Source efficiency as function of fuel and coolant in accelerator-driven systems

We have studied the efficiency of spallation neutron sources for different combinations of coolant and fuel in 80 MWth, sub-critical, cores. It has been found that the proton source efficiency, ψ∗, is reduced by 10% when switching coolant from helium to lead-bismuth eutectic. Substituting MOX fuel with an americium based fuel, results in another 10% reduction of ψ∗. The relatively high source efficiencies found for prototype accelerator-driven systems, using standard MOX fuel and helium coolant, may thus be difficult to achieve in future systems dedicated to the transmutation of higher actinides. Our results are in agreement with previous investigations of the dependence of the source efficiency on the selection of coolant.