Comments on feasible testing program and potential limits of ITER parameters for TBM testing Presented at TBWG-11 Meeting Garching, Germany October 22,

Comments on feasible testing program and potential limits of ITER parameters

for TBM testing

Presented at TBWG-11 Meeting

Garching, Germany

October 22, 2003

Mohamed Abdou

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 “look-alike” 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)

FNT Components from the edge of the Plasma to TF Coils (Reactor “Core”)

1. Blanket Components

2. Plasma Interactive and High Heat Flux Components

3. Vacuum Vessel & Shield Components

4. Tritium Processing Systems

5. Instrumentation and Control Systems

6. Remote Maintenance Components

7. Heat Transport and Power Conversion Systems

a. divertor, limiter

b. rf antennas, launchers, wave guides, etc.

Other Components affected by the Nuclear Environment

Fusion Power & Fuel Cycle Technology

• The Vacuum Vessel is outside the Blanket (/Shield). It is in a low-radiation 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

Notes on FNT:

Blanket and PFC Serve Fundamental and Necessary Functions in a DT Fusion System

• TRITIUM BREEDING at the rate required to satisfy tritium self-sufficiency

• 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 PROTECTIONImportant 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 compatibility5. Identification and characterization of failure modes,

effects, and rates in blankets and PFC’s6. 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 components9. Remote maintenance with acceptable machine shutdown

time.

R&D Tasks to be Accomplished Prior to Demo1) Plasma

2) Plasma Support Systems

3) Fusion Nuclear Technology Components and Materials

4) Systems Integration

- Confinement/Burn- Disruption Control

- Current Drive/Steady State- Edge Control

- Superconducting Magnets - Heating- Fueling

- Materials combination selection and configuration optimization

[Blanket, First Wall, High Performance Divertors, rf Launchers]

- 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

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- ActivationHeat Sources (magnitude, gradient)- Bulk (from neutrons)- SurfaceParticle Flux (energy and density)Magnetic Field- Steady Field- Time-Varying FieldMechanical Forces- Normal- Off-NormalThermal/Chemical/Mechanical/Electrical/Magnetic InteractionsSynergistic Effects- Combined environmental loading conditions

- Interactions among physical elements of components

- 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)

1 to 2

Steady Stateb

1 to 2

0.3

1 to 3

4 to 6c

>6

>10

>5

>4

Neutron wall loada (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)

Stage IIIc: 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)

ValueParameter

FNT Requirements for Major Parameters for Testing in Fusion Facilities with Emphasis on Testing Needs to Construct DEMO Blanket

b - If steady state is unattainable, the alternative is long plasma burn with plasma duty cycle >80%a - Prototypcial surface heat flux (exposure of first wall to plasma is critical)

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

• 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

• Narrow material combination and design concepts

• 10-20 test campaigns, each is 1-2 weeks

• 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 to ~ 1-2 MW · y/m2)

• Data on initial failure modes and effects

• Establish engineering feasibility of blankets (satisfy basic functions & performance, 10 to 20% of lifetime)

• 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-between-failure with sufficient confidence

• Obtain data to predict mean-time-to-replace (MTTR) for both planned outage and random failure

• Develop a data base to predict overall availability of FNT components in DEMO

Size of Test Article

Required Fluence (MW-y/m

2)

Stage:

Stages of FNT Testing in Fusion Facilities

Sub-Modules

~ 0.3

I

Fusion “Break-in”

II III

Design Concept & Performance Verification

Component Engineering Development & Reliability

Growth

1 - 3 > 4 - 6

ModulesModules/ Sectors

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 serious challenge to obtaining meaningful blanket testing results. The magnitude of the challenge can be understood by comparing parameters for DEMO, Required Testing and ITER.

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

Plasma Duty Cycle* ~1 >0.8 0.25

Plasma Burn Time, s

Plasma Dwell Time, s

>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

Total Test Area, m 2 >10 ~7

*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

• 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.

• 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.

- Thus the burn time needs to be hours and the dwell time needs to be a few seconds.

• 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%).

6 s1 to 5 s

1 to 2 s

~1 s5 to 10 s

30 to 100 s300 to 900 s

20 to 100 s180 to 700 s

30 to 70 s80 to 220 s

10 to 30 s40 to 100 s

150 days10 days

1 to 2 h20 to 30 h

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 ProcessTable XX.*

Characteristic Time Constants in Solid Breeder

Blankets

* From Fusion Technology, Vol. 29, pp 1-57, January 1996

Table XXI.*

~30 s~100 s

1 to 2 s ~4 s

1 s 20 s

4 s300 s

40 days

30 days30 min

2230 days62 days

 47 min41 min

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

Tritium Release in the breeder Lithium LiPb Diffusion through: Ferritic Steel 300ºC 500ºC Vanadium 500ºC 700ºC

Time Constant Process

Characteristic Time Constants in Liquid-

Metal Breeder Blankets

* From Fusion Technology, Vol. 29, pp 1-57, January 1996

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. Statistics3. 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. Abdou, M. “ITER Test Program: Key Technical Aspects,” Fusion Technology 19(May 1991) 1439+

2. 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

3. Abdou, M., et al. “A Study of the Issues and Experiments for Fusion Nuclear Technology,” Fusion Technology 8 (1985) 2595

4. Abdou, M., et al. “Technical Issues and Requirements of Experiments and Facilities for Fusion Nuclear Technology,” Nuclear Fusion 27 (1987) 4, 619

5. 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

6. “Test Program Summary,” ITER-IL-NE-3-0-5, ITER Document, February 1990

7. “Test Program Summary,” ITER-IL-NE-3-9-4, ITER Document, July 1989

8. There are numerous topical reports from INTOR, ITER-CDA and ITER-EDA. Contact M. Abdou for copies of the US reports (1980-1997)