1. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft EUROTRANS DM1-WP1.5 Mtg. Stockholm, May 22-23, 2007 Some Recent Results of Blockage Accident and CCI Phenomena Simulations for EFIT IP EUROTRANS DM1 (WP 1.5) Some Recent Results of Blockage Accident and CCI Phenomena Simulations for EFIT W. Maschek, P. Liu, X. Chen, S. Wang, M. Flad * Forschungszentrum Karlsruhe, IKET Postfach 3640, D-76021 Karlsruhe werner.maschek@iket.fzk.de * ProScience GmbH, Parkstrasse 9, D-76275 Ettlingen

2. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft 1. Results of Blockage Accident Simulations for EFIT 2. SIMMER Validation and Recalculation of JEAE Experiments 3. Conclusions and Outlook Content

3. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft BA Simulation for 3-Zone Design Proposals for DM3-AFTRA ADT-400 q 400 MWth three-zone core with MgO matrix fuel and 18/90/216 subassemblies q Core void worth : 6237 pcm q UBA simulation with SIMMER-III (2D) q Blockage assumed at inner subassembly ring inlet with 6% remaining flow q Subassembly ring with high fuel temperatures but low void worth q Identification and investigation of key parameters q Fuel damage, fuel removal phenomena and ‘floating’ in case of pin damage ?

4. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft AFTRA ADT-400 UBA Transient Analyses (1) MgO CERCER 3-Zone Core Blockage Transient  Blockage location (radial & axial)  He & fission gas pressure in pin as parameter - 10 bar to 50 bar  Radial heat exchange between SA is taken into account (or not)  Influence of clad failure conditions/times and pellet behavior  T fail – 1 : clad failure with gas blowdown  T fail – 2 : loss of clad strength and start of pellet/chunk/particle movement  Failure locations  Clad behavior & removal  Unclad fuel pellet (stack) behavior (chunks)  Behavior of upper pin & bundle structures  Upper flow paths

5. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft AFTRA ADT-400 Transient Analyses (2) MgO CERCER 3-Zone Core Blockage Transient  Innermost ring blocked at core inlet  Clad failure at 38 s, He & fission gas blows out, reactivity increase  Rewetting  Clad ‘melting’ at 55 s  Time to pin damage ~ 25 s  Fuel sweep out  Reactivity and power drop  Beam shut-down needed

6. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft Influence of – upper subassembly design in UBA Influence of – upper subassembly design- in UBA Fuel pin breakup happens at around 1500-1700 K (Clad thermal failure), Fuel ‘particles’ volumetrically equal to one pellet  In case upper in-bundle structures (top-cap, etc.) cannot be removed and pellet does not break-up, fuel sweep-out is jeopardized. Fuel Assembly Gas plenum and top cap of the pin AFTRA ADT-400 Transient Analyses (3)

7. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft  In an assumed UBA (unprotected blockage accident), fission gas/He blow- down will take place, which in the current calculations causes a short transient increase in the reactivity and power due to positive coolant voiding effect.  Rewetting after blow-down, further heating up of coolant, clad melting and fuel disintegration  Blockages analyzed not in the ‘high void worth regions’. Investigations on propagation potential for high void regions show no significantly different scenario.  Fuel sweep-out from the blocked SA rings after fuel pin breakup could be a significant reactivity mitigating mechanism (prevention of criticality)  Sweep-out and power reduction additionally important for extending grace-time for blockage detection and beam shut-down.  Scenario dependent on numerous conditions and parameters  Scenario dependent on numerous conditions and parameters (e.g. blockage location) Results of AFTRA ADT-400 Transient UBA Analyses (1)

8. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft  Influence of pellet behavior : if break-up into small particles, sweep-out possible if break-up into small particles, sweep-out possible if pellet does not disintegrate – solid chunk jamming, fuel sweep-out difficult, radial damage propagation into neighboring subassemblies if pellet does not disintegrate – solid chunk jamming, fuel sweep-out difficult, radial damage propagation into neighboring subassemblies nfluence of upper subassembly design and structure behavior :  Influence of upper subassembly design and structure behavior : in case upper pin structure (fission gas plenum part, top-cap) cannot be removed and swept out of bundle, solid jamming will prevent fuel release; mechanical design of importance in case upper pin structure (fission gas plenum part, top-cap) cannot be removed and swept out of bundle, solid jamming will prevent fuel release; mechanical design of importance dependency on pellet behavior, heat transfer conditions etc. dependency on pellet behavior, heat transfer conditions etc. Potential radial damage propagation into neighboring subassemblies Potential radial damage propagation into neighboring subassemblies  Gas plenum pressure of limited influence on ‘voiding’ (impact on failure)  High temperature behaviour of fuels & structures and failure behaviour needs to be understood  ‘Floating fuel’ assumption (prevention of criticality) not easy to defend Results of AFTRA ADT-400 Transient UBA Analyses (2)

9. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft Code Validation : Coolant-Coolant-Interaction Problem (CCI) Integral accident code must be able to simulate FCI phenomena properly. SIMMER-III: Successful validation work in the area of FCI and steam explosion during SIMMER Phase-II assessment (1999-2000) : sodium and water (see table below) Pb/Bi – water interaction experiments: Sibamoto tests by JAEA Some new activities in Fuel-Coolant Interaction (FCI) area: FZK & ENEA & Univ. of Pisa - HLM (Pb, Pb/Bi) and water

10. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft CCI Problem : Code Validation for HLM Multiphase Flow Sibamoto’s Experiments of JAEA – Water-HLM Interaction Tests Experiment#2#3#4#5 v jet [m/s]7.56.96.24.7 T jet [K]298 T pool [K]823778820778 Series A : Injection of water into Pb/Bi pool Cavity depth and void volume measured Simulation by FZK Series B : Injection of Pb/Bi in water pool Vapor production rate measured Simulation by ENEA Series A Tests : Normalized pentration depth

11. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft Experimental Interpretation via Jet Penetration Modes IWGFR/89 : O-arai, June 6-9, 1994: K. Konishi et a. T-H 2 O > T-Jet < T-H 2 O > T-Jet > T-H 2 O < T-Jet >> T-H 2 O << T-Jet >

12. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft CCI Problem : Code Validation for HLM Multiphase Flow Sibamoto’s Experiment of JAEA – A: Water Injection into Pb/Bi SIMMER gives good representation of penetration depths and masses displaced Cavity depth vs. time (variation of jet velocity and pool temperature) Exp. # 2 v jet = 7.5 T pool = 823 Exp. # 3 v jet = 6.9 T pool = 778 Exp. # 4 v jet = 6.2 T pool = 820 Exp. # 5 v jet = 4.7 T pool = 778

13. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft Conclusion – Simmer is O.K ??? Comparison of test results and SIMMER-III simulation Simulation results: G. Bandini CCI Problem : Code Validation for HLM Multiphase Flow Sibamoto’s Experiment – B: Pb Injection into Water Experimental results Measurement of Pb/Bi and void volume: Radiography image processing volume data Good representation of time delay before expansion, slope and maximum vapor generation

14. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft SIMMER Geometric Model for SGTR Simulation 2D R-Z Simulation with axis in target region Modeling of flow paths and pressure drops Simulation of 1, 5 and 91 tubes ruptured Complex problem (physics & numerics) – multiphase flow, coolant-coolant interaction problem (CCI) 3D simulation (SIMMER-IV) requires extensive CPU time => therefore 2D simulation SIMMER Geometric Model EFIT rector FZK Simulation with SIMMER-III (2D)

15. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft SGTR Simulation Result for 1 SGT (91 tubes) SIMMER Simulation: Results SG water discharge: 0.6 kg/s/tube Water vaporizes almost instantaneously Steam escapes to cover gas region and leaves through exits No penetration of steam into core region and no core voiding Cover gas pressurization & sloshing No CCI event observed active zone core SGT H2O Onset of SGTR

16. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft Conclusions and Outlook  Blockage Accident simulation using SIMMER-III (2D)  SIMMER-IV (3D) simulation only warranted in case of severe influence of 3D effects on scenario, phenomena or assessment of scenarios/phenomena  Blockages assumed with minimal rest-flow ~ 5-6 %  Simulations show spread of scenarios depending on fuel, clad and structural behavior  Scenarios with fuel sweep-out (‘floating’) and scenarios with radial damage propagation into neighboring subassemblies or target structures identified  Simulation of SGTR event using SIMMER –III (2D)  SIMMER code improvements for HLM flows and EOS for LBE and Pb, in the past extensive code validation program for FCI  SIMMER simulation of JAEA HLM experiments with good representation of penetration depths and vapor volume generation etc. (CCI).  Further experiments of larger scale needed  According to present calculations no core voiding to be expected for SGTR from 1 tube up to 91 tubes (1 full SG).  Sloshing phenomena and cover gas pressurization identified

17. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft THE END

18. Transmutation and ADS Safety Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft SIMMER-III/IV codes are 2D/3D fluid dynamics code coupled with a structure model and a 2D/3D space-, time- and energy-dependent neutron dynamics model Fluid Dynamics  8 velocity fields (7 for liquid, 1 for gas)  Multi-phase, multi-component flow  Phase transitions  Flow regime (pool-channel)  Interfacial area tracking  Elaborate EOS (fuels, structure, coolants & gases)  Heat and mass and momentum transfer Neutronics  Neutron transport theory (S N DANTSYS)  Improved quasi-static method  Cross-section generation  Decay heating  External neutron source  Transient source importance Structure model  General structure model  Pin model (new fuels - development)  Axial + radial heat transfer  Virtual structure model  Structure disintegration  Freezing on structures C 4 P 1968/560 Group Master Library Basis: JEFF, JENDL, ENDF/B Full Range Neutron Spectrum SIMMER-III (2D) and SIMMER-IV (3D)