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Journal Articles

Progress status and future issues of development of analysis and estimation technology for fuel debris characterization, 5; Progress status of development of Non-Destructive assay technologies for sorting and segregation of fuel debris and others

Kamada, Masaki*; Yoshida, Takuma*; Sugita, Tsukasa*; Okumura, Keisuke

Nihon Genshiryoku Gakkai-Shi ATOMO, 66(2), p.83 - 86, 2024/02

https://doi.org/10.3327/jaesjb.66.2_83

no abstracts in English

Journal Articles

Effect of gamma-ray irradiation on corrosion of stainless steel contacted with Zeolite particle

Kato, Chiaki; Yamagishi, Isao; Sato, Tomonori; Yamamoto, Masahiro*

Zairyo To Kankyo, 70(12), p.441 - 447, 2021/12

https://doi.org/10.3323/jcorr.70.441

Zeolite particles have been used in a Cs adsorption vessel for purification of contaminated water in Fukushima Dai-ich Nuclear Power Station (1F). The used Cs adsorption vessels were kept in storage space on 1F site. The risk of localized corrosion of stainless steel used in the vessel was worried. To evaluate the risk of localized corrosion, using specially designed electrochemical testing apparatus was used under gamma-ray irradiation test. And, real size mock-up test conducted. The results showed the potential change caused by creation of H $_{2}$ O $_{2}$ by water radiolysis decreased by zeolite particles and the enrichment of chloride ion concentration in the vessel do not propagate during dry up procedure of Cs adsorption vessel. These data indicate the risk of localized corrosion of Cs adsorption vessel may stay at considerably low level.

Journal Articles

A Prediction method for the dose rate of fuel debris depending on the constituent elements

Terashima, Kenichi; Okumura, Keisuke

Journal of Advanced Simulation in Science and Engineering (Internet), 8(1), p.73 - 86, 2021/03

https://doi.org/10.15748/jasse.8.73

Journal Articles

An Experimental investigation of influencing chemical factors on Cs-chemisorption behavior onto stainless steel

Nishioka, Shunichiro; Nakajima, Kunihisa; Suzuki, Eriko; Osaka, Masahiko

Journal of Nuclear Science and Technology, 56(11), p.988 - 995, 2019/11

https://doi.org/10.1080/00223131.2019.1633968

Times Cited Count：12 Percentile：80.27(Nuclear Science & Technology)

In order to contribute to improvement of Cs chemisorption model used in severe accident analysis codes, the influence of chemical factors (temperature, atmosphere, concentration of affecting chemical elements etc.) on the Cs chemisorption behaviour onto stainless steel was investigated experimentally. It was found that the surface reaction rate constant used in the current Cs-chemisorption model was influenced by not only temperature, as already known, but also atmosphere, cesium hydroxide (CsOH) concentration in the gas phase and silicon content in SS304. Such chemical factors should be considered for the construction of the improved Cs-chemisorption model. Another important finding is that the chemisorption behavior at lower temperatures, around 873 K, could differ from those above 1073 K. Namely, Cs-Fe-O compounds would form as the main Cs-chemisorbed compounds at 873 K while Cs-Si-Fe-O compounds at more than 1073 K.

Journal Articles

Prediction of the drying behavior of debris in Fukushima Daiichi Nuclear Power Station for dry storage

Nakayoshi, Akira; Suzuki, Seiya; Okamura, Nobuo; Watanabe, Masayuki; Koizumi, Kenji

Journal of Nuclear Science and Technology, 55(10), p.1119 - 1129, 2018/10

https://doi.org/10.1080/00223131.2018.1480429

Times Cited Count：2 Percentile：20.93(Nuclear Science & Technology)

Journal Articles

Effect of seawater on heat transfer without boiling in internally heated annulus

Uesawa, Shinichiro; Liu, W.; Jiao, L.; Nagatake, Taku; Takase, Kazuyuki; Shibata, Mitsuhiko; Yoshida, Hiroyuki

Nihon Genshiryoku Gakkai Wabun Rombunshi, 15(4), p.183 - 191, 2016/12

https://doi.org/10.3327/taesj.J15.024

no abstracts in English

Journal Articles

Effects of gamma-ray irradiation on spontaneous potential of stainless steel in zeolite-containing diluted artificial seawater

Kato, Chiaki; Sato, Tomonori; Ueno, Fumiyoshi; Yamagishi, Isao

Proceedings of 17th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, Vol.2, p.1357 - 1374, 2016/05

With respect to the long-term storage of the zeolite-containing spent Cs adsorption vessels used at the Fukushima Daiichi Nuclear Power Station, the corrosion of the vessel material is one of the most important issues. In this study, we performed electrochemical tests on stainless steel specimens in zeolite-containing artificial seawater under gamma-ray irradiation. The spontaneous potential ESP and critical pitting potential VC of the type 316L steel in systems in contact with various zeolites were measured in order to evaluate the corrosion resistance of the steel. In addition, the water sample was analyzed after being irradiated, in order to determine the concentrations of various dissolved oxidants such as oxygen and hydrogen peroxide, which can accelerate the corrosion process. The steady-state rest potential increased with an increase in the dose rate; however, the increase was suppressed in contact with the zeolites. The VC value of the steel when in contact with the zeolites was slightly smaller than the VC value in bulk water; however, the choice of the zeolite used as herschelite, IE96 and IE911 hardly affect the VC value. The concentration of H $_{2}$ O $_{2}$ in the bulk water under irradiation also increased with the increase in the dose rate. This increase was suppressed in the systems in contact with the zeolites, owing to the decomposition of the H $_{2}$ O $_{2}$ by the zeolites. A clear relationship was observed between ESP and the H $_{2}$ O $_{2}$ concentration. As contact with the zeolites caused the increase in ESP under irradiation to be suppressed, it can be concluded that the presence of zeolites in the spent Cs adsorption vessels can reduce the probability of the localized corrosion of the stainless steel in the vessels.

Journal Articles

Evaluation of seawater effects on thermal-hydraulic behavior for severe accident conditions, 2; Heat transfer and flow visualization experiment by using internally heated annulus

Uesawa, Shinichiro; Nagatake, Taku; Jiao, L.; Liu, W.; Takase, Kazuyuki; Yoshida, Hiroyuki

Proceedings of International Conference on Power Engineering 2015 (ICOPE 2015) (CD-ROM), 11 Pages, 2015/11

Journal Articles

Evaluation of seawater effects on thermal-hydraulic behavior for severe accident conditions, 1; Outline of the research project

Yoshida, Hiroyuki; Uesawa, Shinichiro; Nagatake, Taku; Jiao, L.; Liu, W.; Takase, Kazuyuki

Proceedings of International Conference on Power Engineering 2015 (ICOPE 2015) (CD-ROM), 9 Pages, 2015/11

Journal Articles

Localized corrosion behavior of stainless steel in the diluted artificial sea-water contacted with zeolite under -ray irradiation

Kato, Chiaki; Sato, Tomonori; Nakano, Junichi; Ueno, Fumiyoshi; Yamagishi, Isao; Yamamoto, Masahiro

Nihon Genshiryoku Gakkai Wabun Rombunshi, 14(3), p.181 - 188, 2015/09

https://doi.org/10.3327/taesj.J14.030

In relation to the consideration for long-term storage of spent Cs adsorption vessels containing zeolites in the Fukushima Daiichi Nuclear Power Station, corrosion of the vessel material in the spent Cs adsorption vessel is one of important issues. We performed electrochemical tests of stainless steel (SUS 316L) in the zeolites containing artificial seawater under -ray irradiation. The spontaneous potential ( $E_{rm SP}$ ) and critical pitting potential ( $V_{rm c}$ ), of SUS 316L were measured to understand the corrosion resistance of the stainless steel in this study. The rest potential of the stainless steel increased with increasing time after -ray irradiation. The $E_{rm SP}$ , defined as the steady rest potential, increased with increasing dose rate, while increasing $E_{rm SP}$ was suppressed by contact with the zeolites. Concentration of H $_{2}$ O $_{2}$ in bulk water increased with increasing dose rate. The concentration increasing was suppressed by contact with the zeolites due to decomposition of H $_{2}$ O $_{2}$ . There was good relationship between $E_{rm SP}$ and the concentration of H $_{2}$ O $_{2}$ . The $V_{rm c}$ of SUS 316L contacted with the zeolites decreased with increasing Cl $^{-}$ ion concentration and is slightly smaller than the $V_{rm c}$ in the bulk water. The contact with the zeolites causes the suppressant of increasing $E_{rm SP}$ under the irradiation. The contact with the zeolite can reduce probability in the localized corrosion for SUS 316L.

Journal Articles

Overview and outcomes of Benchmark Study of the Accident at the Fukushima Daiichi NPS (OECD/NEA BSAF Project)

Nagase, Fumihisa; Gauntt, R. O.*; Naito, Masanori*

Proceedings of 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16) (USB Flash Drive), p.7033 - 7045, 2015/08

The OECD/NEA Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Plant (BSAF) Project has been established in November 2012. Fifteen organizations of eight countries calculated thermo-hydraulic behavior with severe accident integral codes. The primary objective of this benchmark study is to estimate accident progression, status in the reactor pressure vessels and primary containment vessels, and status of debris distribution for a debris removal plan. Finally the calculated results submitted by the participants were compared and evaluated to estimate the accident progression and status inside the reactors though the results showed wide variations. Still remaining uncertainties and data needs that are useful to the communication between analysts and decommissioning activities are also summarized as the output from the project.

Journal Articles

The Thermal-hydraulic behavior of seawater in an internally heated annulus

Uesawa, Shinichiro; Nagatake, Taku; Jiao, L.; Takase, Kazuyuki; Yoshida, Hiroyuki

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 8 Pages, 2015/05

Journal Articles

Development of numerical simulation for jet breakup behavior in complicated structure of BWR lower plenum, 6; Influence of the simulant molten fuel properties on jet breakup phenomenon in multi-channels

Suzuki, Takayuki; Yoshida, Hiroyuki; Abe, Yutaka*; Kaneko, Akiko*

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 7 Pages, 2015/05

In order to improve the safety of Boiling Water Reactor (BWR), it is required to know the behavior of the plant when an accident occurred. Especially, it is important to estimate the behavior of molten core jet in the lower part of the reactor pressure vessel at a severe accident. In the BWR lower plenum, the flow characteristics of molten core jet are affected by many complicated structures, such as control rod guide tubes, instrument guide tubes and core support plate. The objective of this study is to develop the simulation method for the flow characteristic of molten core jet including the effects of the complicated structures in the lower plenum based on interface tracking method code TPFIT (Two Phase Flow simulation code with Interface Tracking). To verify and validate the applicability of the developed method in detail, it is necessary to obtain the experimental data that can be compared with detailed numerical results by the TPFIT. Therefore, experimental works by use of multi-phase flow visualization technique were also carried out. In the experiments, time series of interface shapes are observed by high speed camera and velocity profiles in/out of the jet were measured by the PIV method. In this paper, we carried out a numerical simulation of the jet breakup phenomena in the multi-channels with various simulant molten materials to evaluate the influence of properties on the jet breakup phenomena. As a result, it was confirmed that density and surface tension affected on the falling down velocity of the simulant materials and the interface behavior of the molten jet. However, viscosities of the simulant materials have small effects on jet breakup phenomena, including the interface shape and size of fragments.

Journal Articles

Study of treatment scenarios for fuel debris removed from Fukushima Daiichi NPS

Washiya, Tadahiro; Yano, Kimihiko; Kaji, Naoya; Yamada, Seiya*; Kamiya, Masayoshi

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 7 Pages, 2015/05

On March 11, 2011, a severe nuclear accident occurred at Tokyo Electric Power Company (TEPCO)'s Fukushima Daiichi Nuclear Power Plant (hereinafter called as F1). After the accident, the Council for the Decommissioning was established, mainly by the government and TEPCO, and a road map for the F1 decommissioning was drawn up. In the road map, the fuel debris removal from the reactors is scheduled to launch around 2020. In this study, the characteristics and technological issues of each potential treatment scenario were extracted, and the scenarios were prioritized in advance of formal evaluations in the future. The preliminary evaluation results show that long term storage and direct disposal have more positive aspects in terms of economic efficiency and radioactive waste generation. On the other hand, stabilizing processing, aqueous processing, and pyrochemical processing have been estimated to have more disadvantages in such aspects.

Journal Articles

Effect of zeolites on the corrosion potential of type 316L stainless steel in diluted artificial sea water under gamma-ray irradiation

Kato, Chiaki; Sato, Tomonori; Ueno, Fumiyoshi; Yamagishi, Isao; Yamamoto, Masahiro

Zairyo To Kankyo 2015 Koenshu (CD-ROM), p.83 - 86, 2015/05

In relation to the consideration for long-term storage of spent Cs adsorption vessels containing zeolites in the Fukushima Daiichi Nuclear Power Station, corrosion of the vessel material in the spent Cs adsorption vessel is one of important issues. We performed electrochemical tests of stainless steel (SUS 316L) in the zeolites containing artificial seawater under gamma-ray irradiation. The spontaneous potential (ESP) and critical pitting potential (VC), of SUS316L were measured to understand the corrosion resistance of the stainless steel in this study. The rest potential of the stainless steel increased with increasing time after gamma-ray irradiation. The ESP, defined as the steady rest potential, increased with increasing dose rate, while increasing ESP was suppressed by contact with the zeolites. Concentration of H $_{2}$ O $_{2}$ in bulk water increased with increasing dose rate. The concentration increasing was suppressed by contact with the zeolites due to decomposition of H $_{2}$ O $_{2}$ . There was good relationship between ESP and the concentration of H $_{2}$ O $_{2}$ . The VC of SUS316L contacted with the zeolites decreased with increasing Cl $^{-}$ ion concentration and is slightly smaller than the VC in the bulk water. The contact with the zeolites causes the suppressant of increasing ESP under the irradiation. The contact with the zeolites can reduce probability in the localized corrosion for SUS316L.

Journal Articles

Corrosion of the stainless steel in the zeolite containing diluted artificial seawater under -ray irradiation

Kato, Chiaki; Sato, Tomonori; Nakano, Junichi; Ueno, Fumiyoshi; Yamagishi, Isao

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

As a part of consideration for long-term storage of spent zeolite adsorption vessels in the Fukushima Daiichi Nuclear Power Station, corrosion of vessel material in the spent zeolite adsorption vessel is one of important issue. We performed electrochemical tests of stainless steel (type 316L) in the zeolite containing artificial seawater under -ray irradiation. Steady spontaneous potential (Esp) and pitting potential (VC), of type 316L was measurement. $^{60}$ Co -rays source was used under irradiation. Dose rate of -ray irradiation was controlled for 5 kGy/h and 400 Gy/h. In anode polarization curves, there was no clear difference under irradiation and non-irradiation. The corrosion potential of type 316L increased with increasing time after -ray irradiation. The Esp was shifted to nobler by -rays irradiation, while increasing Esp was suppressed by contacted with zeolite.