In-situ sample preparation for radiochemical analyses of surface water

A new method for radionuclide sample analysis of surface water has been demonstrated at the Savannah River Site, an U.S. Department of Energy manufacturing facility, currently in standby. The method makes use of selective solid phase extraction (SPE) disks being placed in a modified portable aqueous sampler. The analytes currently measured by this in-situ preparation are Tc-99, Sr-90, Cs-137 and Co-58.60. The SPE disks are placed singly or in series in an automatic sampler; water is passed through the SPE disks at the time of collection. The disks are then returned to the laboratory for counting; no additional chemical separation is performed prior to analysis. The modified automatic samplers have been placed at several different locations around the Savannah River Site along side traditional samplers. The traditional samplers were used to collect water that was analyzed for the same analytes using standard laboratory methods. Most of the sample results were less than five times the method detection limit, thus a mean difference statistic was used to compare the data. Within the uncertainties of the methods, there was no statistical difference in the Tc-99 results, although a slight negative bias was observed for the in-situ Sr-90 results versus the laboratory method. The in-situ method produces a dissolved (<0.45<mu>m) and particulate Cs-137 result, whereas the traditional laboratory method measures total activity in the sample. As expected, a negative bias was found between the dissolved in-situ result and the laboratory total Cs-137 result, acid a positive bias between the in-situ total (dissolved plus particulate) and laboratory total Cs-137 result.