4 July 2008R. Laesser, F4E ITER Department 1 The Use and Management of TRITIUM in ITER R. Lässer

4 July 2008R. Laesser, F4E ITER Department 2 Content IntroductionIntroduction oInner and outer Fuel Cycle of a Fusion Reactor oRadiotoxicity of tritium oTritium in gases, liquids and metals oPreconditions of safe processing tritium oTritium experiments in Tokamaks The Deuterium Tritium (DT) Fuel CycleThe Deuterium Tritium (DT) Fuel Cycle oSubsystems of the DT Fuel Cycle  Storage and Delivery System, Long Term System  Vacuum Pumping Systems  Tokamak Exhaust Processing System  Isotope Separation System  Water Detritiation System oTopics addressed in WP7 (Tritium Plant) during ITER Design Review  Tritium building layout  Modification of HVAC, ADS and VDS  Tritium Tracking Strategy Tritium in Plasma Facing ComponentsTritium in Plasma Facing Components Tritium Processing in Test Blanket ModulesTritium Processing in Test Blanket Modules Tritium Processing in DEMOTritium Processing in DEMO Acknowledgements

4 July 2008R. Laesser, F4E ITER Department 3 The Inner and Outer Fuel Cycle of Fusion Reactors Among the potential fusion reactions technically most suitable is the reaction between deuterium and tritium 2 D + 3 T→ 4 He (3.5 MeV) + 1 n (14.1 MeV) –0.016 at% Deuterium are contained in natural water. –Tritium needs to be produced. 56 kg tritium is required per GWy of fusion power. About 100 g tritium is produced per year in a standard CANDU fission unit. Breeding of tritium is necessary in a fusion reactor: n + 6 Li → T + 4 He n + 7 Li → T + 4 He + n 20 to 25 kg tritium will be needed for operation of ITER. A few kg tritium will be always needed for starting a power fusion reactor. 08/2 9 Tritium Plant TES

4 July 2008R. Laesser, F4E ITER Department 4 Radiotoxicity of Tritium Tritium decays: 3 T → 3 He + + β - + ν keV. T 1/2 = 12.3 y Tritiated hydrogen (HT, DT, T 2 ) breathed-in by the lounges leads to a local β - dose, but is almost completely breathed out. Also the uptake of hydrogen (tritium) through the skin is very small. Q 2 stands for: H 2, HD, HT, D 2, DT, T 2. Tritiated water vapour (HTO, DTO, T 2 O) is readily incorporated via the lounges and the skin. Within a few hours tritiated water is homogeneously distributed in the body fluids and causes a whole body dose which can easily be determined by measuring the tritium concentration in the urine or in the breathed out air. (Q 2 O stands for: H 2 O, HDO, HTO, D 2 O, DTO, T 2 O. Biological half life: about 10 days. Organically bound tritium: half life time: months. Tritiated water is approximately times more radiotoxic than tritiated hydrogen. In consequence: Tritium is one of the least radiotoxic nuclides. Tritium can induce X-rays.

4 July 2008R. Laesser, F4E ITER Department 5 Effects of Tritium in Gases and Liquids Tritium in gases Composition and pressure of tritiated gas mixtures change due to tritium decay: 3 He is generated. Radicals, new and ionized gas molecules can be created by the decay electrons. Even solid matter such as plastics can be produced if hydrocarbons are present. Tritium in water At high T-concentrations in the water radiolysis occurs with generation of oxygen, hydrogen and tritiated peroxide. Storage of highly tiritiated water needs a recirculation loop with small hydrophobic catalyst to recombine hydrogen and oxygen again (5 liter of HTO create about 20 liter of DT per day). Tritium gas in contact with metal surfaces Metal oxides can be reduced by tritium resulting in clean metallic surfaces (leading to diffusion limited permeation (not any more surface limited)). As a consequence of these reactions the purity of the tritium gas stored in a container will deteriorate.

4 July 2008R. Laesser, F4E ITER Department 6 Solubility and diffusion of Q (Q=H, D, T) in metals Isotherms in PdQ x PdQ 0.30 VQ x phase diagram Hydrogen in Metals H2 molecule Sieverts law Diffusion coefficient for hydrogen isotopes H, D and T in Niobium Hydrogen in Metals

4 July 2008R. Laesser, F4E ITER Department 7 PRECONDITIONS FOR SAFE PROCESSING TRITIUM Tritium compatible materials/equipment: No plastics / oil. Yes: metals / ceramics. Confinement of tritium: o Primary confinement: prevents T-releases into the areas accessible by workers by means of barriers: primary containment can be surrounded by intermediate volumes or secondary containments (glove- or valve box). o Secondary confinement: prevents T-releases into non-controlled/non- supervised areas and into the environment. Simple design and use of well proven techniques: The design must allow easy maintenance and repair. Stringent installation and commissioning procedures: Stringent leak tightness requirement: < Pam 3 /s for facilities and < Pam 3 /s for components. Strict operational and local procedures. Equipment to be installed in well ventilated buildings. Tritium inventories to be limited and segregated as far as possible.

4 July 2008R. Laesser, F4E ITER Department 8 TRITIUM EXPERIMENTS IN TOKAMAKS Preliminary Tritium Experiment (PTE) at JET: end of 1991 First DT experiments in a fusion machine, limited number of plasma shots, less than 0.2 g of tritium on site. No recycling of tritium. Tritium Processing during Tritium Campaign at TFTR ( ) Maximum site inventory 5 g, 78 g were supplied to NBI, most of the T- processing was done at other US site, very limited recycling. Tritium Processing during Deuterium Tritium Experiment (DTE) at JET in 1997 Tritium amount on site: 20 g, Active Gas Handling System (AGHS =JET Tritium Plant) supplied 100 g T, 11.5 g was highest tritium amount trapped in tiles + flakes. Tritium was recycled five times. Trace Tritium Experiment (TTE) at JET in October 2003 Operation of AGHS during TTE in similar way as during the DTE, however only very small amounts of tritium were injected into the machine.

4 July 2008R. Laesser, F4E ITER Department 9 Cryogenic pump: 4.2K cold finger, He dewar was moved by a lifting platform T2 supply from U-beds + injection via NBI 345 liter vessel used for (pVT-c) accountancy Hydrogen/ tritium storage in large JET U-beds, cracking of impurities Very simple Tritium Processing Systems (all equipment shown) PTE at JET U-beds T 6Ø cm 4 U-beds

4 July 2008R. Laesser, F4E ITER Department 10 AGHS Building DTE: Use of Active Gas Handling System (AGHS): 1997 Bridge: Cryogen + active gas lines Stack Cryogenic Forevacuum System Control Room Torus BasementAGHS

4 July 2008R. Laesser, F4E ITER Department 11 The Deuterium Tritium (DT) FUEL CYCLE of ITER Tritium fuelling via Pellet injection, Gas puffing. NBI not used for tritium injection. Closed DT loop required especially with respect to tritium as tritium releases into the environment must be kept as low as reasonable achievable (ALARA).

4 July 2008R. Laesser, F4E ITER Department 12 EU Korea, Fund EU, Fund JA, Fund EU, Fund All Participating Teams US, Fund Fund EU, US All Participating Teams, Fund CN, EU, JA, US, Fund 10/2 9 The ITER DT Fuel Cycle Leak Detection EU

4 July 2008R. Laesser, F4E ITER Department 13 Tritium Plant: 2001 baseline

4 July 2008R. Laesser, F4E ITER Department 14 The ITER ("the way") Project (2/3) 04/2 9 The ITER BUILDINGS Nuclear Buildings

4 July 2008R. Laesser, F4E ITER Department 15 Subsystems of the DT Fuel Cycle Storage and Delivery System (SDS) and Long term Storage (LTS) Vacuum Pumping Systems: Cryo- and Roughing Pumps Tokamak Exhaust Processing System (TEP) Isotope Separation System (ISS) (throughput 200 Pam 3 /s) Water Detritiation System (WDS) Analytical System (ANL) Fuelling Systems oPellet Injection oNeutral Beam Injection oGas Puffing Atmosphere and Vent Detritiation Systems 120 Pam 3 /s for 3000 s (about 1 kg DT/h), 160 Pam 3 /s for 1000 s, 200 Pam 3 /s for 400 s, Fuelling rate can increase for short times 230 Pam 3 /s (for ELMs pacing). Fuelling rates:

4 July 2008R. Laesser, F4E ITER Department 16 Storage and Delivery System + Long Term System (KO) Purpose of Storage and Delivery System (SDS) To store tritium and deuterium in storage beds (70 g tritium/bed), To supply gases of the requested compositions and flow rates to the fuelling systems, To perform accountancy by in-bed calorimetry (accuracy: ~1% for fully loaded bed) and (pVT-c) measurements, To collect He-3. Purpose of Long Term System (MBA-2 in ITER) To store the tritium in 10 getter beds (without accountancy) to keep total tritium inventory in FC at low value. To import and account tritium supplied to ITER, Safest storage technique of tritium today Safest storage technique of tritium today is the use of metal getter beds with high affinity to hydrogen. Advantages: Storage beds can act as pumps at RT and compressors at higher temperatures. Negligible tritium permeation at RT. Purity of the dissolved tritium is conserved. Removal of 3 He from tritium possible. High storage capacity per volume. In-bed calorimetry possible. Disadvantages: needs heating to temperatures around °C. Low thermal conductivity of metal hydride powder critical for achieving high hydrogen supply rates. Powder is pyrophoric. Possibility of He-blanketing. Large volume increase of metal after hydriding due to power production. Creation of tritiated waste.

4 July 2008R. Laesser, F4E ITER Department 17 Storage and Delivery System + Long Term System (KO) ITER Getter beds still to be optimized (requiring thermomechanical / hydraulic calculations) for Fast supply, Fast pumping, Space needed for hydrided materials, Accurate accountancy, Fast cooling. IO and Korea still prefer ZrCo instead of uranium (U). ZrCo disproportionates in the presence of higher hydrogen pressures: (2 ZrCo + H 2 = ZrCo 2 + ZrH 2 ). Pumps are requested to keep the pressure in the beds low to avoid disproportionation. Reproportionation is possible under vacuum at higher temperature. Memory effects exist. No long term experience of ZrCo with tritium exist. However tritium experience with U is huge. U has very broad horizontal plateau pressure, whereas this pressure increases in the case of ZrCo. EU strongly in favor of using uranium as getter material.

4 July 2008R. Laesser, F4E ITER Department 18 Vacuum Pumping: 8 Torus-, 2 cryostat cryopumps 3 HNB-, 1 DNB cryopumps Cold Valve boxes + cryojumpers 4.5K cryosorption panel circuit Integral inlet valve 80K louvre baffles Valve pneumatic actuator Pump connection flange Vacuum Pumping Systems (EU) Purpose: Pumping Torus ( 153 Pam 3 /s ), cryostat and HNB and DNB facilities. Pumping tests with a half size model cryopump successfully finished. Final design of a full prototype torus cryopump (PTC) in progress: 1.8 m diameter; 2.1 m long; 11.2 m 2 charcoal coated, 0.8 m diameter inlet valve with 0.5 m stroke to modify pumping speed. No regeneration required during short plasma pulses (450 s). During long shots (3000 s) quasi-continuous regeneration occurs up to 100K for release of helium and hydrogen to recycle the released hydrogen. Prototype Torus Cryopump

4 July 2008R. Laesser, F4E ITER Department 19 Regeneration separates gas stream: 80K: Q 2 and He (Ne): every 150 seconds. 300K: Air-like impurities (CO, CO 2, lower C n Q m ), daily regeneration of all cryopumps (overnight). 470K: Water-like impurities (higher C n Q m ), regeneration of one cryopump (overnight). Vacuum Pumping Systems (EU) Rough Pumping System: Combination of Roots pump (1 off 4200 and 2 off 1200 m 3 /h and screw- or piston pumps). Separation of pumping and oil filled volumes by special seals (e.g. ferrofluidic seals). Proposal to freeze out the highly tritiated water (from the 470K regeneration) upstream of Roots pumps to avoid condensation. 1 module with 4 sections 1 section HNB cryopump 80 K 5K Schematic of HNB Ion Source Cryopanels Neutraliser

4 July 2008R. Laesser, F4E ITER Department 20 Tokamak Exhaust Processing (TEP) System (US) Purpose of TEP to treat all gases from various systems (NBI, TP, Diagnostics) to extract hydrogen in water vapour and hydrocarbons, discharge the hydrogen depleted streams via vent detritiation (TEP release conditions relaxed from 1 Ci/m 3 to 200 Ci/m 3 ). Replacement of carbon by W will simplify the requirements of TEP as hydrocarbons will be no longer the dominant impurities. Main components of TEP Permeators to extract the unburnt fuel (hydrogen) from the gas mixtures, Catalysts to crack the hydrogen containing molecules and permeators to extract the produced hydrogen, Pumps for circulation of the gases. Unresolved topic: Processing of highly tritiated water

4 July 2008R. Laesser, F4E ITER Department 21 Highly Tritiated Water 1 kg DTO contains 143 g tritium or 1.4 MCi. High tritium concentrations in water are expected from various sources such as 470K regenerations of cryopumps, during dedicated phases for recovery of the tritium trapped inside the VV and from Hot Cell.

4 July 2008R. Laesser, F4E ITER Department 22 Processing Options of Highly Tritiated Water Reduction of DTO to DT by means of –Electrolysis of DTO (1.4 MCi/kg) Electrolysis of liquid water very difficult above 2000 Ci/kg, leads to further enrichment. –Metals such as magnesium, uranium or iron Reaction with iron is not complete (75% conversion at 500°C), however reversible –Decontamination factor limited to about two orders of magnitude Exothermic reaction with magnesium or uranium –Highly tritiated waste (Mg / MgO containing MgO 2 DT) –Carbon monoxide (water gas shift reaction): CO + DTO = CO 2 + DT Isotopic exchange of DTO with H 2 to DT and H 2 O –Exchange in liquid water (Liquid Phase Catalytic Exchange (LPCE)) –Exchange in vapor phase (Vapor Phase Catalytic Exchange (VPCE)) 24/2 9

4 July 2008R. Laesser, F4E ITER Department 23 Use of Isotopic Exchange: DTO + H 2 = H 2 O + DT Use of Liquid Phase Catalytic Exchange (LPCE): Outline conceptual design –4,2 g/h (100 g/day) DTO vapor flow rate –72 g/h H 2 O liquid water feed flow rate (mixing factor 20) Water for mixing could be tritium contaminated Moisture in HT to be condensed and returned –48 g/h H 2 flow rate (molar ratio 6) Trade off to mixing factor, column length, outlet concentration H 2 to be added could also be slightly contaminated –80 g/h (4.2 mol/h) tritiated water flow rate at 150 Ci/kg to Water Detritiation System (capacity > Ci/kg) Column height about 4 m, column diameter about 3 cm Upper section of the column to be easily replaceable –Catalyst lifetime could be limited due to high tritium concentration (no problem for VPCE) 25/2 9 LPCE column or electrolyser 80 g/h Q 2 O/h, 12 Ci/h 4.2 g/h DTO, 5.9 k Ci/h 72 g/h H2O

4 July 2008R. Laesser, F4E ITER Department 24 Isotope Separation System (ISS) utilizes cryogenic distillation and catalytic reaction for isotope exchange to produce the required hydrogen isotope gas mixtures. Purpose of ISS To accept the hydrogen isotope mixtures (up to 200 Pam 3 /s) from TEP, NBI and WDS. To produce the required pure deuterium (<0.02% T, <0.5% H) and 90% T/10% D gas mixtures for the users and SDS. To transfer detritiated (<0.1 ppm T) hydrogen to WDS for further detritiation and final release. 4 columns installed in cold- box ISS Isotope Separation System (EU)