Shielding studies for the LANL Isotope Production Facility

We report on shielding studies, using MCNPX 2.1.5, for the new Isotope Production Facility (IPF) at Los Alamos National Laboratory. The IPF consists of a branch line of 100 MeV protons off of the main LANSCE beam line. Construction is taking place while the main line is operation. We consider the effectiveness of a concrete shield wall and surrounding earth for protection of the construction workers in case of a beam spill at several locations in the main tunnel. The thicknesses of tuff outside the main tunnel and of main part of shield wall is sufficient to limit the dose equivalent rate (DER) to less than 1 mrem/hour for a 10 mu amp beam spill in the main tunnel and to much less than 25 rem/hour for a 1500 mu amp spill. Some regions of the thinner upper shield offer only marginal protection. Following construction, we consider a spill on a beam plug at the face of the shield wall and the subsequent dose rate downstream of the shield. A 500 mu amp beam directed at a 20 " long beam plug results in a DER in the upstream end of the IPF tunnel of 35 mrem/hour. We consider radiation flow through a utility duct due to a beam spill in the IPF tunnel during the operational phase.