Patent Number: 
Section: claims

1. A computer-implemented method of determining pin enrichments for a fuel bundle of a nuclear reactor, comprising:inputting a plurality of input parameters pertaining to a fuel bundle;inputting a plurality of target conditions including each of a target local peaking value, a target exposure peaking value, a target bundle R-factor and a target lattice average enrichment for the fuel bundle;calculating enrichment changes to be made across the fuel bundle, using at least one computer executing response matrix technology so as to satisfy the target conditions; andoutputting fuel bundle pin enrichment data that satisfies the target conditions. 2. The computer-implemented method of claim 1, wherein the input parameters include at least one of user performance criteria, base fuel bundle lattice design, R-factor data related to the base fuel bundle lattice design, and data related to a response surface model used in said calculating of enrichment changes. 3. The computer-implemented method of claim 2, wherein said calculating further includes using the response surface model to calculate pin-by-pin enrichment changes to be made across the fuel bundle so as to satisfy the target conditions. 4. The computer-implemented method of claim 3, wherein the response surface model is a matrix that defines relationships between the input parameters and the target conditions. 5. The computer-implemented method of claim 3, wherein the response surface model includes an exposure dependent local peaking response, an exposure peaking response and R-factor response for every pin in a N by N fuel bundle lattice design as a function of a change in enrichment in each pin in the N by N fuel bundle lattice design. 6. The computer-implemented method of claim 1, wherein said calculating further includes:determining an exposure point for each fuel rod where a margin to the target local peaking value is the most limiting, where a margin to the target exposure peaking value is the most limiting and where a margin to a target bundle R-factor is the most limiting;calculating a pin by pin enrichment change required based on the target local peaking value using a response surface matrix, separately based on target bundle maximum exposure peaking using the response surface matrix and separately based on target bundle R-factor using the response surface matrix;selecting a fuel rod that has the most limiting enrichment change from the calculated enrichment changes based on target local peaking value, exposure peaking value and target bundle R-factor, the most limiting change representing the smallest enrichment change from a base fuel bundle lattice design of the fuel bundle;reducing enrichment, by a given amount, in a pellet in the selected fuel rod where an enrichment change reduction is greater than an acceptable tolerance;calculating an impact on all pellet local peaking, exposure peaking and R-factors across the fuel bundle using the response surface matrix;re-calculating modified pin by pin enrichment changes using based on the impact;selecting a fuel rod that has the most limiting enrichment change from the re-calculated modified enrichment changes;searching for a pellet within the selected fuel rod that exceeds the acceptable tolerance; andupdating current local peaking and R-factors if no further pellet is found to exceed the acceptable tolerance. 7. The computer-implemented method of claim 1, wherein said outputting further includes:outputting a two-dimensional enrichment distribution that satisfies target local peaking and target R-factor requirements. 8. The computer-implemented method of claim 1, further comprising:determining an estimated lattice average enrichment for a desired fuel bundle by applying the enrichment changes to a known average lattice enrichment of a base fuel bundle lattice design; andcomparing a difference between the estimated lattice average enrichment and a target lattice average enrichment to a threshold. 9. The computer-implemented method of claim 8, wherein, if the difference exceeds the threshold, the method further comprises:determining which fuel rod has the most limiting enrichment change from the calculated enrichment changes based on target local peaking, target exposure peaking and target bundle R-factor, the most limiting change representing the smallest enrichment change from the base fuel bundle lattice design;reducing enrichment, by a given amount, in a pellet in the selected fuel rod where an enrichment change reduction is outside an acceptable tolerance;calculating an impact on all pellet local peaking, exposure peaking and R-factors in the fuel bundle using the response surface matrix;re-calculating modified pin by pin enrichment changes based on the impact;comparing the most limiting modified enrichment change to an enrichment tolerance; andcalculating a revised estimated average lattice enrichment when the most limiting modified enrichment change is within the enrichment tolerance. 10. The computer-implemented method of claim 9, further comprising:iteratively repeating each of the steps of claim 9 until the difference equals the threshold; andoutputting a two-dimensional enrichment distribution of the resultant fuel bundle lattice design that meets local peaking, exposure peaking and R-factor target conditions. 11. The computer-implemented method of claim 8, wherein, if the difference is less than the threshold, the method further comprises:determining which fuel rod has the least limiting enrichment change from the calculated enrichment changes based on target local peaking, target exposure peaking and target bundle R-factor, the least limiting change representing the largest enrichment change from the base fuel bundle lattice design;increasing enrichment, by a given amount, in a pellet in the selected fuel rod where an enrichment change increase is outside an acceptable tolerance;calculating an impact on all pellet local peaking, exposure peaking and R-factors in the fuel bundle using the response surface matrix using the response surface matrix;re-calculating modified pin by pin enrichment changes based on the impact;comparing the most limiting modified enrichment change to an enrichment tolerance; andcalculating a revised estimated average lattice enrichment, if the most limiting modified enrichment change is within the enrichment tolerance. 12. The computer-implemented method of claim 11, further comprising:iteratively repeating the steps of claim 11 until the difference equals the threshold; andoutputting a two-dimensional enrichment distribution of the resultant fuel bundle lattice design that meets local peaking, exposure peaking and R-factor target conditions. 13. The computer-implemented method of claim 1, further comprising:determining an estimated lattice average enrichment for the fuel bundle by applying the enrichment changes to a known average lattice enrichment of a base fuel bundle lattice design;storing a list of pellet types useable in the fuel bundle and a list of pellet locations to perturb in the fuel bundle;recursively creating an array of test fuel bundle lattice designs for the fuel bundle using the perturbed pellet locations, andfor each test fuel bundle lattice design:calculating an impact of particular pellet type(s) on all pellet local peaking, exposure peaking and R-factors in the test fuel bundle lattice design using the response surface matrix;calculating pin by pin enrichment changes based on the impact using the response surface matrix;comparing a most limiting enrichment change in the test fuel bundle lattice design to a tolerance; andcalculating a revised estimated average lattice enrichment for those test fuel bundle lattice designs having a most limiting enrichment change that is within the tolerance. 14. The computer-implemented method of claim 13, further comprisingselecting a test fuel bundle lattice design from the test fuel bundle lattice designs where revised estimated average lattice enrichment were calculated based on the fewest number of pellet types used in the design; andoutputting a two-dimensional enrichment distribution of the selected test fuel bundle lattice design. 15. A computer-implemented method of determining pin enrichments for a fuel bundle of a nuclear reactor, comprising:using a computer-implemented response surface model to calculate pin-by-pin enrichment changes to be made across the fuel bundle so as to satisfy target conditions, the target conditions including each of a target local peaking value, a target exposure peaking value, a target bundle R-factor and a target lattice average enrichment for the fuel bundle, wherein the response surface model defines relationships between input parameters which include at least one of user performance criteria, base fuel bundle lattice design, R-factor data related to the base fuel bundle lattice design and data related to the response surface model, and the target conditions; andoutputting a two-dimensional enrichment distribution for the fuel bundle providing modified pin-by-pin enrichments that satisfies target local peaking and target R-factor requirements. 16. An apparatus for determining pin enrichments for a fuel bundle of a nuclear reactor, comprising:inputting means for inputting a plurality of input parameters and target conditions pertaining to a fuel bundle, the target conditions including each of a target local peaking value, a target exposure peaking value, a target bundle R-factor and a target lattice average enrichment for the fuel bundle;calculating means for calculating enrichment changes to be made across the fuel bundle, using at least one computer executing response matrix technology so as to satisfy the target conditions; andoutputting means for outputting fuel bundle pin enrichment data that satisfies the target conditions. 17. The apparatus of claim 16, wherein the input parameters include at least one of user performance criteria, base fuel bundle lattice design, R-factor data related to the base fuel bundle lattice design and data related to a response surface model included in the calculating means. 18. The apparatus of claim 16, wherein said inputting means include one or more of an input device, communication medium and interface for inputting the plurality of input parameters and target conditions. 19. The apparatus of claim 17, wherein the interface is a web-based internet browser. 20. The apparatus of claim 16, wherein said calculating means include one or more of a host computer, memory and a plurality of calculation servers. 21. The apparatus of claim 16, wherein said outputting means include one or more of a host processor, interface, communication medium and terminal unit. 22. The apparatus of claim 21, wherein the interface is a graphical user interface. 23. The apparatus of claim 16, wherein said calculating means employs a response surface model to calculate pin-by-pin enrichment changes to be made across the fuel bundle so as to satisfy the target conditions. 24. The apparatus of claim 23, wherein the response surface model is a matrix that defines relationships between the input parameters and the target conditions. 25. The apparatus of claim 23, wherein the response surface model includes an exposure dependent local peaking and R-factor response for every pin in a N by N fuel bundle lattice design as a function of a change in enrichment in each pin in the N by N fuel bundle lattice design.