DEINVENTORY THE CRITICALITY SAFETY ENDGAME

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. A Kickoff Meeting is held to review planned operations. Then a criticality safety evaluation of the operations is written, and limits and controls are established. In practice, an evaluation may turn out to be significantly more difficult than it at first appeared, primarily due to uncertainties in the quantity and distribution of the residual plutonium and liquid. The evaluation process can sometimes be streamlined by taking advantage of similarities in design, plutonium inventory, and operations to a glovebox previously evaluated. If an existing Criticality Safety Evaluation Report (CSER) can be shown to bound the new operations, it may be used as the basis for establishing limits and controls for the new operations. Otherwise, a new CSER must be completed and approved