Determination Of Isotopic Composition Due To Fuel Cooling After Outage With The Use Of Isotopic Factors

The effect of fuel cooling on the isotopic inventory after the outage of the NPP Krsko is investigated. Several parameters were analysed that affect the isotopic composition, which inturn influences the reactivity of the fuel on re-insertion into the core. Isotopic cooling factors were determined with which the concentrations of the important nuclides were corrected in order to enhance the accuracy of the reactivity prediction with the use of pre-calculated isotopic library. The performance of these enhancements is demonstrated on a simplified geometry of a fuel assembly. The WIMSD-5B lattice code was used to calculate fuel isotopic composition, while the multiplication factor calculations were performed using the GNOMER code.