Study on the evaluation method of radioactivity for dismantling wastes generated from test and research reactors using ORIGEN attached to SCALE6.2.4

Tomioka, Dai; Kochiyama, Mami; Ozone, Kenji; Nakata, Hisakazu; Sakai, Akihiro

JAEA-Technology 2024-023, 38 Pages, 2025/03

JAEA-Technology-2024-023.pdf:1.54MB

Japan Atomic Energy Agency is an implementing organization of near-surface disposal for low-level radioactive wastes generated from research, industrial and medical facilities in Japan. Information on the radioactivity concentration of these radioactive wastes is dispensable for the design and conformity assessment of the waste disposal facilities for the licensing application of the disposal project and its safety review. Radioactive Wastes Disposal Center has been improving the radioactivity evaluation procedure for the dismantling waste generated from the research reactors based on the activation calculation. In order to investigate the applicability of the ORIGEN code (included in SCALE6.2.4), which enables more accurate activation calculations using multigroup neutron spectra, we performed activation calculations with the ORIGEN-code and the ORIGEN-S code (included in SCALE6.0), which has been widely used in the past, for the dismantled wastes from the Rikkyo University Research Reactor, where radioactivity analysis data for the structural materials around the reactor core were compiled. As a result, the calculation time difference between ORIGEN and ORIGEN-S was small and the evaluated radioactivity concentrations of the former were in the range of 0.8-1.0 times those of the latter, which was in good agreement with those of radiochemical analysis in the range of 0.5-3.0 times. The applicability of ORIGEN was confirmed. In addition, activation calculations assuming trace elements in structural materials of nuclear reactor were performed with ORIGEN and ORIGEN-S and the results were compared. The causes of the large differences among 170 nuclides that are important for dose assessment in near-surface disposal were assessed each nuclide.

Evolution of radionuclide transport and retardation processes in uplifting granitic rocks, Part 2; Modelling coupled processes in uplift scenarios

Metcalfe, R.*; Benbow, S. J.*; Kawama, Daisuke*; Tachi, Yukio

Science of the Total Environment, 958, p.177690_1 - 177690_17, 2025/01

https://doi.org/10.1016/j.scitotenv.2024.177690

Uplifting fractured granitic rocks occur in substantial areas of countries such as Japan. A repository site would be selected in such an area only if it is possible to make a safety case, accounting for the changing conditions during uplift. The safety case must include robust arguments that chemical processes in the rocks around the repository will contribute sufficiently to minimise radiological doses to biosphere receptors. To provide confidence in the safety arguments, numerical models need to be sufficiently realistic, but also parameterised conservatively (pessimistically). However, model development is challenging because uplift involves many complex couplings between groundwater flow, chemical reactions between water and rock, and changing rock properties. The couplings would affect radionuclide mobilisation and retardation, by influencing diffusive radionuclide fluxes between groundwater flowing in fractures and effectively immobile porewater in the rock matrix and radionuclide partitioning between water and solid phases, via: (i) mineral precipitation/dissolution; (ii) mineral alteration; and (iii) sorption/desorption. It is difficult to represent all this complexity in numerical models while showing that they are parameterised conservatively. Here we present a modelling approach, illustrated by simulation cases for some exemplar radioelements, to identify realistically conservative process conceptualisations and model parameterisations.

Evolution of radionuclide transport and retardation processes in uplifting granitic rocks, Part 1; Key processes, conceptual models and scenario

Metcalfe, R.*; Tachi, Yukio; Sasao, Eiji; Kawama, Daisuke*

Science of the Total Environment, 957, p.177375_1 - 177375_17, 2024/12

https://doi.org/10.1016/j.scitotenv.2024.177375

A safety case for an underground radioactive waste repository must show that groundwater will not in future transport radionuclides from the repository to the near-surface environment (the biosphere) in harmful quantities. Safety cases are developed step-wise throughout a programme to site and develop a repository. At early stages, before a site is selected, safety cases are generic and based on simplified safety assessment models of the disposal system that have conservative parameter values. Later, when site-specific conditions are known, more realistic models are needed for the long-term geo-environmental evolution and their impacts on radionuclide migration/retention. Uplift is one such environmental change, which may be particularly important in countries near active tectonic plate boundaries, such as Japan. Here we review the state of knowledge about how the properties of fractured granitic rocks evolve during uplift, based on studies in Japan. Hence, we present conceptual models and a generic scenario for mass transport and retardation processes in uplifting granitic rocks as a basis for realistic numerical models to underpin safety assessment.

Horonobe Underground Research Laboratory Project; Investigation program for the fiscal year 2024

Nakayama, Masashi

JAEA-Review 2024-033, 64 Pages, 2024/09

JAEA-Review-2024-033.pdf:5.15MB

The Horonobe Underground Research Laboratory Project is being pursued by the Japan Atomic Energy Agency to enhance the reliability of relevant technologies for geological disposal of high-level radioactive waste through investigating the deep geological environment within the host sedimentary rocks at Horonobe Town in Hokkaido, north Japan. In the fiscal year 2024, we continue R&D on "Study on near-field system performance in geological environment", "Demonstration of repository design options", and "Understanding of buffering behaviour of sedimentary rocks to natural perturbations". These are identified as key R&D challenges to be tackled in the Horonobe underground research plan for the fiscal year 2020 onwards. In the "Study on near-field system performance in geological environment", we continue to obtain data from the full-scale engineered barrier system performance experiment, and work on the specifics of the full-scale engineered barrier system dismantling experiment. We summarise the solute transport experiments for the excavation damaged zone and the effects of organic matter, micro-organisms and colloids, and develop the assessment methodology. We summarise the evaluation methodology using the deep Wakkanai Formation as a case study for block-scale solute transport experiments. As for "Demonstration of repository design options", we summarise the results of investigations and experiments on changes in the geological environment after tunnel excavation and closure, and summarise the applicability and technical challenges of the closure technology for boreholes excavated from tunnels. The systematic integration of technologies towards EBS emplacement, including the organisation of investigation and evaluation methods and analysis, will be promoted. Experiments to confirm the performance of the engineered barrier system under critical conditions, such as high temperatures (100C), continue the in-situ tests started in 2023.

Trial analysis of chemical behavior in high-level radioactive liquid waste tank at accident of evaporation to dryness by boiling of reprocessing plant

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

JAEA-Research 2024-007, 24 Pages, 2024/08

JAEA-Research-2024-007.pdf:2.1MB

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 (Ru) 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. It has been observed experimentally that volatility of RuO is suppressed by HNO generated by HNO radiolysis. The analysis of chemical reactions of NO including HNO and HNO in the waste tank is essential to simulate of these phenomena. To resolve this issue, an analytical approach has been attempted to couple dynamically two computer codes SHAWED and SCHERN. The simulation of boiling behavior in the tank is conducted with SHAWED. SCHERN simulates chemical behaviors of HNO, HNO and NO in the tank. A programmatic coupling algorithm and a trial simulation of the accident are presented in this report.

Investigation of adsorption mechanism of Mo(VI) by baker's yeast and applicability to the uranium liquid waste treatment process

Arai, Yoichi; Hasegawa, Kenta; Watanabe, So; Watanabe, Masayuki; Minowa, Kazuki*; Matsuura, Haruaki*; Hagura, Naoto*; Katsuki, Kenta*; Arai, Tsuyoshi*; Konishi, Yasuhiro*

Journal of Radioanalytical and Nuclear Chemistry, 333(7), p.3585 - 3593, 2024/07

https://doi.org/10.1007/s10967-023-09278-5

Replacement of incinerator adopted to Plutonium Waste Treatment Facility

Yamashita, Kiyoto; Maki, Shota; Yokosuka, Kazuhiro; Fukui, Masahiro; Iemura, Keisuke

JAEA-Technology 2023-023, 97 Pages, 2024/03

JAEA-Technology-2023-023.pdf:8.21MB

The incinerator adopted to incineration room, Plutonium Waste Treatment Facility had been demonstrated since 2002 for developing technologies to reduce the volume of fire-resistant wastes such as vinyl chloride (represented by Polyvinyl chloride bags) and rubber gloves for Radio Isotope among radioactive solid wastes generated by the production of mixed oxide fuels. The incinerator, cooling tower, and processing pipes were replaced with a suspension period from 2018 to 2022, which fireproof materials on the inner wall of the incinerator was cracked and grown caused by hydrogen chloride generated when disposing of fire-resistant wastes. This facility consists of the waste feed process, the incineration process, the waste gas treatment process, and the ash removal process. We replaced the cooling tower in the waste gas treatment process from March 2020 to March 2021, and the incinerator in the incineration process from January 2021 to February 2022. In addition, samples were collected from the incinerator and the cooling tower during the removing and dismantling of the replaced devices, observed by Scanning Electron Microscope and X-ray microanalyzer, and analyzed by X-ray diffraction to investigate the corrosion and deterioration of them. This report describes the method of setting up the green house, the procedure for replacing them, and the results from analysis in corrosion and deterioration of the cooling tower and incinerator.

Progress status and future issues of development of analysis and estimation technology for fuel debris characterization, 5; Progress status of development of Non-Destructive assay technologies for sorting and segregation of fuel debris and others

Kamada, Masaki*; Yoshida, Takuma*; Sugita, Tsukasa*; Okumura, Keisuke

Nihon Genshiryoku Gakkai-Shi ATOMO, 66(2), p.83 - 86, 2024/02

https://doi.org/10.3327/jaesjb.66.2_83

no abstracts in English

Horonobe Underground Research Laboratory Project; Investigation program for the 2023 fiscal year

Nakayama, Masashi

JAEA-Review 2023-019, 70 Pages, 2023/11

JAEA-Review-2023-019.pdf:6.83MB

The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of relevant technologies for geological disposal of high-level radioactive waste through investigating the deep geological environment within the host sedimentary rocks at Horonobe Town in Hokkaido, north Japan. In the fiscal year 2023, we continue R&D on "Study on near-field system performance in geological environment", "Demonstration of repository design options", and "Understanding of buffering behaviour of sedimentary rocks to natural perturbations". These are identified as key R&D challenges to be tackled in the Horonobe underground research plan for the fiscal year 2020 onwards. In the "Study on near-field system performance in geological environment", we conduct the coupled analysis on the full-scale engineered barrier system performance experiment and test the coupled simulation code through comparison with different simulation codes in the international DECOVALEX-2023 collaboration project. Borehole investigations are also carried out for solute transport experiments in the Koetoi Formation. As for "Demonstration of repository design concept", we carry out in situ experiments and data analysis on concrete deterioration under the subsurface conditions. Geophysical surveys are also carried out around an experimental tunnel to be newly excavated at the 350m gallery and characterise the initial conditions of the excavation damaged zone. For the "Understanding of buffering behaviour of sedimentary rocks to natural perturbations", we analyse the results of the hydraulic disturbance tests conducted in previous years and understand the relationship between rock stress / stress state and fault / fracture hydraulic connectivity. Concerning the construction and maintenance of the subsurface facilities, the 350 m gallery is extended and shafts are sank to a depth of 500 m.

Public acceptance of nuclear waste disposal sites; A Decision-making process utilising the "veil of ignorance" concept

Yokoyama, Miki*; Onuma, Susumu*; Osawa, Hideaki; Otomo, Shoji*; Hirose, Yukio*

Humanities & Social Sciences Communications (Internet), 10(1), p.623_1 - 623_10, 2023/09

https://doi.org/10.1057/s41599-023-02139-2

This study demonstrates that a decision-making process utilising "the veil of ignorance" concept, defined in process terms as beginning from a blank slate encompassing the entire country as potential sites and shortlisting candidate sites based on scientific (geological) safety, promotes public acceptance of siting a repository for the geological disposal of high-level radioactive waste and fosters procedural fairness.