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A study of the critical flow in LOBI small break LOCAs has been made. The geometry is a sudden, almost infinite, contraction, perpendicular to the main flow direction, followed by a pipe of constant diameter with length to diameter ratio between 3 and 4. Upstream of the break is steam above a layer of subcooled water. The system codes CATHARE and DRUFAN had predicted the critical flow through this pipe well. A good modelling of interfacial heat transfer and hence the phase change is necessary for a correct prediction. This modelling should take into account the subcooling in the cold leg. The calculation of the velocity difference between the phases is not very important; assuming equal phase velocities gave satisfactory results. The flowrate is also insensitive to the outlet boundary condition (essentially the two-phase sound speed) and to the virtual mass term. This insensitivity is explained using a simplified model.

Additional information

Authors: SHEPHERD I M, JRC Ispra Estab. (IT)
Bibliographic Reference: Paper presented: NURETH-4, Karlsruhe (DE), Oct. 10-13, 1989
Availability: Available from (1) as Paper EN 34893 ORA
Record Number: 198910777 / Last updated on: 1994-12-01
Original language: en
Available languages: en