Grain　boundary　and　triple　junction　diffusion　in　nanocrystalline　Cu　samples　with　grain　sizes,　＜　d　＞,　of　similar　to　35　and　similar　to　44　nm　produced　by　spark　plasma　sintering　were　investigated　by　the　radiotracer　method　using　the　Ni-63　isotope.　The　measured　diffusivities,　D-eff,　are　comparable　with　those　determined　previously　for　Ni　grain　boundary　diffusion　in　well-annealed,　high　purity,　coarse　grained,　polycrystalline　copper,　substantiating　the　absence　of　a　grain　size　effect　on　the　kinetic　properties　of　grain　boundaries　in　a　nanocrystalline　material　at　grain　sizes　d　＞=　35　nm.　Simultaneously,　the　analysis　predicts　that　if　triple　junction　diffusion　of　Ni　in　Cu　is　enhanced　with　respect　to　the　corresponding　grain　boundary　diffusion　rate,　it　is　still　less　than　500.D-gb　within　the　temperature　interval　from　420　K　to　470　K.　(c)　2014　AIP　Publishing　LLC.