaviour is anisotropic.     

缓冲材料热-水-力耦合模型试验研究

高放废物深地质处置采用多重屏障设计体系,缓冲材料是位于废物罐和围岩之间的一道重要的人工屏障。在放射性衰变热、地下水入侵和围岩应力等作用下,缓冲材料经历复杂的热-水-力耦合过程,评价其长期性能对高放废物地质处置库的稳定运行至关重要。缓冲材料模型试验是研究膨润土在多场耦合环境下性能变化的重要途径。中型实验台架是大型实验台架(China-Mock-up)的重要补充,用来模拟与大型实验台架边界相同的环境下,即热量和水分别从缓冲材料的不同侧向另一侧传递和渗透的条件下膨润土的行为特征。通过实时监测缓冲材料在长期加热和加水条件下的温度、相对湿度、力学等特征参数,揭示了在热-水-力耦合条件下缓冲材料的性能变化规律,同时对台架进行了拆解,对拆解样品的含水量、干密度和微观结构等进行了分析测试,研究结果可为高放废物处置库缓冲材料的工程设计提供参数支持。     

Design and development of large-scale in-situ PRACLAY heater test and horizontal high-level radioactive waste disposal gallery seal test in Belgian HADES

In Belgium,the Boom clay was selected as a potential host formation for the disposal of high-level radioactive waste（HLW）.To demonstrate the suitability of Boom clay for bearing thermal load induced by the HLW,a large-scale in-situ heater test,called PRACLAY heater test,will be conducted in the underground research laboratory（URL） in Mol.Owing to the limitations of the test（a short period of time compared with that considered in a real repository,different boundary conditions,etc.）,the test is designed to simulate,in a conservative way,the most critical state and phenomena that could occur in the host rock.The PRACLAY gallery was excavated at the end of 2007;the heating phase will begin in 2010 and will last for at least 10 years.The PRACLAY gallery itself leaves an opportunity to study the possibilities of sealing a disposal drift in Boom clay and testing the feasibility of hydraulic cut-off of any preferential pathway to the main access gallery through the excavation damage zone（EDZ） and the lining with a seal in a horizontal drift（horizontal seal）.Indeed,this is a generic problem for all deep geological disposal facilities for HLW.An annular seal made of compacted swelling bentonite will be installed in the front of the heated part of the PRACLAY gallery for these purposes.This paper provides detailed considerations on the thermo-hydro-mechanical（THM） boundary conditions for the design of the PRACLAY heater test and the seal test with the support of numerical calculations.It is believed that these important items considered in the PRACLAY heater test design also constitute key issues for the repository design.The outcome of the PRACLAY heater test will be an important milestone for the Belgian repository design.     

Numerical thermo-hydro-mechanical modeling of compacted bentonite in China-mock-up test for deep geological disposal

The China-mock-up test is to evaluate the performance of the compacted Gaomiaozi(GMZ) bentonite under coupled thermo-hydro-mechanical(THM) conditions in deep geological disposal.A numerical study of the test is conducted in this paper.The principal THM characteristics of the bentonite are presented at first.A THM model is then presented to tackle the complex coupling behavior of the bentonite.The model of Alonso-Gens is incorporated to reproduce the mechanical behavior of the bentonite under unsaturated conditions.With the proposed model,numerical simulations of the China-mock-up test are carried out by using the code of LAGAMINE.The time variations associated with the temperature,degree of saturation,suction and swelling pressure of the compacted bentonite are studied.The results suggest that the proposed model is able to reproduce the mechanical behavior of the bentonite,and to predict moisture motion under coupled THM conditions.     

比利时高放废物处置库设计及与基岩和工程屏障体系的热-水-力性状的相关研究

在比利时，泥岩中地质处置是高放废物最终处置的首选，处置库在高放废物与生物圈之间的多重屏障基础上设计的，而Boom泥岩作为基岩的研究已有20多年历史，1980年比利时做出重大决定，建立名为HADES的地下研究机构，以研究Boom泥岩在地下223m处的力学性质，并调查和论证处置的可行性，为处置库屏障（天然和人工）提供可靠数据，在HADES的众多现场试验中很多试验用来对基岩和工程屏障体系（包括封口和回填的可行性）热-水-力性状进行研究，包括CACTUS，ATLAS，BACCHUS和RESEAL等项目。自1995年以来，研究开发计划向大型和示范性试验方向发展。最主要成果是运用工业技术建立地下研究设施（竖井和井巷）可行性得到了验证，且这种工业技术给研究提供一个较好机会，便于进一步认识基岩泥岩（CLIPEX方案）的水-力性状及了解隧道开挖工程（SELFRAC课题）对挖掘破坏区的影响，另一个重大成果是成功地实现对一种称为“OPHELE”的预掉膨润土（人工屏障材料）加热和水化地面大型试验。下一步工作内容包括实现大尺寸现场加热器试验（PRACLAY试验），此试验预计于2006年开始，并可持续10a之久，据此，首先简要描述比利时高效废物处置库设计，然后回顾Boom泥岩和工程屏障体系的热-水-力性状相关试验，最后介绍下一步大规模PRACLAY试验。     

High-level radioactive waste disposal in China: update 2010

For geological disposal of high-level radioactive waste (HLW), the Chinese policy is that the spent nuclear fuel (SNF) should be reprocessed first, followed by vitrification and final disposal. The preliminary repository concept is a shaft-tunnel model, located in saturated zones in granite, while the final waste form for disposal is vitrified high-level radioactive waste. In 2006, the government published a long-term research and development (RD) plan for geological disposal of high-level radioactive waste. The program consists of three steps: (1) laboratory studies and site selection for a HLW repository (2006–2020); (2) underground in-situ tests (2021–2040); and (3) repository construction (2041–2050) followed by operation. With the support of China Atomic Energy Authority, comprehensive studies are underway and some progresses are made. The site characterization, including deep borehole drilling, has been performed at the most potential Beishan site in Gansu Province, Northwestern China. The data from geological and hydrogeological investigations, in-situ stress and permeability measurements of rock mass are presented in this paper. Engineered barrier studies are concentrated on the Gaomiaozi bentonite. A mock-up facility, which is used to study the thermo-hydro-mechano-chemical (THMC) properties of the bentonite, is under construction. Several projects on mechanical properties of Beishan granite are also underway. The key scientific challenges faced with HLW disposal are also discussed.     

Experiments on thermo-hydro-mechanical behaviour of Opalinus Clay at Mont Terri rock laboratory,Switzerland

Repositories for deep geological disposal of radioactive waste rely on multi-barrier systems to isolate waste from the biosphere.A multi-barrier system typically comprises the natural geological barrier provided by the repository host rock e in our case the Opalinus Clay e and an engineered barrier system(EBS).The Swiss repository concept for spent fuel and vitrified high-level waste(HLW)consists of waste canisters,which are emplaced horizontally in the middle of an emplacement gallery and are separated from the gallery wall by granular backfill material(GBM).We describe here a selection of five in-situ experiments where characteristic hydro-mechanical(HM)and thermo-hydro-mechanical(THM)processes have been observed.The first example is a coupled HM and mine-by test where the evolution of the excavation damaged zone(EDZ)was monitored around a gallery in the Opalinus Clay(ED-B experiment).Measurements of pore-water pressures and convergences due to stress redistribution during excavation highlighted the HM behaviour.The same measurements were subsequently carried out in a heater test(HE-D)where we were able to characterise the Opalinus Clay in terms of its THM behaviour.These yielded detailed data to better understand the THM behaviours of the granular backfill and the natural host rock.For a presentation of the Swiss concept for HLW storage,we designed three demonstration experiments that were subsequently implemented in the Mont Terri rock laboratory:(1)the engineered barrier(EB)experiment,(2)the in-situ heater test on key-THM processes and parameters(HE-E)experiment,and(3)the full-scale emplacement(FE)experiment.The first demonstration experiment has been dismantled,but the last two ones are on-going.     

Long-term safety analysis and model validation through URL research

In Germany, all types of radioactive wastes will be disposed of in deep geological repositories. While a repository for low-level radioactive waste (LLW) has recently been licensed, different host rock formations are considered for disposal of heat producing high-level waste (HLW). The latter includes directly disposed spent fuel (SF) and vitrified waste from its reprocessing. Different canisters and disposal concepts are considered for spent fuel disposal, i.e. thick-walled iron casks in horizontal drifts or thin-walled BSK3 steel casks in vertical boreholes. GRS is the leading expert institution in Germany concerning nuclear safety and waste management. For the recent 30 years, GRS has developed and continuously improves a set of computer codes, which allow assessing the performance and the long-term safety of repositories in various host rocks (salt, clay or granite) adopting different technical options. Advanced methods for deterministic as well as probabilistic assessments are available. To characterize the host rocks and backfill/buffer materials and to develop disposal technologies, comprehensive laboratory experiments and a large number of in-situ tests have been performed at GRS’ geo-laboratory and underground research laboratories in different host formations. Thermo-hydro-mechanico-chemical (THMC) processes occurring in the host rocks and engineered barrier systems are numerically simulated. The paper presents an overview of GRS’ work highlighting important results of performance assessment (PA) studies for both the salt and clay options. Also, recent results of in-situ investigations and laboratory studies are presented together with modeling results. Special emphasis is dedicated to the consideration of coupled THM processes which are of relevance in PA.     

TIMODAZ: A successful international cooperation project to investigate the thermal impact on the EDZ around a radioactive waste disposal in clay host rocks

Disposal of spent nuclear fuel and long lived radioactive waste in deep clay geological formations is one of the promising options worldwide. In this concept of the geological disposal system, the host clay formation is considered as a principal barrier on which the fulfillment of key safety functions rests. Between 2006 and 2010, the European Commission project TIMODAZ, which gathered 15 partners from 8 countries, has investigated the coupled thermo-hydro-mechanical (THM) effects on clay formations for geological disposal of radioactive waste, and specific attention was paid to investigating the thermal effect on the evolution of the damaged zone (DZ). Three types of potential host clay formations were investigated: the Boom Clay (Belgium), the Opalinus Clay (Switzerland) and the Callovo-Oxfordian argillite (France). Intensive experimental (laboratory and in situ in underground research laboratories) and numerical studies have been performed. Multi-scale approach was used in the course of the project. High degree of similarities between the failure modes, sealing process, stress paths, deformation, etc., observed in laboratories and in situ has been obtained, which increased the confidence in the applicability of laboratory test results and up-scaling perspective. The results of the laboratory and in situ tests obtained allowed the parameters for numerical models at various scales to be derived and provided the basis for the simplified performance assessment models that are used to assess the long-term safety of a repository. The good cooperation between the numerical modeler and experimenters has allowed an in-depth analysis of the experimental results and thus better understanding the underlying processes, and consequently increased the capabilities to model the THM effects in claystones. This paper presents the main achievements obtained by TIMODAZ project and shows how a European scientific community investigates a problem of concern in a collaborative way and how the obtained main results are applied to the performance assessment of a geological repository.     

石英砂掺量对混合型缓冲回填材料抗剪强度的控制机制

高放废物深部地质处置工程中,向膨润土中加入一定比例的石英砂可以优化缓冲回填材料的热传导性和可施工性。从"混合土"的概念出发,设计干密度和含水率相同、掺砂率不同的压实膨润土-砂混合物试样,通过剪切试验揭示掺砂率对抗剪强度的控制机制。试验材料选用内蒙古高庙子膨润土(GMZ001膨润土),石英砂按照质量0%～50%的比率添加。剪切试验结果表明:随着掺砂率的增大,压实混合物由应变软化型向应变硬化型过渡,黏聚力及内摩擦角逐渐减小,即抗剪强度降低。基于混合土孔隙结构假说,通过类比分析,对黏土-砂混合物抗剪强度的界限掺砂率进行估计,提供孔隙结构的扫描电镜证据。引入有效黏土密度和有效含水率的概念,描述石英砂颗粒之间的黏土基质的物理状态,阐释石英砂掺量对混合型缓冲回填材料抗剪强度的控制机制。     

中国高放废物处置库缓冲材料物理性能

深地质处置被国际上公认为处置高放废物的最有效可行的方法。中国深地质处置的概念模型采用多重工程屏障系统（包括废物固化体、废物容器、外包装、缓冲／回填材料）和适宜的地质围岩地质体共同作川来确保高放废物与生物圈的安全隔离。膨润上由于具有极低的渗透性和优良的核素吸附等性能向被国际上选作缓冲材料的基础材料。经过全国筛选，高庙子膨润土矿床被选作我国缓冲材料供应基地。从2000年起，对产自该矿床的钠基膨润土GMZ-1开始了系统的研究工作。介绍了GMZ-1的矿物组成、基本特征和GMZ-1在不同干密度、不同含水量条件下的热传导、水传导、力学性能参数及GMZ-1在不同干密度条件下的膨胀特性参数测定结果。GMZ-1钠基膨润土具有蒙脱石含量高（75％左右）、杂质矿物相对较少的特点，对于该材料的系统和深入研究对于开发我国缓冲回填材料技术，确保高放废物的安全有效处置有重要意义。     

高放核废物地质处置中工程屏障研究新进展

中国对该课题的研究始于1985年，但是长期以来未能引起足够的关注，相关研究项目也非常有限。近年来，随着中国经济的快速增长，能源短缺问题越来越严重，发展和利用核能己作为一种主要的解决方案，因此核废物的安全处置则成为现实的重要课题。中国在利用膨润土作为工程隔绝材料方面的研究工作，主要限于选择合适的膨润土，而高庙子膨润士作为最终选择的缓冲材料，其基本物理-化学特性已得到确定，但有关热-水-力耦合的试验尚未开展，相关课题的研究也尚需努力。鉴于国际上已对多种其他备选膨润土进行过大量研究，有关成果可望用于指导即将在中国进行的高庙子膨润土试验研究。此文的主要目的就是为中国核废物的地质处置研究提供一些有益的经验。首先，介绍使用基于膨润土的工程隔绝核废物地质处置方法，这一方法已为广泛接受；然后，介绍膨润土的选择标准，地质-化学特性、热-水-力性态（包括微观结构、宏观性态、接缝性态和数值分析），以及在放射性废物处置过程中产生的气体对工程隔绝层的影响等，通过不同实例来展示试验原理和主要结果；最后，对近期国内外研究成果和未来发展前景进行总结。     

DECOVALEX_IV TASK_D项目的热-水-力耦合过程的数值模拟

核废料地下处置系统研究的国际合作项目DECOVALEX(development of coupled models and their validation against experiments) 致力于高放射性核废料地质处置系统围岩中多个物理场的耦合过程研究和工程屏障的可行性评估.中国研究小组第一次参加DECOVALEX计划.介绍了其子课题Task_D的情况和阶段性研究结果,包括2种处置方式--瑞士FEBEX和美国Yucca Mountain类型的1×104 a以上的预测模拟及其比较分析.建立一套复杂的非饱和多孔介质中热液力(THM)耦合过程的非等温流动和形变控制方程,涉及到固、液、气三相和四种组分(固体骨架,水,干空气和水蒸汽).其表现为相对独立同时又相互交叠的4类模型(1) 考虑有效应力、热膨胀应力和膨润土的水膨胀应力变形模型;(2) 考虑水与蒸汽在蒸发凝结时物质交换的流动模型;(3) 包含蒸汽/干空气相对运动的蒸汽分子扩散和对流模型;(4) 三相局部非等温过程的热交换模型.在此基础上根据Task_D的设定要求简化为较为实用的方程,并发展了相应的程序对1×106 a THM耦合行为进行了预测模拟,其结果在2005年2月Task_D讨论会和DECOVALEX工作会议与多个国家相互独立的研究结果进行对比,吻合程度很高,这给模型的建立和程序发展都带来了信心.     

高庙子膨润土及其混合材料导热性能研究

导热性能是高放废物地质处置库缓冲/回填材料的重要性能之一。采用瞬变平面热源法,研究了我国高放废物地质处置首选缓冲/回填材料高庙子膨润土,及以其为主料,添加不同含量石英砂、北山花岗岩碎屑组成的混合材料的导热性能。分析了添加剂种类和含量、干密度、饱和度等因素对导热系数的影响。研究结果表明:高庙子膨润土及其混合材料的导热系数、热扩散系数都随干密度和含水量的增大而增大;石英砂、北山花岗岩碎屑能够不同程度提高膨润土的导热系数,石英砂的作用优于北山花岗岩碎屑;饱和度对添加剂发挥其提高缓冲/回填材料导热性能的作用影响明显,饱和度越高,添加剂的作用越显著。     

Numerical analysis of thermal process in the near field around vertical disposal of high-level radioactive waste

For deep geological disposal of high-level radioactive waste(HLW)in granite,the temperature on the HLW canisters is commonly designed to be lower than100fiC.This criterion dictates the dimension of the repository.Based on the concept of HLW disposal in vertical boreholes,thermal process in the nearfield(host rock and buffer)surrounding HLW canisters has been simulated by using different methods.The results are drawn as follows:(a)the initial heat power of HLW canisters is the most important and sensitive parameter for evolution of temperaturefield;(b)the thermal properties and variations of the host rock,the engineered buffer,and possible gaps between canister and buffer and host rock are the additional key factors governing the heat transformation;(c)the gaps width and thefilling by water or air determine the temperature offsets between them.     

Numerical analysis of thermal process in the near field around vertical disposal of high-level radioactive waste简

For deep geological disposal of high-level radioactive waste (HLW) in granite, the temperature on the HLW canisters is commonly designed to be lower than 100 °C. This criterion dictates the dimension of the repository. Based on the concept of HLW disposal in vertical boreholes, thermal process in the near field (host rock and buffer) surrounding HLW canisters has been simulated by using different methods. The results are drawn as follows: (a) the initial heat power of HLW canisters is the most important and sensitive parameter for evolution of temperature field; (b) the thermal properties and variations of the host rock, the engineered buffer, and possible gaps between canister and buffer and host rock are the additional key factors governing the heat transformation; (c) the gaps width and the filling by water or air determine the temperature offsets between them.     

OPHELIE回填混合物的热-水-力耦合特征

在以比利时高放废物处置参考设计方案的OPHELIE地面大型试验的框架为背景下，进行了一套完整的固结试验项目以获取回填材料的热-水-力反应特征。缓冲材料是预先经高压压实的土块，其主要成分为60%的FoCa泥岩，35%的砂以及5%的石墨（干燥重量），除了对温度和吸力控制设备的简要描述之外，还将阐述有代表性的试验结果，包括持水特性，不同应力，不同吸力，不同温度下的压缩性，膨胀性能，以及在吸湿，吸热条件下的塌陷现象。     

OPALINUS硬泥岩热反应的监控与模拟

目前，一些国家选择硬泥岩作为核废物地质深部处置的围岩。为深入理解硬泥岩在热-水-力（THM）耦合作用下的变化特征，在瑞士的Mont Terri地下岩石实验室对Opalinus硬泥岩进行了现场加热试验。该试验是利用-电加热器（直径=30cm，长度=5．4m）对硬泥岩进行了1a多的加热，然后降温0．5a。加热器表面的最高温度达100℃。在试验过程中，安装了80多个测试传感器对硬泥岩中的温度、孔隙水压、气体渗透以及变形进行了监控。通过观察发现围岩受热膨胀且产生明显的孔隙水压升高。距加热器约1m的区域，其孔隙水压从约1MPa增高到4MPa。最后对试验中观测的硬泥岩受热所产生的热-水-力全过程进行了模拟计算，并介绍了现场测量和数值计算的初步结果。     

黏土岩温度–渗流–应力耦合作用的长期力学特性研究若干进展

核废料地质处置库长期处于复杂的耦合环境之中,其安全、稳定、高效的建设与运营需要考虑温度场(T)、渗流场(H)、应力场(M)的长期耦合作用。围绕黏土岩多场耦合作用下的长期力学特性,首先总结了国内外在黏土岩温度–渗流–应力耦合条件下长期力学试验研究成果与不足,主要包括HM与THM耦合长期作用对黏土岩渗透特性的影响、黏土岩TM与THM耦合长期力学特性。其次从微观唯相的角度,论述了温度对黏土岩微观结构特征的影响机制。基于上述认识,提出黏土岩THM耦合蠕变力学模型及其适用性。同时,介绍了笔者团队围绕黏土岩THM耦合长期力学特性方面的相关研究成果,结果表明:BoomClay的长期力学特性与温度、孔压、应力和各向异性等因素相关。最后,提出黏土岩THM耦合研究未来应重点关注的方向。     

Design and validation of the THMC China-Mock-Up test on buffer material for HLW disposal

According to the preliminary concept of the high-level radioactive waste （HLW） repository in China, a large-scale mock-up facility, named China-Mock-Up was constructed in the laboratory of Beijing Research Institute of Uranium Geology （BRIUG）. A heater, which simulates a container of radioactive waste, is placed inside the compacted Gaomiaozi （GMZ）-Na-bentonite blocks and pellets. Water inflow through the barrier from its outer surface is used to simulate the intake of groundwater. The numbers of water injection pipes, injection pressure and the insulation layer were determined based on the nu- merical modeling simulations. The current experimental data of the facility are herein analyzed. The experiment is intended to evaluate the thermo-hydro-mechano-chemical （THMC） processes occurring in the compacted bentonite-buffer during the early stage of HLW disposal and to provide a reliable database for numerical modeling and further investigation of engineered barrier system （EBS）, and the design of HLW repository.