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InternationalThermonuclear Experimental
Reactor(ITER ) Safety Analysis
SATYA PRAKASH SARASWAT
11115061
PhD NET
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The international ITER project for
fusion: Why?
Q 10 represents the scientific goal of the
ITER project: to deliver ten times the power
it consumes.
From 50 MW of input power, the ITER
machine is designed to produce 500 MW of
fusion powerthe first of all fusion
experiments to produce net energy.
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Power Supply
Electricity requirements for the ITER plant
and facilities will range from 110 MW to up to
620 MW for peak periods of 30 seconds
during plasma operation.
The cooling water and cryogenic systems will
together absorb about 80% of this supply.
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ITER component Specification
ITER is based on the 'tokamak' concept of
magnetic confinement, in which the plasma is
contained in a doughnut-shaped vacuum vessel
The fuela mixture ofdeuterium and tritium
two isotopes of hydrogenis heated to
temperatures in excess of 150 millionC, forming
a hot plasma. Strong magnetic fields are used to keep the
plasma away from the walls
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ITER Vacuum Vessel
The vacuum vessel houses the fusion reaction and acts as afirst safety containment barrier.
the larger the vessel, the greater the amount of fusionplasma & power that can be produced.
The ITER vacuum vessel will be twice as large and sixteentimes as heavy as any previous tokamak, with an internaldiametre of 6 metres. It will measure a little over 19 metresacross by 11 metres high, and weigh in excess of5,000tons.
The vacuum vessel will have double steel walls, withpassages for cooling water to circulate between them.
The inner surfaces of the vessel will be covered withblanket modules that will provide shielding from the high-energy neutrons produced by the fusion reactions.
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Cryogenic technology
used at ITER to create and maintain low-temperature conditions for the magnet, vacuumpumping and some diagnostics systems.
cooled with supercritical helium at 4 K (-269C) inorder to operate at the high magnetic fieldsnecessary for the confinement and stabilizationof the plasma
The cryogenic system has been designed to
guarantee cooling and stable operation for ITERmagnets, cryopumps and thermal shields
Cont..
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ITER cryogenic system will be the largestconcentrated cryogenic system in the world with
an installed cooling power of 65 kW at 4.5K(helium) and 1300 kW at 80K (nitrogen)
The ITER cryostat will be 31 metres tall and nearly
37 metres wide. liquid helium boiling 4.2 K at ambientpressure
and provides the cold source to extract andtransfer heat from the components to the
cryoplant. Forced-flow supercritical helium circulates
through ITER components to remove heat andprovides the required low temperatureenvironment.
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Cryoplant
The cryoplant is composed ofhelium and nitrogen refrigeratorscombined with a 80 K helium loop.
Storage and recovery of the helium inventory (25 tons) is providedin warm and cold (4 K and 80 K) gaseous helium tanks.
Three helium refrigerators supply the required cooling power via an
interconnection box providing the interface to the cryodistributionsystem.
Two nitrogen refrigerators provide cooling power for the thermalshields and the 80 K pre-cooling of the helium refrigerators.
The ITER cryogenic system will be capable of providing cooling
power at three different temperature levels: 4 K, 50K and 80K. cryostat is the secondary confinemnt barrier for invessel inventories
in the ITER design
The cryostat is completely surrounded by a concrete layer known asthe bioshield. Above the cryostat, the bioshield is two metres thick
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Cooling Water
ITER will be equipped with cooling water
system to manage the heat generated during
operation of the tokamak.
The internal surfaces of the vacuum vessel (first
wall blanket and divertor) must be cooled to
approximately 240C only a few metres from
the 150-million-degree plasma.
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ITER Cooling Systems
design includes four independent primary
cooling systems for removal of the generated
power
the first-wall cooling system (480 MWth);
the blanket cooling system (710 MWth);
the divertor cooling system (210 MWth);
the vacuum-vessel cooling system (60 MWth ).
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ITER reference accidents
plasma transients
Loss of power
In-vessel coolant leak
Ex-vessel coolant leakage
Heat exchanger (HX) tube leakage
Loss of Vacuum (LOVA)
Accidents involving the ingress of air, helium,or water into the cryostat
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Loss of coolant flow accidents
The consequences of LOFA accidents are mild
If plasma burn is terminated within a fewseconds and pump inertia and natural coolant
convection provide coolant flow in the
primary cooling systems (at a level of at least
2% of the nominal capacity after pump
coastdown)
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Loss of coolant accidents inside the
vacuum vessel
A LOCA due to failure of in-vessel components or
pipework may have the following consequences:
- plasma disruption,
- temperature transients due to loss of heatremoval,
- pressurisation of the vacuum vessel,
- chemical reactions, - radioactivity mobilisation with potential
dispersion from the vacuum vessel.
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Loss of vacuum accidents
A LOVA due to failure of the vacuum vessel or
attached equipment
plasma disruption,
- temperature transients,
- pressurisation of the vacuum vessel,
- chemical reactions,
- radioactivity mobilisation from the vacuumvessel
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Possible tritium inventory in Different
Components of ITER
The dominant mobilizable source terms for ITER aretritium
In in-vessel co-deposited layers: 1 kg,
In primary coolant loops: 10 g per loop,
In tritium plant: generally 100 g per component, (isotope separation system (ISS)250 g),
activation products:
Tokamak dust: 100 kg (tungsten, steel or copper)
Activated corrosion products: 10 kg per
loop (510 times less hazardous compared to Tokamakdust).
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Accidents involvs to
Divertor Cooling System
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The ITER Divertor
The divertor is one of the key components of the
ITER machine.
Situated along the bottom of the vacuum vessel,
its function is to extract heat and helium ash both products of the fusion reaction and other
impurities from the plasma.
divertor cooling system is the most critical system
since it has the largest power density.
D i h t i ti f th di t
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Design characteristics of the divertor
cooling system
Thermal power 210 MW
Pressure at inlet of the divertor plates 3.5 MPa
Coolant temperature inlet divertor plates 333 K Mass flow 3345 kg/s
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Accidents involving the Divertor
Cooling System
three LOCAs
two LOFAs
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LOCAs in Divertor Cooling System
The LOCAs are considered to be initiated by a break
of a coolant pipe. The following LOCAs have been
analyzed
- a break of the cold leg of the main cooling circuit(location A in fig. 1);
- a break of a feeder from an inlet ring collector to a
sector manifold (location B in fig. 1);
- a break of the surge line of the pressurizer (location
C in fig. 1).
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LOFAs in Divertor Cooling System
A LOFA implies a loss of the forced coolant flow in theprimary system. The LOFAs are considered to be initiatedby a loss of the electric power of the primary
coolant pump (pump trip). The following LOFAs have
been analyzed:- a LOFA without plasma shutdown;
- a LOFA with plasma shutdown initiated 10 s after
initiation of the pump trip. The plasma shutdown is
simulated by a linearly decreasing power from 210MW (nominal power) to 0.076 MW (decay heat power) in
10 s.
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Accidents in the first wall cooling
system
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The First Wall Cooling System
primary cooling system of the first wall
consists of four separated first wall quarter
loops.
Each first wall quarter loop removes the heat
generated in four adjacent sectors.
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First wall quarter loop
Each first wall quarter loop has
a hot leg and a cold leg;
an inlet and an outlet ring collector;
a pressurizer connected to the hot leg;
a heat exchanger to transfer the heat from the
primary cooling circuit to the secondary cooling
circuit;
a recirculation pump located in the cold leg.
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First wall quarter loop
h f ll
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Design Characteristics of a First Wall Quarter
Loop
Process parameter Value
Design parameters
Thermal power 120 MW
Coolant temperature inlet manifolds 333 K
Coolant temperature outlet manifolds 433 K
Coolant velocity in primary piping 4.0 m/s
System characteristics
Coolant mass flow 296 kg/s Coolant inventory 22000 kg
Pressurizer pressure 2.12 MPa
System frictional pressure losses 0.66 MPa
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Accidents in the first wall cooling
system
Three ex-vessel LOCAs
Loss-of-Flow Accidents (LOFAs)
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Ex-vessel LOCAs in the first wall
cooling system
An ex-vessel LOCA results from a rupture of a
cooling pipe located outside the vacuum vessel
1. a large break of the cold leg of the main circuit
2. an intermediate break of a sector inlet feeder
3. an intermediate break of the surge line of the
pressurizer.
The analysis of these LOCAs performed without plasmashutdown in order to study the worst case
conditions
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in-vessel LOCAs in the first wall cooling
system
An in-vessel LOCA may result from a rupture of acooling pipe inside the vacuum vessel. Thiscauses an ingress of coolant into the vacuumvessel, resulting in a plasma disruption.
Two in-vessel LOCAs
1. an intermediate break of the outlet feeder of an
outboard segment circuit;2. a small break of one single cooling pipe located
in the outboard first wall.
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LOFAs in the first wall cooling system
A LOFA results from a loss of the forcedcoolant flow. In the present analyses, the lossof the forced coolant flow is caused by a loss
of the electric power of the recirculationpump in the primary circuit
Three LOFAs
1. a LOFA without plasma shutdown;
2. a LOFA with delayed plasma shutdown;
3. a LOFA with prompt plasma scram.
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Ingress of coolant (ICE) event & Loss of
vacuum (LOVA)
the ingress of coolant (ICE) event
and the loss of vacuum (LOVA) event are
considered as one of the most serious
accident.
On the assumption of LOVA occurring after
ICE, it is inferable that activated dusts are
under the wet condition
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ICE event
In ICE event the cooling tubes installed into plasma-facingcomponents are broken and the cooling water enters intothe vacuum vessel.
Then the cooling water boils and evaporates because of
the high temperature of the in-vessel components andthe low pressure in the vacuum vessel.
pressure in the vacuum vessel increases rapidly.
Then safety devices such as the vacuum vessel
pressure suppression system (VVPSS) are suppose to
start
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AIR INGRESS ACCIDENT
The postulated air ingress accident results from a
breach in the cryostat boundary .
result of a material failure, long crack in a weld or
a metal bellows failure at a cryostat penetration
air from an adjoining room enters the cryostat.
Since the cold magnet structures of the cryostat
act as cryosoiption surfaces, the air that enters thecryostat will condense and form air-ice on these
surfaces.
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It has also been postulated that a toroidal field
(TF) magnet could experience an electrical insulationfault that results in an intense electrical arc.
it is assumed that sufficient energy is available to melt
1. helium cooling line.
2. Primary Heat Transport System (PHTS) guard pipe,
3.and the PHTS coolant pipe within the guard pipe.
PARAMETERS FOR AIR INGRESS
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PARAMETERS FOR AIR INGRESS
ACCIDENT: cryostat vessel design pressure is 0.2 MPa
the TF coils fast discharge, raising their temperature upto 55 K
slow train of the Fusion Safety Shutdown System FSSS(60 sec shutdown)
vacuum vessel and its cooling systems are intact; there is no release of radioactive materials from
the vacuum vessel
cold structures in the cryostat serve as natural
cryosorption surfaces, pumping the air and formingice on their surfaces
after 24 hr, the air ingress is assumed to be reversed
by operator actions
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References
http://www.iter.org
LOCA, LOFA and LOVA analyses pertaining to NET/ITER
safety design guidance; Edgar Ebert and Jtirgen Raeder; Fusion Engineeringand Design 17 (1991) 307-312
Safety Analysis Results for Cryostat Ingress Accidents in ITER, B. J. Merrill,2 L. C.
Cadwallader,2 and D. A. Petti2, Journal of Fusion Energy, Vol. 16, Nos. 1/2,1997
Analysis of loss-of-coolant and loss-of-flow accidents in the divertor coolingsystem of NET/ITER, H.Th. Klippel and E.M.J. Komen; Fusion Engineering andDesign 17 (1991) 321-328
ITER reference accidents, H.-W. Bartels a,*, A. Poucet a, G. Cambi b, C. Gordon
a, M. Gaeta c, W. Gulden d; Fusion Engineering and Design 42 (1998) 13
19 Analysis of Loss-of-Coolant and Loss-of-Flow Accidents in
the First Wall Cooling System of NET/ITER,E. M. J. Komen t and H. Koning ; Journalof Fusion Energy, Vol. 13, No. 1, 1994
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Thank you