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.

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.

Study on the residence time of deep groundwater for high-level radioactive waste geological disposal

Residence time of deep groundwater is one of the most important parameters in safety and performance assessment for high-level radioactive waste geological disposal. In this study, we collected the deep groundwater samples of Jijicao in Gansu Beishan pre-selected region. The deep groundwater residence time at two depths estimated by Helium-4 accumulation method were 3.8 ka and 5.0 ka respectively upon measurement and calculation, which indicates that the deep groundwater is not derived from the deep crust circulation process. Hence, deep groundwater is featured with long residence time as well as slow circulation and update rate, and such features are conductive to the safe disposal of high-level radioactive waste.

Implications of safety requirements for the treatment of THMC processes in geological disposal systems for radioactive waste

The mission of nuclear safety authorities in national radioactive waste disposal programmes is to ensure that people and the environment are protected against the hazards of ionising radiations emitted by the waste.It implies the establishment of safety requirements and the oversight of the activities of the waste management organisation in charge of implementing the programme.In Belgium,the safety requirements for geological disposal rest on the following principles:defence-in-depth,demonstrability and the radiation protection principles elaborated by the International Commission on Radiological Protection(ICRP).Applying these principles requires notably an appropriate identification and characterisation of the processes upon which the safety functions fulfilled by the disposal system rely and of the processes that may affect the system performance.Therefore,research and development(R&D)on safety-relevant thermo-hydro-mechanical-chemical(THMC)issues is important to build confidence in the safety assessment.This paper points out the key THMC processes that might influence radionuclide transport in a disposal system and its surrounding environment,considering the dynamic nature of these processes.Their nature and significance are expected to change according to prevailing internal and external conditions,which evolve from the repository construction phase to the whole heatingecooling cycle of decaying waste after closure.As these processes have a potential impact on safety,it is essential to identify and to understand them properly when developing a disposal concept to ensure compliance with relevant safety requirements.In particular,the investigation of THMC processes is needed to manage uncertainties.This includes the identification and characterisation of uncertainties as well as for the understanding of their safety-relevance.R&D may also be necessary to reduce uncertainties of which the magnitude does not allow demonstrating the safety of the disposal system.

Key Scientific Challenges in Geological Disposal of High Level Radioactive Waste

The geological disposal of high level radioactive waste is a challenging task facing the scientific and technical world.This paper introduces the latest progress of high level radioactive disposal programs in the world,and discusses the following key scientific challenges:(1)precise prediction of the evolution of a repository site;(2)characteristics of deep geological environment;(3)behaviour of deep rock mass,groundwater and engineering material under coupled conditions(intermediate to high temperature,geostress,hydraulic,chemical,biological and radiation process,etc);(4)geochemical behaviour of transuranic radionuclides with low concentration and its migration with groundwater;and(5)safety assessment of disposal system.Several large-scale research projects and several hot topics related with high-level waste disposal are also introduced.

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 （R＆D） 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.

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.

Rock Mass Characteristics in Beishan,A Preselected Area for China's High-Level Radioactive Waste Disposal

Geological and hydrological characteristics, joint geometric features, rock physical and mechanical properties and rock mass quality are studied in the Beishan area, preselected for China5 s high-level radioactive waste(HLW) disposal engineering. A comprehensive survey method is developed to study joint geometric features in the outcrop and samples from borehole BS06 into the Xinchang rock mass were tested. The optimal joint sets are determined by rose diagrams and equal-area lower hemisphere plots of joint poles. Results show that: 1) the distribution of joint occurrence obeys a normal distribution, while the distribution of joint spacing obeys a negative exponential distribution; 2) concentric circular and tangent circular sampling windows are applied to study the trace length and the trace midpoint density. Results indicate that tangent circular sampling window is more stable and reasonable; 3) Beishan granite shows high density, low porosity and high strength based on many laboratory tests and the physical properties and mechanical properties are closely related; and4) a synthesis index, Joint Structure Rating(JSR), is applied to evaluate the quality of rock mass. Through the research results of rock mass characteristics, the Xinchang rock mass in the Beishan preselected area has the favorable conditions for China's HLW disposal repository site.

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.

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.

Simulation of groundwater and nuclide transport in the near-field of the high-level radioactive waste repository with TOUGHREACT

In order to know the mechanism of groundwater transport and the variation of ion concentrations in the near-field of the high-level radioactive waste repository,the whole process was simulated by EOS3 module of TOUGHREACT.Generally,the pH and cation concentrations vary obviously in the near-field saturated zone due to interaction between groundwater and bentonite.Moreover,the simulated results showed that calcite precipitation could not cause obvious variations in the porosity of media in the near-filed if the chemical components and their concentrations of groundwater and bentonite pore water are similar to those used in this study.

High-Level Nuclear Wastes and the Environment: Analyses of Challenges and Engineering Strategies

The main objective of this paper is to analyze the current status of high-level nuclear waste disposal along with presentation of practical perspectives about the environmental issues involved. Present disposal designs and concepts are analyzed on a scientific basis and modifications to existing designs are proposed from the perspective of environmental safety. A new concept of a chemical heat sink is introduced for the removal of heat emitted due to radioactive decay in the spent nuclear fuel or high-level radioactive waste, and thermal spikes produced by radiation in containment materials. Mainly, UO2 and metallic U are used as fuels in nuclear reactors. Spent nuclear fuel contains fission products and transuranium elements which would remain radioactive for 104 to 108years. Essential concepts and engineering strategies for spent nuclear fuel disposal are described. Conceptual designs are described and discussed considering the long-term radiation and thermal activity of spent nuclear fuel. Notions of physical and chemical barriers to contain nuclear waste are highlighted. A timeframe for nuclear waste disposal is proposed and time-line nuclear waste disposal plan or policy is described and discussed.

Disposal of high-level radioactive waste in crystalline rock: On coupled processes and site development

Safe disposal of high-level radioactive nuclear waste(HLW)is crucial for human health and the environment,as well as for sustainable development.Deep geological disposal in sparsely fractured crystalline rock is considered one of the most favorable methods for final disposal of HLW.Extensive research has been conducted worldwide and many countries have initiated their own national development programs for deep geological disposal.Significant advancements of national programs for deep geological disposal of HLW in crystalline rock have been achieved in Sweden and Finland,which are currently under site development stage,focusing on detailed site characterization,repository construction,and post-closure safety analysis.Continued research and development remain important in the site development stage to ensure long-term safety of the HLW disposal repository.This work presents an overview and discussion of the progress as well as remaining open scientific issues and possibilities related to site development for safe disposal of HLW in crystalline rock.We emphasize that developing a comprehensive and convergent understanding of the coupled thermal,hydraulic,mechanical,chemical and biological(THMCB)processes in fractured crystalline rock remains the most important yet challenging topic for future studies towards safe disposal of HLW in crystalline rock.Advancements in laboratory facilities/techniques and computational models,as well as available comprehensive field data from site developments,provide new opportunities to enhance our understanding of the coupled processes and thereby repository design for safe geological disposal of HLW in crystalline rock.

Numerical analysis of thermo-hydromechanical process related to deep geological radioactive repository

This paper addresses numerical analysis of thermo-hydromechanical processes in the context of deep geological disposal of radioactive waste.The emphasis is put on modeling of damaged zones induced by excavation,pore pressure and temperature changes.The theoretical background of thermo-poroelasticity for saturated porous media is first recalled.The framework for modeling initiation and evolution of induced cracks is then presented by using a variational approach of phase-field method.A specific model with two crack phase fields and considering thermo-hydromechanical interaction is proposed.A particular attention is paid on the description of shear cracks.The proposed model is implemented in the standard finite element method.An example of application is finally presented on the analysis of thermo-hydromechanical responses and cracked zones evolution around a typical disposal repository in the context of French concept for high level waste disposal.

Current status of the geological disposal programme and an overview of the safety case at the pre-siting stage in Japan

In Japan,high-level radioactive waste and specific low-level radioactive waste which includes long-lived radionuclides are planned to be disposed of in the geological formations at depths greater than 300 m.The disposal site will be selected through a stepwise site investigation process that consists of a Literature Survey,Preliminary Investigation,and Detailed Investigation phases.In October 2020 a Literature Survey was launched in Japan at two municipalities in Hokkaido for the first time since NUMO initiated a nationwide call for volunteer municipalities in 2002,and the outcomes are currently being compiled.To enhance the public’s understanding of how to implement safe geological disposal in Japan based on the latest scientific knowledge and technology,NUMO,as the implementing organisation,developed and published a safety case for geological disposal at the pre-siting stage.This safety case provides multiple lines of arguments and evidence to demonstrate the feasibility of the geological disposal and a basic structure for a safety case that will be applicable to any potential sites in Japan.The safety case also presented some R&D challenges to enhance the technical confidence of the project,including the R&D topics related to rock mechanics.This report presents the current status of the geological disposal programme in Japan,together with the status of the Literature Survey phase and an overview of the NUMO safety case.

围压和裂隙倾角对花岗岩力学行为的影响研究

含裂隙围岩的力学行为对高放废物地质处置库的长期稳定和安全至关重要。为研究围压和裂隙倾角对花岗岩围岩力学行为的影响,以完整花岗岩和含不同倾角贯通单裂隙的花岗岩为研究对象,开展了单轴压缩和三轴压缩试验研究。结果表明:0~10 MPa围压范围内,倾角30°和60°裂隙花岗岩分别发生了穿裂隙面破坏和沿裂隙面滑移破坏;随围压升高,倾角45°裂隙花岗岩由复合破坏转变为穿裂隙面破坏,后又在10 MPa围压条件下再次转变为倾斜“Z”字型裂纹的复合破坏。围压的存在制约了预制裂隙面的劣化作用。三轴压缩条件下低倾角裂隙花岗岩的抗压强度及变形发展曲线与完整花岗岩的结果相近,试样峰值破坏时的轴向应变在围压0,2,5,10MPa条件下分别约为0.38%,0.49%,0.59%和0.75%。沿裂隙面滑移破坏试样的抗压强度以及峰值破坏时的轴向应变均显著低于穿裂隙面破坏试样的相关结果,且其抗压强度与试验前后裂隙面的分形维数差值符合幂函数增长关系。

高放废物处置地下实验室现场试验数据管理顶层设计

我国高放废物地质处置研发已经进入地下实验室建设的关键阶段。在地下实验室建设和运行期间,将开展大量现场试验,这些试验数据具有传输距离长、采集周期长、数据类型多和数据量大等特点,同时数据质量、安全与可追溯性要求高,数据管理难度较大。通过分析我国高放废物地质处置北山地下实验室现场试验数据特点,以iS3智慧数据服务系统为基础,提出现场试验数据管理顶层设计方法,为现场试验和科研工作顺利开展提供重要的数据管理支撑。

我国高放废物地质处置新突破

2019年5月6日,国家原子能机构批复了我国高放废物地质处置地下实验室建设工程立项建议书。2021年6月17日,地下实验室工程正式开工建设,标志着我国高放废物地质处置进入一个新的阶段——地下实验室阶段,实现了新的突破。本文介绍近五年(2019-2024)来我国高放废物地质处置在法律法规、技术标准、场址评价、缓冲材料、工程技术、岩石力学、放射性核素迁移和安全评价等方面取得的新进展,重点介绍北山地下实验室工程建设及研究开发的新进展。

高放废物地质处置中核素迁移研究进展

核技术在工业、农业、医学等领域有广泛应用,但也产生了大量放射性废物,其中高放废物含有大量放射性强、毒性大、半衰期长和释热量大的核素,对自然环境和人类健康构成了巨大的威胁,其安全处置一直是放射性废物管理中的重点难点问题,受到国际社会的广泛关注。目前,深地质处置被认为是高放废物处理处置最有效可行的方法,而地质屏障中放射性核素迁移研究是高放废物地质处置安全评价的关键课题之一。本文首先对高放废物地质处置及核素迁移研究进行概述,然后论述了核素迁移数值模拟研究的关键技术(包括物理模型以及数学模型),最后分析了数值模拟在不同核素迁移研究中的应用进展。通过综合分析可知,目前核素迁移研究还存在以下主要问题:1)核素迁移的机理和规律尚不完全清楚,需要更多的基础研究和数据支撑;2)核素迁移的实验技术和设备还有待改进,需要更高的精度和灵敏度;3)核素迁移的数值模拟还存在不确定性和误差,需要进行更有效的验证和优化。未来的研究方向主要包括:1)加强核素迁移的理论研究,揭示核素在复杂条件下的迁移行为及其控制机制;2)发展核素迁移的实验技术,提高实验数据的质量和可信度;3)创新核素迁移的数值模拟方法,增强模型的适应性和预测能力;4)完善核素迁移的安全评价体系,建立更合理的评价指标和方法。

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。