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.     

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.     

On area-specific underground research laboratory for geological disposal of high-level radioactive waste in China

Underground research laboratories （URLs）, including ＂generic URLs＂ and ＂site-specific URLs＂, are un- derground facilities in which characterisation, testing, technology development, and/or demonstration activities are carried out in support of the development of geological repositories for high-level radioactive waste （HLW） disposal. In addition to the generic URL and site-specific URL, a concept of ＂areaspecific URL＂, or the third type of URL, is proposed in this paper. It is referred to as the facility that is built at a site within an area that is considered as a potential area for HLW repository or built at a place near the future repository site, and may be regarded as a precursor to the development of a repository at the site. It acts as a ＂generic URL＂, but also acts as a ＂site-specific URL＂ to some extent. Considering the current situation in China, the most suitable option is to build an ＂area-specific URL＂ in Beishan area, the first priority region for China＇s high-level waste repository. With this strategy, the goal to build China＇s URL by 2020 mav be achieved, but the time left is limited.     

Influence of fracture orientation on excavatability of soft sedimentary rock using a hydraulic impact hammer: A case study in the Horonobe Underground Research Laboratory

In the Japanese deep geological disposal project for high-level radioactive waste, the ease of excavation of a potential host rock is a key issue for the economics of project implementation. This is because it is estimated that about 300-km of disposal drifts will need to be excavated for the disposal of 40,000 waste packages deep underground. In this study, the influence not only of the mechanical properties of intact host rock, but also fracture characteristics and their effect on the practical excavation rate of drifts using a hydraulic impact hammer were analyzed. The drifts were excavated through soft sedimentary rock in the Horonobe Underground Research Laboratory. Fracture mapping was conducted at the excavation face before every excavation round for the evaluation of fracture characteristics. Equotip hardness testing was also conducted to estimate the strength of intact rock. The results indicate that the excavation rate of the drift excavated in the direction perpendicular to natural fractures was faster than the excavation of the drift excavated in the direction parallel to natural fractures. In addition, the drift excavated in the direction perpendicular to natural fractures had a good correlation with fracture density. This result suggests that the preferred direction of disposal drifts should be perpendicular to the major natural fractures in the host rock to optimize excavatability in any deep geological disposal project.     

高放废物处置库黏土围岩温度-应力耦合测试方法展望

高放废物深地质处置库围岩在温度及应力耦合作用下的工程稳定性是关系环境安全的关键问题.本文对黏土围岩高放废物处置库在放射性物质放热温度及深部地应力环境应力耦合研究工作中采用的测试方法进行了系统的回顾和总结.从黏土岩热学性能测试方法以及温度对黏土岩力学性质影响研究方法两个方面,对目前高放废物温度-应力耦合特性测试的试验方法...     

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.     

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.     

The Beishan underground research laboratory for geological disposal of high-level radioactive waste in China: Planning,site selection,site characterization and in situ tests

With the rapid development of nuclear power in China, the disposal of high-level radioactive waste (HLW) has become an important issue for nuclear safety and environmental protection. Deep geological disposal is internationally accepted as a feasible and safe way to dispose of HLW, and underground research laboratories (URLs) play an important and multi-faceted role in the development of HLW repositories. This paper introduces the overall planning and the latest progress for China's URL. On the basis of the proposed strategy to build an area-specific URL in combination with a comprehensive evaluation of the site selection results obtained during the last 33 years, the Xinchang site in the Beishan area, located in Gansu Province of northwestern China, has been selected as the final site for China's first URL built in granite. In the process of characterizing the Xinchang URL site, a series of investigations, including borehole drilling, geological mapping, geophysical surveying, hydraulic testing and in situ stress measurements, has been conducted. The investigation results indicate that the geological, hydrogeological, engineering geological and geochemical conditions of the Xinchang site are very suitable for URL construction. Meanwhile, to validate and develop construction technologies for the Beishan URL, the Beishan exploration tunnel (BET), which is a 50-m-deep facility in the Jiujing sub-area, has been constructed and several in situ tests, such as drill-and-blast tests, characterization of the excavation damaged zone (EDZ), and long-term deformation monitoring of surrounding rocks, have been performed in the BET. The methodologies and technologies established in the BET will serve for URL construction. According to the achievements of the characterization of the URL site, a preliminary design of the URL with a maximum depth of 560 m is proposed and necessary in situ tests in the URL are planned.     

高压实高庙子膨润土GMZ01的膨胀力特征

 高放废物深地质处置中，缓冲/回填材料系统起着工程屏障、水力学屏障、化学屏障、传导和散失放射性废物衰变热等重要作用，是高放废物地质处置库长期安全性和稳定性的有效保障。前人研究表明，膨润土是理想的缓冲/回填材料。在归纳总结压实膨润土膨胀力的室内试验研究成果的基础上，采用恒体积试验法研究高压实高庙子膨润土GMZ01的膨胀力特性，该膨润土已经被确定为我国高放废物地质处置库首选缓冲材料。结果表明，高压实高庙子膨润土GMZ01膨胀力随时间的变化曲线是一条渐近线，而时间/膨胀力与时间之间存在很好的线性关系；膨胀力发展过程曲线与吸水量曲线具有明显的阶段性特征；高压实高庙子膨润土的膨胀力和干密度之间存在指数关系，干密度是影响膨胀力的一项重要的因素。所取得的膨胀力特性成果，对于高庙子膨润土膨胀性能的正确判定具有非常重要的意义。     

Optimal pricing and environmental improvement for a hazardous waste disposal supply chain with emission penalties

Hazardous waste management has become a municipal problem, associated with industrial development and changing consumption patterns. We study the hazardous waste management system as a supply chain with a disposal facility and a contractor, which serves customers with demand sensitive to price and environment impact. The government intervenes with this supply chain by imposing emission penalties that make the waste disposal facility responsible for reducing disposal process emissions. The Stackelberg game and Nash equilibrium are used to model the decision-making sequence between the disposal facility and the contractor. We specify different scenarios to model the hazardous waste management supply chain. The goal of this research is to find the optimal disposal service price and level of environmental improvement to mitigate adverse impacts and maximize profits. The applicability of dual-channel service in the hazardous waste supply chain is also investigated. Our study shows that the supply chain obtains the highest profit if both the disposal facility and the contractor operate in a centralized model. Under some scenarios, profitability improves if the disposal facility becomes active in waste collection and transportation under a dual-channel supply-chain model. Demand sensitivity to price and environmental impacts can affect the adopted level of improvement by disposal facilities.     

高放废物地质处置及其若干关键科学问题

如何安全处置高水平放射性废物是科学、技术和工程界所面临的挑战性问题。在介绍国内外最新研究进展的基础上，重点讨论高放废物地质处置的若干关键科学问题：处置库场址地质演化的精确预测、深部地质环境特征、多场耦合条件下（中（高）温、地壳应力、水力作用、化学作用、生物作用和辐射作用等）深部岩体、地下水和工程材料的行为、低浓度超铀放射性核素的地球化学行为与随地下水迁移行为及处置系统的安全评价。同时，介绍了国外若干重大科研项目和若干研究热点问题。     

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。     

高放废物地质处置中的地质、水文 地质、地球化学关键科学问题

 深地质处置是目前国际上普遍接受的高放废物最终处置方案。该方案对处置库采用人工屏障和天然屏障的“多重屏障系统”概念设计。天然屏障是处置库长期安全至关重要的保证。如何选择可靠的天然屏障,主要靠地质、水文地质、地球化学等工作来完成。通过对国内外高放废物地质处置研究的回顾,阐述高放废物地质处置研究中与地质、水文地质、地球化学相关的关键科学问题,重点介绍预选场地地质、水文地质、地球化学研究的主要内容、主要方法和手段,讨论目前国际上关注的关键水文地质、地球化学问题,如水文地质、水文地球化学模拟、核素在天然介质中迁移、地下水–废物–岩石相互作用、岩体地球化学封闭性等。     

How rock samples can be representative of in situ condition: A case study of Callovo-Oxfordian claystones

Within the framework of feasibility studies for a reversible, deep geological repository of high- and intermediate-level long-lived radioactive waste (HLW, IL-LLW), the French National Radioactive Waste Management Agency (Andra) is investigating the Callovo-Oxfordian (COx) formation near Bure (northeast part of France) as a potential host rock for the repository. The hydro-mechanical (HM) behaviour is an important issue to design and optimise different components of the disposal such as shaft, ramp, drift, and waste package disposal facilities. Over the past 20 years, a large number of laboratory experiments have been carried out to characterise and understand the HM behaviours of COx claystones. At the beginning, samples came from deep boreholes drilled at the ground surface with oil base mud. From 2000 onwards, with the launch of the construction of the Meuse/Haute-Marne Underground Research Laboratory (MHM URL), most samples have been extracted from a large number of air drilled boreholes in the URL. In parallel, various constitutive models have been developed for modelling. The thermo-hydro-mechanical (THM) behaviours of the COx claystones were investigated under different repository conditions. Core samples are subjected to a complex HM loading path before testing, due to drilling, conditioning and preparation. Various kinds of effects on the characteristics of the claystones are highlighted and discussed, and the procedures for core extraction and packaging as well as a systematic sample preparation protocol are proposed in order to minimise the uncertainties on test results. The representativeness of the test results is also addressed with regard to the in situ rock mass.     

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.     

Excavation of underground research laboratory ramp in granite using tunnel boring machine: Feasibility study

Underground research laboratory (URL) plays an important role in safe disposal of high-level radioactive waste (HLW). At present, the Xinchang site, located in Gansu Province of China, has been selected as the final site for China’s first URL, named Beishan URL. For this, a preliminary design of the Beishan URL has been proposed, including one spiral ramp, three shafts and two experimental levels. With advantages of fast advancing and limited disturbance to surrounding rock mass, the tunnel boring machine (TBM) method could be one of the excavation methods considered for the URL ramp. This paper introduces the feasibility study on using TBM to excavation of the Beishan URL ramp. The technical challenges for using TBM in Beishan URL are identified on the base of geological condition and specific layout of the spiral ramp. Then, the technical feasibility study on the specific issues, i.e. extremely hard rock mass, high abrasiveness, TBM operation, muck transportation, water drainage and material transportation, is investigated. This study demonstrates that TBM technology is a feasible method for the Beishan URL excavation. The results can also provide a reference for the design and construction of HLW disposal engineering in similar geological conditions. © 2020 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).     

Clays in radioactive waste disposal

Clays and argillites are considered in some countries as possible host rocks for nuclear waste disposal at great depth.The use of compacted swelling clays as engineered barriers is also considered within the framework of the multi-barrier concept.In relation to these concepts,various research programs have been conducted to assess the thermo-hydro-mechanical properties of radioactive waste disposal at great depth.After introducing the concepts of waste isolation developed in Belgium,France and Switzerland,the paper describes the retention and transfer properties of engineered barriers made up of compacted swelling clays in relation to microstructure features.Some features of the thermo-mechanical behaviors of three possible geological barriers,namely Boom clay（Belgium）,Callovo-Oxfordian clay（France） and Opalinus clay（Switzerland）,are then described,including the retention and transfer properties,volume change behavior,shear strength and thermal aspects.     

Concept development of an underground research tunnel for validating the Korean reference HLW disposal system

In order to dispose of high-level radioactive waste (HLW) safely in geological formations, it is necessary to assess the feasibility, safety, appropriateness, and stability of the disposal concept at an underground research laboratory (URL) constructed in the same geological formation as the host rock. In this study, minimum requirements and the conceptual design for an efficient construction of a small scale URL were derived based on a literature review. To confirm the validity of the conceptual design for construction at KAERI, a geological survey including a seismic refraction survey, electronic resistivity survey, borehole drilling, and in situ and laboratory tests were carried out. The mechanical stability of the URL was investigated with a consideration of the surface topography, tunnel geometry, tunnel slope, sequential excavation, in situ stress ratio, erosion effect, and rock property variation along the tunnel using the three-dimensional code, FLAC3D. From the study, it was possible to conclude that the small scale URL will be effectively constructed in a granite mass at KAERI and will satisfy the minimum requirements.     

法国ANDRA放射性废物地质处置可行性研究综述

介绍15a来法国国家放射性废物管理局（ANDRA）为研究地下处置放射性废物而开展的主要研究成果，实验室试验、现场试验和数值模拟结果均表明：ANDRA所研究的在法国东部埋深500m、厚达130m的泥岩岩层具备永久处置核废料的地质条件，从地质和学角度上介绍该泥岩岩层一些主要特征，并对ANDRA提出的地质处置总体设计方案和不同类型废物处置单元进行系统论述。     

Acoustic emission in host-rock material for radioactive waste disposal: comparison between clay and rock salt

The use of clay masses for radioactive waste disposal requires a comprehensive analysis of fracture processes in clay. Acoustic emission (AE) was used to obtain a better insight into damage evolution during uniaxial loading of Boom Clay specimens. A comparison of AE in clay and rock salt shows a much lower AE activity in clay. This, together with the higher attenuation, would inhibit the use of the AE technique for large-scale in-situ monitoring in clay masses. Cyclic uniaxial tests showed that, similarly to rock salt, clay exhibits a very well-pronounced Kaiser effect in AE with Felicity ratios around unity. The Kaiser effect takes place at different loading stages (before and at the flow limit) and, during reloading, it coincides with the deformation curve inflection. Further research is required to study the applicability of the Felicity ratio as a measure of the intensity of healing processes in clay. Electronic Publication