A design-centered review of in-situ tracer tests for HLW repositories: an overview of radioactive tracer cases, comparison with non-radioactive tracers, and a Korea-tailored strategy

This review is organized around a design-centered framework that links experimental objectives to design premises, test configurations, tracer selection, and interpretation strategies. On this basis, a strategy tailored to the Korean context is proposed. The contents are as follows: (1) An overview of in-situ tracer tests is presented, including testing methodologies, design strategies, and prerequisites to ensure the reliability of safety assessments. (2) The classification criteria for tracers and the significance of radioactive tracer use are clarified. Tracers are categorized according to sorption properties and quantification methods, and the advantages of radioactive tracers—in terms of feasibility, cost-effectiveness, and improved reliability of safety assessments—are described. (3) Case studies of in-situ radioactive tracer injections conducted in Sweden (two sites), Switzerland, Finland, and Belgium (one site each) are introduced and compared with non-radioactive tracer cases to characterize the comparative advantages of radioactive tracers. (4) The results of non-radioactive in-situ tracer tests in Korea are reviewed. Considering the utility of radioactive tracers alongside the social climate in Korea—where in-situ injection of radioactive materials is virtually impossible—a strategic direction based on a dual approach is proposed, combining in-situ non-radioactive field tests with laboratory radioactive tracer experiments as the most feasible pathway.