A nominal 1500 STP-L Passively Cooled, Electrically heated hydride (PACE) Bed was developed and deployed into tritium service in Savannah River Site (SRS) Tritium Facilities. Process beds to be used for low concentration tritium gas were not fitted with instrumentation to perform the steady-state, flowing gas calorimetric inventory measurement method: In-Bed Accountability (IBA). In some instances, two physical beds, or canisters, were joined together with one process line connection, creating a bed with a total capacity of nominally 3000 STP-L or up to 815 grams of tritium. The IBA detection limit for these beds was estimated to be 9.75 grams tritium. After deployment of these low tritium beds, the need arose to estimate tritium inventories of these beds without installation of IBA instrumentation. Two methods have been developed to estimate the tritium inventory of these low tritium content beds. The first approach assumes the bed is half-full and uses a gas composition measurement to estimate the tritium inventory and uncertainty. The second approach utilizes the bed’s hydride material pressure-composition-temperature (PCT) properties and a gas composition measurement to reduce the uncertainty in the calculated bed inventory.
