Lujan Center Upgrade for Cold Moderators: Current Design and Future Options.

摘要

The upgraded Lujan Center target system is designed to be a split target with two tiers of moderators. The original suite of four moderators serving twelve flight paths has been optimized and an additional pair of moderators, one water and one LH(sub 2), have been added in a new upper moderator tier serving four additional flight paths. The upper moderators are partially coupled and viewed in backscattering geometry, as opposed to the decoupled moderators in the existing Lujan Center target system, which are viewed in transmission geometry. Fabrication of this new target system is currently in progress and installation is expected in 1998. The decoupling scheme for the upper moderator tier is documented. The neutronic performance of the two cold moderators is presented in the form of time and energy spectra with comparisons to the existing Lujan Center LH(sub 2) moderator. Neutronic performance of a partially-coupled flux trap LH(sub 2) moderator is also presented.