The seven-year research project entitled “Development of workflow for integrated 3D geological site descriptive modeling” is being carried out from 2023. This research is funded by Ministry of Trade, Industry, and Energy (MOTIE). Progress of the research is discussed here. The integrated 3D geological SDM (site descriptive model; GSDM hereafter) consists of three part; 1) three dimensional representation of geologic elements, 2) database for material properties and modeling results from SDMs of other disciplines (e.g., rock mechanics), and 3) a visualization tool for geology, material properties and modeling results. The GSDM is comparable to the GDSMs of SKB and POSIVA in its representation of geology by volume of geologic elements. However, our GSDM is different in that extra information of material properties and an extra tool for visualization is included in the GDSM. The rationale for incorporating material properties and a visualization tool into the GSDM is to expedite the development of the GSDM and SDMs of other disciplines by allowing single institution to integrate database and visualization with the GSDM. SKUA-GOCAD is used for representation of geologic surfaces for ductile and brittle shear zones, and also for surfaces for delineation of volumes of rock units. We have adopted SKUAGOCAD because the program offers powerful functions of interpolation including borehole data and geophysical prospecting. So far, we have tested the program for five different geologies, including sedimentary, high-grade metamorphic, and intrusive igneous geology. The test results are promising. Incorporation of data and modeling results for the SDMs of other disciplines is at conceptual stage. The working conceptual model involves the following steps, 1) to provide the modeler of other disciplines with surface information representing geologic elements, 2) the modeler returns not only material properties but the results of numerical analysis, and 3) incorporation of material properties and modeling results into database. Since the numerical codes in other disciplines adopt different types of formats for 3D geology, we plan to adopt the widely used FEM format prepared by Gmsh. The visualization tool will also adopt Gmsh for graphical representation of 3D geology as well as database for material properties and modeling results. When the working model of GSDM becomes available, rapid and significant progress is expected in the SDMs of other disciplines and related areas, for example, geotechnical investigation for deep geological repository.

In Korea, research on the development of safety case, including the safety assessment of disposal facility for the spent nuclear fuel, is being conducted for long-term management planning. The safety assessment procedure on disposal facility for the spent nuclear fuel heavily involves creating scenarios in which radioactive materials from the repository reach the human biosphere by combining Features, Events and Processes (FEP) that describe processes or events occurring around the disposal area. Meanwhile, the general guidelines provided by the IAEA or top-tier regulatory requirements addressed by each country do not mention detailed methods of ‘how to develop scenarios by combining individual FEPs’. For this reason, the overall frameworks of developing scenarios are almost similar, but their details are quite different depending on situation. Therefore, in order to follow up and clearly analyze the methods of how to develop scenarios, it is necessary to understand and compare case studies performed by each institution. In the previous companion paper entitled ‘Research Status and Trends’, the characteristics and advantages/disadvantages of representative scenario development methods were described. In this paper, which is a next series of the companion papers, we investigate and review with a focus on details of scenario development methods officially documented. In particular, we summarize some cases for the most commonly utilized methods, which are categorized as the ‘systematic method’, and this method is addressed by Process Influence Diagram (PID) and Rock Engineering System (RES). The lessons-learned and insight of these approaches can be used to develop the scenarios for enhanced Korean disposal facility for the spent nuclear fuel in the future.

Identifying plausible scenarios is necessary to evaluate the performance of the repository reliably over a very long period. All features, events, and processes (FEPs) expected in the repository should be comprehensively well-defined and structured into scenarios based on the relation analysis. A platform for the FEP DB management and relation analysis is needed to facilitate the efficient composition of the scenarios. For this purpose, the CYPRUS program was developed, but abandoned due to suspended FEPs and scenario research. Thus, it became necessary to build a new easy-tomaintain platform that inherits the legacy of CYPRUS and reflects the latest research. The data structure and user interface configuration were derived to develop a new platform. The new platform provides extensive data such as the assessment context, the FEP DB, the interaction between FEP contents, the relevance to other project FEPs, the influence on performance, the scenarios for the TSPA, the AMF, and the PA Data. The platform displays the long-term evolution FEPs developed by KAERI, the international and major project FEPs in table format. The correlation between FEP items is composed of a detailed interaction matrix and visualized as the chord diagram or arc diagram. The relevance and linkages between the project FEP items are mapped and presented in the form of network diagrams and network tables. The platform designed in this study will be used to manage the FEP DB, analyze and visualize the relationship between the FEP and scenarios, and finally construct the performance assessment scenarios. It is expected that the platform itself will be used as a part of the knowledge management system and facilitate efficient collaboration and knowledge exchange among experts.

Since July 2021, the Korea Radioactive Waste Agency has been conducting a safety case development study for the Korean deep geological repository program. The safety case includes generating scenarios in which radioactive materials from spent nuclear fuel repository reach the human biosphere by combining selective FEPs (Features, Events, and Processes). This safety case should be able to transparently explain the process in which conclusions have been drawn not only to stakeholders but also to the public by presenting safety arguments. The scenario development stage consisting of FEP screening, scenario generation, and uncertainty analysis procedures should have a database management system. Database management system was performed in countries such as Sweden, which obtained approval for the construction of spent nuclear fuel repositories, and the United States, where various preliminary research was carried out. Korea Atomic Energy Research Institute also has experience in designing and operating its own database, which has conducted preliminary research on disposal of the spent nuclear fuel. Currently, the safety assessment of the Korean spent nuclear fuel repository is in the early stages of research, but it is necessary to set up a basic framework for database design while the collection of FEP data from domestic and international preliminary studies is under development, and it is advantageous for efficient database construction and operation. Therefore, this paper presents the current status of database design considering completeness and transparency from the FEP screening stage to the scenario development stage in the safety assessment process of the Korean spent nuclear fuel repository. In this process, the functional requirements that the database should provide, the database schema capable of implementing them, and simple examples are presented together. The objectives of this database design are flexible FEPs management, high integrity and consistency, and expandability for linking with the safety case database. The FEP data to be inputted into the database includes a list of major opened FEPs, including International FEPs from Nuclear Energy Agency, which were referred for PFEPs (Project-specific FEPs), and PFEPs applied to POSIVA's Olkiluoto repository. As an additional function, queries from the database are used to visually express the process of deriving scenarios through Rock Engineering System, a widely known scenario generation methodology.

사용후핵연료 심지층처분장 부지선정과 최종 처분장부지의 처분적합성을 평가하는 업무는 시행-착오 를 줄이고 기술적 신뢰성 확보와 합리적이고 효율적인 업무수행을 추구하여야 한다. 이에 선행하여, 우리 나라에 적용 가능한 처분장부지의 지질환경 요건 설정을 위한 기본방향과 개별 인자의 처분적합성지표를 가능한 한 정량화하여 설정하고 업무에 적용하여야 한다. 사용후핵연료 처분장부지 선정과 최종처분장 부지의 안전성확보를 위한 처분요건과 관련하여 IAEA 및 OECD 회원국들과 처분연구 및 상용사업 수행 관련 선진국가들의 사례를 바탕으로 요건 별로 구분하여 현황을 분석하였다. 여기서는 사용후핵연료 처 분장 부지로서 암석·암반이 갖추어야 할 충분 혹은 선호요건에 대한 이해 제고와 관련 세부 기술지침을 도출하는데 기여하고자 하였다. 이를 토대로 어떠한 암석·암반이 상대적으로 보다 유리한 조건을 가지 는 선호요건으로 제시해야 하는지, 그리고 충분요건과 선호요건을 적용하여 후보부지 조사·선별평가 기 간 동안 부지선정업무에 반영하고 평가하고 결정하여야 하는 방법론을 도출할 수 있도록 기본 골격을 제 시하였다. 또한 처분안전성 확보를 위해 필요한 기본적인 사항을 검토하고 서술하였다. 본 논문에서 기술 한 항목들은 처분안전성 확보를 위한 처분요건의 기술지침 구성 체계, 처분안전성 확보개념, 다중방벽 기 능 조건, 천연방벽의 지질환경 기본요건, 그리고 우리나라에 적용 가능한 처분장부지 지질환경 기본요건 (안) 등으로 구성된다. 우리나라의 사용후핵연료 심지층처분장 부지의 위치에 관한 사업자 기술지침 요건 으로 제안하였다. 이와 관련하여 충분요건과 선호요건으로, 화산활동, 지진활동, 단층운동 융기·침강 운 동 및 기후·해수면변동 등 장기지질안정성 요건을 비롯한 15개 충분요건과 48개 선호요건을 제안하였 다. 이들 요건은 우리나라의 지질환경 특성을 충분히 반영하여 후속되는 각 부문별 특성에 적합한 정량적 인 기술 기준 및 지침으로 개발되어야 할 것이다. 정량적 기술지침의 도출은 상용 처분장부지 선별평가과 정 및 처분장 부지적합성평가 과정으로부터 확립될 수 있을 것이다. 또한 다양한 부문별 안전사례(safety case) 작성 혹은 연구용 지하처분연구시설 (underground research laboratory: URL)을 이용한 처분시스 템의 실증과정 등을 통하여 객관적이고 신뢰성있는 정량적인 지침들이 확립될 수 있을 것이다.