Numerical approach to calculate the decay heat of actinides for short cooling time

► Numerical calculation of the decay heat power for 235U and 239Pu after short cooling time. ► Runge-Kutta technique is used to reduce the truncation error. ► Prediction of the nuclids suffering from ''pandemonium effect” in the ENDF/B-VII.0 and ENDF/B-VII.I.