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Vacuum Pumping Systems M. Wykes

Vacuum Pumping Systems M. Wykes. FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide # 1/29. Components of the ITER Vacuum Pumping System. Primary torus cryopumps handling tritium during normal DT operation.

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Vacuum Pumping Systems M. Wykes

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  1. Vacuum Pumping Systems M. Wykes FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #1/29

  2. Components of the ITER Vacuum Pumping System Primary torus cryopumps handling tritium during normal DT operation Mechanical forepumps handling tritium during normal DT operation Type 2 diagnostics handling tritium during normal DT operation Type 1 diagnostics handling small amounts tritium during off- normal DT operation (+permeation?) NB cryopumps handling small amounts of tritium during dwell pumping (PFC desorption) Service Vacuum Pumping System handling small amounts of tritium during off- normal DT operation (leaks to primary vacuum) Cryostat high vacuum pumps handling small amounts of tritium during off- normal operation (i.e. T in cryostat, magnets warm) Heating & CD (excl. NB) pumping systems handling small amounts of tritium during off-normal DT operation FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #2/29

  3. Block diagram of ITER vacuum pumping systems FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #3/29

  4. Flow diagram of forepumping system FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #4/29

  5. ITER torus cryo-sorption pumps Not quite up to date! 4 years experimental data from scale model pump (4 m2 sorbent area) in TIMO test facility at FZK Test results form technical basis for design of 1:1 full scale pumps FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #5/29

  6. ITER torus cryo-sorption pumps- operation modes Pumping during bakeout: H isotopes, impurities (water, O2 bearing gases) GDC: H isotopes, He and impurities: 0.1-0.5 Pa, max. throughput 50 Pa.m3/s EC/IC discharge cleaning: H isotopes, He and impurities: 0.01-0.1 Pa, max. throughput 50 Pa.m3/s Transient pumpdown from crossover to base pressure after vent; air, residual gases, water etc Transient pumpdown from crossover to base pressure after 90 K regen; H isotopes (many cycles) Transient pumpdown from crossover to base pressure after 300 K & 470 K regen; H isotopes and impurities (water, CxHy, QH3) Diverted plasma exhaust: H isotopes, CxHy, noble+impurity gases; up to 120 Pa.m3/s, 1<P<10 Pa Leak detection: sorbent panels at 40 K to supress leak tracer helium pumping – all other gases pumped More detailed info in section 4.13 of PID FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #6/29

  7. ITER torus cryo-sorption pumps- operation modes 54 divertor cassettes 4 torus pumping ducts Branched cryopump Direct cryopump Pumping duct pressure distribution Torus cryopump FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #7/29

  8. ITER torus cryopumps – T & H limits {1} • There is an administrativelimit of 120 g of T inventory in all torus cryopumps open to the torus • This T limit, being Administrative is somewhat arbitrary but any increase would be problematic on account of overall T plant inventory and ALARA • There is a physical hydrogenic inventory limit for INDIVIDUAL torus cryopumps (inlet valve closed) such that the deflagration pressure must be < the design pressure (presently 0.2 MPa) of the vacuum vessel duct which forms the pump housing • For the reference torus cryopump design the free (H explosion pertinent) volume is ~ 8.5 m3 and with a hydrogen concentration of 3 g/m3 (4.5 g/m3 of 50:50 DT), this leads to a deflagration pressure of 2 bara. More background is given in: M. ISELI, “In-vessel hydrogen deflagration and detonation”, Fusion Eng. and Design 54 (2001), 421 &M. Wykes, “Minimisation of the hydrogenic inventory of the ITER neutral beamline cryo-sorption pumps,” 7th International Conference on Tritium Science and Technology, 13-17 September 2004, Baden-baden, Germany • THESE LIMITS BOUND THE MAXIMUM PUMPING TIME OF AN INDIVIDUAL TORUS CRYOPUMP FOR LONG PULSE OPERATION→NEXT SLIDE FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #8/29

  9. ITER torus cryopumps – T & H limits {2} • Reference ITER DT exhaust throughput (PID Table 4.13-3) is: q=120 Pa.m3/s 50:50 DT (@273 K) = 60 Pa.m3/s T at 273 K = 0.6 NL/s of T 22.41 NL~ 1 mole ~ 6 g T; 0.6 NL T~ 6 (g) x 0.6 (NL)/22.41 (NL) ~ 0.1606 g/s T MASS FLOW 4 pumps pumping, 4 in regeneration (see next viewgraph for pattern) T ADMIN LIMIT (q/4) xt x {4+3+2+1}  120 g T {0.1606/4} x t x {4+3+2+1}  120 g T Elaborated in next Slide t  298 s [~ 100 % margin] BUTAllowance needed for T in CxQy (on-going R&D), inadvertent over-fuelling and indeterminate factors t is the “Incremental time”, important for vacuum and cryogenic functional aspects. Reference Value of t: t=150 s 2 bar deflagration limit= 4.5 (g T/m3) x 8.5 (m3) = 38.3 g TINDIVIDUAL PUMPDEFLAGRATION 2 BAR LIMIT {0.1606/4} x t x {4}  38.3 g T t  238 s [~ 100 % margin] BUT Allowance needed for inadvertent over-fuelling and indeterminate factors Reference value oft= 150 is deemed to be conservative (but not overly so) and also satisfies the functional vacuum and cryogenic requirements. FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #9/29

  10. 8 pump+4 ducts, sequential pulsing at maximum repetition rate (400 s burn) 400 s pulse 400 s pulse 1400 s dwell 1400 s dwell Pulse Dwell Pulse Dwell Pump No 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 1 2 3 4 5 6 7 8 t Regeneration period of 8 pumps=150 x 11=1650 s Regeneration key Cold helium exhaust Warm-up & gas release Evacuate Cool-down Minimum repetition time ~1400 s for 8pumps+4 ducts Torus cryopump regeneration pattern FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #10/29

  11. ITER torus cryopumps – T & H limits {1} FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide 11/29

  12. FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide 12/29

  13. FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide 13/29

  14. FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide 14/29

  15. FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide 15/29

  16. FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide 16/29

  17. FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide 17/29

  18. Hydrogen explosion hazard in cryopump forevacuum system (1) • At time of design, ITER rules evolving so JET rules used: • T1 so Q1 PRIMARY WELDS • Only butt welds allowed • All welds must allow 100% radiography SECONDARY WELDS • Fillet welds allowed • Longitudinal welds allowed • No radiography requirement • Visual+ leak test only Secondary pipe Cutaway of regeneration foreline at Tee connection Primary pipe • Interspaces are segmented and filled with He at 50 kPa after evacuation (pressure monitored) • Increase in interspace pressure – leak in outer • Decrease in interspace pressure – leak in primary (He in fuel cycle process stream) ITER safety design guidelines recommend double confinement with inerted interspace for hydrogenic regeneration forelines between cryopumps and T-plant (under review) In reference design, all foreline elements are doubly contained along complete path from cryopumps to forelines FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #18/29

  19. Hydrogen explosion hazard in cryopump forevacuum system (2) Cryopump foreline filter Pipe chase Cryopump isolation valve Cryopump Port Cell floor Torus cryopump regeneration foreline ITER safety design guidelines recommend double confinement with inerted interspace for hydrogenic regeneration forelines between cryopumps and T-plant (under review) In reference design, all foreline elements are doubly contained including the cryopump isolation valve FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #19/29

  20. Hydrogen explosion hazard in cryopump forevacuum system (3) • The issue of the need or not for double confinement of the cryopump regeneration forelines is presently under review by the ITER Safety Group • The outcome is important for the design of the forelines > simplified, particularly with regard to double confinement of vacuum valves > would allow the “secondary” pipe envelope to become the primary diameter, giving more margin on the transient pumpdown time (pipe conductance varies as d4 in viscous flow) > it might be possible to significantly ease the cryoplant liquefaction demand by increasing the cool-down time of the cryopumps • When the outcome of the review is known the design will be adjusted accordingly (or not if no change) FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #20/29

  21. Illustration of need for double confinement: e.g. torus cryopumps, Type 2 Diagnostic (shown here) 2ndary confinement (cryostat) Primary confinement (Vacuum Vessel) Vacuum barrier Low pressure needed to give acceptable signal/noise ratio Optical slit P~50 kPa Detector Diagnostic signal Isolation valve c Cryosorption pump DIAGNOSTICS (1) Isolation valve Torus cryopump regeneration foreline To T-Plant FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #21/29

  22. Example of an ITER directly couple (type 2) diagnostic: VUV at Upper Port 10 Isolation valve Detector units: Need good vacuum to prevent signal degradation DIAGNOSTICS (2) VUV rays FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #22/29

  23. Illustration of need for single confinement: e.g. Type 1 Diagnostic (shown here) 2ndary confinement (cryostat) Primary confinement (Vacuum Vessel) P~50 kPa Detector Diagnostic signal Possible connection to SVS for feedthrough with Paschen issue or leak proneness Service Vacuum System SVS See next viewgraph DIAGNOSTICS (3) FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #23/29

  24. Vacuum Pumping Room Client Systems A V1 Forepumps V7 SGVS V2 X V3 Changeover Valve Box SRS V6 SLDS V8 MSLD Service Vacuum System (SVS) Schematic For legend see next viewgraph V5 V4 FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #24/29

  25. SVS Client systems (CVB,CCB, CTB CTCB, diagnostics) Legend for SVS schematic Cryo-sorption refrigerator pumps of Service Guard Vacuum System (at least 8 {TBD}) Cryo-condensation refrigerator pumps of Service Leak /Detection System (at least 6 {TBD}) Operational Overview 1 Rough pump down to crossover pressure of whole system: 1.1 Open all valves between Forepumps and SVS/Clients. Forepumps pumpdown all pipework, manifolds, refrigerator pumps of SVS and clients (Note clients) 1.2.Close V1, V3, V4, V7, V8 (referring to Client System A only, all other similar valves for other clients) to isolate SGVS and SLDS from forevacuum and cooldown all refrigerator pumps to evacuate SGVS and SLDS manifolds to <0.1 mPa 1.3. Sequentially open Client system isolation valves (V7 etc for other clients) one at a time to evacuate Client systems to <0.1 mPa 2. Leak detection mode 2.1 Close V7 and V4 to isolate leaking client from SRS and SGVS and open V4 and V 8 to connect client to SLDS 2.2 Using turbo pump in MSLD, evacuate branch pipe from MSLD to SLDS. Spray helium to external side of leak site and monitor response of MSLD 2.3 Isolate leaking client from SVS by closing valves V1 and V7 (client A) and vent client using Vent Gas System. Repair leak, repeat leak test per 2.1 and 2.2 above. When no leak, rough down client using SRS and re-connect to SGVS 3. Refrigerator pump regeneration (For example cryopump X in Fig , other cryopumps similar).One cryopump at a time 3.1 Close valves V2 and V6, open valve V3. Warm up cryopump X and pump away released gas with Forepump set. 3.2 Close valve V3 and cool-down cryopump X. Open valve V3 when pump cold to restore crypump X to SGVS pumping 3.3 The 3 manifolds and all interconnecting pipes can be likewise isolated and connected to the SLDS for leak testing FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #25/29

  26. Interspace 1 (Duct bellows) (1) Cryostat penetration To Equ. SVS Incl. He supply Rectangular duct wall Cryostat volume ~ 8400 m3 Pump plug Duct port wall Bellows interspace volume ~ 0.2 m3 Connection pipe Primary confinement Secondary confinement Inlet valve Actuator shaft Pump CL ASSUMPTION: the duct bellows interspace has to be monitored to reveal as leak in the inner (cryostat side) or outer (torus side) bellows since the existence of a leak lowers the protection status of the magnets (particularly epoxy) against accidental tritiation. Bellows interspace needs a connection pipe to the Port Cell side of the pump plug where pressure sensors located FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #26/29

  27. Actuator shaft bellows interspace To Equ. SVS Incl. He supply Primary confinement Secondary confinement Inlet valve Interspace internal volume 0.1 m3 pre-filled with He at 50 kPa Inlet Valve Actuator Shaft Double edge welded bellows Leak test shroud around pressurized he containing elements needed to preclude having to evacuate these elements prior to leak testing (reduce leak test cycle time) FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #27/29

  28. Other safety interface areas of Vacuum Pumping systems • Recovery from in-vessel (& cryostat) Ice events (MWS paper at TPWG3, 21-23 Nov); basically best ways of moving T from vessel/cryostat to T-plant following ICE • Dust: Although affecting the vacuum system, this is a generic ITER issue and not just vacuum (foreline filters are provided to protect vacuum valves) but not generally to prevent migration • The NB pump system is not explicitely treated herein, but it is a T system as it is used to assist torus cryopumps during dwell pumping (see ‘M. Wykes’, “Assessment of the ITER Dwell Pump-down”, SOFE05, Knoxville, 24-26 Sept. 2005); however, T inventory insignificant (few NL T) compared to H2, D2 peak inventory (10’s of moles) • An area that should receive a lot more attention is individual and collective worker doses during leak testing. ANY SINGLE BARRIERS BETWEEN TORUS VACUUM & AIR WILL CONSUME LARGE DOSE BUDGET TO LOCALISE (PEOPLE IN PORT CELLS FOR LONG TIME).MONITORED INTERSPACE ALLOWS REMOTE LOCATION, SIZING AND MITIGATION OF PRIMARY LEAKS!!!. FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #28/29

  29. Concluding remarks • In the time available, only a fleeting overview of the many vacuum pumping systems involved in T handling has been possible • The intention has been to give a flavour of the safety issues involved as an initiating event to a continuing dialogue with safety colleagues • I will be more than happy to liaise with safety colleagues on any aspect deemed to need attention – indeed I look forward to it WITH MANY THANKS FOR YOUR ATTENTION FMEA Update Kick-off Meeting (ITA 81-12, TW-SEA 4.2), Garching, 17-10-05 Slide #29/29

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