Material Balance Period (MBP)
A material balance period (MBP) refers to the time between two consecutive physical inventory takings (PITs), which should correspond to the IAEA timeliness goal. There are three main methods to base MBPs on: Batch, Batch data, and Stratum.
Batch: a portion of nuclear material handled as a unit for accounting purposes at a KMP and for which the composition and quantity are defined by a single set of specifications or measurements. An example of this would be if the material had the same element concentration, enrichment, or came from the same production run.
Batch data: the total weight of each element of nuclear material and isotopic composition when appropriate. This could correspond to:
- grams of contained Pu
- grams of total U and grams of contained U-235 plus U-233 for U enriched in these isotopes
- kilograms of contained thorium, natural uranium or depleted uranium
Stratum: grouping of items and/or batches having similar physical and chemical characteristics (e.g. isotopic composition) made for the purpose of facilitating statistical sampling. This helps with sampling because items in a particular stratum are more like one another. This also simplifies verification, making it possible to formulate the sampling plans needed to verify a material balance and to calculate its uncertainty (σMUF). The operator and the IAEA should co-operate in defining strata so that the purposes of stratification are met.
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