ITER Water Detritiation System; Basis for FMEA

1. ITER Water Detritiation System; Basis for FMEA An outline of the ITER WDS design is presented. A comprehensive R&D and design programme on Water Detritiation is under way in the EU. This includes a test facility at FZK where process and mechanical component development will be carried out and a planned, larger installation at JET which will serve as a pilot plant for ITER.

2. T/D from external sources Protium Release Fuelling Systems (FS) Neutral Beam Injec. (NBI) Cryo Pumps Water Detritiation System (WDS) Storage and Delivery System (SDS) Torus Tritiated Water Tritium Breeding Test Blanket (TBM) IsotopeSeparation System (ISS) Analytical System (ANS) Release of detritiated gas via Vent Detritiaton System Torus Cryo-Pumps Roughing Pumps Tokamak Exhaust Processing (TEP) Tritium Plant ITER Fuel Cycle Simplified Block Diagram

3. Overall ITER WDS Process Block Flow Diagram

5. Water Detritiation System; outline description (extracted from ITER PID) Tritiated Water Sources During operation of ITER, tritiated water will be produced in various systems. The expected sources are: • condensate generated from the normal operation of various atmosphere and vent gas detritiation systems and HVACs, • tritium process component maintenance, • condensate from the air coolers in the containment volume (designed to limit overpressures from an ex-vessel coolant leak), • air detritiation dryers in the TCWS vault annex, • the tokamak cooling water system maintenance drain and the tokamak cooling water system vent gas condensate, • in-vessel component maintenance drain collected in the hot cell, and • condensate from the standby vent detritiation system and the standby atmosphere detritiation system operated during tritium contamination accidents.

6. Water Detritiation System; outline description (extracted from ITER PID) The source water (a) - (d) will be processed by the water detritiation system to minimize tritium-bearing waste water to be rejected to the environment, whereas the water (e) and (f) is recycled to the tokamak cooling water system. The water (g) will be stored in the emergency holding sump tanks. Tritiated Water Source Classification The source water will be stored in the holding tank system with the following level classification: • H Level > 3.7 GBq/g (> 100 Ci/kg); • M Level 37 kBq/g – 3.7 GBq/g (10-3 Ci/kg – 100 Ci/kg); • L Level 60 Bq/g – 37 kBq/g (1.6 x 10-6 Ci/kg - 10-3 Ci/kg); • LL Level < 60 Bq/g (<1.6 x 10-6 Ci/kg) for direct release after assaying; • Emergency holding sump tanks: total capacity 400 m3 (1g Tritium ~10,000 Ci, 1Ci = 3.7e10 Bq)

7. Water Detritiation System; outline description (extracted from ITER PID) • The high (H) level and the medium (M) level tanks receive condensate from the atmosphere detritiation systems and the local air coolers in the hot cell building and the tritium plant building, and the process blow-down water of the water detritiation system at maintenance. • In case of an event leading to a large amount of tritium contamination, condensate produced by the standby atmosphere detritiation system and the standby vent detritiation system will be stored in either the H level or the emergency holding sump tanks. • The low (L) level tanks receive drainage from tritium process equipment during its maintenance. • The low low (LL) level tank receives water generated in the HVACs, and the water can be directly rejected to the environment after assaying the tritium concentration.

8. Water Detritiation System; outline description (extracted from ITER PID) Water Detritiation Process • Tritiated water sent from the holding tank system is purified by the front-end processing system composed of demineralizer and charcoal beds to remove hazardous ions and organic species to the catalytic exchange process and electrolysis. • The purified water (tritium concentration < 370 MBq/g (< 10 Ci/kg)) is then fed (~ 20 kg/h) either to the catalytic exchange towers (tritium feed concentration < 370 MBq/g (< ~ 10 Ci/kg)) or to the electrolysers (tritium feed concentration ~ 3.7 GBq/g – 20 GBq/g (~ 100 – 500 Ci/kg)). • Pure water is fed (~ 20 kg/h) to the top of the catalytic exchange tower. • The catalytic exchange towers are composed of a combination of hydrophobic catalyst and hydrophilic packing section (this may be arranged as a homogeneous mixture of catalyst and packing or as alternating discrete layers).

9. Water Detritiation System; outline description (extracted from ITER PID) Water Detritiation Process • Through counter-current catalytic exchange reactions, tritium (T) is enriched in the water which is flowing to the bottom of the towers, and hydrogen gas which contains virtually no tritium is flowing to the top of the tower. The enriched water is then dissociated into hydrogen gas H2 (T) and O2 gas by the electrolysers. The H2 (T) is returned to the bottom of the tower, and a part of the hydrogen gas stream (280 mol/h) is sent to the hydrogen isotope separation system to recover tritium via a membrane permeator system. • The H2 stream at the hydrogen separating column (CD1) in the ISS, which recovers tritium included in the H2 (T), is then recycled to the bottom section of the water detritation tower for further reduction of tritium in the H2 prior to discharge into the environment. • The hydrogen stream from the top of the tower is rejected to the environment through the flame arrester. The O2 stream from the electrolysers is sent to the normal vent detritiation system (N-VDS 1) via the O2 gas processing system composed of molecular sieve dryers.

10. Water Detritiation System; outline description (extracted from ITER PID) Water Detritiation Process • The membrane permeator and molecular sieve dryer, which are operated at elevated temperature, and electrolysers, are placed in a secondary enclosure to avoid tritium leakage/permeation to the room. The atmosphere (dry N2 gas) of the secondary enclosure is sent to the N-VDS 1 with a small flow rate. • The water detritiation system can be operated with high availability (more than 300 days/year). Demineralizers and charcoal beds require frequent replacement (every two years), and the electrolyser, based on solid polymer electrodes, may need electrode replacement once per year depending on the degradation rate of the electrolyser. (R&D to improve and demonstrate the durability of the electrolyser under ITER-relevant high tritium concentration of water is ongoing in JA- and EU-PT).

11. Inputs & output streams of JET WDS-CD(valid also for ITER) Stack Tritium depleted oxygen Tritium depleted hydrogen-deuterium Demineralized water WDS CD Tritiated water SDS Tritium enriched products

12. Requirements for tritium enriched product • Tritium fed into the WDS, as tritiated water, has to be withdrawn as a product of the CD system. • The duty of the CD system is to produce tritium (90%T; 10%D) DT and deuterium streams for refuelling and to strip unwanted protium from the feed. • The protium is detritiated in the CD1 column and discharged to the environment via the WDS, which provides an additional processing step to retain any residual tritium not removed in CD1.

13. Requirements for tritium depleted streams • The Tritium daily discharge limit adopted for the generic ITER will be confirmed for Cadarache. It is desirable that WDS’s contribution to ITER’s daily tritium discharge is ~10% (TBD) of that value. • Decontamination Factor: Based on the HTO feed rate to WDS of 20kg/h and the maximum tritium concentration in the tritiated water (to be confirmed), a decontamination factor (DF) needed to meet the WDS discharge limit can be derived. • (The JET WDS should provide DF > 10 000. It is likely that the required DF for ITER will be considerably higher.)

14. Block diagram of JET-WDS

15. Outcome requirements from HAZOP studies (for JET WDS) The main outcome requirements from HAZOP studies are: • To consider design of purification unit for ease of maintenance e.g. removing as a complete unit. • To provide secondary containment around flanges, which is purged to a tritium monitor to identify and locate a leaking flange. • To review performance of design in the light of information on deuterium content of HTO • To define maximum flow rate of nitrogen in to stripping column and column to be designed for that maximum flow rate of Nitrogen

16. Process Flow Diagram of JET-WDS

17. Supporting R&D for WDS

18. HOGEN Electrolyser controller

19. HOGEN electrolyser of 6 m3h-1

20. 3-D layout of JET-WDS

21. Rear view of JET-WDS

22. PreliminaryTime schedule for construction of JET WDS(now delayed for approx. twelve months)

23. Conclusions • WDS design for ITER completed in 2001 FDR; basic concept is fixed. • Some updating of design details will take place to reflect R&D at FZK and JET WDS operating results. • Comprehensive data base of R&D (much carried out in JET FT tasks) is available to support design and safety studies.