Special features of ITER Cryogenic system A. Girard*, JY Journeaux, JM Poncet*, and CEA cryogenic group CEA Grenoble* and Cadarache Outline 1. Tokamak operation from CEA Tore Supra experience 2. ITER: A very compact system, with complex scenarios 3. Challenges for refrigerators 4. Challenges for the Cryodistribution 5. Cryogenic instrumentation close to the torus IBF 10-11 dec- A. Girard CEA-Grenoble/DSM/DRFMC/SBT - 1
Tore Supra experience: some conclusions Tore Supra: the first superconducting tokamak; Superfluid helium, only TF coils are superconducting => limits the pulsed load However: buffering of 4 K pulsed loads through ct volume buffers with HX Heat loads: keep a safety factor sufficient ( ~1.5) Safety of the installation: avoid any accidental warm up above 80 K Instrumentation: install enough sensors to derive a reliable energy balance IBF 10-11 dec- A. Girard CEA-Grenoble/DSM/DRFMC/SBT - 2
Challenges for ITER: magnet scenarios ITER: more ac losses than in TS + large nuclear heating => Strongly pulsed heat loads reference scenario :: 15 MA, 400s 35000 30000 25000 Heat Load (W) 20000 15000 10000 5000 0 00 1800 3600 5400 7200 9000 10800 time (s) IBF 10-11 dec- A. Girard CEA-Grenoble/DSM/DRFMC/SBT - 3
Challenges for ITER: cryopump scenarios It is mandatory to limit Hydrogen inventory => frequent regenerations at 100K 4 phases (each 150 s) 1 Helium recovery: SHe that fills the cryopump is pushed with warm (80K) He gas and liquefied through a JT valve 2 Warm up of the pump at 100 K: by using 80 K and 300 K temperature re level 3 Desorption of the gas by keeping the pump and the thermal shield at 100 K: by using 80 K and 300 K temperature level 4 Cool down of the gas: by using 4.5 K level This step requires liquefaction from the cryoplant Efficiency of the first phase? 100 %? 50 %? IBF 10-11 dec- A. Girard CEA-Grenoble/DSM/DRFMC/SBT - 4
Challenges for refrigerators: pulsed operation TS: large buffer => low pulsed heat load et the refrigerator LHC : ~ W/s ITER: 20 W/s for magnets without smoothing from by-pass valve Heat Load (W) 35000 30000 25000 20000 15000 10000 5000 0 Load from magnets Reference scenario : 15 MA, 400s/1800s Total Power - casing mass flow rate : 2.5 Kg/s - Voff 0 1800 3600 5400 7200 9000 10800 time (s) Load (kw) 20 18 16 14 12 10 8 6 4 2 0 Load from cryopumps Heat Load from cryopumps in the 3000 s scenario 0 5000 10000 15000 20000 25000 30000 Time (s) IBF 10-11 dec- A. Girard CEA-Grenoble/DSM/DRFMC/SBT - 5
Challenges for refrigerators: parallel operation 80K 20bar Quench Tanks PF, CS, CC SVs, 20bar (quench line) PF CS TF and structures SVs HP Dirty helium storage Cvbs cryopump 16 bar Current leads LN2 plant Dryers Warm buffer 1-18 bar MP LP HP LN2 Plant Module for cryopumps 50K 50K 80K He Loop 80K He Loop Purifiers 100 m3 LN2 Tank(s) GHe 80K GHe 100K SHe 4.5K GHe 5K GHe 50K To Tokamak building ACBs Magnets and Structures LHe 4.5K GHe 80K GHe 100K SHe 4.5K GHe 5K ACB Cryopumps LHe 4.5K Cold valve Warm valve 300K 18bar to 470K box LN2 plant LHe 25m 3 tank IBF 10-11 dec- A. Girard CEA-Grenoble/DSM/DRFMC/SBT - 6
Refrigerators: towards a reliable modelling (1/2) Modelling of transients => better confidence in the controllability of the cryoplant + training of operators IBF 10-11 dec- A. Girard CEA-Grenoble/DSM/DRFMC/SBT - 7
Refrigerators: towards a reliable modelling (2/2) Validation, comparison with experiment of the Brayton cycle: Perturbation: Fast reduction of the inlet valve of the Turbine (30%=> 15%) Inputs = measured data Débit (en g/s) 80 70 60 50 40 30 20 Débit 3_HP Mesuré Débit 3_HP Simulé 0 200 400 600 800 1000 1200 1400 1600 Temps (en Seconde) 8 T4_LP P NEF4 NEF3 P,T T3_HP Température (en K) 7,5 7 6,5 6 5,5 5 4,5 T3_LP T2_HP 4 3,5 T1_HP mesurée T1_HP Simulée NEF2 Expander 3 0 200 400 600 800 1000 1200 1400 1600 Temps (en Seconde) T2_LP 60 NEF1 55 T1_LP LHe - 4.5K 1.25b NS1 LHe Storage T1_HP Niveau (en %) 50 45 40 35 Niveau NS1 Mesuré Niveau NS1 Simulé W 30 0 200 400 600 800 1000 1200 1400 1600 Temps (en Seconde) IBF 10-11 dec- A. Girard CEA-Grenoble/DSM/DRFMC/SBT - 8
Cryodistribution HX in the ACB Structures : Fins Lhe bath property : 1.09 bar ; 4.3K Supercritical helium property : 6 bars ; Temperature Inlet 5.25 K ; Temperature Outlet 4.4 K ; Mass flow rate : M = 4.5 kg/s Power evacuated ~ 16 kw SHe => T ~ 0.1 K, operation between 3.6 and 4.3 K LHe Plates Cold Circulation pumps in the ACBs Mass flow rate > existing circulators ( 1.2 kg/s) High efficiency IBF 10-11 dec- A. Girard CEA-Grenoble/DSM/DRFMC/SBT - 9
Cryodistribution: cold boxes (ACB and CVB) Very compact design small LHe bath of the ACB => no «buffering effect» access conditions questionable magnetic field high radiation level? IBF 10-11 dec- A. Girard CEA-Grenoble/DSM/DRFMC/SBT - 10
Cryogenic instrumentation Heavy constraints: * magnetic field => shielding * neutron radiation => electronics should be put far away * Large temperature range : for Cryopumps, 4 K -> 470 K! Efforts to determine the instrumentation adapted: * sensors: temperature, pressure, mass flow rate, strain. * electromechanical devices (valves, ) IBF 10-11 dec- A. Girard CEA-Grenoble/DSM/DRFMC/SBT - 11
Conclusion Past experience from Tore Supra and LHC gives us a good confidence to solve the technological challenges raised by the ITER cryogenic system. However, these challenges, involving all the partners (magnets, current leads and CTBs, cryopumps, cryodistribution ) will need combined efforts of ITER, DAs, associations, CEA, and industrials IBF 10-11 dec- A. Girard CEA-Grenoble/DSM/DRFMC/SBT - 12