Download pptx - Safety Considerations for the EU DCLL DEMO Blanket Dario Carloni 2nd EU-US DCLL Workshop 14-15th November 2014 UCLA

Safety Considerations for the EU DCLL DEMO Blanket

Dario Carloni

2nd EU-US DCLL Workshop

14-15th November 2014

UCLA

Overview

The Strategy for ITER

Future FPPs

DEMO Blanket

Open Issues

The strategy for ITER

• No in-vessel component is given any safety credit• No safety function for in-vessel components• In-vessel components regarded as “experimental”• In safety analyses, in-vessel components always

assumed to fail in an in-vessel incident/accident• This 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 function

Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 3

Future Fusion Power Plant

• High availability will be essential• interruptions to electricity generation unacceptable

• High reliability required of all components

• In-vessel components must not fail

• May be possible to give them full safety credit for the

confinement function

• This would simplify part of the confinement strategy

• Can’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 systemsNeill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 4

Possible safety functions for in-vessel components

Safety 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 accident

• e.g. blanket box, to avoid in-box LOCA pressurizing the vacuum vessel

• Barrier to avoid contact with certain fluids

• e.g. to avoid water reaching Be pebbles following divertor in-vessel

LOCA

• Removal of decay heat following loss of cooling

• ShieldingNeill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 5

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 Radioactivity

DCLL

Tritium will be mostly present in the PbLi and a non-negligible amount may permeate into the

He circuit

Erosion/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 Radioactivity


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 Pressure


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 conditionsLiM 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 LMIf 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 Energy


DCLL

Structural 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 Removal

DCLL blanket concept PbLi activation products (Po-210, Hg-203)

Confinement Strategy

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?

Thank you!

Objectives of 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 risks

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)

Options for confinement barriers

Requirements of confinement barrier:• SIC• Fully and regularly inspectable.

ITER Port Closure Plate:


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.


Consequences of assigning function to a component

• Safety 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 lifetime• including 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 ITER

• Component will be classified Safety Important (SIC)• high quality fabrication with inspections by safety authority• in-service inspection requirements


Background

• In the event of a Loss of Coolant Accident (LOCA), escaping coolant may be radiologically contaminated• contains permeated tritium, Activated Corrosion Products,

sputtering products• in case of in-vessel LOCA, may also carry substantial part of in-

vessel tritium and active dust inventory

• Flow rate too high to send through detritiation systems and filters and then vent to environment

• Escaping coolant must be contained• For water, can use suppression pool (like ITER)• For helium, very large expansion volume may be needed

• For PPCS Model B (HCPB), 50,000 m3 required.


PPCS approach

• Rupture disks connect Steam Generator Hall and Vacuum Vessel to Expansion Volumes


Options to consider for DEMO

• Segmenting He loops to limit maximum spill• still need to consider multiple-loop LOCAs as beyond design

basis event

• Isolation valves to limit spill• can 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 pressure

• Use parts of building volumes as expansion volumes• some large volumes available, but can they be leak-tight?• may contaminate building rooms, but could they be used only in

extremely unlikely events?


Further issue

• May need to consider simultaneous water and helium LOCA in-vessel (from divertor and blanket)

• May be design extension condition, but cannot be excluded

• How to separate, to condense steam and to cool and contain He?
