Holdup Measurements under Realistic Conditions*

Quantification of holdup, the residual nuclear material remaining in process equipment, has long been a challenge to those who work with nuclear material accounting systems. Fortunately, nuclear material has spontaneous penetrating radiation emissions that can be measured. If gamm-ray measurements can be made, it is easy to determine what isotope the holdup deposit contains. Unfortunately, it can be quite difficult to relate this measured signal to an estimate of the mass of the nuclear deposit. Typically, the measurement expert must work with incomplete or inadequate information to determine a quantitative result. Simplified analysis models, the distribution of the nuclear material, the intervening attenuators, background(s), and the source-to-detector distance(s) can have significant impacts on the quantitative result.