High power spallation target design for accelerator-driven waste transmutation

The reference design Accelerator Driven System (ADS), developed under the U. S. DOE's Advanced Accelerator Applications Program is based upon a sodium-cooled, fast-spectrum, 840-MWth sub-critical multiplier (SCM) that is powered by a spallation neutron source. A number of spallation target concepts using molten lead-bismuth eutectic (LBE) or sodium-cooled solid tungsten are considered for this high-power application. The molten LBE option is more desirable because LBE has a higher neutron yield per incident proton. In addition, the stopping distance is larger in LBE, leading to lower power densities within the target material. However, the corrosive and erosive characteristics of molten LBE require careful chemistry control, and the solid target is retained as a reserve option. In the ADS target system, a beam of protons with an energy of 600 MeV and a beam current of ∼28 mA is focused upon heavy metal target nuclei for the production of neutrons through spallation. The nominal target uses a concentric annular geometry with liquid lead bismuth entering the target through an outer annulus, turning 180 degrees, expanding to fill the bulk target region, passing over a hemispherical beam window, and exiting through an inner annulus. CFD analysis has been employed to demonstrate the viability of this design. However, while these studies have shown this target concept satisfies the performance requirements of the system, the concept presents significant challenges in the construction, handling and operation of the system because of its large size. Therefore, alternative target configurations that would address these operational concerns are under consideration.