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JAEA Reports

Development of MIG2DF Version 2

Takai, Shizuka; Kimura, Hideo*; Uchikoshi, Emiko*; Munakata, Masahiro; Takeda, Seiji

JAEA-Data/Code 2020-007, 174 Pages, 2020/09

JAEA-Data-Code-2020-007.pdf:4.23MB

The MIG2DF computer code is a computer program that simulates groundwater flow and radionuclide transport in porous media for the safety assessment of radioactive waste disposal. The original version of MIG2DF was released in 1992. The original code employs a two-dimensional (vertical or horizontal cross-section, or an axisymmetric configuration) finite-element method to approximate the governing equations for density-dependent saturated-unsaturated groundwater flow and radionuclide transport. Meanwhile, for geological disposal of radioactive wastes, landscape evolution such as uplift and erosion needs to be assessed as a long-term geological and climate events, considering site conditions. In coastal areas, the impact to groundwater flow by change of salinity distribution to sea level change also needs to be considered. To deal with these events in the assessment, we have revised the original version of MIG2DF and developed the external program which enables MIG2DF to consider unsteady landscape evolution. In these developments, this report describes an upgrade of MIG2DF (Version 2) and presents the configuration, equations, methods, and verification. This reports also give the explanation external programs of MIG2DF: PASS-TRAC (the particle tracking code), PASS-PRE (the code for dataset preparation), and PASS-POST (the post-processing visualization system).

JAEA Reports

Dose estimation in recycling of removed soil as seaside protection forest (Contract research)

Sawaguchi, Takuma; Takai, Shizuka; Takeda, Seiji

JAEA-Research 2020-005, 47 Pages, 2020/06

JAEA-Research-2020-005.pdf:5.09MB

After the Fukushima Daiichi Nuclear Power Station accident, large quantities of radiocesium-contaminated soil were generated from decontamination activities in the Fukushima prefecture. The removed soil has been stored in the prefecture until its final disposal. To complete the final disposal outside Fukushima prefecture, reducing the disposal volume through recycling can prove effective. The Ministry of the Environment, Japan (MOE) has presented a policy to recycle low-radioactive removed soil as recycled materials under the management of public authority. The recycling is limited to civil engineering structures in public projects. In this study, to contribute to guideline development for removed soil recycling by MOE, dose estimation in recycling of removed soil as embankment materials of seaside protection forest was conducted. First, additional doses to workers and the public in construction and service scenarios were evaluated. From the result, the radioactive cesium concentration level of recycled materials, where all additional doses meet the radiation criterion of 1 mSv/y, was derived to be 5,000 Bq/kg. Then, construction conditions were reviewed to reduce additional doses to the public in a service scenario. With the derived radioactivity level of 5,000 Bq/kg, the covered soil thickness of 39 cm or more limited the doses to less than 10 $$mu$$Sv/y. Finally, additional doses in a disaster scenario were evaluated. The doses were confirmed to be below 1 mSv/y when the removed soil of 5,000 Bq/kg was used.

Journal Articles

Dose estimation for contaminated soil storage in living environment

Takai, Shizuka; Shimada, Asako; Sawaguchi, Takuma; Takeda, Seiji; Kimura, Hideo

Radiation Protection Dosimetry, 188(1), p.1 - 7, 2020/01

 Times Cited Count:0 Percentile:100(Environmental Sciences)

After the Fukushima Nuclear Power Plant accident, most of radiocesium-contaminated soil generated from decontamination activities outside Fukushima prefecture has been stored at decontamination sites such as schools, parks and residential lands (storage at sites) according to the Decontamination Guidelines. However, additional exposure due to the present storage has not been evaluated. Moreover, entering storage sites, which is not restricted for storage at sites, was not considered in safety assessment conducted in the guidelines. To continue the storage and confirm the effectiveness, understanding of present possible exposures is important. In this study, we evaluated exposure doses for residents and users of storage sites based on the present situation. As a result, annual doses due to residence were 10$$^{-2}$$ to 10$$^{-3}$$ mSv y$$^{-1}$$ and doses due to annual entries were of the order of 10$$^{-3}$$ mSv y$$^{-1}$$. Hence, we confirmed that the exposure due to present storage outside Fukushima is significantly less than 1 mSv y$$^{-1}$$.

Journal Articles

Dose estimation in recycling of decontamination soil resulting from the Fukushima NPS accident for road embankments

Takai, Shizuka; Sawaguchi, Takuma; Takeda, Seiji

Health Physics, 115(4), p.439 - 447, 2018/10

 Times Cited Count:3 Percentile:46.85(Environmental Sciences)

After the Fukushima Nuclear Power Station accident, large quantities of radiocesium-contaminated soil generated from decontamination activities have been stored in the Fukushima Prefecture. To reduce the disposal volume, the Ministry of the Environment of Japan has presented a policy to recycle low-radioactive decontamination soil limited to civil engineering structures. However, there has been no practical instance or safety assessment of decontamination soil recycling. In this study, the way of ensuring the safety for decontamination soil recycling for road embankments was discussed. First, based on Japanese construction standards, additional doses to workers and the public in construction and service scenarios were evaluated. From the result, the radioactive cesium concentration level of recycled materials, where all additional doses meet the radiation criterion of 1 mSv y$$^{-1}$$, was derived to be 6,000 Bq kg$$^{-1}$$. To confine additional doses to the public in a service scenario below 0.01 mSv y$$^{-1}$$, soil slope protection of 40 cm or more was needed. Finally, additional doses in a disaster scenario were confirmed to be below 1 mSv y$$^{-1}$$.

Journal Articles

Dose estimation in recycling of decontamination soil due to Fukushima NPS accident as coastal levees

Takai, Shizuka; Sawaguchi, Takuma; Takeda, Seiji

Proceedings of International Waste Management Symposia 2018 (WM 2018) (Internet), 14 Pages, 2018/03

After the Fukushima Nuclear Power Station accident, large quantities of radiocesium-contaminated soil generated from decontamination activities have been stored in the Fukushima prefecture. To complete the final disposal of decontamination soil, the Ministry of the Environment of Japan presented policy to reduce the disposal volume by using low-level decontamination soil as recycled materials. The use will be limited to civil engineering structures in public projects, such as coastal levee and road embankment. However, there has been no example or safety assessment of recycling of decontamination soil. To contribute to guideline development for the recycling by the Ministry of the Environment, we conducted the safety assessment for recycling of decontamination soil as coastal levee. First, we evaluated additional doses to workers and the public in the case of construction and service of coastal levee. From the result, the radioactive cesium concentration level of recycled materials was derived to be 6,800 Bq/kg. For general designs of coastal levee in Japan, additional doses to the public in the case of service were below 0.01 mSv/y with derived radioactivity level. Finally, we confirmed additional doses in the case of disaster to be below 1 mSv/y.

Journal Articles

JAEA Reports

Scenario development on application of engineering technology for geological disposal; Study of influence of earthquake at site construction, operation and closure stages and that impact on safety functions after closure of disposal facility (Contract research)

Takai, Shizuka; Takayama, Hideki*; Takeda, Seiji

JAEA-Data/Code 2016-020, 40 Pages, 2017/03

JAEA-Data-Code-2016-020.pdf:2.42MB

In this report, another group of scenarios for occurrence of earthquake at construction stage, operation stage and closure stage of disposal facility was presented. At first, we compiled information about damage cases of tunnel by earthquake and analyzed conditions for occurrence of damage. Base on this result and the previous report, information of influence of the accidents and human factors on safety functions and information of FEP about THMC variation, we specified events to be considered, which occur by earthquake and influence engineering barriers, natural barriers and long-term safety after closure stage of disposal facility. We compiled influence of the events on safety functions after closure stage of disposal and showed the chains of the influence on long-term safety as scenarios. These results were integrated as a database that could support development of scenarios caused by application of engineering technologies to geological disposal.

Journal Articles

Evaluation of influence of splay fault growth on groundwater flow around geological disposal system

Takai, Shizuka; Takeda, Seiji; Sakai, Ryutaro*; Shimada, Taro; Munakata, Masahiro; Tanaka, Tadao

Nippon Genshiryoku Gakkai Wabun Rombunshi, 16(1), p.34 - 48, 2017/03

In geological disposal, direct effect on geological repositories by active faults is avoided at a stage of site characterization; however, uncertainty remains for avoidance of faults derived from the active faults, which are concealed deep under the ground and difficult to detect in advance. In this research, the influence of growth of undetected splay faults on natural barrier in a geological disposal system, which will caused by attack of the faults in the future, was evaluated. We investigated examples of splay faults in Japan and set conditions for growth of splay faults. Furthermore, we assumed a disposal site composed of sedimentary rocks and made a hydrogeological model of growth of splay faults. We carried out groundwater flow analyses, changing parameters such as location and depth of repository and growth velocity of splay faults. The results indicate that main flow path from the repository is changed into upward flow along the splay fault due to its growth and the average velocity to the ground surface becomes one or two orders of magnitude higher than that before its growth. The results also suggest that the splay fault growth leads into the possibility of downward flow of oxidizing groundwater from ground surface area.

JAEA Reports

Scenario development on application of engineering technology for geological disposal; Study on engineering measures for accidents and human factors (Contract research)

Takai, Shizuka; Takayama, Hideki*; Takeda, Seiji

JAEA-Data/Code 2015-018, 96 Pages, 2015/11

JAEA-Data-Code-2015-018.pdf:4.24MB

In the safety assessment for the high-level radioactive waste geological disposal, scenarios need to be developed in consideration of influence on barrier features by accidents and human factors caused by application of engineering technologies at each stage of site characterization, construction, operation and closure of disposal facility. To develop scenarios on application of engineering technologies from the point of view of safety regulation, deviation events which are deviated states of engineered and natural barriers from intended states were specified and possible evolution of features of barriers or loss/reduction of safety functions of barriers was shown as a scenario in JAEA-Data/Code 2014-026. In this study, we compiled information of existence of engineering measures against the accidents and human factors and deviation events, application performance and development status of the measures. From this information, we identified deviation events which need developing of engineering measures as remarkable deviation events. These results were integrated as a database that could support development of scenarios caused by application of engineering technologies to geological disposal.

Journal Articles

Dose estimation for the reuse of wooden chips contaminated by radioactive cesium

Takai, Shizuka; Seki, Masaya; Kimura, Hideo; Takeda, Seiji

Hoken Butsuri, 50(1), p.50 - 66, 2015/03

Wood (thinned wood from forest etc.) and wooden wastes (demolished wood etc.) potentially contaminated by radioactive cesium released by Fukushima Daiichi Nuclear Power Plant have been used for various purposes as wooden chips. However, there has been no dose estimation for use of such contaminated wood so far. Up to now, use of wood has been conducted according to a standard value of 100 Bq/kg for radioactive cesium based on clearance level of concrete and metal generated at nuclear power plant. The purpose of this study is to evaluate the safety of present use of wood by dose estimation for reuse of contaminated wooden chips, which are reused for main five use purposes (particle board, paper, compost, biomass power fuel, mulching). We also calculated activity concentrations of radioactive cesium in wooden chips corresponding to standard dose for safety reuse of radioactive wastes and regarded the minimum calculated activity concentration as a standard value of activity concentration for each reuse purposes. From the result, the minimum standard value of activity concentration of radioactive cesium in wooden chips for all reuse purposes is estimated to be 120 Bq/kg for reuse of wooden chips for particle board. Since this standard value is more than 100 Bq/kg, the safety of present use of wood is confirmed.

JAEA Reports

Dose estimation for the use of recycled products from waste affected by radioactive cesium

Takai, Shizuka; Takeda, Seiji; Kimura, Hideo

JAEA-Research 2014-028, 13 Pages, 2015/02

JAEA-Research-2014-028.pdf:1.92MB

A large amount of waste contaminated by radioactive cesium released by Fukushima Daiichi Nuclear Power Plant has been recycled as much as possible in order to reduce the quantity to be disposed of and to use resources effectively. At present, a standard concentration of radioactive cesium for recycled products from disaster waste is defined as 100 Bq/kg. In order to understand the actual situation of radioactivity concentration of recycled products, Ministry of the Environment conducted a survey on recycled products. The survey found that several recycled products had relatively high radioactive cesium concentration. In this study, we specified exposure pathways to calculate doses for using the recycled products detected high cesium concentration in the survey. We calculate the doses based on the survey of concentration of the recycled products and compare them with a dose criterion of 10$$mu$$Sv/y for the use of recycled products. It was shown that the calculated doses were less than 10$$mu$$Sv/y for all recycled products but one sample of recycled asphalt with 26$$mu$$Sv/y. However, 26$$mu$$Sv/y is within the range of trivial dose indicated in ICRP Pub.104 and safety for reuse of the recycled asphalt is ensured.

JAEA Reports

Scenario development on application of engineering technology for geological disposal; Study on accidents and human factors caused at site characterization, construction, operation and closure stages and that impact on safety functions after closure of disposal facility (Contract research)

Takayama, Hideki*; Takai, Shizuka; Takeda, Seiji

JAEA-Data/Code 2014-026, 189 Pages, 2015/02

JAEA-Data-Code-2014-026.pdf:8.03MB

In the safety assessment for the high-level radioactive waste geological disposal, scenarios need to be developed in consideration of influence on barrier features by applying engineering technologies at each stage of site selection, construction, operation and closure of disposal facility. To develop scenarios on application of engineering technologies from the point of view of safety regulation, it is important to grasp information of the engineering technologies which are possibly applied to geological disposal and to organize relationships between accidents and human factors caused by application of engineering technologies and influence by the factors on safety functions of engineered and natural barriers after closure stage. In this study, the engineering technologies are listed for site selection, construction, operation and closure activities at disposal site. From this information, "deviation events" which are deviated states of engineered and natural barriers from intended design were identified. We assumed influence on geological disposal facility due to the occurrence of the deviation events and identified the accidents and human factors which can progress the deviation events. Finally, we showed the sequence of influence by the accidents and human factors on long-term safety after closure of the disposal facility as scenarios. We provided a database with these results for development of scenario on engineering technology of geological disposal.

Journal Articles

Nuclear transmutation of long-lived nuclides with laser Compton scattering; Quantitative analysis by theoretical approach

Takai, Shizuka; Hagino, Koichi*

Nuclear Back-end and Transmutation Technology for Waste Disposal, p.3 - 11, 2015/00

One of the major problems of fuel cycle is the disposal of high-level radioactive waste which contains long-lived nuclides and high-decay heating nuclides. Transmuting such nuclides into short-lived or stable nuclides is one possible way to resolve this problem. Neutron capture reactions have been proposed for transmutations of such fission products. However, this transmutation method is not effective for nuclides with small neutron capture cross sections such as $$^{137}$$Cs. Recently, the photo-neutron ($$gamma$$,n) reactions via giant dipole resonance with laser Compton scattering $$gamma$$-rays has been suggested as an alternative method for nuclear transmutations. In this paper, we investigate in detail the effectiveness of the transmutation of $$^{137}$$Cs quantitatively. For the transmutation of $$^{137}$$Cs of 1g with photon flux $$10^{18}$$/s, $$10^{19}$$/s and $$10^{20}$$/s for 24 hours, 10%, 70% and 99% reduction of the initial amount of $$^{137}$$Cs is theoretically possible.

Oral presentation

Oral presentation

Dose estimate for reuse of disaster wastes contaminated by radioactive material

Takai, Shizuka

no journal, , 

Disaster wastes contaminated by the Fukushima Daiichi nuclear disaster are desired to reuse positively to reduce their amount and to utilize effectively. The part of materials contaminated in the living environment has been reused for various uses. In this research, we analyzed the dose for worker and public when contaminated concrete is reused as road construction materials, and we estimated the condition which contaminated disaster wastes can be reused in. As a result, if we set the shielding materials under 30 cm from the ground, contaminated concrete up to 2700 Bq/kg can be reused as the road construction materials. This result is used for the guide for reuse of disaster wastes in ministry of the environment. We also analyzed the dose for public considering the investigation in ministry of the environment on the present use of reused products, and we checked the safety for the investigated use of reused product.

Oral presentation

Dose estimate for the reuse of wooden chips

Takai, Shizuka; Seki, Masaya; Kimura, Hideo; Takeda, Seiji

no journal, , 

Wood (thinned wood from forest etc.) and wooden wastes (demolished wood etc.) potentially contaminated by radioactive cesium released by Fukushima Daiichi Nuclear Power Plant have been used for various purposes as wooden chips. However, there has been no dose estimation for use of such contaminated wood so far. Up to now, use of wood has been conducted according to a standard value of 100 Bq/kg for radioactive cesium based on clearance level of concrete and metal generated at nuclear power plant. The purpose of this study is to evaluate the safety of present use of wood by dose estimation for reuse of contaminated wooden chips, which are reused for main five use purposes (particle board, paper, compost, biomass power fuel, mulching). We also calculated activity concentrations of radioactive cesium in wooden chips corresponding to standard dose for safety reuse of radioactive wastes and regarded the minimum calculated activity concentration as a standard value of activity concentration for each reuse purposes. From the result, the minimum standard value of activity concentration of radioactive cesium in wooden chips for all reuse purposes is estimated to be 120 Bq/kg for reuse of wooden chips for particle board. Since this standard value is more than 100 Bq/kg, the safety of present use of wood is confirmed.

Oral presentation

Establishing criteria for reuse of disaster wastes contaminated by the Fukushima Daiichi NPP accident

Takeda, Seiji; Takai, Shizuka; Kimura, Hideo

no journal, , 

Reuse of slightly contaminated disaster wastes is effective for volume reduction of disaster wastes. Reuse of the contaminated wastes should be carried out based on ensuring the safety of radiation for the workers and the public by dose estimation approach. As a first step, we derived the cesium concentration for the limited purposes of reuse based on two types of scenarios; reuse for subbase course materials of pavements and that for embankment materials of seaside protection forest. The calculated results concluded that concrete wastes less than about 3,000 Bq/kg can be used for two types of scenarios under the design conditions such as thickness of shielding materials. As a next step, it is important to confirm the validity of the criteria of 100 Bq/kg by the effective dose estimation for comprehensive scenarios relate to reusing wooden wastes. In this study, we estimated the dose for reuse of wooden wastes to confirm the validity of 100 Bq/kg in the present reuse.

Oral presentation

Evaluation methodology for influence of splay fault growth on geological disposal system, 2; Analysis of radionuclide migration with consideration of fault growth

Shimada, Taro; Takubo, Kazuya; Takai, Shizuka; Takeda, Seiji; Tanaka, Tadao

no journal, , 

There is a residual uncertainty not able to avoid geological and climate events because some indications of them are difficult to be detected, while direct damage by the events such as active fault is avoided at site selection. Therefore radionuclide migration analysis was carried out considering safety functions of engineered barrier decreased or lost by intersection of fault and temporal and spatial changes of nuclide migration pathway under the assumption that concealed spray fault reaches the disposal system. And we evaluated the affects by inflow of fluid from deep region and of acidic groundwater from the surface along the grown spray fault. Based on the results of groundwater flow analysis, we calculated the nuclides migration fluxes at the outlet of engineered and natural barriers using nuclides migration parameters such as migration pathway, its length and groundwater velocity and sorption distribution coefficients estimated by combination of groundwater composition and geology. And important factors to affect the fluxes were extracted.

Oral presentation

Evaluation methodology for influence of splay fault growth on geological disposal system, 1; Analysis of groundwater flow with consideration of fault growth

Takai, Shizuka; Takeda, Seiji; Sakai, Ryutaro*; Shimada, Taro; Munakata, Masahiro; Tanaka, Tadao

no journal, , 

In geological disposal, direct effect caused by geological and climatic disruptive events like active faults is avoided at the stage of site characterization; however, for some events, uncertainty about avoidance in advance still remains. In this research, we researched about growth of splay fault lying concealed, which is one of such events, and developed an integrated assessment methodology from occurrence of the event to radionuclides migration based on previous studies. Furthermore, we assumed a disposal site composed of sedimentary rocks and carried out groundwater analyses with parameters of a location of repository and growth velocity of splay fault. We indicated the result of effect on migration paths and salt concentration by splay fault growth.

Oral presentation

Safety assessment for on-site storage of removed soil

Takai, Shizuka

no journal, , 

Removed Soils generated by decontamination after Fukushima Daiichi Nuclear Accident are stored on sites like schools, parks and houses where decontamination were carried out. The safety of on-site storage is assured under the control of Decontamination Guidelines. However, whether to enter or dig up the site depends on personal decision of landowners without safety evaluation. In this research, we calculated dose caused by entering or digging up of the site based on the present situation of on-site storage outside Fukushima. As a result, dose caused by entering the site is about one-hundredth of 1 mSv/y which is a safety standard in Decontamination Guidelines and also the dose limit for exposures of the public by ICRP. In addition, dose caused by digging up the site is around one-tenth of the dose limit.

28 (Records 1-20 displayed on this page)