EQUIVALENCE AND PROPORTIONALITY

Two key concepts in nuclear accountancy and the management of the safeguards system are equivalence and proportionality. Atoms of uranium, as with atoms of many other commodities, are indistinguishable from one another. As described by DFAT/ASO:

II.13 The large scale physical and chemical processes which nuclear material from a variety of sources must undergo at a limited number of processing facilities mean that it is impossible to track the identity of individual atoms or quantities of nuclear material. This circumstance has led to the development of two principles used universally in the industry and in the application of safeguards: equivalence and proportionality. All safeguards, both bilateral and multilateral, are applied on the basis of the equivalence of similar quantities of the same type of nuclear material.

II.14 The equivalence principle provides that where AONM loses its separate identity because of process characteristics, e.g., mixing, an equivalent quantity is designated as AONM, based on the fact that atoms or molecules of the same substance are indistinguishable, any one atom or molecule being identical to any other of the same substance. In such circumstances, equivalent quantities of the products of such nuclear material may be derived by calculation or from operating plant parameters. However, equivalence does not permit substitution of batches of nuclear material of a different category, e.g., enriched uranium cannot be replaced by natural or depleted uranium, and cannot be used to circumvent safeguards designed to ensure exclusively peaceful uses of AONM.

II.15 The proportionality principle provides that where AONM is mixed with other nuclear material, and is processed or irradiated, a proportion of the resulting material will be regarded as AONM corresponding to the same proportion as was AONM initially.

II.16 A simple banking analogy illustrates these principles. Individual depositors use an accounting system to be sure that they are correctly credited with their share of a bank's assets, but they do not expect to withdraw the exact notes and coins they originally deposited. Nuclear materials accountancy tracks exports of Australian uranium in the same way.

II.17 The application of the equivalence and proportionality principles provides Australia with the assurance that at all times a quantity of nuclear material precisely equivalent to the quantity exported is identified as being subject to Australian safeguards obligations and treated and accounted for as AONM. (S 60, II.13-17, 8)