Determination of delayed neutron fraction for reactor transient analysis

A method has been developed to calculate effective delayed neutron fractions and delayed group decay constants by introducing the three dimensional flux weighting and the isotopic correction in nuclear fission associated with local burnup histories, as a basic study preceded to analyze any kinetic problems of a nuclear reactor. Furthermore, these computed values have been used to solve the inhour equation, and thereby the stable reactor period has been related to the reactivity change. The method has been used for the BOC and EOC of the first cycle, and the BOC of the second cycle of Kori-1 reactor. The calculated values of effective delayed neutron fractions and delayed group decay constants have been compared with the design data of Westinghouse for the same model. The results show that the calculated values turn out to be in good agreement with those of Westinghouse within 2.49%. It is, therefore, concluded that the method developed in this study can be used as an effective and competent tool for determining core-averaged delayed neutron fractions at any burnup stage. (Author)