At a nuclear fuel reprocessing plant the special nuclear materials (SNM) are received as constituents of spent fuel assemblies, are converted to liquid form, and undergo a series of chemical processes. Uncertainties in measurements of SNM at each stage of reprocessing limit the accuracy of simple material balance accounting as a safeguards method. To be effective, a formal safeguards program must take into account all sources of measurement error yet detect any diversion of SNM. The objective of this study is to demonstrate an analytical method for assessing the accountability of selected constituent SNM. A combined discrete-continuous, time-dependent model using the GASP IV simulation language is developed to simulate mass flow, material accountability and measurement error at each stage of the reprocessing plant. The study demonstrates that the simulation method may be utilized to estimate the magnitude of SNM loss in an operating reprocessing plant which could reasonably be detected. Thus, the simulation method provides a level of confidence for effective loss/no-loss decisions. / Ph. D.