A neutron booster for the SINQ neutron source using thin fissile layers

The possibility of using thin fissile layers to improve the flux of the SINQ spallation neutron source at the Paul Scherrer Institut is studied. Two concepts are considered: a local booster, placed between two beam ports where at present a water scatterer is placed, and a global booster, consisting of a fissile layer placed around the spallation target. Neutronic calculations have been performed with MCNPX, and the complete SINQ facility has been modeled, using two types of target: liquid metal (MEGAPIE) and a solid Pb target cooled by heavy water. Fissile layers of pure 235U of variable thickness, up to 0.5 mm, have been considered. The following quantities have been calculated: neutron fluxes at the beam lines, power deposition, keff. The results indicate that large flux increases can be achieved. The limitation appears to be on the power deposited in the fissile layer, which is of the order of the MW. Some considerations on the coolability of the system will be made. (author)