Improved Axial Flux Shape Generator for a Quick Departure from Nucleate Boiling Test

Axial power shapes that develop during power-maneuvering simulations in pressurized water reactors must be analyzed to ensure that an adequate margin to avoid departure from nucleate boiling (DNB) is maintained during these transients. To reduce the number of flux shapes that need to be analyzed in detail to determine the DNB ratio (DNBR), often generic axial flux shapes are analyzed and maximum-allowable-peaking (MAP) limits are determined to conservatively filter those actual axial power shapes that are clearly safe. Current generic MAP limits, obtained for axial flux shapes generated by a two-parameter-based axial flux shape generator, are overly conservative for some power shapes and are nonconservative for others, leading to unnecessary operational restrictions on conservative cases. A penalty is imposed on nonconservative cases. To reduce the number of overly conservative and nonconservative cases, a new generic axial power shape generator that is based on three parameters is developed. Generic MAP limits have been developed for the new axial flux shape generator and tested using real flux shapes by plotting the percent deviation of MAP limits for generic flux shapes from the corresponding value for actual flux shapes. A new axial flux shape generator, which is clearly superior because it leads to a significantly lower percent deviation, will lead to reduced man-hours for detailed DNBR analyses and remove some of the unnecessary operational restrictions imposed by the old flux shape generator.