This open access book describes the nondestructive assay techniques that are used for the measurement of nuclear material (primarily uranium and plutonium) for nuclear material accountancy purposes. It is a substantial revision to the so-called PANDA manual that has been a standard reference since its publication in 1991. The book covers the origin and interactions of gamma rays and neutrons as they affect nuclear measurements and also describes the theory and practice of calorimetry. The book gives a description of many instruments based on these techniques that are applied in the field. Although the basic physics has not changed since PANDA was first published, the last thirty years have seen many advances in analysis methods, instrumentation, and applications. The basic descriptions of the origin and interactions of radiation have been updated and include newer references. There have been extensive revisions of the description of gamma detection methods, attenuation correction procedures, and analysis methods, including for the measurement of uranium enrichment and the determination of plutonium isotopic composition. Extensive revisions and additions have also been made to the description of neutron detectors and to the explanation of neutron coincidence techniques. The chapter on neutron multiplicity techniques is a new addition to this edition. The applications of gamma and neutron techniques have been completely overhauled to remove obsolete systems and to include many current applications. The values of, and references to, nuclear data have been updated. This updated edition is an essential reference for academic researchers and practitioners in the field. This is an open access book.

Passive neutron and other nondestructive assay techniques have been used extensively by the International Atomic Energy Agency to verify plutonium metal, powder, mixed oxide, pellets, rods, assemblies, scrap, and liquids. Normally, the coincidence counting rate is used to measure the 24°Pu-effective mass and gamma-ray spectrometry or mass spectrometry is used to verify the plutonium isotopic ratios. During the past few years, the passive neutron detectors have been installed in plants and operated in the unattended/continuous mode. These radiation data with time continuity have made it possible to use the totals counting rate to monitor the movement of nuclear material. Monte Carlo computer codes have been used to optimize the detector designs for specific applications. The inventory sample counter (INVS-III) has been designed to have a higher efficiency (43%) and a larger uniform counting volume than the original INVS. Data analyses techniques have been developed, including the ''known alpha'' and ''known multiplication'' methods that depend on the sample. For scrap and other impure or poorly characterized samples, we have developed multiplicity counting, initially implemented in the plutonium scrap multiplicity counter. For large waste containers such as 200-L drums, we have developed the add-a-source technique to give accurate corrections for the waste-matrix materials. This paper summarizes recent developments in the design and application of passive neutron assay systems.

A high-quality materials accounting system and effective international inspections in uranium fuel-fabrication facilities depend heavily upon accurate nondestructive assay measurements of the facilitys̀ nuclear materials. While item accounting can monitor a large portion of the facility inventory (fuel rods, assemblies, storage items), the contents of all such items and mass values for all bulk materials must be based on quantitative measurements. Weight measurements, combined with destructive analysis of process samples, can provide highly accurate quantitative information on well-characterized and uniform product materials. However, to cover the full range of process materials and to provide timely accountancy data on hard-to-measure items and rapid verification of previous measurements, radiation-based nondestructive assay (NDA) techniques play an important role. NDA for uranium fuel fabrication facilities relies on passive gamma spectroscopy for enrichment and U isotope mass values of medium-to-low-density samples and holdup deposits; it relies on active neutron techniques for U-235 mass values of high-density and heterogeneous samples. This paper will describe the basic radiation-based nondestructive assay techniques used to perform these measurements. The authors will also discuss the NDA measurement applications for international inspections of European fuel-fabrication facilities.

Passive Neutron Albedo Reactivity (PNAR) is one of fourteen techniques that has been researched and evaluated to form part of a comprehensive and integrated detection system for the non-destructive assay (NDA) of spent nuclear fuel. PNAR implemented with 3He tubes for neutron detection (PNAR-3He) is the measurement of time correlated neutrons from a spent fuel assembly with and without a Cadmium (Cd) layer surrounding the assembly. PNAR utilizes the self-interrogation of the fuel via reflection of neutrons born in the fuel assembly back in to the fuel assembly. The neutrons originate primarily from spontaneous fission events within the fuel itself (Curium-244) but are amplified by multiplication. The presence and removal of the Cd provides two measurement conditions with different neutron energy spectra and therefore different interrogating neutron characteristics. Cd has a high cross-section of absorption for slow neutrons and therefore greatly reduces the low energy (thermal) neutron fluence rate returning. The ratios of the Singles, Doubles and Triples count rates obtained in each case are known as the Cd ratios, which are related to fissile content. A potential safeguards application for which PNAR-3He is particularly suited is 'fingerprinting'. Fingerprinting could function as an alternative to plutonium (Pu) mass determination; providing confidence that material was not diverted during transport between sites. PNAR-3He has six primary NDA signatures: Singles, Doubles and Triples count rates measured with two energy spectra at both shipping and receiving sites. This is to uniquely identify the fuel assembly, and confirm no changes have taken place during transport. Changes may indicate all attempt to divert material for example. Here, the physics of the PNAR-3He concept will be explained, alongside a discussion on the development of a prototypical PNAR-3He instrument using simulation. The capabilities and performance of the conceptual instrument will be summarized, in the context of (a) quantifying Pu mass in spent fuel assemblies and (b) detecting pin diversion (through a discrepancy between declared and measured properties of the fuel assembly) when the instrument is deployed. These quantitative capabilities are complementary to the 'fingerprinting' capability which is part of ensuring continuity of knowledge and custody of spent nuclear fuel.