Tritium extraction from Pb16Li and He: EU experience and proposals

1. Tritium extraction from Pb16Li and He: EU experience and proposals I. Ricapito, ENEA CR Brasimone, FPN-FISING

2. OBJECTIVE To summarise the EU experience on tritium extraction from Pb16Li and He for DEMO and Power Plant, presenting at the same time the proposals to ITER for TBM tritium processing systems. Moreover possible fields of collaboration are indicated. OUTLINE • Tritium extraction from Pb-16Li • Tritium extraction from He (TRPS; CPS) • Proposals for EU TBMs T-systems • TES/TRPS • CPS • Possible developments

3. Tritium Extraction from Pb-16Li Different technologies have been proposed and studied in EU spray columns • GAS LIQUID CONTACTORS • V GETTERS • BUBBLE COLUMN-PERMEATOR (SiC-SiCf) plate columns bubble columns packed columns

4. Tritium Extraction from Pb-16Li Most of the experimental activities on GL contactors were carried out on Melodie loop MELODIE LOOP: PFD

5. Tritium Extraction from Pb-16Li Results from Melodie loop on GL contactors Bubble columns:experimental results on Melodie loop 800 mm height, 54 mm diameter, 673 K

6. Tritium Extraction from Pb-16Li Results from Melodie loop on GL contactors Packed columns:experimental results on Melodie loop 800 mm height, 54 mm diameter, packing area: 750 m2/m3, T:673 K

7. Tritium Extraction from Pb16Li • G-L contactors, experimental results: summary • disappointing results were obtained by bubble columns because of the small G-L interface area: particularly, coalescence of gas bubble, already at low gas flow-rate, was claimed to be the main reason of the low efficiency • maximum extraction efficiency was nearly 0.3, achieved with packed columns (0.8 m in height) • the effect of hydrogen addition to the purge gas on the extraction efficiency was not studied • L/G molar ratio was not optimised

8. Tritium Extraction from Pb16Li TES: V Getters • V was selected because of the high Sieverts’ constant for tritium and good compatibility with Pb-16Li • A deuterium gettering rate constant in the range 10-710-8mol m-2 s-1 mbar-1/2 was experimentally determined, increasing with the temperature because of the increasing deuterium diffusivity in the LM boundary layer (controlling step in the mass transfer) • the system is more compact than G-L contactors for a given extraction efficiency • a cyclic operation is intrinsically necessary (two beds in parallel)

9. Tritium Extraction from Pb16Li TES: bubble column- permeator He +Q2 Pb-16Li inlet • tritium is recovered by two channels in parallel: • a tritium flow from LM to ascending bubbles • tritium permeation through 2D- SiCf/SiC with a sweep He flow recovering permeated Q2 or by vacuum He He +Q2 Pb-16Li outlet High extraction efficiency is claimed to be achievable with a very compact system, but experimental confirmation is necessary

10. Tritium Extraction from Pb16Li Ongoing activities on TRIEX loop at ENEA CR Brasimone • Aims: • study and optimisation of GL contactors (first phase) • study and optimisation of alternative technologies (integrated bubble column-permeator) in the ambit of international collaboration • column operative temperature: 623-723 K; • internal diameter of the column: 12.8 cm; • column height: 20-120 cm • specific surface of the filler: 350 m2/m3 • mass flow rate of Pb-16Li: G 0.2-1.0 kg/s; Segmented packed column

11. SG H2 P TES CPS Pb-16Li Q2 HCS ISS H2O, H2 to fuelling He+Q2+ imp. Q2 TRPS impurities Q2 He WGS to stack Tritium Extraction from He purge (TRPS) • TRPS is the process downstream a GL based TES • TRPS feed stream depends on the GL contactor design specification

12. Tritium Extraction from He purge (TRPS) Tritium Removalfrom Purge Gas: TRPS Candidate Processes • VPSA (Vacuum Pressure Swing Adsorption) • TSA (Thermal Swing Adsorption) • PdAg Permeator battery

13. Tritium Extraction from He purge (TRPS) VPSA process Adsorption column VP He+Q2 V1 V2 V5 Q2 to ISS V3 V4 H2 V6 To Imp. Processing pure He to TES • Process steps • Feed pressurisation (all valves closed except V1) • Adsorption at 77 K and 1-2 MPa (all valves closed except V1, V3) • Co-current blow-down (all valves closed except V2, V4) • H2 addition (all valves closed except V6) • Co-current evacuation (all valves closed except V2, V5)

14. Tritium Extraction from He purge (TRPS) TSA process Alternative to VPSA is a cryogenic TSA process. For this application TSA is operated at 77 K in adsorption phase, while the regeneration of the adsorbent beds takes place under counter-current He stream at RT or under vacuum, depending on the bed dimensions. RecoveredQ2, concentrated in the He regeneration stream, is then processed by Q2 permeators (Pd-Ag)

15. Tritium Extraction from He purge (TRPS) Pd-Ag Permeators (solution proposed for DEMO) In the last reactor-permeator HT partial pressure in the shell side is virtually zero by oxygen addition

16. Tritium Extraction from He purge (TRPS) • Considerations on TRPS • TSA is more technologically mature than VPSA, especially when operated at cryogenic temperature, because of the simplicity of the regeneration phase • in TSA tritium inventory is higher than in VPSA: in VPSA configuration, the adsorbent beds are much more compact than in TSA • Pd-Ag permeators require large surface area and pumping power because of the low differential Q2 partial pressure (driving force)

17. Tritium Extraction from He purge (CPS) About CPS… CPS is the most critical tritium system in HCLL blanket (DEMO or Power Plant) because of: • large feed flow-rate to be processed: in the worst conditions (PRF=1, low LM flow-rate) it exceeds10 % of the total coolant flow-rate, which is unacceptable • relatively small Q2 concentration in the feed stream • presence of Q2O and impurities at very low partial pressure (range of Pa)

18. Tritium Extraction from He purge (CPS) Possible Working Points LM flow-rate (kg/s) 80016001600 PRF 10 10 10 TES efficiency 80% 80% 60% CPS efficiency 95% 95% 90% T_perm. rate (g/d)12.3 4.8 9.0 Average T conc. in LM (mol m-3) 2.3x10-2 1.2x10-2 1.8x10-2 CPS feed flow-rate (Nm3/h) 2.1x106 8.2x105 1.6x106 Fraction of the coolant flow-rate 2.7% 1.1% 2.1%

19. He+ Q2 +Q2O + imp. H2O + H2 IN oxidizer (Cu2O-CuO) 700-750 K RHE CT He Q2O ADSORBERS 2 impurities to WGDS Tritium Extraction from He purge (CPS) CPS: possible configuration for DEMO/Power Plant (possibly to be tested in ITER) OUT

20. Proposals for EU TBMs T-systems General Statements • Each TBM will have a Tritium Extraction System (TES) to extract the small amount of tritium generated • Each TBM will have a Coolant Purification System (CPS) for the extraction of tritium permeated into coolant • Processing of tritium within the Tritium Plantcould be carried out, alternatively, through: the Tokamak Exhaust Processing System with the subsequent tritium recovery by the Isotope Separation System or the Vent Detritiation System with subsequent tritium removal / recovery by Water Detritiation System and, in series, Isotope Separation System

21. Proposals for EU TBMs T-systems Integration of TES/CPS in the ITER Fuel Cycle He purge gas TES TRPS to SDS TBM ISS Q2 TEP HCS CPS A/VDS WDS

22. Proposals for EU TBMs T-systems In view of ITER For the EU TBMs (HCLL and HCPB), the tritium extraction from He purge could be accomplished by two diferent systems for the low duty and high duty DT phase, respectively Low duty: isolated pulses, low amount of Q2 to be extracted High duty: sequence of standard pulses (back to back pulse series) or long pulses

23. Proposals for EU TBMs T-systems TES in the low-duty DT phase (isolated standard pulses) • For the low duty DT phase, a simple “Tritium Measurement System” (TMS) could be used as TES. TMS (FZK concept) • is based on a Zn reducing reactor, followed by a U getter bed • it has to be equipped by suitable tritium accounting system (on line or in the tritium building) • has to be placed close to the TBM (port cell) • requires a space approximately 2.3x1.3x1.5 m (LxWxH) for both HCPB and HCLL TBMs

24. Proposals for EU TBMs T-systems EU TBMs: gas stream to be processed by TES/TRPS HCPB-TBM HCLL-TBM

25. Proposals for EU TBMs T-systems TES/TRPS • For the high duty DT phase (back to back pulse series and long pulses), different alternatives could be envisaged. One of them is here proposed which is, in principle: • able to recover Q2 with a good efficiency (90%) and in a wide range; • - able to distinguish between HTO and HT generated in the breeder; • - DEMO relevant • A candidate process consists, essentially, oftwo in series TSA systems, the first one operated at RT in adsorption phase for Q2O removal and the second one at LN2 temperature for Q2 removal. • In this process the main components are: • - a cooler to cool down the He stream from the TBM outlet (450°C) up to RT • - a TSA for Q2O removal operated at RT in adsorption phase (for HCPB-TBM) • - a pre-cooler to cool down the dry He stream close to LN2 temperature • - a TSA for Q2 removal operated at LN temperature in adsorption phase • - a heater to bring the pure He stream to RT • - a blower to circulate the He stream into HCPB-TBM

26. Proposals for EU TBMs T-systems TES/TRPS Properties of the Q2O-TSA and Q2-TSA Analytical instrumentation consists of: - n. 7 ionization chambers, located in different points of the circuit. Their measurement range is 1E3÷1E6 Bq/ml - n. 3 H2 detectors, with a range of 1E-3÷1E0 % in He - n. 2 hygrometers, located in the regeneration loop of Q2O-TSA; measurement range -60÷+10 °C (d.p.) -n. 1gas-chromatograph, with a measurement range of the impurities as 1E-1÷1E2 vppm

27. Proposals for EU TBMs T-systems EU TBMs: gas stream to be processed by CPS

28. Proposals for EU TBMs T-systems CPS /1 The proposed CPS for HCPB-TBM is a three stage process, derived from the DEMO conceptual design: 1) oxidation of Q2 and to Q2O and CO to CO2 by means of an oxidising reactor (Cu2O-CuO) operated at 280 °C; 2) removal of Q2O by a room temperature PTSA (Pressure Temperature Swing Adsorption); 3) removal of the impurities by a cryogenic PTSA

29. Proposals for EU TBMs T-systems CPS /2 Analytical instrumentation consists of: - n. 4 ionization chambers, operated in the range 1E2÷1E4 Bq/ml - n. 3 hygrometers, with a measure range -80÷0 °C (d.p.) - n. 1 gas-chromatograph with detectable range of impurities 1E-1÷1E2 vppm Size:4.5x1.8x2.8 m (LxWxH) close to HCS compressor (TWCS vault)

30. Possible developments /1 Tritium Extraction from PbLi • Although many experiments were done in the past years on Melodie loop at CEA, experimental and modelling activities on the optimisation of tritium extraction systems from LLE need to be continued. • An extensive experimental campaign is foreseen in TRIEX loop on GL contactors, particularly for packed columns, with the aim to optimise them with respect to different operating parameters: G/L, H2 content in the stripping gas, hydrodynamics. • TRIEX loop is available to test other tritium extraction technologies for their study and optimisation (e.g.: permeators and coupled bubble columns/permeator)

31. Possible developments /2 Tritium Extraction from He • Technologies of tritium extraction from He have been identified for both tritium extraction from the purge gas (TRPS) and coolant purification systems (CPS) but no related experimental campaigns have been carried out so far. • Adsorption technologies are potentially attractive for such applications but experiments on lab scale • adsorption multicomponent equilibria on different microporous materials under relevant pressure, temperature and gas composition; • adsorption kinetics and on pilot plants appear necessary taking into account the demanding performance and the very unusual feed stream properties. • Modelling of the system is the next step activity, useful also to refine the sizing of TES/TRPS and CPS for ITER