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Diffusion is the dominant process involved in the transport of 129I through geological media; therefore, the evaluation of the experimental results on the diffusion of I− through compacted bentonite was performed by three diffusion models, CC-CC, CC-VC, and VC-VC. Multiple experiments were cross-checked to verify internal consistency and thereby obtain reliable diffusion parameters. The results showed that I− diffusion coefficients ranged from 1.15 × 10–12 to 4.67 × 10–12 m2/s, which were consistent with those of the literature. These techniques could potentially be performed to measure the diffusion coefficients of non-sorbing or weakly sorbing radionuclides onto compacted bentonite in radioactive waste repositories. [ABSTRACT FROM AUTHOR]

Colloids present high sorption for many solutes and are considered potential contaminant carriers in geological environments. Experimental quantitative data are required for an adequate description of colloid-mediated transport within natural media. In this paper, the line scan function of SEM/EDS was firstly applied to study colloid diffusion by depth profile in crystalline rock and the apparent diffusion coefficient was estimated to be ~ 6E−18 m2/s for 20 nm gold colloids. This technique can be applied to the prediction of colloid-facilitated radionuclide transport through water-saturated fractured porous rock for safety assessment of geological disposal for high-level radioactive waste. [ABSTRACT FROM AUTHOR]

TOA-MC was developed to act as absorbent for selective separation of 99Tc(VII) from high-level radioactive liquid waste. The uptake (%) of Re(VII) a substitute for Tc(VII) due to similar chemical behavior by TOA-MC normally exceeding 95% in the presence of dilute HNO3 was strongly retained and decreased with higher HNO3 concentration by batch method. The surface morphology, thermal stability and diameter/size distribution of the microcapsules were examined by scanning electron microscopy, thermogravimetric analysis and digital microscope, respectively. The chemical structure was characterized using Fourier transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy. [ABSTRACT FROM AUTHOR]

Two kinds of measuring methods were described for the determination of Plutonium-241 in low level wastes in this study. Plutonium isotopes were separated and purified by highly selective UTEVA and TRU resin. LSC, alpha spectrometry, and ICP-MS were applied and compared for determination of Plutonium-241. There is a good agreement with the analytical results and also shows that the different analytical methods have high chemical recovery yields. [ABSTRACT FROM AUTHOR]

In this study, bentonite with an excellent sorption property for Cs and Sr were encapsulated in the biopolymer matrices (sodium alginate, NaALG) to look into the removal of Cs and Sr in the contaminated water induced by an emergency accident of nuclear power facilities. The results revealed that a relatively higher distribution coefficient (Kd) of Cs for bentonite-alginate MCs than Sr. The sorption capacity of different bentonite-alginate MCs in Cs were (233.96-266.57 mg/g) higher than Sr (19.40-63.01 mg/g). [ABSTRACT FROM AUTHOR]

In this study, we characterized the physical properties of bentonite colloids, conducted stability tests, and examined the effects of the colloids on the sorption of radionuclides in groundwater (Cs-137). The resulting data provides a valuable reference for safety assessments of final disposal sites for spent nuclear fuel and high-level radwaste. Our results demonstrate that Cs-137 is easily adsorbed by bentonite colloids. Adsorption capacity of colloidal solutions was shown to be greater than that of colloidal gel type, and the adsorption rate decreases with an increase in ionic strength in a groundwater environment. [ABSTRACT FROM AUTHOR]

Diffusion characteristics in bentonite are essential to quantify the transport of radionuclides through buffer/backfill materials in waste repositories. This study employs through-diffusion techniques to investigate the diffusion behavior of 99TcO4− through SPV bentonite with various densities. The apparent diffusion coefficients for bentonite densities are estimated using Marquardt-Levenberg optimization algorithm in the HYDRUS-1D model. Based on the experimental and calculation results, 99Tc could be considered as non-sorbing radionuclides. The data obtained in this study provide a valuable reference for the safety assessment of waste repositories. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS) and synchrotron X-ray techniques of absorption near edge structure (XANES) were used to probe the coordination numbers and chemical states of absorption atoms to characterize the retention processes of uranium and cesium transportation in bentonite. The results of XPS showed that minor Van der Waals force interaction near the surface of bentonite were found while cesium adsorbed onto bentonite. The result of XANES showed that the uranium valence state greater than 6, and the cesium valence state also find greater than 1. The uranium valence state of mixture of bentonite and UO(NO)·6HO solvent is greater than 6. It maybe due to the strong electron negativity of NO . From the results of added CsNO to bentonite also find the cesium valence state greater than 1. Checking the atom valence state may be able to identify nuclide migration mechanism, which is fundamental information to estimate nuclide migration to biosphere in natural environments. [ABSTRACT FROM AUTHOR]

In this study, a practical method for the determination of Ni in radwaste samples was established. The results showed that the condition of duplicate elution with the Ni-resin column and the presence of the carrier Mn can effectively remove unwanted interfering radionuclides with decontamination factors of >10 for Co. The highest activity of Ni in radwaste samples was determined to be 2.86 ± 0.04 Bq/g, whereas the minimum detectable amount was approximately 0.04 Bq/g. The established separation technique can be used for the practical determination of Ni in radwastes and for the classification of radwastes. [ABSTRACT FROM AUTHOR]

Diffusion and sorption are important processes associated with radionuclides migration in crystalline rock. These processes are studied in the laboratory using borehole core samples. In this study, we obtained distribution coefficients ( K ), apparent diffusion coefficients ( D ) and retardation factor ( R ) using batch and through-diffusion experiments. The $$ R_{\text{f}}^{\text{H/Tc}} $$ and $$ K_{\text{d}}^{\text{H/Tc}} $$ values obtained using the accumulative concentration method were lower than those derived in the batch experiments. These findings demonstrate that reliable R and K values of Tc can be obtained using through-diffusion experiments with a non-reactive radiotracer, thereby bolstering confidence in the assessment of the long-term performance of disposal repositories. [ABSTRACT FROM AUTHOR]

The batch and through-diffusion experiments in this study were conducted and compared in order to investigate the sorption and diffusion of cesium (Cs) for two potential host rocks in Taiwan: argillite from Taitung and granite from Kinmen Island, with the purpose of establishing a reliable safety-performance assessment methodology for the final disposal of low level radioactive waste. The results of Cs mapping by scanning electron microscope equipping by energy dispersive spectrometer (SEM-EDS) showed that the distribution of Cs on argillite and granite were enriched in illite and biotite, respectively. In addition, it showed that higher sorption capacities were found for argillite than granite; due to the clay mineral content (illite) in the argillite. Experiments for diffusion of Cs is agreement to the values estimated for the diffusive results ( D ) of Cs in argillite were revealed to be lower than those of granite. [ABSTRACT FROM AUTHOR]

Zeolite, a natural mineral (Na(AlO)(SiO)·20HO) with an exchanger having high selectivity toward Cs, was encapsulated in a biopolymer matrices (sodium alginate, NaALG). The sorption of Cs on different microcapsules was investigated using batch methods under different conditions, such as time (1-24 h), acid (0.1-6 M HNO), and salt concentration (0.001-1 M NaCl). Spherical and elastic granules were obtained, and the particle size of the microcapsules was about 700 μm. A relatively high sorption ratio of Cs (above 90 %) for MCs enclosing zeolite was obtained in the presence of 0.1-6 M HNO and 0.001-1 M NaCl solutions, with an equilibrium being attained within 5 h. The sorption isotherm of Cs followed a Langmuir-type equation. The relatively larger K value, 120 and 50 cm/g, for Cs showed a selective sorption property in the presence of various metal ions under 2.5 M HNO and 1 M NaNO. [ABSTRACT FROM AUTHOR]

This study investigates sorption and diffusion of strontium (Sr) in two potential host rocks (granite from Kingman Island and basalt from Penghu Island) by using batch and column methods. According to solid-phase analysis, the sorption component primarily contained iron-magnesium (Fe-Mg) minerals in basalt and granite. Moreover, the distribution coefficient ( K) of Sr in various concentrations obtained from batch tests indicated a higher sorption capacity in basalt than that in granite because of the 10 % Fe-Mg mineral content. According to the diffusive results in crushed and intact rocks, it showed that major retardation of Sr depended on the micro-porous structure of tested media, such as decreases of constrictivity and increases of tortuosity. [ABSTRACT FROM AUTHOR]

In this study, a systematic analysis of cesium through crushed granite (0.297-0.840 mm) was constructed where synthetic groundwater and seawater were employed as the liquid phase. To build such models, multi-stage advection-dispersion column tests were conducted in order to determine the major transport processes and the calibration/validation of the hypothesized reactive transport models. The experimental breakthrough curves (BTCs) for HTO and Cs were both matched with their corresponding numerical BTCs by adjusting reaction and transport parameters such as forward or backward reaction rate constants ( k or k), dispersivity ( α), and porosity( θ). [ABSTRACT FROM AUTHOR]

This paper proposes a rapid, accurate method of measuring Tc in low-level radioactive waste using microwave digestion, TEVA resin for chemical separation, and inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS). The minimum detectable activity of ICP-QMS for the determination of Tc was 8.5 mBq g (13.6 pg g). The proposed method achieved chemical recovery of 88 % and with sensitivity superior to that of alternative radiochemical methods (e.g., liquid scintillation analyzer or LSA) when the data acquisition time for identical, low-concentration samples was taken into account. [ABSTRACT FROM AUTHOR]

This study proposed a direct absorption C collection system (CCS) aimed at trapping CO obtained from thermal oxidation in large samples of up to 3 g. This capacity would be appropriate for the routine monitoring of environmental samples and radwaste at nuclear facilities. The average recovery of the proposed CCS was 90 % of C using samples of 1, 2, and 3 g under the optimal conditions of 14 °C/min heating rate and final temperature of 500 °C. The average accuracy, precision and minimum detectable activity were estimated at 13 %, 6.0 % and 1.5 dpm/g, respectively. [ABSTRACT FROM AUTHOR]

Accurate determination of technetium-99 (Tc-99) is very important because any overestimation will cause the examined radioactive wastes to be categorized into super C class, which dramatically increases the cost of waste management. Herein, we demonstrated that by adopting the analytical method comprising TEVA resin pretreatment and ICP-MS measurement, the determined Tc-99 concentrations in representative waste stream samples from the Lan-Yu low-level radioactive waste temporary storage site in Taiwan were approximately two orders of magnitude lower than those determined from the beta radiation measurement using a low background liquid scintillation counter. Two important concerns emerged from our results. First, severe interferences from other nuclides residing in the matrix considerably affect the determination of Tc-99, even when a low background liquid scintillation counter was used. Second, the currently used Tc-99/Cs-137 scaling factor should be carefully revised, or it might lead to a considerable overestimation of the Tc-99 concentration. [ABSTRACT FROM AUTHOR]

The objective of this paper was to characterize the corrosion products deposited on fuel cladding surfaces under hydrogen water chemistry (HWC) conditions in the boiling water reactor unit of a nuclear power plant. Inductively coupled plasma-optical emission spectroscopy and gamma spectrometry were used to determine the elemental composition and radioactivity along the fuel rods. Scanning electron microscopy/energy dispersive X-ray spectroscopy was used to evaluate crud morphology and X-ray diffraction analysis was employed to determine the crystalline phase. Most of the iron in the crud comprised irregular shapes and flakes, with a number of crystallites (e.g. small quantities of ferrites, MnFeO). The major constituent of the outer layer was a loosely attached, stable form of hematite (α-FeO). The amount of deposition on the fuel rods following the fourth fuel cycle of HWC (~1.0 mg cm) was significantly greater than after the third cycle, due to extended burn-up time. In addition, the radioactivity ratio of Co to Co was lower for EOC22 than for EOC21, due to a longer storage period in the spent fuel pool. No apparent changes were observed in the characteristics (composition or oxidizing nature) of crud in the fuel bundles. Finally, no direct negative impact was observed on the fuel cladding surfaces following four fuel cycles of HWC, compared with normal water chemistry conditions. [ABSTRACT FROM AUTHOR]

It plays a very important role for characterizing sorption behaviors of cesium (Cs) and selenium (Se) on Taiwanese mudrocks to retard the migration of radionuclides from a radioactive waste repository. In this study, two non-linear heterogeneity-based isotherms, Langmuir-Freundlich model (LF) and generalized-Freundlich model (GF), were applied for the evaluation of the sorption characteristics of Cs and Se on Taiwanese mudrocks. The batch sorption experiments were carried out and the experimental data were simulated by LF and GF heterogeneity-based isotherm models. In addition, the results showed that both of the LF and GF models could fit the experimental data more perfectly than the Langmuir one. The heterogeneity of sorption behaviors for Cs and Se could be well characterized by the LF and GF models from the root mean square error calculation and plot of the affinity spectrum. The results demonstrated that the sorption mechanism of Cs and Se on mudrock is quite different and Cs sorption is more heterogeneous and complicated than that in Se. [ABSTRACT FROM AUTHOR]

The sorption capacity of cesium (Cs) and selenium (Se) in crushed mudrock was demonstrated in this study through a 2-site Langmuir model. To employ such a numerical analysis, batch tests were applied in this study in synthetic seawater and groundwater with sorption/desorption kinetic experiments (time-dependent) and different concentrations (10-10 M). The 2-site sorption models, which correspond to two rate constants ( λ and λ), might be more adequate than 1-site sorption models in characterizing Cs and Se sorption/desorption according to the least square errors between the numerical analysis and the results of the batch tests. The fitting results showed that a 2-site Langmuir model is capable of appropriately describing Cs and Se sorption in mudrock. Consequently, the sorption capacity was calculated at about 0.06 mol/kg for Cs and at 0.015 mol/kg for Se. [ABSTRACT FROM AUTHOR]

This paper aimed at the characterization of the metallic composition and surface analysis of fuel rod Chalk River Unidentified Deposit (crud) for a BWR-6 unit at a nuclear power plant. In this study, inductively coupled plasma-atomic emission spectroscopy and gamma spectrometry were carried out to analyze the corrosion product distributions and to determine the elemental compositions along the fuel rod under conditions of hydrogen water chemistry (HWC) switched from normal water chemistry (NWC) as the reactor coolant. Most of the crud consisted of flakes and irregular shapes via scanning electron microscope morphology. The loosely adherent oxide layer was mostly composed of hematite (α-FeO) with amorphous iron oxides, as determined using X-ray diffractometer results. The deposited amount of crud was the order of 0.2 mg/cm, suggesting that the fuel surface of this plant under the HWC environment appeared to have lower crud deposition due to low feedwater iron levels. There was also no significant difference in comparison with the NWC condition. [ABSTRACT FROM AUTHOR]

This study investigates sorption and diffusion of Cs in two potential host rocks (granite from Kinmen Island and basalt from Penghu Island) by using batch and through-diffusion methods in order to establish a reliable safety assessment methodology. These methods were applied to crushed and intact rock samples to investigate the actual geological environment. According to solid-phase analysis, including X-ray diffraction, elemental analysis, auto radiography, and polar microscopy, the sorption component primarily contained iron-magnesium (Fe-Mg) minerals in basalt and granite. Moreover, the distribution coefficient ( K) of Cs in various concentrations (~10-10 M) obtained from batch tests indicated a higher sorption capacity in basalt than that in granite because of the 10% Fe-Mg mineral content. The diffusion of Cs in both crushed granite and basalt reached steady state after 110 days, and the apparent diffusion coefficients ( D) were 2.86 × 10 and 1.82 × 10 m/s, respectively. However, the value of D for Cs in intact rocks was estimated to be 1.45 × 10 m/s in granite and 0.56 × 10 m/s in basalt, lower than the values obtained using crushed rocks. In addition to the microporous structure (major sorption minerals), it showed that the major retardation of Cs depended on the porosity (θ) of compacted media, according to through-diffusion tests. In fact, the solid/liquid ( S/ L) ratio decreased as is the case when switching from batch to column experiments and the sorption effect on minerals became even more negligible in retardation of radionuclide migration. [ABSTRACT FROM AUTHOR]

ivity concentrations using gamma-ray spectrometer and distributions of natural radionuclides in soil samples collected were investigated to assess the environmental radioactivity and characterization of radiological hazard. The average concentrations of U, Th series and K in the 5 cm depth soil were 22.53, 33.43 and 406.62 Bq kg, respectively, which was within world median ranges in the UNSCEAR 2000 report. The average absorbed dose rate estimated by soil activity and annual effective doses were 49.32 nGy h and 60.48 μSv, respectively. Since the soil is an important building material, the mean radium equivalent activity ( Ra), external ( H) and internal ( H) hazard index using various models given in the literature for the study area were evaluated as 101.72 Bq kg, 0.27 and 0.34, respectively, which were below the recommended limits. The effects of pH value, conductivity, true density and textural properties of soil samples on the natural radionuclide levels were also studied. The application of cluster analysis (CA) and principal component analysis (PCA), coupled with Pearson correlation coefficient analysis, were utilized to analyze the data, identify and clarify the effects of physico-chemical properties on natural radioactivity levels. The CA and PCA results showed that the former method yielded three distinctive groups of the soil variables whereas the latter one yielded the number of variables into three factors with 87.5% variance explanation. [ABSTRACT FROM AUTHOR]