Safety Considerations for the - PowerPoint Presentation

Slide1

Safety Considerations for the EU DCLL DEMO Blanket

Dario Carloni2nd EU-US DCLL Workshop14-15th November 2014UCLASlide2

Overview

The Strategy for ITER

Future FPPs

DEMO Blanket

Open

I

ssuesSlide3

The strategy for ITERNo in-vessel component is given any safety creditNo safety function for in-vessel componentsIn-vessel components regarded as “experimental”In safety analyses, in-vessel components always assumed to fail in an in-vessel incident/accidentThis puts additional burden on some ex-vessel components for the confinement function

e.g. because in-vessel part of primary cooling loop is always considered failed, ex-vessel parts of the loop are first confinement barrier (up to and including first isolation valve)Some in-vessel components do have shielding functionNeill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 3Slide4

Future Fusion Power PlantHigh availability will be essentialinterruptions to electricity generation unacceptableHigh reliability required of all components

In-vessel components must not failMay be possible to give them full safety credit for the confinement functionThis would simplify part of the confinement strategyCan’t do this for DEMO.But how far can we go?Safety analysis must demonstrate that any IVC failure will not affect the safety function of other systems

Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page

4Slide5

Possible safety functions for in-vessel componentsSafety functions we might assign to IVCs:First confinement barrier

Cannot be achieved with adequate reliability by some components (e.g. First Wall)Barrier to prevent propagation of accidente.g. blanket box, to avoid in-box LOCA pressurizing the vacuum vesselBarrier to avoid contact with certain fluidse.g. to avoid water reaching Be pebbles following divertor in-vessel LOCARemoval of decay heat following loss of coolingShielding

Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page

5Slide6

General Requirements

To

protect every inventory of radioactive, toxic or hazardous

material

to prevent mobilisation into rooms where personnel could be exposed

to prevent release to the environment that could lead to public exposure

To meet DEMO general safety objectives in compliance with the environment in operational / accidental situation

To

reduce potential impacts to the extent reasonably practicable

Confinement of RadioactivitySlide7

DCLL

T

ritium

will be mostly present in the

PbLi

and a non-negligible amount

may

permeate into the He

circuit

E

rosion

/corrosion

phenomena due to high metal velocity within the modules and manifolds

Fouling

High contamination

Activation

products, as Po-210 and Hg-203 (relatively volatile and highly radiotoxic

) and Fe-55 or Mn-54 may be transported in the coolant Draining of the breeder blanket in accidental scenario not possible

Confinement of RadioactivitySlide8

General Requirements

DCLL

To avoid over-pressurization of the VV

 Pressure Suppression Systems / EV

To avoid over-pressurization of the second confinement (EV/TB)

He

at 8

MPa

nominal

pressure with T

Permeation against vacuum (PAV)

for T extraction

PbLi

pressure is of vital importance since a sudden overpressure can cause the total damage of the PAV with consequences for safety.

Confinement of PressureSlide9

General Requirements

DCLL

Plasma

/(first) wall interactions causing erosion on the first wall

surface

The plasma-facing side of the first wall should be plated with 2-3 mm

tungsten

The produced micron range dust could ignite under

accidental

oxidation

conditions

Exothermic reactions of

PbLi

with air and water may take

place in accidental conditions

LiM

spill: several

possible configurations of interactions should be addressed dependent on contact modes: LM droplets sprayed in water, LM veins in water, and steam/ water jets into

LM

If high LM oxidation takes place (case of Li in LM droplets, steam in LM loop) a high hydrogen production

could occur

hydrogen explosion

Confinement of Chemical EnergySlide10

General Requirements

DCLL

S

tructural material shall remain

below

critical temperature values

Redundancy by

means of two or more circuits with the nominal working fluids will be

investigated

The

main heat removal function from structural material will be provided by

PbLi

, while He will provide backup function, even split in two parallel

circuits

Redundancy

Nevertheless

, common cause failure of all circuits should be addressed, depending on the specific blanket design, when mature enough, similarly to old concept activities.

Management of Long Term Heat RemovalSlide11

DCLL blanket concept

PbLi

activation products (Po-210, Hg-203)

Confinement StrategySlide12

Open Issues

The

number of

circuits will

affect the fraction of total radioactive inventory assumed to be released in postulated accidents, as in-vessel LOCA, ex-vessel LOCA, etc.

 to be decided basing on safety analyses

Safety

draining not

available

Passive pressure relief

systems to be provided

Interaction

between He and

PbLi

during accidental scenario

Safety

function for breeding blanket, 0 barrier

?Slide13

Thank you!Slide14

Objectives o

f DEMO confinement

Internal

hazards with potential radiological impact in case of

accident

To

protect every inventory of radioactive, toxic or hazardous

material

to prevent mobilisation into rooms where personnel could be exposed

to prevent release to the environment that could lead to public exposure

To meet DEMO general safety objectives in compliance with the environment in operational / accidental situation

To

reduce potential impacts to the extent reasonably practicable

internal

fire

internal explosion

thermal releases

plasma

transients / disruption

internal

flooding

missile

effects and pipe whip

Loss of Vacuum (

LOV)

mechanical risks

chemical risks

magnetic and electromagnetic risksSlide15

Passive safety methods

Passive Containment Cooling System (PCCS)

meets the single-failure criteria and probabilistic risk assessments (PRA) used to verify reliability.

relies on heat removal only by naturally occurring forces such as gravity, natural circulation, condensation and evaporation to keep the containment within the design limits of pressure and temperature.

automatically activate in the unlikely event of a plant emergency

.

can be applied

for DEMO WCLL concept using water

cooling.

passive pressure relief systems and rupture

panels

VV is connected to the VVPSS

/EV

by pressure relief devices with rupture

disks.

pressure relief system

to

reduce overpressure of

containment (HCPB, HCLL)For the DCLL concept interaction between He and PbLi ?Safety function for breeding blanket, 0 barrier?Confinement requirement due to different blanket concepts (e.g. He/PbLi interaction in the confinement of DCLL concept)Slide16

Options for confinement barriersRequirements of confinement barrier:SICFully and regularly inspectable.

ITER Port Closure Plate:Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 16Slide17

In-box LOCA Scenarios

To limit the in-box pressure a pressure relief valve outside the bioshield into a large volume in the building could be considered:HCPB: In the He purge gas loop this might be feasible.WCLL, HCLL, DCLL: In the LiPb loop a fast expansion of the liquid metal towards the relief valve will be prevented by MHD effects.

Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page

17Slide18

Consequences of assigning function to a componentSafety function must be assured in all loading conditions within design basis (Cat.1 – Cat.4)Appropriate Codes and Standards must be used for design and fabrication (probably, “nuclear” codes)Materials must be fully characterized in all conditions (to Cat.4) and for full component lifetimeincluding effects of irradiation, neutron damage, corrosion, etc.if not included in the Code, it may be adequate

to develop DEMO Structural Design Criteria (SDC-IC), as at ITERComponent will be classified Safety Important (SIC)high quality fabrication with inspections by safety authorityin-service inspection requirementsNeill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page

18Slide19

BackgroundIn the event of a Loss of Coolant Accident (LOCA), escaping coolant may be radiologically contaminatedcontains permeated tritium, Activated Corrosion Products, sputtering productsin case of in-vessel LOCA, may also carry substantial part of in-vessel tritium and active dust inventoryFlow rate too high to send through detritiation systems and filters and then vent to environment

Escaping coolant must be containedFor water, can use suppression pool (like ITER)For helium, very large expansion volume may be neededFor PPCS Model B (HCPB), 50,000 m3 required.Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 19Slide20

PPCS approach

Rupture disks connect Steam Generator Hall and Vacuum Vessel to Expansion VolumesNeill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 20Slide21

Options to consider for DEMOSegmenting He loops to limit maximum spillstill need to consider multiple-loop LOCAs as beyond design basis eventIsolation valves to limit spillcan they close fast enough?dividing coolant flow into multiple pipes to reduce biggest leak size and thereby reduce maximum He flow rate

Heat exchanger on duct entering Expansion Volume, to cool hot He and reduce peak pressureUse parts of building volumes as expansion volumessome large volumes available, but can they be leak-tight?may contaminate building rooms, but could they be used only in extremely unlikely events?Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 21Slide22

Further issueMay need to consider simultaneous water and helium LOCA in-vessel (from divertor and blanket)May be design extension condition, but cannot be excludedHow to separate, to condense steam and to cool and contain He?Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page

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