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.

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.

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.

高放废物处置预选区地学信息数据模型构建

针对高放废物地质处置选址与场址评价阶段的信息化建设工作,采用GIS技术、数据管理技术、数据分析技术等,旨在基于地学信息数据模型的构建,建立统一的、一体化的、高度综合的高放废物地质处置预选区地学信息库,以覆盖地质、水文地质、地球物理、地球化学等多学科研究内容。着重讨论了预选区地学信息数据模型建设的方法和技术,并通过预选区地学信息库的工程实例说明了数据模型的成功应用。预选区地学信息数据模型的建设可以为场址筛选、场址性能评价等研究工作提供技术支持,对高放废物地质处置研发工作的推进也将起到积极作用。

Influence of Heating and Water Exposure on Liquid Limit of Bentonite

Bentonite has been considered as the buffer material for embedding canisters with high-level radioactive waste(HLW)in the deep geology repositories. GMZ bentonite deposit which is located in Xinghe County,Inner Mongolia has been proposed as buffer/backfill material for HLW repository in China. Liquid limit of natural Na-bentonite GMZ01 and commercial Na-bentonite MX80 which were previously put in the oven at 80℃and 95℃,and exposed to water for different times were measured.The liquid limit of GMZ01 increased slightly at the beginning, and then decreased as the heating time increased.

Influence of heating and water-exposure on the liquid limits of GMZ01 and MX80 bentonites

Bentonite has been considered as a buffer material for embedding canisters with high-level radioactive waste（HLW） in deep geological repositories.GMZ bentonite deposit,located in Xinghe County,Inner Mongolia Autonomous Region,China was proposed as a buffer/backfill material for HLW repository in China.The liquid limits of natural Na-bentonite GMZ01 and commercial Na-bentonite MX80,which are previously heated at 80 ℃ and 95 ℃,respectively,and exposed to water for different times are measured.It is observed that the liquid limit of GMZ01 increases slightly at the beginning,and then decreases as the heating time increases,while the liquid limit of MX80 decreases with the heating time.The liquid limits of both GMZ01 and MX80 decrease with increasing water-exposure time.After the samples are heated at 80℃and 95 ℃ for several months,the mineralogical composition of GMZ01 does not exhibit evident change,whereas MX80 experiences some changes.In addition,the chemical composition,cation exchange capacity（CEC） and exchangeable cation of all the samples do not change significantly.

Experimental Studies on Penetration of Pulverized Clay-Based Grout

For the geological disposal of high level radioactive wastes, an excavation damaged zone （EDZ） having high hydraulic conductivity resulting from the development of fractures in the rock adjacent to the tunnels will be one of the potential pathways for radioactive contaminant transport. The potential pathways will be sealed by closure components, that is, a combination of tunnel plug, backfill and grout, the latter material being a clay-based mixture in consideration of the need for long-term stability of the seals. Clay-based grout is one of the effective candidate materials that can be used to interrupt the migration of radionuclides through an EDZ. Laboratory testing of clay-based grout using pulverized bentonite, with the objective of improvement in grout penetration into a rockmass, was conducted. The results showed that the pulverization of clay-based grout had a positive effect on filtration.