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 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 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 -Activation Heat Sources (magnitude, gradient) -Bulk (from neutrons) -Surface Particle Flux (energy and density) Magnetic Field -Steady Field -Time-Varying Field Mechanical Forces -Normal -Off-Normal Thermal/Chemical/Mechanical/Electrical/Magnetic Interactions Synergistic 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 State b 1 to to 3 4 to 6 c >6 >10 >5 >4 Neutron wall load a (MW/m 2 ) Plasma mode of operation Minimum COT (periods with 100% availability) (weeks) Neutron fluence at test module (MW·y/m 2 ) Stage I: initial fusion break-in Stage II: concept performance verification (engineering feasibility) Stage III c : component engineering development and reliability growth Total neutron fluence for test device (MW·y/m 2 ) Total test area (m 2 ) Total test volume (m 3 ) 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 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/m 2 ) 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” IIIII Design Concept & Performance Verification Component Engineering Development & Reliability Growth 1 - 3> Modules Modules/ Sectors DEMODEMO

ITER Provides the First Integrated Experimental Conditions for Fusion Technology Testing Simulation of all Environmental Conditions Neutrons Plasma Particles Electromagnetics Tritium VacuumSynergistic 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 FeatureDEMO (Typical) Testing Requirements (derived in fusion literature) ITER (Feat) Neutron Wall Load, MW/m 2 2 to 41 to Plasma Mode of OperationSteady State (or long pulses) Steady StateHighly pulsed Plasma Duty Cycle * ~1> Plasma Burn Time, s Plasma Dwell Time, s >10,000 <100 >1000 < Minimum COT (period of 100 % availability), weeks many1 to 2?? Neutron Fluence, MW. y/m to 60.1 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 (t b ) > 3  c plasma dwell time (t d ) < 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 s 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 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 Li 2 O (400 to 800ºC) 10 MW/m 3 1 MW/m 3 LiAlO 2 (300 to 1000ºC) 10 MW/m 3 1 MW/m 3 Solid breeder bulk temperature rise Li 2 O (400 to 800ºC) 10 MW/m 3 1 MW/m 3 LiAlO 2 (300 to 1000ºC) 10 MW/m 3 1 MW/m 3 Tritium Diffusion through steel 300ºC 500ºC Release in the breeder Li 2 O 400 to 800ºC LiAlO to 1000ºC Time ConstantProcess Table 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 s 300 s 40 days 30 days 30 min 2230 days 62 days 47 min 41 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 ConstantProcess 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 Scaling2. 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.Abdou, M. “ITER Test Program: Key Technical Aspects,” Fusion Technology 19(May 1991) Gierszewski, P., Abdou, M., Bell, et al. “Engineering Scaling and Quantification of the Test Requirements for Fusion Nuclear Technology,” Fusion Technology 8 (July 1985) Abdou, M., et al. “A Study of the Issues and Experiments for Fusion Nuclear Technology,” Fusion Technology 8 (1985) Abdou, M., et al. “Technical Issues and Requirements of Experiments and Facilities for Fusion Nuclear Technology,” Nuclear Fusion 27 (1987) 4, 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) “Test Program Summary,” ITER-IL-NE-3-0-5, ITER Document, February “Test Program Summary,” ITER-IL-NE-3-9-4, ITER Document, July There are numerous topical reports from INTOR, ITER-CDA and ITER-EDA. Contact M. Abdou for copies of the US reports ( )