Diffusion of Radionuclides in Brine-Saturated Backfill Barrier Materials

1982 ◽  
Vol 15 ◽  
Author(s):  
E. J. Nowak
Keyword(s):  
Sodium Titanate ◽  
Distribution Coefficients ◽  
Barrier Materials ◽  
Compacted Bentonite ◽  
Metal Diffusion ◽  
Diffusion Cells ◽  
Linear Sorption ◽  
Backfill Materials ◽  
Cylindrical Diffusion ◽  
Apparent Distribution

ABSTRACTThe diffusion of cesium(I), strontium(II), pertechnetate and europium in brine-saturated backfill materials was measured. Plastic diffusion cells containing cylindrical diffusion columns were used for low density backfill materials. The diffusion of gamma-emitters was followed by a gamma scanning technique. Metal diffusion cells constructed entirely from Hastelloy C-276 were used for the diffusion of pertechnetate in highly compacted bentonite. Apparent distribution coefficients calculated from diffusion data are (a) 0.02 m3 /kg for cesium(I) in 40 wt.% mordenite and 60 wt.% bentonite; (b) 0.04 m3/kg for strontium(II) in 10 wt.% sodium titanate and 90 wt.% bentonite; (c) 0.5 m3/kg for pertechnetate in 70 wt.% charcoal and 30 wt.% bentonite; and (d) 3 m3/kg for europium in 100% bentonite. Backfill effectiveness estimates based on batch sorption measurements were supported by these results;however, the diffusion results for europium did not agree well with a model for diffusion retarded by linear sorption. First measurements of pertechnetate diffusion in highly compacted bentonite suggest that anion exclusion may play a role in reducing mass transport rates of anions in this material. Needs for diffusion measurements that take into account site-specific materials interactions are described.

Diffusion of Colloids and Other Waste Species in Brine–Saturated Backfill Materials

1983 ◽  
Vol 26 ◽  
Author(s):  
E. J. Nowak
Keyword(s):  
Colloidal Gold ◽  
Diffusion Theory ◽  
Distribution Coefficients ◽  
Low Density ◽  
Sorption Data ◽  
Simple Diffusion ◽  
Diffusion Cells ◽  
Backfill Materials ◽  
Cylindrical Diffusion ◽  
Waste Repositories

ABSTRACTThe diffusion of plutonium (IV) and pertechnetate and the migration of colloidal gold in brine-saturated bentonite was measured. High ionic strength brine characterizes potentially intruding groundwater for radioactive waste repositories in salt. Plastic diffusion cells containing cylindrical diffusion columns were used for low density bentonite. Metal diffusion cells constructed entirely from Hastelloy C-276 were used for the diffusion of pertechnetate in highly compacted bentonite. Apparent distribution coefficients calculated from plutonium diffusion in two columns of low density bentonite are 2 m3/kg and 3 m3/kg. These values are in good agreement with the value of 3m3/kg that was calculated from previous batch sorption data. Pertechnetate anions migrated out of a brine-saturated high density bentonite diffusion column at rates that are too large to be rationalized with a simple diffusion theory. Additional measurements that take into account possible channeling of pertechnetate are required. Colloidal gold was excluded from low density brine-saturated bentonite, but colloidal gold may have channeled between the bentonite and the wall of the diffusion cell. These results support the effectiveness of brine-saturated bentonite as an engineered barrier to plutonium. The results also highlight the need for additional measurements of pertechnetate and gold transport in bentonite. Needs for transport measurements that take into account site-specific materials interactions are also described.

Distribution Coefficients and Apparent Diffusion Coefficients of Cesium in Compacted Bentonites

1999 ◽  
Vol 556 ◽  
Author(s):  
Akiko Okamoto ◽  
Kazuya Idemitsu ◽  
Hirotaka Furuya ◽  
Yaohiro Inagaki ◽  
Tatsumi Arima
Keyword(s):  
Diffusion Coefficients ◽  
Distribution Coefficients ◽  
Dry Density ◽  
Apparent Diffusion Coefficients ◽  
Compacted Bentonite ◽  
Apparent Diffusion ◽  
Tracer Solution ◽  
Cesium Concentration ◽  
Penetration Profile ◽  
Very High

AbstractDistribution coefficients and apparent diffusion coefficients of cesium in some compacted bentonites were determined by the penetration profile method. Cylindrical compacted bentonites with the dry density of 0.8 to 1.6 Mg/m3 were contacted with tracer solutions containing 1000, 100 or 10 ppm of cesium. The apparent diffusion coefficients were obtained from the concentration profiles of cesium in compacted bentonites. The distribution coefficients were obtained concurrently by dividing the intercepts of the profiles by the concentration of the tracer solution. The apparent diffusion coefficients of cesium in compacted bentonite were obtained in the range of 0.42 to 9.6· 10−12 m2/s. The apparent diffusion coefficients in the compacted bentonite contacted with three different concentrations of cesium tended to decrease with increasing dry density of the specimen; but, they had no dependence on cesium concentration within a factor of 3 at the same dry density. The distribution coefficient of cesium for the specimens contacted with three different concentrations of cesium were obtained in the range of 0.3 to 90 L/kg and had little dependence on dry density. The distribution coefficients obtained in the compacted bentonites were dependent on pH of the solution rather than concentration of cesium. These distribution coefficients obtained in the compacted bentonites were 10 to 1000 times smaller than those obtained by batch experiments. The data suggest that not all sorption sites for cesium are available in highly compacted bentonite. It is necessary to consider surface diffusion as a significant migration mechanism of cesium through the compacted bentonites at very high pH condition such as 12.

Experimental investigation on buffer/backfill materials for radioactive waste repository downward facing sorption additivity of cesium, strontium and cobalt with different concentrations

Kerntechnik ◽  
2021 ◽  
Vol 86 (5) ◽  
pp. 375-381
Author(s):  
C.-P. Lee ◽  
Y. Hu ◽  
Y. Sun ◽  
Y. Shi ◽  
N.-C. Tien ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Distribution Coefficients ◽  
Test Method ◽  
Radioactive Waste Disposal ◽  
Batch Test ◽  
Backfill Materials ◽  
Mixing Proportion ◽  
Synthetic Groundwater ◽  
Waste Repository ◽  
Sorption Characteristics

Abstract Buffer/backfill materials for radioactive waste disposal sites consist of pure bentonite or bentonite-rock mixtures. In this study, the batch test method was used to obtain the sorption characteristics of important radionuclides such as Cs, Sr and Co on buffer/backfill materials; i. e., mixing Wyoming MX-80 bentonite or local Taiwanese Zhi-Shin bentonite with possible host rock (argillite and granite) in different proportions (0∼100%). The distribution coefficients (Kd) for Cs, Sr and Co were obtained from the experiments. The distribution coefficient for the bentonite-rock mixtures were found, with more than 50% of mixing proportion of bentonite to argillite or granite, to have very similar values to that of pure bentonite. Furthermore, it was clearly found that the sorption of Cs, Sr and Co to bentonite-rock mixtures is decreased as ionic strength of the liquid phase is increased from 0.001M to 1M for NaCl solutions. According to the experimental results, in synthetic groundwater, it is quite convenient and helpful to assess the distribution coefficients (Kd) of Cs, Sr and Co for buffer/backfill materials using batch sorption experiments with bentonite-rock mixtures of fixed mixing proportions.

scholarly journals Experimental study on the influence of preliminary desiccation on the swelling pressure and hydraulic conductivity of compacted bentonite

Clay Minerals ◽  
2018 ◽  
Vol 53 (4) ◽  
pp. 733-744 ◽  
Author(s):  
Lin Zhi Lang ◽  
Wiebke Baille ◽  
Snehasis Tripathy ◽  
Tom Schanz
Keyword(s):  
Hydraulic Conductivity ◽  
Swelling Pressure ◽  
Shrinkage Strain ◽  
Volumetric Shrinkage ◽  
Barrier Materials ◽  
Compacted Bentonite ◽  
Swelling Capacity ◽  
Pressure Tests ◽  
Volumetric Shrinkage Strain ◽  
Volume Swelling

ABSTRACTIn deep geological repositories, compacted bentonites have been proposed for use as barrier materials for isolating nuclear waste. The prevailing thermo-hydro-mechanical boundary conditions in the repositories may affect the swelling capacity and permeability of the compacted bentonites. In this study, the effect of preliminary desiccation on the subsequent hydro-mechanical behaviour (swelling pressure and hydraulic conductivity) of compacted Calcigel bentonite was investigated experimentally at 22°C and 80°C. In the first stage of the test, the compacted specimens were subjected to suction-controlled desiccation at 22°C and 80°C using the vapour-equilibrium technique. After the water content reached equilibrium at a given suction, the axial, radial and volumetric shrinkage strains were measured. Afterwards, constant-volume swelling-pressure tests were performed on the desiccated specimens (second test stage) by saturating the dried specimens with deionized water at 22°C and 80°C. At the end of the swelling-pressure test, the hydraulic conductivities of four saturated specimens were measured at each temperature. The volumetric shrinkage strain of the compacted bentonite during desiccation is controlled by suction instead of temperature. In addition, the preliminary desiccation increases both the swelling pressure and hydraulic conductivity of compacted bentonite, particularly if compacted bentonite undergoes extreme desiccation at an applied suction of >700 MPa.

Retrieval and Analysis of Simulated Defense HLW Package Experiments at the WIPP

1988 ◽  
Vol 127 ◽  
Author(s):  
Martin A. Molecke ◽  
N. Rob Sorensen
Keyword(s):  
Rock Salt ◽  
Waste Form ◽  
High Level Waste ◽  
General Corrosion ◽  
Uniform Corrosion ◽  
Geochemical Environment ◽  
Waste Package ◽  
Barrier Materials ◽  
Backfill Materials

ABSTRACTIn situ waste package performance experiments involving simulated (non-radioactive) defense high-level waste (DHLW) containers have been in progress since late 1984 at the Waste Isolation Pilot Plant (WIPP) facility. These experiments involve full-size, simulated DHLW containers of several metals and designs emplaced in the WIPP bedded rock salt. These test containers are surrounded by granular backfill (packing) materials, have in many cases been intentionally injected with brines, and are heavily instrumented. A majority of the test packages also contain nonradioactive DHLW borosilicate glass waste form, either within the container and/or outside of it. The primary purpose of these WIPP simulated DHLW experiments is to evaluate the in situ durability and performance of all waste package engineered barrier materials, and to perform package concept validation testing.Twelve of the test DHLW containers, emplaced in WIPP test Room B, have been in heated operation since 1985 and had a maximum surface temperature of about 190°C. These containers were recently retrieved, after about 3 years of heated exposure, for detailed posttest laboratory analyses of: general corrosion and metallurgical degradation, waste form and backfill materials alterations, and other rock salt-brine-barrier materials near-field interactions with the “repository” geochemical environment. Test canisters and overpacks made of ASTM Grade-12 titanium showed essentially no visible degradation in either the base metal or welds; cast mild steel A216/WCA over-packs have suffered some uniform corrosion. Significant degradation of the removed instruments and associated test apparatus has been found: pieces of stainless steel (both 304L and 316) apparatus have undergone extensive stress-corrosion cracking failure and non-uniform attack; Inconel 600-sheathed instruments have undergone both extensive uniform and localized (pitting) attack. Granular backfill materials have been significantly compacted by creep closure to about a density of 2 kg/m. Laboratory analyses are still in progress. Further details on these materials results plus instrumentation data and other in situ WIPP waste package test observations are discussed.

Adsorption Characteristics of Estrone to Aerobic Activated Sludge

2013 ◽  
Vol 295-298 ◽  
pp. 12-16 ◽  
Author(s):  
Qing Ling Zeng ◽  
Lu Wang ◽  
Chun Hua Shen ◽  
Fei Li ◽  
Zhen Ming Zhou
Keyword(s):  
Activated Sludge ◽  
Sorption Process ◽  
Distribution Coefficients ◽  
Effect Of Temperature ◽  
Isotherm Models ◽  
Sorption Rate ◽  
Increased Temperature ◽  
Linear Sorption ◽  
Sorption Thermodynamics ◽  
Lower Temperature

Batch experiments were conducted to measure the sorption capacities of estrone (E1) to aerobic activated sludge. The effect of temperature on E1 sorption was investigated at the temperatures of 5-35oC. The results showed that E1 sorption equilibrium was reached at 15min. E1 sorption on the sludge fitted both Freundlich and linear sorption isotherm models. Distribution coefficients (Kd) of E1 to aerobic inactivated sludge was 546.5 L∙kg-1 at 25oC. The effect of temperature on sorption indicated that lower temperature benefited the sorption. The distribution coefficients (Kd) and sorption rate both decreased with the increased temperature. Kd of E1 to aerobic inactivated sludge was decreased by about 44%; the sorption rate was decreased by about 13% when temperature increased from 5 to 35oC. The specific sorption coefficient KOM or KOC was also used to describe the sorption capacity, which also decreased with increased temperature. Sorption thermodynamics indicated that the sorption process was exothermic and spontaneous.

Enhancement of the Glass Corrosion in the Presence of Clay Minerals: Testing Experimental Results with an Integrated Glass Dissolution Model

1992 ◽  
Vol 294 ◽  
Author(s):  
Enzo Curti ◽  
N. Godon ◽  
E.Y. Vernaz
Keyword(s):  
Kinetic Equation ◽  
Clay Content ◽  
Distribution Coefficients ◽  
Mineral Surfaces ◽  
Glass Dissolution ◽  
Corrosion Rates ◽  
Glass Corrosion ◽  
Dissolution Model ◽  
Backfill Materials ◽  
Range Of Values

ABSTRACTRecent glass dissolution experiments, conducted at 90°C in the presence of potential backfill materials, indicate remarkably faster glass corrosion in the presence of clay, compared to tests where the glass is leached either alone or with alternative backfill materials. This effect correlates with the clay content in the backfill, and may be attributed to the removal of silica from solution. Sorption, or dissolution with reprecipitation of a silica-rich clay, have been proposed as possible mechanisms for the silica consumption.The results of some experiments have been tested against a glass dissolution model, in which a widely used kinetic equation for glass corrosion is coupled with diffusive silica transport through a single porosity, linearly sorbing medium, which represents the backfilling. Because the glass corrosion rates imposed by the kinetic equation are inversely proportional to the silicic acid concentration of the leachant contacting the glass, the model predicts enhanced glass dissolution if silica is sorbed by the porous medium.The experimental data proved to be consistent with the predicted enhancement of the glass dissolution. Moreover, the model-estimated distribution coefficients for silica sorption (Kd) fall within the range of values extracted from available literature data, thus supporting the hypothesis that the observed high corrosion rates are due to sorption of silica on the clay mineral surfaces.

Comparison of Measured and Calculated Diffusion Coefficients for Iodide in Compacted Clays

Clay Minerals ◽  
1994 ◽  
Vol 29 (2) ◽  
pp. 145-151 ◽  
Author(s):  
D. W. Oscarson
Keyword(s):  
Diffusion Coefficients ◽  
Bulk Water ◽  
Distribution Coefficients ◽  
Organic Carbon Content ◽  
Lake Agassiz ◽  
Sorption Behaviour ◽  
Barrier Materials ◽  
Order Of Magnitude ◽  
Compacted Clays ◽  
High Level

AbstractAn understanding of the behaviour of contaminants in compacted clays is important in assessing the effectiveness of clay-based barrier materials used in many waste containment strategies. Here the diffusion and sorption behaviour of I− with selected compacted clays is examined (129I is a relatively long-lived radioisotope present in high-level nuclear fuel waste.) Diffusion coefficients, D, and distribution coefficients, Kd, were measured for I− with four clays: bentonite, Lake Agassiz clay (a glacial lake clay composed mainly of smectite, illite, kaolinite, and quartz), interstratified illite-smectite, and kaolinite. For the diffusion experiments the clays were compacted to a dry bulk density, ρ, of ∼1.2 Mg m−3. The mean measured D values, Dm, were as follows: bentonite, 310 µm2 s−1; Lake Agassiz clay, 0.62 µm2 s−1; illitesmectite, 190µm2s−1; and kaolinite, 74µm2s−1. The measured values were compared with those calculated, Dc, from the following model: D=Doτan/(n + ρKd), where Do is the diffusion coefficient in pure bulk water, τa the apparent tortuosity factor, and n the solution-filled porosity of the clay. Except for the Lake Agassiz clay, where Dm was about an order of magnitude lower than Dc, the Dm and Dc values agreed within a factor of about two. The Lake Agassiz clay has a markedly higher organic carbon content than the other three clays, and this could affect τa, which may be overestimated in the model.

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