EU DCLL DEMO Blanket Dario Carloni 2nd EUUS DCLL Workshop 1415th November 2014 UCLA Overview The Strategy for ITER Future FPPs DEMO Blanket Open I ssues The strategy for ITER No invessel component is given any safety credit ID: 573161
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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
22