Bubble behavior in LMFBR core disruptive accidents. Annual report Oct 80-Sep 81

Research performed at the University of Virginia during FY '81 for the Advanced Reactor Safety Research Division of the U.S. Nuclear Regulatory Commission is reported. The research is part of the LMFBR Aerosol Release and Transport Program. Principal areas investigated were (1) analysis of ORNL FAST underwater tests, (2) pretest parametric analysis of ORNL under sodium tests, (3) axial motion of large expanding and collapsing bubbles, and (4) measurement of droplet sizes from flashing. Analysis of the FAST tests with the UVABUBL code showed the strong influence of water vapor during the bubble expansion; water vapor rapidly replaces UO2 vapor as the vapor that drives the bubble. In the case of the under sodium tests, it is expected that entrained sodium will vaporize and influence bubble behavior, but, unlike water, sodium will not be vaporized from the bubble surface. Earlier analyses of axial motion of the French EXCOBULLE experiments were improved. Experimental methods in the experiment on droplet sizes from flashing were developed further