Transmutation and activation of reduced activation ferritic martensitic steel in molten salt cooled fusion power plants

Neutron activation analysis was conducted for the reduced activation ferritic/martensitic (RAFM) steel used in flibe molten-salt cooled fusion blankets. After 22.4 MW yr/m2 of neutron exposure, the RAFM steel first wall in a molten salt blanket with 40% lithium-6 enrichment in lithium was found to be within 1 mSv/h in contact dose rate after 100 yr of cooling. The contact dose rate drops to 30 and 20 μSv/h or less, respectively, when the cooling times are 300 and 500 yr after discharge. The RAFM steel discharged from the high-temperature shield component would be allowed for hands-on recycling after 100 yr of cooling, when the contact dose rate is 10 μSv/h or less. The most significant changes found in the RAFM steel first wall due to nuclear transmutation, are 10% decrease in W and 10% increase in Ti. Additionally, there are minor elements produced: Mn – <1.2%, V – <0.26%, Re – <0.2%, Ta – <0.08%, and Os – <0.1%, all in weight percent. The gaseous elements generated are H and He, and the, respectively, accumulated quantities are about 260 and 190 wppm.