1. SCWR Thermal-Hydraulic Instability Analysis
SCWR Information Exchange Meeting
University of Wisconsin, Madison
April 29-30, 2003
SCWR Thermal-Hydraulic Instability Analysis
J. Zhao, P. Saha, M. S. Kazimi, P. Hejzlar
Massachusetts Institute of Technology
Cambridge, MA 02139
CANES
Center for Advanced Nuclear Energy Systems
April,2003

2. 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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3. U.S. Gen-IV Reference Design
Fuel
Assembly
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4. U.S. Gen-IV Reference Design
RPV
Diagram
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5. 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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6. 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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7. Single (Average) Channel Representation.
0.195m Non-heated MPa
Node N
4.27m MPa MPa
(spacers MPa)
Node 1
0.195m Non-heated MPa
0.0662MPa
Kin= 47
Pin= 25 MPa
Tin= 280oC
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8. 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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9. 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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10. Characteristic Equation
Total transfer matrix
Mtran=Mnou* Mcore* Mnod * Mori
Characteristic equation
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11. Decay Ratio Input function impulse function of t Decay ratio R=
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12. Average Channel Decay Ratio
Average channel: Kin=47, R=0.0059
Channel is stable for decay ratio < 0.5 (Typical BWR Criterion)
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13. Hot Channel Analysis Hot channel power: q’h=1.4q’ave
With the same inlet orifice coefficient of Kin=47,
Very high exit enthalpy (unrealistic)
Reduced inlet orifice coefficient to maintain the same heat flux to flow rate ratio as the average channel
Gh=1.4Gave Kin=2.95
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14. Hot Channel Decay Ratio
Hot channel: Kin=2.95, R=0.38
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15. Sensitivity to System Pressure
Changed system pressures to 23MPa, 25MPa and 27MPa, keeping other parameters unchanged
P=23MPa, R=0.51; P=25MPa, R=0.38; P=27MPa, R=0.29
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16. Conclusion
U. S. Gen-IV SCWR design is stable for both average and hot channels
For average channel, high inlet orifice coefficient (Kin=47) 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 Kin=2.95 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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17. Future work Loop thermal-hydraulic stability analysis for SCWR
Thermal-Nuclear coupled stability analysis for both parallel channel and system loop
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