Method for improving burnup credit of spent fuel

The method involves creating a series of enrichment curves relative to a present fuel irradiation level, where each curve represents a number of used fuel assemblies (2) that have an unfavorable axial distribution of the level. Number of the assemblies that have the distribution is marked. One curve of the series applied to a new used fuel assembly among the marked number of assemblies is identified. A point corresponding to the level and an initial enrichment for the assembly is found on a graph in which the curve is traced. Determination is made when the point is above the curve.