Technical Brief

Analytical Study of Flow Instability in a Natural Circulation Pressurized Water Reactor Auxiliary Feedwater System1

[+] Author and Article Information
Jong Chull Jo

Fellow ASME
Korea Institute of Nuclear Safety,
62 Gwahak-ro, Yusung-gu,
Daejon 305-338, Republic of Korea
e-mail: jcjo@kins.re.kr

Frederick J. Moody

Fellow ASME
GE (retired),
2125 N. Olive Ave. D-33,
Turlock, CA 95382
e-mail: fmoody@goldrush.com

Kyu Sik Do

Korea Institute of Nuclear Safety,
62 Gwahak-ro, Yusung-gu,
Daejon 305-338, Republic of Korea
e-mail: starry@kins.re.kr

Revision of the paper PVP2013-97123 presented at the FSI-1-2 Session “Fluid Flow and Heat Transfer II,” ASME PVP Conference, July 14–18, 2013, Paris, France.

2Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received February 19, 2014; final manuscript received June 30, 2014; published online October 15, 2014. Assoc. Editor: Samir Ziada.

J. Pressure Vessel Technol 137(2), 024501 (Oct 15, 2014) (5 pages) Paper No: PVT-14-1031; doi: 10.1115/1.4027948 History: Received February 19, 2014; Revised June 30, 2014

A pressurized water reactor (PWR) incorporates a passive auxiliary feedwater system (PAFS), a closed natural circulation loop which is aligned to feed condensed water to its corresponding steam generator (SG). During its operation, saturated steam in the SG secondary side moves up due to buoyancy force and passes through a steam line, and then flows into a tube-tank type passive condensation heat exchanger (PCHX) where steam is condensed inside the tubes while the tube outer surfaces are cooled by the pool water. The condensate water is passively fed into the bottom of the SG secondary side by gravity. Because a natural circulation loop is susceptible to two-phase flow instability, it is requisite to confirm the system is designed adequately to avoid the potential challenges to its operational safety due to the instability. This paper presents an analytical approach for assessing if the PAFS has possible thermal and fluid mechanical characteristics which could lead to an undesirable unstable or oscillating condensate water level in the vertical pipe section. Both steady and unsteady analytical solutions for a simplified natural circulation loop model of the PAFS were derived in terms of the condensate water level and velocity in the vertical pipe section. From the solutions, the criteria for determining a potential for flow instability in the system were obtained.

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KHNP, 2011, “APR+ Standard safety Analysis Report.”
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Fig. 1

Schematic of the PAFS [1]

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Fig. 2

Simplified analysis model of the PAFS

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Fig. 3

Control volumes around the condensate water

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Fig. 4

Effects of β and H on the PAFS instability for the case: Y = 30.0 m and KL = 50.0

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Fig. 5

Effects of β and Y on the PAFS instability for the case: H = 70.0 m and KL = 50.0

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Fig. 6

Effects of β and KL on the PAFS instability for the case Y = 30.0 m and H = 70.0 m




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