Refine your search:     
Report No.
 - 
Search Results: Records 1-20 displayed on this page of 22

Presentation/Publication Type

Initialising ...

Refine

Journal/Book Title

Initialising ...

Meeting title

Initialising ...

First Author

Initialising ...

Keyword

Initialising ...

Language

Initialising ...

Publication Year

Initialising ...

Held year of conference

Initialising ...

Save select records

Journal Articles

Vertical distributions of Iodine-129 and iodide in the Chukchi Sea and Bering Sea

Miwa, Kazuji; Obata, Hajime*; Suzuki, Takashi

Journal of Nuclear Science and Technology, 57(5), p.537 - 545, 2020/05

 Times Cited Count:1 Percentile:23.13(Nuclear Science & Technology)

This study investigated the vertical distribution of Iodine-129 ($$^{129}$$I) which is mainly produced by European nuclear reprocessing plants in the Chukchi Sea and Bering Sea. $$^{129}$$I was found to be distributed almost uniformly in fallout level, and an increasing in $$^{129}$$I concentration levels caused by high $$^{129}$$I water inflow from the Atlantic Ocean was not observed. Additionally, we revealed the vertical distribution of iodide, one chemical form of iodine, from the Bering Shelf area to the Chukchi Sea for the first time. The increasing tendency of iodide near sea bottom was observed.

Journal Articles

Development of dose estimation system integrating sediment model for recycling radiocesium-contaminated soil to coastal reclamation

Miwa, Kazuji; Takeda, Seiji; Iimoto, Takeshi*

Radiation Protection Dosimetry, 184(3-4), p.372 - 375, 2019/10

 Times Cited Count:0 Percentile:0.01(Environmental Sciences)

The Ministry of the Environment has indicated the policy of recycling the contaminated soil generated by decontamination activity after the Fukushima accident. By recycling to coastal reclamation which is one of effective recycling application, dissolved radiocesium and absorbed radiocesium on soil particles will flow out to the ocean by construction, therefore evaluating radiocesium transition in ocean considering the both types of radiocesium is important for safety assessment. In this study, the radiocesium outflow during constructing and after constructing is modeled, and radiocesium transition in ocean is evaluated by Sediment model suggested in OECD/NEA. The adaptability of sediment model is confirmed by reproducing evaluation of the coastal area of Fukushima. We incorporate the sediment model to PASCLR2 code system to evaluate the doses from radiocesium in ocean.

Journal Articles

Student and Young researcher's view of research on health physics and environment science

Miwa, Kazuji; Terasaka, Yuta; Ochi, Kotaro; Futemma, Akira; Sasaki, Miyuki; Hirouchi, Jun

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 61(9), p.687 - 691, 2019/09

This report summarizes the contents of the session of the Health Physics and Environment Science Division, which was held in Atomic Energy Society of Japan 2019 Spring Meeting. In this session, six students and young researchers who engaged in the field of nuclear energy and radiation gave a lecture about health physics and environmental science research through their expertise. After the all presentations end, we took discussion time about the issues and future development in this field with all attendees. In this report, we summarized each lecture outline and discussion contents.

Journal Articles

Current status and issues for clearance, 5; Concept of restricted use of contaminated rubbles in the Fukushima Daiichi NPS

Shimada, Taro; Miwa, Kazuji; Takeda, Seiji

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 61(7), p.531 - 534, 2019/07

Rubbles less than 5 $$mu$$Sv/h of surface dose rate, which are stored outdoor in the Fukushima Daiichi NPS (1F) site, will be recycled and applied in a restricted reuse only within 1F site in the future. However, there is no precedent for establishing the reference values such as dose and/or concentration for reuse or recycling under the existing exposure situation. In this study, we suggested a concept for establishing the reference radioactive concentration of recycling material for the restricted use in the 1F site. In addition, based on the concept, we calculated the reference radiocesium concentrations of the recycling material used for paved roads and the bases of concrete building.

Journal Articles

Joint meeting of young researchers in the field of radiation protection and radiation biology

Kataoka, Noriaki*; Nakajima, Junya; Miwa, Kazuji; Hirota, Seiko*; Tsubota, Yoichi; Yamada, Ryohei; Fujimichi, Yuki*; Ishikawa, Junya*; Sunaoshi, Masaaki*

Hoken Butsuri (Internet), 54(2), p.140 - 145, 2019/06

It is the written report of the joint meeting of young researchers in the field of radiation protection and radiation biology.

Journal Articles

Study on restricted use of contaminated rubble on Fukushima Daiichi NPS site, 2; Validation of reference radiocesium concentration for recycling materials

Miwa, Kazuji; Shimada, Taro; Takeda, Seiji

Progress in Nuclear Science and Technology (Internet), 6, p.166 - 170, 2019/01

In this study, in order to validate the restricted use of recycling material at the reference radiocesium concentration (determined in series report (1)), we evaluated worker annual doses, air dose rate at the site boundary and impact of migrated radiocesium into groundwater. Firstly, we evaluated the additional annual dose for workers, on the assumption that typical workers coming in contact with the source after construction (Road: 1.2 mSv/y, Building: 1.3 mSv/y). Secondly, we evaluated the air dose rates by distance from road and building including recycling material, and investigated the distance for not exceeding 1 mSv/y (including additional dose rate by recycling and background dose rate of 0.6 mSv/y) at the site boundary (Road: 25 m, Building: 1 m). Thirdly, we evaluated the Cs migration in groundwater, and investigated the distance required for satisfying the operation target value ($$^{134}$$Cs: 1 Bq/L, $$^{137}$$Cs: 1 Bq/L) at the boundary (coastal line) (Road: 10 m, Building: 10 m).

Journal Articles

Study on restricted use of contaminated rubble on Fukushima Daiichi NPS site, 1; Estimation of reference radiocesium concentration for recycling materials

Shimada, Taro; Miwa, Kazuji; Takeda, Seiji

Progress in Nuclear Science and Technology (Internet), 6, p.203 - 207, 2019/01

Rubbles less than 5 $$mu$$Sv/h of surface dose rate, which are stored outdoor in the Fukushima Daiichi NPS (1F) site, will be recycled and applied in a restricted reuse only within 1F site in the future. In this study, we suggested a concept for establishing the reference radioactive concentration of recycling material for the restricted use in the 1F site. Reference radiocesium concentration is calculated so that increased dose rate by restricted reuse does not exceed 1 $$mu$$Sv/h which is the minimum value of dose rate map in the 1F entire site. In order to justify the restricted reuse under the reference concentration calculated, additional occupational dose, dose rate at the site boundary and groundwater concentration at the outlet to the ocean are evaluated and confirmed that the values are below 2 mSv/y, 1 mSv/y and 1 Bq/cm$$^{3}$$ of $$^{134}$$Cs and $$^{137}$$Cs, respectively. And then calculated the reference radiocesium concentrations of the recycling material used for paved roads and the bases of concrete building.

Oral presentation

Iodine speciation and iodine-129 distribution in the Chukchi Sea and Bering Sea

Obata, Hajime*; Miwa, Kazuji*; Kondo, Yoshiko*; Gamo, Toshitaka*; Otosaka, Shigeyoshi; Suzuki, Takashi

no journal, , 

Distributions chemical species of iodine (iodide, iodate and organic iodine) in seawater were investigated in the Chukchi Sea and Bering Sea, Arctic northern marginal seas. $$^{129}$$I, which is a good tracer for anthropogenically released iodine to the marine environments, were also revealed by this study. Iodide concentrations in seawater often increased toward the seafloor. This tendency was remarkable with iodide and organic iodine, indicating that these iodine species are released from the sediments of the continental shelf. Concentrations of $$^{129}$$I ranged from 0.79 to 2.89$$times$$10$$^{7}$$ atom/L. While this level was several times higher than those in the North Pacific, significant increase of $$^{129}$$I concentration due to seawater inflow from the North Atlantic was not observed. Considering latitudinal range of this study area, it can be estimated that most $$^{129}$$I detected by this study was derived by atmospheric deposition of $$^{129}$$I originates from Europe.

Oral presentation

Distribution and source of I-129 in Chukchi Sea and Bering Sea

Miwa, Kazuji; Obata, Hajime*; Suzuki, Takashi; Otosaka, Shigeyoshi

no journal, , 

I-129 in a global environment is originated from the European nuclear fuel reprocessing plants (NFRP), Sellafield in U.K. and La Hague in France, and it is observed a large amount of I-129 inflows from European NFRP into the eastern and central Arctic Ocean. Previous studies on I-129 at surface indicated seawater with high I-129 concentration does not inflow from eastern and central Arctic Ocean to Chukchi Sea, located in western Arctic Ocean. However, there is a possibility of inflow of I-129 because the vertical distribution of I-129 has not observed at the ocean. The purpose of this study is to identify the inflow of seawater with high I-129 concentration from eastern and central Arctic Ocean by observing the vertical distribution of I-129 and water mass structure in Chukchi Sea and Bering Sea. Seawater with high temperature at surface of southern Chukchi Sea (- 66$$^{circ}$$N) and with low temperature at bottom of the northern Chukchi Sea (69$$^{circ}$$N - ) were observed. The seawater with low temperature might include high I-129 concentration. However, I-129 concentration in some points was observed ranging from 0.79 to 2.89 (10$$^{7}$$atoms/L), which was two orders of magnitude lower than that in the eastern and central Arctic Ocean. And no significant difference of I-129 concentration between seawater at surface and at bottom was shown. Therefore, we could not identify the inflow of seawater with high I-129 concentration from eastern and central Arctic Ocean to Chukchi Sea.

Oral presentation

Evaluation of radiocesium concentration in contaminated debris for restricted recycling in the site of Fukushima Daiichi NPS

Miwa, Kazuji; Shimada, Taro; Takai, Shizuka; Nabekura, Nobuhide; Takeda, Seiji

no journal, , 

A part of the debris with relatively lower radioactive concentrations, which have been stored in the site of Fukushima Daiichi Nuclear Power Station (1F), have been planned to be recycled for restricted purpose in the 1F site. In this study, we evaluated reference values of upper radiocesium concentrations which are practicable to recycle materials for some applications such as road. Radiation doses for all workers in the 1F site are controlled. There is no previous reference values estimated for restricted recycling under the condition of controlled radiation doses for workers in the 1F site. Therefore, we evaluated the reference values not to exceed the additional air radiation dose as 1$$mu$$Sv/h with recycling the debris, which is the estimated minimum dose rate in the 1F site regarded as background. As a result, the highest value of radiocesium concentration of recycling materials was evaluated to be 100,000 Bq/kg in the case of use as the sub-base in the concrete paving road.

Oral presentation

Study on restricted use of contaminated debris on Fukushima Daiichi NPS site, 1; Estimation of reference radioactive concentration for recycling materials

Shimada, Taro; Miwa, Kazuji; Takeda, Seiji

no journal, , 

Rubbles less than 5$$mu$$Sv/h of surface dose rate, which are stored in the Fukushima Daiichi NPS (1F) site, will be recycled and applied in a restricted use only within 1F site in the future. In this study, we suggested a concept for establishing the reference radioactive concentration of recycling material for the restricted use in the 1F site, and then calculated the reference radiocesium concentrations of the recycling material used for paved roads and the bases of concrete building. In order to prevent the working time from being decreased, it is necessary for the restricted use to suppress the additional dose to a level of value. Therefore, focusing on the current background air dose rate in the 1F site, we suggested the required condition that air dose rate increased by use of contaminated recycling material instead of non-contaminated did not exceed the variation range of the background dose rate. In addition, to validate the restricted use under the reference concentration, following three items should be confirmed; (1) additional dose for worker using the recycling material does not exceed 2mSv/y, 10% of worker dose limit; (2) the impact to air dose rate evaluated at the 1F site boundary does not exceed the 1mSv/y including direct and skyshine radiations from wastes stored in the site; (3) the impact of migrated radionuclides into groundwater does not exceed the operational target value. The reference radiocesium concentrations for recycling aggregate taken from contaminated concrete rubbles were evaluated for paved road and bases of concrete building.

Oral presentation

Study on restricted use of contaminated debris on Fukushima Daiichi NPS site, 2; Validation confirming of reference radioactive concentration for recycling materials

Miwa, Kazuji; Shimada, Taro; Takeda, Seiji

no journal, , 

In this study, in order to validate the restricted use of recycling material at the reference radiocesium concentration (determined in series report (1)), we evaluated worker annual doses, air dose rate at the site boundary and impact of migrated radiocesium into groundwater. Firstly, we evaluated the additional annual dose for workers, on the assumption that typical workers coming in contact with the source after construction (Road: 1.3 mSv/y, Building: 1.3 mSv/y). Secondly, we evaluated the air dose rates by distance from road and building including recycling material, and investigated the distance for not exceeding 1mSv/y (including additional dose rate by recycling and background dose rate of 0.6 mSv/y) at the site boundary (Road: 25 m, Building: 1 m). Thirdly, we evaluated the Cs and Sr migration in groundwater, and investigated the distance required for satisfying the operation target value (Cs-134: 1 Bq/L, Cs-137: 1 Bq/L, Sr-90: 5 Bq/L) at the boundary (coastal line) (Road: 10 m, Building: 10 m).

Oral presentation

Concept of restricted use of contaminated rubbles in the Fukushima Daiichi NPS

Shimada, Taro; Miwa, Kazuji; Takeda, Seiji

no journal, , 

Rubbles less than 5 $$mu$$Sv/h of surface dose rate, which are stored outdoor in the Fukushima Daiichi NPS (1F) site, will be recycled and applied in a restricted reuse only within 1F site in the future. However, there is no precedent for establishing the reference values such as dose and/or concentration for reuse or recycling under the existing exposure situation. In this study, we suggested a concept for establishing the reference radioactive concentration of recycling material for the restricted use in the 1F site. In addition, based on the concept, we calculated the reference radiocesium concentrations of the recycling material used for paved roads and the bases of concrete building.

Oral presentation

Development of ocean radiocesium distribution estimation system for recycling radiocesium-contaminated soil to coastal reclamation

Miwa, Kazuji; Takeda, Seiji; Iimoto, Takeshi*

no journal, , 

The Ministry of the Environment has indicated the policy of recycling the contaminated soil generated by decontamination activity after the Fukushima accident as material. By recycling to coastal reclamation which is one of effective recycling application, dissolved radiocesium and absorbed radiocesium on soil particles will flow out to the ocean by construction. It is suggested by previous studies that the both types of radionuclides affect concentration of radionuclides in marine organism. In safety assessment for the recycling, it is necessary to consider transition of nuclides in both types. Therefore, we developed a model to evaluate the radionuclides transition in the ocean considering the both types of radionuclides which flow out during constructing and operation. The concentration of radiocesium in ocean is estimated with time, and the impact of internal exposure dose by sea food ingestion is evaluated through comparison with other major exposure pathway.

Oral presentation

Development of dose evaluation method for confirmation of completion of decommissioning, 1; Development of estimation method of contamination distribution for dose evaluation

Shimada, Taro; Nabekura, Nobuhide*; Miwa, Kazuji; Takeda, Seiji

no journal, , 

It is required to confirm that dose of public using the land after site release for is less than the criteria by dose evaluation based on the contamination distribution obtained by site survey before the completion of the decommissioning of nuclear facilities. Therefore JAEA is developing the methodology to evaluate public dose. We studied estimating methods for contamination distribution based on the data from the scoping survey and the final sampling measurement with errors using external drift kriging. As a result, it is indicated that estimated distribution by external drift kriging using scoping survey results with measurement errors is the same as that without measurement error. Estimation variance was increased with measurement errors. Therefore the evaluation method will be applied to determine the radioactivity distribution with uncertainty.

Oral presentation

Development of dose evaluation method for confirmation of completion of decommissioning of nuclear facilties, 2; Development of dose evauation method caused by surface soil contamination after site release

Miwa, Kazuji; Namekawa, Masakazu*; Shimada, Taro; Takeda, Seiji

no journal, , 

For development of technical foundation to confirm the completion of the decommissioning of nuclear facilities, JAEA is developing the methodology to evaluate the dose in considering radionuclides migration by not only groundwater migration but also surface water migration and surface soil migration. We studied estimating methods for radionuclide migration between the surface water and surface contaminated soil, changes of radionuclide distribution, and direct outflow of radionuclides to the sea. In addition, preliminary analysis of the surface water migration and soil migration based on the topography and rainfall conditions is performed by using a general-purpose water and soil runoff evaluation code. The methodology will be applied to evaluate the dose by using the out put of the surface water migration and soil migration.

Oral presentation

Approach of radiation protection on recycling materials contaminated by radionuclides

Miwa, Kazuji; Iimoto, Takeshi*

no journal, , 

ICRP Publ.103 shows that reference levels are used for radiation protection of public exposure in existing exposure situation. However, there is no specific description about actual operation of reference levels. There is a possibility that a more rational radiation protection concept can be applied depending on the scale of environmental pollution in the existing exposure situation. This study proposes variation of radiation protection concept for public exposure assuming reusing radiation contaminated material which is in existing exposure situation.

Oral presentation

Development of dose evaluation method for confirmation of completion of decommissioning, 1; Development of radioactivity distribution evaluation combined with scoping survey and sampling measurement

Shimada, Taro; Nabekura, Nobuhide*; Miwa, Kazuji; Takeda, Seiji

no journal, , 

It is necessary for confirmation of completion of decommissioning of nuclear facilities to comply with dose criteria for public using the land after site release, based on the radioactivity distribution at the land of the site. We are developing a methodology of public dose evaluation based on the survey results of evaluation of the radioactivity distribution. In this report, the external drift kriging method combined with scoping survey and sampling measurement were applied to 1km square area, and a cross validation method was applied to validate the evaluated distribution. Index of Mean Absolute Error is appropriate to evaluate the difference between evaluation and measurement. In addition, upper limit of 95% single side confidence interval for the evaluation of non-measured point was suggested to input for dose evaluation.

Oral presentation

Development of dose evaluation method for confirmation of completion of decommissioning, 3; Development of dose estimation method considering changes in surface soil contamination distribution

Miwa, Kazuji; Namekawa, Masakazu*; Shimada, Taro; Takeda, Seiji

no journal, , 

The distribution of surface soil contamination on the site of nuclear facilities after confirmation of the decommissioning may be changed by rainfall. In this study, the radionuclides migration model is developed to evaluate the radiation dose to the public including radionuclides distribution change. The result of radionuclides migration estimation on virtual site condition suggests that radionuclides which is migrated by surface water and soil migration gather in depression area. It is also shown that radionuclides migration on surface is more significant path to the ocean than radionuclides migration in groundwater. Based on these findings, it is suggested that the radiation dose considering change of radionuclides distribution may be larger than that from initial radionuclides distribution.

Oral presentation

Radiation protection perspectives needed for discussions of recycling radionuclides contaminated materials

Miwa, Kazuji

no journal, , 

There are large amount of radionuclides contaminated soil and debris in Fukushima Prefecture after Fukushima Daiichi Nuclear Power Station accident. It is difficult to dispose the entire amount of soil and debris as radioactive waste from the view point of preparing the disposal site. Therefore, we focused on the recycling as one of the way to reduce the quantity of the radionuclides contaminated materials. In this study, we organised the issues when assuming recycling in the current concept of radiation protection, and propose the way of applying the concept of radiation protection to the regulation in the field. Specifically, we proposed five ways of applying the reference level in radiation protection from radionuclides contaminated material in existing exposure situation. In addition, we calculated radionuclides concentrations for two model case of recycling applying proposed radiation protection concept.

22 (Records 1-20 displayed on this page)