Cesium transport

In considering the operational safety and accident analyses of sodium-cooled fast reactors, similar information on the release of fission products from sodium is needed. Although the extent of vaporization can often be calculated from thermodynamic considerations (3, 4), appropriate transport models are required to describe the rate phenomena. In this chapter the results of an analytical and experimental investigation of cesium transport from sodium into flowing inert gases are presented. The limiting case of maximum release is also considered. 

In 1982, /Mert-butyl-cal i x n larenes were studied by Izatt et al. for their capacity to transport cesium from an alkaline medium ([MOH] = 1M) through bulk liquid membranes made of a mixture of diluents able to dissolve these compounds methylene chloride, carbon tetrachloride, and dichloromethane. Experiments were carried out using p-tert-calix[8]arene to measure the rate of cesium transport under conditions of varying source pH. The values of the transport rate, small below a pH of 12, rise rapidly beyond this value, hence confirming that a proton is removed from the ligand in the complexation process. Under such conditions, tetramer, hexamer, and octamer (n = 4, 6, and 8, respectively) display a high selectivity for cesium over the other... 

A two-site model has been used (18) to model cesium transport in soils. In this model a Langmuir-type model, Equation 3,was used to represent surface sorption and a first-order model, Equation 1, was used to approximate interparticle diffusion. Extraction with CaC was used to verify the exchangeable site inventory. 

The success of the two-site sorption models for dissimilar testing conditions clearly indicates its superiority over single-site sorption models for modelling cesium transport. 

The interaction of cesium ions with feldspars at 150°C and 200°C has been studied in distilled water, granite groundwater and saline solution Pollucite, CsAlSi206, was identified by infrared spectroscopy, and was formed as a cubic crystalline phase. Surface analytical techniques (XPS, SAM, SIMS and SEM/ EDX) show Cs to be sorbed onto the mineral surfaces and alteration products. The mechanism of pollucite formation and its relevance to cesium transport/ retardation in the near field of a nuclear waste-disposal vault is discussed. 

Levitskaia, T. G., Lamb, J. D., Fox, K. 1.., Moyer, B. A. (2002). Selective carrierme-diated cesium transport through polymer inclusion membranes by calix[4] arene-crown-6 carriers from complex aqueous mixtures. Radiochimica Acta 90 43-52. 

Radiocesium is an excellent indicator for the behavior of inactive cesium in the biosphere because its radiation can be detected rather quickly, its passage through the compartments of biosystems can be studied much more easily than by direct estimation of the inactive cesium content. Thus, the behavior of radiocesium in ecosystems supplies much information relating to cesium transport in the atmosphere, soil, plants, and animals. 

It is clear that the behavior of radiocesium reflects the behavior of inactive cesium, though information on the total amounts of cesium transported in biological systems cannot be derived from these data. Following the Chernobyl accident, extensive data relating to cesium behavior in biological systems was obtained, though the actual quantities of inactive cesium involved remained unknown. 

Table A1.19 Cesium Transport through Supported Liquid Membranes ...

When failed fuel rods are present in the reactor core, fission product cesium isotopes will also appear in the primary coolant in significant activity concentrations. The high solubility of the cesium compounds deposited in the gap of the fuel rod facilitates the transport to the coolant which, however, is only possible via the liquid phase. This means that under constant-load operating conditions a significant cesium transport will only occur when such fuel rod failures are present in the core that allow a direct contact between fuel and liquid coolant in addition, the shutdown spiking results in a considerable cesium transport to the coolant with almost all types of fuel rod defects. The comparatively low cesium retention on the primary circuit purification resins which are saturated with LiOH occasionally leads to the buildup of activity concentrations of cesium isotopes in the coolant on the same order of magnitude as that of the iodine isotopes 1 and 1, even at comparatively low cesium source strengths or those which are not constant over time. 

Cesium Transport Through Supported Liquid Membranes (SLMs). 

Equation 2 shows that is proportional to Dj which directly depends on the organic carrier concentration in the SLM. That is why the cesium transport isotherms shown in Figures 3 and 4 for compound 2 reproduced the same trends as those found previously in extraction isotherms figures 1 and 2) ... 

The toxicology, occupational health hazards, and transportation regulations of cesium compounds result from the anion rather than the cesium cation. Producers and distributors provide an MSDS as well as detailed shipping requirements for each product. 

Other recent works in this field, studies on the transport of alkali and alkaline earth cations with p-zerr-butyl calix[n]arene esters and amides, were carried out by Arnaud-Neu et al. [20] and Casnati et al. [21]. They prepared 1,3-alternate calix[4]arene-crown-6 as a new class of cesium selective ionophore. 

Table i. Active and selective transport of sodium, potassium and cesium ions with synthetic ionophores ... 

Cadwell, L.L., R.G. Schreckhise, and R.E. Fitzner. 1979. Cesium-137 in coots (Fulica americana) on Hanford waste ponds contribution to population dose and offsite transport estimates. Pages 485-491 in Low-Level Radioactive Waste Management Proceedings of Health Physics Society. Twelfth Midyear Topical Symposium. February 11-15, 1979, Williamsburg, VA. 

With the larger racemic cr-hydroxy-l-naphthaleneacetic acid too, extraction takes place in the presence of 1309] and the appropriate cations but enantiomeric differentiation is not observed. These results were confirmed in transport experiments in which the alkali mandelate is carried through a liquid membrane of [309] dissolved in chloroform. Lehn et al. (1978) explain these observations in terms of an ion pair included in the cavity of the crown ether. The reversal of chiral recognitions between potassium and cesium mandelate of 25% indicates that the structures of the two complexes are different. 

Dozol, J.-F., Casas, J., Sastre, A. M., Transport of cesium from reprocessing concentrate solutions through flat-sheet-supported liquid membranes Influence of the extractant, Sep. Sci. Technol, 30, 435-448,1995. 

The Transport of Fission-Product Cesium from Sodium... 

Transport Model. A general release equation is developed by considering diffusion in both the liquid and gaseous phases. Figure 1 is a sketch of a vessel containing liquid sodium, blanketed by a flowing inert gas and maintained at constant temperature. The assumed cesium concentration profiles for both phases are shown in the sketch. Fick s law of diffusion may be applied to the liquid phase ... 

The most important chemical parameter affecting the deposition and subsequent mobility of radioactive aerosols, such as the nuclides 90Sr and 137Cs examined in this study, is their solubility in rainwater. If these aerosols are dissolved in precipitation, the main factor in their transport is the movement of the rainwater, not the transport of insoluble aerosol particles. Huff and Kruger (2) examined the solubility products of strontium and chemically similar compounds which may carry trace amounts of 90Sr, and they estimated that strontium should be soluble in precipitation. Solubility tables also indicate that cesium compounds likely to exist in precipitation should be soluble. It was noted that the possibility did exist that some of the fission product "Sr and 137Cs might be bound within the structure of insoluble natural aerosols or nuclear weapon debris. 

The problem of estimating aerosol transport is thus focused on the study of watershed media effects on the transport of substances in solution rather than in insoluble aerosol particles. Thus, sorption by watershed media is a prime factor in determining the hydrologic transport of soluble radioaerosols, such as cesium and strontium. Removal of soluble radioaerosol elements from runoff by formation of insoluble compounds is considered unlikely. 

Casnati, A., Pochini, A., Ungaro, R. et al. 1995. Synthesis, complexation and membrane transport studies of 1,3-altemate calyx[4]arene crown-6 conformers A new class of cesium selective ionophores. J. Am. Chem. Soc. 117 2767-2777. 

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