Iter Satya

7/31/2019 Iter Satya

1/41

InternationalThermonuclear Experimental

Reactor(ITER ) Safety Analysis

SATYA PRAKASH SARASWAT

11115061

PhD NET


2/41

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.


3/41

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.
http://www.iter.org/content/com/mach/CoolingWaterhttp://www.iter.org/content/com/mach/VacuumCryohttp://www.iter.org/content/com/mach/VacuumCryohttp://www.iter.org/content/com/mach/CoolingWater


4/41

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


5/41


6/41

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.
http://www.iter.org/content/com/mach/CoolingWaterhttp://www.iter.org/content/com/mach/CoolingWaterhttp://www.iter.org/content/com/mach/Blankethttp://www.iter.org/content/com/mach/Blankethttp://www.iter.org/content/com/mach/Blankethttp://www.iter.org/content/com/mach/CoolingWater


7/41

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..


8/41

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.


9/41

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


10/41

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.


11/41

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 ).


12/41

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


13/41

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)


14/41

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.


15/41

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


16/41

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).


17/41

Accidents involvs to

Divertor Cooling System


18/41

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


19/41

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


20/41


21/41

Accidents involving the Divertor

Cooling System

three LOCAs

two LOFAs


22/41

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).


23/41

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.


24/41


25/41

Accidents in the first wall cooling

system


26/41

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.


27/41

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.


28/41

First wall quarter loop

h f ll


29/41

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


30/41

Accidents in the first wall cooling

system

Three ex-vessel LOCAs

Loss-of-Flow Accidents (LOFAs)


31/41

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


32/41

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.


33/41

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.


34/41


35/41

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


36/41

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


37/41

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.


38/41

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


39/41

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


40/41

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


41/41

Thank you

Documents

Iter Satya