High-level Waste Disposal System Research Articles

KAERI underground research laboratory: Overview of in-situ experiments

Social concerns regarding the safety of high-level radioactive waste have increased with growing public awareness of environmental issues and nuclear power. The performance assessment of deep geological disposal systems is crucial to reduce the uncertainties associated with high-level radioactive waste disposal and enhance the overall public confidence in nuclear safety. Accordingly, the Korea Atomic Energy Research Institute (KAERI) has undertaken various studies on the development of a deep geological disposal system for high-level waste and disposal safety evaluation. The KAERI Underground Research Tunnel (KURT), South Korea's only underground research laboratory dedicated to radioactive waste disposal, was constructed in 2006 and expanded in 2015. Since its construction, numerous in-situ experiments have been conducted and are currently underway in the KURT. The KURT plays a significant role in assessing the feasibility, safety, stability and appropriateness of a deep geological disposal system in South Korea and also provides an opportunity to revitalize industrial-academic-scientific cooperation between related institutions. This report summarizes two key in-situ experiments and international joint research conducted between 2007 and 2017 to assess the performance of the engineered and natural barriers of the KURT. The research experiences from the in-situ tests conducted at the KURT will provide crucial information on the safety and feasibility validation of the deep geological disposal system and will be an important contributor to the success of the Korean high-level radioactive waste disposal program in the future.

Implementation of In-DEBS (In-situ Demonstration of Engineered Barrier System)

The paper describes the process of developing and implementing In-DEBS (In-situ Demonstration of Engineered Barrier System) for analyzing thermal-hydraulic-mechanical (THM) coupled behavior characteristics of an engineered barrier system in a high-level waste disposal system. The engineered barrier system is composed of a disposal canister, buffer, and near field rock. In-DEBS is designed to analyze the THM coupled behavior due to the inflow of underground water and the heat of disposal canisters in the buffer and near field rock. Since it is difficult to assemble the buffer block while installing sensors and heaters in a disposal hole, the buffer blocks were assembled from the outside. OBPA (One-Body Pre-Assembly) assembled with buffer blocks, sensors and heater requires special transport equipment to accurately insert it into the disposal hole because the total weight is about three tones. In this study, the fully assembled buffer block was inserted by developing a crane exclusively for In-DEBS, which can be moved into an accurate position by lifting more than five tones. To analyze the THM coupled behavior of the near field rock, 4 test holes were cored around In-DEBS and a total of 40 temperature sensors and 5 pore pressure sensors were installed in the test hole. A total of 185 sensors for temperature, relative humidity, pressure and displacement sensors were installed in the In-DEBS. All sensors were connected to a multichannel measuring system that stores field data in real time.

DEVELOPMENT OF GEOLOGICAL DISPOSAL SYSTEMS FOR SPENT FUELS AND HIGH-LEVEL RADIOACTIVE WASTES IN KOREA

Two different kinds of nuclear power plants produce a substantial amount of spent fuel annually in Korea. According to the current projection, it is expected that around 60,000 MtU of spent fuel will be produced from 36 PWR and APR reactors and 4 CANDU reactors by the end of 2089. In 2006, KAERI proposed a conceptual design of a geological disposal system (called KRS, Korean Reference disposal System for spent fuel) for PWR and CANDU spent fuel, as a product of a 4-year research project from 2003 to 2006. The major result of the research was that it was feasible to construct a direct disposal system for 20,000 MtU of PWR spent fuels and 16,000 MtU of CANDU spent fuel in the Korean peninsula. Recently, KAERI and MEST launched a project to develop an advanced fuel cycle based on the pyroprocessing of PWR spent fuel to reduce the amount of HLW and reuse the valuable fissile material in PWR spent fuel. Thus, KAERI has developed a geological disposal system for high-level waste from the pyroprocessing of PWR spent fuel since 2007. However, since no decision was made for the CANDU spent fuel, KAERI improved the disposal density of KRS by introducing several improved concepts for the disposal canister. In this paper, the geological disposal systems developed so far are briefly outlined. The amount and characteristics of spent fuel and HLW, 4 kinds of disposal canisters, the characteristics of a buffer with domestic Ca-bentonite, and the results of a thermal design of deposition holes and disposal tunnels are described. The different disposal systems are compared in terms of their disposal density.

TOUGH2 code를 이용한 처분장 절리암반 내 벤토나이트 완충재의 포화도 변화

This paper briefly introduces the scope and objectives of SKB Task 8, which is an international cooperative research project. In addition, the hydraulic behaviors of bentonite buffer focusing on the interactions between bentonite and a rock mass with a joint were investigated using TOUGH2 code as part of a sub-mission of Task 8a. The effects of a rock joint and high capillary pressure of bentonite on the re-saturation properties and pressure distribution in a buffer were identified and successfully incorporated in the TOUGH2 code. Based on the numerical results, it was found that the speed of re-saturation in bentonite surrounded by a rock mass with a joint is 2.5 to 12 times faster than that in a condition without a rock joint, while the degree of saturation in the lower part of the buffer material is generally higher than in the upper part in both the cases of with and without a joint. It can be anticipated that the results obtained from this study can be applied to an estimation of the full saturation time and a determination of optimum thickness with regard to the design of the bentonite buffer in a high level waste disposal system.