Analytical Techniques in Nuclear Safeguards

In this chapter, we present an overview of the measurement and analysis techniques used to quantify the mass of special nuclear material in containers that are typically sealed. Other item characteristics, such as enrichment for uranium or isotopic composition for plutonium, may also be measured. These measurements are performed in support of safeguards objectives. Nuclear safeguards is the system of policies and technical measures developed to ensure that fissionable materials are being used for their intended purposes and are controlled through the implementation of technologies, procedures, and policies. Fissionable material of safeguards concern is often referred to as Special Nuclear Material (SNM). The most commonly performed measurement techniques fall into one of three categories: photon measurements, which include x-ray, gamma-ray, and Cerenkov radiation; neutron measurements, which include the use of total neutron rates or careful analysis of the time correlation between neutron detection events (neutron coincidence analysis or neutron multiplicity analysis); and heat flow calorimetry, the measurement of the decay heat produced by nuclear materials, primarily through alpha particle decay. In almost every case, the results obtained from more than one of these measurements must be combined to obtain the mass of special nuclear material. The most common analytical techniques are discussed in terms of theory of operation, limitations, accuracy/precision, and operational considerations. This chapter is not an exhaustive discussion of the measurement techniques applied to special nuclear material in safeguards or for other reasons, but it should serve as an excellent starting point for studying the topic, and further information for more detailed study is available in the references or in the publications of the Institute for Nuclear Material Management or the International Atomic Energy Agency.