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Thermohydraulic Analysis of Tore Supra/WEST TF Coil Quench

Investigating smooth quench occurrences in tokamak with associated data analysis and conclusions from CHATS 2019 workshop.

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Thermohydraulic Analysis of Tore Supra/WEST TF Coil Quench

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  1. ThermohydraulicAnalysis of Tore Supra / WEST TF CoilQuench: ASSOCIATED SMOOTH QUENCH OCCURRENCE IN TOKAMAKCHATS Workshop08-13/07/2019Szczecin, PolandS. Nicollet, A. TORRE, S. GIRARD, B. LACROIX, C. REUX, P. PROCHETCEA, IRFM, F-13108 Saint-Paul-lez-durance, FRance • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  2. SUMMARY • 1) Tore Supra / WEST TFC, Cooling circuit and QuenchDetection System • 2) SuperMagnet (THEA and FLOWER) Model • 3) Energy Balance, Runawayselectrons & Initial QuenchEnergy • 4) Results: Helium Pressure, Voltage, Resistance, Joule Energy, Hot Spot Temperature, Heliumexpulsed Mass Flow, Thermal Flux • 5) Discussion on Associated SmoothQuenchOccurence in Tokamak • 6) Conclusion | PAGE 2 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  3. 1) TORE SUPRA / WEST TFC COIL AND QUENCH 18 Coils: 165 t I Nom : 1400A L tot : 613 H B Nom : 9T (4,5T at plasma radius) I Op : 1255A E tot : 479 MJ B Op : 8,1T (3,9T at plasma radius) SuperconductingCoils: F av. 2,6 m - 2,5 t 26 double-pancakes, 39 turns 2028 spires StainlessSteelthick Casing: Fext : 3,3 m - 6,6 t Monolithicconductor: NbTi/Cu/CuNi 2.8 x 5.6 mm 11000 filaments - 1400A The 18 NbTiToroidal Field Coils (TF) Tore Supra/West Tokamak cooled by staticsuperfluidhelium bath at 1.8 Kand carry I=1255A. The Tokamak is operating since 1988 (IRFM). 19th december 2017, end of Plasma N°52205, (14:02:59), a quench on TFC09 detected first on an heliumliquidlevel (TNL) has triggered a currentfastdischarge. The Voltage quenchdetection (V) was at that time nearly to betrigerred. | PAGE 3 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  4. 2.1) SUPERMAGNET AND THEA MODEL • SuperMagnetmodel developedfor the CoilWinding Pack (CICC-likeTHEA model) • Monolithicconductorsrepresentinglarge strandswithheliumvoid fraction of 0,36 • THEA Quench initiation at x= 2 m (Ltot=7,17 m ), whereB=5,5 T and Tcs = 7,5 K Estimation of transient Voltage ThresholdUmodel,t: CICC-like Friction factor, void fraction Vf=36,1%: Colburn-Reynolds Analogy, Heat Exchange coefficient: NbTiBottura’s Law for Jc: Bc20 = 14.292 T, Tc0 = 9.767 K, C0= 50454.38377 106 AT/m², α = 1.137, β = 1.135, γ = 2.467, n = 1.70 | PAGE 4 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  5. 2.2) FLOWER MODEL • Externalquench circuit modelled by FLOWER: tubes, cold/warm safety valves, burstdisk, magnetic valve with pressure set) • TFC09 cooledwith a statichelium bath (at Tini=2,5 K) • Artificiallyadded manifold (inlet + outlet) & zero initial mass flow • Necessity to reducedrastically time step in the calculations | PAGE 5 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  6. 3.1) ENERGY BALANCE AND RUNAWAY ELECTRONS ComparisonScheme: Calculation/Measurements, Runaway/THEA Runawayelectrons of High Energy (30 MeV): Code GEANT4 At Plasma end: disruption + runawaywhichcollided on outboard plasma facing components creating high neutron and gamma flux  Energy=6,84 kJ in thick casing & 1,3 kJ in Coil. Small initiation zone: 0,3< dL <0,5 m, dY ~0,24 m and dR ~ 1 cm withMinimum QuenchEnergy | PAGE 6 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  7. 3.2) INITIAL QUENCH ENERGY: MQE THEA Minimum QuenchEnergy (MQE) from 2,5K to Tcs= 6,5K • QuenchedconductorsNumber ~ 100 • N_Y=39  dY=0,24 m, • N_R=3 dR=7,4mm E_1,69-2,5 K/ E_2,5 K-Tcs ~ 7% total He mass & heatcapacity ~ 16% with convective heat exchange coefficient Hconv E_2,5 K-Tcs ~ 2 *THEA MQE (temperature gradients) AvailableEnthalpyfrom 1,69 to 2,5 K: Simple Model ) eY=2,8 mm and Ncond=20 (Y-axis) τcond= 0,62 ; 1,39 ; 2,6 ; 4,6 s at T= 3 ; 4 ; 5 ; 6 K | PAGE 7 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  8. 4.1) COIL HELIUM PRESSURE Measured and CalculatedQuenchHelium Pressure in the Coil • Depending of Minimum QuenchEnergy, initiation length, duration and Umodel,t, • the calculatedcoilhelium pressurehas been used as comparison. • Maximal measured Pressure : 0,9 MPa & « Quenched » initial Length : 0,3 < dLength < 0,5 m • Near x=2 m and over 2,6 s duration for dL=0,4 m and Umodel,t = 100 mV (Ncond=20) | PAGE 8 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  9. 4.2) ESTIMATION OF THE VOLTAGE Measured and CalculatedQuenchResistive Voltage • Maximal measuredVoltage : 1400 V & • Maximal Calculated Voltage = 1300 V for 2,6 s duration for dL=0,4 m and Umodel,t = 100 mV (Ncond=20) • SlowerExperimentaldecreasedue to additionalfield(Tdischarge=120 s) for non-quenchedCoils& • Cuppermagneto-resistanceEffect | PAGE 9 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  10. 4.3) ESTIMATION OF THE RESISTANCE Deducedfrom Voltage Measurements and CalculatedQuenchResistance • Maximal deducedfrom Voltage Measurements, Resistance : ~ 6 W • Maximal CalculatedResistance = 3,5 Wfor 2,6 s duration for dL=0,4 m and Umodel,t = 100 mV (Ncond=20) • SlowerCalculated Values due to additionalfield(Tdischarge=120 s) for non-quenchedCoils& • Cuppermagneto-resistanceEffect | PAGE 10 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  11. 4.4) JOULE ENERGY DISSIPATED DURING AND AFTER QUENCH Deducedfrom Voltage Measurements and CalculatedQuench Joule Energy • Maximal deducedfrom Voltage Measurements, Joule Energy : ~ 18 MJ • Maximal Calculated Joule Energy = 20 MJ for 2,6 s duration for dL=0,4 m and Umodel,t = 100 mV (Ncond=20) • Good agreement betweenexperimental and calculatedresults | PAGE 11 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  12. 4.5) HOT SPOT TEMPERATURE Deducedfrom Voltage Measurements and CalculatedQuench Maximal Temperature • Maximal deducedfrom Voltage Measurements, Maximal Temperature: ~ 100 K • Maximal CalculatedTemperature = 100 K for 2,6 s duration for dL=0,4 m and Umodel,t = 100 mV (Ncond=20) • Good agreement betweenestimated (fromexperiments) and calculatedresults | PAGE 12 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  13. 4.6) HELIUM EXPULSED MASS FLOW QuenchCalculatedExpulsedHelium Mass Flow : • Opening of the cold safety valve and increase of Pressure  70 % of the 200l Heliumexpulsed in 5 s ! • Massflow of 5 to 6 kg/s (total helium mass ~ 30 kg = 25 kg in coil + 5 kg in cold tube) • Onlysmalleffect of quench conditions on mass flow (soundvelocity at outlet) • Decoupling of thick casing refrigeration circuit fromrefrigerator system smoothing of heatloads & TmaxHe thick casing : 27K. | PAGE 13 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  14. 4.7) HEAT FLUX DURING QUENCH • TS/WEST Quench Propagation Velocity 0,45 m/s (4 s to « inlet at 1,8 m & 11 s to « outlet » at 5,37 m) • Heat Flux average value near 0,15 W/cm² • SuperfluidHeliumStabilizingDisturbance (G. Claudet, 1979): 0,36 W/cm² (4,2 K) & 0,7 W/cm² (1,8 K) • LHC prototype magnet string heliumrecovery (Chorowski, 1998): few W/cm² | PAGE 14 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  15. 5) Discussion on Associated Smoothed Quench Occurrence in Tokamak ITER TFC Supercriticalheliumforced flow TS/ WEST TFC StaticsuperfluidHelium Bath JT-60SA TFC Supercriticalheliumforced flow Thermal Flux (W/cm²) vQ= 0,45 m/s 4 s to « inlet »& 11 s to « outlet » [CHATS, 2019] Bath All directions propagation Transversally Propagation (adjacent pancakes): < 1 s Normal Length (m) 16,1 < vQ < 22,6 m/s 113 m in 5 to 7 s [MT25, 2017] Quench Propagation Velocity vQ =20 m/swithpeaks at 70 m/s 380 m in 19 s [SOFT, 2010] CICC supercriticalheliumforced flow TransversallyPropagation(adjacent pancakes): >5 s for JT-60SA & 20 s for ITER Criticality and possible occurence of « smooth » quenchwithsmallheatdepositionlength at lowfieldregion (TS/WEST)  impact could lead to exceedsafety design « hot spot » criteria (ITER) [CEC-ICMC 2013] | PAGE 15 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  16. 6) CONCLUSION • A new SuperMagnetmodel has been successfullydeveloped for a Coil(CICC-like THEA model)cooled in staticsuperfluidhelium bath (Tini=2,5 K, Pini=0,13 MPa) • Depending of Minimum QuenchEnergy, initiation length, duration and model transientthreshold Voltage, the calculatedcoilhelium pressurehas been used as comparison. • The initiation zone issmall: dLength ~0,4 m (2,6 s duration & Umodel,t=100 mV , Ncond,ini=20) • Maximal Voltage ~ 1300 V & Maximal Resistance ~ 4 Ω (differencecaused by discharge time constant of non-quenchedcoils), Maximal Joule Energy ~ 20 MJ, Hot Spot temperature ~ 100 K (good agreement) • Calculatedexpulsedhelium mass flow rate of 6 kg/s confirms the observations • Thermal Heat Flux ~0,15 W/cm² and Quench Propagation velocity ~ 0,45 m/s • This eventconfirms the criticality and the possible occurrence of a socalled « smoothquench » caused by small initial heatdepositionlength at lowfieldregion. • The secondarydetection by thermohydraulicsignalsis more rapidthan the socalledprimarydetection by Voltage (2V, 1s) • This isusefull for other Tokamak magnetsquenchstudies and safeoperation • Aftercompleteelectrical, thermohydraulical and mechanicalanalysis and tests, WEST TFmagnetintegrity has been confirmedand has reoperated in 2018. | PAGE 16 • CHATS 2019, S. Nicollet, TS/WEST TFC Quench

  17. THANK YOU FOR YOUR ATTENTION Commissariat à l’énergie atomique et aux énergies alternatives Centre de Cadarache| 13108 Saint Paul Lez Durance Cedex T. +33 (0)4 42 25 62 25 | F. +33 (0)4 42 25 26 61 Etablissement public à caractère industriel et commercial | RCS Paris B 775 685 019 DSM IRFMSTEP 21-22 January 2015

  18. A-5.1) TORE SUPRA/ WEST QUENCH TFC09 (DECEMBER 2017) FEEDBACK (1/2) SOFT 2018 POSTER: ANALYSIS OF TORE SUPRA / WEST TOROIDAL FIELD COIL QUENCH AND THERMOHYDRAULIC MODEL WITH SUPERMAGNET Toroidal Field (TF) system of Tore Supra/West Tokamak: 18 NbTisuperconductingcoils, cooled by a staticsuperfluidhelium bath at 1.8 K carrying a current of 1255A. The Tokamak is operating since 1988 in CEA/IRFM 19th december 2017, at end of Plasma N°52205, (14:02:59), a quench on TFC09 detected first on an heliumliquidlevel (TNL) has triggered a currentfastdischarge. The Voltage quenchdetection (V) was at that time nearly to betrigerred. • SuperMagnetmodel has been developedfor a Coil(CICC-like THEA model)cooled in staticsuperfluidhelium bath (Tini=2,5 K, Pini=0,13 MPa) | PAGE 18 • RST, JT-60SA Résultats Tests & Modélisations TFC, 20/05/2019, S. Nicollet

  19. A-5.2) TORE SUPRA/ WEST QUENCH TFC09 (DECEMBER 2017) FEEDBACK (2/2) dL=0,3 m dY = 0,26 m dR= 2 cm Runawayelectrons of High Energy (30 MeV): GEANT4, At Plasma end: disruption + runawaycolliding on outboard plasma facing components creatinghigh neutron & gamma flux  E=6,84 kJ (thick casing) & 1,3 kJ (Coil). • Depending on Minimum QuenchEnergy, initiation length& duration,calculatedcoilheliumpressureusedas comparison. • Small initiation zone: 0,3<dL<0,5 m, dY~0,24 m and dR ~ 1 cm. • Calculated = Observedexpulsedhelium mass flow=6 kg/s • This eventconfirms the criticality and the possible occurrence of a socalled « smoothquench »caused by small initial heatdepositionlength at lowfieldregion. • Secondarydetection by thermohydraulicsignalsmore rapidthanprimarydetection by Voltage (2V, 1s) • Aftercompleteelectrical, thermohydraulical and mechanicalanalysis and tests, WEST TFmagnetintegrity has been confirmedand has reoperated in 2018. CHATS 2019 PAPER: THERMOHYDRAULIC ANALYSIS AND MODELS OF TORE SUPRA / WEST TF COIL QUENCH AND ASSOCIATED SMOOTH QUENCH OCCURRENCE RISKS IN TOKAMAK | PAGE 19 • RST, JT-60SA Résultats Tests & Modélisations TFC, 20/05/2019, S. Nicollet

  20. A-5.3) ITER QUENCH STUDIES and Calculation FEEDBACK: Hot spot for smoothquench • Range inductive voltage is [-0.1 V ; 0.1 V] • Range of resistive voltage threshold Vr= 0.2 V • Current decay will be initiated only after an action time Ta = Th + Tk + Tcb= 1.5 s pancake #8 (counter clockwise direction) at plasma end of burn, CICC Length =380 m Heat Input (173-174 m or 173.00-173.05 m) • TCO temperature (210 K) exceed the criterion of 150 K which is not respected. • Note: Thermal gradient between strands and jacket is nearly 40 K. • These results should be discussed considering also the likelihood of such a quench • Tore Supra /WEST Quench Feedback Smooth Quench appears near inner turns • (near CICC helium inlets) | PAGE 20 • RST, JT-60SA Résultats Tests & Modélisations TFC, 20/05/2019, S. Nicollet

  21. A-5.4) ITER QUENCH STUDIES and Calculation FEEDBACK: DETECTION by mass flowS On CICC Coils and especially JT-60SA (and ITER): complexquenchdetection,forced flow, possibility of « smooth » quench and « slow » propagation • 2 ITER-IO / CEA Contracts, Support Site Agreement, 2012-2015 •  Modelisation and analyses of quench of all cryo-magnetic system of ITER Tokamak • Proposed Classification of quench cases as a function of impacts/risks on Magnets • Aim: Assure the security of the Installation(ETF= 40 GJ and secondary detection “safety class”) • Recommendation of secondary quench detection based on He mass flows measurements • Question ?: Possibility for JT-60SA of quench detection studies based on “Cryogenic Sensors” (Signals from Cryogenic System) even far from the coil (several –tens- meters) Local Perturbation  propagation of the normal zone (quenched) Inlet He Outlet He • S. Nicollet et al., Thermal Behaviour and Quench of the ITER TF System during a Fast Discharge and Possibility of a Secondary Quench Detection, IEEE Trans. Appl. Superc., Vol. 22, N° 3, 2012. • S. Nicollet et al., Quench of ITER PFC Influence of some initiation parameters on thermohydraulic detection signals and main impact on cryogenic system, Cryogenics Vol 53, pp. 86-93, 2013. TFC 310 t H=17 m B=11,8 T Cold Terminal Box CTB 17 m Localisation of Thermohydraulic sensors, ~20 m Coil inlet Difference He mass flow, TCO, TF quenchwithoutFastDischarge | PAGE 21 • RST, JT-60SA Résultats Tests & Modélisations TFC, 20/05/2019, S. Nicollet

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