A method of implementing an economical initial core having not yet experienced any burnup for a light water nuclear reactor, said method comprising: providing a plurality of fuel assemblies (208, 206, 204) having different average enrichments of uranium 235, including at least highly enriched fuel batches, less enriched fuel batches, and least enriched fuel batches, arranging said plurality of fuel assemblies (208, 206, 204) in an initial core configuration structured to emulate, at least in terms of spatial reactivity distribution, a known equilibrium cycle reload core including batches of feed fuel assemblies, once-burned fuel assemblies and twice-burned fuel assemblies wherein the feed fuel assemblies have the highest average enrichment, said arranging step including taking data obtained through years of monitoring the equilibrium cycles of various reactors and applying it to emulate the reactivity distribution of said equilibrium cycle reload core in the initial core in order to replicate the desired equilibrium cycle by using highly enriched fuel batches having approximately the same size and enrichment as the feed fuel assemblies of said equilibrium cycle reload core, and by approximating the reactivity of the once-burned fuel batches and the twice-burned fuel batches of the equilibrium cycle reload core through use of fuel batches (204, 206) which have initial average enrichments based upon reactivity of the non-zero, beginning of cycle bumup and initial enrichment of the once and twice-burned fuel of the equilibrium cycle reload core, and providing an advanced lattice design for at least some of the highly enriched fuel assemblies that are adjacent to low enrichment fuel assemblies of the initial core, employing radial zoning of the fuel assembly to reduce the enrichment of the fuel rods at the edges of the fuel assembly, disposing the lowest enrichment fuel rods at the corners of the lattice and the next lowest enrichment rods along the sides or edges of the lattice. providing a plurality of fuel assemblies (208, 206, 204) having different average enrichments of uranium 235, including at least highly enriched fuel batches, less enriched fuel batches, and least enriched fuel batches, arranging said plurality of fuel assemblies (208, 206, 204) in an initial core configuration structured to emulate, at least in terms of spatial reactivity distribution, a known equilibrium cycle reload core including batches of feed fuel assemblies, once-burned fuel assemblies and twice-burned fuel assemblies wherein the feed fuel assemblies have the highest average enrichment, said arranging step including taking data obtained through years of monitoring the equilibrium cycles of various reactors and applying it to emulate the reactivity distribution of said equilibrium cycle reload core in the initial core in order to replicate the desired equilibrium cycle by using highly enriched fuel batches having approximately the same size and enrichment as the feed fuel assemblies of said equilibrium cycle reload core, and by approximating the reactivity of the once-burned fuel batches and the twice-burned fuel batches of the equilibrium cycle reload core through use of fuel batches (204, 206) which have initial average enrichments based upon reactivity of the non-zero, beginning of cycle bumup and initial enrichment of the once and twice-burned fuel of the equilibrium cycle reload core, and providing an advanced lattice design for at least some of the highly enriched fuel assemblies that are adjacent to low enrichment fuel assemblies of the initial core, employing radial zoning of the fuel assembly to reduce the enrichment of the fuel rods at the edges of the fuel assembly, disposing the lowest enrichment fuel rods at the corners of the lattice and the next lowest enrichment rods along the sides or edges of the lattice.