«Russian» Inventory Difference as a Cumulative Sum of «Western» Inventory Differences

The inventory difference is well-known to represent an effective tool of nuclear material mass safe-keeping control, specifically the materials that underwent transformations over the last inventory period (IP) – a time interval between the current and previous physical inventory taking. If as a result of this inventory taking no anomalies were indicated in nuclear material control and accounting, a weighted-mean value of two quantities (with account for measurement uncertainty) should be taken as the beginning inventory of nuclear material for the subsequent IP: • First – the so-called book (accounting) values estimated on the basis of accounting data; • Second - the so-called physical (inventory) accounting values estimated on the basis of accounting measurements for the moment of physical inventory taking. Actually in various national MC&A systems either book accounting values (in this case there is no need to modify MC&A data - based financial documents of the facility accounts department) are retained as the beginning nuclear material inventory for the subsequent IP, or physical (inventory) accounting values which accumulate the measurement uncertainty not as fast as the book accounting values (Denny Weier (PNNL, USA). Presentation at the Tripartite Seminar On Assessment of Nuclear Materials Content and Inventory in By-product Streams, Obninsk, Russia, 14-18 October, 2002) This paper asserts that if the book values are retained as the beginning inventory of nuclear material for the subsequent IP in compliance with the Russian regulatory documents, then the inventory difference Russ IDi of the i-th IP should be considered as a cumulative sum (CUSUM) of the inventory differences IDj obtained when physical (inventory) accounting values were retained as the NM beginning inventory for the subsequent IP as is customary at western nuclear facilities. To put it otherwise: Russ IDi = CUSUM(IDj) - «Russian» inventory difference is a cumulative sum of «western» inventory differences.