OECD/NRC BWR Peach Bottom-2 Turbine Trip Benchmark – 2 nd Workshop, Villigen,October 2001

1. PAUL SCHERRER INSTITUT PB2 TTRIP Phase 2 Coupled 3D Kinetics/Core Thermal-Hydraulic BC Analysis with CORETRAN H. Ferroukhi, W. Barten, P.Coddington OECD/NRC BWR Peach Bottom-2 Turbine Trip Benchmark – 2nd Workshop, Villigen,October 2001

2. PAUL SCHERRER INSTITUT CONTENTS • CORETRAN and RETRAN-3D at PSI • PB2 TTRIP Phase 2: 3-D Kinetics with Core T/H Boundary Conditions • Steady-State Results • Transient Results • Summary

3. CORETRAN • 2 Group, 3-D • Core Static Depletion and Transients • Neutronics • ARROTTA (ANM) • ANM-NEM /CMFD • Thermal-Hydraulics • VIPRE-02 • Stand Alone Sub- Channel Analyses • 3 Eq. HEM to 6 Eq. • RETRAN-3D • 2 Group, 3-D • Core and Plant System Transients • Neutronics • ARROTTA (ANM) • ANM-NEM /CMFD • RETRAN Thermal-Hydraulics • 3 Eq., 4 Eq., 5 Eq. PAUL SCHERRER INSTITUT CORETRAN and RETRAN-3D at PSI • PSI transient code environment with CORETRAN / RETRAN-3D

4. PAUL SCHERRER INSTITUT PB-2 Phase 2: Objectives at PSI • ANALYSIS WITH CORETRAN: Coupled 3-D Kinetics/Core Thermal-Hydraulic BC Model • Steady-state at both TT2 Conditions and HZP • Transient Analysis: • Analysis performed and submitted • ANALYSIS WITH RETRAN-3D: Coupled 3-D Kinetics/Core Thermal-Hydraulic BC Model • RETRAN-3D Model needs to be set-up for Phase 3 but can also be used for Phase 2 • Model set-up based on CORETRAN • Lumped Model necessary in RETRAN-3D (Homogenized T/H Feedback Variables !) • Steady-State analysis at HZP to verify consistency in Neutronic Solution CORETRAN-RETRAN-3D • Steady-State and Transient Analysis at TT2 Conditions with 33-T/H Lumped Model • Assess differences between CORETRAN and RETRAN-3D • Influence of T/H solution and void model • Influence of T/H feedback homogenization • Analysis with RETRAN: 1-D Kinetics • Additional exercise if time available • Valuable to assess differences 1-D/3-D

5. PAUL SCHERRER INSTITUT PB2 Phase 2: CORETRAN Model of PB2 • ANM Neutronic Algorithm (ARROTTA) • 6 Equation 2 Fluid T/H Model (VIPRE-02) • Full Core Representation • 1x1 Neutronic and T/H Radial Mesh • Bypass = 1 Additional T/H Channel • No Bypass Void • Detector Model • X-S model modified • X-S tables read directly • Use of provided X-S interpolation routine • Xenon densities read as Restart file • No Decay Heat Model

6. PAUL SCHERRER INSTITUT PB2 Phase 2: CORETRAN Steady-State Results

7. PAUL SCHERRER INSTITUT Note on Spacer Void Model • Spacer Void Model (SVM) available in SIMULATE-3 to treat void accumulation at Spacer Grids • PSI Experience with Swiss BWRs shows very good agreement with TIP with the SVM • Assessment CORETRAN/SIMULATE performed at PSI for Swiss LWRs show that the SVM has a • Strong impact on the axial power shape in the boiling zone • Strong impact on the core reactivity (more negative void coefficient in boiling zone)

8. PAUL SCHERRER INSTITUT PB2 Phase 2: CORETRAN Transient Results • Analysis 1: Boundary Condition = Total Core Flow versus Time • 6 Eq. + NBC • FIBWR Flow Split Model in quasi-static mode • Pressure-Flow Convergence Problems Power and LPRM Core Flow Pressure

9. PAUL SCHERRER INSTITUT PB2 Phase 2: CORETRAN Transient Results • Analysis 2: Boundary Condition = (33 T-H Channels) + ( Bypass Channel) Flow versus Time • No FIBWR Model No Bypass Correction (Nominal) With Bypass Correction (BC1)

10. PAUL SCHERRER INSTITUT PB2 Phase 2: CORETRAN Transient Results • Sensitivity Studies: Boundary Condition = (33 T-H Channels) + ( Bypass Channel) Flow versus Time • Time Step Size • SCRAM Signal Time Step Size SCRAM Signal

11. PAUL SCHERRER INSTITUT PB2 Phase 2: Summary • CORETRAN Model for PB-2 Exercise 2 Set-Up • Steady-State Analysis at TT2 Conditions • Good agreement with PB1 Edit • Axial Power Shape (Caution on spacer void) • Core Average Void Fraction, Average Exit Quality, Core Pressure Drop • Very High K-eff • Transient Results • Analysis with total ore flow BC + FIBWR flow split UNAPPLICABLE • Analysis with 33-TH Channel flow BC • No Bypass Correction gives slight under prediction of power peak (Nominal Case Submitted) • Later analysis with Bypass Correction shows better agreement with measurements • Sensitivity Analysis • Large sensitivity on time-step size • Small Time-Step size of 1ms selected • Choice of SCRAM on 95% power instead of defined t=0.63 s seems more adequate • but leads to earlier and lower power peak magnitude • Next Step is to perform similar analysis with RETRAN-3D before Phase 3

12. PAUL SCHERRER INSTITUT PAUL SCHERRER INSTITUT PB2 Phase 2: CORETRAN Bypass Model • CORETRAN PB2 Bypass Model • Defined Leakage Paths • Core Support Plate • Control Rod Drive Housing • Assembly Lateral Leakage • Path a: Through Lower Tie Plate Holes (9 in FIBWR) • Path b:between Channel Box and Lower Tie Plate (8 in FIBWR) • Path c:Water Rods • All Paths to ONE SINGLE BYPASS T/H CHANNEL • Bypass Geometry • Assumed Core Shroud Diameter • D_CS = 5.6 m (220.47 in) • Based on EPRI Report NP-563 • Assumed Assembly Outer Pitch • P_OUT = 0.1365 m (5.37 in) • Bypass Flow Area = 7.5 m2 (11570 in2) 1 FIBWR Model All Leakage Paths defined by Flow-Pressure Drop Correlations