The Deposition densities of radiocesium and the air dose rates in undisturbed fields around the Fukushima Dai-ichi Nuclear Power Plant; Their temporal changes for five years after the accident

Mikami, Satoshi; Tanaka, Hiroyuki*; Matsuda, Hideo*; Sato, Shoji*; Hoshide, Yoshifumi*; Okuda, Naotoshi*; Suzuki, Takeo*; Sakamoto, Ryuichi*; Ando, Masaki; Saito, Kimiaki

Journal of Environmental Radioactivity, 210, p.105941_1 - 105941_12, 2019/12

AA2019-0019.pdf:2.65MB

https://doi.org/10.1016/j.jenvrad.2019.03.017

The deposition densities of radiocesium and the air dose rates were repeatedly measured in a large number of undisturbed fields within the 80km zone that surrounds the Fukushima Dai-ichi Nuclear Power Plant site between 2011 and 2016, and features of their temporal changes were clarified. The average air dose rate excluding background radiation in this zone decreased to about 20% of the initial value during the period from June 2011 to August 2016, which was essentially a result of the radioactive decay of Cs with a half-life of 2.06y. The air dose rate reduction was faster than that expected from the decay of radiocesium by a factor of about two, with most of this reduction being attributed to the penetration of radiocesium into the soil. The average deposition densities of Cs and Cs in fields that were not decontaminated were found to have decreased nearly according to their expected radioactive decay, which indicated that the movement of radiocesium in the horizontal direction was relatively small. The effect of decontamination was apparently observed in the measurements of air dose rates and deposition densities. Nominally, the average air dose rates in the measurement locations were reduced by about 20% by decontamination and other human activities, of which accurate quantitative analysis is and continue to be a challenge.

Estimation of doses from radioactively contaminated disaster wastes reused for pavements

Sawaguchi, Takuma; Takeda, Seiji; Kimura, Hideo; Tanaka, Tadao

Hoken Butsuri, 50(1), p.36 - 49, 2015/03

It is desirable that the disaster wastes contaminated by radioactive cesium after the severe accident at the Fukushima Nuclear Plant are reused as much as possible in order to minimize the quantity to be disposed of. Ministry of the Environment showed the policy that the wastes containing cesium of higher concentration than the clearance level (100 Bq/kg) were reusable as materials of construction such as subbase course materials of pavements under controlled condition with measures to lower exposure doses. In this study, in order to provide technical information for making a guideline on the use of contaminated concrete materials recycled from disaster wastes as pavement, doses for workers and the public were estimated, and the reusable concentration of radioactive cesium in the wastes was evaluated. It was shown that the external exposure of the public (children) residing near the completed pavement gave the minimum radiocesium concentration in order to comply with the dose criteria. The recycled concrete materials whose average concentration of cesium lower than 2,700 Bq/kg can be used as the subbase course materials of pavements.

Development of evaluation models of manpower needs for dismantling the dry conversion process-related equipment in Uranium Refining and Conversion Plant (URCP)

Izumo, Sari; Usui, Hideo; Tachibana, Mitsuo; Morimoto, Yasuyuki; Takahashi, Nobuo; Tokuyasu, Takashi; Tanaka, Yoshio; Sugitsue, Noritake

Proceedings of 15th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM 2013) (CD-ROM), 9 Pages, 2013/09

https://doi.org/10.1115/ICEM2013-96097

Turbulence spectra, transport, and flows in helical plasmas

Watanabe, Tomohiko*; Nunami, Masanori*; Sugama, Hideo*; Satake, Shinsuke*; Matsuoka, Seikichi*; Ishizawa, Akihiro*; Maeyama, Shinya; Tanaka, Kenji*

Proceedings of 24th IAEA Fusion Energy Conference (FEC 2012) (CD-ROM), 8 Pages, 2012/10

http://www-naweb.iaea.org/napc/physics/FEC/FEC2012/papers/460_TH81.pdf

Study on evaluation of project management data for decommissioning of uranium refining and conversion plant

Usui, Hideo; Izumo, Sari; Shibahara, Yuji; Morimoto, Yasuyuki; Tokuyasu, Takashi; Takahashi, Nobuo; Tanaka, Yoshio; Sugitsue, Noritake; Tachibana, Mitsuo

Proceedings of International Waste Management Symposia 2012 (WM2012) (CD-ROM), 13 Pages, 2012/02

https://www.wmsym.org/archives/2012/papers/12234.pdf

Dismantling of dry conversion facility in the uranium refining and conversion plant at Ningyo-toge began in 2008. During dismantling activities, project management data have been collected. Establishment of the calculation formula for dismantling of each kind of equipment makes it possible to evaluate manpower for dismantling the whole facility. However, it is not easy to prepare calculation formula for all kinds of equipment in the facility. Therefore, a simpler evaluation method was considered to calculate manpower based on facility characteristics. The results showed promise for evaluating dismantling manpower with respect to each chemical process. To create an effective dismantling plan, it is necessary to carefully consider use of a GH preliminarily. Thus, an evaluation method of project management data such as manpower and secondary waste generation was considered. The results showed promise for evaluating project management data of GH by using established calculation formula.

Assessment on long-term safety for geological disposal of high level radioactive waste; Application of probabilistic safety assessment methodology to uncertainties in hypothetical geological disposal system (Contract research)

Takeda, Seiji; Yamaguchi, Tetsuji; Nagasawa, Hirokazu; Watanabe, Masatoshi; Sekioka, Yasushi; Kanzaki, Yutaka; Sasaki, Toshihisa; Ochiai, Toru; Munakata, Masahiro; Tanaka, Tadao; et al.

JAEA-Research 2009-034, 239 Pages, 2009/11

JAEA-Research-2009-034.pdf:33.52MB

In safety assessment for geological disposal of high level radioactive waste, it is of consequence to estimate the uncertainties due to the long-term frame associated with long-lived radionuclides and the expanded geological environment. The uncertainties result from heterogeneity intrinsic to engineered and natural barrier materials, insufficient understanding of phenomena occurring in the disposal system, erroneous method of measurement, and incomplete construction. It is possible to quantify or to reduce the uncertainties according to scientific and technological progress. We applied a deterministic and a Monte Carlo-based probabilistic method simulation techniques to the uncertainty analysis for performance of hypothetical geological disposal system for high level radioactive waste. This study provides the method to evaluate the effects of the uncertainties with respect to scenarios, models and parameters in engineering barrier system on radiological consequence. The results also help us to specify prioritized models and parameters to be further studied for long-term safety assessment.

Present status of the liquid lithium target facility in the international fusion materials irradiation facility (IFMIF)

Nakamura, Hiroo; Riccardi, B.*; Loginov, N.*; Ara, Kuniaki*; Burgazzi, L.*; Cevolani, S.*; Dell'Ocro, G.*; Fazio, C.*; Giusti, D.*; Horiike, Hiroshi*; et al.

Journal of Nuclear Materials, 329-333(1), p.202 - 207, 2004/08

https://doi.org/10.1016/j.jnucmat.2004.04.013

International Fusion Materials Irradiation Facility (IFMIF), being developed by EU, JA, RF and US, is a deuteron-lithium (Li) reaction neutron source for fusion materials testing. In the end of 2002, 3 year Key Element technology Phase (KEP) to reduce the key technology risk factors has been completed. This paper describes these KEP tasks results. To evaluate Li flow characteristics, a water and Li flow experiments have been done. To develop Li purification system, evaluation of nitrogen and tritium gettering materials have been done. Conceptual design of remote handling and basic experiment have been donde. In addition, safety analysis and diganostics design have been done. In the presentation, the latest design and future prospects will be also summarized.

Field tests on migration of TRU-nuclide, 5; Validation study of safety assessment code system of shallow land disposal (GSA-GCL)

Munakata, Masahiro; Kimura, Hideo; Tanaka, Tadao; Mukai, Masayuki; Maeda, Toshikatsu; Ogawa, Hiromichi

Nihon Genshiryoku Gakkai Wabun Rombunshi, 2(3), p.361 - 367, 2003/09

https://doi.org/10.3327/taesj2002.2.361

no abstracts in English

Shielding experiments and analyses on proton accelerator facility at TIARA

Nakashima, Hiroshi; Sakamoto, Yukio*; Tanaka, Shunichi; Tanaka, Susumu; Baba, Mamoru*; Nakamura, Takashi*; Hirayama, Hideo*; Shin, Kazuo*; JAERI-Universities Collaboration Working Group for Accelerator Shielding Study

Proceedings of 6th International Meeting on Nuclear Applications of Accelerator Technology (AccApp '03), p.959 - 968, 2003/00

In order to validate shielding design methods on proton accelerator facilities, a series of shielding experiments in several tens of MeV energy region were carried out at the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) of Japan Atomic Energy Research Institute (JAERI). The experiments include thick target neutron yield (TTY) measurements by charged particles, deep penetration experiments on concrete, steel and polyethylene shields using p-Li monoenergetic neutron source and radiation streaming experiment at a labyrinth of TIARA using p-Cu white neutron source. These experimental results are compared with calculation results with some high-energy particle transport codes such as MCNPX and NMTC/JAERI. The TTY measurements were analyzed by a code developed by Shin with a moving source model, and the streaming experiment was also analyzed by the DUCT-III code based on Shin's equation. This paper reviews the experimental results and the analyses on the results.

Status of activities on the lithium target in the key element technology phase in IFMIF

Nakamura, Hiroo; Burgazzi, L.*; Cevolani, S.*; Dell'Ocro, G.*; Fazio, C.*; Giusti, D.*; Horiike, Hiroshi*; Ida, Mizuho*; Kakui, Hideo*; Loginov, N.*; et al.

Journal of Nuclear Materials, 307-311(Part.2), p.1675 - 1679, 2002/12

https://doi.org/10.1016/S0022-3115(02)01108-X

This paper describes the latest design of the IFMIF liquid Li target system reflecting the KEP results. Future prospects will be also summarized. To handle an averaged heat flux of 1 GW/m2 under a continuous 10 MW D beam deposition, a high-speed Li flow of 20 m/s, a double reducer nozzle and a concaved flow are applied to the target design. Hydraulic characteristics of the Li target design have been validated in a water jet experiment. To obtain a control scenario of the Li loop in an accident of the D beam trip, a transient analysis has been done. To control tritium and impurities in Li, a cold trap and two kinds of hot trap are adopted in Li purification loop. To maintain reliable continuous operation, various diagnostics are attached to the target assembly. To exchange the target assembly and back wall, a remote handling system with a multi axis arm and welding/cutting tool are designed. As an option, design of a replaceable back wall with a mechanical seal is being in progress. In a next phase of IFMIF beyond 2004, a Li test loop will be constructed for engineering validation.