The Separation and Radioactive Assay of Fission Products From Samples Obtained From High-Temperature Pressurized-Water Loops

Abstract

Summary Two radiochemical separation procedures for the analysis of samples from the pressurized-water loops at Chalk River are presented. A description is given of a typical loop and the associated sampling facilities, which include autoclaves for activity deposition and corrosion samples, hot and cold probes for filtering out insoluble materials in the loop water, and ion-exchange columns for use in determining soluble and insoluble activities in the loop water. A number of different types of samples are obtained from these facilities. The types of samples and the various methods of attack which are used to convert the samples to a form suitable for analysis are described. In the first method, the separation of Ru, Ce, Ba, Sr, I, Te, Zr and Mo from samples such as loop water, crud (insoluble corrosion products), etch solutions from metal specimens, and ion-exchange resins is described. This method is applied to crud or resin samples after decomposition by an alkaline fusion, or to water or etch-solution samples after digestion with an NaOH-Na 2 CO 3 solution. The attack is carried out in the presence of carriers. An initial separation of the fission products is effected by boiling the alkaline carbonate solution from the liquid samples with HIO 4 or leaching the solidified melt from the fusion with water. Under these conditions, Ru, I and Mo are soluble, while the other elements are present as insoluble hydroxides, carbonates, or sulfates. The two fractions are separated into the individual components by normal chemical methods. The individual components are then purified by modified standard procedures which are described. In the second method, the separation of fission gases from loop water is described. No chemical separation of the mixture of gases is carried out. The assay of the individual elements and nuclides is based on the careful choice of time intervals for the various steps in the initial separation and for counting the individual nuclides. Further separation is obtained by the use of differential γ - ray counting to select various nuclides for counting at set time intervals after sampling. Fission products from the first separation were mounted on flat filter paper sources and counted by beta proportional counting, either directly or through absorbers. Details are given of the counter and the mathematical methods used to compute absolute disintegration rates. The gases, as has been mentioned, were determined by differential gamma counting. A full description is given of the counting equipment and the sample containers. The theoretical and practical details relative to the energies counted and the time intervals between counts are given, together with the mathematical methods necessary for calculating the results.