Transcript Slide 1

The Use and Management of
TRITIUM in ITER
R. Lässer
R. Laesser, F4E ITER Department
4 July 2008
1
Content
•
Introduction
o
o
o
o
o
•
Inner and outer Fuel Cycle of a Fusion Reactor
Radiotoxicity of tritium
Tritium in gases, liquids and metals
Preconditions of safe processing tritium
Tritium experiments in Tokamaks
The Deuterium Tritium (DT) Fuel Cycle
o Subsystems 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
o Topics addressed in WP7 (Tritium Plant) during ITER Design Review
 Tritium building layout
 Modification of HVAC, ADS and VDS
 Tritium Tracking Strategy
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•
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Tritium in Plasma Facing Components
Tritium Processing in Test Blanket Modules
Tritium Processing in DEMO
Acknowledgements
R. Laesser, F4E ITER Department
4 July 2008
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The Inner and Outer Fuel Cycle of Fusion Reactors
Among the potential fusion reactions
technically most suitable is the
reaction between deuterium and
tritium
2D
3T→ 4He
Be
Breeding
Blanket
1n
+
(3.5 MeV) + (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:
TES
Tritium
Recovery
Plasma
DT Fuel
Supply
Plasma
Exhaust
Deuterium
Supply
He Purge Gas
+ Tritium from
Blanket
Blower
Vacuum Pumps
n + 6Li → T + 4He
n + 7Li → T + 4He + n
Clean-up and DT
Fuel Recovery
• 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.
R. Laesser, F4E ITER Department
Li
Li
4 July 2008
Tritium Plant
Helium to Stack
Tritium
Supply
3
08/2
Radiotoxicity of Tritium
Tritium decays:
3T
→ 3He+ + β- + ν + 18.6 keV. T1/2 = 12.3 y
Tritiated hydrogen (HT, DT, T2) breathed-in by the lounges leads to a local βdose, but is almost completely breathed out. Also the uptake of hydrogen
(tritium) through the skin is very small. Q2 stands for: H2, HD, HT, D2, DT, T2.
Tritiated water vapour (HTO, DTO, T2O) 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. (Q2O stands for: H2O, HDO, HTO, D2O, DTO, T2O.
Biological half life: about 10 days. Organically bound tritium: half life time:
months.
Tritiated water is approximately 25000 times more radiotoxic than tritiated
hydrogen.
In consequence: Tritium is one of the least radiotoxic nuclides.
Tritium can induce X-rays.
R. Laesser, F4E ITER Department
4 July 2008
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Effects of Tritium in Gases and Liquids
Tritium in gases
Composition and pressure of tritiated gas mixtures change due to tritium decay:
• 3He 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.
R. Laesser, F4E ITER Department
4 July 2008
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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/nonsupervised 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: <10-10 Pam3/s for facilities and <10-11 Pam3/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.
R. Laesser, F4E ITER Department
4 July 2008
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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 (1994-1997)
Maximum site inventory 5 g, 78 g were supplied to NBI, most of the Tprocessing 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.
R. Laesser, F4E ITER Department
4 July 2008
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PTE at JET 1991
4 U-beds
T
2 U-beds
T2 supply from U-beds +
injection via NBI
Very simple
Tritium
Processing
Systems (all
6Ø cm
Hydrogen/
tritium
storage in
large JET
U-beds,
cracking
of
impurities
equipment shown)
Cryogenic
pump: 4.2K
cold finger,
He dewar
was moved
by a lifting
platform
R. Laesser, F4E ITER Department
4 July 2008
345 liter
vessel used
for (pVT-c)
accountancy
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YO
Diagnostics
CR
Cryogenic
Forevacuum
(CF)
Exhaust
Detritiation
(ED)
Impurity
Processing
(IP)
OPUMP
NIB 8
T2
Isotope
Separation
Gas chromatography
(GC)
D2
GIM 15
D2
TDGIS
TDGIS
T2
T2
D2
D2
Intermediate Storage
(IS)
D2
Isotope
Separation
Cryodistillation
(CD)
D2
T2
H2 (D2)
T2
D2
Gas
Introduction
box (GI)
Gas Distribution
Box (GD)
T2
Product
Storage
(PS)
JG00.34/1c
YOPUMP
YO
CR
CR
Analytical
Laboratory
(AN)
T2
Amersham UÐbed
NIB 4
C
TORUS
NIB Auxiliary ventilation
Mechanical
Forevacuum
(MF)
Monitoring
Torus Hall
RY
DTE: Use of Active
Gas Handling
System (AGHS):
1997
NIB Crown
Torus Crown
ML2
ML1
T2
Torus Basement
Torus Basement
Active Gas Handling System (AGHS)
Stack
AGHS
Bridge: Cryogen +
active gas lines
Building
Cryogenic
Forevacuum
System
R. Laesser, F4E ITER Department
4 July 2008
Control Room
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AGHS
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).
R. Laesser, F4E ITER Department
4 July 2008
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The ITER DT Fuel Cycle
CN, EU, JA, US, Fund
Fuelling Systems
Neutral Beam Heating
Korea, Fund
Storage and Delivery
System
Tritium / Deuterium
from External Sources
Korea, Fund
Long Term Storage
EU
EU, Fund
Neutral Beam Injector
Cryo Pumps
Isotope Separation
System
Torus
MBA 2
EU, Fund
Water Detritiation
US, Fund
All Participating Teams
EU
Leak
Detection
Tritium Breeding
Test Blanket
All Participating Teams, Fund
EU, US
Torus Cryo Pumps
Roughing Pumps
Diagnostics
First Wall Cleaning
Tokamak Exhaust
Processing
Fund
JA,
Fund
Atmosphere and Vent
Detritiation Systems
Analytical System
Fund
Off-gas
Release
Protium
Release
Automated Control System & (Hard Wired) Safety System
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R. Laesser, F4E ITER Department
4 July 2008
Tritium Plant:
13
2001 baseline
Nuclear
Buildings
The ITER BUILDINGS
The ITER ("the way") Project
(2/3)
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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 Pam3/s)
Water Detritiation System (WDS)
Analytical System (ANL)
Fuelling Systems
o Pellet Injection
o Neutral Beam Injection
o Gas Puffing
Atmosphere and Vent Detritiation Systems
Fuelling rates:
• 120 Pam3/s for 3000 s (about 1 kg DT/h),
• 160 Pam3/s for 1000 s,
• 200 Pam3/s for 400 s,
Fuelling rate can increase for short times 230 Pam3/s (for ELMs pacing).
R. Laesser, F4E ITER Department
4 July 2008
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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 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
3He from tritium possible. High storage capacity per volume. In-bed calorimetry possible.
Disadvantages: needs heating to temperatures around 400-500°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.
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4 July 2008
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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 + H2 = ZrCo2 + ZrH2).
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.
R. Laesser, F4E ITER Department
4 July 2008
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Vacuum Pumping Systems (EU)
Vacuum Pumping:
•
•
•
Pump connection flange
8 Torus-, 2 cryostat cryopumps
3 HNB-, 1 DNB cryopumps
Cold Valve boxes + cryojumpers
Valve pneumatic
actuator
Purpose: Pumping Torus (153 Pam3/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 m2 charcoal
coated, 0.8 m diameter inlet valve with
0.5 m stroke to modify pumping speed.
80K louvre
baffles
4.5K cryosorption
panel circuit
Integral inlet valve
Prototype Torus Cryopump
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.
R. Laesser, F4E ITER Department
4 July 2008
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Vacuum Pumping Systems (EU)
Cryopanels
Ion Source
Neutraliser
Regeneration separates gas stream:
•
•
•
80K: Q2 and He (Ne): every 150 seconds.
300K: Air-like impurities (CO, CO2, lower
CnQm), daily regeneration of all cryopumps
(overnight).
470K: Water-like impurities (higher CnQm),
regeneration of one cryopump (overnight).
Schematic of HNB
HNB cryopump
1 section
Rough Pumping System: Combination of
Roots pump (1 off 4200 and 2 off 1200 m3/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.
R. Laesser, F4E ITER Department
4 July 2008
5K
80 K
1 module with 4
sections
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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/m3 to 200 Ci/m3).
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
R. Laesser, F4E ITER Department
4 July 2008
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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.
R. Laesser, F4E ITER Department
4 July 2008
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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 MgO2DT)
– Carbon monoxide (water gas shift reaction): CO + DTO = CO2 + DT
Isotopic exchange of DTO with H2 to DT and H2O
– Exchange in liquid water (Liquid Phase Catalytic Exchange (LPCE))
– Exchange in vapor phase (Vapor Phase Catalytic Exchange (VPCE))
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4 July 2008
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Use of Isotopic Exchange: DTO + H2 = H2O + DT
Use of Liquid Phase Catalytic Exchange (LPCE): Outline
conceptual design
72 g/h H2O
liquid water
4.2 g/h DTO, 5.9 kCi/h
DTO vapor from
– 4,2 g/h (100 g/day) DTO vapor flow rate
sublimation
– 72 g/h H2O 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 H2 flow rate (molar ratio 6)
• Trade off to mixing factor, column length, outlet
concentration
• H2 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 > 20 kg/h @ 10 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)
HT
(saturated)
packing
catalyst
LPCE
column
H2
tritiated water
bottled
supply
to ITER
ISS
to ITER
WDS
80 g/h Q2O/h, 12 Ci/h
or electrolyser
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4 July 2008
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Protium (Deuterium) Reject
Column-1
Isotope Separation System (ISS) utilizes
cryogenic distillation and catalytic
reaction for isotope exchange to
produce the required hydrogen isotope
gas mixtures.
ISS
HD (T)
Feed
Pump
Isotope Separation System (EU)
Eq-1
Column-2
Eq-2
D2 (NB
Injection)
Column-3
Purpose of ISS
•To accept the hydrogen isotope
mixtures (up to 200 Pam3/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.
R. Laesser, F4E ITER Department
4 July 2008
D2 (T) for
Refueling
Eq-6
Eq-3
Eq-4
Column-4
Plasma
Exhaust
Eq-7
Eq-5
DT (50 %)
Product
90 % T / 10 % D
4 columns
installed in
cold- box
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