137CS Activity Profiles in Soil of the Province of Buenos Aires-Argentina

M.L. MONTES; R.C. MERCADER; L. M. S. SILVA; C. S. A. SÁ; M.A. TAYLOR; J. RUNCO; P.C. RIVAS; J. DESIMONI

Salamanca

Congreso; ? 1st International Congress on Water, Waste and Energy Management; 2012

Universidad de Salamanca

MODELLNING 137CS ACTIVITY PROFILES IN SOIL OF THE PROVINCE OF BUENOS AIRES-ARGENTINA L.M.S. Silva1, C.S.A. Sá1, M. L. Montes2, R. C. Mercader2, M. A. Taylor2, J. Runco2, P. C. Rivas3 and J. Desimoni2 1Departamento de Engenharia Química, Instituto Superior de Engenharia do Porto, IPP, CIETI, Rua Dr. António Bernardino de Almeida, 4200-072 Porto - Portugal 2Departamento de Física, Facultad de Ciencias Exactas, UNLP, IFLP ? CONICET, Argentina. desimoni@fisica.unlp.edu.ar 3 Facultad de Ciencias Agrarias y Forestales, UNLP, IFLP ? CONICET, Argentina. 1. Introduction - The fallout of radioactive debris coming from South Hemisphere atmospheric nuclear weapon had polluted the South Hemisphere soils with long live radionuclides, like 137Cs [1]. The principal factors that affect migration this nuclide in the soil are pH, organic matter content, textural class, mineralogy and concentration of radionuclides in the soil-liquid phase, among others [2]. We present here, activities depth profiles down to 50 cm of the 137Cs of unperturbed soil of the neighbourhood of La Plata city, together with pH, texture and organic carbon content of soils. The dimensional convection-dispersion equation with constant parameters is the most used approach to estimate the 137Cs transport parameters [3], however it do not reproduce all the 137Cs profiles. So, the convection-dispersion-fixation model was used [4]. 2. Experimental - The gamma spectra were taken inside an EG&G Ortec low-background chamber in the range of 30 keV to 1.8 MeV, using a GMX10 gamma EG&G Ortec detector with a standard electronic chain and 8192 channels multichannel. The pH, texture and organic carbon measurements were performed using the international protocols. 3. Results and Discussion - The determined mean average value of 137Cs inventory was 891 ± 220 Bq m-2. Differences in depth distributions were detected attributed principally to the clay and illite content. Two profiles were satisfactory fitted with the the dimensional convection-dispersion equation, but other two show important deviations to this model. So, the convection-dispersion-fixation model was used, and it satisfactory fit all 137Cs profiles. The obtained convection velocity and diffusion parameter are in agree with bibliography data [5]. The deviations form the approach can be explained by the clay and illite soil content. The model fixation parameter, in general, enhances with the increment of clay soil content, and the maximum value was obtained for pH 8. 4. Conclusions ? The determined inventory is in agreement with with the fallout coming from nuclear weapons atmospheric test. Not all the 137Cs soil profiles can be reproduced by the convection-dispersion with constant parameters, probably due to predominance of illite phase in the studied soils, which is a known receptor of cesium in a irreversibly way. References [1] UNSCEAR, 2008. In: Sources and effects of ionizing radiation, Report of the General Assembly with Scientific Annexes, Vol. 1, New York [2] Cornell, R.M. 1993. Adsorption of cesium on minerals: a review. Journal of radioanalytical and nuclear chemistry, 171, 2, 483 ? 500. [3] Bossew, P. and Kirchner, G. 2004. Modelling the vertical distribution of radionuclides in soil. Part 1: the convection? dispersion equation revisited. Journal of Environmental Radioactivity 73, 127-150. [4] Toso, J.P., Velasco, R.H. 2001. Describing the observed vertical transport of radiocesium in specific soils with three time-dependent models. Journal of Environmental Radioactivity, 53, 133-144 [5] IAEA Technical Report Series nº 42. Handbook of Parameter values for the Prediction of Radionuclide Transfer in Terrestrial and Freshwater Environments. (2010).