WM 00 Conference, February 27 March 2, 2000, Tucson, AZ

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1 START OF RADIOACTIVE TEST IN THE QUANTITATIVE ASSESSMENT RADIONUCLIDE EXPERIMENTAL FACILITY (QUALITY) FOR FUNDAMENTAL STUDIES ON NUCLIDE MIGRATION BEHAVIOR IN A DEEP GEOLOGICAL ENVIRONMENT H. Igarashi, K. Kawamura, K. Yamada, M. Yui and J. Ohuchi Waste Isolation Research Division, Waste Management and Fuel Cycle Research Center, Japan Nuclear Cycle Development Institute (JNC), Tokai Works ABSTRACT A new radioactive research facility to study on radionuclide migration behavior for radioactive waste disposal was constructed and its radioactive operation started in August The experimental results obtained on solubility, sorption, and diffusion supplemented and supported The second progress report on research and development for the geological disposal of HLW in Japan, submitted to the government in Nov This facility will play an important role in research on the radioactive waste disposal from now on. INTRODUCTION Japan Nuclear Cycle Development Institute (JNC), the successor to the Power Reactor and Nuclear Fuel Development Corporation (PNC) as of October 1, 1998, has conducted research and development for the geological disposal of high-level radioactive waste (HLW) in Japan. JNC prepared The second progress report on research and development for the geological disposal of HLW in Japan [1] (henceforth the second progress report), which documents the progress made since the publication of the first progress report in The second progress report was submitted for review to the Atomic Energy Commission (AEC) of Japanese government in November The primary objective of the report was to present an outline of the technical reliability of geological disposal in Japan as specified by the AEC. The report also provides input knowledge for the siting and regulatory procedure for the repository. The report is now under the review procedure by the AEC.

2 The establishment of an implementation body for disposal is planned for the fall of the year The implementation body will select a disposal site among the candidates through a stepwise process considering that the operation will start in 2030 to the mid 2040s. The rationale of regulatory system for disposal of HLW is now being studied and the establishment of a regulatory system will also proceed in accordance with the progress of the disposal implementation. In the safety evaluation of the geological disposal of HLW, it is required to study the radionuclide migration behavior in the engineered barrier and geosphere. The study of migration is focused on developing the migration model and database and on evaluating the effect of individual phenomena on the performance assessment. Since the redox condition is reducing in deep geological environment, the database development on the migration behavior under reducing condition has been required for redox sensitive elements. This study on stable elements has been done in the non-radioactive facility, Engineering-scale Test and Research Facility called ENTRY [2,3] in the Tokai Works of JNC. The study on radioactive elements has been and is being done in the international collaboration and partly on the basis of the chemical analogy of radioisotope elements. Hence it is important to obtain the basic data on migration from the experimental studies using radioisotopes particularly from the viewpoint of assuring the reliability of the performance assessment. Therefore, a research facility where these studies can be implemented has been required [4]. Due to such a requirement, the new research facility, Quantitative Assessment Radionuclide Migration Experimental Facility (QUALITY) was constructed alongside the ENTRY in Tokai Works. This paper describes the features of the QUALITY and some experimental results on solubility, sorption, and diffusion that have been obtained, plus discussions on research program in this facility. FEATURE OF THE QUALITY The QUALITY is a research facility where the systematic study on migration of radionuclide can be performed with atmospheric controlled chambers simulating the deep geological environment and with high-performance analytical equipments. In the facility the data on migration such as solubility, sorption, etc. can be obtained by using radioisotopes, for example actinides and fission products elements. Radioactive testing started on August 18, 1999

3 after a complete safety check of the facility [5,6]. Part of the experimental results obtained from the experiments executed before October 1999 were used to support and supplement the second progress report [7]. It is planned that the research in this facility will be open to the domestic and international collaboration, such as accepting qualified researchers. HISTORY The conceptual and basic design were done in fiscal years 1994 and 1995, respectively. Detailed design was started in 1996 and finished in the mid An application to use radioisotopes was made on March 31, 1998 and the permission from the regulatory authority was given on August 5, The construction of the facility was started in January 1998 and finished by the end of July Radiation control was implemented in the facility and the operation with radioisotope started on August 18. FACILITY The facility building is two stories above ground and one story underground. The dimension is L 35 x W 32 x H 14 (above ground) m and D 8.4 m below ground level. Its base area is 1,200m 2 and total floor area is 3,600m 2. Figures 1a and b show the outside view and the sectional view of the facility, respectively. Figures 2a, b and c show the plan view of the floors in the facility.

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6 Figure 3 shows the outside view of atmospheric controlled chambers installed in the experimental room. The oxygen concentration can be maintained below 1 ppm in 12 chambers and the carbon dioxide concentration can also be controlled below 1 ppm to 1,000 ppm in three of the chambers. Figure 4 shows the flow sheet of the atmospheric control system. Nitrogen or argon gas is maintained in these chambers. The inner pressure of the chamber is controlled at mmh 2 O negative compared to laboratory room. The ambient gas in the chamber is circulated via the gas purification unit where residual oxygen reacts with hydrogen under the contact with platinum as the catalyst. The resultant product that is condensed water, is removed and drained out.

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8 Additionally, five chambers with ambient air were installed for the testing and analysis. Three hood boxes were installed for the preparation of chemical analysis. Liquid waste generated from the experiments in these chambers is classified into two groups: aqueous and organic liquid waste. The main organic waste is from the scintillater and solvent used in chemical extraction for analysis. Two 10m 3 tanks were installed for storage of the aqueous waste and one 2m 3 tank for the organic waste. Liquid waste generated in the controlled area is stored in two 20m 3 tanks. After the confirmation that the radioactivity is less than the limit, the liquid is discharged from the facility. ANALYTICAL EQUIPMENT Analytical equipment has been installed in the facility for the analysis of radionuclides such as aqueous speciation under reducing environment. For example, the equipments are laser induced speciation analyzer with LPAS and TRLFS, ICP-Mass, FT-IR, radiation counter, etc. as shown in Table 1. Since the oxygen in ambient air affects the analysis, wet-xrd, LPAS, TRLFS, and FT-IR were installed in the atmospheric controlled chamber. Table I Analytical Equipment in QUALITY -Spectrometer -Spectrometer 2 Gasflow Counter Liquid Scintillation Counter wet-x-ray Diffractometer(XRD) Electron Probe Micro Analyzer (EPMA) wet-scanning Electron Microscope(SEM) Laser-Induced Speciation Analyzer with Time-Resolved Laser-induced Fluorescence Spectroscopy (TRLFS) and Laser-induced Photoacoustic Spectroscopy (LPAS) Particle Size Distribution Analyzer Total Organic Carbon (TOC) Analyzer Ion Chromatograph Absorption Spectrophotometer Fourier Transform Infrared Spectroscope(FT-IR) Atomic Absorption Spectrometer (AAS) High Resolution Inductively Coupled Plasma Mass Spectrometer (ICP-MS) Gas Chromatography Mass Spectrometer (GC-MS)

9 RESEARCH PROGRAM ON GEOLOGICAL DISPOSAL Beyond the year 2000 Since the first progress report (1992), the research and development (R&D) has been executed to demonstrate the technical reliability of geological disposal and to provide key input for site selection and establishment of a regulatory system. At this time, the effort of R&D on geological disposal is being made to follow up on the review by the AEC. The program of R&D work on geological disposal after the year 2000 is under discussion, as well as the discussion on sharing of research roles among the implementation body and participating research institutes such as JNC. However, the purpose of the program will be to cover their contributions to the activities of the implementation body and the establishment of the regulatory system in addition to obtaining public acceptance, through improvements in the reliability of the geological disposal. The R&D effort will be oriented to be more site-specific for the phase of implementation and include the investigation of geological environment, R&D on disposal technology, and research on performance assessment. Based on the progress of candidate site selection and evaluation, research work will be necessary for the safety evaluation in addition to the investigation of the geological environment. For example, the development and verification of the model and thermodynamic database of radionuclides considering the geological environment will be necessary to analyze the hydrology, geochemistry, mass transport, and thermo-hydro-mechanical behavior. Further the experimental data on the sorption and solubility will be required for the analysis of radionuclide migration. Role of research facilities From the viewpoint on the research beyond the year 2000 mentioned above, it is necessary to utilize the underground research laboratory (URL), ENTRY, and QUALITY on the basis of the accumulated R&D accomplishments. The ENTRY and QUALITY will play important roles in the laboratory experiments based on the specific geological environment data, the supplement to the database of radionuclide migration, and the analysis for improving the reliability of the performance assessment of disposal system. For the underground test facility, it is expected to develop the investigation technology for the geological environment and to verify the evaluation model, database, and technology of construction/operation such as the emplacement of wastes.

10 MIGRATION STUDY PROGRAM IN THE QUALITY Radionuclide migration study for HLW disposal Some results of the study before until October 1999 were used to supplement the second progress report. During the review by the AEC, studies are being carried out to assure the conservatism and reliability of the database on radionuclide migration in this report. After completing the review of the report, the QUALITY in the combination with the ENTRY and the URL will play an important role by providing data to supplement the safety analysis and to understand the migration mechanism. These results will be provided for preparing the safety standards for regulatory system. This facility will be used for disposal research on HLW, and for transuranium (TRU) waste. As the studies of radionuclide migration, the solubility, sorption, and diffusion experiments will be carried out under reducing conditions. These are associated with the confirmation of the reliability of thermodynamic data, the availability of chemical analogy, and the effect of colloids, organic compounds, and geological environment conditions. Experiments will also be conducted for the elements that are difficult to quantify in very low concentration relative to high natural background. Totally 26 radionuclides are presently available for use as shown in Table 2. Speciation analysis of radionuclides in the deep geological environment is also an important theme in the QUALITY to understand migration mechanism.

11 Group Nuclide one day (MBq) 1 Po Ra Ac Pa Np Am Am Cm Table 2 Radionuclides planned for usage-- (based on the legal permission given in August 1999) ne day in each group (MBq) 10 (Hood 0.1) Cm (Hood 0.3) C Ni-63 2 Se-75 2 Se-79 2 Zr-95 1 Nb-95 1 Pd Sn Sb I Cs Sm Bi Pb H-3 C months (MBq) One year (MBq) Tc Important theme on solubility is the evaluation of thermodynamic data and confirmation of availability of chemical analogy such as lanthanide (III) and actinide (III) from the viewpoint of safety analysis. In these studies, quantification and speciation of dissolved elements and identification of solubility-controlled solid phase are required for understanding the complexation behavior of actinide with inorganic/organic ligand, such as carbonate and humic substances. Besides, the understanding of coprecipitation behavior is also necessary for the estimation of dissolution behavior of relevant elements such as Ra. These themes are also important for the sorption and diffusion studies.

12 The theme in the sorption study is to investigate the mechanism of radionuclides sorption in compacted bentonite and various types of rock under reducing conditions in order to improve the data reliability and confirm the availability of chemical analogy. Through this study, mechanistic sorption model will be developed for the prediction of distribution coefficient (Kd). In the diffusion study, the main theme is to understand the sorption and diffusion mechanisms in the microstructure of compacted bentonite and rock under different geochemical conditions. For example, the effect of ionic strength and bentonite-silica ratio in buffer material will be studied. From this viewpoint, it is necessary to identify the migration pathway to develop the diffusion model for predicting the effective diffusion coefficient. Migration study in TRU waste disposal The experiments on migration behavior for TRU waste are also considered in the QUALITY. The theme of this study will include the migration behavior of I-129, Cl-36, and C-14. The effect of high ph due to cement material and the effect of organic material on migration are also to be studied. CURRENT PROGRESS OF MIGRATION STUDY Studies on the chemical and migration behavior of radionuclides were carried out in the QUALITY for assuring the reliability of the data concerning radionuclide migration used in the second progress report. The following five studies on solubility, sorption, and diffusion were carried out. The data obtained from these studies were all reflected to the second progress report. The details for these studies are described in the report [7]. Effect of carbonate on Np solubility The solubility of Np(IV) was measured as a function of ph and carbonate concentration under reducing conditions. For the ph dependency experiments, the solubility of Np(IV) was measured in a ph range of 8.5 to 12.5 with a total carbon concentration [C] T of 0.1M. For the carbonate concentration dependency experiments, the measurements were carried out in [C] T range of 10-3 to 10-1 M at ph10.5. The [C] T values were adjusted by NaHCO 3 and the ionic strengths (I) were adjusted at 0.5 and 1.0 by NaClO 4. The ph was adjusted by HClO 4 and NaOH during the experiment, and Na 2 S 2 O was used as a reducing reagent to keep reducing

13 WM'00 Conference, February 27 - March 2, 2000, Tucson, AZ conditions. At the end of experiments, the oxidation state of Np(IV) was checked by thenoyltrifluoroacetone (TTA, 0.5M) extraction in xylene[8]. All solubility experiments were carried out in an Ar-atmospheric controlled chamber, in which the oxygen concentration was maintained below 1ppm. The obtained solubility data are shown in Fig. 5 and are described based on two hydroxo-carbonate complexes, Np(OH) 2 (CO 3 ) 2-2 and Np(OH) 4 (CO 3 ) 4-2. These stability constants were found to be (at 0.5M of ion strength) and 44.14(1.0M) and comparable with the literature data [9, 10].

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15 Effect of carbonate on Np sorption on smectite Distribution coefficients (Kd) of Np(IV) on smectite were measured as a function of carbonate concentration under reducing conditions. The sorption experiments were carried out by batch method. The purified Na-smectite sample was prepared following the removal of impurities from Kunipia-F. The concentration of carbonate and ph were adjusted between 0.04 and 0.15M by NaHCO 3 and between 8 and 10 by HCl and NaOH, respectively. The sorption experiments were all carried out in a N 2 -atmospheric controlled chamber. At the end of the experiments, the oxidation state of Np was checked in the same way as the solubility experiments. Moreover, desorption experiments of Np from smectite were also carried out by 1M KCl and 1M HCl in order to understand the sorption mechanism. The obtained Kd values were approximately constant between 0.4 and 1m 3 /kg over the range of carbonate concentration. The results of desorption experiments by 1M KCl and 1M HCl showed two different desorption behavior; Np was effectively removed by HCl in low carbonate concentration (NaHCO M) and by KCl in high carbonate concentration (NaHCO 3 0 The results of desorption experiments show a possibility that Np predominantly sorbed on the edge site and the ion exchange site of smectite in low and high carbonate concentrations, respectively. Distribution coefficient measurements for Cs, Pb and Cm on rocks and bentonite Distribution coefficients for Cs, Pb, and Cm on Japanese major rocks (basalt, mudstone, sandstone, granodiorite, and tuff) and bentonite were measured as a function of ionic strength. All experiments were carried out by batch methods. For Cs, the sorption experiments were done at room temperature under aerobic conditions and those for Pb and Cm were at room temperature in a N 2 -atmospheric controlled chamber. To investigate the effect of ionic strength, all experiments were carried out in 0.01 and 0.1M NaCl solution systems. The Kd values of Cs were on the order of 10-2 to 10 0 m 3 /kg, with tuff > sandstone > basalt > mudstone. The Kd values on all kinds of rocks showed a tendency to decrease with increasing ionic strength. The Kd values of Pb in the order of 10 0 to 10 2 m 3 /kg were particularly high in basalt, mudstone, tuff, and sandstone, but lower in bentonite and quite low on granodiorite. No effect of ionic strength on Kd was found for Pb. The Kd values of Cm were on the order of 10 0 and 10 1 m 3 /kg and no effect of ionic strength on Kd was found. The Kd values obtained for all cases were either in the same orders of magnitude or higher compared with the data set used in

16 both fresh and saline groundwater systems in the second progress report. This means that the Kd data used in the second progress report are conservative, at least for the changes in water chemistry. Diffusion behavior of Pb in compacted bentonite Apparent diffusion coefficients (Da) of Pb in compacted bentonite were measured as a function of the dry density of bentonite (0.8~1.8Mg/m 3 ), content of silica sand in the bentonite (30 and 50wt% for 1.6Mg/m 3 ), and temperature (room and 60Û& The diffusion experiments were carried out under anaerobic conditions in a N 2 -atmospheric controlled chamber by in-diffusion method [11]. A sodium bentonite (Kunigel-V1 ), which contains approximately 50wt% smectite, was packed into a diffusion column to obtain a given density after drying at 110Û&RYHUQLJKWDQGLPPersed in degassed distilled water. After the saturation, a Pb-210 solution of 50µl (815Bq) was pipetted on one end of the bentonite specimen and the experiment was started. The bentonite specimen was sliced after a certain period and the concentration profile in the bentonite was obtained by counting the radioactivity for each slice. Almost all measured concentrations showed a tendency to gradually decrease with depth from the source end and became approximately constant beyond around 10mm depth. Backgrounds were subtracted from all analyzed data, but the concentrations in the area deeper than 10mm were nearly equal to background. From this observation, it can be said that the accuracy to the background and the width of data variation in the analysis are important to obtain appropriate Da. The Da values were conservatively derived based on the results of in-depth profile of concentration presently obtained. Consequently, the calculated Kd was appropriate or conservative in comparison with the report. Effect of ionic strength on diffusion behavior of Cs in compacted smectite Apparent diffusion coefficients of Cs in compacted smectite, in which soluble salts originally contained in bentonite as impurities were totally removed, were measured as a function of dry density (0.8~1.8Mg/m 3 ) and ionic strength (0.01~0.5M NaCl). The diffusion experiments were carried out under aerobic conditions in the same way as Pb. For a density of 1.4Mg/m 3, silica sand was mixed by 50wt% to simulate Kunigel-V1.

17 WM'00 Conference, February 27 - March 2, 2000, Tucson, AZ The obtained Da values were on the order of to m 2 /s and showed a tendency to decrease with increasing dry density, but no significant effect of ionic strength on Da was found. The Da values of smectite with silica sand were higher than those of smectite without silica sand. The obtained Da values were normalized with smectite density [12], in which the composition of smectite as a constituent in bentonite was considered. Figure 6 shows the effect of the smectite density on Da of Cs. The Kd was also calculated from Da to compare with data set used in the second progress report. Consequently, a clear correlation between Da and smectite density was observed. This indicates that Da can be described by smectite density, further supporting the presumption that Cs predominantly diffuses in the interlayer of smectite. Since the diffusion in the interlayer of smectite is not easily affected by ionic strength, this presumption in the diffusion mechanism also agrees with experimental observation that there was no significant effect of ionic strength.

18 WM'00 Conference, February 27 - March 2, 2000, Tucson, AZ CONCLUSION The QUALITY was successfully constructed and it started radioactive experiments in August This facility is a unique research facility where the migration behavior of radionuclides can be studied systematically under reducing conditions and a simulated deep geological environment for a repository expected in Japan. The data on solubility, sorption, and diffusion obtained in this facility supplemented and supported the analysis in the second progress

19 report submitted to the government in November The QUALITY will play an important role in carrying out the research on radioactive waste disposal from the viewpoint of promoting the implementation of disposal business and preparing the safety standards for the regulatory system. This facility also has the feature that research activities are open to the domestic and international collaboration, including the acceptance of visiting scientists. ACKNOWLEDGEMENT The authors would like to thank T. Ashida, H. Sato, T. Shibutani, Y. Tachi, and A. Kitamura for the contribution to the studies on radionuclide migration behavior in the QUALITY. REFERENCES [1] Japan Nuclear Cycle Development Institute, H12 Project to Establish Technical Basis for HLW Disposal in Japan -The Second Progress Report on Research and Development for the Geological Disposal of HLW in Japan-, in Japanese, November 1999 [2] A. Yamato, et al., The High level radioactive waste management program in Japan, High Level Waste Management, Proceeding of the Third International Conference, Las Vegas, Nevada, April 12-16, pp [3] M. Uchida, et al., Entry-2 project contribution of engineering scale laboratory experiments to performance assessment of geological disposal, International Conference on Future Nuclear systems (GLOBAL 97), Yokohama, Japan, October 5-10, 1997, pp [4] M. Yui, Construction of QUALITY (Quantitative Assessment Radioactive Migration Experimental Facility) and Its Importance for Radioactive Waste Disposal, in Japanese, KURRI-KR-17, Proceedings of the Specialists Meeting on Radioactive Waste Management, Kyoto Univ., November 25-26, 1997, pp [5] T. Ashida, et al., The outline of QUALITY (Quantitative Assessment Radioactive Migration Experimental Facility), L56, in Japanese, 1999 Fall Meeting of the Atomic Energy Society of Japan, Kashiwazaki, September 10-12, 1999, p773. [6] T.Ashida, et al., The outline of QUALITY (Quantitative Assessment Radioactive Migration Experimental Facility), JNC TN , in Japanese, No.5, Dec pp9-13.

20 [7] T. Ashida, et al., Nuclide Migration Study in the QUALITY-Data Acquisition for the Second Progress Report, JNC TN , in Japanese Nov [8] S. C. Foti, et al., The Determination of the Oxidation States of Tracer Uranium, Neptunium and Plutonium in Aqueous Media, Talanta, 11, 1964, p.395. [9] A. I. Moskvin, Complex Formation of Neptunium (IV, V, VI) in Carbonate Solutions, Sov. Radiochem. (Engl. Transl.), 13, 1971, p.694. [10] D. Rai, et al., Neptunium(IV) Hydrous Oxide Solubility under Reducing and Carbonate Conditions, Inorg. Chem., 24, 1985, p.247. [11] T. Eriksen, et al., Ion Diffusion through Highly Compacted Bentonite, SKBF/KBS TR81-16, [12] K. Idemitsu, et al., Diffusion of Cs and Sr in Compacted Bentonites under Reducing Conditions and in the Presence of Corrosion Products of Iron, Scientific Basis for Nuclear Waste Management XXI, Vol.506, pp , 1998.