"an area in or outside of a facility such that:

• The quantity of nuclear material in each transfer into or out of each 'material balance area' can be determined
• The physical inventory of nuclear material in each 'material balance area' can be determined when necessary, in accordance with specified procedures, in order that the material balance for Agency safeguards purposes can be established" (INFCIRC 153*)

Design information made available to the IAEA shall be used: "To determine material balance areas to be used for Agency accounting purposes and to select those strategic points which are key measurement points and which will be used to determine the nuclear material flows and inventories; in determining such material balance areas the Agency shall use the following criteria:

• The size of the material balance area should be related to the accuracy with which the material balance can be established
• In determining the material balance area advantage should be taken of any opportunity to use containment and surveillance to help ensure the completeness of flow measurements and thereby simplify the application of safeguards and concentrate measurement efforts at key measurement points
• A number of material balance areas in use at a facility or at distinct sites may be combined into one material balance area to be used for Agency accounting purposes when the Agency determines that this is consistent with its verification requirements; and (iv) If the State so requests, a special material balance area around a process step involving commercially sensitive information may be established" (INFCIRC 153*)