ACTIVITY CONCENTRATIONS OF ~(238)U AND ~(226)Ra IN SCALES FORMED ON PIPES OF INDUSTRIAL BOILERS IN THE STATE OF PERNAMBUCO, BRAZIL

摘要

The procedures employed in the industry can generate significant amounts of solid, liquid and gaseous wastes that usually contain toxic or materials of difficulty degradation. One of the facts that contribute to the formation of such wastes is the generation of steam used in operating processes and industry segments. Currently, steam supplied by boilers is the most economical and practical mode of heat transfer in industrial processes. Due to the high temperature of water used in these processes, compounds which were previously soluble become insoluble, generating residues called scales. This material, which contains stable ions, can also present naturally occurring radionuclides such as ~(238)U and ~(226)Ra, which concentrate over time in piping and equipment surfaces. If not disposed correctly, this material also can contaminate the environment. The main origin of these radionuclides is the use of groundwater in industrial processes. Thus, in regions of naturally enriched in radionuclides such as the Region of Pernambuco, including the municipalities of Paulista and Goiana, there is a greater possibility of radioactive scale formation. Therefore, this study aimed to determine the activity concentrations of ~(238)U and ~(226)Ra present in the solid wastes generated by industries situated in Paulista and Goiana, in order to assess radionuclide disequilibrium. For the sake of comparison, scale samples collected from industries located in the municipality of Caruaru, far from the previous municipalities, were also analyzed. The determination of the activity concentrations for ~(238)U and ~(226)Ra was performed by High Resolution Gamma-Ray Spectrometry. Samples were collected, prepared, packed in plastic containers and set aside for a minimum time of 21 days, for the secular equilibrium to occur between ~(226)Ra and its short lived descendants. The counting time was 80,000 seconds. Gamma energies used for determination of activity concentrations were 1001 keV for ~(238)U, and 352 keV, 609 keV and 1120 keV, for ~(226)Ra. The concentrations ranged from 53 to 1,300 Bq.kg~(-1) for ~(226)Ra and from < 237 to 410 Bq.kg~(-1) for ~(238)U. According to the results one can conclude that, for the samples analyzed, statistically different values for ~(238)U and ~(226)Ra indicate different transport and deposition dynamics for radionuclides of the same decay series.