Isotopic and chemical analysis of gadolinium oxide nuclear grade

Abstract

Natural gadolinium oxide is added in nuclear fuels of compact design reactors to control the power mainly on the start of operation, as neutronic poison. Gadolinium has a high neutron absorption cross section (σγ). All Gd isotopes have significant σγ, specially 155 and 157 (60,900 and 254,000b (10−24cm2), respectively). It is important the isotopic and chemistry purity of the nuclear fuels materials to avoid the generation of unwished radioactive elements or extra neutron poisons. Main possible impurities that could be presented are the rest of Rare Earths (REEs) like Eu, Sm, Tb, Yb, and Dy. The objective of the present contribution was to develop methods for the certification of isotopic composition in natural nuclear grade Gd2O3 and also to determine the content of REE impurities. Two methodologies were explored for isotopic analysis by Thermal Ionization Mass Spectrometry (TIMS): Total Evaporation (TE) and Conventional Analysis (CA). Results are comparable with both methodologies, although CA uncertainties are better. The analysis of impurities was performed with a Quadrupole Inductively Coupled Plasma Mass Spectrometer (Q-ICPMS). Concentration of different REEs is in agreement with certificate of supplier and nuclear specifications.