Download - ITER and Fusion Safety Aspects
ITER and Fusion Safety Aspects
H.-W. Bartels, ITERPrague, 13.November 2006
Fusion and nuclear safety
D
T n
He-4
+ 17.6 MeV
==> nuclear safety related issues:
1) radioactivity of tritium (~5 kg in reactor)2) activation from 14 MeV neutrons (~1/2 of activity of PWR)
Tritium
• Half-life: 12.3 a
• ß—radiator: <Ee-> = 5.7 keV range organic matter: 6 µm Horny layer skin: 70 µm
Incorporation: Inhalation, skin absorption, Ingestion
Very Mobile: HTO, HT
Biological half-life:~10 days
Hazard/Bq: tritium <1000*Cs137
Tritium in human body:i) fast component t1/2 ~10 daysii) slow component t1/2 ~ 30 – 300 d (organically bound tritium)
0.01
0.10
1.00
10.00
100.00
1000.00
0 50 100 150 200 250 300 350 400 450
days
mic
ro-C
i/l
Activation Products
Problematic isotopes:steel:
60Co: t1/2 ~ 5 years1.2 MeV -radiation
tungsten:
185W: t1/2 ~ 75 days 0.4 MeV -radiation
Favorable elements: - Vanadium (V)- Chromium (Cr)- Titanium (Ti)
1.E-09
1.E-07
1.E-05
1.E-03
1.E-01
1.E+01
1.E+03
1.E+05
1.E+07
0 1 100 10000 1000000
time after plasma shutdown [years]
dose
rate
[Sv/
h]
Ag
Mo
W
FeV
recycling limit
hands-on-limit
natural dose 2 mSv/a
Neutron activation in some elements(5 MW/m2 in 2.5 years)
Schematic Fusion Reactor Build-up
cryostat
roomfor systems:1) diagnostics2) fueling3) heating4) maintenance
Magnets
plasma
vacuum vessel
plasma-facingcomponents
Normal operational effluents
• ALARA principle– lower project release limits
• Tritium 1 g/a• Activated dust 10 g/a• Corrosion products 50 g/a
• Dose limits:– vary by country: 0.1-5 mSv/a– average natural dose: 2 mSv/a
• Doses < 1% of natural dose
• Technical precedence used:– tritium plants– chemical plants (beryllium)– fission reactors
(esp. CANDU’s)– tokamak (D_T: JET, TFTR)
• Analysis for last year ITER shielding blanket operation
• Initial releases small:– limited use of tritium– low level of activation– time delay permeation of
tritium into coolant
Accidents:Design guideline atmospheric release
Ultimate safety margin:Evacuation threshold for ground level releases:Tritium: < 100 gTungsten dust: < 4 kg
Event
Category Incidents AccidentsHTO [g/event] 0.1 5Dust [g/event] 1 50
Accidents: Energy Sources
0.1 1 10 100 1000
plasma
fusion power-10s
magnetics
decay heat-1day
decay heat-1week
chemical
thermal
Energy Inventory [GJ]
Schematics of computer model for integrated accident analysis
Cryostat
Upper HTS Vault
Lower HTS Vault
ConnectingDuct
SuppressionPool
HTO &CPs
HTO &CPs
LeakFilteredDried
LeakFilteredDried
LeakFilteredDried
GenericBypassRoom
Leak
Cold magnetstructure,crowns,thermalshields
HTO &CPs
VV H-3
Dust
FW/ShieldandDivertor
EquatorialPit
PenetrationBypass Line
Accidents: Pressurization and decay heat
In-vessel decay heat driventemperature transient
VV cooled by natural circulation
• Accident scenario:
– multiple FW failure – all FW cooling pipes in
two toroidal rings damaged
– fast pressurization plasma chamber
– pressure limited by suppression system
– Maximum pressure ITER: 2 bar
– no in-vessel cooling
0
50
100
150
200
250
300
350
400
0.01 0.10 1.00 10.00 100.00
time [d]
T [C
]
FWshield-frontshield-backVV
1.E-12
1.E-10
1.E-08
1.E-06
1.E-04
1.E-02
200 400 600 800 1000 1200Temperature [C]
[kg
-H2/
m2
s] Be
W
C
Accidents: Hydrogen in ITER
Combustion wave propagates ~2000 m/s
Pressures from 15 to 20 bar
H2 formation in fusion:chemical reactions with hotplasma facing components, e.g.:
Be + H2O BeO + H2
H2 + air explosion
Accident: Loss of coolant w/o shutdown
Vault
Crane hall
Divertor
In-vessel LOCA
Pressuriser
Heat exchanger
VVPSS
Cryostat
Ex-vesselLOCA
Vacuum Vessel
10%/day
Environment No confinement credit
10%/day
Accident: Loss of coolant w/o shutdown
• In case of on-going plasma burn temperature increase in affected components.– failure of in-vessel
components at elevated temperatures
– ingress of steam into VV– Be/steam chemical
reactions– hazard of hydrogen
formation– bypass 1. confinement
barrier
• ==> plasma burn will be terminated by fusion shutdown system
Ex-vessel LOCA w/o plasma shutdown
0
400
800
1200
Tem
pera
ture
(°C
)
FW
0
0.050.1
0.150.2
0.25
Pre
ssu
re (
MPa)
PHTS Vault
VV
0
1
23
4
5
0.01 1 100 10000 1000000
Time (s)
Hyd
rog
en
(kg
)
in VV
20
40
kg-H
2
Accident analysis margins
• Large margins maintained because:
– limitation of radioactive inventories;
– inherent plasma termination processes;
– long time for component heat-up;
– gross structural melting impossible;
– multiple layers and lines of defense to implement radioactive confinement;
– design tolerant to safety system failures
• Maximum doses < 2 mSv (annual natural dose)
• ITER accident analysis has confirmed safety potential of Fusion Energy.
0.1 1.0 10.0 100.0
Loss of confinement in hot cell
Cryostat water/helium ingress
Cryostat air ingress
Arc near confinement barrier
Toroidal filed coil short
Failure of fueling line
Isotope separation system failure
Transport hydride bed
Stuck DV cassette
Air ingress during maintenance
DV ex-vessel coolant pipe break
VV coolant pipe break
Heat exchanger tube rupture
Pump seizure in divertor HTS
Loss of vacuum
Multiple FW pipe break
Blackout for one hour
Loss of off-site power (32 hours)
Loss of plasma control
% of release limit
totalACPdusttritium
Accident: Wet bypass
• Hypothetical event:– loss of coolant plus 2 failures
in one heating or diagnostic line (“wet bypass”)
– Analysis results:• plasma chamber
pressurizes• opening bypass /
suppression tank• transport radioactivity into
room• capture tritium, dust in
tank, settling of dust by gravity, condensation of HTO in room
• cleaning of room after 8 hours:
~15 g tritium released
Building
Divertor
In-vessel LOCA
VVPSS
Cryostat
Tube breakVacuum Vessel
Environment
Generic bypass room
100%/day
Heating or diagnostic system
Window break
Accidents: Loss of cooling Fusion Reactor
-300
0
300
600
900
1200
0.01 0.10 1.00 10.00 100.00days
tem
pe
ratu
re [
C]
First Wall
Vacuum Vessel
TF magnet
cryostat
Is it true ?
• V&V: verification & validation–verification
• correct coding• comparison between different codes and performers
–validation• comparison codes / data
Verification thermo-hydraulic codes
• Two codes used in ITER:– MELCOR (US)– INTRA (EU)
• benchmark: large loss of cooling accident in ITER vacuum vessel– initially some differences,
but both below design pressure 5 bar
– differences could be explained by different treatment of mixed flow of steam and water
• ==> feedback to design: lower pressures for separation of phases, e.g. pressure suppression system on top of vacuum vessel
0
0.5
1
1.5
2
2.5
3
ab
solu
te p
ress
ure
[atm
]
3.5
4
0 5 10 15 20 25
time [s]
30 35 40
INTRA
MELCOR-NSSR-2
MELCOR-seperate-phase-flow
Validation experiments steam vacuum
Validation thermo-hydraulic codes
• Two codes used for ITER:– MELCOR (US)– INTRA (EU)
• Comparison of code results with experimental data of water injection into vacuum vessel
• Problem is scaling: length 1/10 of ITER
• ==> larger surface/volume
0
100
200
300
400
500
0 20 40 60 80 100
seconds
pre
ssu
re [
kP
a]
ExperimentMELCORINTRA
14 MeV n-Source Experiment
SS316
Be
H2O
SS316
D-T Source #1 Beam Duct (160x80)
R
Z
50.8660.4609.8203.2
101.6
SS316 or CopperSupport
W alloy
600
400
382.
4
Fusion Neutron Source (FNS)
ITER Decay Heat R&D
.
0
-0.1
C-E
/E
time, days
0 1 2 3 4 5 6 7
AC T- 4/ FE NDL /A-2
ANI TA- 4M / FEN DL/A- 2
DKR -PUL SAR 2.0 / FEND L/A- 2
FISPAC T / FEND L/A- 2
R EAC - 3/ FE NDL/A -2
-0.05 .
.
.
.
.
.
0 1 2 3 4 5 6 7
A CT-4/ F EN DL/A -2
A NITA/ F EN DL/A -2
D KR-PULSA R2.0/ FEND L/ A-2
F ISP ACT/ FEN DL/A -2
REA C-3/ F EN DL/A -2
0.1
0
-0.1
C-E
/E
time, days
- 14 MeV n-irradiation at FNS at JAERI- Decay heat measurement: sum of ß, radiation
SS-316, 7 hours irradiation
-International code validation effort:- Uncertainties < 15%
Cu, 7 hours irradiation
JA dust mobilization experiments
Russian hydrogen detonation experiments
What if it is not true ?
”No-evacuation” limit and cliff-edge effects
• Release assumptions: ground level, duration 1 h, worst case weather
• No-evacuation limit (early dose):IAEA, ITER: 50 mSv
ITER “no-evacuation” limit met for tritium release < 90 g, in HTO form
No cliff-edge effect for tritium (For a hypothetical tritium release of 1 kg no-evacuation limit exceeded for < 1 km2)
Are
a [
km
2]
Long term contamination
Tritium concentration in soil after contamination
0.01
0.10
1.00
10.00
100.00
0.1 1.0 10.0 100.0 1000.0
days
[Bq
/g]
background level
Waste volumes fusion reactor
• Fusion optimized materials:
– V-alloys
– steel without Ni, Co
– impurities need careful attention (Nb, Ag, Co, U)
• Significant part (~30%) of activated material can be cleared
• Volume ~1-2 x larger than fission waste (not counting U-mining~1.5 Mm3)
• large fractions could be recycled
0
20
40
60
80
100
120
140
160
PM-1 (V-alloy/He)
PM-2(LAM/H20)
PM-3(LAM/He)
Plant Model
Acti
vate
d m
ate
rial (t
on
nes x
1000)
Non Active Waste (clearable)
Simple Recycle Material (<2 mSv/h)
Complex Recycle Material (2-20 mSv/h)
Permanent Disposal Waste (>20 mSv/h)
No burden to future generations
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
0 100 200 300 400 500
Time after final shutdown [years] .
PWR
Fusion-Vanadium
Fusion-steel-He/Be
Fusion-steel-H2O/LiPb
Coal
Radiotoxicity index for power plant waste
Conclusion
• Normal operation– dose < 1% of natural background
• Accidents– source term ~ 1000 times smaller compared to fission– if properly designed: no destruction due to internal
accidents– large reactions times– tritium and dust largest hazard >> allowable releases
• Waste– volumes comparable (~2 * larger) compared to fission– toxicity 1000 times smaller compared to fission– recycling might be feasible
• Safety and environmental features dependent on design
Other fusion reactions
(1a) D + D 3He + n + 3.3 MeV
(1b) D+D T + p + 4.0 MeV
(2a) D + 3He 4He + p + 18.4 MeV
(2b) D + T 4He + n + 17.6 MeV
(3) p + 11B 3 * 4He + 8.7 MeV
(4) p + 6Li 3He + 4He + 3.9 MeV
Equations (1a) – (2b) can be summarized as
3D 4He + p + n + 21.6 MeV
D in water ~3.3*e-5 energy content 1 liter water ~ 350 l gasoline
Advantages of fusion
• No radioactive raw material
• No chain reactions (small amount of fuel ~1 g in plasma)
• Moderate decay heat (large surfaces)
• Low biological toxicity and half-life time of activation products
• Generates no greenhouse gases (no SO2, NOx)