Development of radiochemical methods for the determination of radionuclides in water samples

Depending on the composition of minerals, ores, soils and the properties of water various amounts of radionuclides of natural origin are released into different types of water i.e. surface and ground water, mineral and well water. Furthermore, man-made radionuclides can contaminate the surface waters in the form of fallout from nuclear incidents followed by migration of the deposited isotopes into water. Measurement of radionuclides in water helps prevent the consumption of radioactive water causing high radiation doses and also enables the early discovery of contamination sources. For the latter reason monitoring radioactivity in ground water in the vicinity of nuclear installations is of great importance. High sensitivity radiochemical methods have been developed/adopted for the simultaneous determination of 90Sr-Pu nuclides, 137Cs-90Sr-Pu nuclides in 50-100 L of water. Typically, procedures contain a pre-concentration step most likely by means of co-precipitation followed by a selective separation procedure preferably by means of extraction chromatography. In most cases Sr and Pu are extracted with a crown ether and an organic phosphonate compound, respectively, while Cs is concentrated using AMP. In the presence of extremely high salt content e.g. in case of 100 L of sea water the standard extraction chromatographic procedure has to be replaced by the conventional technique of Sr-Ca separation based on the different solubilities of the nitrate precipitates. Selection criteria as well as description of the procedures will be given in detail. A high sensitivity procedure has been developed for the analysis of 129I in 100 L of ground water based on pre-concentration with AgCI and separation by extraction with CCl4. The following nuclear measuring techniques were applied: LSC, alpha spectrorhetry, gamma spectrometry, neutron activation (including gamma spectrometry) for 90Sr, 239,240Pu, 137Cs, and 129I, respectively. Sensitivities of the given methods are high, in the range of 10-4-10-6 Bq/L. 90Sr and Pu nuclides have been determined in the surveillance wells of the Hungarian nuclear power plant for several years. Ground level measurements have been performed in the area of the future radioactive waste disposal site. Radionuclides of natural origin have typically significantly higher concentrations than those of artificial nuclides, thus methods of moderate sensitivities have been developed/adopted for the determination of U and Th as well as Ra and Po isotopes. Uranium and thorium are separated in a combined procedure by extraction chromatography using an organic phosphonate compound. Ra and Po are consecutively separated from the same sample aliquot, Po is spontaneously deposited onto Ag disc, while from the supernate Ra is co-precipitated with Ba sulfate. Alpha spectrometry is used for the sensitive detection of 238U, 235U, 234U, 232Th, 230Th, 228Th, 210Po and 226Ra. Analyzing 100-1000 ml water samples detection limits in the range of 10-2-10-4 Bq/L were obtained. The procedure has been successfully applied for ground level determination in tile area of the future radioactive waste disposal site in Hungary. To increase the accuracy of each method radioactive tracers or stable carriers were added to each sample/each analyte before chelnical processing and results were corrected for chemical losses. Methods were validated by measuring reference materials and performing proficiency tests. (authors)