Physics and technology of spallation neutron sources

A substantial body of research is necessary in order to be able to make rel iable predictions on the performance and safety of Accelerator Driven Syste ms (ADS), in particular of their spallation targets. So far, practical expe rience has resulted from the development of research neutron sources only. Next to fission and fusion, spallation is an efficient process for releasin g neutrons from nuclei. Unlike the other two reactions, it is an endotherma l process and can, therefore, not be used per se in energy generation. In o rder to sustain a spallation reaction, an energetic beam of particles, most commonly protons, must be supplied onto a heavy target. Spallation can, ho wever, play an important role as a source of neutrons whose flux can be eas ily controlled via the driving beam. Although sophisticated Monte Carlo cod es exist to compute all aspects of a spallation facility, many features can be understood on the basis of simple physics arguments. Technically a spal lation facility is very demanding, not only because a reliable and economic accelerator of high power is needed to drive the reaction, but also, and i n particular, because high levels of radiation and heat are generated in th e target which are difficult to cope with. Radiation effects in a spallatio n environment are different from those commonly encountered in a reactor an d are probably even more temperature dependent than the latter because of t he high gas production rate. A commonly favored solution is the use of molt en heavy metal targets. While radiation damage is not a problem in this cas e, except for the container, other issues need to be considered. R&D carrie d out for the development of spallation neutron sources will thus be benefi cial also directly fur ADS. (C) 2001 Elsevier Science B.V. All rights reser ved.