Neutron physics analyses of accelerator-driven subcritical assemblies

In order to improve the safety characteristics of nuclear systems, accelerator driven assemblies have been proposed for energy production and for the incineration of the residuals of the back-end of the nuclear fuel cycle like plutonium, minor actinides and long-lived fission products. For the neutron physics analysis of such source driven systems calculation procedures have been established and qualified at FZK. Necessary extensions to the conventional methods for fission reactors are discussed in some detail, especially for the spallation processes initiated by protons with energies of about 1 GeV. The application of these methods in an IAEA benchmark for an energy amplifier type of ADS identified the problem of the unfavorable power distribution in such sub-critical systems. In order to improve the power distributions the application of multiple sources, radial distributed over the reactor assembly has been proposed. Investigations for an ADS with three proton beams are performed with respect to the capability of incineration of plutonium and minor actinides.