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Advanced Course in Heat Transfer in Nuclear Reactor Safety
September, 1-5, 1980, Dubrovnik, Yugoslavia

DOI: 10.1615/ICHMT.1982.AdvCourHeatTransfNucReactSaf


ISBN Print: 978-0-89116-223-0

2.8 Thermodynamics of Critical Two-Phase Discharge from Long Pipes of Initially Subcooled Water

pages 391-407
DOI: 10.1615/ICHMT.1982.AdvCourHeatTransfNucReactSaf.200
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SINOPSIS

For the application to a hypothetical break in the coolant system of a pressurized water reactor, the relative importance of the period of discharge of initially subcooled water depends mainly on the size of the break. In the case of a large break, the period during which the water is subcooled at the stagnation state is short. For a small break, however, these conditions would exist for a long time even assuming a break near the hot leg (with the nominal operating conditions of 16 MPa and 325°C, the subcooling is 22°C). Nonequilibrium then plays a decisive role when the liquid passes from the single phase stagnation state into the two phase region near the break.
HENRY and FAUSKE [l] among others have dealt with two phase critical flow in nozzles and short tubes. This paper presents an analysis of the flashing of hot water in a rather long pipe when the downstream pressure is a small fraction of the upstream pressure, i.e. when the discharge rate is limited by critical flow. The pipe considered in the analysis could be a piece of the emergency core cooling system near its junction with the main pipe of a normal coolant loop or with the reactor vessel.
The following points will be presented in turn : in the first section, the basis of the analysis ; in section 2, a geometrical interpretation and in section 3, a comparison with experimental results.

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