Sodium--oxide aerosols have been generated in the Nuclear Safety Pilot Plant (NSPP) experiment under vessel conditions appropriate for the LMFBR secondary containment following an HCDA. The primary goal of the NSPP program is to provide experimental validation for the HAARM-3 aerosol behavioral code. Validation can be determined by direct comparison of code predictions and integral test results using the same initial and boundary conditions. In addition, separate physical models within the code (e.g., for agglomeration, plate-out, and gravitational fallout) may be validated by a comparison of predicted values with measured instantaneous values. A comparison is presented for the gravitational fallout rate which is considered to be the primary depletion mechanism under prototypic secondary containment conditions
