Effect of water purification on its radioactive content

We have analyzed the dissolved activity of various radionuclides of natural origin (Ra-226 and U-234,U-235,U-238) and artificial origins (Sr-90 and Pu239+240), together with other non-radioactive physico-chemical parameters (pH, conductivity, dry residue, [Ca2+], [Mg2+], [K+] and [Fe-2+,Fe-3+], in both pre-potable and potable water from 17 treatment plants in Extremadura (Spain). We have established a series of criteria and complementary techniques to the traditional methods of purification, aimed at the quantitative elimination of the presence in solution of the mentioned radionuclides. We highlight: (a) the increment of the mineral content of the water in its treatment succeeds in eliminating Ra-226, until reaching values close to 70%; (b) the increment of the mineralization of the water by addition of chemical reagents, conducted within the pH values 7.1 and 7.8, succeeds in eliminating up to 90% of the total uranium in dissolution; (c) the elimination of Sr-90 during the purification is poor, in general, reaching average levels of only 15% when the purification process is practiced within concrete ranges for potable water (pH > 7, conductivity > 150 muS/cm, dry residue > 150 mg/l, [Ca2(+)] > 10 mg/l and [Mg2+] > 1.2mg/l), and finally, (d) the decrease of the solubility of the iron, as low as it can get during the purification process, together with an increase of the conductivity associated, in principle, to parallel increments of other variables not analyzed in this work, such as SO42-, CO32-, etc. the activity of dissolved Pu-239divided by240 decreases to 90%. The application of the traditional processes of water purification outside the ranges and criteria formulated can increase the presence in dissolution up to 400%, for some radionuclides, largely the consequence of its redissolution from the non-soluble fraction of the water. (C) 2002 Elsevier Science Ltd. All rights reserved.