Obtaining denaturated plutonium with 238Pu/Pu 6% in CANDU reactors can be achieved by introducing either 241Am or 237Np into the nuclear fuel. It was found that about the same results are obtained by doping the fuel with 241Am or 237Np. In order not to reduce the fuel burnup, there is a need to enrich the uranium to 0.8% for both 241Am and 237Np doping.