Comments on feasible testing program
and potential limits of ITER parameters
for TBM testing
Mohamed Abdou
Presented at TBWG-11 Meeting
Garching, Germany
October 22, 2003
Purpose of Presentation
- This presentation has been prepared in response to a
request from TBWG Chair, Dr. L. Giancarli, to summarize
the experience gained during the last 20 years on how to
plan useful blanket tests in the fusion environment. In
particular:
-Blanket Testing Issues
-Engineering Scaling considerations for design of “Act-Alike” test
articles
-Requirements on fusion testing device parameters
-Usefulness and LIMITATIONS of current ITER Design for blanket
testing
-Note that there is considerable information available in
literature based on scholarly and engineering research
efforts in INTOR, FINESSE, ITER-CDA, ITER-EDA, VNS
(IEA-HVPNS). See list of journal papers and reports.
Key Points We Learned about the Blanket Test Program
1. Blanket/First Wall has serious, yet unresolved feasibility
issues.
-
-
Non-fusion facilities can not fully resolve any of the critical
issues for blankets or PFC’s
There are critical issues for which no significant information can
be obtained from testing in non-fusion facilities (examples
include the identification and characterization of failure modes,
effects and rates)
The feasibility of Blanket/PFC Concepts can NOT be
established prior to testing in fusion facilities
2. The purpose of testing in fusion testing facilities such as
ITER is to obtain data on the feasibility and
performance limits of blanket concepts for DEMO and
Reactors.
-
Since these are the “first” tests in the “fusion environment,” they
are aimed at investigating feasibility and performance limits of
various concepts, configurations, material combinations, etc.
They are NOT, and Can Not be, merely “Confirmation” Tests
Key Points We Learned About the Blanket Test Program
(cont’d)
3. Since ITER testing parameters (e.g., wall load, surface heat flux,
plasma duty cycle, etc.) are substantially below those of DEMO,
SERIOUS Engineering Scaling and an Elaborate Testing Strategy
are required to obtain meaningful results from testing in ITER
-
Merely inserting blanket testing modules that physically “look like” a
DEMO blanket will NOT produce meaningful data
We need to design “act alike” test articles that produce meaningful
test results on various technical issues under ITER scaled-down
parameters
It is impossible to have one “Act alike” test article to simulate all
phenomena and technical issues. The number of test articles needed
per blanket concept is large. Typically 3 test modules (one “lookalike” and two “act-alike” plus 3 submodules per blanket concept.
4. ITER-EDA parameters, even with the best engineering scaling
and testing strategy, are not ideal nor sufficient to do all the fusion
testing required for the blanket.
-
The current ITER parameters are less adequate for testing than ITER
EDA. The challenge for TBWG is even greater!
Fusion Nuclear Technology (FNT)
Fusion Power & Fuel Cycle Technology
FNT Components from the edge of the
Plasma to TF Coils (Reactor “Core”)
1. Blanket Components
2. Plasma Interactive and High Heat Flux
Components
a. divertor, limiter
b. rf antennas, launchers, wave guides, etc.
3. Vacuum Vessel & Shield Components
Other Components affected by the
Nuclear Environment
4. Tritium Processing Systems
5. Instrumentation and Control Systems
6. Remote Maintenance Components
7. Heat Transport and Power Conversion
Systems
Notes on FNT:
• The Vacuum Vessel is outside the
Blanket (/Shield). It is in a lowradiation field.
• Vacuum Vessel Development for
DEMO should be in good shape
from ITER experience.
• The Key Issues are for
Blanket / PFC.
• Note that the first wall is an
integral part of the blanket (ideas
for a separate first wall were
discarded in the 1980’s). The
term “Blanket” now implicitly
includes first wall.
• Since the Blanket is inside of the
vacuum vessel, many failures
(e.g. coolant leak from module)
require immediate shutdown and
repair/replacement.
Adaptation from ARIES-AT Design
Blanket and PFC Serve Fundamental and
Necessary Functions in a DT Fusion System
• TRITIUM BREEDING at the rate required to satisfy tritium selfsufficiency
• TRITIUM RELEASE and EXTRACTION
• Providing for PARTICLE PUMPING (plasma exhaust)
• POWER EXTRACTION from plasma particles and radiation
(surface heat loads) and from energy deposition of neutrons
and gammas at high temperature for electric power production
• RADIATION PROTECTION
Important Points
• All in-vessel components (blankets, divertor, vacuum pumping, plasma heating
antenna/waveguide, etc.) impact ability to achieve tritium self-sufficiency.
• High temperature operation is necessary for high thermal efficiency. And for
some concepts, e.g. SB, high temperature is necessary for tritium release and
extraction.
• All the above functions must be performed safely and reliably.
Summary of Critical R&D Issues for Fusion Nuclear Technology
1.
D-T fuel cycle tritium self-sufficiency in a practical system
depends on many physics and engineering parameters / details: e.g. fractional burn-up
in plasma, tritium inventories, FW thickness, penetrations, passive coils, etc.
2. Tritium extraction and inventory in the solid/liquid breeders
under actual operating conditions
3. Thermomechanical loadings and response of blanket and PFC
components under normal and off-normal operation
4. Materials interactions and compatibility
5. Identification and characterization of failure modes, effects, and
rates in blankets and PFC’s
6. Engineering feasibility and reliability of electric (MHD) insulators
and tritium permeation barriers under thermal / mechanical /
electrical / magnetic / nuclear loadings with high temperature and
stress gradients
7. Tritium permeation, control and inventory in blanket and PFC
8. Lifetime of blanket, PFC, and other FNT components
9. Remote maintenance with acceptable machine shutdown time.
R&D Tasks to be Accomplished Prior to Demo
1) Plasma
- Confinement/Burn
- Disruption Control
- Current Drive/Steady State
- Edge Control
2) Plasma Support Systems
- Superconducting Magnets
- Fueling
- Heating
3) Fusion Nuclear Technology Components and Materials
[Blanket, First Wall, High Performance Divertors, rf Launchers]
- Materials combination selection and configuration optimization
- Performance verification and concept validation
- Show that the fuel cycle can be closed (tritium self-sufficiency)
- Failure modes and effects
- Remote maintenance demonstration
- Reliability growth
- Component lifetime
4) Systems Integration
Where Will These Tasks be Done?!
• Burning Plasma Facility (ITER) and other plasma devices will address 1, 2, & much of 4
• We must strive to maximize the utilization of ITER for Fusion Nuclear Technology
components and materials testing even if another dedicated testing facility is required
Key Fusion Environmental Conditions for Testing Fusion
Nuclear Components
Neutrons (fluence, spectrum, spatial and temporal gradient)
-
Radiation Effects
(at relevant temperatures, stresses, loading conditions)
Bulk Heating
Tritium Production
Activation
-
Bulk (from neutrons)
Surface
Heat Sources (magnitude, gradient)
Particle Flux (energy and density)
Magnetic Field
-
Steady Field
Time-Varying Field
-
Normal
Off-Normal
-
Combined environmental loading conditions
-
Interactions among physical elements of components
Mechanical Forces
Thermal/Chemical/Mechanical/Electrical/Magnetic Interactions
Synergistic Effects
FNT Requirements for Major Parameters for Testing in Fusion Facilities with
Emphasis on Testing Needs to Construct DEMO Blanket
- These requirements have been extensively studied over the past 20 years, and they have been agreed to internationally
(FINESSE, ITER Blanket Testing Working Group, IEA-VNS, etc.)
- Many Journal Papers have been published (>35)
- Below is the Table from the IEA-VNS Study Paper (Fusion Technology, Vol. 29, Jan 96)
Parameter
a
Neutron wall load (MW/m2)
Plasma mode of operation
Minimum COT (periods with 100% availability) (weeks)
Neutron fluence at test module (MW·y/m2)
Stage I: initial fusion break-in
Stage II: concept performance verification (engineering feasibility)
c
Stage III : component engineering development and reliability growth
Total neutron fluence for test device (MW·y/m2)
Total test area (m2)
Total test volume (m3)
Magnetic field strength (T)
Value
1 to 2
b
Steady State
1 to 2
0.3
1 to 3
c
4 to 6
>6
>10
>5
>4
a - Prototypcial surface heat flux (exposure of first wall to plasma is critical)
b - If steady state is unattainable, the alternative is long plasma burn with plasma duty cycle >80%
c - Note that the fluence is not an accumulated fluence on “the same test article”; rather it is derived from testing
“time” on “successive” test articles dictated by “reliability growth” requirements
Stages of FNT Testing in Fusion Facilities
Fusion
“Break-in”
Stage:
Required
Fluence
2
(MW-y/m )
Size of Test
Article
I
~ 0.3
SubModules
• Initial exploration of performance in
a fusion environment
• Calibrate non-fusion tests
• Effects of rapid changes in
properties in early life
• Initial check of codes and data
• Develop experimental techniques
and test instrumentation
Design Concept &
Performance
Verification
Component Engineering
Development & Reliability
Growth
II
III
1-3
>4-6
Modules
Modules/
Sectors
• Tests for basic functions and phenomena
(tritium release / recovery, etc.),
interactions of materials, configurations
• Verify performance beyond beginning of
life and until changes in properties
become small (changes are substantial up
2
to ~ 1-2 MW · y/m )
• Data on initial failure modes and effects
• Narrow material combination and
design concepts
• Establish engineering feasibility of
blankets (satisfy basic functions &
performance, 10 to 20% of lifetime)
• 10-20 test campaigns, each is 1-2
weeks
• Select 2 or 3 concepts for further
development
• Identify failure modes and effects
• Iterative design / test / fail / analyze /
improve programs aimed at improving
reliability and safety
• Failure rate data: Develop a data base
sufficient to predict mean-time-betweenfailure with sufficient confidence
• Obtain data to predict mean-time-toreplace (MTTR) for both planned outage
and random failure
• Develop a data base to predict overall
availability of FNT components in DEMO
D
E
M
O
ITER Provides the First Integrated Experimental
Conditions for Fusion Technology Testing
• Simulation of all Environmental Conditions
Neutrons
Plasma Particles
Electromagnetics
Tritium
Vacuum
Synergistic Effects
• Correct Neutron Spectrum (heating profile)
• Large Volume of Test Vehicle
• Large Total Volume, Surface Area of Test Matrix
But ITER Operating Parameters pose a
challenge
to obtaining meaningful blanket
results.
The magnitude of the challenge
understood by comparing parameters for
Required Testing and ITER.
serious
testing
can be
DEMO,
Comparison of Key Blanket Testing Parameters
Parameter or Feature
DEMO
(Typical)
Testing Requirements
(derived in fusion
literature)
ITER
(Feat)
Neutron Wall Load, MW/m2
2 to 4
1 to 2
0.55
Plasma Mode of Operation
Steady State
(or long pulses)
Steady State
Highly pulsed
~1
>0.8
0.25
>10,000
<100
>1000
<100
400
1200
Minimum COT (period of 100 %
availability), weeks
many
1 to 2
??
Neutron Fluence, MW.y/m2
7-20
4 to 6
0.1
>10
~7
Plasma Duty Cycle*
Plasma Burn Time, s
Plasma Dwell Time, s
Total Test Area, m 2
*Plasma duty cycle = burn time/(burn time + dwell time)
Effects of Pulsed Plasma Operation on
Nuclear Technology Testing
Plasma cycling means time-dependent changes in
environmental conditions testing
- nuclear (volumetric) heating - surface heating
- poloidal magnetic field
- tritium production rate
Results in time-dependent changes in response of
test modules
- effects can be, in some cases, more dominant than the
steady state effects for which testing is desired
- effects can complicate tests and make results difficult
to model and understand
Examples of Effects
- Thermal Conditions
- Tritium concentration Profiles
- Failure Modes/Failure Mechanisms
- Time to Reach Equilibrium
Mode of Plasma Operation and Burn/Dwell Times
• This issue was investigated extensively in several studies including the
ITER Test Blanket Working Group in both ITER-CDA and ITER-EDA,
IEA-VNS. The conclusion reached: need steady state (or if unattainable,
long burn/short dwell with plasma duty cycle >80%).
• Extensive Investigation of Blanket Testing Requirements using detailed
engineering scaling to preserve phenomena, etc. show that:
plasma burn time (tb) > 3 c
plasma dwell time (td) < 0.05 c
Where c is a characteristic time constant (for a given blanket
phenomena)
• Characteristic time constants for various responses/phenomena in the
blanket range from a few seconds to a few hours (even days for some
phenomena). See Tables.
- Thus the burn time needs to be hours and the dwell time needs
to be a few seconds.
• Example of Difficulty: In ITER-FEAT scenario of 400 s burn and 1200 s
dwell time, even temperature equilibrium can not be attained. Most
critical phenomena in the blanket have strong temperature
dependence.
Table XX.*
Characteristic
Time Constants
in Solid Breeder
Blankets
* From Fusion Technology, Vol. 29,
pp 1-57, January 1996
Process
Flow
Solid breeder purge residence time
Coolant residence time
Thermal
Structure conduction (5-mm metallic alloys)
Structure bulk temperature rise
5 mm austenitic steel / water coolant
5 mm ferritic steel / helium coolant
Solid breeder conduction
Li2O (400 to 800ºC)
10 MW/m3
1 MW/m3
LiAlO2 (300 to 1000ºC)
10 MW/m3
1 MW/m3
Solid breeder bulk temperature rise
Li2O (400 to 800ºC)
10 MW/m3
1 MW/m3
LiAlO2 (300 to 1000ºC)
10 MW/m3
1 MW/m3
Tritium
Diffusion through steel
300ºC
500ºC
Release in the breeder
Li2O
400 to 800ºC
LiAlO2 300 to 1000ºC
Time Constant
6s
1 to 5 s
1 to 2 s
~1 s
5 to 10 s
30 to 100 s
300 to 900 s
20 to 100 s
180 to 700 s
30 to 70 s
80 to 220 s
10 to 30 s
40 to 100 s
150 days
10 days
1 to 2 h
20 to 30 h
Table XXI.*
Characteristic Time
Constants in LiquidMetal Breeder
Blankets
Process
Flow
Coolant residence time
First wall (V=1 m/s)
Back of blanket (V=1 cm/s)
Thermal
Structure conduction (metallic alloys,
5mm)
Structure bulk temperature rise
Liquid breeder conduction
Lithium
Blanket front
Blanket back
LiPb
Blanket front
Blanket back
Corrosion
Dissolution of iron in lithium
* From Fusion Technology, Vol. 29,
pp 1-57, January 1996
Tritium
Release in the breeder
Lithium
LiPb
Diffusion through:
Ferritic Steel
300ºC
500ºC
Vanadium
500ºC
700ºC
Time Constant
~30 s
~100 s
1 to 2 s
~4 s
1s
20 s
4s
300 s
40 days
30 days
30 min
2230 days
62 days
47 min
41 min
Potential Limits of ITER Parameters
for TBM Testing
- Key Problem Areas in ITER Blanket Testing:
low wall load, short plasma burn, long
plasma dwell time, very low fluence, very
short COT
- This is a challenge! We have to work harder
in TBWG to find ways to improve ITER
testing
Engineering Scaling
Engineering Scaling is a Process to Develop
Meaningful Tests at Experimental Conditions
and Parameters Less than those in a Reactor
• Testing is for DEMO Blanket. We need to see how the
blanket behaves in DEMO conditions.
• Since ITER has a factor of 3 or 4 lower power density
than DEMO, we need to alter the test module to “Act
Alike” rather than “Look Like” DEMO to preserve
behavior
“Look-Alike” Test Modules Do Not Provide
Meaningful Information Under Scaled-Down
Conditions
Examples
• Thermal Stresses are not maintained at lower values
of surface heat flux and/or neutron wall load
• Tritium Transport, inventory altered because of
different neutron wall load, temperature profiles
• Cycling, burn and dwell times affect time to reach
quasi-equilibrium, temperatures, stresses, tritium
recovery, etc.
• Corrosion rates and fluid flow characteristics cannot
be maintained at lower surface heat flux, neutron wall
load, temperature
“Act-Alike” Test Modules Are Necessary
Simple Examples
At Lower surface heat flux, neutron wall load:
•Increase structure thickness to increase (preserve) thermal
stresses
- Hoop stress: Lower at larger thickness, Can preserve total
stress
- Temperature Gradient: Cannot be preserved; Important?
•Increase solid breeder plate thickness, preserve temperature
window for tritium recovery
- Tritium production rate: lower; important for tritium recovery?
Effect on TBR
Limited size for liquid metal blanket test: shorten blanket test module;
But, temperatures and fluid flow are not always fully developed in fusion
liquid metal blankets; many important parameters (e.g., heat transfer
coefficient, MHD pressure drop, etc.) sensitive to geometry (also to B
field, nuclear heating)
Cycling, Burn and Dwell Times substantially alter many effects: Time to
reach equilibrium, values at quasi-equilibrium, failure modes, etc.
Burn and Dwell Time Requirements for Maintaining Solid
Breeder Temperature Distribution
Engineering Scaling In “Act-Alike” Test
Modules Has Limitations
Engineering Scaling Laws Must Be Followed
•
Preserve important Phenomena
Not All Parameters Can Be Scaled Down
Simultaneously
•
Simulation is never perfect
•
Trade-offs among parameters results
Complex Engineering Issues Are Involved
•
Large uncertainties in individual issues
•
Value judgements on relative importance of different
issues and environmental conditions
How Many Modules/Submodules Need to Be Tested in ITER
For Any Given One Blanket Concept?
•
•
Never assume one module, because engineering science for testing
shows the need to account for:
1. Engineering Scaling
2. Statistics
3. Variations required to test operational limits and
design/configuration/material options
US detailed analysis indicates that a prudent medium risk
approach is to test the following test articles for any given One
Blanket Concept:
- One Look-Alike Test Module
- Two Act-Alike Test Modules
- (Engineering Scaling laws show that at least two modules are
required, with each module simulating a group of phenomena)
- Four supporting submodules (two supporting submodules
for each act-alike module to help understand/analyze test
results)
- Two variation submodules (material/configuration/design
variations and operation limits)
Test Module Design Strategy
• Because of the reduced operating conditions of ITER vs.
Demo (i. e. neutron and surface wall loads), an engineering
scaling test module design approach is necessary
 calculate Demo key performance parameters
 design test module to reproduce these parameters, such as
resizing wall thickness, coolant spacing, etc.
• 3 Types of Test Module Designs:
 Demo Act-Alike (majority of tests)
 Demo Look-Alike (useful for neutronics)
 ITER FEAT optimized component concepts (for ITER extended
phase?!)
• Suggestion?
 Can we do a benchmark problem for engineering scaling?
 To do this, we need a specific and detailed reference blanket
design for a DEMO blanket. (We can use anyone from the
Parties)
List of Journal Papers & Reports
(examples only)
1.
2.
3.
4.
5.
6.
7.
8.
Abdou, M. “ITER Test Program: Key Technical Aspects,” Fusion
Technology 19(May 1991) 1439+
Gierszewski, P., Abdou, M., Bell, et al. “Engineering Scaling and
Quantification of the Test Requirements for Fusion Nuclear
Technology,” Fusion Technology 8 (July 1985) 1100
Abdou, M., et al. “A Study of the Issues and Experiments for Fusion
Nuclear Technology,” Fusion Technology 8 (1985) 2595
Abdou, M., et al. “Technical Issues and Requirements of
Experiments and Facilities for Fusion Nuclear Technology,” Nuclear
Fusion 27 (1987) 4, 619
Abdou, M., Berk, S., Ying, A., et al. “Results of an International
Study on a High-Volume Plasma-Based Neutron Source for Fusion
Blanket Development,” Fusion Technology 29 (1996) 1-57
“Test Program Summary,” ITER-IL-NE-3-0-5, ITER Document,
February 1990
“Test Program Summary,” ITER-IL-NE-3-9-4, ITER Document, July
1989
There are numerous topical reports from INTOR, ITER-CDA and
ITER-EDA. Contact M. Abdou for copies of the US reports (19801997)