Methods for Calculating Vapor and Fuel Transport to the Secondary Containment in an LMFBR Accident

Calculational models were developed for estimating the transport of sodium vapor and the relatively large (≥10-µm) fuel particles resulting from a fuel-coolant interaction to the secondary containment in an LMFBR core disruptive accident. Following the formation of a large sodium vapor bubble resulting from a fuel-coolant interaction, a potential sequence of events was analyzed. This analysis covers bubble condensation, bubble rise time, aerosol fallout during the bubble rise, gas flow rate through the cover, cover-gas escape during the bubble rise, bubble and cover-gas mixing, and aerosol escape to the secondary containment. Two parametric calculations were made for specified accident conditions for a 1000-MW(e) LMFBR conceptual design. The bubble did not condense in this analysis. Results of the analysis indicated that 2 and 10% of the fuel that took part in the fuel-coolant interaction eventually reached the secondary containment for the two assumed flow areas through the cover, i.e., 0.1 and 1.0 ft², respectively.