[en] Combustion Engineering has contributed to Nonproliferation Alternating Systems Assessment Program (NASAP) of the Department of Energy by the evaluation of four alternative approaches which could have merit during a deferral of plutonium use. They are: evaluation of improvements in the once-through uranium cycle by changes only in fuel and core design; LWR modifications-substitution of heavy water for soluble boron long-term reactivity control; major changes in water reactor design (Candu-type design); major change in LWR-FBR fuel cycle: development of thorium fuel cycle, use of denatured fuel in dispersed LWRs and conversion of plutonium to U/sup 233/ in FBRs. It is concluded that these changes do not significantly alter the need for the breeder reactor