Proceedings of the 7th International Meeting on Nuclear Reactor Thermal-Hydraulics NURETH-7. Volume 1, Sessions 1-5 Page: 811 of 864

                                
COUNTER-CURRENT FLOW IN A VERTICAL
TO HORIZONTAL TUBE WITH OBSTRUCTIONS
P. Tye,(') A. Matuszkiewicz,(') A. Teyssedou,(')
A. Tapucu,(') and W. Midvidy(2)
(1) Institut de Genie Nuclaire
Ecole Polytechnique de Montreal
Montreal, Quebec, Canada H3C 3A7
(2) Ontario Hydro
1. ABSTRACT
This paper presents experimental results on counter-current flow and flooding in an
elbow between a vertical and a horizontal run. The experimental technique used allowed
not only the flooding limit to be determined, but also the entire partial delivery region
to be studied as well. The influence that various size orifices placed in the horizontal run
have on both the delivered liquid flow rates and on the flooding limits is also examined.
It is observed that both the flooding limits and the delivered liquid flow rates decrease
with decreasing orifice size. Further, it is also observed that the mechanisms that govern
the partial delivery of the liquid are significantly different when an orifice is present in the
horizontal leg as compared to the case when no orifice is present.
2. INTRODUCTION
Counter-Current Flow (CCF) in general and the Counter-Current Flooding Limit
(CCFL) in particular are of great importance in the area of nuclear reactor safety analy-
sis. In CANDU reactors, during a postulated loss of coolant accident (LOCA), the water
coming from the inlet and outlet headers enters the fuel channels through the feeder pipes.
These pipes consist of vertical and horizontal runs. In some feeders, orifices and/or venturi
type flow obstructions are installed for flow adjustments and measurements. Steam pro-
duced in the feeders and/or in the fuel, channels may flow in the direction opposite to that
of the water, thereby creating vertical and horizontal counter-current two-phase flows in
the feeder pipes. Under these conditions, the rate at which cooling water can enter the fuel
channels may be limited by the flooding phenomena. During flooding, the liquid is partly
entrained in the same direction as the steam flow. The liquid delivery is greatly affected
by the geometry of the feeder pipes, shape and number of fittings, flow area restrictions
and the way the feeder pipe is connected to the header and to the end-fitting. Thus,
knowledge of the flooding phenomena in a geometry similar to the header-feeder system
in a CANDU reactor is of prime importance in the safety analysis of nuclear reactors in
order to improve the prediction of the time required for the emergency cooling injection
system to refill the fuel channels. The objectives of this research are to study the influence
of a 90* elbow between a vertical and a horizontal run and the affects of its interaction
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