This International Standard specifies a nondestructive method for the simultaneous determination of volumetricuranium and plutonium concentrations in nitric acid feed solutions from reprocessing plants. The method is directlyapplicable, without interference, to the original feed solution, which typically contains about 150 g˜l-1 to 300 g˜l-1uranium and 1 g˜l-1 to 2,5 g˜l-1 plutonium in the presence of fission products with a total ß,°-activity of up to10 TBq˜l-1.