Determination of erbium in nuclear fuels by isotope dilution thermal ionization mass spectrometry and glow discharge mass spectrometry

Abstract

A thermal ionization mass spectrometer (TIMS) and a laboratory-built glow discharge mass spectrometer (GDMS) have been employed for the determination of the isotopic composition of erbium and its concentration, with respect to uranium, in nuclear fuel samples before irradiation. First, the GDMS results on erbium isotopic composition in erbium metal and erbium oxide samples have been compared with those obtained from TIMS measurements. Then, the isotopic composition of uranium and erbium has been measured by TIMS after dissolution of inactive erbium-doped molybdenum-uranium fuel samples. The atomic ¹⁶⁶ Er: ²³⁸ U ratio has also been determined with the double spike isotope dilution method. A ¹⁶⁷ Er: ²³³ U spike solution has been prepared and calibrated for this determination. However, to avoid matrix effects in TIMS analyses, it has first been necessary to perform chemical separations to isolate U and Er from the high quantities of molybdenum and iron present in the liquid samples. The glow discharge mass spectrometer has been used for the analyses of the same samples. For the evaluation of this technique, the isotopic compositions of U and Er have been measured directly on the solid samples and the atomic ¹⁶⁶ Er: ²³⁸ U ratio has been determined by a calibration procedure with home-made standards. Results are compared in terms of accuracy and precision with the analyses performed by TIMS, used as the reference technique.