Lithium isotopic ratio analysis of lithium aluminate ceramics in tritium producing burnable absorber rods (TPBAR) by laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS)

Tritium producing burnable absorber rods (TPBARs) contain LiAlO2 ceramic pellets that, when irradiated by neutrons, produce tritium. Measurement of the ⁶Li/⁷Li ratio in the pellets both prior to and post irradiation is important both as part of the manufacture control process as well as to better understand the mechanics of tritium production in a dynamic nuclear reactor environment. To support this need, the use of laser ablation multicollector inductively coupled mass spectrometry (LA-MC-ICP-MS) to measure the bulk ⁶Li/⁷Li ratio in unirradiated TPBAR pellets was investigated. Unirradiated TPBAR pellets were found to be isotopically homogenous to within 0.3% measurement precision, indicating that the precision of LA-MC-ICP-MS measurements is comparable to those generated via sample digestion and solution analysis by MC-ICP-MS. Several LiAlO2 tablets were also pressed and sintered from powders of known isotopic composition and characterized to investigate their use as a bracketing standard in the LA-MC-ICP-MS analytical protocol. No significant isotopic alteration from the manufacture process was detected, though several analytical artifacts were observed and described. Accurate measurement of samples (to within 0.3% tolerance of the expected value) required the use of standards with an identical manufacture process and thus, LiAlO2 phase. This work paves the way for the use of LA-MC-ICP-MS for highly precise and accurate, spatially resolved, isotopic characterization of post irradiation LiAlO2. This will help in the understanding of the mechanics of tritium production on the micro-scale by performing spatially resolved measurements to assess radial and axial burnup gradients.Mechanical Engineerin