OnLine Vibration Monitoring of

1
IAEA Meeting on On-line Condition Monitoring of
Equipment and Process in Nuclear Plants Using
Advanced Diagnostic Systems, Knoxville, TN, USA
On-Line Vibration Monitoring of Core Support
Barrel in Korean NPP
Won-Young YUN, Ph.D. Korea Institute of Nuclear
Safety
2
Contents

• Introduction
• Noise Spectrum Analysis of Uljin Unit 1 Reactor
• Simulation Study on CSB Vibrations of Uljin Unit
  1 Reactor
• Concluding Remarks

3
1. Introduction

• Background of Study
• Reactor Noise Descriptors
• Reactor Noise Analysis Results in Literature

4
Background of Study

• Reactor noise is defined as fluctuation of
  measured instrumentation signal during full power
  reactor operations.
• Reactor noise signals have information on reactor
  system dynamics such as neutron kinetics,
  thermal-hydraulics, structural dynamics, etc.
• The goal of our study is to establish on-line
  monitoring technique to diagnose the core support
  barrel movements using reactor noise signal of
  Uljin unit 1 NPP.

5
Background of Study

• Noise Sources in Reactor Operation
• - Nuclear Noise Sources
• - Thermal Noise Sources
• - Hydrodynamic Noise Sources
• - Structural Vibration Noise Sources
• Structural Vibration Noise Sources
• - CSB / Thermal Shield movements
• - Fuel Assembly Movements
• - Instrument Thimble Movements
• - Reactor Vessel Movements

6
Reactor Noise Descriptors

• Auto Power Spectral Density (APSD)
• Gxx(f) 4?Rxx(t) cos 2pftdt ?Gxx(f)?
  e-jT(f)
• Cross Power Spectral Density (CPSD)
• Gxy(f) ?Gxy(f)? e-jT(f) Cxy(f)
  jQxy(f)
• Cxy(f) 2?Rxy(t) Rxy(t )cos 2pftdt
  ?Gxy(f)?cosTxy(f ) Cxy(-f)
• Qxy(f) 2?Rxy(t) Rxy(t )sin 2pftdt
  ?Gxy(f)?sinTxy(f ) Qxy(-f)
• Coherence Function (CF)
• ?xy2 ?Gxy(f)?2/Gx(f) Gy(f) 1.0
• Phase Difference (PD)
• Txy tan-1Qxy(f)/Cxy(f)
• Where, Rxx(t) Exk(t) xk(tt)
  Auto-correlation
• Rxy(t) Exk(t) yk(tt)
  Cross-correlation

7
Reactor Noise Descriptors

• Beam Mod Vibration
• - Low coherence and 180o/0o phase difference
  between adjacent detector signals.
• - High coherence and 180o phase difference
  between opposed detector signals.
• Shell Mode Vibration
• - High coherence and 180o phase difference
  between adjacent detector signals.
• - High coherence and 0o phase difference
  between opposed detector signals.

8
Reactor Noise Descriptors
9
Noise Analysis Results in Literature
10
Noise Analysis Results in Literature
11
Noise Analysis Results in Literature

• 0.5 2 Hz Thermodynamic/Nuclear Noise
• 2 5 Hz FA 1st Bending Mode Vibration
• 5 7.5 Hz FA 2nd Bending Mode Vibration
• 5 14 Hz CSB/TS Beam Mode Vibration
• 14 18 Hz RPV Swing Mode Vibration
• 18 24 Hz CSB Shell Mode Vibration

12
Noise Analysis Results in Literature
13
Noise Analysis Results in Literature
14
Noise Analysis Results in Literature
15
Noise Analysis Results in Literature
16
2. Noise Spectrum Analysis of Uljin Unit 1 Reactor

• Uljin Unit 1 Reactor Configuration/ Reactor
  Design Data
• Noise Data Measurement/Reactor Operating
  Conditions
• Noise Descriptor Measurements/ Analysis Results

17
Uljin Unit 1 Reactor Configuration
18
Uljin Unit 1 Reactor Design Data
19
Noise Data Acquisition System
Ex-Core Detector N4
Pre-Amp
Reactor Vessel
4 Channel Power Range Nuclear Instrumentation
Isolation Amp.
Ex-Core Detector N2
Ex-Core Detector N1
Pre-Amp
Ex-core Detector N3
AC Coupling Network
Pre-Amp
Pre-Amp
FM Recorder BK Model 7005
FFT Spectrum Analyzer BK Model 2032(24CH)
Digital Plotter HP Model 7470A
Data Storage System PC 486 Post Processor
Digital Plotter HP Model 7470A
Data Acquisition System HP Model 3835 S
Work Station System HP Model 9000-4335
20
Noise Data Measurement Reactor Operating
Conditions
Note Commercial Operation Date of Uljin Unit 1
NPP 1988. 9.10
21
Power Spectral Density Measurements
22
Power Spectral Density Measurements
23
Power Spectral Density Analysis Results
24
Power Spectral Density Analysis Results
25
Cross Power Spectral Density, Phase, Coherence
Measurement
26
Cross Power Spectral Density, Phase, Coherence
Measurement
27
Cross Power Spectral Density, Phase, Coherence
Measurement
28
Cross Power Spectral Density Analysis Results
29
Noise Descriptor Analysis Results

• FA 1st Bending Mode Vibration 3.06Hz
• FA 2nd Bending Mode Vibration 6.18Hz
• CSB Beam Mode Vibration 8.25Hz
• CSB Shell Mode Vibration 20.6Hz
• Unknown Vibrations 4.7/ 17.4Hz

30
3. Simulation Study on CSB Vibrations of Uljin
Unit 1 Reactor

• Structural Modeling for CSB Vibration
• Structural Modal Analysis Results
• Simulation of Abnormal Vibrations
• Discussions

31
Structural Modeling for CSB Vibration

• ANSYS 5.0 version 4.3 computer code was used.
• 3 dimensional cylindrical model was introduced
  for the modeling of CSB/TS (4444 model).
• Z-directional movement effect was neglected
  because the upper flange of CSB is clamped.
• Mechanical properties of CSB assumed fixed values
  (?7,900?/m3, E171.6GPa, ?0.3).
• Hydraulic and structural effects caused by
  reactor coolant, fuel assemblies and support
  structures were considered with the use of
  vertical mass concept.
• To simulate abnormal conditions, stepwise
  relaxation of CSB clamping were considered.

32
Structural Modeling for CSB Vibration
33
Structural Modal Analysis Results
Fundamental Beam Mode Vibration
Fundamental Shell Mode Vibration
34
Structural Modal Analysis Results
Beam Mode 1 / Shell Mod 3 Vibration
Beam Mode 1 / Shell Mod 4 Vibration
35
Structural Modal Analysis Results
Beam Mode 2 / Shell Mod 3 Vibration
Freq. Response for Forced Harmonic Exciting
36
Structural Modal Analysis Results
37
Simulation of Abnormal Vibrations
38
Simulation of Abnormal Vibrations
Freq. Shift Rate ( Normal Res. Freq.
Shifted Freq.) / (Normal Res. Freq.)
39
Discussions

• Resonance frequencies obtained from FFT analysis
  relatively well indicate the CSB vibration
  conditions.
• Resonance frequency of 1st beam mode vibration
  shift to lower frequency region when CSB clamping
  is released.
• Resonance frequency of 2nd shell mode vibration
  shift to lower frequency region when CSB clamping
  is released.
• For other vibration modes, resonance frequencies
  are shifted slightly but negligible when CSB
  clamping is released.

40
4. Concluding Remarks

• Reactor noise analysis technique can be a useful
  tool to diagnose abnormal vibration of reactor
  internals if sufficient base-line database are
  provided.
• The CSB 1st beam/2nd shell mode vibration
  frequencies serve as an structural integrity
  criteria of CSB nozzle and flange clamping.
• For the practical application of reactor noise
  analysis technique to nuclear plants, intelligent
  instrumentation system should be developed.