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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.
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.
Nakata, Hisakazu; Izumo, Sari; Okada, Shota; Sakai, Akihiro
JAEA-Technology 2024-010, 65 Pages, 2024/10
JAEA-Technology-2024-010.pdf:5.26MB
Japan Atomic Energy Agency plans to install a trench disposal facility for waste generated from research, industrial and medical facilities. The technical standards for the facility, which are stipulated by the rule of Nuclear Regulation Authority, state that "the waste disposal site shall be filled with soil and sand, etc., so that there will be no voids left after the disposal facility is closed. The voids are those that may impair safety function of the disposal site. Therefore, when storing waste to be buried in a trench disposal facility in a square steel container, it is necessary to take measures to sufficiently reduce the voids inside the container. A method of filling sandy soil to reduce the voids was investigated. Simulated waste was stored in a square steel container and silica sand was gradually filled into the gaps of the stored waste while accelerating and vibrating it using a vibrator. The void ratio was calculated for a variety of vibration condition (19 cases). The result of this sand filling test shows that it is possible to reduce the ratio of voids in the container to about 20% or less by volume, which is the provisional waste acceptance criteria. To reduce the voids in the square steel container, it is necessary to conduct a filling experiment using an actual machine and the square container to be used, to verify the fillability and the vibration condition. This paper summarized the result of filling experiment and illustrated test contents and procedures.
Iwamura, Toko; Nakata, Hisakazu; Maekawa, Keisuke; Sakai, Akihiro; Sakamoto, Yoshiaki
JAEA-Review 2024-032, 39 Pages, 2024/08
JAEA-Review-2024-032.pdf:6.5MB
Japan Atomic Energy Agency (JAEA) is responsible for the disposal of low-level radioactive waste generated by JAEA itself and research facilities under the revised JAEA Act of 2008 and subsequently developed a "Plan for the Implementation of Disposal Operations" (implementation plan) in 2009. Furthermore, based on the results of the survey on the amount of waste generated by research facilities, the quantity of wastes for the near surface disposal was set at 600,000 in terms of 200L drums, and the results of the consideration on the conceptual design of the disposal facility were summarized in 2012. In 2018 JAEA published its long-term outlook and policy regarding back-end measures in "Back-end Roadmap", and in this "Back-end Roadmap", the amount of waste generated by JAEA was also organized and published. Therefore, the amount of waste materials from waste generators outside JAEA was re-examined, and as a result, the size of the burial facility was changed from 600,000 to 750,000 in terms of 200L drums, and approval was obtained for a change in the implementation plan. In addition, the conceptual design of the disposal facility was revised to accommodate the increased size of the facility. This report summarizes the results of the updated assumptions and disposal facility design from the 2012 conceptual design.
Nakata, Hisakazu; Okada, Shota; Amazawa, Hiroya; Sakai, Akihiro
JAEA-Technology 2023-021, 31 Pages, 2024/01
JAEA-Technology-2023-021.pdf:2.53MB
Radioactive waste packages, which Japan Atomic Energy Agency (JAEA) plans to dispose of, must meet the technical criteria specified by the Order of Nuclear Regulation Authority. One criteria is newly specified in 2019 such that it shall be impact resistant performance so as to be few in quantity of radionuclides released from the waste package in case of dropping from the maximum height assumed in the disposal process. Then, JAEA needs to prove the compliance of the waste package with the technical criteria by estimating the leakage of radionuclides. In this report, the amounts of scattering materials inside two waste packages caused by dropping impact from 8m height was estimated by numerical analysis, providing the ratio of the amounts of scattering materials to the weight of the waste package. The analysis objects were 1m
cube container-filled and solidified waste package containing metal waste, which are expected to emplace into a vault-type disposal facility. Some considerations relating to the production method of the waste package using 1m cubic container and its waste acceptance criteria are provided on the basis of the drop analysis in this report.
Nakata, Hisakazu
Genkan Senta Topikkusu, (147), p.4 - 11, 2023/10
no abstracts in English
Ogawa, Rina; Amazawa, Hiroya; Nakata, Hisakazu; Sugaya, Toshikatsu; Sakai, Akihiro
JAEA-Review 2023-011, 116 Pages, 2023/08
JAEA-Review-2023-011.pdf:2.6MB
Japan Atomic Energy Agency (JAEA) is the implementing agency for the disposal business of radioactive waste generated from research, industrial and medical facilities (Institutional radioactive waste). In 2010, JAEA implemented a conceptual design of the disposal facility that conformed to the laws and regulations at the time. However, since 2013, the laws and regulations for nuclear facilities including the Category-2 Waste Disposal were amended. Since then, design of various nuclear facilities including disposal facilities has been reviewed. Therefore, JAEA decided to do additional studies toward the basic design for the disposal facility. When JAEA gets a license of the disposal business of Institutional radioactive waste, it is necessary to show that the disposal facility complies with the rule of design for disposal facility under the law. Therefore, JAEA is examining technical studies of the disposal facility to conform to the new standard. In this report, we organized the requirements of the rule for design of trench disposal facility and extracted the issues to design the disposal facility that conform to the requirements.
Nakamura, Mizuki; Izumo, Sari; Ogawa, Rina; Nakata, Hisakazu; Amazawa, Hiroya; Sakai, Akihiro
JAEA-Technology 2022-025, 73 Pages, 2022/12
JAEA-Technology-2022-025.pdf:1.64MB
Japan Atomic Energy Agency (JAEA) has been establishing as the implementing body of the near surface disposal of low-level radioactive waste (LLW) generated from research facilities and other facilities in order to actualize the near surface disposal. It is necessary to evaluate the effective doses by direct and skyshine 
-rays from disposal facilities and reduce the doses below the target dose (50
Sv/y) at the site boundary for the safety assessment during operation. It was shown at the results of conceptual design that the distance from the trench disposal facilities to site boundary needed to be kept more than 120m in order to satisfy the target dose. However, the design of trench disposal facilities was changed because of increasing amount of waste subject to the trench disposal. Therefore, the dose by skyshine -rays from trench disposal facilities was recalculated by use of two-dimensional discrete ordinates Sn code DOT 3.5. As a result, it was evaluated that the dose by skyshine -rays from each trench facility at the site boundary whose distance was 120m from a trench facility was lower than 50 Sv/y, respectively, and the dose added up the doses from trench facilities was also lower than 50 Sv/y. In addition, it was suggested to reduce the target skyshine dose by thickening the covered soil on the top layer.
Sakuma, Kota; Abe, Daichi*; Okada, Shota; Sugaya, Toshikatsu; Nakata, Hisakazu; Sakai, Akihiro
JAEA-Technology 2022-013, 200 Pages, 2022/08
JAEA-Technology-2022-013.pdf:8.41MB
Japan Atomic Energy Agency has aims to carry out near surface disposal of low-level radioactive waste generated from research, medical, and industrial facilities. Therefore, Radioactivity Concentration Corresponding to Dose Criterion for near surface disposal for nuclides in the waste were calculated for the purpose of discussion for radioactivity limits between trench and concrete vault disposal, and key nuclides related to them. This report uses the results of sensitivity analysis and evaluation of the amount of leachate from the disposal facility for concrete vault disposal, and incorporates a new assessment pathway and exposure form that widely assume the conditions of the disposal facility. This trial calculation was carried out and compared with the trial calculation in the previous report, "Evaluation of Radioactivity Concentration Corresponding to Dose Criterion for Near Surface Disposal of Radioactive Waste Generated from Research, Medical, and Industrial Facilities, Volume 1". The results of Radioactivity Concentration Corresponding to Dose Criterion calculated in this report will be used as reference values when selecting key nuclides and for classification into concrete vault disposal when the location has not been decided. After deciding the location of the site, it is necessary to evaluate the dose based on the location conditions.
Ogawa, Rina; Nakata, Hisakazu; Sugaya, Toshikatsu; Sakai, Akihiro
JAEA-Technology 2022-010, 54 Pages, 2022/07
JAEA-Technology-2022-010.pdf:11.07MB
Japan Atomic Energy Agency has considered trench disposal as one of the disposal methods for radioactive wastes generated from research facilities and other facilities. The trench disposal facility is regulated by "Act on the Regulation of Nuclear Source Material, Nuclear Fuel Material and Reactors". In particular, the design of the trench facility is regulated by a rule under the law. When the rule was amended in 2019, the design of the trench disposal facility required equipment to reduce ingress of rain water and groundwater. In the report, studies on the design of a trench disposal facility to adapt to the amended rule were performed. The trench disposal facility has considered being established in a place lower than groundwater level. Therefore, it was decided to study covering soil at the upper part of the trench facility, because the ingress water in the facility is mainly derived from rain water. In this study, it was decided to evaluate the design of covering soil of the radioactive waste categorized into chemically stable materials. Therefore, as the examination method, a parameter study on varying the permeability coefficient and thickness of the layers composing cover soil. In the parameter study, the velocity of the water infiltrating into the trench facility was evaluated. Based on the results, more efficient design of the layers composing the covering soil was considered. The result showed that the impermeable efficiency of the covering soil was different depending on the thickness and the permeability conductivity of each layer. As a result, it was possible to understand the impermeable performance of covering soil by the permeability coefficient and thickness of each layer. We will plan to decide the specification of the cover soil while examination of future tasks and cost in the basic design.
Nagao, Rina; Namekawa, Maki*; Totsuka, Masayoshi*; Nakata, Hisakazu; Sakai, Akihiro
JAEA-Technology 2021-009, 139 Pages, 2021/06
JAEA-Technology-2021-009.pdf:13.96MB
Japan Atomic Energy Agency is the implementing body of the near surface disposal of low-level radioactive waste (LLW) generated from research facilities and other facilities. Concrete-pit disposal are considered as a method of disposing of the LLW. Since the concrete-pits are placed at deeper position than the groundwater level, we need to consider that radionuclides might migrate with the flow of groundwater. Accordingly, in order to explain the safety of the concrete-pit disposal facility, it is necessary to investigate the flow of groundwater and the volumetric flow rate of leaching water from the facility. Therefore, in this report, sensitivity analysis of the volumetric flow rate of leaching water from concrete-pit was carried out by varying the permeability of cover-soil filled with in outside of the lateral sides of the bentonite mixed soil (BMS) and the conditions of the BMS on the upper part of the concrete-pits. As a result of the analysis, when the BMS is normal condition, the volumetric flow rate of leaching water from the concrete-pits is reduced by lowering permeability of the lateral cover-soil. However, in the case of occurring the deterioration of the function of BMS on the upper part of the concrete-pit, significant reduction of the volumetric flow rate of leaching water is not seen even if the permeability of the lateral cover-soil is lowered. Therefore, taking into consideration the possibility of the deterioration of the function of BMS on the upper part of the concrete-pit, it is necessary to consider that cover-soil with low permeability is equipped on the upper part of the BMS.
Nakagawa, Akinori; Oyokawa, Atsushi; Murakami, Masashi; Yoshida, Yukihiko; Sasaki, Toshiki; Okada, Shota; Nakata, Hisakazu; Sugaya, Toshikatsu; Sakai, Akihiro; Sakamoto, Yoshiaki
JAEA-Technology 2021-006, 186 Pages, 2021/06
JAEA-Technology-2021-006.pdf:54.45MB
Radioactive wastes generated from R&D activities have been stored in Japan Atomic Energy Agency. In order to reduce the risk of taking long time to process legacy wastes, countermeasures for acceleration of waste processing and disposal were studied. Work analysis of waste processing showed bottleneck processes, such as evaluation of radioactivity concentration, segregation of hazardous and combustibles materials. Concerning evaluation of radioactivity concentration, a radiological characterization method using a scaling factor and a nondestructive gamma-ray measurement should be developed. The number of radionuclides that are to be selected for the safety assessment of the trench type disposal facility can decrease using artificial barriers. Hazardous materials, will be identified using records and nondestructive inspection. The waste identified as hazardous will be unpacked and segregated. Preliminary calculations of waste acceptance criteria of hazardous material concentrations were conducted based on environmental standards in groundwater. The total volume of the combustibles will be evaluated using nondestructive inspection. The waste that does not comply with the waste acceptance criteria should be mixed with low combustible material waste such as dismantling concrete waste in order to satisfy the waste acceptance criteria on a disposal facility average. It was estimated that segregation throughput of compressed waste should be increased about 5 times more than conventional method by applying the countermeasures. Further study and technology development will be conducted to realize the plan.
Sugaya, Toshikatsu; Abe, Daichi*; Okada, Shota; Nakata, Hisakazu; Sakai, Akihiro
JAEA-Technology 2021-004, 79 Pages, 2021/05
JAEA-Technology-2021-004.pdf:2.86MBJAEA-Technology-2021-004(errata).pdf:0.38MB
JAEA has aims to carry out near surface disposal of low-level radioactive waste generated from research, medical, and industrial facilities. Therefore, radioactivity concentration corresponding to dose criteria of near surface disposal for 220 nuclides in the waste were calculated for the purpose of discussion for radioactivity limits between trench and concrete vault disposal, and key nuclides related to them. We calculated the radioactivity concentrations with consideration of not only the exposure pathways used at calculation of the radioactivity concentration limits of waste packages for near surface disposal by Nuclear Safety Commission but also ones used at the concentration limits for intermediate depth disposal. We also assumed the capacities of the disposal facilities as 44,000 m for pit disposal and 150,000 m for trench disposal. The radioactivity concentrations calculated in this report is used as the reference values because the disposal site has not been decided yet. Addition to this, the radioactivity concentrations will be revised according to circumstances of development of disposal facilities and so on. In the future, we will decide the radioactivity and radioactive concentration of a waste package described in the license application documents based on the dose assessment taken into consideration the disposal site conditions.
Izumo, Sari; Hayashi, Hirokazu; Nakata, Hisakazu; Amazawa, Hiroya; Motoyama, Mitsushi*; Sakai, Akihiro
JAEA-Technology 2018-018, 39 Pages, 2019/03
JAEA-Technology-2018-018.pdf:2.8MB
JAEA has planed the near surface disposal of LLW generated from research, industrial, and medical facilities. Maximum radioactivity concentration of each waste and total radioactivity of disposed wastes are needed to be less than the permitted values in the license of disposal facility. Thus, it is important not to evaluate the radioactivity of each waste in unduly conservative ways so as to dispose of the total amount of the waste that is originally planned. Accordingly, the detection limit is required to be as low as the clearance level for the very low level radioactive waste planned to be disposed of trench-type. In this report, the feasibility of the non-destructive assay method is studied by model calculations for gamma emitters. It is confirmed that the detection limit less than the clearance level can be achieved as regards the box type metal container that is difficult to measure. This report summarizes the requirements for the non-destructive measuring equipment.
Nakata, Hisakazu; Takao, Hajime*; Chijimatsu, Masakazu*; Noma, Yasutaka*; Amazawa, Hiroya; Sakai, Akihiro
JAEA-Technology 2018-014, 43 Pages, 2019/03
JAEA-Technology-2018-014.pdf:5.91MB
Japan Atomic Energy Agency plans to install disposal facilities for radioactive waste arising from research institutes. One relevant technical standard by the safety regulation is that the disposal facility shall be performance so as not to be left with harmful voids after backfilling with soil. Additionally no harmful void needs to exist in the waste packed in metal containers. The harmful void is supposed to result in the collapse of the disposal facility after structural materials of the container deteriorate and then become a state that can not retain the structure on its own. That leads to have an adverse impact on the facility such that the shape of cover soil deforms the way in which stagnant water is likely to occure. For which reason, a waste acceptance criteria relating to the quantity of voidage in a waste package needs to be defined quantitatively, which is preliminary less than 20% in a volum ratio based on this study.
Nakata, Hisakazu; Amazawa, Hiroya; Izumo, Sari; Okada, Shota; Sakai, Akihiro
Dekomisshoningu Giho, (58), p.10 - 23, 2018/09
Low level radioactive wastes are generated in the research and development of the nuclear energy, medical and industrial use of radioisotope except NPP in Japan. The disposal of wastes arising from NPP has already been implemented while not the one for wastes from research institutes etc. Japan Atomic Energy Agency therefore has been assigned an implementing organization for the disposal legally in 2008 in order to promote the disposal program as quickly and firmly as possible. Since then, JAEA has conducted their activity relating to the disposal facility design on generic site conditions and developing Waste Acceptance Criteria for LLW from research institutes. This report summarizes the WAC and current challenges.
Hayashi, Hirokazu; Izumo, Sari; Nakata, Hisakazu; Amazawa, Hiroya; Sakai, Akihiro
JAEA-Technology 2018-001, 66 Pages, 2018/06
JAEA-Technology-2018-001.pdf:4.12MBJAEA-Technology-2018-001(errata).pdf:0.54MB
It is necessary to establish evaluation methodology of radioactivity concentrations of each radionuclide in waste packages for operation of the Near-surface Trench disposal and Sub-surface Pit disposal facility in near future, which has been preparing for low-level radioactive wastes generated from research facilities in JAEA. The radionuclides containing in waste packages generated from both JRR-2 and JRR-3, which are H-3, C-14, Cl-36, Co-60, Ni-63, Sr-90, Nb-94, Tc-99, Ag-108m, I-129, Cs-137, Eu-152, Eu-154, U-234, U-238, Pu-239+240, Pu-238+Am-241, Cm-243+244, were evaluated their density based on radiochemical analysis data, and the Evaluation Methodology of the Radioactivity Concentration such as Scaling Factor method and mean activity concentration method was studied in this report.
Sakai, Akihiro; Nakata, Hisakazu; Amazawa, Hiroya
JAEA-Technology 2017-030, 176 Pages, 2018/02
JAEA-Technology-2017-030.pdf:4.09MB
At present, the reuse method for the contaminated soil generated from the decontamination of radioactive materials caused by the accident of the Tokyo Electric Power Cooperation Fukushima Daiichi Nuclear Power Plant after intermediate storage is being discussed. The radioactivity concentration of contaminated soil with about 20 million cubic meters within total arising volume of the soil is less than 100 kBq/kg. Therefore, when it is assumed that contaminated soil was disposed of in the trench facility, exposure doses to public at the various exposure pathways resulting from Cs-134 and Cs-137 contained in the removal soil were calculated. From the dose calculation results, the radioactivity concentrations corresponded to reference doses that are assumed to be 0.01 mSv/y or 0.3 mSv/y were evaluated. Then, variation of the radioactivity concentrations was evaluated when the volume of disposal facility was increased taking into account variation of the volume of contaminated soil.
Nakata, Hisakazu; Hayashi, Hirokazu; Amazawa, Hiroya; Sakai, Akihiro
JAEA-Technology 2017-031, 41 Pages, 2018/01
JAEA-Technology-2017-031.pdf:5.27MB
JAEA plans to install disposal facilities for radioactive waste arising from research institutes. It must meet the technical standards specified in the relevant rule. One technical standard is that the disposal facilities shall be performance so as not to be left with the voids after the backfilling with soil. Additionally, the rule also requires this radioactive waste be enclosed in a container in which no harmful voids remain. In order to contribute to the development of a method that adapts the disposal facilities to these technical standards, JAEA adopts a waste conditioning artifice that aims for reducing a quantity of voidage in each waste container by a vibration filling method using sandy soil, providing with average void ratios inside the disposal facilities being adequately controlled. In this reports, filling property tests are conducted in the light of filling sand characteristics, types of metal waste and vibration conditions.
Okada, Takashi; Takeda, Seiji; Nakata, Hisakazu
Nihon Genshiryoku Gakkai-Shi ATOMO
, 59(10), p.603 - 607, 2017/10
Because the reclaimed material is used, quantity of disposal of the removal soil can decrease. It is a strategic key to utilize the reclaimed material. As for this report, it is explained to about the fundamentals of the safe use of the reclaimed materials derived from the removed soil.
