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Technical Challenges
on the path to DEMO
Derek Stork
Euratom-CCFE Fusion Association,
Culham Science Centre,
Abingdon, OX14 3DB, UK
International Meeting “MFE Roadmapping in the ITER Era”
PPPL, 7th-10th September 2011
(this work was supported by UK EPSRC and Euratom)
CCFE is the fusion research arm of the United Kingdom Atomic Energy Authority
This is a personal
opinion…………
… intended as a contribution to a debate …
How can we gain back time on Fusion’s
Development Roadmap?
International Meeting “MFE Roadmapping in the ITER Era”
PPPL, 7th-10th September 2011
(this work was supported by UK EPSRC and Euratom)
CCFE is the fusion research arm of the United Kingdom Atomic Energy Authority
Outline
• Comments on Fusion Roadmap ‘standard model’
– DEMO mission and critical path
• Dividing resources for a “DEMO programme” into:
– Baseline
– Optimisation programme
– Strategic Risk Reduction programme
• Categorisation of DEMO Technical Challenges
– Baseline, Optimisation or Strategic Risk Reduction?
– Characteristic of challenge
– Motivate definition of the ‘DEMO Stage’
– Use in refining the Accompanying Programme to ITER (and perhaps
ITER “Phase II”?)
• Baseline DEMO Technical Challenges & programme elements
• ‘DEMO Optimisation’ Technical Challenges & programme
elements
• ‘DEMO Strategic Risk Reduction’ programme elements
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Fusion Roadmap
(still a Fast Track ?)
Concept improvements
Satellite ?
Tokamak
JET + Power
Other m/c ITER DEMO
DEMO
Plants
IFMIF
(Materials
testing)
? Need to define the
Technology Programme ‘DEMO stage’ mission
and facilities
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Roadmap: DEMO’s mission
• The main DEMO reactor is the ‘last research machine’
before the First of a Kind Fusion Power Plant (FPP).
• In Europe DEMO’s mission has been quoted as:
– completion of nuclear lifetime testing of in-vessel components;
– demonstration of tritium self-sufficiency – integration of full breeding
blankets into full tritium fuel-cycle plant;
– demonstration of efficient and low-turnaround remote maintenance
and replacement of the key tokamak systems (divertor and blanket);
– demonstration of fusion’s environmental (low activation materials)
and safety (safe operation; acceptable licensing/safety case) credits;
– supply of nett electricity to the grid;
supply of nett electricity (several 100 MWs) at intermittent times
– demonstration of high level of reliability and availability;
Demonstration economically competitive electricity. at end of programme
– supply of of high levels of reliability and availability
allow economic assessment of a fusion power plant
Urgent to have early DEMO implementation – ‘existence proof’ important for
those outside Fusion! – de-emphasise the economics.
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Roadmap: DEMO’s critical items (I)
Load Assembly remains the core of any DEMO machine
System and Detailed design and validation of
Load Assembly in-vessel items requires
full nuclear qualification of
structural materials.
finalised/qualified Blanket concept
finalised/qualified Divertor concept
Moreover System and Detailed design of
Balance-of-Plant and Remote Maintenance
requires
finalised/qualified Blanket and
Divertor concepts
Clearly these items are the ‘critical three’ for
DEMO concept
DEMO
based on PPCS Model C) – KIT, CEA (2007)
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Roadmap:DEMO’s critical items (II)
For the Blanket, the Divertor and the nuclear degradation of their structural and
PF materials
Engineers must have validated data and engineering rules for final
design against anticipated Load conditions and degradation of properties.
Everything is inter-dependent in a complex way.
Detailed examples abound
Eurofer embrittlement
Creep issues for Eurofer
…Use active cooling?
…or..
… use ODS?
…or…
Source – 2008 Ann Report of the Association FzK/Euratom – EFDA/06-1454 study E Magnini et al
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Roadmap: DEMO critical paths (I)
• No timetabled path to Requires IFMIF tests
producing at divertor with
~50 MW.m-2 handling .
• Other key items for
DEMO detailed design ITER schedule gives this as ~2029
are on critical paths with
relatively fixed long lead
duration:
– nuclear qualification of
structural materials to
~ 4-6 MW.a.m-2 14 MeV
neutron flux;
– output of post-
experimentation testing of
TBMs from ITER DT
operation.
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Roadmap: DEMO critical paths (II)
IFMIF
No accepted timetable for IFMIF, but we take ‘Critical’ (middle of the road)
timescale from EU Road-mapping presentation §
At 20 dpa/fpy 40 dpa is reached in 2030
Conclusion: crucial data from Blankets and Nuclear Materials is not
available until ~ 2029-30: marks the point at which ‘system design’ can start
§ Moslang, Baluc, Diegele, Fischer et al., CCE-Fu Workshop on EU Fusion Roadmap – Garching April 2011
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Dividing the DEMO stage
programme areas
• ‘DEMO Baseline programme’
– aim to realise the DEMO machine at the earliest possible time;
– Handle the ‘DEMO-phase’ major risks.
• ‘DEMO optimisation programme’
– Concentrates on developing technologies/techniques which
Resources
• make cost-of-electricity more attractive;
• Improve reliability of plant
• can be ‘feasibly’ incorporated relatively late into DEMO-phase.
• ‘DEMO strategic risk management programme’
– handles the ‘long-term’ programme technical risks
– develops technologies/systems which will ‘future proof’ a Fusion Economy
All potential programme expenditure (Technology Facilities,
Satellite Machines, Development Lines) should fit into one of these
programmes.
Use this categorisation to determine where the contributions of eg.
ITER can best be utilised, and avoid duplication of effort.
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baselining DEMO choices
…carry out preparation/evaluation phase with the basic philosophies of…
• Using ‘Systems engineering’ and ‘Systems code’ approach
• Not introducing further competing critical paths –
Baseline should be conservative.
• Aiming for a reliable and available product – maximum use of Industry
at this stage in Baseline programme R&D.
• Maximising use of synergy/common cause with other technology
development fields
– Generation IV fission materials, High Temperature superconductors etc.
-- both for inclusion and exclusion from the baseline!
….In an EU context – ‘Preparation Phase’ would run to mid-2010s to allow
evaluation of the Baseline options, establish Core Design Team(s) and
complete BA activities.
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
‘Baseline’ will be an evolving entity
can’t fix everything on ‘Day 1’ but all have to be firm in time
System Reviews Overall SDR
Baseline
Programme
Optimisation
Programme
Re-baseline Final baseline
(n – off) decision
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline Programme Elements:
characteristics
Baseline programme should concentrate on:
showstoppers to operation – where ‘existence
proof is needed’ eg, Divertor
the novel elements of the DEMO stage – where
full-scale integrated tests will occur for the first
time eg, Blanket and Ancillary systems
the core of the Load Assembly
key drivers for Machine Integrity and
Availability eg, Structural Materials, Remote Handling
decisive tests to enable focussing selection from
competing solutions to core needs. eg, H&CD systems
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline:Structural Materials (I)
• DEMO mission + Systems approach with ‘Conservative Baseline’ filter should
produce an operating concept to give Baseline structural material.
Conservative approach favours existing Reduced Activation Ferritic-Martensitic
(RAFM) steels eg. Eurofer.
– Improving engineering database for RAFM steels exists
• Engineering parameters
• Radiation effects
• Joining techniques
but:
– RAFM steels have known narrow temperature operating window
• must be ~ > 350ºC to avoid radiation embrittlement
• Must be ~ <550ºC to avoid loss of strength/creep rupture issues
– and He-induced swelling at high dpa values
• If, more developmental HT steels eg. Oxide Dispersion Strengthened (ODS)
alloys are to be in the Baseline, they must pass clear, simple criteria for basic
properties (eg. ductility at room temperature) by an early date.
• Baseline risk-mitigation is needed for known Eurofer shortcomings, eg:
– characterise as far as possible ahead of IFMIF tests;
– minimise by design choices;
– seek common solutions from Fission developments
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline:Structural Materials (II)
Eurofer risk-mitigation by design/system choices
Baseline slightly higher Cost-of Electricity Design for (examples!):
(CoE) target for the first DEMO -- high temperature operation
– system studies (PROCESS) show (no change in DBTT)or
decreasing gains above ~ 60 dpa. -- high temperature annealing cycles
-- Availability (dependent on Blanket (ductility restored)
Lifetime) can be sustained by increasing
machine size.
15
Cost of electricity (cents/kWh)
10
5
85
0
0 5 10 15 20 25
Plant Availability (%)
2
Blanket lifetime fluence (MW.year/m ) 80
75
Ward & Dudarev :
70
IAEA FEC 2008 7 8 9 10 11
Major Radius (m)
Gaganidze: J Nucl Matls & IAEA FEC 2008
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline:Structural Materials (III)
Risk-mitigation by characterisation of Eurofer ahead of IFMIF
Transmutation in pure Fe Lattice helium: He ‘eyes’ – 5.8 103 appm
– realistic reactor FW spectrum simulated
– reactor PPCS Model B simulation
[Gilbert & Sublet: Nucl Fusion 2011]
[Materna-Morris et al: IAEA FEC 2008]
103 appm/ Surface helium:He2+ beam
~ 100 dpa
Use ‘isotopic tailoring’ to produce He-in lattice [Jitsukawa et al: IAEA FEC? 2008]
• Simulated by (example!) 10 B- doped RAFM steel He significantly increases
brittleness at
~ > 400 appm (lattice results) – in conjunction with ~ 17 dpa
Simulate by Ion beam bombardment – He2+ (Caution! – representative of bulk??)
• Surface He bombardment shows enhanced embrittlement at ~ 10 – 100 appm/dpa
September 2011
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting
Baseline:Structural Materials (IV)
Eurofer risk-mitigation seeking common solutions with Fission steels
“Future steels development options will be based on
evolutionary (ingot metallurgy/classical precipitation) and
revolutionary (nanoscale ODS) approaches” – S Zinkle – 23rd SOFT
• Generation IV Fission programme
needs high-temperature steels ODS-Eurofer
• If we aim for ~50 dpa for early DEMO
ODS Ferritics
baseline then we overlap requirements
of many GenIV concepts (Zinkle,
Diegele)
Eurofer
• Industry is much more at home with
classical metallurgy
• Common developments to obtain RA
versions of Fission ‘3rd and 4th
generation’ FM steels?
(research melts have >105 hours at
~ 620ºC)
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline: EU Blankets (I)
EU Power Plant Conceptual Studies (PPCS-2005) featured blanket concepts
PPCS Structural Blanket concept Divertor
Model material (breeder/coolant) (coolant)
A Eurofer WCLL W/Cu/water
(LiPb/water)
AB Eurofer HCLL W/He
(LiPb/He)
B Eurofer HCPB W/He
(Li4SiO4/Be/He)
C Eurofer/ODS DCLL W/He
(LiPb/He/LiPb)
D ODS/SiC SCLL W/LiPb
(LiPb/LiPb)
These Blanket concepts chosen for EU ITER TBM.
EU has a pair for ‘baseline’ concepts – one eventually to ‘optimisation’?.
Programmatically, ITER programme pays for this DEMO development
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline: EU Blankets (II)
Boccacini - Invited Talk; 26th SOFT, Porto, 2010 + 2 Orals; + 14 Posters
HCPB HCLL
He Collector He Feeding
FW + SP & He FW + SP
feeding CP
PbLi outlet
PbLi collector
He inlet FW
He outlet
CP
PbLi inlet
SP
PbLi feeding
Figure 1 : He Series flow configuration of HCLL blanket module.
Concepts differ in Balance of Plant Tritium extraction details
… but at least the Helium balance of plant will have similar issues
Common advantage potential high thermal efficiency from helium cooling.
Common disadvantages: high helium pumping power; lack of developed helium
Balance of Plant (compared to PWR ‘off the shelf’ BoP for water-cooled blanket)
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline:EU Blankets (III)
• ‘Leading concept’ choice needed eventually to progress DEMO conceptual
design of BoP- facility-based R&D to decide this.
• ‘Systems Engineering’ based choice - focus on merits & drawbacks:
– Corrosion of Eurofer piping by the Lithium-lead coolant - lack of data at blanket flows
(few mm/sec to avoid MHD)
modelling shows acceptable corrosion rates, ~ 20 mm.yr-1 for the low flow rates;
– fabrication of the Li- ceramic pebbles without the cracking currently seen, and also
without key impurities which delay hands-on recycling (eg. Pt-193 in the Lithium-ortho-
silicate pebbles);
– higher radiation damage in the solid breeder - embrittlement of the beryllium pebbles
and occurrence of high swelling above 550°C,- compromising high temperature ops;
– tritium release from beryllium pebbles poor until temperatures (~750°C) -- too high for
known steels ( inadequate tritium recovery and high in-situ tritium inventory);.
Alternative beryllide alloys (eg. Be12Ti) with more acceptable tritium release
are in development, [Japan-EU BA ] currently no pebble-based solution.
• liquid breeder, with low radiation damage issues appears advantageous,
but needs more highly enriched fuel (90% 6Li cf. 40% for HCPB) to achieve
similar tritium breeding ratios (HCLL TBR, = 1.12; HCPB TBR = 1.15).
• HCPB might eventually be regarded as an ‘optimisation programme’ item?
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline: EU Blankets (IV):
Determine Remote Handling concept
‘Multi Module Segment’
concept
MMS now the favoured EU concept - applies to HCPB and HCLL advantages :
- pipe re-welding (He production limit) located in a low neutron flux region
- improved manifold design - decreases He pressure drop;
- limits EM loads on module attachments in case of disruption
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline: Divertor (I)
Divertor power loading is a show-stopper issue for a DEMO reactor –
~ 50 MW.m-2 ‘unshielded’
As a solid, only Tungsten can satisfy criteria of melt-damage resistance, high
thermal conductivity and low-erosion under plasma bombardment.
Tungsten validation:
JET ILW should further validate Tungsten as Divertor PFC material (2013-4)
JET DT experiments to validate low-tritium retention in tungsten
(seen eg. in D+ plasma streams on Pilot PSI) (2015)
ITER ‘Phase II’ should run a full Tungsten divertor – water-cooled ~ 15 MW.m-2
ITER Divertor monobloc
~ 15 MW.m-2
W
This programme is important, but not sufficient to test a DEMO concept
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline: Divertor (II)
• Divertor baseline will be actively cooled – even if clever
concepts can give (see later) order of magnitude relief.
• Chosen concept needs a full-power density test:
- on a HHF facility but also
- in a tokamak environment.
• This mission alone is important enough to justify a
‘DEMO stage satellite’ machine – as part of the DEMO
Stage baseline programme.
• DEMO Divertor satellite would require:
– Long pulse (cf. tR) capability for ‘steady-state’ plasmas;
– heating, current drive, fuelling, plasma (& ELM??) control
systems to enable high radiation fraction plasmas at high b for
testing the Divertor.
– High pressure, high temperature Helium or water coolant loop
(or both!)
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline: Divertor (III) Physics Scenarios
System studies, eg. PROCESS code in Fusion Power Plan
studies show:
CoE depends more heavily on operational and
engineering parameters than on physics variables:
1 0.6 1 1
CoE ( ) D J Ward, CCFE EFDA-
A th.5 Pe0.4 b N.4 N GW
0 0 0.3 RP-RE-5.0[2004]
Availability Physics - high b,
Thermodynamic Net electrical power high density
efficiency
Thus technology development is more important than physics
development at the DEMO Stage.
However the physics
determines if the scenario is basically feasible/attractive
scenario interacts with the technology as a key selection
criterion (via the Divertor and the H&CD)
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Choosing Baseline Physics Scenarios :
- better avoid too much science fiction
EU PPCS - 2005 • PPCS invoked
-- high density operation – significantly above
Greenwald and
-- enhanced energy confinement
to achieve high b and high fusion yield
PPCS A PPCS B PPCS C PPCS D
Ip (MA) 30.5 28.0 20.1 14.1
Pfus (GW) 5.0 3.6 3.4 2.5
R (m) 9.55 8.6 7.5 6.1
BT @ R (T) 7.0 6.9 6.0 5.6
Energy confinement 20% above ITER 30% above 20%
enhancement ITER above
ITER
PPCS plasma cross-sections
(& ITER for comparison) Density Limit 20% above ITER 50% above ITER
D Maisonnier et al. NF47 bN (thermal pressure) 2.8 2.7 3.4 3.7
(2007) 1547 PCD (MW) 246 270 112 71
High b gives high Q 20 13.5 30 35
Bootstrap current Bootstrap current 0.45 0.43 0.63 0.76
fraction
reduces external CD
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Choosing Baseline Physics Scenarios (II):
– site your machine conservatively.- better find out the scaling laws in DEMO-like plasmas
‘Advanced’ DEMOs are not sited DEMO Plasmas will be in a novel
conservatively eg. - bN regime. [D J Ward EPS 2010]
Choice between High density and
stable High temperature both with
high radiation fraction
bT,lim =bNx(I/aB) - impurity-driven radiation for
Divertor power reduction and/or
- synchrotron radiation
In such plasmas, for a baseline, we
need to know asap:
- confinement scaling laws?
- high-b stability limits?
- Confinement of high bF content at
high bth –relevant populations!
Baseline DEMO programme role for
ITER Q=10; present/approved tokamaks?
PPCS Mod A/B
(JT-60SA/JET)
PPCS Mod C
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline: Divertor (III):
High-temperature Helium-cooled divertor?
System simplification if Divertor and Blanket coolants are the same.
For EU urgent to evaluate seriously He-cooled divertor development potential
• Conservative baseline for DEMO would
favour Helium-cooled divertor,
as foreseen in PPCS DEMO Model B
‘Only’ ~ 65% radiation required for this design
• Tungsten ductile operating window
~ 750°C (set by DBTT) and
~ 1200°C (set by recrystallisation)
DEMO He-cooled Tungsten-armoured concept (KIT)
W W-La2O3 W-26%Re
-Helium-cooled
modular
divertor (HEMJ) 830ºC
1200ºC
Thimbles tested at 12 MW.m-2 ≤ 200 cycles
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline H&CD system(s)
• Conservative (bN< 3) DEMO Studies call for very high
installed Current Drive powers
240 – 270 MW for PPCS Models A/B and AB..
• PPCS assumptions were:
– ‘wall plug efficiency’ wp=0.6
– ‘current drive efficiency’ as 1.5 MeV NNBI gCD=0.45 (1020 A.W-1.m-
2)
• On today’s H&CD technology/operational achieved status
required H&CD grid demand would be much higher
• For all real systems:
– wall plug efficiency is much less than 0.6
– non-NNBI systems have lower gCD. – but latest ECCD expts?
• In all ‘near-term’ designs H&CD systems dominate the
power balance (circulating power, nett power to grid) and
contribute plant complexity.
• A serious andonfocussedD development programme September 2011
Technical Challenges the path to DEMO - Stork invited talk PPPL MFE Roadmapping meeting
is needed.
Baseline H&CD system(s) (II)
• DEMO Baseline should have a minimum number of separate systems.
– Each system chosen should have maximal separate task capability (avoid
‘one system per task’ mindset!)
– Systems justified on the basis of elaborate feedback loops should be
critically examined (are the required diagnostics forming the feedback loop
really likely to be on a reactor?
– Baseline choice would emphasise those systems which couple easily and
flexibly to a range of plasma configurations (NNBI, ECRH)
• Initial phase of evaluation should establish for each system:
– R&D status – does a source exist?
– does a launching system exist?
– will the ITER programme, by the end of Phase I, prove
the source and launch concept?
– what are the R&D needs for developing and optimising
the system for DEMO? Can they be handled on ITER?
– Physics status – does the database for this system show it can generate
relevant high-performance plasmas on its own?
– does the database for CD efficiency exist?
– will it exist post- ITER Phase I?
– what are the urgent needs for demonstration(s) on
tokamaks other than ITER?
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline H&CD (III):
assumptions vs reality - ITER System efficiencies
Source – courtesy R S Hemsworth - ITER
Auxiliary power (Ion Dump,
HV and Source power
water cooling pump, Cryo)
= 4.4 MW = 58.2 MW
‘source’ ~ 40.8/(58.2+4.4) ~ 0.66
Accelerated beam
=40.8 MW
NB to plasma = 18.8 MW Neutralised Beam = 23.2 MW TR ~ 18.8/40.8 ~ 0.46
For NBI WP ~ 0.66x0.46 ~ 0.30 – half the PPCS assumed value!
For ECRH WP ~ 0.52 – but gCD ~ 0.15 – 1/3 the assumed PPCS value
Implies DEMO CD powers of ~ 490 MW – 920MW required!
Motivator for a Pulsed DEMO baseline? Do we need steady-state ?
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Reactor Power Flow with ‘realistic’ H&CD
(representative - figures in MW)
Generator
Neutron Blanket Thermal
power power =0.42
Electricity Grid
Plasma 4140
3600 2346 1351
R
Fusion Power 5587
4500
1114 1114-R
a- power +
Aux power
94 119 Divertor
214 994
‘Current
Drive’ ‘Heating’ 333
Heating and ~ 1GW
Helium coolant
Current Drive
285 359 pump circulating
power!!
644 350
Recirculating
power
Conceptual 4.5GW (fusion); 1.35GW (Electrical) reactor - similar to PPCS Model A
– helium cooled – H&CD systems 33% efficient
-- Neutron power multiplication in blanket -- divertor takes all charged particle
(conducted ) power
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline H&CD (IV):
pulsed or steady-state DEMO?
Motivation for a Pulsed DEMO concept depends on Current Drive scenario and
technology prospect:
‘Advanced’ tokamak – hence mainly intrinsic CD?
Can external CD overall efficiency be raised?
Major engineering issue for Pulsed Machine would be fatigue life
– for pulse length of 8 hours – then loading of > 30000 cycles during 30 year life.
For discussion see David Ward’s talk.
Pulsed DEMO would inevitably be bigger
– larger solenoid required for flux swing
– predict coe increase by ~ 20%
-- but some H&CD power alleviates
machine size/ flux needs.
Fixed pulse length – 8 hrs
D J Ward (CCFE) –
PROCESS
–EFDA Study 2008
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline: Diagnostics & Control
Baseline DEMO diagnostics will be limited by: DIIID
limited views, blanket module
maintenance simplification;
required radiation hardness for
systems (especially windows).
systems engineering-based
simplification & conservative approach
need to reach high-level of reliability –
favours limited, simple systems
Thus number of active feedback control loops will be limited on a reactor.
Multi- diagnostic actuator loops will fall foul of ‘one H&CD system’ philosophy
transfer of some concepts to reactor (eg. in-vessel coils complex & uncertain
Baseline should be framed using ‘sparse control’ concepts as developed in other fields.
JT-60SA would be an appropriate machine on which to test baseline strategies
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Baseline for other systems
• Pumping
– Major issue ITER batch-regeneration cryopumps don’t scale to DEMO
– Re-assessment of the existing technological alternatives and choice of
most promising continuous regeneration technique (eg. snail
cryopumps?) then vigorous development programme.
• Magnet Technology
– to enable database gathering from ITER - baseline should be Low
Temperature Superconductors (Nb3Sn and NbTi) as in ITER
– (HTSC development will be handled by other technology programmes).
• Safety and Licensing issues
– ITER experience has to be taken for the baseline regulatory rules.
• Remote Handling
- determined by Blanket and Divertor concepts.
• Balance of Plant
– Blanket choices drive EU towards Helium circulation systems;
– should capitalise on Generation IV fission systems developing these but
to minimise risk Helium BoP development be part of Baseline.
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
DEMO Optimisation programme
• The Optimisation Programme should run
concurrently with the Baseline Programme,
taking a fraction of the resources and aiming
to realise results by the time the critical path
detailed design decision is made (2028-2029).
• Optimisation Programme content depends on
Baseline Choices!
– pulsed vs steady-state;
– Baseline H&CD ‘set’ (or single system) – for the
baseline system, optimisation in Baseline Prog!;
– Eurofer alone or +RAFM ODS;
– HCPB or HCLL; etc.
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Optimisation of DEMO H&CD: NBI challenges
Wall plug efficiency of 50-60% requires simultaneously:
Improvement in neutralization efficiency from 58% (gas) to ~95%
Development of photoneutralizer and/or
Energy recovery of the dumped ion beam
Improvement in transmission from 75% to 95%
Reduction of beam divergence
Removal of halo
Increased current density
Choice of Materials – potential show-stopping issues
In the Drift Duct liner --Copper and CuCrZr eliminated due to irradiation damage
GlidCop is a possible replacement but untested in HHF and HV applications
Beamline structural material within 4m of First-wall has same issues as FW.
Achieving reliability requires simultaneously:
Demonstrating HV holding of >1MV at 10-50A current
Present status: 750keV/221mA & 500keV/20A (few seconds) at JAEA
Breakdown follows clump theory but degraded for large grids
Replacement or control of caesium
Alternative proving elusive; understanding role for improved management
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
EU Roadmap to DEMO NB
DEMO design process
define defin Power/ voltage
type of e NB geometry injector design integration
DEMO role
efficiency
neutralisation
EFDA transmission
work source energy recovery
programme
high voltage materials
ITER ops exp ops exp ops exp
programme SPIDER MITICA ITER
maintainability
operational
requirements reliability
E Surrey – EFDA PPP&T meeting – Garching – March 2011
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Optimisation of DEMO H&CD: ICRF
Technical status of ICRF sources/transmission at ITER frequencies shows
advantages:
commercial (tetrode) sources/generators 60-70% efficient;
transmission line relatively standard – developed for ITER ~95% efficient
launcher (ITER development) ~ 95% efficient Experimental current drive efficiency
in agreement with theory
However:
maximum RF power coupled into H-mode
is still ≤12MW (and data is from 1989-1990!)
RF coupling to shaped plasmas with H-mode/
ELMy edge is problematical and not proven by
large experimental database.
FW current drive efficiency is low (scales to ~0.15
at Te(0) ~ 20 keV) needs experimental proof
If ICRF is to be retained in the baseline, high power
(>20MW) systems need to prove generation and
sustainment (CD) of high performance plasmas.
ITER Physics Basis [NF 39(1999)2512
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Optimising ICRF: High frequency FW?
Develop HF system for FWCD off-axis?
DEMO simulation at 250 MHz
Ntor=90
Ntor=30
Promising in theory but:
- ITER will not test the system (needs modified
launcher for high k⁄⁄ - new source development)
- what would then be the purpose of ITER ICRF? [Van Eester & Lerche EFDA CCIC-08 ]
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Near-Term EU FWCD Assessment
Confirm , k// R Koch – EFDA PPP&T Meeting
– Garching March 2011
Options
Assess g Assess Assume ITER
Coupling SOL
Comments:
DEMO ICD Systems Design -community should then review ITER ICRF
Requirement - please include strong large Tokamak-
based programme!
Option Assessment: Impact on DEMO;
RAMI analysis; cost; R&D requirements.
• Performance estimate.
Option •SWOT Analysis
Recommendation • Sensitivity studies.
• Strawman design(s)
Arcing inside in-tokamak structure? Materials • R&D programme
and dielectrics to withstand FW 14MeV flux? • Cost, manpower, timescale
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Optimisation of ECRH systems
ECRH has great advantages over NBI of small
‘nuclear island’ extension (capital cost reduction)
ECRH has few coupling problems, but still not employed as
the dominant heating system in a high performance plasma
context.
Key experiment for development ECRH
would be 100% ECR-heated
plasmas with high performance
(20+ MW on JET or raise
ECRH power on JT-60SA?)
Also for ECRH, experimental
investigation of current drive
efficiency merits special
programme. NNBI
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Optimisation of ECRH systems(II)
Investigate reduction in complexity of in-tokamak launch by
developing frequency tuneable EC H&CD - allows for
antennas with fixed launching angle and removal of the
remote/front steering mirror concepts fundamentally
different development branches of EC H&CD components.
Develop the broadband synthetic diamond window options and
improve diamond window reliability?
Gyrotron efficiency (ITER prototype at JAEA) is now ~55%
and transmission is ~95%. Improvements in gyrotron
efficiency could come by improving the electron gun
performance and making use of multi-stage depressed
collectors the gyrotron 55% to > 70% possible?
RAMI analysis especially Materials assessment of radiation
hardness of in-port launcher system – identification of
issues. M Thumm – EFDA PPP&T meeting – Garching – March 2011
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
DEMO Divertor Optimisation :
‘advanced divertors’ – magnetic shaping, not technology
Super-X divertor concept
‘Super-X’ is one concept where
magnetic geometry could handle
extremely high Divertor loads
• SOL taken to large major radius
– natural flux expension;
• SOL passes through low PF region
- connection length is increased
– further spread of power –
- volume to enable power radiation Kotschenreuther,
Valanju,
before striking target. U Texas
Concept to be tested on
MAST-Upgrade.
If successful could be incorporated
into Divertor satellite and DEMO
Issues – in-vessel coil shielding
EFDA evaluation beginning
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Other DEMO Optimisation programme elements?
• Other likely programme lines:
– Development of high purity versions of Eurofer, and low
activation versions of conventional high temperature FM steels.
– Development of ODS Ferritic steels (if not in baseline!).
– Resolution of issues relating to ‘second string’ Helium-cooled
blanket concept.
– Other solutions to Divertor problem by magnetic concept
(‘snowflake’?) rather than engineering.
• Possible programme lines:
– Divertor technology back-ups (water-cooled as back –up form
helium or vice-versa!); Liquid lithium divertor?
– (If baseline is pulsed) Fusion-relevant energy storage systems.
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
DEMO Strategic Risk Reduction
An assessment of strategic risks to a DEMO
programme is urgent (elements of this are
proposed in the EFDA 2012 PPP&T
programme)
Two elements stand out for this presenter:
Component Test Facility
High Temperature superconductors, as a guard
against future Helium shortages
[associated to this – helium leak reduction
programme.]
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
DEMO Strategic risk reduction (I):
A Component Testing programme?
Critical paths mean DEMO is unlikely to be ready for
commissioning before the late 2030s.
Consequently it is high priority to ensure an efficient DEMO
programme – high availability for Blanket Testing.
Should get to ‘plateau’ region of radiation embrittlement (~> 6
MW.a.m-2 or 60 dpa) as soon as possible.
This is 3 full power years. At 30% availability takes 10 years.
DEMO requires to breed tritium, relying for high availability
operation on some of the components under test;
DEMO is a large and complex machine. Mean-Time-To-Replace
(MTTR) test components will thus be large – leading to possible
significant delays in a test programme.
IFMIF does not test components.
As a strategic risk reduction exercise, the goals of a
Components testing programme and the feasibility of a pre-
DEMO Components Test Facility (CTF) should be examined.
[EU Fusion Facilities Review -2008; UK 20 year Fusion Review 2009]
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
CTF
• To be useful a CTF must:
– produce long periods of steady-state plasma burn to
achieve the required integrated neutron yield –
• with a fusion spectrum;
• in a tokamak environment with accompanying stress fields;
– be compact and tritium efficient enough not to depend on
tritium breeding;
– accommodate fully functional test components on the
scale of ~ 1 m2 (relevant scale for component issues);
– deploy significant area, over 10 m2, to test several scaled
components in parallel(e.g. blanket modules);
– be able to test prototype components up to some level
before the serious start of a DEMO programme.
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Compact CTF design – testing capability
ST-CTF (Culham, EU)
MAST-Upgrade will test ST physics
Compact Spherical Tokamak Testing to 20 dpa (2 MW.a.m-2)
Fusion power ~ 36 MW
at 1MW.m-2 and 33% availability
Neutron wall- load ~ 1.0 MW.m-2
PDIV ~ 30 MW.m-2 takes ~ 6 years.
2009 version has Super-X concept Does CTF have a consistent
Tritium consumption ~ 1.8 kg/fpy DEMO-stage mission??
Tritium bred ~ 47% of usage
Tritium would be available from Candu programme for both ITER and a CTF.
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
A tentative time-line
CTF looks late unless we move fast
2010--15 2016--20 2021--25 2026--30 2031--35 2036--40
Pre-concept +
Baseline select
Baseline Concept
+ R&D
Concept DR
(Baseline Blanket )
Baseline Scheme
+R&D
Site Commission 60 dpa Irrad
IFMIF
Design + Constuct
ITER TBM data
Detailed DEMO
Design 20 dpa
Construct DEMO CTF ?
DEMO Divertor Design Construct
Operate
Satellite
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
DEMO Strategic Risk reduction (II):
High-Temperature superconducting magnets
• High-temperature superconductors as a replacement for ~ 4K
technology lead to:
– Very modest power savings ( ~ 20 MW out of 570 MW BoP power for
‘Model B HCLL reactor goes to cryoplant);
– simplification of cryogenic plant & shields etc.
very much ‘Generation II’ issues – other industries will develop HTSC
and we cannot match their huge research budgets.
• …but strategically, high-T superconductors are needed in Fusion
Technology because of the Helium resource problem.
• Terrestrial Helium presently comes from
Natural Gas exploration – finite resources (~100 years)
• Huge reserves in atmosphere ~ 4 109 tonnes – enough for ~ 107
ITER cryosystems
• ….. air separation of helium will be expensive to develop (can we
afford it in our baseline???)
…… Problem will hit ‘roll-out’ of Fusion Economy
(CCFE/Cambridge/Linde modelling).
• Long-term Fusion should unlink itself from Helium where possible,
(and strategically needs to develop leak-tight He systems!)
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Superconductors – helium free?
Neon can be air-separated
routinely
(~ 4* concn of atmospheric
A Helium)
B
HTSC ‘Roebel’ cable -
1.3m length
‘A’ -- field at the ITER TF conductor surface
‘B’ -- field at the ITER PF conductor surface
YBCO-type HTS can get SC performance above Liquid Neon temperatures
– developments are clearly needed.
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Summary and Conclusions
• To optimise the ‘DEMO Stage’ schedule we propose alignment into:
– Baseline;
– Optimisation/Short term risk reduction;
– Strategic Risk Reduction
• DEMO Mission clarification + Systems Engineering approach
should guide the Baseline design selection
the existing critical path is through IFMIF structural materials
qualification and ITER TBM results - conservative choices and de-risking
should be used to avoid making the critical path situation more complex!
• DEMO electrical grid supply is maintained but downplayed. Pulsed
Operation may be a conservative early choice.
• Maximum use of parallel programmes (Generation IV, HTSC
developments) is urged for political and economic reasons.
• A ‘DEMO Divertor satellite’ is identified as a baseline facility.
• The key optimisation issue is the Improvement of H&CD efficiency.
• A Components Test Facility should be examined as a strategic risk
reduction programme element.
• High temperature superconducting magnets should not be in the
baseline, but are needed in the longer run to reduce reliance on
increasingly scarce Helium resources. September 2011
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting
Appendix slides
International Meeting “MFE Roadmapping in the ITER Era”
PPPL, 7th-10th September 2011
(this work was supported by UK EPSRC and Euratom)
CCFE is the fusion research arm of the United Kingdom Atomic Energy Authority
Blanket choices affect complete DEMO design
• Energy use of secondary circuits (and hence nett plant
efficiency) eg. high pumping power required for:
– MHD-induced pressure drops for Liquid-metal designs;
– high-flow, high pressure Helium cooling ( ~400 MW pump power!).
• Character of ‘Balance of Plant’:
– Water-cooled blanket PWR - like primary circuits piggy-back
on Fission-plant engineering;
– High-pressure He cooling primary circuits – may be developed by
Generation IV fission – or needs dedicated Fusion development ?
• In-vessel operational safety/availability:
– hazards of interaction between coolant and blanket material
(eg. H2O – Li ceramics or H2O – beryllium);
– hazards from corrosion by coolant (Li molten salts, liquid LiPb);
– rupture of high pressure coolant (water raises steam – rupture to
vessel?; He ruptures module – regenerates cryopump?).
• Minimisation of blanket change duration drives aspects of
in-vessel design (pipe connections, supports.
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Accelerator challenge
‘5 dpa’
route
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Decay of Blanket structure RAFM steel:
irradiation period 5 years
EUR
EUROFER
Ref [2]
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Fusion Reactor Materials environmental basis:
Manufacturability
EUROFER (data in wt%)
Element Case 1 Case 2 Case 3
Real materials have (specification, (real material) (achievable
trace impurities Al
without impurities)
0.008
material)
0.0001
Eurofer Chemical As
B
0.02
0.001
0.001
0.0001
composition C 0.11 0.11 0.11
Ca 0.0002 0.0001
(wt%): Ce 0.003 0.0001
Co 0.005 0.001
Cr 9.0 9.0 9.0
1.Pure - ideal Cu 0.0037 0.001
Fe bal bal bal
2.Real - present day Hf 0.0001 0.0001
3.Achievable K
Mn 0.40
0.0002
0.40
0.0001
0.40
Mo 0.0012 0.0001
N 0.03 0.03 0.001
Nb 0.001 0.00001
Nd 0.0002 0.0001
Ni 0.005 0.001
O 0.01 0.001
P 0.005 0.001
Re 0.0001 0.0001
Ru 0.001 0.001
S 0.003 0.001
Sb 0.01 0.001
Si 0.05 0.05 0.05
Sn 0.003 0.001
Reference Eurofer Ta 0.07 0.07 0.07
Ti 0.01 0.01 0.01
V 0.20 0.20 0.20
W 1.1 1.1 1.1
Zr 0.0001 0.0001
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Fusion Reactor Materials environmental basis:
Manufacturability – effect on waste
EUROFER Blanket Material
• replace every 5 years;
• Pfus = 3 GW;
• Neutron Wall Load = 2.3 MW.m-2
for 5 years
For EUROFER to achieve
Reference composition
Nb impurity needs to be
further decreased by two
orders of magnitudes to
0.00001% (~0.1 ppm)
Hands-on recycling level
Ref [11] : P Batistoni et al.
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
H&CD efficiency for DEMO:
assumptions vs reality (II) - ECRH system efficiency: ITER System
Decel PS
~28kv
PLaunch
PPS to gyrotron
Accel PS
~72kv
PRF=1MW
PRF
TR
gyro =PRF/PPS
Japanese Gyrotron Beam current ~38A
gyro= 55%
For ECRH WP ~ 0.55x0.95 ~ 0.52
TR ~ 600/630 ~ 0.95 See eg. Kasugai et al., and refs therein; IAEA FEC Geneva 2008
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
Fusion economy – helium demand
Aggressive Leak-learning and recycling scenario
3500 GWe
(~30% of market)
Saving by using HTSC
sustainable economy
Fusion roll-out
with LTSC+
He-cooled
Blanket
and Divertor
Cai Zhiming – Univ of Cambridge; Richard Clarke - CCFE
Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting September 2011
