Non-Destructive Assay NDA

Nondestructive assay (NDA) for safeguards describes analytical techniques to measure, check, and verify the amount of nuclear material or of the elemental or isotopic concentration of an item without producing significant physical or chemical changes in the item. It allows inspectors to determine both the quantity and composition of nuclear material without ever sampling it directly. Ultimately, NDA techniques provide for the independent verification of the total amount of nuclear material held at a nuclear facility. The main nuclear materials of interest are uranium (U) and plutonium (Pu). Usually, no single measurement method can 

The most widely used NDA instruments rely on the detection of nuclear radiation such as gamma rays and/or neutrons. Physical measurement techniques are also used with available instruments that measure heat, weight, liquid volume, thickness, and light emission/absorption. These physical techniques may be applied by themselves, or they may be used in combination with other nuclear measurements to provide quantitative measurements of the nuclear material. The general reference on the theory and application of passive NDA (PANDA) is given by reference (Reilly et al. 1991) and its addendum (Reilly et al. 2007). 

In the context of neutron and gamma-ray measurements, NDA techniques used by the inspectorate can be categorized as passive NDA or active NDA. Passive NDA refers to techniques that measure radiation emitted spontaneously from nuclear material. This method is often applied to Pu samples, because of the large spontaneous fission rate of the even-even Pu isotopes. Active NDA, on the other hand, refers to techniques that measure induced radiation responses from a sample, often using an external neutron source. These active methods are usually applied to perform uranium measurements where the spontaneous fission rate is low. 

In addition to the quantitative measurements performed by an inspector, in some cases a quahtative measurement (attribute testing) is sufficient, e.g., simply confirming the presence of a representative isotope based on a typical gamma ray. 

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