Evaluation of the flow rate of leachate from near surface waste disposal facilities of radioactive wastes from research, industrial and medical facilities based on the latest knowledge

Kitatani, Hikari; Ozone, Kenji; Nakata, Hisakazu

JAEA-Technology 2025-011, 57 Pages, 2025/12

JAEA-Technology-2025-011.pdf:5.32MB

Japan Atomic Energy Agency is responsible for near-surface disposal of research-related low-level radioactive waste and is considering two types of facilities: trench and concrete-pit. In safety assessment of such facilities, dose evaluation requires data on infiltration water. Evaluating infiltration involves uncertainties due to waste conditions and disposal environment. Therefore, in this report, a reference model was established based on the conceptual design conditions of near-surface disposal facilities, and leachate from the facilities was estimated by groundwater flow analysis, using applications by prior operators as reference and reflecting the latest knowledge for safety assessment. This allowed evaluation of how the hydraulic conductivity of each facility layer and surrounding soil affects leachate. Specifically, the 2D FEM groundwater flow code MIG2DF was used: trench facilities were evaluated assuming cover degradation, and concrete-pit facilities assuming salt effects in waste packages. Results showed that in trench facilities, deterioration of clay hydraulic conductivity increased inflow to the waste layer, especially when drainage layer conductivity decreased, as horizontal flow paths failed and infiltration into clay was promoted. In concrete-pit facilities, clay fracturing increased local flow and water through the waste layer. These results quantitatively demonstrate how changes in hydraulic conductivity of each layer affect leachate, providing useful insights for scenario development in safety assessment and for facility management.

Design and characterisation of different characteristics of metakaolin-based geopolymer for fuel debris removal (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Hokkaido University*

JAEA-Review 2025-041, 79 Pages, 2025/12

JAEA-Review-2025-041.pdf:9.8MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2023. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2023, this report summarizes the research results of the "Design and characterisation of different characteristics of metakaolin-based geopolymer for fuel debris removal" conducted in FY2023. This study aims to demonstrate the potential of metakaolin-based geopolymer, which has high fluidity and confinement performance, and incorporates neutron absorption capability through boron addition, for the stabilization and solidification of radioactive waste from fuel debris and contaminated water treatment. In this year, the research focused on the design and evaluation of metakaolin geopolymer with and without boron, the interaction between metakaolin-based geopolymer and Fe2O3 colloids, the characterization of geopolymer, and the property evaluation of simulated waste solidification samples. The influence of metakaolin's particle size and firing temperature on its leaching rate, and fluidity, hardening properties of geopolymer was investigated in detail. Additionally, the effects of boron addition in alkaline solution properties and extended hardening time were confirmed. In the interaction with colloids, the confinement of colloids and dimensional changes within the geopolymer were evaluated. Furthermore, solidification samples with simulated waste were prepared, and viscosity changes during the curing process were measured. Hardening time and temperature changes during curing were measured. Compression strength measurements and -ray irradiation tests were also conducted, and through the measurement of hydrogen generation, important basic data on the properties of the solidified bodies were obtained. In research promotion, collaboration with Hokkaido University, JAEA, Sobueclay Co. Ltd., and the University of Sheffield was strengthened through regular meetings and data sharing, and plans for the following years were finalized. Additionally, a human resource development program was launched.

Improvement of the RuO vapor-liquid transfer model in the chemical behavior analysis code SCHERN for accident of evaporation to dryness by boiling of reprocessed high level liquid waste

Yoshida, Kazuo; Hiyama, Mina*; Tamaki, Hitoshi

JAEA-Research 2025-011, 25 Pages, 2025/11

JAEA-Research-2025-011.pdf:2.15MB

An accident of evaporation to dryness by boiling of high-level radioactive liquid waste (HLLW) is postulated as one of the severe accidents caused by the loss of cooling function at a fuel reprocessing plant. In this case, volatile radioactive materials, such as ruthenium (RuO) are released from the tanks with water and nitric-acid mixed vapor into the atmosphere. Accurate quantitative estimation of released Ru is one of the important issues for risk assessment of those facilities. RuO is expected to be absorbed chemically into water dissolving nitrous acid (HNO). This behavior has been experimentally confirmed and plays an important role in the migration of Ru in the facility. A new model has been proposed as a chemical and physical absorption model based on the experimental results of the migration of RuO into nitric acid-water mixtures. In this study, to improve the analytical performance of SCHERN, these new analytical models have been incorporated and attempted to analyze the behavior of RuO in each phase. As a result, it has been observed a tendency that HNO in the liquid phase increases rapidly during the late boiling phase, when RuO release increases rapidly, and confirmed that this HNO concentration change significantly affects the subsequent migration behavior of RuO. These results indicate that it is essential to improve the analytical accuracy of the chemical behavior of HNO in each phase.

Challenge of novel hybrid-waste-solidification of mobile nuclei generated in Fukushima Nuclear Power Station and establishment of rational disposal concept and its safety assessment (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Institute of Science Tokyo*

JAEA-Review 2025-016, 143 Pages, 2025/10

JAEA-Review-2025-016.pdf:10.71MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2023. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station (hereafter referred to "1F"), Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2021, this report summarizes the research results of the "Challenge of novel hybrid-waste-solidification of mobile nuclei generated in Fukushima Nuclear Power Station and establishment of rational disposal concept and its safety assessment" conducted from FY2021 to FY2023. This study aims to establish the rational waste disposal concept of various wastes generated in 1F based on the hybrid-waste-solidification by the Hot Isostatic Press (HIP) method. The ceramics form with target elements, mainly iodine, which is challenging to immobilize, and Minor Actinides such as Am, an alpha emitter and heat source, are HIPed with well-studied materials such as SUS and zircaloy, which make the long-term stability evaluation and safety assessment possible. In 2024, the project's final year, we demonstrated the effectiveness of the hybrid solidification concept by linking all the sub-themes, from waste synthesis to disposal considerations. The compatibility of various wastes, such as ALPS, AREVA sediment wastes, AgI, waste silver adsorbent, ceria adsorbent, and iodine apatite, with metals and oxide matrices was investigated. which involves investigating the HIPed hybrid wastes after exploring the compatibility of various metals and oxide matrices using the rapid sintering method, spark plasma sintering (SPS), proposed in this project. It revealed that hybrid waste solidification with SUS matrix was superior for many wastes. Furthermore, we studied waste disposal concepts based on nuclide migration calculations. Finally, we could connect the waste fabrication to safety assessment for the first time, leading to finding an appropriate waste disposal scenario for 1F decommissioning.

Study on water stopping, repair and stabilization of lower PCV by geopolymer, etc. (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; The University of Tokyo*

JAEA-Review 2025-008, 134 Pages, 2025/09

JAEA-Review-2025-008.pdf:10.0MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2023. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2021, this report summarizes the research results of the "Study on water stopping, repair and stabilization of lower PCV by geopolymer, etc." conducted from FY2021 to FY2023. Since the final year of this proposal was FY2023, the results for 3 fiscal years were summarized. In order to retrieve fuel debris, it is necessary to shut off the water at the bottom of the dry well and repair it in order to control the PCV water level. Therefore, in this study, we evaluated a construction method of stopping the water of the jet deflector with an improved geopolymer and repairing the lower part of the dry well by experiments and simulations. In addition, after understanding the properties of the fuel debris coated with the geopolymer, the long-term life of the waste body was evaluated. As a result, it was predicted that by utilizing geopolymers, it is possible to stop water and repair the lower part of the PCV in consideration of steps from construction to waste management.

Sorption behavior of alpha-ray emitting nuclides on concrete in contact with radioactive contaminated water

Aihara, Haruka; Hinai, Hiroshi; Shibata, Atsuhiro; Tomita, Sayuri*; Koma, Yoshikazu

Progress in Nuclear Science and Technology (Internet), 8, p.324 - 328, 2025/09

https://doi.org/10.15669/pnst.8.324

Pu and Am contained in the contaminated water at Fukushima Daiichi Nuclear Power Station is concerned to contaminate inside the buildings concrete. To understand or estimate the state of contamination, investigation on contamination mechanisms have become quite important. Therefore, the distribution ratio of Pu and Am to cement paste and aggregates was obtained by experiments. Cement paste and aggregate were immersed in Pu and Am solution to obtain distribution ratio. Those of Pu and Am to cement paste was high values, suggesting that they have sorbed and accumulated in the building concrete.

Development of a theoretical scaling factor method for the inventory estimation of difficult-to-measure nuclide Cs-135 in fuel debris and radioactive wastes

Sakamoto, Masahiro; Okumura, Keisuke; Kanno, Ikuo; Matsumura, Taichi; Terashima, Kenichi; Riyana, E. S.; Kaneko, Junichi*; Mizokami, Masato*; Mizokami, Shinya*

Journal of Nuclear Science and Technology, 62(8), p.756 - 765, 2025/08

https://doi.org/10.1080/00223131.2025.2478926

Verification of analytical model of MELCOR code for accident of evaporation to dryness by boiling of reprocessed high level liquid waste

Yoshida, Kazuo; Hiyama, Mina*; Tamaki, Hitoshi

JAEA-Research 2025-003, 24 Pages, 2025/06

JAEA-Research-2025-003.pdf:2.06MB

An accident of evaporation to dryness by boiling of high-level radioactive liquid waste (HLLW) is postulated as one of the severe accidents caused by the loss of cooling function at a fuel reprocessing plant. In this case, volatile radioactive materials, such as ruthenium (RuO) are released from the tanks with water and nitric-acid mixed vapor into the atmosphere. Accurate quantitative estimation of released Ru is one of the important issues for risk assessment of those facilities. RuO is expected to be absorbed chemically into water dissolving nitrous acid. Condensation of mixed vapor plays an important role for Ru transporting behavior in the facility building. The thermal-hydraulic behavior in the facility building is simulated with MELCOR code. The latent heat, which is a governing factor for vapor condensing behavior, has almost same value for nitric acid and water at the temperature range under 120 centigrade. Considering this thermal characteristic, it is assumed that the amount of nitric acid is substituted with mole-equivalent water in MELCOR simulation. Compensating modeling induced deviation by this assumption have been assembled with control function features of MELCOR. The comparison results have been described conducted between original simulation and modified simulation with compensating model in this report. It has been revealed that the total amount of pool water in the facility was as same as both simulations.

DECOVALEX-2023: An International collaboration for advancing the understanding and modeling of coupled thermo-hydro-mechanical-chemical (THMC) processes in geological systems

Birkholzer, J. T.*; Graupner, B. J.*; Harrington, J.*; Jayne, R.*; Kolditz, O.*; Kuhlman, K. L.*; LaForce, T.*; Leone, R. C.*; Mariner, P. E.*; McDermott, C.*; et al.

Geomechanics for Energy and the Environment, 42, p.100685_1 - 100685_17, 2025/06

https://doi.org/10.1016/j.gete.2025.100685

A Review on the effect of iron on bentonite stability

Wilson, J.*; Sasamoto, Hiroshi; Tachi, Yukio; Kawama, Daisuke*

Applied Clay Science, 275, p.107862_1 - 107862_15, 2025/05

https://doi.org/10.1016/j.clay.2025.107862

High-Level Radioactive Waste (HLW) repositories include iron or steel-based containers/overpack and bentonite buffers. Over the last 25 years or so, research efforts have attempted to elucidate the nature of iron-bentonite interactions, especially the potential for the deleterious alteration of the swelling clay component (smectite), to iron-rich layer silicates, some of which lack the capacity for intracrystalline swelling. This could result in a reduction or loss in swelling pressure in the bentonite buffer which is designed to protect waste containers from shear forces and also acts to restrict water and solute transport, as part of an engineered barrier system. Most data on iron-bentonite interactions come from experimental and geochemical modelling studies, as natural analogue data are lacking. The data suggests that there is the potential for the development of an iron-rich bentonite alteration zone with smectite (generally present as the aluminous montmorillonite type) undergoing alteration to iron-rich solids, including layer silicates and steel corrosion products such as green rust or magnetite. The evidence available is complex, arguably incomplete, with many potential complex couplings. Many uncertainties remain despite efforts taken over the last 25 years, but plausible scenarios for iron-bentonite interactions have been identified and possible implications for buffer properties have been suggested.