Convective boiling heat transfer in narrow annular gaps. Progress report, September 1, 1981-May 15, 1982

One of the major problems facing the utility industry in the next decade is the probability of extensive steam generator tube failures in existing pressurized-water nuclear reactor power plants. Failures, as in the recent failure at the Ginna power plant in New York State, are due to combined corrosion and thermal cycling. Alternate dryout and rewetting can occur where the tubes pass through the tube support plates (TSP) or the tubesheet. Hence an understanding of the mechanics of convective boiling in narrow crevices is essential. The present work is designed to contribute to that understanding. Previous work with the existing flow loop focussed on an eccentric annular gap, in which the tube was in line contact with the circular hole in the TSP. Because it is difficult to determine the effect of local crevice width in that geometry, the present work is aimed at concentric annular crevices, using the actual steam generation tubing, over a pressure range up to 100 psi on the secondary side. As a result of experiments over several months, it was determined that some important modifications to the secondary flow loop are needed