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Journal Articles

Study on criticality in natural barrier for disposal of fuel debris from Fukushima Daiichi NPS

Shimada, Taro; Takubo, Kazuya*; Takeda, Seiji; Yamaguchi, Tetsuji

Progress in Nuclear Science and Technology (Internet), 5, p.183 - 187, 2018/11

After fuel debris is removed from the reactor containment vessel at Fukushima Daiichi NPS (1F) and collected in waste containers in the future, the waste containers will be disposed at a deep geological repository. The uranium inventory and uranium-235 ($$^{235}$$U) enrichment of the fuel debris are larger than those of high-level vitrified wastes which are produced from liquid waste during reprocessing of spent nuclear fuels. Therefore, there is a possibility not to be excluded that a criticality occurs in the geological media where the uranium precipitates at the far-field from the repository, after the uranium located in the repository is dissolved by groundwater. In this study, we calculated the quantity of uranium precipitated at the natural barrier, and studied dimension of uranium deposited in the natural barrier and carried out the criticality analysis.

Journal Articles

Analysis on the effect of forest decontamination on reducing the air dose rate using the three-dimensional transport code MCNP

Hemmi, Ko; Yamaguchi, Tetsuji; Takeda, Seiji; Kimura, Hideo

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 24(1), p.3 - 14, 2017/06

Conditions of contaminated sources and ranges of forest decontamination that significantly reduce the air dose rate in residential areas were investigated by means of a sensitivity analysis related to the decontamination of the forest contaminated by radiocesium deriving from the accident at Fukushima Daiichi Nuclear Power Station. The contaminated sources including $$^{134}$$Cs and $$^{137}$$Cs were assumed to be a layer of sedimented organic matter (the A$$_{0}$$ layer) and surface soils (the A$$_{1}$$ layer). The air dose rates were calculated using the three-dimensional Monte Carlo transport code MCNP. A slope number of the forest, angles, state of contaminant distribution, radiocesium content in the forest soils, decontamination ranges, distance from the forest boundary to an evaluation point, and height at the evaluation point were adopted as the parameters. The decontamination of a litter (A$$_{0}$$) layer within the distance of 20 m from the forest boundary was revealed to be effective in reducing the air dose rate when the source distribution was homogeneous. The air dose rates were significantly reduced by the decontamination of the A$$_{0}$$ layer within a distance of 40 m from the forest boundary on condition that the radiocesium content of the A$$_{0}$$ layer was larger than that of the A$$_{1}$$ layer and the source distribution was non-homogeneous, such as the forest areas beyond 20 m from the forest boundary, which were more heavily contaminated than those within 20 m.

Journal Articles

The Survey for the integrity of containers for secondary wastes generated from contaminated water treatment

Iida, Yoshihisa; Nakadoi, Yasumasa; Yamaguchi, Tetsuji

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 24(1), p.53 - 64, 2017/06

The information on the contaminated water treatment in Fukushima Daiichi Nuclear Power Station announced by Tokyo Electric Power Co., Inc. (TEPCO) were summarized in terms of the management of the secondary wastes, for the purpose of accumulating technical knowledge for long-term storage of the wastes. Concerns for the long-term soundness of waste storage containers were pointed out as follows, corrosion of stainless steel containers exposed to radiation in the presence of chloride ions, corrosion of stainless steel containers under acidic conditions or in the presence of activated carbon, and radiation degradation of the high-performance container (HIC) in which slurry was stored.

Journal Articles

ERRATUM; Effects of OH$$^{-}$$ activity and temperature on the dissolution rate of compacted montmorillonite under highly alkaline conditions [Clay Minerals, vol.51, p.275 (2016), Corrected Fig. 7.]

Sawaguchi, Takuma; Tsukada, Manabu; Yamaguchi, Tetsuji; Mukai, Masayuki

Clay Minerals, 51(5), P. 815, 2016/12

ERRATUM; Effects of OH$$^{-}$$ activity and temperature on the dissolution rate of compacted montmorillonite under highly alkaline conditions [Clay Minerals, vol.51, p.275 (2016), Corrected Fig. 7.]

Journal Articles

Sorption behavior of thorium onto granite and its constituent minerals

Iida, Yoshihisa; Yamaguchi, Tetsuji; Tanaka, Tadao; Hemmi, Ko

Journal of Nuclear Science and Technology, 53(10), p.1573 - 1584, 2016/10

 Times Cited Count:2 Percentile:57.25(Nuclear Science & Technology)

The sorption behavior of thorium (Th) onto granitic rock and its major constituent were investigated by batch sorption experiments. Experiments were carried out under variable pH and carbonate concentrations. Distribution coefficients decreased with increased carbonate concentrations and showed the minimal value at pH 9-10. This sorption tendency was likely due to forming the hydroxide-carbonate complexes of Th in the solutions. The order of sorbability for Th was mica $$>$$ feldspar $$>$$ quartz = granite. The sorption behaviors of Th onto these minerals were analyzed by the triple-layer surface complexation model with the Visual Minteq computer program. The model calculations assuming the inner-sphere surface complexation of Th were able to explain the experimental results reasonably well. It was shown that the sorption behavior of Th onto granite can be explained primarily by the complexation with the surface sites of feldspar.

Journal Articles

Sorption behavior of thorium onto montmorillonite and illite

Iida, Yoshihisa; Barr, L.; Yamaguchi, Tetsuji; Hemmi, Ko

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 23(1), p.3 - 8, 2016/06

Thorium (Th)-229 is one of the important radionuclides for the performance assessment calculations for high-level radioactive waste repositories. The sorption behavior of Th onto montmorillonite and illite were investigated by batch sorption experiments. Experiments were carried out under variable pH and carbonate concentrations. The sorbability of montmorillonite was higher than that of illite. Distribution coefficients, $$K_{rm d}$$ (m$$^{3}$$ kg$$^{-1}$$), decreased with increased carbonate concentrations and showed the minimal value at around pH 10. The sorption behaviors of Th were analyzed by the non-electrostatic surface complex model with PHREEQC computer program. The model calculations were able to explain the experimental results reasonably well. The decreases of $$K_{rm d}$$ was likely due to the stabilization of aqueous species by hydroxo-carbonate complexations in the solutions.

Journal Articles

Effects of OH$$^{-}$$ activity and temperature on the dissolution rate of compacted montmorillonite under highly alkaline conditions

Sawaguchi, Takuma; Tsukada, Manabu; Yamaguchi, Tetsuji; Mukai, Masayuki

Clay Minerals, 51(2), p.267 - 278, 2016/05

 Times Cited Count:1 Percentile:88.06(Chemistry, Physical)

The dependences of the dissolution rate of compacted montmorillonite on activity of OH$$^{-}$$ (a$$_{rm OH}$$-) and temperature (T) were investigated. The dissolution rate of montmorillonite ($$R_{rm A}$$) in compacted pure montmorillonite, which was formulized as $$R_{rm A}$$ = 10$$^{4.5}$$ (a$$_{rm OH}$$-)$$^{1.3}$$ e$$^{-55000/RT}$$, was higher than that in the compacted sand-bentonite mixtures: $$R_{rm A}$$ = 3500 (a$$_{rm OH}$$-)$$^{1.4}$$ e$$^{-51000/RT}$$. The difference can be explained by considering the decrease in a$$_{rm OH}$$- in the mixtures accompanied by dissolution of accessory minerals such as quartz and chalcedony. The dissolution rate model developed for pure montmorillonite is expected to be applied to bentonite mixtures if quantification of the decrease in a$$_{rm OH}$$- is achieved somehow.

Journal Articles

Mineralogical changes and associated decrease in tritiated water diffusivity after alteration of cement-bentonite interfaces

Yamaguchi, Tetsuji; Sawaguchi, Takuma; Tsukada, Manabu; Hoshino, Seiichi*; Tanaka, Tadao

Clay Minerals, 51(2), p.279 - 287, 2016/02

 Times Cited Count:2 Percentile:76.41(Chemistry, Physical)

Alteration of bentonite-cement interfaces and accompanying changes in diffusivity of tritiated water was experimentally investigated using intact hardened cement specimens. The alteration by carbonate solution was accompanied by mineralogical changes at the interface and a decrease in the diffusivity to 70% of the initial value after 180-day period. Another alteration under silicate system contacting hardened cement and compacted bentonite was accompanied by mineralogical changes at the interface and a decrease in the diffusivity to 71% of the initial value after 600-day period. The changes in the diffusivity were much less than those observed for mixed specimens of granulated hardened cement and bentonite where the diffusivity decreased down to 20% of the initial value over 180 days. The results were extrapolated to 15 years under simple assumptions and showed good agreement with those observed in the cement-argillite interface at Tournemire URL. Such an explanation enhances our confidence in our assessment of alteration of cement-bentonite systems and can be a base for using our data and models in long term assessment of radioactive waste disposal.

Journal Articles

Demonstrative experiments on the migration of radiocesium from buried soil contaminated by the accident at Fukushima Daiichi Nuclear Power Station

Yamaguchi, Tetsuji; Shimada, Taro; Ishibashi, Makoto*; Akagi, Yosuke*; Kurosawa, Mitsuru*; Matsubara, Akiyoshi*; Matsuda, Yuki*; Sato, Shigeyoshi*

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 22(2), p.21 - 28, 2015/12

It is predictable from previous studies that radiocesium hardly migrate into surrounding soils and groundwater from soils contaminated by the Fukushima Daiichi Nuclear Power Plant accident if they are buried and covered with indigenous soils. This study demonstrated the prediction by performing in-situ migration experiments over a year in a public park in Miho, Ibaraki prefecture and in two public parks in Misato, Saitama prefecture. Contaminated soils were buried at a depth range of 0.3 - 1.0 m or at 0.3 - 1.3 m and covered with indigenous soil layer of 0.3 m, and were sprinkled with water to accelerate the radiocesium migration. Migration of radiocesium was not observed from radiometric analyses of boring cores and soil water samples. Laboratory column and sorption experiments revealed that the radiocesium hardly leach out of the soil and even if they leach out from the contaminated soil, radiocesium is sorbed on surrounding soils and hardly migrate through the soli layer. Simulation of Cs-137 migration for 100 years by an advection-diffusion model showed that Cs-137 hardly migrate and decay out in the contaminated soil.

Journal Articles

Distribution coefficients of iodine and tin on granodiorite and tuffaceous sandstone specimens

Hemmi, Ko; Yamaguchi, Tetsuji; Iida, Yoshihisa

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 22(1), p.3 - 10, 2015/06

Iodine and tin are important elements in performance assessment of geological disposal of radioactive wastes. Sorption experiments of iodine were carried out under varying nitrate concentration with a range of 0 to 5 mol dm$$^{-3}$$ at neutral pH range in order to determine the distribution coefficient of iodine was zero or non-zero value. The experimental results with estimated statistical errors showed non-zero values for tuffaceous sandstone except for NaNO$$_{3}$$ concentration 0.5 mol dm$$^{-3}$$. Non-zero values were also obtained under NaNO$$_{3}$$ concentrations higher than 0.5 mol dm$$^{-3}$$ for granodiorite. Sorption experiments of tin were carried out at high pH range in order to check whether the distribution coefficient of tin decreases significantly with pH as a result of formation of anionic hydrolysis species of tin. The distribution coefficients of tin on granodiorite decreased from 9.79$$times$$10$$^{-2}$$ m$$^{3}$$ kg$$^{-1}$$ at pH10.4 to 2.46$$times$$10$$^{-3}$$ m$$^{3}$$ kg$$^{-1}$$ at pH12.4. The distribution coefficient of tin on tuffaceous sandstone was about one order of magnitude higher (about 2$$times$$10$$^{-2}$$ m$$^{3}$$ kg$$^{-1}$$) than that of granodiorite at pH around 12.4.

Journal Articles

An Attempt to select thermodynamic data and to evaluate the solubility of radioelements with uncertainty under HLW disposal conditions

Yamaguchi, Tetsuji; Takeda, Seiji; Nishimura, Yuki; Iida, Yoshihisa; Tanaka, Tadao

Radiochimica Acta, 102(11), p.999 - 1008, 2014/11

 Times Cited Count:1 Percentile:85.45(Chemistry, Inorganic & Nuclear)

An attempt was made to select thermodynamic data with uncertainties and to evaluate the solubility of radioelements with uncertainties considering variation in groundwater chemistry. The thermodynamic data was selected by reviewing the JAEA-TDB released in 2012. Data for Nb, Pd and Pa were revised from the viewpoint of the consistency of the data selection process. Data for Se, U and Pa were revised from the viewpoint of the conservativeness. Up-to-date ternary calcium-metal(IV)-OH complexes were adopted for Zr, Th, U, Np and Pu. A Monte Carlo-based probabilistic calculation code, PA-SOL, was used for probabilistic analysis of the solubility.

Journal Articles

Experimental verification of models assessing Eh evolution induced by corrosion of carbon steel overpack

Sakamaki, Keiko; Kataoka, Masaharu; Maeda, Toshikatsu; Iida, Yoshihisa; Kamoshida, Michio; Yamaguchi, Tetsuji; Tanaka, Tadao

Corrosion Engineering, Science and Technology, 49(6), p.450 - 454, 2014/09

 Percentile:100(Materials Science, Multidisciplinary)

Corrosion experiments of a carbon steel plate embedded in bentonite mixture were conducted toverify our models assessing Eh evolution induced by corrosion of carbon steel overpack. Theexperimental results showed that the Eh decreased for the first 200 days and was subsequentlystabilised at around -450 mV; corrosion products were identified as magnetite and Fe waspresent mostly as divalent Fe within a 5 mm range from the carbon steel plate. Reactive transportmodelling was performed to assess the Eh evolution in the system using kinetic dissolution modelfor metallic iron and thermodynamic equilibrium models for other chemical reactions and closelyreproduced the experimental results. The models were verified only under the conditionsemployed in this study.

Journal Articles

Sorption behavior of hydroselenide (HSe$$^{-}$$) onto iron-containing minerals

Iida, Yoshihisa; Yamaguchi, Tetsuji; Tanaka, Tadao

Journal of Nuclear Science and Technology, 51(3), p.305 - 322, 2014/03

 Times Cited Count:3 Percentile:61.51(Nuclear Science & Technology)

Sorption behaviors of HSe$$^{-}$$ onto iron-containing minerals, magnetite, goethite, ferrous oxide and biotite, were investigated by batch sorption experiments under reducing conditions. The sorption ratios for goethite, as representative examples, show negative dependence on pH and independence of the NaCl concentration. The results indicate that the sorption behavior of HSe$$^{-}$$ is inner sphere surface complexation to ferrol sites. The triple layer model was used in the analysis of the sorption behavior of HSe$$^{-}$$ with Visual Minteq computer program. The intrinsic equilibrium constant was determined by the fitting of model calculations to the experimental results to be 5.5. The value was close to the value of HS$$^{-}$$ (5.3) which is chemically analogous to HSe$$^{-}$$.

Journal Articles

Alkaline dissolution behavior of montmorillonite under compacted condition

Sawaguchi, Takuma; Kadowaki, Mitsushi*; Yamaguchi, Tetsuji; Mukai, Masayuki; Tanaka, Tadao

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 20(2), p.71 - 78, 2013/12

The dissolution rate for montmorillonite under compacted condition was studied in order to evaluate long-term alteration behavior of bentonite buffer materials by highly alkaline groundwater. The dissolution rate of compacted montmorillonite was found to be larger than that of montmorillonite in compacted sand-bentonite mixtures at 130 $$^{circ}$$C, which revealed that the dissolution of montmorillonite was inhibited by decreasing the activity of hydroxide ions (${it $alpha$$_O$$_H$$^-$}$) in the compacted mixtures including accessory minerals such as silica. In order to provide reliability for the analysis of bentonite-alteration using a formula of dissolution rate of montmorillonite, it is important to quantify the decrease of ${it $alpha$$_O$$_H$$^-$}$ in the compacted mixtures and to formulate the dissolution rate of compacted montmorillonite.

Journal Articles

Corrosion rate of zircaloy-4 in deoxidized deionized water at 80-120$$^{circ}$$C

Maeda, Toshikatsu; Chiba, Noriaki; Tateishi, Tsuyoshi*; Yamaguchi, Tetsuji

Nippon Genshiryoku Gakkai Wabun Rombunshi, 12(2), p.158 - 164, 2013/06

no abstracts in English

Journal Articles

Diffusion of Cs, Np, Am and Co in compacted sand-bentonite mixtures; Evidence for surface diffusion of Cs cations

Sawaguchi, Takuma; Yamaguchi, Tetsuji; Iida, Yoshihisa; Tanaka, Tadao; Kitagawa, Isamu

Clay Minerals, 48(2), p.411 - 422, 2013/05

 Times Cited Count:2 Percentile:88.54(Chemistry, Physical)

Diffusive transport of Cs$$^{+}$$ in compacted sand-bentonite mixtures was studied by a through diffusion method. Experiments were performed under variable aqueous compositions. Effective diffusivity ($$D$$$$_{e}$$) values of 5.2E-10$$ sim$$ 5.9E-9 m$$^{2}$$ s$$^{-1}$$ were obtained. The variation was somewhat large in the $$D$$$$_{e}$$ values. Apparent diffusivity ($$D$$$$_{a}$$) values, on the other hand, were 2.0E-12 $$sim$$ 6.2E-12 m$$^{2}$$ s$$^{-1}$$, which shows small variation. The results indicate that, in applying Fick's 1st law of diffusion, diffusive flux is proportional to the apparent concentration gradient of Cs in the sand-bentonite mixture rather than the gradient of Cs concentration in pore water. Since the apparent concentration gradient in sand-bentonite mixtures is nearly equal to the gradient of adsorbed Cs, diffusion of Cs under adsorbed state would be the main mechanism of diffusion of Cs in sand-bentonite mixtures.

Journal Articles

Development of a reactive transport code MC-CEMENT ver.2 and its verification using 15-year ${it in-situ}$ concrete/clay interactions at the Tournemire URL

Yamaguchi, Tetsuji; Kataoka, Masaharu; Sawaguchi, Takuma; Mukai, Masayuki; Hoshino, Seiichi; Tanaka, Tadao; Marsal, F.*; Pellegrini, D.*

Clay Minerals, 48(2), p.185 - 197, 2013/05

 Times Cited Count:2 Percentile:88.54(Chemistry, Physical)

Highly alkaline environments induced by cement based materials are likely to deteriorate the physical and/or chemical properties of the bentonite buffer materials in radioactive waste repositories. Predicting long-term alteration of concrete/clay systems requires physico-chemical models and a number of input parameters. In order to provide reliability to the long-term prediction of bentonite buffer performance under disposal conditions, it is necessary to develop and verify reactive transport codes for concrete/clay systems. In this study, a PHREEQC-based, reactive transport analysis code (MC-CEMENT ver.2) was developed and was verified by comparing results of the calculations with ${it in situ}$ observations of the mineralogical evolution at the concrete/argillite interface. The calculation reproduced the observations such as the mineralogical changes limited within one cm in thickness, formation of CaCO$$_{3}$$ and CSH, dissolution of quartz, decrease of porosity in argillite and increase in concrete. These agreements indicate possibility that the models based on lab-scale ($$sim$$ 1 y) experiments can be applied to longer time scale. The fact that the calculation did not reproduce the dissolution of clays and the formation of gypsum indicates that there is still room for improvement in our model.

Journal Articles

Changes in hydraulic conductivity of sand-bentonite mixtures accompanied by alkaline alteration

Yamaguchi, Tetsuji; Sawaguchi, Takuma; Tsukada, Manabu; Kadowaki, Mitsushi*; Tanaka, Tadao

Clay Minerals, 48(2), p.403 - 410, 2013/05

 Times Cited Count:4 Percentile:77(Chemistry, Physical)

Montmorillonite is the main constituent of bentonite clay buffer materials in radioactive waste repositories. Highly alkaline environments induced by cement based materials are likely to alter montmorillonite, and to deteriorate the physical and/or chemical properties of the buffer materials. The deterioration may cause variation in hydraulic conductivity of the buffer and induce major uncertainties in the radionuclide migration analysis. Empirical data on the variation of hydraulic conductivity are, however, scarce mainly because the alteration of compacted buffer materials, sand-bentonite mixture specimen, is extremely slow. In this study, laboratory experiments were performed to observe changes in hydraulic conductivity of sand-bentonite mixtures accompanied with their alkaline alteration using NaOH based solutions at 80-90 $$^{circ}$$C. Three types of experiments proved that the alkaline alteration of bentonite buffer can increase the hydraulic conductivity. The data obtained in this study are useful for verification of the code that will be used for assessing the alteration.

Journal Articles

Identification of the cathode reaction accompanied with overpack corrosion

Otsuka, Ichiro*; Iida, Yoshihisa; Yamaguchi, Tetsuji; Kato, Osamu*; Tateishi, Tsuyoshi*; Tanaka, Tadao

Materials Research Society Symposium Proceedings, Vol.1475, p.507 - 512, 2012/06

We conducted corrosion experiments of carbon wires to identify the cathode reaction with overpack corrosion. Carbon steel wires were immersed in selected aqueous solutions of distilled water, sodium hydrogen carbonate solution and sodium sulfate solution sealed in glass ampoules. The ampoules were kept at 60 $$^{circ}$$C for 150 days. Corrosion products, liquid phase and gas phases were analyzed. The results showed that hydrogen gas generation by reduction of hydrogen ions was dominant cathode reaction. Reduction of sulfate and carbonate anions was not observed. Amorphous ferrous hydroxide and/or iron oxides were identified in all the experiments as the corrosion products. Iron carbonate was also identified in the sodium hydrogen carbonate solution. This result indicates that the hydrogen generation reaction might be the dominant cathode reaction under geological disposal environment and that the Eh of the pore water would reach the equilibrium potential of the hydrogen generation reaction.

Journal Articles

Experimental and modeling study on diffusion of selenium under variable bentonite content and porewater salinity

Iida, Yoshihisa; Yamaguchi, Tetsuji; Tanaka, Tadao

Journal of Nuclear Science and Technology, 48(8), p.1170 - 1183, 2011/08

Effective diffusion coefficients of selenium through bentonite sand mixtures under reducing and anaerobic conditions were obtained by the through-diffusion method. Experiments were carried out under variable bentonite content and porewater salinity. The employed bentonite material was Kunigel V1. The dominant diffusion species were determined to be HSe$$^{-}$$ and SeO$$_{3}$$$$^{2-}$$ under reducing and anaerobic conditions, respectively. The effective diffusion coefficients of selenium species decreased with increasing bentonite content and with decreasing salinity. This tendency is primarily due to anion exclusion which caused by negative surface charge of montmorillonite. A diffusion model for anionic species was developed based on the electric double layer theory and the pore diffusion model, to evaluate diffusion behaviors of HSe$$^{-}$$ and SeO$$_{3}$$$$^{2-}$$ in bentonite porewater. The effective diffusion coefficients of selenium species predicted by this model showed good agreement with experimentally measured ones.

125 (Records 1-20 displayed on this page)