There has been a significant amount of reactor grade (RG) plutonium accumulated from the conventional nuclear reactors' spent fuel. Destruction or reducing this RG plutonium is very important to prevent its misuse and/or release accidentally into the environment. Using very energetic fusion neutrons in fusion-fission (hybrid) reactors call burn the RG plutonium effectively. This study presents the burning of the mixed fuel containing RG plutonium and Uranium in a helium cooled hybrid reactor for in operation period of 24 months. Effect of various fuel mixtures and tritium breeders oil the neutronic performance of the reactor as well as the burning of the RG plutonium was investigated. Calculations were carried out on an experimental hybrid blanket with the aid of SCALE4.3 by solving the Boltzmann transport equation with the XSDRNPM code. Numerical results showed that increasing RG plutonium content in the fuel increased the burning of plutonium and fusion energy multiplication substantially. The tritium breeder having the lowest lithium atomic density allowed the highest fission of the fuel in the blanket. (c) 2008 Elsevier Ltd. All rights reserved.