Transmutation efficiency of the spallation neutron target measured with the actinide sandwiches

We used actinide sandwiches composed of U-233, U-235, U-236, U-238, Np-237, Pu-238, and Pu-239 isotopes to study the transmutation efficiency of the natural uranium spallation target Quinta bombarded with 660-MeV protons. The efficiency, defined as a ratio of fission to production, was determined by measuring simultaneously the production of transuranium isotopes via the (n,gamma) and (n,xn) reactions, and fission incineration of their reaction products. For example, with the U-238-Pu-239 sandwich, measured was the production of Pu-239 from U-238 via the (n,gamma) reaction, as well as Pu-239 transmutation via fission. The efficiencies were measured using gamma spectroscopy. All the measured efficiencies were greater than 1.0, which demonstrates that the fast neutron spectrum at Quinta is highly suitable for actinide transmutation. Experimental results were compared with computer simulations employing the latest versions of the MCNP6 code and ENDF/B-VIII and JENDL/HE data libraries. A good agreement within one standard deviation was reached, which validates the utilized computation suite and shows that the suite is well capable of performing neutronic simulations related to actinide transmutation, spallation neutron sources and accelerator-driven systems.