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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.

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

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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.

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

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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