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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
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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) November-11-18
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U.S. Gen-IV Reference Design
Fuel Assembly November-11-18
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U.S. Gen-IV Reference Design
RPV Diagram November-11-18
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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 November-11-18
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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 November-11-18
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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 November-11-18
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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 November-11-18
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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) November-11-18
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Characteristic Equation
Total transfer matrix Mtran=Mnou* Mcore* Mnod * Mori Characteristic equation November-11-18
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Decay Ratio Input function impulse function of t Decay ratio R=
November-11-18
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Average Channel Decay Ratio
Average channel: Kin=47, R=0.0059 Channel is stable for decay ratio < 0.5 (Typical BWR Criterion) November-11-18
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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 November-11-18
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Hot Channel Decay Ratio
Hot channel: Kin=2.95, R=0.38 November-11-18
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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 November-11-18
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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 (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. November-11-18
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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 November-11-18
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