MATERIALS SELECTION CRITERIA AND PERFORMANCE ANALYSIS FOR THE TITAN-II REVERSED-FIELD-PINCH FUSION POWER CORE

The TITAN-II reactor is a compact, high-neutron-wall-loading (18 MW/m2 ) design. The TITAN-II fusion power core (FPC) is cooled by an aqueous lithium-salt solution that also acts as the breeder material. The use of an aqueous solution imposes special constraints on the selection o f structural and breeder material because of corrosion concerns, hydro gen embrittlement, and radiolytic effects. In this paper, the material s engineering and design considerations for the TITAN-II FPC are prese nted. Material selection criteria, based on electrochemical corrosion mechanisms of aqueous solutions coupled with radiolysis of water by io nizing radiation, resulted in the choice of a low-activation ferritic steel as structural material for TITAN-II. Stress corrosion cracking, hydrogen embrittlement, and changes in the ductile-to-brittle transiti on temperature of ferritic alloys are discussed. Lithium-nitrate (LiNO 3) salt was chosen over lithium hydroxide (LiOH) because it is less co rrosive and reduces the net radiolytic decomposition rate of the water . The dissolved salt in the coolant changes the thermophysical propert ies of the coolant results in trade-offs between the lithium concentra tion in the coolant, neutronics performance, thermal and structural de sign. The TITAN-II design requires a neutron multiplier to achieve an adequate tritium breeding ratio. Beryllium is the primary neutron mult iplier, assuming a maximum swelling of about 10% based on continuous s elf-limiting microcracking/sintering cycles.