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Introduction to Nuclear Material Accountancy

IAEA Safeguard inspectors doing a physical inventory of fuel assemblies stored on a fresh fuel rack. (Source: Dean Calma/IAEA)
IAEA Safeguard inspectors doing a physical inventory of fuel assemblies stored on a fresh fuel rack. (Source: Dean Calma/IAEA) 

Nuclear Material Accountancy (NMA) is the principle means employed by the International Atomic Energy Agency (IAEA) to independently verify the correctness of the accounting information produced by facility operators and the State Systems for Accountancy and Control (SSAC).  This is complemented by containment and surveillance (C/S) measures.  NMA responsibilities exist at three different levels:  Facility, State, and the IAEA.

Facility Level

A facility that contains nuclear material will perform several tasks to insure that the nuclear material is accounted for.  Several of these tasks are as follows:

  • Dividing operations involving nuclear material into Material Balance Areas (MBAs)
  • Maintaining records on the quantities of nuclear material held within each MBA
  • Measuring and recording all transfers of nuclear material from one MBA to another or changes in the amount of nuclear material within MBAs
  • Determining periodically the quantities of nuclear material present within each MBA through the taking of the Physical Inventory
  • Closing the material balance over the period between two successive physical inventory's and computing the Material Unaccounted For (MUF) for that period
  • Providing for a measurement control program to determine the accuracy of calibrations and measurements and the correctness of recorded source and batch data
  • Testing the computed MUF against its limits of error for indications of any unrecorded nuclear loss or accidental gain
  • Analyzing the accounting information to determine the cause and magnitude of mistakes in recording unmeasured losses, accidental losses and unmeasured inventory (hold-up)

State Level

The State in which the facility is located must also account for all materials in its facilities and in the country as a whole.  To account for these materials the State does the following tasks:

  • Preparing and submitting nuclear material accounting reports to the IAEA
  • Ensuring that nuclear material accounting procedures and arrangements are adhered to
  • Providing for IAEA inspector access and co-ordination arrangements to enable the IAEA to carry out its verification activities
  • Verifying facility operators' nuclear material accountancy performance, as provided for in the SSAC regulations

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