Strontium Migration Research Articles

Migration processes of 137Cs and 90Sr in compartments of a lake ecosystem

The dispersion of radioactive substances in the environment following nuclear weapon tests in atmosphere since 1954 and accidents to nuclear plants, like that in Chernobyl in 1986, have allowed us to study the migration processes of some radionuclides in complex ecosystems such as lakes are. In the present paper the behavior of 137Cs and 90Sr in different compartments of the Monterosi Lake (central Italy) was assessed. The 137Cs concentration was measured in lake water as well as sediment, stream water, aquatic plant and fish samples. 90Sr concentration in water and sediments was also determined. A total inventory of 4206±76 Bq . m-2 and 958±79 Bq . m-2 (on 27/6/01) has been found for 137Cs and 90Sr, respectively. The experimental data presented here allow to calibrate theoretical models predicting the temporal trend of radionuclide concentration in similar ecosystems. Moreover, information on cesium and strontium migration processes can be extended to other pollutants having similar environmental behavior.

Formation of hydroxyapatite in soils using calcium citrate and sodium phosphate for control of strontium migration

Summary 90Sr contamination is a major problem at several U.S. sites. At some sites, 90Sr has migrated deep underground making site remediation difficult. In this paper, we describe a novel method for precipitation of hydroxyapatite, a strong sorbent for 90Sr, in soil. The method is based on mixing a solution of calcium citrate and sodium phosphate in soil. As the indigenous soil microorganisms mineralize the citrate, the calcium is released and forms hydroxyapatite. Soil, taken from the Albuquerque desert, was treated with a sodium phosphate solution or a sodium phosphate/calcium citrate solution. TEM and EDS were used to identify hydroxyapatite with CO3 2- substitutions, with a formula of (Ca4.8Na0.2)[(PO4)2.8(CO3)0.2](OH), in the soil treated with the sodium phosphate/calcium citrate solution. Untreated and treated soils were used in batch sorption experiments for Sr uptake. Average Sr uptake was 19.5, 77.0 and 94.7% for the untreated soil, soil treated with sodium phosphate, and soil with apatite, respectively. In desorption experiments, the untreated soil, phosphate treated soil and apatite treated soil released an average of 34.2, 28.8 and 4.8% respectively. The results indicate the potential of forming apatite in soil using soluble reagents for retardation of radionuclide migration.

Migration of Strontium, Calcium, Fluorine, and Boron in the Caucasian Coastal Area of the Black Sea

The distribution of dissolved Sr, Ca, F, and B in the mouths of small streams and the coastal areas of Golubaya and Gelendzhic bays is studied.

Strontium Migration in Groundwater of Fluvioglacial Sediments in the Khibiny Massif

The regularities of Sr absorption by different Quaternary fluvioglacial sediments, containing groundwater within the Khibiny massif, have been studied. The studied sediments have been shown to adsorb Sr as a result of the cation exchange and complexing on the solid phase surface, which is responsible for the absorbing capacity of the sediments in the wide range of natural water pH. The base exchange capacity of Sr has been established to largely depend on the concentration of the macrocomponents (Ca2+ and Mg2+) in the groundwater. It has been noted that the migration mobility of Sr is low under the conditions of almost neutral water typical of the soil horizon in the studied area.

Validation of a physically based catchment model for application inpost-closure radiological safety assessments of deep geological repositoriesfor solid radioactive wastes

The physically based river catchment modelling system SHETRAN incorporatescomponents representing water flow, sediment transport and radionuclidetransport both in solution and bound to sediments. The system has been appliedto simulate hypothetical future catchments in the context of post-closureradiological safety assessments of a potential site for a deep geologicaldisposal facility for intermediate and certain low-level radioactive wastes atSellafield, west Cumbria. In order to have confidence in the application ofSHETRAN for this purpose, various blind validation studies have beenundertaken. In earlier studies, the validation was undertaken againstuncertainty bounds in model output predictions set by the modelling team onthe basis of how well they expected the model to perform. However, validationcan also be carried out with bounds set on the basis of how well the model isrequired to perform in order to constitute a useful assessment tool. Herein,such an assessment-based validation exercise is reported. This exerciserelated to a field plot experiment conducted at Calder Hollow, west Cumbria,in which the migration of strontium and lanthanum in subsurface Quaternarydeposits was studied on a length scale of a few metres. Blind predictions oftracer migration were compared with experimental results using bounds set by asmall group of assessment experts independent of the modelling team. Overall,the SHETRAN system performed well, failing only two out of seven of the imposedtests. Furthermore, of the five tests that were not failed, three werepositively passed even when a pessimistic view was taken as to how measurementerrors should be taken into account. It is concluded that the SHETRAN system,which is still being developed further, is a powerful tool for application inpost-closure radiological safety assessments.

Silicate diagenesis in deep-sea sediments from the Tonga forearc (SW Pacific): a strontium and Rare Earth Elements signature

87Sr/ 86Sr isotopic ratios, strontium and Rare Earth Element concentrations obtained on volcano-sedimentary rocks and separated clay mineral and zeolite fractions reveal a formation by pore water–volcanic rock interaction for most of the hydrous silicate minerals of the Site 841 ODP collected from the Tonga forearc. Unusual strontium concentrations and isotopic ratios recorded in the Miocene tuffs associated with specific REE patterns indicate that the formation of these hydrous silicates does not follow a simple burial diagenesis model, but was related to the cooling of intruding basaltic sills in the Miocene volcano-sedimentary series. Migration of strontium into the pore water in response to the heat flow induced the formation of Sr-bearing zeolites such as clinoptilolite, heulandite and chabazite. No evidence of any influence of a further thermal pulse in the Eocene rhyolitic tuffs could be found. As recorded by the chemistry of their clay mineral fraction, the rhyolitic tuffs developed a polyphasic diagenetic process, which might have been influenced by a possible circulation of a fluid into structurally weak areas. © 2000 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS Tonga / silicates / strontium / Rare Earth Elements / diagenesis / heat flow

Intercomparison between TRIO-EF and IMPACT codes with reference to experimental strontium migration data

This work presents an intercomparison exercise between two geochemical migration codes, TRIO-EF (an object-oriented finite element code) and IMPACT (a chemical engineering code using mixing cells in series). The predictions of the two codes are compared with the reference experimental results obtained in a previous study of strontium transport in soil columns. This simulated geochemical system is well documented and includes ion exchange and dissolution-precipitation reactions. The solution transport is simulated by a one-dimensional advection-dispersion model. The predictions of TRIO-EF and IMPACT are both in good agreement with the experimental results. However, slight differences can be observed between the two codes, especially when concentration discontinuities are involved, such as precipitation fronts or changes in boundary conditions. These discrepancies between the two codes can mainly be attributed to the different discretisation approaches.

Migration of strontium in clayey and calcareous sandy soil: Precipitation and ion exchange

An equilibrium model for describing strontium transport through a clayey and calcareous sandy soil is presented. The speciation model includes calco-carbonic equilibria, water dissociation, Ca/Sr ion exchange, and precipitation/dissolution of strontianite and calcite. This speciation mechanism is included in a flow model taking into account dispersion and advection. The transport model is validated by column experiments performed with sand from Güe, France. The model allows the prediction of strontium transport in a wide concentration range. Strontium retardation is mainly governed by strontianite precipitation and Ca/Sr exchange. The ability of the driving water to dissolve the precipitated strontianite can be responsible for an overconcentrated strontium peak, and determines its retardation.

Numerical Simulation of Cesium and Strontium Migration Through Sodium Bentonite Altered by Cation Exchange with Groundwater Components

ABSTRACTNumerical simulations have been used to investigate how spatial and temporal changes in the ion exchange properties of bentonite affect the migration of cationic fission products from high-level waste. Simulations in which fission products compete for exchange sites with ions present in groundwater diffusing into the bentonite are compared to simulations in which the exchange properties of bentonite are constant.

Simulation of solute transport in a chemically reactive heterogeneous system: Model development and application

One‐dimensional transport of solutes in a saturated porous medium has been simulated using a numerical model CHEMTRN. This model includes dispersion/diffusion, advection, ion exchange, formation of complexes in the aqueous phase, and the dissociation of water. The mass action, transport, and site constraint equations are expressed in a differential/algebraic form and solved simultaneously. In the mass action equations describing complexation and sorption processes, the activities of the species in the aqueous phase are approximated using the Davies equation. A solubility constraint can be set at the inner boundary. The model was applied to a study of the migration of strontium in groundwater. Results show that surface site competition is important when the strontium concentration is comparable to the background electrolyte concentration, in which case a constant kD model does not simulate the transport of chemical species adequately. In addition, the pH level was buffered to a level of approximately 10 near the wasteform due to the incorporation of the solubility constraint. For the particular case studied, the incorporation of aqueous complexation did not significantly enhance strontium mobility.

Evaluation of distribution coefficients for the prediction of strontium and cesium migration in a uniform sand

The validity of using a distribution coefficient (Kd) in the mathematical prediction of strontium and cesium transport through uniform saturated sand was investigated by comparing measured breakthrough curves with curves of simulations using the advection-dispersion and the advection equations. Values for Kd were determined by batch equilibration tests and, indirectly, by fitting the mathematical model to breakthrough data from column experiments. Although the advection-dispersion equation accurately represented the breakthrough curves for two nonreactive solutes (chloride and tritium), neither it nor the advection equation provided close representations of the strontium and cesium curves. The simulated breakthrough curves for strontium and cesium were nearly symmetrical, whereas the data curves were very asymmetrical, with long tails. Column experiments with different pore-water velocities indicated that the shape of the normalized breakthrough curves was not sensitive to velocity. This suggests that the asymmetry of the measured curves was the result of nonlinear partitioning of the cations between the solid and liquid phases, rather than nonequilibrium effects. The results indicate that the distribution coefficient, when used in advection-dispersion models for prediction of the migration of strontium and cesium in field situations, can result in significant error.

Zircon U-Pb and Whole-Rock Rb-Sr Ages and Early Crustal Development near Rainy Lake, Ontario

Early Precambrian rocks near Rainy Lake, on the Ontario-Minnesota border, are comprised of a thick section of metasediments and paragneisses (Coutchiching) overlain conformably by metavolcanics (Keewatin) and intruded by Laurentian Igneous rocks. Eight of ten zircon samples from these units lie within experimental error (±30 m.y.) of a 2750-m.y. Concordia chord. We conclude that the zircon ages are primary and not a result of metamorphic resetting. There is thus no evidence for an older sialic source region from which the detrital Coutchiching zircons were derived. It is probable that these detrital zircons were derived locally from contemporaneous volcanics and shallow intrusives within the geosyncline. There is little recorded time difference ( The Rb-Sr isochron for the volcanics gives an age of 2770 m.y. (initial Sr 87 /Sr 86 = 0.7010) which is not statistically different from the Coutchiching isochron age of 2690 m.y. (initial ratio = 0.7002). Both isochrons are in agreement with the zircon intercept age of 2750 m.y. (using λRb 87 = 1.39 X 10 −11 yr −1 ). At least some of the paragneisses are shown to be open to strontium migration during regional metamorphism. The Coutchiching isochron age of 2690 m.y. probably represents an early stage of metamorphism during the Algoman orogeny. Samples of one Laurentian intrusive give an isochron age of 2520 m.y., which is distinctly younger than the ages of the Laurentian zircons. This intrusive has been highly sheared and the rocks have probably been reset during the shearing event.