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Totsuka, Masayoshi; Kurosawa, Ryohei*; Sakai, Akihiro; Nakata, Hisakazu; Hayashi, Hirokazu; Amazawa, Hiroya
JAEA-Technology 2017-001, 40 Pages, 2017/03
JAEA-Technology-2017-001.pdf:2.24MB
Japan Atomic Energy Agency is planning for the near surface disposal of low level radioactive wastes generated from research, industrial and medical facilities industry in Japan. This document provides the values of radioactivity concentrations equivalent to dose criterion for trench-type disposal. These values are derived based on the safety assessment for ground water scenarios by using a model which describes the release of radionuclides from wastes to a cover soil caused by elution. These concentrations are compared with the one calculated by a model that describes the nuclide release mechanisms as solid-liquid partitioning equilibrium. Additionally, the change in the concentrations is evaluated when the amount of water percolating into a disposal facility varies.
Sakai, Akihiro; Kurosawa, Ryohei*; Totsuka, Masayoshi; Nakata, Hisakazu; Amazawa, Hiroya
JAEA-Technology 2016-032, 117 Pages, 2017/02
JAEA-Technology-2016-032.pdf:12.84MB
JAEA has been planning to implement near surface disposal of low level waste generated from research, medical, and industrial facilities. JAEA plans to carry out 3d analysis of groundwater flow in geological model around the disposal site because of development of migration assessment modeling of radioactivity materials in the site. In the safety demonstration test in JAEA, 3d analysis of groundwater flow was carried out on 1999. The analysis was calculated by using the code "3D-SEEP". But it is necessary to improve the conditions of the model in the analysis. Therefore, we improved the geological model which had been developed carried out 3d analysis of groundwater flow by using the current 3D-SEEP for the specified disposal site in the future. From the result, we expect that 3d analysis of groundwater flow in the environment around the specified near surface disposal site will be able to be sufficiently conducted by developing an appropriate model for the disposal site.
Sakai, Akihiro; Kurosawa, Ryohei*; Nakata, Hisakazu; Okada, Shota; Izumo, Sari; Sato, Makoto*; Kitamura, Yoichi*; Honda, Yasutake*; Takaoka, Katsuki*; Amazawa, Hiroya
JAEA-Technology 2016-019, 134 Pages, 2016/10
JAEA-Technology-2016-019.pdf:8.25MB
Japan Atomic Energy Agency has been developing to design trench disposal facility with impermeable layers in order to dispose of miscellaneous waste. Geomembrane liners have a function that prevent seepage of leachant and collect the leachant. However, the geomembrane liners do not necessarily provide the expected performance due to damage generated when heavy equipment contacts with the liner. Therefore, we studied the impermeable layers having high performance of preventing seepage of leachant including radioactivity taking into account characteristics of low permeable materials and effect of multiple layer structure. As results, we have evaluated that the composite layers composed by a drainage layer, geomembrane liners and a low permeable layer are most effective structure to prevent seepage of leachant. Taking into account disposal of waste including cesium, we also considered zeolite containing sheets for adsorption of cesium were installed in the impermeable layers.
Nakata, Hisakazu; Sakai, Akihiro; Okada, Shota; Izumo, Sari; Tsuji, Tomoyuki; Kurosawa, Ryohei; Amazawa, Hiroya
JAEA-Technology 2016-001, 112 Pages, 2016/03
JAEA-Technology-2016-001.pdf:16.71MB
The waste packages must meet the technical requirements that radioactive waste shall be solidified in a container by a method determined by the Nuclear Regulation Authority to prevent from radiation hazards. JAEA has been preparing operating procedure manual on quality control for radioactive waste disposal in order to promote the manufacturing the waste package. This report presents that simulant waste packages were produced by placing wastes in a 200 liter drum, which was then filled with mortar of a novel mix proportion, followed by curing in a controlled manner. Determination of the presence of harmful voidage and raw waste immobility were performed by direct measurement and visual inspection of a vertical cross section of the waste packages respectively.
Okada, Shota; Kurosawa, Ryohei; Sakai, Akihiro; Nakata, Hisakazu; Amazawa, Hiroya
JAEA-Technology 2015-016, 44 Pages, 2015/07
JAEA-Technology-2015-016.pdf:5.8MB
In this report, we calculated radioactivity concentration of radionuclides potentially contained in low level radioactive waste (LLW) generated from research, medical, and industrial facilities corresponding to dose criterion (10 
Sv/y) for near surface disposal. 220 kinds of nuclides whose half-life are more than 30 days were selected. Radioactivity concentrations corresponding to dose criterion of 40 nuclides among 220 ones were calculated by using the representative model because the concentrations of 40 nuclides had not been calculated yet. Skyshine dose from each of 19 nuclides, whose radioactivity concentration were invalid values that are larger than the specific radioactivity of nuclides, during operation of disposal facility was calculated. These radioactivity concentrations can be used as criteria of categorization of LLW between trench type and concrete vault type disposal and of preliminary selection of important nuclides of these disposals in the generic conditions.
Kurosawa, Ryohei; Okada, Shota; Sakai, Akihiro; Nakata, Hisakazu; Amazawa, Hiroya
JAEA-Data/Code 2015-005, 82 Pages, 2015/06
JAEA-Data-Code-2015-005.pdf:3.47MB
The calculation tool of neutron flux at materials within and around the research reactor was developed so that the user more easily evaluate radioactivity inventory in radioactive waste generated from the decommissioning of research reactors at various conditions. The tool consists of some computer programs which calculate macroscopic effective cross section at materials, calculate the neutron flux at materials within and around the research reactor, and edit the neutron flux to evaluate the radioactive inventory. This report describes the outline of evaluation method of neutron flux at materials within and around the research reactor, the structure and functions of the calculation tool of neutron flux, input and output data, and sample run with the tool.
Kurosawa, Ryohei; Sakai, Akihiro; Nakata, Hisakazu; Amazawa, Hiroya; Sakamoto, Yoshiaki
JAEA-Technology 2014-013, 89 Pages, 2014/06
JAEA-Technology-2014-013.pdf:23.93MB
In the safety assessment for the trench disposal facilities, outflow of radioactive material to the environment is assumed to be due to the percolating rain water into the waste layer, because the waste layer is established above the groundwater level. Therefore, in dose assessment of trench type disposal facilities, it is important to evaluate how the structure of the upper cover soil layers affects the suppressed amount of water infiltration to the waste layer due to rainfall.
Sakai, Akihiro; Kurosawa, Ryohei; Hara, Hironori*; Nakata, Hisakazu; Amazawa, Hiroya; Arikawa, Masanobu*; Sakamoto, Yoshiaki
JAEA-Technology 2013-039, 228 Pages, 2014/02
JAEA-Technology-2013-039.pdf:24.05MB
The sensitivity analysis of doses in terms of the environmental conditions was performed by statistical method in order to make the technical basis for the siting criteria of near surface disposal facility for low level radioactive waste generated from research, industrial and medical facilities. Doses calculated at all assumed pathways in more than 97.5% of calculation cases were able to be reduced below the target dose after control period (0.01 mSv/y) by means of equipping the disposal facility with additional engineered barriers. As a result, we concluded it was possible to safely and rationally design disposal facilities in most of the environmental parameters related to safety assessment. Another sensitivity analysis was done in order to discuss the area of disposal site. Dose at the site boundary were able to be reduce below the target dose during operation (0.05 mSv/y) whenever the distances from these facilities to the site boundary were more than 120 m, respectively.
Nakata, Hisakazu; Amazawa, Hiroya; Sakai, Akihiro; Kurosawa, Ryohei; Kanno, Naohiro*; Kashima, Takahiro*; Sakamoto, Yoshiaki
JAEA-Technology 2013-036, 47 Pages, 2014/02
JAEA-Technology-2013-036.pdf:5.27MB
The Low-level Radioactive Waste Disposal Project Center will construct near surface disposal facilities. The disposal facilities consist of concrete pit type for low-level radioactive wastes and trench type for very low level radioactive wastes. As for the trench type disposal facility, two kinds of facility designs are on projects -one for normal trench type disposal facilities and the other for trench type disposal facilities with geomembrane liners that could prevent from causing environmental effects of non radioactive toxic materials. This study examined mechanical strength and permeability properties to assess the durability on the basis of an indoor accelerated exposure experiment targeting the liner materials presumed to avail the conceptual design so far. Its results will be used for the basic and detailed design henceforth by confirming the empirical degradation characteristic with the progress of the exposure time.
Amazawa, Hiroya; Sakai, Akihiro; Nakata, Hisakazu; Hara, Hironori; Kurosawa, Ryohei; Yamamoto, Masayuki*; Kawata, Yosuke*; Sakamoto, Yoshiaki
JAEA-Technology 2012-031, 338 Pages, 2012/10
JAEA-Technology-2012-031.pdf:19.43MB
JAEA is responsible for siting a proper location to establish new disposal facilities with siting criterion and procedure, in consideration of transparency and impartial for the siting process, based on Plan Concerning the Disposal Business Execution. As a part of the study to draw up siting criterion and procedure, Sensitivity analysis of the disposal facilities from the viewpoint of dose evaluation and cost estimation under various siting condition will be carried out. Therefore, Conceptual design of disposal facilities as a reference case is necessary. The basic condition of the design conforms to the property, quantity, radioactivity of waste packages, technical standards and likely siting condition. This report summarizes the results of the reasonable design of our disposal facilities and the layout of the place of activity where the disposal facilities and associated facilities to be installed.
Nakata, Hisakazu; Kurosawa, Ryohei; Sakamoto, Yoshiaki
no journal, ,
In the shallow land disposal system for radioactive waste arising from research, industrial and medical facilities, effect of environmentally hazardous substances must be considered adding to radiation effect on human. Some environmentally hazardous substances will be regulated following to the Waste Management and Public Cleansing Law, however, boron, fluoride and nitric ion are not regulated by the Waste Management and Public Cleansing Law. Therefore, in this study, the limitation of the amount of boron, fluoride and nitric ion in the waste forms were evaluated in concrete pit and trench facilities.
Kurosawa, Ryohei; Sakai, Akihiro; Nakata, Hisakazu; Amazawa, Hiroya; Sakamoto, Yoshiaki
no journal, ,
In the safety assessment for the trench disposal facilities, outflow of radioactive material to the environment is assumed to be due to the percolating rain water into the waste layer, because the waste layer is established above the groundwater level. Therefore, in dose assessment of trench type disposal facilities, it is important to evaluate the effect of facility designs that suppresses the amount of water infiltration to the waste layer due to rainfall. Therefore, using the weather conditions in Japan, and evaluated the penetration water into the upper cover soil in trench type disposal facility other than the surface runoff and evapotranspiration. The evaluation was carried out of the water penetration leading to waste layer by migrating the upper cover soil fitted with a water barrier sheet or low-permeable layer soil layer of in trench type disposal facility. As evaluation result, by the influence of vegetation state of the upper cover soil surface, it was found that the amount of water from about 0.2 times to 0.7 times the precipitation have infiltrated to the upper cover soil. By setting the value corresponding to the clay hydraulic conductivity of low permeability soil layer, penetration amount of water to the waste layer from the top upper cover soil, it has been found that it is possible to reduce the penetration amount of water to the upper cover soil from the rain.
Sakai, Akihiro; Nakata, Hisakazu; Amazawa, Hiroya; Kurosawa, Ryohei*; Sato, Makoto*; Kitamura, Yoichi*
no journal, ,
We consider that very low level waste slightly including chemical toxicity material among radioactive waste generated from research, industrial and medical facilities is disposed of in trench disposal facility which is equipped with impermeable layers. We studied the impermeable system which has high performance to prevent the radioactive material from leaching out of waste layer taking into account the combination of geomembrane liners and low permeable materials.
Hayashi, Hiroko*; Kido, Hiroko*; Kurosawa, Ryohei*; Sone, Koichiro*; Nogami, Mitsuhiro*; Kitayama, Yoshiharu; Hitomi, Keitaro*; Torii, Tatsuo*
no journal, ,
no abstracts in English