Transmutation of 126 Sn in Spallation Targets of Accelerator-Driven Systems

The practical feasibility of 126Sn transmutation in spallation targets of accelerator-driven systems was evaluated from the viewpoints of accumulation of radioactive spallation products and neutron production as well as transmutation amount of 126Sn. A cylindrical liquid 126Sn target whose length depends on proton beam energy was described, based on a Pb-Bi target design of accelerator-driven system being developed in JAEA. A proton beam of 1.5 GeV-20mA was estimated to give the transmutation rate of 126Sn 6.4 kg/yr, which corresponds to the amount of 126Sn annually discharged in 27 LWRs of 1GWt and 33 GWd/THM. The equilibrium radioactivity of spallation products would reach 9% of that of 126Sn transmuted in the spallation target, and the equilibrium toxicity would be just 3%. Some parametric analyses showed that the effective half-life of 126Sn could be reduced through a proper reduction of the target size. The 126Sn target was calculated to produce 40 neutrons per proton of 1.5 GeV and give a neutron spectrum very similar to that of the reference Pb-Bi target. As a result, the transmutation of 126Sn in the spallation target has a high feasibility in terms of better transmutation performance and comparable target performance.