GCFR grid plate shield design confirmation experiment

This report presents measurements of neutron fluxes and energy spectra made in the Grid Plate Shield Design Confirmation Experiment at the ORNL Tower Shielding Facility (TSF) for the Gas Cooled Fast Breeder Reactor (GCFR) shielding program. The experimental configuration consisted of four basic segments: a concrete shadow shield placed directly in the Tower Shielding Reactor II (TSR-II) reactor beam; a simulated GCFR core positioned behind the shadow shield; a prototypic grid plate shield following the simulated core; and, finally, a prototypic grid plate. The segments were added to the configuration in sequence with measurements made beyond each segment. Calculations indicated the presence of the concrete shadow shield reduced the TSR-II neutron contribution to the source term beyond the fuel pins to less than 10%. Because radiation damage to the GCFR grid plate due to neutrons streaming through the helium coolant passages of the core was of primary concern, the experiment included measurements in which both the spacing between subassemblies in the simulated core and grid plate shield and the pitch of the fuel pins within the subassemblies were varied. In addition, neutron streaming measurements were made beyond an iron-rod configuration and an iron-plate configuration, each being positioned immediately behind the concrete shadow shield