Development of an analytical theory to describe the PNAR and CIPN nondestructive assay techniques

This paper develops an analytical theory to describe how neutron albedo (reflection) increases the multiplication of neutrons by a used fuel assembly. With this theory, the two nondestructive assay (NDA) techniques of Passive Neutron Albedo Reactivity (PNAR) and Californium-252 Interrogation with Prompt Neutron Detection (CIPN) can be compared directly. Specifically, the theory derives expressions for the PNAR and CIPN metrics in terms of the physical properties of the used fuel assembly, such as the neutron multiplications and fate probabilities. The theory thus clarifies the interpretation of these two NDA techniques and suggests ways to improve both the design of the NDA instruments and the algorithms for analyzing the measurement results.