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Journal Articles

Development of methods for recovering uranium from sludge-like uranium generated in decontamination of metal wastes

Ohashi, Yusuke; Tanaka, Yoshio; Tsunashima, Yasumichi; Ikeda, Yasuhisa*

Journal of Nuclear Science and Technology, 54(3), p.382 - 390, 2017/03

 Times Cited Count:8 Percentile:61.68(Nuclear Science & Technology)

Sludge-like uranium wastes (SUWs) have been generated with neutralization of acidic aqueous solutions used for decontamination of metal wastes containing a large amount of iron. We have examined the method for recovering uranium from such SUWs using ${{it N-cyclohexyl}}$-2-pyrrolidone (NCP) as a precipitate. As a result, it was found that precipitation ratios (PRs) of uranium in the solutions prepared by dissolving SUWs in HNO$$_{3}$$ is 97.7% at [NCP]/[U(VI)] = 20, and that the PRs of iron, aluminum, fluorine, and sulfate species are less than 1%. This indicates that uranium species are precipitated selectively. The content ratios of U, Fe, Ca, F, and S in the materials after calcining precipitates obtained at [NCP]/[U(VI)] = 20 were in accordance with the conditions of uranium ore concentrate. From these results, it is expected that highly purified uranium can be efficiently recovered from SUWs by using NCP as the precipitant.

Journal Articles

Technique for recovering uranium from sludge-like uranium-bearing wastes using hydrochloric acid

Ohashi, Yusuke; Nomura, Mitsuo; Tsunashima, Yasumichi; Ando, Shion; Sugitsue, Noritake; Ikeda, Yasuhisa*; Tanaka, Yoshio

Journal of Nuclear Science and Technology, 51(2), p.251 - 265, 2014/02

 Times Cited Count:8 Percentile:53.55(Nuclear Science & Technology)

Sludge-like uranium-bearing wastes generated from uranium refining and conversion R&D facilities are stored at the Ningyo-toge Environmental Engineering Center. We have proposed an aqueous process for recovering uranium from spent filter aid and CaF$${_2}$$ precipitate using hydrochloric acid. The distributions of the dissolved species in the sample solutions at different pH levels were calculated using the chemical equilibrium modeling system. Calculated results of fluorine contents of recovered uranium were compared with the experimental results. The fluorine content in the recovered uranium decreased as the aluminum concentration of the solution increased. On the other hand, uranium of spent filter aid was recovered selectively. The size of the particles of recovered uranium tends to decrease with increasing pH in the precipitation treatments. Also, the uranium concentration of the precipitate generated by the neutralization of the barren solution falls below 1 Bq/g.

Journal Articles

Separation technology of uranium using inorganic acid for sludge

Ohashi, Yusuke; Tsunashima, Yasumichi; Tanaka, Yoshio; Sugitsue, Noritake

Proceedings of 5th International Conference and Exhibition on Decommissioning Challenges; Industrial Reality and Prospects (CD-ROM), 10 Pages, 2013/04

Technologies for uranium refining and conversion for production of UF$$_{6}$$ had been developed in Ningyo-Toge environmental engineering center. As a result, a significant sludge like uranium bearing waste and adsorbent was generated. These wastes total 1500 tons. They are dissolved using hydrochloric acid and dissolved uranium is recovered as uranium peroxide. Impurities in uranium peroxide and uranium content were compared with the requirement defined by ASTM. Consequently, highly pure uranium which met the requirement was recovered at low pH. The uranium remaining in the solution was removed using chelating resin in order to decrease uranium radioactivity of the neutralized precipitate that is generated later in the process. It is confirmed that aluminum in the neutralized precipitate is recovered selectively using sodium hydroxide.

JAEA Reports

Preliminary test for elution of uranium waste; Concept and application for elution test

Hata, Haruhi; Yokoyama, Kaoru; Tsunashima, Yasumichi; Ohashi, Yusuke; Koga, Osamu; Sugitsue, Noritake

JAEA-Research 2011-022, 35 Pages, 2011/09

JAEA-Research-2011-022.pdf:2.92MB

For disposal of Very low-level radioactive Waste (VLLW) from nuclear related facilities, one of important factors for safety assessment is the characteristics of elution. As for VLLW from the nuclear power plant, concrete pit and trench disposals have been performed and the evaluation methods for the characteristics have been established. On the other hand, as for the uranium waste, the concept on how to test the elution characteristics is not shown yet. Based on these circumstances, preliminary tests have been conducted to study elution characteristics of uranium waste. The results show that the important factors for the uranium elution are how uranium exists in waste. In addition, the elution characteristics also depend on the precipitation amount on the disposal site. Therefore, to assess the elution rate from uranium waste, these factors must be considered.

JAEA Reports

Study on efficiency of dry decontamination technique by numerical method (Joint research)

Hyakutake, Toru*; Muto, Akinori*; Sasakura, Mariko*; Minowa, Hirotsugu*; Suzuki, Kazuhiko*; Yokoyama, Kaoru; Takahashi, Nobuo; Tsunashima, Yasumichi; Ema, Akira; Sugitsue, Noritake

JAEA-Research 2009-047, 92 Pages, 2010/01

JAEA-Research-2009-047.pdf:5.13MB

System decontamination has been generally carried out with the aim of reducing the amount of radioactive waste generated and minimizing human exposure to radiation released from nuclear fuel facilities. At the Ningyo-Toge Environmental Engineering Center, metal surfaces that are contaminated by uranium are dry decontaminated by using iodine heptafluoride (IF$$_{7}$$) as a system decontaminator. In this dry decontamination technique, a chemical reaction occurs between the uranium compound attached to the metal surface and IF$$_{7}$$. Only a few studies have been carried out on the decontamination efficiency, mechanism, level, etc. of dry decontamination techniques that use a decontamination gas. Therefore, the generalization of dry decontamination techniques is required. In the present study, the efficiency of a dry decontamination technique was assessed by a numerical method using decontamination data obtained at the Ningyo-Toge Environmental Engineering Center.

Journal Articles

Study of an aqueous process using hydrochloric acid for radioactive waste containing uranium

Ohashi, Yusuke; Tsunashima, Yasumichi; Murata, Masato

Proceedings of 2nd International Conference on Sustainable Development through Nuclear Research and Education (Nuclear 2009) (CD-ROM), p.161 - 168, 2009/05

Solid and liquid radioactive waste derived from various research such as technology development for uranium refining and conversion stored currently totals 1500tons. NaF waste, used as an absorbent of UF$$_{6}$$ contains about 20-30wt% uranium. CaF$$_{2}$$ waste, which is generated from the disposal of waste water including fluoride, contains up to 20wt% uranium. Most of these are classified as intermediate disposal waste. Hence it is necessary to recover uranium to dispose waste as a shallow ground disposal waste. Dissolution experiments were carried out by charging CaF$$_{2}$$ waste and NaF waste into 1N HCl. The dissolution rates of CaF$$_{2}$$ waste and NaF waste were 99.8% and 100% respectively. The recovery rates of uranium from CaF$$_{2}$$ solution and NaF solution were 98.2% and 99.7% respectively. It was confirmed that we could dispose these waste reasonably.

JAEA Reports

Study on reducing the generation of general waste

Aoki, Isao; ; Haga, Tetsuya; ; Sudo, Katsuo; Tsunashima, Yasumichi;

JNC TN8420 2000-005, 42 Pages, 2000/04

JNC-TN8420-2000-005.pdf:2.09MB

On August 1999, the Director of Tokai Work proposed an activity regarding recycling and reuse of general waste generated from Tokai Works. The activity was initiated by the Waste Management and Fuel Cycle Research Center, and is now being in progress through out the Tokai Works. In the course of this activity, Plutonium Fuel Center had settled the Working Group and the issues related to the waste reduction have been examined. This report collects the problems that became obvious through the survey of existing segregation method, treatment process, and the amount of the waste generation, and accounts for the concrete methodology for the recycling and reuse of general waste. In order to reduce waste, it is necessary to aware of the facing issues and adopt the countermeasures proposed in this report whenever possible. The activity will then leads us to reduce waste generation, which in turn will enable us to make 100 % waste recycling possible.

Oral presentation

Development of technology for treating and disposing of sludge contaminated with uranium, 2; Examination for recovering uranium from sludge contaminated with uranium by wet process

Ohashi, Yusuke; Nakatsuka, Yoshiaki; Kawatsuma, Shinji; Hata, Haruhi; Tsunashima, Yasumichi; Murata, Masato; Tokizawa, Takayuki; Sugitsue, Noritake

no journal, , 

Sludge waste derived from research and discussion for uranium refining and conversion exclude much uranium. We must recover uranium from them from the point of view of use of resource and we dispose of residue generated by the process. We recovered uranium from real waste by water or hydrochloric acid. The dissolution rates of uranium from sludge from neutralization and NaF, filter medium, alumina, MgF$$_{2}$$ wastes were more than 99% by 2 hour 1N HCl treatment. The dissolution rate of uranium from bed material waste was more than 99% by 24h 1N HCl treatment and addition of hydrogen peroxide. The dissolution rates of NaF, filter medium waste by water treatment were 99% and 88%. From the results, we confirmed dissolution characteristics of real waste as basic data to study recovery process of uranium.

Oral presentation

Development of technology for treating and disposing of sludge contaminated with uranium, 3; Confirmation examination for cement solidifications of sludge

Tsunashima, Yasumichi; Nakatsuka, Yoshiaki; Kawatsuma, Shinji; Ohashi, Yusuke; Murata, Masato; Tokizawa, Takayuki; Sugitsue, Noritake; Hata, Haruhi

no journal, , 

The operation waste generated from the uranium handling facilities of the uranium conversion and uranium enrichment, etc. is called a sludge. They are assumed to be execution of the uranium collection if necessary, cement solidification, and disposal. Therefore, the examination that confirmed the range where cement solidifies was executed. The cement kind, the water cement ratio, and the sludge mixture rate were assumed to be a parameter and the solidification test was executed. The range of solidification was confirmed by the bleeding water after 24 hours had passed. The uniaxial compression was measured with cement in the solidification condition. A possibility miscible from 40wt% to about 60wt% was able to be confirmed from these examination results in the absorbent (NaF pellet and active alumina), the bed materials (no active alumina), Neutralizing precipitation.

Oral presentation

Examination about the solidification for disposing of the sludge containing fluoride

Tsunashima, Yasumichi

no journal, , 

The uranium enrichment plant and conversion plant is keeping many operation wastes called sludge. Sludge contains many fluoride like the neutralization precipitate (the main component is CaF$$_{2}$$), NaF pellet, MgF$$_{2}$$ pellet which are used adsorption material. Fluoride is deleterious material and affects acceptance of a disposal site. In order to make sludges disposal, it is important to grasp the action of fluoride. This report explains the influence of elution of fluoride, a solidification agent, and a mixture agent in solidification of sludges.

Oral presentation

Solidification and leaching property of sludge containing fluoride

Tsunashima, Yasumichi; Shimazaki, Masao; Ohashi, Yusuke; Tanaka, Yoshio; Nomura, Mitsuo

no journal, , 

The operation waste of uranium conversion plant and uranium enrichment plant is called sludge, and contains many fluoride which is deleterious material. For disposal, elution of fluoride is a problem. Moreover, sludge contains many calcium sulfate and we are anxious about expansion of cement solidification object by superfluous generation ofettringite. Therefore, we report solidification and the leaching property of the cement solidification object of the sludge containing many fluoride. Moreover, we report solidification and the leaching property of sludge using magnesium oxide solidification material as a method of controlling elution and expansion of fluoride.

Oral presentation

Development of treatment processes of uranium contaminated wastes using adsorbent with high selectivity to uranium

Ohashi, Yusuke; Ando, Shion; Tsunashima, Yasumichi; Harada, Masayuki*; Ikeda, Yasuhisa*; Asanuma, Noriko*

no journal, , 

Sludge like uranium bearing waste and adsorbent were dissolved using hydrochloric acid. Uranium in the solution is recovered using PVPP. Recovered uranium was desorbed from PVPP using pure water and then uranium was recovered as uranium peroxide. As a result, it was confirmed that highly pure uranium was recovered.

Oral presentation

Solidification and leaching property by time progress of the sludge containing fluoride

Tsunashima, Yasumichi; Ohashi, Yusuke; Shimazaki, Masao; Nomura, Mitsuo; Tanaka, Yoshio

no journal, , 

The operation waste of uranium conversion plant and uranium enrichment plant is called sludge, and contains many fluoride which is deleterious material. For disposal, elution of fluoride is a problem. Moreover, sludge contains many calcium sulfate and we are anxious about expansion of cement solidification object by superfluous generation of Ettringite. In order to solve these subjects, the solidification examination of the sludge which used calcium hydrogen phosphate is considered as magnesium oxide system solidification material. The solidification and leaching property by time progress of the sludge containing fluoride are reported.

Oral presentation

Development of technology for separating uranium from sludge-wastes containing iron

Ohashi, Yusuke; Tsunashima, Yasumichi; Murashita, Shinji; Ando, Shion; Tanaka, Yoshio; Ikeda, Yasuhisa*

no journal, , 

The sludge - like uranium generated by neutralization of the acid water used for decontamination of metal wastes contains much iron. We have examined the aqueous method for recovering uranium from sludge - like uranium containing iron using N-cyclohexyl-2-pyrrolidone (NCP). Precipitation ratio of uranium in the solution prepared by dissolving sludge - like uranium containing iron using HNO$$_{3}$$ increases as additive amount of NCP increases and it became 97%. The precipitation ratio of iron, aluminum, fluorine and sulfate are less than 1% at all additive amounts of NCP investigated, which indicates that uranium can be selectively recovered by NCP.

Oral presentation

Elucidation of heavy-metal tolerance mechanism in ${it Phragmites australis}$ (Cav.) Trin. ex Steud. without iron plaque formation

Okuma, Miyu*; Yamaji, Keiko*; Nakamoto, Yukihiro*; Fukuyama, Kenjin*; Tsunashima, Yasumichi

no journal, , 

At our study site, mill tailing pond, which is used as a temporary storage site to treat mine water containing iron, manganese, etc., ${it Phragmites australis}$ (Cav.) Trin. ex Steud. has been found to grow naturally there; therefore, this plant was considered to have some metal tolerance mechanisms. Actually, ${it P. australis}$ was previously reported to enhance heavy metal tolerance through the formation of iron plaques; however, few iron plaques were observed on roots of ${it P. australis}$ growing Fe deposition site close to the entrance of mine water at our study site, suggesting that they may have another heavy metal tolerance mechanisms. The objective of this study was to elucidate the heavy metal tolerance mechanisms of ${it P. australis}$, without iron plaque formation. Elemental analysis clarified that high concentrations of Fe, Al, and Zn were accumulated in healthy nodal roots; especially, excessive Fe accumulation was confirmed compared with normal plants. Detoxicant analysis in the roots indicated that phenolics and organic acids were not produced well to contribute to the tolerance. Due to the observation of sections of ${it P. australis}$ nodal roots stained with potassium ferrocyanide solution, Fe localization was observed in the epidermis and the cell walls of the outermost layers of the cortex cells. Since immobilization of heavy metals in the cell walls is known as one of the heavy metal tolerance mechanisms in plants, our results suggest that ${it P. australis}$ would show the tolerance to immobilize Fe in the cell walls to prevent from migrating into the interior cells.

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