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The analysis of flow-induced vibration and design improvement in KSNP steam generators of UCN #5, 6

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Abstract

The KSNP Steam Generators (Youngkwang Unit 3 and 4, Ulchin Unit 3 and 4) have a problem of U-tube fretting wear due to Flow Induced Vibration (FIV). In particular, the wear is localized and concentrated in a small area of upper part of U-bend in the Central Cavity region. The region has some conditions susceptible to the FIV, which are high flow velocity, high void fraction, and long unsupported span. Even though the FIV could be occurred by many mechanisms, the main mechanism would be fluid-elastic instability, or turbulent excitation. To remedy the problem, Eggcrate Flow Distribution Plate (EFDP) was installed in the Central Cavity region of Ulchin Unit 5 and 6 steam generators, so that it reduces the flow velocity in the region to a certain level. However, the cause of the FIV and the effectiveness of the EFDP was not thoroughly studied and checked. In this study, therefore the Stability Ratio (SR), which is the ratio of the actual velocity to the critical velocity, was compared between the value before the installation of EFDP and that after. Also the possibility of fluid-elastic instability of KSNP steam generator and the effectiveness of EFDP were checked based on the ATHOS3 code calculation and the Pettigrew’ s experimental results. The calculated results were plotted in a fluid-elastic instability criteria-diagram (Pettigrew, 1998, Fig. 9). The plotted result showed that KSNP steam generator with EFDP had the margin of Fluid-Elastic Instability by almost 25%.

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Abbreviations

D:

Outside diameter of tube

De:

Equivalent diameter of flow boundary

fn, f:

Natural frequency

K:

Instability constant

mk :

Hydraulic (Added) mass

mo :

Effective mass of tube

P:

Pitch of tube array

Vcrit :

Critical velocity

Veff :

Effective velocity

Vp :

Gap velocity

V(x):

Cross flow velocity spanwise variation

x:

Spanwise coordinate measured along tube axis

P/D:

Pith to diameter ratio

α:

Void fraction

δ5o :

Logarithmic decrement ( = 2πζ)

φ(x):

Spanwise variation in normalized modal displacement

ρo :

Secondary fluid density (average)

ρ(x):

Secondary fluid density spanwise variation

ρtp :

Two phase density

ζ:

Damping ratio

ζfd:

Film dynamic damping

ζs:

Structural damping

ζtp:

Two-phase damping

ζv:

Viscous damping

Vf:

Kinetic viscosity of liquid

Vg :

Kinetic viscosity of gas

DSH1C:

Doo San Heavy Industry Company

EFDP:

Eggcrate Flow Distribution Plate

KSNP:

Korea Standard Nuclear Plant

SR:

Stability Ratio

WEC LLC:

Westinghouse Electric Company Limited Liability Company

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Authors and Affiliations

  1. Department of Nuclear Engineering, Kyunghee University, Seocheon- ri #1, Kiheung- up, Youngin- city, 449-701, Kyung- gi- do, Korea

    Sang-Nyung Kim & Yeon-Sik Cho

Authors
  1. Sang-Nyung Kim
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  2. Yeon-Sik Cho
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Correspondence to Sang-Nyung Kim.

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Kim, SN., Cho, YS. The analysis of flow-induced vibration and design improvement in KSNP steam generators of UCN #5, 6. KSME International Journal 18, 74–81 (2004). https://doi.org/10.1007/BF03028792

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  • DOI: https://doi.org/10.1007/BF03028792

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