A technique for synthesizing metal tritide standards

Before surplus plutonium pits can be decommissioned and converted into metal oxides to be used as reactor fuels, residual tritium must be reduced to an acceptable level. We have developed two analytical methods involving melting and acid dissolution, combined with liquid scintillation counting as a quantitative and sensitive technique for measuring residual tritium in Pu metal. The detection limit, linearity, and reproducibility of these analytical methods must be validated with a series of metal tritide standards. Since there are no commercially available metal tritide standards, we have developed a technique for their synthesis. The synthesis of these low-level metal tritide standards is accomplished by charging cerium powder with a known amount of tritium to form a master cerium tritide alloy and then by aliquoting from this master alloy and diluting with pure cerium powder to form a series of standards with different tritium concentrations. The major difficulty in synthesizing these standards is that the samples contain extremely low levels of tritium, which span over three decades of concentrations. The synthesis technique and initial data obtained for cerium hydride samples will be presented.