Criticality safety begins with the design and evaluation of a Fissionable material operation and continues even after the operation has been shut down. An interest in criticality safety is maintained until all fissionable material has been removed. This paper examines the process of removing Fissionable material with the goal of no longer requiring criticality safety control. The word 'de-inventory' (usually written deinventory) was coined at the Plutonium Finishing Plant on the Hanford Atomic Reservation to describe this process. The cleanout of gloveboxes at the Plutonium Finishing Plant illustrates typical deinventory operations. Although tanks may have been previously drained of their solutions, residual contents remain for which the plutonium content must be estimated. Normally, this is accomplished using Non-Destructive Assay (NDA) techniques that require conservative correction factors to compensate for tank wall shielding apparatus geometry, fissile material distribution, detector efficiencies, and detector locations. The plutonium inventory is usually overestimated.
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