Potential Causes of Inventory Differences at Bulk Handling Facilities and the Importance of Inventory Difference Action

Accountancy for nuclear material can be split into two fundamental categories. Firstly, where possible, accountancy should be in terms of items which are objects that can be transferred as discrete packages and their contents are fixed at the time of their creation. All items must remain accounted for at all times and a single missing item is considered significant. Secondly, where nuclear material is unconstrained, for example in a repr ocessing plant where it can change form, there is an uncertainty that relates to the amount of material present in any location. Cumulatively, these uncertainties can be summed and provide a context for any estimate of material in a process. Any apparent l oss or gain between what has been physically measured within a facility during its physical inventory take and what is reported within its nuclear material accounts is known as an inventory difference. The cumulative measurement uncertainties can be used t o set an action level for the inventory difference so that if an inventory difference is observed outside of such action levels, the difference is classified as significant and an investigation to find the root cause(s) is required. The purpose of this pap er is to explore the potential causes of inventory difference and to provide a framework within which an inventory difference investigation can be carried out.