Engineering design of the Eurisol multi-MW spallation target

The European Isotope Separation On-line Radioactive Ion Beam project (EURISOL) is set to design the 'next-generation' European Isotope Separation On-line (ISOL) Radioactive Ion Beam (RIIIJ facility. It will extend and amplify current research on nuclear physics, nuclear astrophysics and fundamental interactions beyond the year 2010. In EURISOL, four target stations are foreseen, three direct targets of approximately 100 kW of beans power and one multi-MW target assembly, all driven by a high-power particle accelerator. In this high-power target station, high-intensity RIBS of neutron-rich isotopes will he obtained by inducing fission in several actinide targets surrounding a liquid metal spallation neutron source. This article summarises the work carried out within Task 2 of the EURISOL Design Study, with special attention to the coupled neutronics of the mercury proton-to-neutron converter and the fission targets. The overall performance of the facility, which will sustain fast neutron fluxes of the order of 1014 n/cm2/s, is evaluated, together with the production of radionuclides in the actinide targets, showing that the targeted 1015 fissions/s can be achieved. Some of the greatest challenges in the design of high-power spallation sources are the high-power densities, entailing large structural stresses, and the heat removal, requiring detailed thermo-hydraulic calculations. The use of a thin martensitic steel beam window and a well-controlled mercury flow has been shown to reduce the von Misses stress in the former below the 200 MPa limit, with reasonably maximum flow rates of ∼6 m/s. Alternatively, a windowless target configuration has been proposed, based on a liquid mercury transverse film. With this design, higher power densities and fission rates may be achieved, avoiding the technical difficulties related to the beam window. Experimentally, several tests have been performed at IPUL (Riga, Latvia) in order to study the stability of the liquid metal flow and validate the mercury loop design. (authors)