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Fusion Nuclear Technology Development and the Role of CTF (and ITER TBM)

Fusion Nuclear Technology Development and the Role of CTF (and ITER TBM). Mohamed Abdou (web: www.fusion.ucla.edu/abdou/ ) Distinguished Professor of Engineering and Applied Science Director, Center for Energy Science and Technology (CESTAR) ( www.cestar.seas.ucla.edu/ )

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Fusion Nuclear Technology Development and the Role of CTF (and ITER TBM)

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  1. Fusion Nuclear Technology Development and the Role of CTF (and ITER TBM) Mohamed Abdou (web: www.fusion.ucla.edu/abdou/) Distinguished Professor of Engineering and Applied Science Director, Center for Energy Science and Technology (CESTAR) (www.cestar.seas.ucla.edu/) Director, Fusion Science and Technology Center (www.fusion.ucla.edu/) University of California, Los Angeles (UCLA) Presented at Workshop on CTF, Culham Conference Centre Culham, United Kingdom, May 22-23, 2007

  2. Fusion Nuclear Technology Development and the Role of CTF/VNS (and ITER TBM) Outline • What is Fusion Nuclear Technology? • Brief Statement of Technical Issues and Role of Fusion Testing • Framework for FNT Development and Requirements • Stages • Parameters • Role of ITER TBM • Top Level Issues for FNT Development Facilities - Reliability / Maintainability / Availability (and Reliability Growth Strategy) • Tritium Consumption and Supply • Technical Details on Parameters Required for VNS/CTF • Wall Load • Steady State Plasma • Fluence • Test Area • Issues yet to be resolved for CTF

  3. 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 (includ. FW) 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

  4. Notes on FNT: • 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 the 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

  5. Pillars of a Fusion Energy System • Confined and Controlled Burning Plasma (feasibility) • Tritium Fuel Self-Sufficiency (feasibility) • Efficient Heat Extraction and Conversion (attractiveness) • Safe and Environmentally Advantageous (feasibility/attractiveness) • Reliable System Operation (attractiveness) The Blanket is THE KEY component and determines the critical path to DEMO Yet, No fusion blanket has ever been built or tested!

  6. R&D Tasks to be Accomplished Prior to Demo 1) Plasma - Current Drive/Steady State - Confinement/Burn - Edge Control - Disruption Control 2) Plasma Support Systems - Superconducting Magnets - Fueling - Heating 3) Fusion Nuclear Technology Components and Materials [Blanket (including First Wall), 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 • How and Where Will Fusion Nuclear Technology (FNT) be developed?

  7. FNT Development Issues and Pathways • Numerous technical studies were performed over the past 30 years in the US and worldwide to study issues, experiments, facilities, and pathways for FNT development. (This is probably the most studied subject in fusion development) • This is an area where the US has played a major leadership role in the world program and provided major contributions such as engineering scaling laws for testing, VNS/CTF concept, and blanket designs • These studies involved many organizations (universities, National Labs, Industry, and utilities) and many scientists, engineers, and plasma physicists. Industry participation was particularly very strong from Fission and Aerospace and they provided substantial contributions. • Examples of Major Studies on FNT/Blanket • Blanket Comparison and Selection Study (1982-84, led by ANL) • FINESSE Study (1983-86, led by UCLA) • IEA Study on VNS/CTF (1994-96 US, EU, J, RF) • ITER TBM (1987-2007) , US ITER TBM (2003-2007) • Other studies that provided important input: DEMO Study (led by ANL 1981-1983) and many Power Plant Studies (UWMAKs, STARFIRE, ARIES, others in EU,J,RF) • Many Planning activities discussed FNT and provided input (TPA, FESAC, etc) These Studies resulted in important conclusions and illuminated the pathways for FNT and fusion development

  8. Summary of Critical R&D Issues for Fusion Nuclear Technology • D-T fuel cycle tritiumself-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, doubling time • 2. Tritium extraction and inventory in the solid/liquid breeders under actual operating conditions • 3.Thermomechanicalloadings 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 • 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 • Tritium permeation, control and inventory in blanket and PFC • 8. Remote maintenance with acceptable machine shutdown time. • 9. Lifetime of blanket, PFC, and other FNT components

  9. [0.5-1.5] mm/s [18-54] mm/s Neutron Multiplier Be, Be12Ti (<2mm) Tritium Breeder Li2TiO3 (<2mm) PbLi flow scheme First Wall (RAFS, F82H) Surface Heat Flux Neutron Wall Load Blanket systems are complex and have many integrated functions, materials, and interfaces

  10. Fusion environment is unique and complex:multi-component fields with gradients • Particle Flux(energy and density, gradients) • Magnetic Field (3-component with gradients) • Steady Field • Time-Varying Field • Mechanical Forces • Normal/Off-Normal • Thermal/Chemical/Mechanical/ Electrical/Magnetic Interactions • Neutrons (fluence, spectrum, temporal and spatial gradients) • Radiation Effects (at relevant temperatures, stresses, loading conditions) • Bulk Heating • Tritium Production • Activation • Heat Sources (magnitude, gradient) • Bulk (from neutrons and gammas) • Surface • Synergistic Effects • Combined environmental loading conditions • Interactions among physical elements of components Multi-function blanket in multi-component field environmentleads to: • Multi-Physics, Multi-Scale PhenomenaRich Science to Study - Synergistic effectsthatcannotbe anticipated from simulations & separate effects tests. Even some key separate effects in the blanket can not be produced in non-fusion facilities (e.g. volumetric heating with gradients) A true fusion environment is ESSENTIAL to activate mechanisms that cause prototypical coupled phenomena and integrated behavior

  11. Types of experiments, facilities and modeling for FNT Theory/Modeling Design Codes Basic Separate Effects Multiple Interactions Partially Integrated Integrated Component Design Verification & Reliability Data • Fusion Env. Exploration Property Measurement Phenomena Exploration • Concept Screening • Performance Verification Non-Fusion Facilities (non neutron test stands, fission reactors and accelerator-based neutron sources) Testing in Fusion Facilities • Non fusion facilities (e.g. non-neutron test stands, fission reactors and neutron sources) have important roles • Testing in Fusion Facilities is NECESSARY for multiple interactions, partially integrated, integrated, and component tests

  12. Stages of FNT Testing in Fusion Facilities D E M O Component Engineering Development & Reliability Growth Engineering Feasibility & Performance Verification Fusion “Break-in” & Scientific Exploration Stage I Stage II Stage III 1 - 3 MW-y/m2 > 4 - 6 MW-y/m2 0.1 – 0.3 MW-y/m2 1-2 MW/m2, steady state or long pulse COT ~ 1-2 weeks 1-2 MW/m2, steady state or long burn COT ~ 1-2 weeks 0.5 MW/m2, burn > 200 s Sub-Modules/Modules Modules Modules/Sectors • Initial exploration of coupled phenomena in a fusion environment • Uncover unexpected synergistic effects, Calibrate non-fusion tests • Impact of rapid property changes in early life • Integrated environmental data for model improvement and simulation benchmarking • Develop experimental techniques and test instrumentation • Screen and narrow the many material combinations, design choices, and blanket design concepts • Uncover unexpected synergistic effects coupled to radiation interactions in materials, interfaces, and configurations • Verify performance beyond beginning of life and until changes in properties become small (changes are substantial up to ~ 1-2 MW · y/m2) • Initial data on failure modes & effects • Establish engineering feasibility of blankets (satisfy basic functions & performance, up to 10 to 20 % of lifetime) • Select 2 or 3 concepts for further development • Identify lifetime limiting failure modes and effects based on full environment coupled interactions • Failure rate data: Develop a data base sufficient to predict mean-time-between-failure with confidence • Iterative design / test / fail / analyze / improve programs aimed at reliability growth and safety • Obtain data to predict mean-time-to-replace (MTTR) for both planned outage and random failure • Develop a database to predict overall availability of FNT components in DEMO

  13. Fusion “Break-in” & Scientific Exploration Stage I 0.5 MW/m2, burn > 200 s 0.1 – 0.3 MW-y/m2, Sub-Modules/Modules • Initial exploration of coupled phenomena in a fusion environment • Uncover unexpected synergistic effects, Calibrate non-fusion tests • Impact of rapid property changes in early life • Integrated environmental data for model improvement and simulation benchmarking • Develop experimental techniques and test instrumentation • Screen and narrow the many material combinations, design choices, and blanket design concepts

  14. Engineering Feasibility & Performance Verification Stage II 1 - 3 MW-y/m2, 1-2 MW/m2, steady state or long pulse, COT ~ 1-2 weeks Modules • Uncover unexpected synergistic effects coupled to radiation interactions in materials, interfaces, and configurations • Verify performance beyond beginning of life and until changes in properties become small (changes are substantial up to ~ 1-2 MW · y/m2) • Initial data on failure modes & effects • Establish engineering feasibility of blankets (satisfy basic functions & performance, up to 10 to 20 % of lifetime) • Select 2 or 3 concepts for further development

  15. Component Engineering Development & Reliability Growth Stage III > 4 - 6 MW-y/m2, 1-2 MW/m2, steady state or long burn, COT ~ 1-2 weeks Modules/Sectors • Identify lifetime limiting failure modes and effects based on full environment coupled interactions • Failure rate data: Develop a data base sufficient to predict mean-time-between-failure with confidence • Iterative design / test / fail / analyze / improve programs aimed at reliability growth and safety • Obtain data to predict mean-time-to-replace (MTTR) for both planned outage and random failure • Develop a database to predict overall availability of FNT components in DEMO

  16. 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 Testing Blanket Working Group, IEA-VNS, etc.) • - Many Journal Papers published (>35), e.g. IEA-VNS Study Paper (Fusion Technology, Vol. 29, Jan 1996) a - Prototypical surface heat flux (exposure of first wall to plasma is critical) b - For stages II & III. If steady state is unattainable, the alternative is long plasma burn with plasma duty cycle >80% c - Initial fusion break-in has less demanding requirements than stages II & III d - 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

  17. ITER TBM is a Necessary First Step in Fusion Environment Testing to enable future Engineering Development D E M O Role of ITER TBM Component Engineering Development & Reliability Growth Engineering Feasibility & Performance Verification Fusion “Break-in” & Scientific Exploration Stage III Stage I Stage II 1 - 3 MW-y/m2 > 4 - 6 MW-y/m2 0.1 – 0.3 MW-y/m2 1-2 MW/m2, steady state or long pulse COT ~ 1-2 weeks 1-2 MW/m2, steady state or long burn COT ~ 1-2 weeks 0.5 MW/m2, burn > 200 s Sub-Modules/Modules Modules/Sectors Modules • Initial exploration of coupled phenomena in a fusion environment • Uncover unexpected synergistic effects, Calibrate non-fusion tests • Impact of rapid property changes in early life • Integrated environmental data for model improvement and simulation benchmarking • Develop experimental techniques and test instrumentation • Screen and narrow the many material combinations, design choices, and blanket design concepts • Uncover unexpected synergistic effects coupled to radiation interactions in materials, interfaces, and configurations • Verify performance beyond beginning of life and until changes in properties become small (changes are substantial up to ~ 1-2 MW · y/m2) • Initial data on failure modes & effects • Establish engineering feasibility of blankets (satisfy basic functions & performance, up to 10 to 20 % of lifetime) • Select 2 or 3 concepts for further development • Identify lifetime limiting failure modes and effects based on full environment coupled interactions • Failure rate data: Develop a data base sufficient to predict mean-time-between-failure with confidence • Iterative design / test / fail / analyze / improve programs aimed at reliability growth and safety • Obtain data to predict mean-time-to-replace (MTTR) for both planned outage and random failure • Develop a database to predict overall availability of FNT components in DEMO

  18. Critical Factors in Deciding where to do Blanket / FNT Fusion Testing • Tritium Consumption / Supply Issue • Reliability / Maintainability / Availability Issue • Cost, Risk, Schedule • The Key FNT Testing Requirements are : • - Fusion Power only 20-30 MW • - Over about 10m2 of surface area (with exposure to plasma) • - With Steady State Plasma Operation (or plasma cycle >80%) • - Testing Time on successive test articles equivalent to neutron fluence “experience” of ~ 6 MW • y/m2

  19. What is CTF (VNS)? • The idea of CTF is to build a small size, low fusion power DT plasma-based device in which Fusion Nuclear Technology experiments can be performed in the relevant fusion environment: 1- at the smallest possible scale, cost, and risk, and 2- with practical strategy for solving the tritium consumption and supply issues for FNT development. • In MFE: small-size, low fusion power can be obtained in a low-Q plasma device. • Equivalent in IFE: reduced target yield and smaller chamber radius. • This is a faster, much less expensive approach than testing in a large, ignited/high Q plasma device for which tritium consumption, and cost of operating to high fluence are very high (unaffordable!, not practical).

  20. Tritium Consumption in Large and Small Power DT Devices AND Tritium Supply Issue AND Impact on the Path to FNT Development Note: Projections of world tritium supply available to fusion for various scenarios were generated by Scott Willms, including information from Paul Rutherford’s 1998 memo on “Tritium Window”, and input from M. Abdou and D. Sze.

  21. Projections for World Tritium Supply Available to Fusion Reveal Serious Problems 30 25 CANDU Supply 20 w/o Fusion Projected Ontario (OPG) Tritium Inventory(kg) 15 World Max. tritium supply is 27 kg 10 Tritium decays at a rate of 5.47% per year 5 0 2000 2010 2020 2030 2040 Year Tritium Consumption in Fusion is HUGE! Unprecedented! 55.8 kg per 1000 MW fusion power per year Production & Cost: CANDU Reactors:27 kg from over40 years, $30M/kg (current) Fission reactors:2–3 kg per year, at a cost of ~$200M/kg It takes tens of fission reactors to supply one fusion reactor. $84M-$130M per kg, per DOE Inspector General* *DOE Inspector General’s Audit Report, “Modernization of Tritium Requirements Systems”, Report DOE/IG-0632, December 2003, available at www.ig.doe.gov/pdf/ig-0632.pdf

  22. Projections for World Tritium Supply Available to Fusion for Various Scenarios (Willms, et al) See calculation assumptions in Table S/Z • World Tritium Supply would be Exhausted by 2025 if ITER were to run at 1000 MW fusion power with 10% availability • Large Power DT Fusion Devices are not practical for blanket/PFC development. • We need 5-10 kg of tritium as “start-up” inventory for DEMO (can be provided from CTF operating with TBR > 1 at later stage of operation) • Blanket/PFC must be developed in the near termprior to DEMO (and we cannot wait very long for blanket/PFC development even if we want to delay DEMO).

  23. Canadian + Korean Inventory without supply to fusion Canadian + Korean Inventory with ITER Updated projections of Canadian + Koreantritium supply and consumption using ITER current schedule. (From Scott Willms [March 2007]). Notes & assumptions given on a separate slide.

  24. ITER Impact on Canadian/Korean Candu Tritium Inventory (March 2007) (from Scott Willms, LANL) • Following the methodology developed for the Snowmass and 35-year fusion development plan exercises, the impact of ITER (the seven party agreement signed 11/07) on tritium available from both Canada and Korea was analyzed. • The assumptions were: • Use the same assumption for Canadian tritium as was used for the 35-yr development plan • In addition to the Canadian tritium, Korean tritium is available for fusion (about a 25% additional amount of tritium) • ITER has a 2 kg tritium working inventory which is built up over two years beginning in 2018 • ITER first plasma is 2016 with 3 yr HH, 1 yr DD following by tritium operations • ITER tritium operations are 6 yr followed by 1 year maintenance (no tritium burned) followed by 10 year tritium • The first 10 year campaign includes three yr HH, 1 yr DD and then builds to 1.08 kg tritium burned per year over a five year period, then remains flat to the end of the first 10 years (modification of scenario communicated by Janeschitz at Snowmass 2002) • The second 10 years burns 1.43 kg tritium per year for each of the 10 years. This builds the wall irradiation to 0.3 MW-yr/m2 (neutrons) average over a 680 m2 wall • Between the two 10-yr campaigns there is a one year maintenance phase which presumably includes a first wall replacement. The first 10 year would not irradiate the first wall to 0.3 MW-yr/m2. The new first wall installed at the beginning of the second 10-yr increases from 0 to 0.3 MW-yr/m2 linearly over the second 10 yr. • At the end of ITER a total of 1 kg of tritium is lost to waste and 1 kg of tritium is returned to Canada/Korea • The only demand on the Canadian/Korean tritium is 0.1 kg/yr for sales and ITER. That is, there is no accounting for other demands on this tritium such as CTF or Demo. • There is no tritium breeding in ITER • Note: There has been no signaling from Korea that they will supply tritium to ITER. They are only recovering tritium to get it out of their heavy water. Canada assisted Korea with the installation of their tritium recovery system, and it is not known what contractual agreements they may have. Korean tritium sales, if they took place, would be in competition with Canada. • The results on the following figure show: • Upper Curve: The Canadian/Korean tritium inventory without fusion. This assumes the only demand on this tritium is decay and 0.1 kg/yr sales. • Middle Curve: The Canadian/Korean tritium inventory with the above + ITER • Lower Curve: The yearly ITER transactions with the Canadian/Korean tritium due to ITER tritium inventory build up (down) + decay + burn • Observations: • With these assumptions there is enough tritium for ITER, and about 5 kg of tritium would remain at the end of ITER • The tritium supply would not accommodate any significant extension of ITER, loss of tritium or significant fusion experiment requiring tritium • There is a marginal amount of tritium remaining to startup one Demo, and tritium breeding on that one machine would have to work “out of the box”

  25. Reliability / Maintainability / Availability Critical Development Issues Unavailability = U(total) = U(scheduled) + U(unscheduled) This you design for This can kill your DEMO and your future Scheduled Outage: Planned outage (e.g. scheduled maintenance of components, scheduled replacement of components, e.g. first wall at the end of life, etc.). This tends to be manageable because you can plan scheduled maintenance / replacement operations to occur simultaneously in the same time period. Unscheduled Outage: (This is a very challenging problem) Failures do occur in any engineering system. Since they are random they tend to have the most serious impact on availability. This is why “reliability/availability analysis,” reliability testing, and “reliability growth” programs are key elements in any engineering development.

  26. Availability (Due to Unscheduled Events) Availability: = represents a component (Outage Risk) = (failure rate) • (mean time to repair) = MTBF = mean time between failures = 1/failure rate MTTR = mean time to repair • A Practical Engineering System must have: 1. Long MTBF: have sufficient reliability - MTBF depends on reliability of components. One can estimate what MTBF is NEEDED from “availability allocation models” for a given availability goal and for given (assumed) MTTR. But predicting what MTBF is ACHIEVEABLE requires real data from integrated tests in the fusion environment. 2. Short MTTR: be able to recover from failure in a short time - MTTR depends on the complexity and characteristics of the system (e.g. confinement configurations, component blanket design and configuration, nature of failure). Can estimate, but need to demonstrate MTTR in fusion test facility.

  27. ( 1 / failure rate ) + 1 / failure rate replacemen t time Reliability/Maintainability/Availability is one of the remaining “Grand Challenges” to Fusion Energy Development. FNT R&D is necessary to meet this Grand Challenge. Need High Power Density/Physics-Technology Partnership - High-Performance Plasma Need Low - - Chamber Technology Capabilities Failure Rate × + + replacement cost C i O & M = COE × × × h P Availability M fusion th Energy Need High Temp. Multiplication Energy Extraction Need High Availability / Simpler Technological and Material Constraints · Need Low Failure Rate: - Innovative Chamber Technology · Need Short Maintenance Time: - Simple Configuration Confinement - Easier to Maintain Chamber Technology

  28. An Example Illustration of Achieving a Demo Availability of 49% (Table based on information from J. Sheffield’s memo to the Dev Path Panel) Assuming 0.2 as a fraction of year scheduled for regular maintenance. Demo Availability = 0.8* [1/(1+0.624)] = 0.49 (Blanket Availability must be .88)

  29. The reliability requirements on the Blanket/FW (in current confinement concepts that have long MTTR > 1 week) are most challenging and pose critical concerns. These must be seriously addressed as an integral part of the R&D pathway to DEMO. Impact on ITER is predicted to be serious. It is one of the key DRIVERS for CTF/VNS. A = Expected with extensive R&D (based on mature technology and no fusion-specific failure modes C = Potential improvements with aggressive R&D

  30. Reliability/Availability is a challenge to fusion, particularly blanket/PFC, development • Fusion System has many majorcomponents (TFC, PFC, plasma heating, vacuum vessel, blanket, divertor, tritium system, fueling, etc.) - Each component is required to have high availability • All systems except the reactor core (blanket/PFC) will have reliability data from ITER and other facilities • There is NO data for blanket/PFC (we do not even know if any present blanket concept is feasible) • Estimates using available data from fission and aerospace for unit failure rates and using the surface area of a tokamak show: PROBABLE MTBF for Blanket ~ 0.01 to 0.2 yr compared to REQUIRED MTBF of many years Need Aggressive “Reliability Growth” Program We must have an aggressive “reliability growth” program for the blanket / PFC (beyond demonstrating engineering feasibility) 1) All new technologies go through a reliability growth program 2) Must be “aggressive” because extrapolation from other technologies (e.g. fission) strongly indicates we have a serious CHALLENGE

  31. Component Technology Facility (CTF) MISSION The mission of CTF is to test, develop, and qualify Fusion Nuclear Technology Components (fusion power and fuel cycle technologies) in prototypical fusion power conditions. The CTF facility will provide the necessary integrated testing environment of high neutron and surface fluxes, steady state plasma (or long pulse with short dwell time), electromagnetic fields, large test area and volume, and high neutron fluence. The testing program and CTF operation will demonstrate the engineering feasibility, provide data on reliability / maintainability / availability, and enable a “reliability growth” development program sufficient to design, construct, and operate blankets, plasma facing and other FNT components for DEMO.

  32. Major Activities and Example Timeline for Fusion Nuclear Technology Development • ITER TBM Provides Timely Information to CTF • R&D Activities are critical to support effective FNT/Blanket testing in ITER and CTF • Arrows indicate major points of FNT information flow

  33. Quantification of Test Requirements General Observations of FINESSE Study Results • In many cases, a true integrated test in the strictest sense cannot be performed under significantly scaled-down conditions for certain parameters (e.g., power density, surface heat load, geometry) • Under scaled-down environmental conditions, the function of an integrated test module has to be divided into two or more “act-alike” tests. Each act-alike test emphasizes a group of issues/phenomena. • While an overlap among the various act-alike tests can be included to account for certain interfaces, a concern about possibly missing some phenomena remains. • Perfect quantitative engineering scaling is not possible because it requires complete quantitative models for all (including interactive) phenomena. • If fusion testing will have to be carried out under scaled-down conditions, then: • - Engineering scaling needs to continue to be nourished as a key technical discipline in fusion. • - The need for a more thorough understanding of phenomena and more analytical modeling will become more critical.

  34. How Many Modules/SubmodulesNeed to Be Tested 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) These requirements are based on “functional” and engineering scaling requirements. There are other more demanding requirements for “Reliability Growth” (See separate section on this)

  35. Neutron Wall Load Requirements Importance Neutron wall load is a primary source of both heating and nuclear reactions in the blanket Bulking heating Surface heating Reaction rate (e.g., tritium production) Fluence Neutron wall load requirements determined by: Engineering scaling requirements (conclusion: should not scale down by more than a factor of 2-3 Tradeoffs between device availability and wall load for a given testing fluence and testing time Wall Load and Availability Required to Reach 6 MW•y/m2 Goal Fluence in 12 Calendar Years For pulsed plasma operation, this becomes the product of availability and plasma duty cycle. Therefore, at any given wall load, higher availability would be required.

  36. Importance of Steady State Operation for Nuclear Testing • To substantially increase the capability for meaningful nuclear technology testing • To reduce the failure rate and improve the availability of the testing device • - Many papers and presentations on this topic from the last 20 years. It is well understood and accepted(see, for example, www.fusion.ucla.edu/abdou)

  37. Effects of Pulsed Plasma Operation on Nuclear Technology Testing Time-Dependent Changes in Environmental Conditions for Testing Nuclear (volumetric) heating Surface heating Poloidal magnetic field Tritium production rate Result in Time-Dependent Changes and Effects in Response of Test Elements that: Can be more dominant than the steady-state effects for which testing is desired Can complicate tests and make results difficult to model and understand Examples of Effects Thermal conditions Tritium concentration profiles Failure modes/fracture mechanism Time to reach equilibrium

  38. Recommended COT for FNT: 1-2 weeks COT Requirements Test Schedule Issues It is desirable to complete a test campaign before the machine is shut down for a significant period of time The objective of design/test/fix iterative program requires timely data acquisition as input to redesign and construction of new test modules. It is therefore desirable to complete test campaigns as quickly as possible. Requirements on Environmental Control The level of control over conditions within test modules and ancillary systems during shutdown is uncertain.

  39. Device Fluence vs Test Module Fluence • Must make a distinction between: • Fluence achievable at test module ( modules will fail and will be replaced. Module Fluence is the “cumulative” experience accumulated on successive test articles, in “reliability growth” terminology) • Test facility “lifetime fluence” (The device itself will need to have a longer lifetime than the test articles. The blanket is an exception because it is the “object of testing”, depending on testing strategy) • Benefits to FNT testing as a function of neutron fluence have been recognized: • Many issues show continuous increase in benefits at higher fluences • Some issues show distinct fluence regions of highest benefit • There is inevitably a long period of fail/replace/fix for test modules • Time required to perform the three testing stages: The reliability growth testing phase is the most demanding on fluence requirements.

  40. Testing Fluence In this study, we derive fluence directly for each of the three stages of fusion testing Stage I: Scoping (~ 0.1 - 0.3 MW • y/m2) Just enough time to explore environment, develop instrumentation, and get initial data Stage II: Concept Verification (1-3 MW • y/m2) 1 MW • y/m2 is barely enough to establish engineering feasibility (~10% of minimum life) Stage III: Engineering Development & Reliability Growth (4-6 MW • y/m2) This fluence is derived from detailed analysis of reliability growth testing

  41. Reference: M. Abdou et. al., "FINESSE: A Study of the Issues, Experiments and Facilities for Fusion Nuclear Technology Research & Development, Chapter 15 (Figure 15.2-2.) Reliability Development Testing Impact on Fusion Reactor Availability", Interim Report, Vol. IV, PPG-821, UCLA,1984. It originated from A. Coppola, "Bayesian Reliability Tests are Practical", RADC-TR-81-106, July 1981. “Reliability Growth” Upper statistical confidence level as a function of test time in multiples of MTBF for time terminated reliability tests (Poisson distribution). Results are given for different numbers of failures. Example, To get 80% confidence in achieving a particular value for MTBF, the total test time needed is about 3 MTBF (for case with only one failure occurring during the test). TYPICAL TEST SCENARIO

  42. Achievable DEMO Reactor and Blanket System Availabilities (for a given confidence level) depend on: • Testing Fluence at the Blanket Test Module & No. of test modules • Achievable Mean Time to Replace (MTTR) for Blankets

  43. Findings of Testing Fluence Requirements on Achievable Reactor Availability Analyses • Achieving a “ cumulative” fluence of ~ 5-6 MW • y/m2 at the test modules with ~ 6-12 test modules is crucial to achieving DEMO reactor availability on the 40% to 50% range with 90% confidence, • Achieving DEMO reactor availability of 60% with 90% confidence may not be possible for any practical blanket test program, • The mean downtime (MTTR) to recover (or replace) from a random failure in the blanket must be on the order of one week or less in order to achieve the required blanket and reactor system availabilities, and • Determining (and shortening) the length of the MTTR (how long it takes to replace a failed blanket module) must be by itself one of the critical objectives for testing in fusion facilities (e.g. in CTF).

  44. Level of Confidence based on Figure 15-2.2 in "FINESSE: A Study of the Issues, experiments and Facilities for Fusion Nuclear Technology Research & Development, Chapter 15 Reliability Development Testing Impact on Fusion Reactor Availability", Interim report, Vol. IV, PPG-821, UCLA, 1984. Obtainable Blanket System Availability with 50% Confidence for Different Testing Fluences and Test Areas MTTR = 1 month 1 failure during the test 80 blanket modules in blanket system Experience factor =0.8 Neutron wall load = 2 MW/m2

  45. Device Surface Area Requirements No. of Modules per Specific Design Concept Need for Engineering Scaling and Statistics. A large number of test modules lead to a faster reliability growth and a higher precision level. Full scale test preferable There are many problems that were solved only after setting up a full scale test. There are also many problems that surfaced only in the full scale test but did not show in the reduced scale. Account for neutron flux spatial variation in poloidal direction. If each module first wall area is about 1 m2 Test area required = (6 – 12) x A (for engineering scaling) m2 per concept. If test 3 concepts, use 6 modules per concept; or 2 concepts use 12 modules per concept. Total test area at the first wall required: > 10 m2

  46. Level of Confidence Obtainable for Different Testing Scenarios • Neutron wall load = 2 MW/m2 • MTBF per module = 26 years • Experience factor = 0.8 • (*test fluence of 0.1 MWyr/m2 is too low to consider) • Note • Assuming that the reactor has 16 sectors, 80 blanket modules (each module is about 1(toroidal) x 8 (poloida) m2). “Engineering scaling” is applied to the test article design in order to have meaningful data extrapolated from a 0.5 m2 • The irradiation effects on material properties are not considered in the estimation. • Level of Confidence based on Figure 15-2.2 in "FINESSE: A Study of the Issues, experiments and Facilities for Fusion Nuclear Technology Research & Development, Chapter 15 Reliability Development Testing Impact on Fusion Reactor Availability", Interim report, Vol. IV, PPG-821, UCLA, 1984.

  47. The base machine includes 10 major components. CTF FW area 100 m2 with 64 blanket modules Demo (ITER like FW area 680 m2 and 440 blanket modules) Lifetime of Demo FW/blanket 10 years Reliability/Availability is a challenge to fusion, particularly FW/blanket, development • Fusion System has many majorcomponents (TFC, PFC, plasma heating, vacuum vessel, blanket, divertor, tritium system, fueling, etc.) • All components except the reactor core (FW/blanket) will have reliability data from ITER and other facilities • The reliability requirements on the FW/Blanket are most challenging and pose critical concerns (due to a large number of modules). These must be seriously addressed as an integral part of the R&D pathway to DEMO. • Predicting Achievable MTBF (mean-time-between-failure) requires real data from integrated tests in the fusion environment. 3 Availability decreases due to the number of module increases 1 2 1 Availability increases due to improved base machine availability 2 Availability increases due to a shortened MTTR for blanket 3

  48. Conclusions on Blanket and PFC Reliability Growth • Blanket and PFC tests in ITER alone cannot demonstrate DEMO availability higher than 4% • Blanket and PFC testing in VNS (CTF) allows DEMO blanket system and PFC system availability of > 50%, corresponding to DEMO availability > 30% Recommendations on Availability/Reliability Growth Strategy and Goals - Set availability goal for initial operation of DEMO of ~ 30% (i.e. defer some risk) - Operate CTF and ITER in parallel, together with other facilities, as aggressively as possible - Realize that there is a serious decision point with serious consequences based on results from ITER and CTF • If results are positive proceed with DEMO • If not, then we have to go back to the drawing board

  49. BACKUP SLIDES

  50. Examples of possible Failure Modes in Blanket/First Wall (for solid and liquid breeder blanket concepts) • Cracking around a discontinuity/weld • Crack on shutdown (with cooling) • Solid breeder loses functional capability due to extensive cracking • Cracks in electrical insulators (for liquid metal blankets) • Cracks, thermal shock, vaporization, and melting during disruptions • First wall/breeder structure swelling and creep leading to excessive deformation or first wall/coolant tube failure • Environmentally assisted cracking • Excessive tritium permeation to worker or public areas • Cracks in electrical connections between modules • Our concern is that failure rates may be much higher in fusion blankets because they appear to be much more complex than steam generators and the core of fission reactors because of the following points: • Larger numbers of subcomponents and interactions (tubes, welds, breeder, multiplier, coolant, structure, insulators, tritium recovery, etc.). • More damaging, higher energy neutrons. • Other environmental conditions: magnetic field, vacuum, tritium, etc. (for example, a leak from the first wall or blanket module walls into the vacuum system results in failure, while in steam generators and fission reactors, continued operation with leaks is often possible). • Reactor components must penetrate each other; many penetrations have to be provided through the blanket for plasma heating, fueling, exhaust, etc. • Ability to have redundancy inside the blanket / first wall system is practically impossible.

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