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Journal Articles

Vertical distribution of $$^{129}$$I released from the Fukushima Daiichi Nuclear Power Plant in the Kuroshio and Oyashio current areas

Suzuki, Takashi; Otosaka, Shigeyoshi; Kuwabara, Jun; Kawamura, Hideyuki; Kobayashi, Takuya

Marine Chemistry, 204, p.163 - 171, 2018/08

 Percentile:100(Chemistry, Multidisciplinary)

To investigate the penetration of radionuclides released from Fukushima Daiichi Nuclear Power Plant (FDNPP), depth profiles were revealed at Kuroshio current, transition, and Oyashio current areas. The FDNPP-derived $$^{129}$$I was found in surface layer at Oyashio current and transition areas and in sub-surface layer at Kuroshio current area. Moreover, it was found that the FDNPP-derived $$^{129}$$I/$$^{134}$$Cs ratios in the Oyashio current and transition areas were higher than that in the FDNPP reactor. The higher FDNPP-derived $$^{129}$$I/$$^{134}$$Cs ratios suggest three potential mechanisms for the migration of radionuclides in the environment: (1) radioiodine was released more easily than radiocesium by the FDNPP accident, (2) $$^{129}$$I was supplied from the atmosphere by re-emitted $$^{129}$$I from contaminated areas around Fukushima, (3) leaked water that removed radiocesium reached the sampling stations. The FDNPP-derived $$^{129}$$I in sub-surface layer would be transported by the meander of the Kuroshio Extension current.

Journal Articles

Challenges for enhancing Fukushima environmental resilience, 7; Behavior and abundance of radiocesium in the coastal area off Fukushima

Otosaka, Shigeyoshi; Kobayashi, Takuya; Machida, Masahiko

Nippon Genshiryoku Gakkai-Shi, 59(11), p.659 - 663, 2017/11

It is estimated that about 70% of radiocesium released to the environment by the Fukushima Daiichi nuclear accident was carried to the ocean. In addition to monitoring surveys by the government, oceanographic research by many institutions has revealed the distribution and behavior of the accident-derived radiocesium in the ocean. Numerical simulations are efficiently used in such oceanographic investigations, and further improvements are being made based on findings newly obtained after the accident. In this paper, we review the abundance and behavior of radiocesium in the coastal area of Fukushima, deepen the scientific understanding of the current situation of environmental restoration, and explain the issues to be addressed in the future.

Journal Articles

Study on fundamental process of seawater pool nucleate boiling heat transfer

Uesawa, Shinichiro; Koizumi, Yasuo; Shibata, Mitsuhiko; Yoshida, Hiroyuki

Thermal Science and Engineering, 25(4), p.65 - 74, 2017/10

no abstracts in English

Journal Articles

Radiolysis of mixed solutions of Cl$$^{-}$$ and Br$$^{-}$$ and its effect on corrosion of a low-alloy steel

Hata, Kuniki; Inoue, Hiroyuki*; Kojima, Takao*; Kasahara, Shigeki; Hanawa, Satoshi; Ueno, Fumiyoshi; Tsukada, Takashi; Iwase, Akihiro*

Proceedings of Symposium on Water Chemistry and Corrosion in Nuclear Power Plants in Asia 2017 (AWC 2017) (USB Flash Drive), p.304 - 314, 2017/09

A model simulation of $$gamma$$ radiolysis of mixed solutions of NaCl and NaBr was carried out. The simulation result agreed well with the experimental result, and Br$$^{-}$$ played an important role in determining the amounts of products from water radiolysis. The simulation result also showed that, in highly pure NaCl solutions, the steady-state concentration of a radolytic product, H$$_{2}$$O$$_{2}$$, was mainly controlled by three reactions (Cl$$^{-}$$ + $$^{.}$$OH $$rightarrow$$ ClOH$$^{.-}$$, ClOH$$^{.-}$$ $$rightarrow$$ Cl$$^{-}$$ + $$^{.}$$OH, and ClOH$$^{.-}$$ + H$$^{+}$$ $$rightarrow$$ Cl$$^{.}$$ + H$$_{2}$$O), which indicated that accurate evaluation of the rate constants of these reactions was very important in improving the radiolysis simulation of solutions containing Cl$$^{-}$$. An immersion test using a low-alloy steel, SQV2A, in the mixed solutions was also carried out under irradiation. The corrosion rate increased or decreased depending on the pH or the concentrations of the halide ions in a similar way to the change in concentration of H$$_{2}$$O$$_{2}$$ produced from water radiolysis, which is affected by the presence of Cl$$^{-}$$ and Br$$^{-}$$. However, at high pH values ($$>$$12), the corrosion rate was almost zero even though the concentration of H$$_{2}$$O$$_{2}$$ was high. This could be attributed to enhancement of the passivity of test specimens at higher pH values.

Journal Articles

Study on forced-convective boiling heat transfer of seawater with sea salt deposition

Uesawa, Shinichiro; Koizumi, Yasuo; Shibata, Mitsuhiko; Nagatake, Taku; Yoshida, Hiroyuki

Konsoryu, 31(2), p.162 - 170, 2017/06

no abstracts in English

Journal Articles

Study on fundamental process of seawater pool nucleate boiling heat transfer

Uesawa, Shinichiro; Koizumi, Yasuo; Shibata, Mitsuhiko; Yoshida, Hiroyuki

Dai-54-Kai Nihon Dennetsu Shimpojiumu Koen Rombunshu (CD-ROM), 8 Pages, 2017/05

no abstracts in English

Journal Articles

Study on pool nucleate boiling heat transfer of suspension liquid with deposits on heat transfer surface

Uesawa, Shinichiro; Koizumi, Yasuo; Shibata, Mitsuhiko; Yoshida, Hiroyuki

Thermal Science and Engineering, 25(2), p.17 - 26, 2017/04

no abstracts in English

Journal Articles

Dissolved radiocaesium in seawater off the coast of Fukushima during 2013-2015

Fukuda, Miho*; Aono, Tatsuo*; Yamazaki, Shinnosuke*; Nishikawa, Jun*; Otosaka, Shigeyoshi; Ishimaru, Takashi*; Kanda, Jota*

Journal of Radioanalytical and Nuclear Chemistry, 311(2), p.1479 - 1484, 2017/02

 Times Cited Count:2 Percentile:42.02(Chemistry, Analytical)

In order to investigate processes affecting distribution of radiocaesium in seawater in the adjacent region of Fukushima Daiichi Nuclear Power Plant (FDNPP), relationships between $$^{137}$$Cs activity in seawater and physical properties of seawater (salinity, temperature, and potential density) were observed in seven stations within 10 km radius from the FDNPP. As a whole, $$^{137}$$Cs concentrations in seawater were higher in the vicinity of the FDNPP, and were negatively correlated with potential density. From these results, it can be considered that river water discharge or export of seawater from the FDNPP's harbor has affected the higher activity levels of $$^{137}$$Cs in seawater. It was also observed that the $$^{137}$$Cs-elevated seawater can be advected to the 20$$sim$$50 m depths.

Journal Articles

Electrochemical corrosion tests for core materials utilized in BWR under conditions containing seawater

Shizukawa, Yuta; Sekio, Yoshihiro; Sato, Isamu*; Maeda, Koji

Proceedings of 54th Annual Meeting of Hot Laboratories and Remote Handling (HOTLAB 2017) (Internet), 5 Pages, 2017/00

Electrochemical corrosion behavior under salt water in a type 304L stainless steel used to a part of BWR core materials was investigated to evaluate the possibility of crevice corrosion occurrence for the fuel assemblies which experienced seawater exposure in Fukushima Daiichi Nuclear Power Plant (1F) accident. Especially, focusing on the upper end plug part having the 304L SS crevice structure, measurement of repassivation potential for crevice corrosion ($$E_{rm R,CREV}$$) were carried out using the crevice test pieces fabricated by 304L SS plates. From the results, $$E_{rm R,CREV}$$ was lower than the spontaneous potential ($$E_{rm SP}$$) when the conditions of 2500 ppm chloride ion concentration at over 50 $$^{circ}$$C or that of 2500 ppm at over 80 $$^{circ}$$C, which are included in the SFP water quality conditions. Therefore, in the 304L SS parts of the 1F fuel assemblies that experienced seawater exposure, there is a possibility of crevice corrosion occurrence.

Journal Articles

Study on occurrence mechanism of critical heat flux condition of heat transfer surface with deposition

Uesawa, Shinichiro; Koizumi, Yasuo; Shibata, Mitsuhiko; Yoshida, Hiroyuki

Nippon Kikai Gakkai Netsu Kogaku Konfarensu 2016 Koen Rombunshu (USB Flash Drive), 2 Pages, 2016/10

no abstracts in English

Journal Articles

GTHTR300 cost reduction through design upgrade and cogeneration

Yan, X.; Sato, Hiroyuki; Kamiji, Yu; Imai, Yoshiyuki; Terada, Atsuhiko; Tachibana, Yukio; Kunitomi, Kazuhiko

Nuclear Engineering and Design, 306, p.215 - 220, 2016/09

 Percentile:100(Nuclear Science & Technology)

The latest design upgrade has incorporated several major technological advances made in the past ten years to both reactor and balance of plant in GTHTR300. As described in this paper, these advances have enabled raising the design basis reactor core outlet temperature to 950$$^{circ}$$C and increasing power generating efficiency by nearly 5% point. Further implementation of seawater desalination cogeneration is made through employing a newly-proposed multi-stage flash process. Through efficient waste heat recovery of the reactor gas turbine power conversion cycle, a large cost credit is obtained against the conventionally produced water prices. Together, the design upgrade and the cogeneration are shown to reduce the GTHTR300 cost of electricity to under 2.7 cent/kW h.

Journal Articles

Study on pool nucleate boiling heat transfer of suspension liquid with deposits on heat transfer surface

Uesawa, Shinichiro; Koizumi, Yasuo; Shibata, Mitsuhiko; Yoshida, Hiroyuki

Dai-53-Kai Nihon Dennetsu Shimpojiumu Koen Rombunshu (CD-ROM), 8 Pages, 2016/05

no abstracts in English

Journal Articles

Hydrogen generation by water radiolysis with immersion of oxidation products of zircaloy-4

Matsumoto, Yoshinobu*; Do, Thi-Mai-Dung*; Inoue, Masao; Nagaishi, Ryuji; Ogawa, Toru

Journal of Nuclear Science and Technology, 52(10), p.1303 - 1307, 2015/10

 Times Cited Count:2 Percentile:66.76(Nuclear Science & Technology)

Effects of zirconium oxides and oxidation products of zircaloy-4 on water radiolysis were investigated to predict the hydrogen generation from the water-immersed debris after a severe accident of a nuclear power plant. Observed yields of hydrogen in water containing the oxides were measured as a function of their weight fractions. Assuming that energies of Co-60 $$gamma$$-ray deposited to water and the oxides brought about the water radiolysis to generate hydrogen independently, the radiolysis showed an additional term of hydrogen generation due to the energy deposition to the oxides. This term seemed to be dependent on the specific surface area or particle size of oxides, but not on the crystal structure of oxides in our experimental results. The oxides in distilled water gave the strong enhancement of term. The enhancement tended to saturate with increasing the weight fraction of oxides and was not apparent in the seawater.

Journal Articles

Removal of cesium ions from contaminated seawater in closed area using adsorptive fiber

Someya, Takaaki*; Asai, Shiho; Fujiwara, Kunio*; Sugo, Takanobu*; Umeno, Daisuke*; Saito, Kyoichi*

Nippon Kaisui Gakkai-Shi, 69(1), p.42 - 48, 2015/02

A large amount of seriously contaminated sea water with radioactive Cs has been reserved in semi-enclosed coastal sea area which is separated by silt fences and embankments. Insoluble cobalt ferrocyanide (Co-FC) microparticles-impregnated fiber was developed for removing Cs from the contaminated sea water. The resultant Co-FC-impregnated fiber was immersed in either nonradioactive or radioactive Cs solution. The adsorption isotherm well correlated with a Langmuir-type equation. In addition, mass-transfer capacity coefficients were determined by fitting the experimental data of the rate of Cs adsorption onto the Co-FC-impregnated fiber to theoretical adsorption curves based on the Cs concentration difference between the bulk and the interface in seawater as a driving force of the overall adsorption rate. Decontamination factors as functions of fiber weight and the contact time required for the removal of cesium ions from the contaminated seawater in a closed area were estimated.

Journal Articles

Consideration of radiolytic behavior in diluted and concentrated systems of seawater for computational simulation of hydrogen generation

Nagaishi, Ryuji; Inoue, Masao; Hino, Ryutaro; Ogawa, Toru

Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 9 Pages, 2014/10

Since seawater has been used as a coolant for reactors and spent fuel pools in broken reactor buildings at Fukushima Daiichi NPS accident, radioactive contaminated water emitted following the accident has contained salt content of seawater at high concentrations, different from that at TMI-2 accident. Radiolysis of seawater leading to hydrogen generation and corrosion has been simulated and reported by several groups. However, the proposed radiolysis models cannot be always applied to water radiolysis at the wide range of salt concentrations present in the NPS, mainly because primary yields of radiolysis products of water and radiation-induced reactions are dependent on the salt concentration. In this study, the radiolytic behavior in diluted and concentrated systems of seawater was considered on the basis of results in steady state and pulse radiolysis experiments, in which the above salt effects were demonstrated from the obtained results.

Journal Articles

Nobel system for uranium recovery from seawater

Seko, Noriaki; Kasai, Noboru; Shimizu, Takao*; Tamada, Masao

Nippon Kaisui Gakkai-Shi, 59(5), p.316 - 319, 2005/10

Braid adsorbent having functional group of amidoxime is a promising material for the recovery of uranium dissolved in the seawater. This long braid adsorbent was made by polyethylene multi-fibers in which amidoxime groups were introduced by radiation-induced graft polymerization and subsequent chemical treatment. The braid adsorbent obtained was moored at the offing of Okinawa Island. The average U adsorption of the adsorbent became 1.5 g-U/kg-adsorbent for 30 d soaking. The mooring system for braid adsorbent has possibility which reduced the cost for the recovery of uranium from seawater. Annual product of 1200 tons of uranium needs 134 km$$^{2}$$ of mooring area. In addition, there is 6000 km$$^{2}$$ and more of suitable sea area for the collection of the uranium in the regions from Okinawa Islands to Tosa Bay in Japan.

Journal Articles

Development of the ocean forecasting system for Shimokita region

In, Teiji*; Shima, Shigeki*; Nakayama, Tomoharu*; Ishikawa, Yoichi*; Togawa, Orihiko; Kobayashi, Takuya; Kawamura, Hideyuki

Gekkan Kaiyo, 37(9), p.674 - 680, 2005/09

no abstracts in English

Journal Articles

Synthesis and practical scale system of braid adsorbent for uranium recovery from seawater

Tamada, Masao; Seko, Noriaki; Kasai, Noboru; Shimizu, Takao*

FAPIG, (169), p.3 - 12, 2005/03

Braid adsorbent having functional group of amidoxime is a promising material for the recovery of uranium dissolved in the seawater. This braid adsorbent was made by polyethylene multi-fibers in which amidoxime groups were introduced by radiation-induced graft polymerization and subsequent chemical treatment. Reaction time for graft polymerization was 5 h and the resulted braid adsorbent had 2.8 mmol/g-adsorbent of amidoxime group. The braid adsorbent obtained was moored at the offing of Okinawa Island. The adsorption of uranium reached 1.5g/kg-adsorbent for 30 d soaking. The mooring system for braid adsorbent has possibility which reduced the cost for the recovery of uranium from seawater. It is shown that 134 km$$^{2}$$ of mooring area is needed for annual product of 1200 tons of uranium. In addition, there is 6000 km$$^{2}$$ and more of suitable sea area for the collection of the uranium in the regions from Okinawa Islands to Tosa Bay in Japan.

Journal Articles

Establishement for the measurement of $$^{129}$$I by accelerator mass spectormetry

Suzuki, Takashi; Kitamura, Toshikatsu; Kabuto, Shoji*; Togawa, Orihiko; Amano, Hikaru

Dai-46-Kai Kankyo Hoshano Chosa Kenkyu Seika Rombun Shorokushu (Heisei-15-Nendo), p.109 - 110, 2004/12

no abstracts in English

117 (Records 1-20 displayed on this page)