Japan's strategy for structural material development for DEMO reactors is the staged approach, focusing on the development of reduced activation ferritic/martensitic (RAFM) steel F82H (Fe-8Cr-2W-V, Ta), which is the main optional material for in-core structures . Full qualification of RAFM steel F82H to be used as fusion in-vessel structural materials in a “real” fusion environment of high-dose 14 MeV fusion neutron irradiation and high heat flux from the fusion plasma, as well as high magnetic fields of up to 10 T to confine the plasma, can only be achieved through actual DEMO service. Therefore, the goal of irradiation database construction up to the third decision point (decision of DEMO construction) should be the construction of irradiation database by fission neutron irradiation up to the critical condition where the 14 MeV fusion neutron irradiation effect is expected to be different from the fission neutron irradiation effect . This assumption of criticality conditions must be verified, especially first for material property changes that may affect the safety strategy of the fusion reactor. This is a short-term goal for the D-Li neutron source (A-FNS) until DEMO operation begins and is an important step toward the initial design final verification of the DEMO in-vessel structures and approval of DEMO operation.
The A-FNS high flux test module must be designed to meet these requirements, of which the reliability of irradiation temperature is the most important requirement; the HFTM design of the A-FNS is aimed at meeting such requirements. Further development of the irradiation database is necessary in parallel with the DEMO operation in order to obtain the authorization to expand the DEMO operation limit step by step. The expansion of the irradiation database by A-FNS is expected to meet the irradiation up to the dose preceding the DEMO operation limit, which will enable to get extensive authorization for the DEMO operation.
 T. Muroga and H. Tanigawa, Fusion Sci. Tech. 72 (2017) 389-397
 H. Tanigawa, E. Gaganidze, et.al., Nucl. Fusion 57 (2017) 092004