Diffusion Of Cesium Research Articles

Leaching behavior of 60Co and 173Cs from spent ion exchange resins in cement matrix

The leaching rate of cobalt-60 and cesium-137 in cement has been studied. The solidification matrix was a standard Portland cement mixed with 300–360 (kg/m 3) spent ion exchange resins, with or without 2–5% of bentonite clay. The leaching rates from the cement matrix were measured as Co-60: (4, 2–6, 9) × 10 −5 (cm/d), and for Cs-137: (3,2–6, 6) × 10 −4 (cm/d), after 720 days. From the leaching data the apparent diffusivity of cobalt and cesium in cement matrix with a waste load of 300–360 kg/m 3 spent ion exchange resins, was measured as Co-60: (1, 0–4, 0) × 10 −6 (cm 2/d) and for Cs-137: (0, 5-2, 6) × 10 −4 (cm 2/d), after 750 days.

Computer Simulation Study of Transient Diffusion of Cesium through Granite with Unsteady-State Diffusion Model

Computer Simulation Study of Transient Diffusion of Cesium through Granite with Unsteady-State Diffusion Model

Diffusion of cesium in sodium borosilicate glasses for nuclear waste immobilisation, studied by low-energy ion scattering

Low-energy ion scattering (LEIS) is shown to be a convenient technique for measuring the diffusion coefficient of cesium in sodium borosilicate glass. A 3 keV 4He+ ion beam is first used to create an alkali depletion layer in the outermost 60 nm of the glass. After annealing, to remove the vacancies from the glass matrix, the return of cesium to the surface is monitored. Diffusion coefficients at 815 and 842 K are determined. Both are found to agree, within experimental error, with the values from the concentration couple method. The latter analyzes the cesium profiles by SEM/EDS. The present technique, however, can be applied at lower temperatures, where the concentration couple method would require too long measuring times. This gives the possibility to predict the diffusion coefficient of cesium at actual temperatures in nuclear waste glass cylinders.

Computer Simulation Study of Transient Diffusion of Cesium through Granite with Unsteady-State Diffusion Model.

A steady-state diffusion model has been used widely to determine the diffusivities of radionuclides in rocks. Buffer container at the source solution side is used to keep the concentration constant. It is suitable for non-sorptive species, but not for sorptive species. Some researchers proposed a unsteady-state diffusion model recently. It is possible to use simple experimental apparatus without buffer container to measure the diffusivity with this model. To obtain the diffusional information more easily according to the sorption properties of radionuclides, through- diffusion experiments were performed in granites. Methods of determining of diffusivities are discussed according to sorption properties of species. For the non-sorptive species, the steady- state diffusion model was effective to determine the diffusivity. For the sorptive species, the analytical solution of the unsteady-state diffusion model found to be more appropriate to determine the diffusivity. Surface diffusion of sorbed species on roc...

Diffusion of the fission metals cesium and silver in reactor-grade graphite

Studies of cesium and silver diffusion in reactor graphite are reported. The diffusant concentration distribution in samples after annealing is found to contradict that expected from Fick's laws. A model for diffusion through several types of sites (channels of migration) is proposed. Some features of diffusion sites are pointed out which may make the multichannel mechanism of migration evident in a short-duration diffusion experiment. The calculations performed indicate that the proposed mechanism conforms to the picture observed in experiment. Cesium diffusion parameters through three channels of migration in reactor graphite are given.

Rydberg states of cesium in the flux from surfaces at high temperatures

Diffusion of cesium through an Ir foil at high temperature is used to give a flux of desorbing atoms and/or ions, which is not in equilibrium at the surface temperature. The desorbing flux is studied with electrostatic fields in a grid-collector combination, to determine the charge states and the interaction of the different states with an electric field and with a surface. At low Cs flux densities to the back of the foil, the desorbed flux contains positive ions and ordinary neutrals. At large flux densities from the source, however, both neutral Rydberg states and negative ions in the form of multiply-excited states of cesium are found in the flux. The negative ion states do not dissociate (detach) readily in such weak external electric fields where the neutral Rydberg state atoms ionize. Instead, they can emit two of their outer electrons in contact with the collector surface, thus giving positive collector currents when the field accelerates the electrons away from the collector. The large flux of such states indicates that the electron affinity is large for Rydberg state atoms. The origin of the excited states leaving the hot Ir surface is discussed. It appears to be related to the close coincidence of the desorbing ionic state and the Rydberg state at low work function.

Calcium-activated chloride current in rat vascular smooth muscle cells in short-term primary culture.

Isolated cells from rat portal vein smooth muscle in short-term primary culture were studied using patch-clamp technique (whole-cell configuration). In order to study a calcium-activated chloride current, the potassium currents were blocked by intracellular cesium diffusion. Without EGTA in the pipette solution, depolarizing voltage pulses from a holding potential of -70 mV to positive potentials activated an early inward and a late outward current. The latter persisted as a long-lasting inward tail current when the membrane was repolarized to -70 mV. The outward current measured at the end of the pulse and the tail current were blocked by extracellular cobalt, after replacement of external calcium with barium, after removal of external calcium, and when the calcium concentration of the pipette solution was less than 0.5 microM, suggesting that they were calcium-dependent. The tail current decay was voltage sensitive, becoming faster with hyperpolarization. The reversal potential of the calcium-activated current was near the equilibrium potential for chloride ions, and was shifted as predicted by the Nernst equation when the extracellular or intracellular chloride concentration was changed. The calcium-activated current was blocked by adding micromolar concentrations of niflumic acid or millimolar concentrations of DIDS. This effect of compounds known to interfere with chloride channels together with the data on the equilibrium potential for chloride ions indicated above suggested the existence of a calcium-activated chloride current in vascular smooth muscle cells.

On predicting the fate of radioactive caesium in soil beneath grassland

SUMMARYA simple mechanistic model is developed for predicting the fate of radioactive caesium in the soil beneath grassland. A continuity equation is derived describing the diffusion, leaching and reaction of caesium in soil, with uptake by a uniformly distributed root system. The soil reaction is characterized by three phases: an instantaneous exchange, a moderately‐fast reversible reaction and a slow reversible reaction. The time‐dependent reactions and root uptake have first‐order kinetics. It is shown that caesium is unlikely to be removed from the root zone by leaching and diffusion, even under prolonged high rainfall. Therefore, since the rates of the soil reactions and root uptake are much greater than the rates of diffusion and leaching, it is not necessary to calculate the concentration profile to find the rate of uptake. The computer program for the model is just 30 lines of fortran, and requires only a few seconds of micro‐computer CPU time for each year of simulation.Some predicted rates of plant uptake and distributions in the soil are given. It is seen that the fate of the caesium is markedly influenced by soil parameters dependent on soil clay content, clay mineralogy, organic matter content, cation saturation and pH, and by the rooting density. The predicted rates of uptake vary from about 0.5% to 50% per annum, which is compatible with data reported elsewhere. The predictions are intended to expose gaps in knowledge of the fate of caesium in soil: in particular, the mobility of sorbed radio‐nuclides on soil surfaces needs further study. Predictions are not given for the fate of caesium in any real situations because insufficient data are available.

Potassium ions play a role in the glycine-induced inhibition of rat substantia nigra zona compacta neurones

Glycine directly inhibits the firing, it hyperpolarizes and/or depolarizes the dopaminergic neurones and increases the membrane conductance. In voltage clamp experiments (near resting potential) either outward and/or inward currents were produced. These actions were present in tetrodotoxin and in 0-calcium-cobalt-treated slices and were antagonized by strychnine. The hyperpolarization depended on the extracellular concentration of potassium and was prevented by cesium diffusion into the cell. Thus potassium ions participate in the glycine mediated inhibition of the firing of substantia nigra zona compacta cells.

Diffusion of Nickel, Strontium, Iodine, Cesium and Americium in Loosely Compacted Bentonite at High pH

Diffusion of Nickel, Strontium, Iodine, Cesium and Americium in Loosely Compacted Bentonite at High pH

Diffusion and Sorption of Cesium, Strontium, and Iodine in Water-Saturated Cement

Diffusion and sorption in cementitious materials are important factors influencing radionuclide migration in radioactive waste disposal. Four different experimental techniques have been used to study these processes for Cs+, Sr2+, and I− ions in Sulphate Resisting Portland Cement paste saturated with water. The results of different experimental methods are compared and their relative merits discussed. The observations can be rationalized only by taking into account departures from the usual simple description of transport in porous media. These are that the cement pore structure has fast and slow diffusivity networks, that all ions do not have the same diffusibility, and that some ions (in this case I−) have nonlinear sorption isotherms. When these factors are taken into account, the present observations are also found to be compatible with the results of other studies.The most appropriate values of characteristic parameters for diffusion and sorption in this system are deduced.

Caesium and strontium diffusion through sodium montmorillonite at elevated temperature

SUMMARYCounter ionic migration rates of dilute Cs+ and Sr2+ against sodium in a Na‐montmorillonite gel are measured using a radially perfused diffusion cell. Enhanced or surface diffusion for caesium is observed both at ambient and elevated temperature. To quantify these surface diffusivities the ion‐exchange properties of the diffusing species are required. Thus, exchange isotherms for caesium against sodium on montmorillonite at 22 and 90°C are given for 10−1, 10−2, and 10−3M background NaCl concentrations. Caesium counterion surface diffusivities at 22 and 90°C are 2.2*10−6 and 8.0 * 10−6 cm2 s−1, respectively. These values are found to be essentially independent of background ionic strength over the range 10−3 to 10−1m NaCl. Experimental evidence of enhanced transport through Na‐montmorillonite for the divalent cation Sr2+ is also confirmed with a surface diffusivity of 2 * 10−6 cm2 s−1 at 22°C and in 10−1m NaCl.

Diffusion of radionuclides from spent oxide fuel into compacted bentonite

An experimental technique for studies of diffusion of radionuclides from spent oxide fuel into compacted bentonite is described. Results obtained for the diffusion of caesium will be briefly discussed.

Measurements of cesium and strontium diffusion in biotite gneiss

A significant retardation of radionuclides transported by flowing water from an underground repository can be expected if the nuclides are able to diffuse into the water filled micropores in the rock. This diffusion into the pores will also increase the surface available to interactions between the nuclides in the groundwater and the rock material, such as sorption. To calculate the retardation, it is necessary to know the sorption properties and the diffusivities in the rock matrix for the radionuclides. Diffusion experiments with cesium and strontium in biotite gneiss samples have been performed. Both the transport of strontium and cesium through rock samples and the concentration profiles of cesium and strontium inside rock samples have been determined. The result shows that diffusion of cesium and strontium occurs in the rock material. A diffusion model has been used to evaluate the diffusivity. Both pore diffusion and surface diffusion had to be included in the model to give good agreement with the experimental data. If surface diffusion is not included in the model, the effective pore diffusivity that gives the best fit to the experimental data is found to be higher than expected from earlier measurements of iodide diffusion in the same type of rock material. This indicates that the diffusion of cesium and strontium (sorbing components) in rock material is caused by both pore diffusion and surface diffusion acting in parallel.

Leaching of Cesium from a Cement Matrix

ABSTRACTThe leaching rate of cesium has been studied in cement. The solidification matrix was a standard Portland cement with increased sulphate resisting properties mixed with 300 kg/m3 or 350 kg/m3 powdered ion exchange resins, and with or without 5 weight-% zeolite added to the grout. The leaching rates from an ordinary cement matrix and a cement matrix mixed with zeolite were measured to be (1.3 to 2.6)×10–7 kg/m2s and (1.6 to 2.1)×10−8 kg/m2s, respectively. From the leaching data the apparent diffusivity of cesium in an ordinary cement matrix with a waste load of 300–350 kg/m3 powdered ion exchange resins was measured to be (0.6 to 1.3)×10−10 m2/s, and in a cement matrix mixed with 5 weight-% zeolite and the same waste load, the diffusivity was measured to be (0.8 to 1.0)×10−12m2/s.

Behaviour of composites used in the confinement of nuclear wastes. 3. Diffusion of ions through epoxide networks

The diffusion of cesium and chloride ions through epoxide membranes was studied under a variety of conditions including self-diffusion, the presence of other salts in the aqueous solution, an excess of either reagent used in the manufacture of the membrane, the addition of various fillers in the epoxide network and two temperatures. At 23°C, the diffusion coefficient D was (2–6) × 10-13cm2s−1 for most systems, except when the epoxide was prepared with an excess of the dioxirane component or when untreated glass beads were added to the network. In the latter instance D increased and most notably with glass beads. On the contrary, addition of sand to the epoxide resulted in a more effective barrier against diffusion as shown by a decrease in D. It is concluded that most of these materials should be suitable for the confinement of low and medium activity nuclear wastes.

Characterization of cesium diffusion in silicon dioxide films using backscattering spectrometry

The diffusion of ion-implanted cesium in thermally grown SiO2 has been examined in the temperature range 700–1000 °C using Rutherford backscattering spectrometry (RBS). Silicon samples were oxidized and implanted with 5×1014 cm−2 133Cs at 145 keV and then annealed in nitrogen using a rapid thermal system for times ranging from several seconds to several hours. Cesium concentration profiles were measured using RBS for each anneal time and temperature. By observing the decay in the peak cesium concentration as a function of anneal time, a diffusivity of DCs =0.50 exp(−2.9eV/kT) cm2/s has been obtained. Other diffusion effects including cesium pile-up at the oxide interfaces and outdiffusion of cesium into the ambient have been studied qualitatively.

Retardation of Cs+ and Cl- Diffusion Using Blended Cement Admixtures

Diffusion of cesium chloride through thin plates of hardened cement pastes was studied. Blast-furnace slag and condensed silica fume were used as blending admixtures in an attempt to retard the diffusion of cesium and chloride ions. The curing and diffusion temperatures were varied from 27° to 60°C, and the water/solid ratio was varied from 0.30 to 0.40. Results indicate that the cesium ion diffuses more slowly than the chloride ion in hardened cement paste systems. Blending admixtures caused a further reduction in diffusivity for both ions, which is important for preventing corrosion or restricting radionuclide transport.

Diffusion Mecflanisms of Srrontium and Cesium in Compacrtd Sodium Bentonite

AbstractIn this research the diffusion of strontium and cesium through bento- nite slabs in stationary state has been measured. The measurement gives directly the transport through the sample and the corresponding effective diffusivity. The apparent diffusivity, diffusivity of the sorbed ions as well as the sorption factors can also be evaluated on the basis of the same diffusion measurement. The sorption on the coxmpacted bentonite has also been measured in a special sorption test where a radioactive tracer has been allowed to diffuse into compacted bentonite until equilibrium was reached.The measured effective diffusivities were clearly higher than they would be in the case of pure pore diffusion. The effective diffusivities also increase with K and the apparent diffusivities are almost independent on KD. This supports the theory that also the sorbed ions diffuse in their own phase. The sorption factors of the compacted bentonite correspond to the values of the batch experiments.

Diffusion of cesium in silver bromide: A surprising observation of the strain effect due to an oversize solute.

The diffusion of ${\mathrm{Cs}}^{+}$ in AgBr has been measured in the temperature range 300--420 \ifmmode^\circ\else\textdegree\fi{}C by a tracer and serial-sectioning technique. The diffusion of ${\mathrm{Cs}}^{+}$ proceeds by a vacancy mechanism. ${\mathrm{Cs}}^{+}$, oversized in comparison to the host ${\mathrm{Ag}}^{+}$, produces local strain in the AgBr lattice, causing diffusivities larger than those of substitutional ${\mathrm{Ag}}^{+}$ and compensating partially the intrinsic curvature in the Arrhenius plot expected from the nonlinear decrease in ${g}_{f}$ with increasing temperature. Surprisingly, the diffusivity of ${\mathrm{Cs}}^{+}$ in AgBr is lower than that in AgCl, presumably due to the larger size effect in a more compact lattice.