SCWR%20Thermal-Hydraulic%20Instability%20Analysis

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SCWR Thermal-Hydraulic Instability Analysis
SCWR Information Exchange Meeting University of
Wisconsin, Madison April 29-30, 2003

• J. Zhao, P. Saha, M. S. Kazimi, P. Hejzlar
• Massachusetts Institute of Technology
• Cambridge, MA 02139

CANES Center for Advanced Nuclear Energy Systems
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Objective

• To Study Thermal-Hydraulic Stability for SCWR
• Note
• 1. Large change in coolant density (777kg/m3
  to 90kg/m3 )
• 2. Low coolant flow rate (Average core
  inlet velocity of
• 1.3m/s)
• 3. High linear power (19.5kW/m in average
  channel)

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U.S. Gen-IV Reference Design

• Fuel
• Assembly

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U.S. Gen-IV Reference Design

• RPV
• Diagram

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Stability Analysis (Type Methodology)

• Type of Instabilities
• 1. Single/parallel channel instability
• 2. Loop instability
• Methodology
• 1. Time domain
• 2. Frequency domain

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Present Analysis

• Single Core Channel Average and Hot
• Frequency Domain
• - Used Small Perturbation, Linearization and
• Laplace Transformation Technique
• - Imposed Constant Pressure B. C.
• - Determined Transfer Function between
  Channel
• Pressure Drop and Inlet Velocity
• - Determined Decay Ratio for the most
  dominant pole

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Single (Average) Channel Representation

• .
• 0.195m Non-heated
  0.0054MPa
• Node N
• 4.27m
  0.0764MPa 0.15MPa
  
• 
  (spacers 0.01438MPa)
• Node 1
• 0.195m Non-heated
  0.0020MPa
• 
  0.0662MPa
• 
  Kin 47
• 
  Pin 25 MPa
• 
  Tin 280oC

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Single Channel Analysis

• Governing Equations
• Mass conservation equation
• Momentum conservation equation
• Energy conservation equation
• Equation of state
• ASME software based on IAPWS-IF97 is
  used to calculate water properties

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Transfer Functions or Matrices

• Orifice inlet to core inlet (non-heated region)
• Non-heated region to heated region (first node)
• Heated region (first node to node N)
•  
• Node N to core exit (non-heated region)

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Characteristic Equation

• Total transfer matrix
• MtranMnou Mcore Mnod Mori
• Characteristic equation

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Decay Ratio

• Input function
• impulse function of
• 
  t
• Decay ratio
• R

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Average Channel Decay Ratio

• Average channel Kin47, R0.0059

Channel is stable for decay ratio lt 0.5 (Typical
BWR Criterion)
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Hot Channel Analysis

• Hot channel power
• qh1.4qave
• With the same inlet orifice coefficient of
  Kin47,
• Very high exit enthalpy (unrealistic)
• Reduced inlet orifice coefficient to maintain the
  same heat flux to flow rate ratio as the average
  channel
• Gh1.4Gave Kin2.95

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Hot Channel Decay Ratio

• Hot channel Kin2.95, R0.38

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Sensitivity to System Pressure

• Changed system pressures to 23MPa, 25MPa and
  27MPa, keeping other parameters unchanged
• P23MPa, R0.51 P25MPa, R0.38 P27MPa, R0.29

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Conclusion

• U. S. Gen-IV SCWR design is stable for both
  average and hot channels
• For average channel, high inlet orifice
  coefficient (Kin47) is needed to produce core
  pressure drop of 0.15MPa
• Average channel is very stable (a very small
  decay ratio) due to large inlet orifice
  coefficient
• For hot channel, the inlet orifice coefficient is
  reduced to Kin2.95 to maintain the same heat
  flux to flow rate ratio as the average channel
• Hot channel is also stable, although its decay
  ratio is larger than that of the average channel
• Channel T-H stability is sensitive to pressure.
  Reducing pressure will destabilize system, while
  increasing pressure will stabilize system.
  Similar to a BWR system.

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Future work

• Loop thermal-hydraulic stability analysis for
  SCWR
• Thermal-Nuclear coupled stability analysis for
  both parallel channel and system loop