This is essentially a reflection of the time a reactor spends off line owing to planned outages or unplanned stoppages for technical reasons. Some electricity utilities take this into account in their performance measures whereas others do not. If they ignore availability as a constraint, these two measures will also be identical. This is frequently used by conversion and enrichment companies to average chemical impurities of feed material and also by fuel fabrication companies to alter the uranium-235 assay of UF 6 or UO 2 powder. The uranium-235 concentration is diluted through blending the HEU with material having a lower assay, while the composition of other isotopes is also corrected.
Purification is needed to remove traces of plutonium and other elements.
Book inventory Nuclear material credited to a party s account maintained by a nuclear fuel custodian, for example the natural uranium component and SWU component. There must be a physical counterpart of the nuclear materials held in the book inventory. Book transfer may or may not be accompanied by a transfer of title. As part of their toll service operation, custodians such as converters, enrichers and fuel fabricators may maintain inventory accounts on behalf of their customers, other third parties and themselves. Burnup Measure of the total energy released by nuclear fuel per unit of its mass.