Beam-tube design for the high-flux beam reactor

Abstract

The Brookhaven High-Flux Beam Reactor (HFBR) is being constructed primarily to satisfy a need for neutron beams that are more intense than those available from other research reactors. The design principles chosen have also made it possible to provide neutron beams that are tailored to the requirements of individual experiments. That is, each beam will emphasize some region of the neutron energy spectrum, with an associated reduction of emission of neutrons of unwanted energies, and also of γ-rays. Special discrimination is provided against the very high-energy neutrons which are health hazards, and which add to background problems. The reactor is not designed solely for neutron beam users. Two irradiation thimbles will make possible the exposure of small samples (such as single crystals) to an intense and relatively pure flux of high-energy neutrons. These facilities will permit radiation damage studies at temperatures near that of liquid helium. Two irradiation thimbles in a region of somewhat poorer quality neutron flux can also be used in experiments of this kind. Three isotope irradiation facilities will be placed in regions where the thermal neutron flux is large and the fast flux contamination is small. To a greater extent than has been common in the past, the design of this reactor is based on experiment. Critical experiments have not only established the necessary core size, but they also have been relied on for much additional information normally found by theoretical methods. Experiments have been especially valuable in setting the design of the experimental facilities. The combination of unusual neutronic properties and of complex geometry made it necessary to make this departure from customary design practice.