Contemporary fleet of nuclear power reactors consists mostly on units cooled and moderated by water. Uranium based fuels are used in those reactors, and uranium isotope of U-235 is the only fissile material in a fresh fuel. However, the fraction of U-235 in metallic uranium being a part of a nuclear fuel is ranging between 0.7% (mass fraction) in case of using the natural uranium, up to 4%-5% in case of enriched uranium fuels. The rest is U-238, which is named as the fertile material. Absorption of neutrons by U-238 nuclei leads to creation of U-239, which decays by beta mode and creates protactinium Pa-239. The later also decays emitting beta particles and finally the plutonium isotope of Pu-239 is created. This is an artificial fissile material, which may be responsible for generation of up to 30% of heat in a nuclear reactor of the considered type. The problem is that not all the fissile nuclei contained in the fuel may be fissioned during a reactor’s operation. The remaining part may be recovered by reprocessing the spent fuel. Recovered U-235, as well as Pu-239 may be next used for production of fresh nuclear fuels, named as the MOX (Mixed Oxide Fuels). This is a way to enhance the efficiency of use the nuclear fuel, and also limits the risk of nuclear materials proliferation. The work deals with an estimate analysis of plutonium inventory recovered from a sample spent fuel of a light water nuclear reactor. The analysis includes single spent fuel reprocessing, as well as a multiple reprocessing option. Results indicates possibility of significant increase of a nuclear fuel utilization efficiency, and also controlling the plutonium inventory. Simplified nuclear reactor kinetics calculations have been accomplished in order to asses the plutonium impact on controlling a nuclear reactor operation.