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C. Waldon | 3rd IAEA DEMO Progr. Workshop|HEFEI| 11-14/05/2015| Page 1
3rd IAEA DEMO Programme Workshop
Topic 2: In-vessel Systems Design &
Engineering
Chris Waldon
11 May 2015
C. Waldon | 3rd IAEA DEMO Progr. Workshop|HEFEI| 11-14/05/2015| Page 2
Overview
What is the main driver for machine size:
• Power Density? (HHF Component resilience)
• Remote Maintenance (larger accessible
versus heavier)
• Pulse length? (Non inductive CD power)
• Power Conversion?
• Confinement?
• Cost?
C. Waldon | 3rd IAEA DEMO Progr. Workshop|HEFEI| 11-14/05/2015| Page 3
Gap Identification • E.G. Power Handling Capacity
Gap
• Plasma
Performance
• Plasma Control
• Plasma
Geometry
• Particle Exhaust
• Etc
• Thermal
Performance
• Structural
Performance
• Etc
MW/m2
Ca
pa
city
Margin
Require
ments
C. Waldon | 3rd IAEA DEMO Progr. Workshop|HEFEI| 11-14/05/2015| Page 4
C. Waldon | 3rd IAEA DEMO Progr. Workshop|HEFEI| 11-14/05/2015| Page 5
Morris, KSTAR Programme Advisory Committee, 23-26 March 2014
5
Today to ITER to DEMO H Zohm, IAEA DEMO workshop Dec 2013
Morris, KSTAR Programme Advisory Committee, 23-26 March 2014 5
Assuming Prad,core/Ptot = 0.25
Assuming Psep = 1.2PLH
H Zohm, IAEA DEMO workshop Dec 2013
C. Waldon | 3rd IAEA DEMO Progr. Workshop|HEFEI| 11-14/05/2015| Page 6
Target heat fluxes
Small changes in Prad
large changes in target heat
flux If Prad=90%: a drop to 80% may
double power density at target,
or, worse, burn through
detached region
C. Waldon | 3rd IAEA DEMO Progr. Workshop|HEFEI| 11-14/05/2015| Page 7
Options 1) SN deep divertor (ITER) 2) Shallow SN divertor 3) Shallow DN divertor
Advantages Compatible with BB vertical RH Compatible with BB vert. RH improved T breeding
higher plasma performance with improved vertical position control
Shortcomings Elongation constrained by VS Marginal T breeding Limited power handling near
upper secondary null
Elong. constrained by VS Problems of heat loads near
upper secondary null?
T breeding to be assessed compatibility with BB vertical
maintenance scheme questionable. Requires study.
Plasma VS is an important design driver. A variation of Beta or li (e.g., due to loss of NBI, RF, or impurity influx) or loss of H-mode would lead to a V moment that in the case of an asymmetric configuration (SN) would challenge control requirements.
C. Waldon | 3rd IAEA DEMO Progr. Workshop|HEFEI| 11-14/05/2015| Page 8
Load
Safety limits Safety factor
How can irradiation effects be take in to account? P
rob
abili
ty D
ensi
ty F
un
ctio
n
Material Strength
Refractory/Structural interface is a key feature and has limited evidence to support performance expectations at high dose.
Irradiated material strength
Irradiation effects
Variable
C. Waldon | 3rd IAEA DEMO Progr. Workshop|HEFEI| 11-14/05/2015| Page 9
AVAILABILITY
C. Waldon | 3rd IAEA DEMO Progr. Workshop|HEFEI| 11-14/05/2015| Page 10
So What?
Performance Confidence Impact Value
Plasma Low –Heat Load Prediction
Low –Heat Load Stability
Low –Interface with Core Plasma
Low Reliability
Restrictive Operating Window
Fault Intolerance
Balance of Plant
COE – Highly Sensitive to
physics uncertainties
Structural Medium – Short term irradiation
Low – Erosion
Low –Synergistic Effects
High –Safety Infrastructure
Low Availability
Incremental Operation – Surveillance
Reliance on physics processes for
heat load reduction.
Only incremental gains.
Restricts thermal
performance.
Safety importance on main
chamber integrity and relief
streams.
Thermal High – 20MW/m2
Restrictive Operating Window
Balance of Plant – Integration
Only incremental gains but
any improvements alleviate
reliance on physics.
C. Waldon | 3rd IAEA DEMO Progr. Workshop|HEFEI| 11-14/05/2015| Page 11
Exhaust is critical path, what
are the issues for DEMO?
1. How to spread the power
2. How to maximise dissipation in the divertor
3. How to balance with the main plasma (ITER is low main plasma
radiation, DEMO high)
4. How to translate results to DEMO (atomic physics not easily scaled
– no dimensionless parameters)
It is vital to combine experiments with modelling, since there are few if any
physics-based scaling parameters that work for exhaust (with its wide
range of plasma parameters even in one discharge). This, with validation of
the ingredients of the models, will be a key element of the UK exhaust
programme. There will also be a strong element of empirical/semi-empirical
exploration.
C. Waldon | 3rd IAEA DEMO Progr. Workshop|HEFEI| 11-14/05/2015| Page 12
Compromise
There are countless physical and technological
conflicts in DEMO, but most of these come down
to a principal conflict:
•The size, cost and performance vs. its
technological viability
• Attractiveness vs. technical risk
C. Waldon | 3rd IAEA DEMO Progr. Workshop|HEFEI| 11-14/05/2015| Page 13
History
‘The Practical reactor designer must live with these same technical details. Although recalcitrant and awkward, they must be solved and cannot be put off to tomorrow. Their solutions require manpower, time and money’
H.G Rickover 5 June 1953
Director of US Naval Nuclear propulsion development programme
C. Waldon | 3rd IAEA DEMO Progr. Workshop|HEFEI| 11-14/05/2015| Page 14
Thank you
