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Nuclear Safeguards Education Portal

Measurement System

A system of measurements must exist to determine the quantities of nuclear material in inventory as well as that received, produced, shipped, lost or otherwise removed from inventory.  This includes procedures, personnel, and equipment.  The system should conform to the latest international standards and provide for the following:

  • identification of KMPs
  • specification of the measurement performance desired and techniques/equipment employed
  • calibration standards and procedures
  • routine measurement and data analysis procedures
  • procedures for controlling measurement quality
  • procedures for generating sample plans and obtaining representative samples
  • procedures for combining measurements and measurement uncertainties so as to calculate material unaccounted for (MUF) and uncertainty (σMUF)

International Standards of Measurement Accuracy

There exist standards for what we expect the measurement uncertainty (δE) for closing a material balance to be.  These values are based on operating experience at the various types of bulk handing facility and are considered achievable under the condition of normal operation.  The δE values are general estimates of what we would expect from an accounting measurement.  These values can be used along with the International Target Values to determine whether a facility's measurement system meets international standards.

International Target Values (ITV) are used for random and systematic measurement uncertainty components for destructive analysis (DA) and non-destructive assay (NDA) measurements performed on nuclear material.  These values are based on actual practical measurement experiences and are intended to be used as a reference for routinely achievable measurement quality.  In addition, these values are periodically updated with the latest being published in November 2010.

Every time nuclear materials are transported, the measured shipped mass is compared to the measured received mass.  This is called the Shipper/Receiver Difference (SRD).  Said differently, the SRD is the difference between the quantity of nuclear material in a batch as stated by the shipping MBA and as measured at the receiving MBA.  The SRD should be zero for item accounting and maybe non-zero for materials, but should correspond to measurement uncertainties.  The cumulative SRD is the algebraic sum of the SRDs for an MBA over time.

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