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Miwa, Kazuji; Namekawa, Masakazu*; Shimada, Taro; Takeda, Seiji
MRS Advances (Internet), 7(7-8), p.165 - 169, 2022/03
We have developed evaluation method of radiocesium (RCs) migration by surface runoff and soil erosion in considering vertical distribution of RCs in initial contaminated soil and concentration of RCs in different particle size. RCs migration on ground surface during single year has been evaluated in virtual site contaminated uniformly by Cs-137. As a result, RCs has concentrated in the impoundment, and 0.18% of total inventory in the site migrated into the sea. These results suggest that surface migration of RCs effects increasing of external exposure at impoundment and internal exposure from ingestion of marine product.
Goto, Takahiro*; Mitsui, Seiichiro; Takase, Hiroyasu*; Kurosawa, Susumu*; Inagaki, Manabu*; Shibata, Masahiro; Ishiguro, Katsuhiko*
MRS Advances (Internet), 1(63-64), p.4239 - 4245, 2016/00
NUMO and JAEA have conducted a joint research since FY2011, which is designed to enhance the methodology of repository design and performance assessment in preliminary investigation stage for deep geological disposal of radioactive waste. As a part of this joint research, we have been developing glass dissolution models which consider various processes in EBS, such as precipitation of Fe-silicates associated with iron overpack corrosion, and Si transport through corrosion products in the cracked overpack. The objectives of the modeling work are to evaluate relative importance of relevant processes and to identify further R&D issues towards development of a convincing safety case. Sensitivity analyses suggested that predicted glass dissolution time ranges from 1
10
to 110
years or more due to uncertainties in the current understanding of the key processes, namely precipitation of Fe-silicates and transport characteristics of the altered glass layer.
Shimada, Taro; Takeda, Seiji; Sakai, Ryutaro*; Takubo, Kazuya; Tanaka, Tadao
MRS Advances (Internet), 1(61), p.4081 - 4086, 2016/00
Volcanic eruption which may affect geological disposal system directly depends on the regional location in Japan. It is required that the disposal site should be located far from existing volcanos. However, there are regions where it is impossible to exclude the possibility of appearance of new volcanic activity on the site even if the site is located far from existing volcanos. In order to identify the influence of volcanic eruption at disposal site to public if it occurs public exposure doses were evaluated based on the two scenarios considering types of eruption at new volcanic activity in Japan. One is the exposure by tephra widespread by Strombolian eruption and deposited on the ground surface, including radionuclides from vitrified waste forms after a volcanic conduit penetrated disposal galleries. The other is that by waste forms appeared at the surface by Merapi type pyroclastic flow. Exposure doses of the residents living on the tephra do not exceed 1mSv/y even when the eruption occurs at 1,000 years after closure of disposal site. Dose rate for the volcanic researchers temporarily approaching waste forms becomes less than 1mSv/h when the eruption occurs 100,000 years after. It indicated that attention should be paid to the impact by Merapi type pyroclastic flow on researchers approaching waste forms appeared rather than that by Strombolian eruption on residents living on the tephra widespread.
Soler, J. M.*; Landa, J.*; Havlov
, V.*; Tachi, Yukio; Ebina, Takanori*; Sardini, P.*; Siitari-Kauppi, M.*; Martin, A. J.*
Materials Research Society Symposium Proceedings, Vol.1665, p.85 - 91, 2014/09
Matrix diffusion is a key process for radionuclide retention in crystalline rocks. An in-situ diffusion experiment in granite matrix was performed at the Grimsel Test Site (Switzerland). Several tracers (HTO, Na
, Cs) were circulated through a borehole and the decrease in tracer concentrations was monitored for 2.5 years. Then, the borehole section was overcored and the tracer profiles in the rock were analyzed. Transport distances in the rock were 20 cm for HTO, 10 cm for Na and 1 cm for Cs. The dataset was analyzed with diffusion-sorption models by different teams using different codes, with the goal of obtaining effective diffusivities (
e) and rock capacity factors. There was a rather good agreement between the values from different teams, implied that e and capacity factors in the borehole damaged zone are larger than those in the bulk rock. However, HTO seems to display large discrepancies between measured and modeled results, which have to be investigated in more detail.
setting approach through semi-quantitative estimation procedures and thermodynamic sorption models; A Case study for Horonobe URL conditionsTachi, Yukio; Ochs, M.*; Suyama, Tadahiro; Trudel, D.*
Materials Research Society Symposium Proceedings, Vol.1665, p.149 - 155, 2014/09
Sorption of radionuclides (K) in host rocks depends critically on relevant geochemical conditions, need to correspond to the specific performance assessment (PA) conditions. The integrated approaches for site-specific K setting have been developed focusing two transferring procedures, semi-quantitative estimation procedures and thermodynamic sorption models. The present paper focused on illustrating the derivation of K values and their uncertainties of Cs, Ni, Am and Th for geochemical conditions from the Horonobe URL. These K-setting results were compared with the measured K values, indicating that the magnitude of sorption can be quantitatively evaluated when adequate data and models were available. These comparative discussions between transferring procedures and measured data are effective to enhance the reliability of K setting, and the careful selections from transferred results are needed according to the situation in the existing data and process understanding.
Shimoda, Satoko*; Nakazawa, Toshiyuki*; Kato, Hiroyasu*; Tachi, Yukio; Seida, Yoshimi*
Materials Research Society Symposium Proceedings, Vol.1665, p.179 - 184, 2014/09
The potential effect of alkaline perturbation caused by the cementitious materials must be evaluated in the performance assessment for HLW geological disposal. In this study, sorption of Cs, Ni and Th was investigated using the altered and unaltered samples of sedimentary rock from Horonobe underground research laboratory. The K values of Cs, Ni and Th measured by batch method using synthetic groundwater changed as a function of degrees of alteration. The K values of Cs increased with increasing degrees of alteration, indicating secondary minerals contributes to the increase in Cs sorption by ion exchange mechanism. On the other hand, the K values of Ni and Th decreased with the increase of degrees of alteration. This change may be caused by dissolution of clay minerals controlling Ni and Th sorption by surface complexation. These results imply that the effect of alkaline perturbation on K values of rocks depend on the surface property of the altered rock and sorption mechanism.
Takeda, Seiji; Sawaguchi, Takuma; Kimura, Hideo
Materials Research Society Symposium Proceedings, Vol.1665, p.103 - 109, 2014/09
Some kinds of material in the environment due to the accident at the Fukushima Nuclear Plant have been contaminated by radioactive cesium, which are represented by dehydrated sludge, surface soil, disaster wastes generated by the 2011 off the Pacific coast of Tohoku Earthquake and so on. Treatment (transportation, temporary storage or incineration) and disposal of the contaminated materials should be carried out while ensuring the safety of radiation for the workers and the public. In this study, in order to provide the technical information for making the guideline, the dose estimate for scenarios on the treatment and disposal is conducted, based on the method used for driving the clearance levels in Japan. Minimum activity concentration in contaminated material is calculated from the dose results, corresponding to the effective dose criterions indicated by the Nuclear Safety Commission of Japan (June 3, 2011). From the calculation result, it is suggested that it is necessary to forbid reusing the disposal site as construction, resident and agriculture in which the calculated doses for the public are higher than those in the other exposure pathways. Minimum activity concentration of radioactive cesium is derived to be 8.9 Bq/g for exposure pathway in landfill work under the condition of limited reuse of the site. In the case of the activity concentration below 8.9 Bq/g, the calculated dose of the resident due to direct and sky-shine radiation from the temporary storage place is less than 1 mSv/y, irrespective of the distance from the storage place.
Funaki, Hironori; Hagiwara, Hiroki; Tsuruta, Tadahiko
Materials Research Society Symposium Proceedings, Vol.1665, p.165 - 170, 2014/09
Ebashi, Takeshi; Kawamura, Makoto*; Inagaki, Manabu*; Koo, Shigeru*; Shibata, Masahiro; Itazu, Toru; Nakajima, Kunihiko*; Miyahara, Kaname; Apted, M. J.*
Materials Research Society Symposium Proceedings, Vol.1665, p.39 - 45, 2014/07
In Japan, the likelihood of uplift/erosion on repository performance and waste isolation can be typically greatly reduced or excluded by careful siting, however, the inability to completely exclude the uplift/erosion scenario may require an analysis of the consequences of such a scenario. For this purpose, an assessment approach has been developed to more realistically treat the effect of uplift/erosion for a hypothetical repository located in sedimentary host rock. A key advantage to this approach is the extrapolation of the geohistory of modern analogue sites to develop credible initial inputs for future volunteer sites that may be poorly characterized at the initial stages of site investigation. In addition, the approach provides a systematic basis for bounding the range of possible evolution in thermal-hydrological-mechanical-chemical conditions of a repository experiencing different uplift/ erosion rates.
Yotsuji, Kenji; Tachi, Yukio; Nishimaki, Yuichiro*
Materials Research Society Symposium Proceedings, Vol.1665, p.123 - 129, 2014/07
The integrated sorption and diffusion (ISD) model has been developed to quantify these processes in compacted bentonite. The ISD model assuming averaged narrow porespace and the electric double layer (EDL) theory could give quantitative agreement with diffusion data of monovalent cations and anions under wide range of conditions. However, the systematic disagreements were observed for multivalent cations, anions and complex species. In this study, the excluded volume effect and the dielectric saturation effect were introduced into the current ISD model and the modified Poisson-Boltzmann equations were numerically solved. The ionic distributions were influenced at the near surface, however, these changes were canceled by averaging for the porespace. As a result, these modified models had little effect on the effective diffusivity. On the other hand, the modified model considering hydrated ions with the effective electric charge could give good reproducibility of diffusion data.
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 
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.
Mitsui, Seiichiro; Fujii, Atsuhiro*; Higuchi, Megumi*; Nishimura, Kosuke*
Materials Research Society Symposium Proceedings, Vol.1475, p.545 - 550, 2012/06
An ancient iron sword (ca 2,000 year old) excavated from Ohtake-nishi archaeological site in Osaka Prefecture, is one of the oldest cast iron swords in Japan. Because of a good state of preservation, we studied relationship between burial environment and corrosion. As environmental conditions, we investigated groundwater chemistry and corrosion rate with iron probe monitor, etc. As for corrosion state, we analysed corrosion depths with a X-ray CT and corrosion products with a portable XRD/XRF. As results, we found that the redox potential and dissolved oxygen level as environmental conditions were very low, and that the maximum corrosion rate evaluated from measured corrosion depths was smaller than the probe corrosion rate by two orders of magnitude and identified siderite as a corrosion product. The results suggested that the siderite precipitated on the surface of the iron sword inhibited corrosion reaction.
Yoshikawa, Hideki; Kawakita, Masakazu*; Fujiwara, Kazuhiro*; Sato, Tomofumi; Asano, Takahiro*; Sasaki, Yoshito
Materials Research Society Symposium Proceedings, Vol.1475, p.617 - 622, 2012/06
Since it was suggested that the microbes have ability to generate their biofilm in deep underground condition, we examined the effects of biofilm on radionuclide migration scenario. To estimate the effect on matrix diffusion, through diffusion experiment for a biofilm of Desulfovivrio desullfuricans were performed. The effective diffusion coefficient of the biofilm was 10
m
/s order which was about ten times smaller than that in free water. It is suggesting that the microbes and biofilm will not interfere with matrix diffusion as a retardation of radionuclide in rock.
Miyahara, Kaname; Inagaki, Manabu; Kawamura, Makoto; Ebina, Takanori*; McKinley, I. G.*
Materials Research Society Symposium Proceedings, Vol.1193, p.177 - 184, 2009/05
Uplift and erosion cannot be generally precluded in Japan, therefore needs to be treated. In particular, uplift and erosion will cause major disruption of the engineered and natural barriers when the repository is exposed at the ground surface, although erosion of the repository should be excluded for very long times by careful siting and design. In Japan, uplift/erosion scenarios must be analysed, even if they occur far in the future as no assessment cut-off times have yet been defined. For this purpose, an argumentation method is being developed to allow sensible scenarios to be constructed. This paper discusses procedures to derive relevant conceptual models and resultant analyses in a credible manner which illustrates the effectiveness and robustness of the HLW disposal system, using relevant yardsticks based on natural radionuclide fluxes.
Mitsui, Seiichiro; Makino, Hitoshi; Inagaki, Manabu; Ebina, Takanori*
Materials Research Society Symposium Proceedings, Vol.1193, p.397 - 404, 2009/05
The results of a sensitivity analysis for long-term glass dissolution taking into account Si release from the glass and its migration through the buffer material are presented to illustrate the impact of this near-field process on the lifetime of the vitrified waste. The lifetime of the glass estimated by the analysis showed a strong dependence on Si diffusion and distribution coefficients in the buffer material and groundwater flow rate in the EDZ. This indicates the significance of these parameters for the long-term evolution of vitrified waste. We also discuss the impact of glass hydration, which proceeds simultaneously with matrix dissolution considering Si release, on the lifetime of the vitrified waste. The results show that glass hydration is less important for the long-term evolution than matrix dissolution in an open system and it can be concluded that Si migration through the buffer material will be an important process for estimating the lifetime of the vitrified waste.
Yoshikawa, Hideki; Inagaki, Manabu; Miyasaka, Iku*
Materials Research Society Symposium Proceedings, Vol.1193, p.375 - 380, 2009/05
The scenario analysis was performed for microbial effect on the performance assessment (PA) of high level radioactive waste disposal system based on recent literature review. The consideration for PA with these effects was clarified and important FEPs were selected in the point of safety function under various uncertainties for microbe information. It is clear that the biological effect on groundwater components evolution, which is caused by the microbial redox reaction, is one of the most important issues to assess on PA. And we developed a biological parameter database which has growth and metabolism data for interactive six microbial groups. The database composed some significant data like specific growth rate, maximum growth rate, constant decay rate, and experimental condition for model assessment.
Inagaki, Yaohiro*; Mitsui, Seiichiro; Makigaki, Hikaru*; Idemitsu, Kazuya*; Arima, Tatsumi*; Bamba, Tsunetaka; Noshita, Kenji*
Materials Research Society Symposium Proceedings, Vol.1193, p.219 - 228, 2009/05
We developed a new flow-through test method using micro-reactor, and applied it to measurement of the dissolution/alteration kinetics for a simulated HLW glass (P0798). In this method, a glass coupon is placed just on a Teflon plate having a micro-channel, and a solution is injected into the inlet of micro-channel by micro-syringe pump at a constant flow rate. The injected solution flows through the micro-channel reacting with the glass to the outlet, and the outlet solution is retrieved at certain intervals to be analyzed for determination of the dissolution/alteration rate. This method has some major features, i.e., simple test apparatus with compact size, high S/V ratio, sensitive/precise measurement of the glass dissolution/alteration rate, adequate glass shape for analysis of reacted glass surface, and so on. By use of this method the dissolution/alteration rate for P0798 was measured as a function of pH, temperature, flow rate, and time, and some available results were obtained to evaluate the dissolution/alteration kinetics.
Makigaki, Hikaru*; Inagaki, Yaohiro*; Idemitsu, Kazuya*; Arima, Tatsumi*; Mitsui, Seiichiro; Bamba, Tsunetaka; Noshita, Kenji*
Materials Research Society Symposium Proceedings, Vol.1193, p.307 - 314, 2009/05
By using micro-reactor flow-through test method we measured the initial dissolution rate of P0798 glass at 25C as a function of pH between 5.6 and 12. The results showed that the initial dissolution rate determined by dissolution rate of Si has "V-shaped" pH dependency similar to R7T7 glass reported by CEA, France. We also measured the initial dissolution rate at pH 5.6 as a function of temperature between 25 and 90C, and the activation energy was evaluated to be 51 kJ/mol, which value is slightly smaller than that of R7T7 glass at pH 9 reported by CEA. On the basis of these results and comparison, we discussed the dissolution kinetics of P0798 glass.
Tachi, Yukio; Yotsuji, Kenji; Seida, Yoshimi; Yui, Mikazu
Materials Research Society Symposium Proceedings, Vol.1193, p.545 - 552, 2009/05
Diffusion of Cs and I in compacted montmorillonite were examined from the viewpoints of mechanistic understanding of salinity effects. The effective diffusivity and capacity factor for Cs and I were measured in compacted montmorillonite saturated with 0.01, 0.1 and 0.5M NaCl by through-diffusion experiments, coupled with multiple curve analysis including tracer depletion, breakthrough, and depth concentration curves. The De values obtained for Cs decreased as salinity increased, and those for I showed the opposite dependency. The distribution coefficient of Cs decreased as salinity increased. The diffusion and sorption parameters for Cs were also obtained by in-diffusion and batch sorption experiments, showing good agreement with those by the through-diffusion. The diffusion model based on electrical double layer theory predicted the salinity dependence of De reasonably well, the apparent diffusivity which includes sorption effect was also interpreted by the sorption coupled model.
Kuno, Yoshio; Sasamoto, Hiroshi
Materials Research Society Symposium Proceedings, Vol.1124, p.581 - 586, 2009/00
Column experiments were carried out using an artificial fracture within the granite rock in order to investigate the migration behavior of bentonite colloids. A sufficient fraction of colloids was immobilized within the fractured granite in 10
M NaCl solution. In case of comparatively high ionic concentration, retardation of bentonite colloids is expected in the geological medium.
