Molybdenum and lanthanum as alternate burn-up monitors – development of chromatographic and mass spectrometric methods for determination of atom percent fission

Abstract

Abstract A rapid high performance liquid chromatography (HPLC) and thermal ionisation mass spectrometric (TIMS) methods have been developed for the separation and estimation of fission product elements molybdenum and lanthanum for the burn-up measurements on the dissolver solution of Indian pressurised heavy water reactor (PHWR) spent fuel. Reverse phase chromatography method was developed to separate molybdenum from dissolver solution using mandelic acid as mobile phase and a dynamic ion exchange chromatography technique was used for the separation of lanthanum as well as neodymium from a dissolver solution. Sample loading methods which resulted in enhanced ionisation efficiency have been developed for the TIMS analysis of HPLC separated molybdenum and lanthanum fractions. Ascorbic acid mixed with silicic acid in HCl medium was used for loading the molybdenum on to a rhenium filament to obtain stable and intense ion beam. A novel sample loading method for lanthanum in which a mixture of graphite + boric acid (H3BO3) + silica gel was employed to achieve enhanced and steady ion beam formation of LaO+. Concentrations of species of interest were determined employing suitable spikes by isotope dilution mass spectrometry (IDMS) method. The developed methods were adopted for PHWR dissolver solution to establish molybdenum and lanthanum as alternate burn-up monitors. The burn-up data obtained were compared with the well established method of neodymium as fission product monitor. This is a first study of its kind where the data obtained by using molybdenum and lanthanum as fission product monitors were compared with that obtained by Nd-148 method.