An analysis of the Oak Ridge National Laboratory Tower Shielding Facility gas-cooled fast breeder reactor (GCFR) grid-plate shield design confirmation experiment was performed and inferences were made concerning the effectiveness of the grid-plate shield design. The experiment was designed with three major objectives:

  1. to verify our ability to calculate the energy and angular distribution of neutrons streaming in fuel-pin arrays
  2. to verify our ability to calculate the maximum fast neutron exposure to the grid plate
  3. to verify our ability to calculate the energy and angular distribution of neutrons leaving the grid plate.
The overall objective was to verify the grid-plate shield design. Comparisons between calculated and measured responses indicated that objectives 1 and 2 were achieved. Objective 3 was achieved in part in that the energy distribution seemed to be calculated well On the other hand, depending on the quadrature, there was either conservative overprediction or gross underprediction of the detector responses. For the design calculation, it was estimated that the nonconservative case might mean up to a factor of 4 underprediction of the fluxes in the GCFR inlet plenum. The overall objective was achieved since there was good agreement between calculated and measured responses in the vicinity of the grid-plate shields.