Abstract: This study presents a new formulation for the calculation of nuclear reactivity using the integral of the inverse point kinetics equation, known as the nuclear power history. The calculation of this integral can be made by approximating the area under the integrand curve through a process of zero-order numerical summation. This method is based on the discrete Fourier transform. This analysis is based on the fact that the reactivity can be written in terms of the summation of a circular convolution with impulse response which is characteristic of linear systems.