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THE COUPLED TRAB-3D-SMABRE CODE FOR 3D TRANSIENT AND ACCIDENT ANALYSES

THE COUPLED TRAB-3D-SMABRE CODE FOR 3D TRANSIENT AND ACCIDENT ANALYSES. J. Miettinen & H. Räty VTT Processes SAFIR mid-term seminar, January 20-21, 2005, Espoo. Coupled TRAB-3D - SMABRE code. GOAL OF DEVELOPMENT CODES TRAB-3D SMABRE COUPLING parallel Internal

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THE COUPLED TRAB-3D-SMABRE CODE FOR 3D TRANSIENT AND ACCIDENT ANALYSES

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  1. THE COUPLED TRAB-3D-SMABRE CODE FOR 3D TRANSIENT AND ACCIDENT ANALYSES J. Miettinen & H. Räty VTT Processes SAFIR mid-term seminar, January 20-21, 2005, Espoo

  2. Coupled TRAB-3D - SMABRE code • GOAL OF DEVELOPMENT • CODES • TRAB-3D • SMABRE • COUPLING • parallel • Internal • TRAB-3D - SMABRE STATUS, January 20, 2005

  3. Basic nuclear data Nuclear data processing Nuclear data libraries (25 - 70 energy groups) Calculation of assemblywise two group constants Calculation of reactivities, power and burnup distributions etc. Data transfer and condensation for one- dimensional group constants One-dimensional dynamics codes Three-dimensional dynamics codes Reactor analysis calculation system of VTT Processes ENDF/B, JEF = codes developed by VTT = codes partly developed by VTT NJOY = codes applied by VTT CASMO libraries CASMO-4 CASMO-HEX Steady state fuel rod behaviour (also probabilistic analyses) hexagonal Square hexagonal HEXBU-3D SIMULATE ENIGMA, FRAPCON ARES square VVER CROCO Fuel rod behaviour during RIAs and LOCAs TRAB SMATRA BWR PWR SCANAIR, FRATRAN TRAB-3D HEXTRAN FRAPTRAN- GENFLO BWR, PWR VVER

  4. Goal of TRAB-3D - SMABRE development • Replace the hydraulics solution in the 3D core with SMABRE • Quick remedy to known deficiencies in the model => calculation of transients with flow reversal in core and by-pass • General SMABRE thermal hydraulics possibly not as accurate in the core as with the present model of TRAB-3D or with a future application using the accurate PLIM hydraulics solver • SMABRE solution allows new features into the circuit modelling • May act as a reference for a later TRAB-3D - PLIM calculation • Opens options to model an open core or couple to other system codes • High priority, high uncertainties

  5. TRAB-3D transient and accident analysis code • 3D neutronics with quadratic core geometry • A fast two-level iteration nodal method with only one solved variable for each node in the outer iteration • Implicit time-discretization methods allow flexible time-step choices • 1D parallel channel hydraulics for the core • Includes for a BWR circuit: the main circulation system inside the pressure vessel, steam lines, pumps and control systems • Core and circuit thermal hydraulics iterated together with neutronics during each time step • Separate core model can be coupled to the fast-running SMABRE system code for PWR calculations

  6. Validation summary of TRAB-3D

  7. TRAB-3D applications • Olkiluoto BWR • typically 500 channels in the core, • 25 axial nodes, 11 radial mesh • points in the fuel pellet • Olkiluoto 3 EPR • (coupled to SMABRE) • SWR1000 concept • BWR90+ concept • Best estimate or conservative analyses, stability studies • Accurate calculation of core with actual fuel types of the loading • Reasonable computing effort

  8. SMABRE circuit model • A node-junction hydraulic circuit code similar to RELAP • Solution method non-iterative • Five flow equations • Very fast • Used coupled to core codes for modelling PWR circuits • Includes a point kinetics neutronics model

  9. ­­­­­­­­­­­ Reference plant Volume Scaling Experiments carried out LOFT Westingh. 1:50 2.5 % cold leg SBLOCA, RCP on LOBI/ Mod1 KWU 1:712 0.4 % cold leg SBLOCA LOBI/ Mod2 KWU 1:712 1.0 % cold leg SBLOCA PIPER-ONE GE BWR 1:2200 2.6 % recirculation line break, ISP-21 DOEL real plant 1:1 Real plant SGTR accident, ISP-20 SPES Westingh. 1:427 Loss of feedwater, with core heatup, ISP-22 ROSA-IV Westingh. 1:48 5 % cold leg SBLOCA, ISP-26 PMK VVER 1:2070 7.4 % cold leg SBLOCA SMABRE VALIDATION OF THERMOHYDRAULICS

  10. SMABRE TYPICAL APPLICATION • Loviisa VVER-440 • SBLOCA and ATWS • Loop seal effects • Multilayer steam generator • Reactor vessel with parallel channels

  11. Present coupling of TRAB-3D and SMABRE cores,= PARALLEL COUPLING • Totally independent codes coupled together • Thermal-hydraulics of the core is calculated with both codes. • Connection by data exchange once in a time-step • First applications with 3-D neutronics in 1991 - 1992, with 1-D neutronics 1988

  12. Power to coolant HEAT CONDUCTION IN FUEL ROD HYDRAULICS Heat transfer mechanisms Coolant and soluble poison properties Surface temperature of fuel rod Heat flux HEAT TRANSFER FROM CLADDING TO COOLANT Power Directly to coolant Doppler temperature Power in fuel DIFFUSION PARAMETERS WITH FEEDBACKS NEUTRONICS New coupling of TRAB-3D and SMABRE cores,= INTERNAL COUPLING Coupling of physical processes in the core calculation

  13. New coupling of TRAB-3D and SMABRE cores,= INTERNAL COUPLING • Core hydraulics with SMABRE for each assembly • Heat transfer, neutronics with TRAB-3D • Connection by data exchange in every node • Iteration during a time-step • Connection analogous to that of TRAB-PLIM application • New approach at VTT, used in other organizations but usually with only a few channels in hydraulics and heat transfer by the system code

  14. COUPLED CORE CORE CHANNEL TRAB-3D SMABRE to circuit Heat Transfer Hydraulics Neutronics Local power directly to coolant Local - pressure - mass flux Local - coolant power temperature - heat flux Local Local fuel cladding temperature temperature Local - coolant density - soluble poison density from circuit - coolant temperature New coupling of TRAB-3D and SMABRE cores,= INTERNAL COUPLING

  15. New coupling of TRAB-3D and SMABRE cores,= INTERNAL COUPLING • Options in thermal hydraulics geometry Standard TRAB features for describing BWR bundle geometry are maintained • Each bundle described with its own core channel • Different zones with different core inlet pressure drops (illustrated with colours in the picture) • Axial subregions in core with different characteristics (for describing part length rods) New SMABRE features allowing to include some three-dimensional phenomena in the lower and upper plena • lower plenum, core and upper plenum divided into circumferencial sectors and radial zones

  16. TRAB-3D - SMABRE, STATUS January 20, 2005 => A working steady state solution has been created and is being tested Challenges in modelling: • Two basically different modelling philosophies coupled together: TRAB-3D solutions designed for coupled iterations SMABRE solution non-iterative • Especially in steady state: SMABRE proceeds into a "steady state" by calculating forward in time, while TRAB-3D iterates • The coupled processes themselves are complex • TRAB-3D includes 20 years of reactor dynamics experience inside the integral model

  17. TRAB-3D - SMABRE, STATUS January 20, 2005 • Hydraulics solution separated from TRAB calculation • SMABRE's matrix solution has been developed to allow solutions of a large number of channels with a reasonable computing time • Interface created: connection at node level inside iterations • Macro for generation of SMABRE core geometry has been completed • A platform created for running different coupling schemes • Output routines for core hydraulics from SMABRE being tested: radial and axial core distributions, inlet, outlet and averaged variables • Steady state procedure and converge criteria completed and being tested • Connection options in heat transfer being tested

  18. TRAB-3D - SMABRE, STATUS January 20, 2005 cont. Next steps: • Once the steady state is found adequate, dynamics is more straightforward • An iterative matrix solution looks effective and will probably be applied • Testing of flow reversal • Validation Further possibilities in later development: • Use existing porosity model PORFLO for full 3D core thermal hydraulics in the open core • Connecting TRAB-3D to other system codes

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