In this paper, we present a new method to compute rapidly, wave particle interaction induced pitch angle and momentum diffusion coefficients. Those terms are normally obtained by the numerical solving of equations based on the quasi-linear theory. However, this bulk resolution leads to a high computational cost, preventing the integration of plasma density and VLF waves nowcasts and forecasts. Therefore, and in the context of the SAFESPACE project (H2020), we implemented a new wave particle interaction code called FARWEST (FAst Radiation diffusion with Waves ESTimator), with an efficient interpolation based method. The proposed implementation was validated against reference results obtained by WAPI, ONERA's wave particle interaction legacy code, with a substantial reduction of the computing time while conserving the physical accuracy of the generated coefficients. The FARWEST code is later used to measure the impact of a time-dependent plasma density distribution (numerically computed by BIRA's plasmaspheric model SPM) on the coefficients and on the representation of the electron flux map by Salammbô, ONERA's radiation belt code.