Fusion technology is attracting attention as the ultimate new source of energy based on the abundance of its fuels and the social and environmental acceptability. A breeding blanket, which will be employed in K-DEMO tokamak, is an important mechanical and functional component for both tritium breeding and neutron multiplying. However, it should be radio-activated due to the neutron irradiation, and thus accompany decay heat generation. A component of reduced activation ferritic martensitic layer and tungsten first wall accompanies significant decay heats by tens of kilowatts. We evaluate their radio-activated characteristics under the neutron irradiation and demonstrate that managements should be designed in the light of heat transfer aspects of cooling.