The total 235U content of low enrichment power reactor fuel assemblies has been determined by interrogation with Li(p,n) neutrons (200 to 500 keV) produced by a Van de Graaff proton accelerator and by measurement of fission-induced delayed neutrons. To extend the application of this assay technique and to optimize its implementation, numerical calculations have been performed using a modified Monte Carlo approach. Experimental measurements from a BWR-type fuel assembly have verified the mathematical model employed. By incorporating results from both calculation and measurement, a system is being designed to assay the total 235U content of power reactor fuel elements with an overall uncertainty within 2%. Using commercially available fuel handling equipment, the analysis time for the entire element is estimated to be ∼30 min.