Against the Spread of Nuclear Weapons - Assurance of Non-Diversion of Declared Material

Assurance of Non-Diversion of Declared Material

The IAEA uses nuclear material accountancy as its basic measure for the safeguarding of declared material. Measures to monitor access to the nuclear material, e.g. the use of seals on containers or doors, and surveillance by cameras and other devices of the material and/or of routes through which material must pass, are used to complement the information obtained from material accountancy (see picture: Seal verification system with laser disk recording). The purpose of nuclear material accountancy is to establish the quantities of nuclear material present in a nuclear facility and the changes in these quantities that take place. The essential elements of such an accounting system are that:

The operator identifies, counts or measures the nuclear material in the facility and maintains an inventory;
The operator keeps records of all use and production of nuclear material, and of transfers into and out of the facility, i.e. all the inventory changes;
The operator prepares reports on the inventory and inventory changes and submits these reports to the IAEA through a central national authority;
IAEA inspectors visit the facility to verify the inventories and inventory changes and to determine the correctness of the reports. Verification of the inventories and inventory changes includes on-the-spot measurement of the material and the taking of samples for subsequent analysis by the IAEA. Verification is concentrated on, but not confined to, nuclear material which is directly usable in nuclear weapons.

Accountancy in IAEA terms thus begins with the determination by the operator of the stock of nuclear material in a facility and the recording of that stock in a book, or computer system, in which subsequent changes are also recorded. The results of periodic stock-taking by the operator and their relation to the corresponding book stocks are fundamental to nuclear material accountancy and to subsequent verifications by the IAEA. Any difference between the book stock and the physical stock is called 'material unaccounted for' (MUF) and may be positive or negative, i.e. either an apparent loss or an apparent gain of nuclear material. MUF may arise from measurement uncertainties or other acceptable technical reasons. If the MUF cannot reasonably be attributed to such causes, the safeguards inspector must consider the possibility that a diversion has taken place.

MATERIAL BALANCE--A normal engineering procedure which is used also for nuclear material accountancy. A balance compares the amount of nuclear material calculated to be present against measurements of the nuclear material found to be present, thus yielding an objective determi nation of the amount if any which appears to be unaccounted for. The result is evaluated inter alia by comparison with the limits of accuracy of the measurements involved, thus incorporating a fair and objective standard for IAEA conclusions.

The results and conclusions drawn from the nuclear material accountancy and the other measures used by the IAEA safeguards inspectors are sent by the IAEA to the State concerned. If there were evidence that a diversion of nuclear material might have occurred a report would be made by the Director General to the Board of Governors. If the Board finds that the IAEA is not able to verify that there has been no diversion of nuclear material required to be safeguarded under the agreement, the Board may take the actions provided for in the safeguards agreement, such as reporting to the Security Council and to the General Assembly of the United Nations.

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