Patent Number: 
Section: claims

1. An advanced first core for a pressurized water nuclear reactor, the advanced first core comprising:an interior;a periphery;a plurality of new fuel assemblies which are configured in the advanced first core to have a plurality of regions of the new fuel assemblies that emulate energy output and discharge burn-up of a corresponding plurality of regions that make up a target equilibrium reload cycle core, each of said regions of the target equilibrium reload cycle core comprising a plurality of equilibrium reload cycle core fuel assemblies, each of said new fuel assemblies having a vertical length and having not been previously irradiated in a reactor core, a majority of said new fuel assemblies having a different elemental make up than a corresponding one of the equilibrium reload cycle core fuel assemblies, some of said new fuel assemblies having different average enrichments of uranium 235 than other of said new fuel assemblies, including high enrichment fuel assemblies and low enrichment fuel assemblies, the new fuel assemblies being the only fuel assemblies within the advanced first core, wherein said advanced first core comprises:said plurality of new fuel assemblies are arranged in the advanced first core of the pressurized water nuclear reactor based upon energy output and discharge burn-up data obtained for substantially all of the plurality of the regions that makeup the target equilibrium reload cycle core, to emulate said target equilibrium reload cycle core in terms of spatial reactivity distribution,wherein substantially all of said high enrichment fuel assemblies are loaded toward the interior of said advanced first core, andwherein an advanced lattice design and associated structure are provided for at least some of said plurality of new high enrichment fuel assemblies of said advanced first core, the advanced lattice design having a plurality of sides in which there is no extended barrier which would prohibit cross flow of a coolant over the vertical length of said new fuel assemblies, in order that lateral circulation of said coolant across said fuel assemblies is provided as said coolant moves vertically, with the advanced lattice design having a peripheral row of fuel rods extending around at the sides of the fuel assembly and a number of interior rows of fuel rods wherein most of the fuel rods in the peripheral row have a lower enrichment than most of the fuel rods in the interior rows. 2. The advanced first core of claim 1 including bundles of said plurality of new fuel assemblies, wherein said bundles include fuel batches each having an average enrichment of uranium; wherein said fuel batches include high enrichment fuel batches having fuel assemblies substantially each having a high average enrichment of uranium, medium enrichment fuel batches having fuel assemblies substantially each having a medium average enrichment of uranium and low enrichment fuel batches having fuel assemblies substantially each having a low average enrichment of uranium. 3. The advanced first core of claim 2 wherein said equilibrium cycle reload core includes batches of feed fuel assemblies, once-burned fuel assemblies and twice-burned fuel assemblies; wherein said batches of feed fuel assemblies, said batches of once-burned fuel assemblies, and said batches of twice-burned fuel assemblies each have an average enrichment of uranium 235, and a size; wherein the size of a particular one of said batches is defined by the quantity of fuel assemblies within the batch; wherein the average enrichment of uranium 235 of said feed fuel assemblies is highest, the average enrichment of uranium 235 of the once-burned fuel assemblies is less than the average enrichment of uranium 235 of said feed fuel assemblies but greater than the average enrichment of uranium 235 of said twice-burned fuel assemblies, and the average enrichment of uranium 235 of the twice-burned fuel assemblies is the least; and wherein said high enrichment fuel batches of said advanced first core are generally the same size and average enrichment as said batches of feed fuel assemblies of said equilibrium cycle reload core. 4. The advanced first core of claim 3 wherein each of said once-burned fuel batches and said twice-burned fuel batches of said equilibrium cycle reload core further includes a beginning of cycle burn-up, an initial enrichment, and a reactivity; and wherein said advanced first core approximates the reactivity of said once-burned fuel batches and said twice-burned fuel batches of said equilibrium cycle reload core through use of fuel batches in said advanced first core which have initial average enrichments based upon the reactivity of the beginning of cycle burnup and initial enrichment of said once-burned and twice-burned fuel batches of said equilibrium reload cycle core. 5. The advanced first core of claim 3 wherein one or more of said fuel batches of said advanced first core include one or more sub-batches comprising fuel assemblies of substantially the same average enrichment. 6. The advanced first core of claim 5 including as said high enrichment fuel batches, a plurality of high enrichment sub-batches sized and enriched to emulate said feed fuel batches of said target equilibrium reload cycle core. 7. The advanced first core of claim 6 wherein said high enrichment sub-batches are primarily loaded at the interior of said advanced first core; and wherein the low enrichment fuel batches are primarily loaded at the periphery of said advanced first core. 8. The advanced first core of claim 1 wherein the resulting average enrichment within said advanced first core ranges from about 1.5 percent weight of uranium 235 to about 5.0 percent weight of uranium 235. 9. The advanced first core of claim 2 wherein at least one of said high enrichment fuel batches is disposed adjacent at least one of said low enrichment fuel batches within said advanced first core configuration; and wherein said advanced first core further comprises radial zoning of said new fuel assemblies in order that said advanced lattice design is structured to compensate for a large thermal neutron flux peak which results from said highly enriched fuel batches within said advanced first core configuration being disposed adjacent less enriched fuel batches within said advanced first core configuration. 10. The advanced first core of claim 9 wherein said advanced lattice design includes a generally square pattern of adjacent rows of fuel rods; wherein said fuel rods include at least six different fuel rod types ranging in average enrichment from least enriched to most enriched; wherein said six different fuel rod types ranging in average enrichment from least enriched to most enriched comprise very low enrichment fuel rods, low enrichment fuel rods, medium enrichment fuel rods, medium enrichment fuel rods with integral fuel burnable absorbers, high enrichment fuel rods, and high enrichment fuel rods with integral fuel burnable absorbers; wherein said generally square pattern has four corners; and wherein said advanced lattice design disposes said very low enrichment fuel rods at the four corners of said generally square pattern, said low enrichment fuel rods at the outermost rows of said generally square pattern and said high enrichment fuel rods and said high enrichment fuel rods with integral fuel burnable absorbers toward the center of said generally square pattern.