1. 1 Breeding Blanket Concepts for Fusion and Materials Requirements A. R. Raffray 1, M. Akiba 2, V. Chuyanov 3, L. Giancarli 4, S. Malang 5 1 University of California, San Diego, 458 EBU-II, La Jolla, CA 92093-0417, USA 2 Blanket Engineering Laboratory, JAERI, Naka-machi, Naka-gun, Ibaraki-ken, 311-0193 Japan 3 ITER Garching Joint Work Site, Boltzmannstr. 2, Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany 4 CEA-Saclay, DEN/CPT, 91191, Gif-sur-Yvette, France. 5 Forschungszentrum Karlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany Plenary Presentation at ICFRM-10 Baden Baden, Germany October 15-19, 2001

2. 2 Outline of Presentation Highlight key performance and attractiveness parameters for breeding blanket concepts Summarize range of blanket concepts being currently considered –Focus on MFE (although significant IFE/MFE synergies) –Differentiate between class of concepts (material basis) –Example description for each class of blanket concepts –Highlight key material-related issues associated with each class of blanket concepts. Evolve an example classification of concepts based on the level of attractiveness and the development risk associated Propose a strategy for blanket development and supporting material R&D

3. 3 Performance and Attractiveness Factors Guide the Blanket Design Process Design and material impact on all these factors Require close interaction between design and material communities Electrical power production –Neutron energy multiplier –Power cycle efficiency Safety –Short-term activation: possibility of passive accommodation of off-normal scenarios without major consequences –Long-term activation: waste disposal requirements Availability –Commercial reactors would require high availability –Key parameters: reliability, lifetime and downtime of the blanket system Design and Fabrication –Simplicity Tritium –Need for tritium self-sufficiency from blanket tritium breeding –Total tritium inventory in blanket and tritium permeation Economics: –Ultimate economic measure: COE –Affected by all other factors E.g. Why High Temp. Material?

4. 4 A Number of Different Breeding Blanket Concepts Have Been Considered Recently Focus on solid wall concepts but material issues also applicable to thin liquid film concepts Blanket concepts can be classified based on the structural and breeder materials – Ceramic Breeder + Ferritic/Martensitic Steel Concepts (water-cooled and He-cooled) – Pb-17Li + Ferritic/Martensitic Steel Concepts (self-cooled and water-cooled) –Self-Cooled Lithium + Vanadium Alloy Concepts –SiC f /SiC Based Concepts (self-cooled Pb-17Li and He-cooled ceramic breeder) –Other concepts (less studied) Advanced concepts FLiBe For each class of concept, an example blanket design is described and key material issues discussed

5. 5 Ceramic Breeder + Be and Ferritic/Martensitic Steel Concepts Have Been Considered with Water and He as Coolant Generally good compatibility among CB, structural material and coolant No MHD effects CB and Be in form of sintered blocks or pebble beds Candidate breeder materials: –Ternary CB (Li 4 SiO 4, Li 2 TiO 3, Li 2 ZrO 3 ) –Li 2 O Struc. T max =550°C Cool. T max =320°C Cool. P =15 MPa Cycle Eff.=35% Energy Multip. =1.3 Lifetime>10MW-a/m 2 Example Water-Cooled Concept: SSTR (JAERI) Modular design Use of reduced activation F82H steel Binary Be & CB pebble beds –Maximize k eff and T breeding performance PWR-like water conditions Possible use of supercritical-pressure water –500°C/25 MPa –Increase cycle efficiency to ~40-45 % –Results in high stresses - use of advanced FS, such as Dispersion Strengthened FS, might be required

6. 6 Chemical compatibility between Be and water/air (hydrogen production) –Water-cooled concept –Accidental water/air ingress –Possible solution to reduce H 2 production: Use of Be 12 Ti, which has better compatibility with water. Tritium inventory in blanket and permeation to coolant Thermo-mechanical interactions among pebbles and between pebbles and structure including neutron irradiation effects Limits on blanket lifetime due to irradiation damages in ceramic breeder and beryllium Fabrication and re-processing of the ceramic breeder –Cost and waste considerations indicate need for re-processing of replaced blanket modules and re-use of the Li Key Material Issues of Ceramic Breeder Concepts

7. 7 Pb-17Li + Ferritic/Martensitic Steel Concepts Include Self-Cooled and Water-Cooled Options Example Dual Coolant Concept: FZK DC Uncouple FW cooling from blanket cooling –He coolant for more demanding FW cooling (no MHD uncertainties) –Self-cooled Pb-17Li with SiC f /SiC flow channel insulating inserts for blanket region Use of ODS-steels would allow for higher temperature but more demanding welding requirements –Compromise: ferritic steel structure with ~mm’s ODS layer at higher temperature FW location Pb-17Li is an attractive breeder material –Good tritium breeding capability –Possibility to replenish 6 Li on-line –Almost inert in air and relatively mild reaction with water –In general limited extrapolation of blanket technology Simplest FMS and Pb-17Li concept is a self-cooled configuration (ARIES-ST and FZK DC concepts) Water-cooled option to avoid MHD effects (WCLL concept) Struc. T max =550°C Pb-17Li T max =700°C He Cool. T max /P =480°C/14 MPa Cycle Eff.=45% Energy Multip. =1.17 Lifetime =15MW-a/m 2

8. 8 Key Material Issues for Pb-17Li + Ferritic/Martensitic Steel Concepts Performance of this concept is limited by : –Maximum allowable FW temperature –Structural material compatibility with Pb-17Li (~ 500  C) –Possible development of advanced ODS steel to allow for higher temperature Fabrication/joining For water-cooled concept, need to limit tritium permeation from Pb-17Li to water –Development of permeation barriers

9. 9 Self-Cooled Lithium and Vanadium Alloy Concept Example Li +V Concept: ARIES-RS Simple box-like structure Insulating coating on V alloy to reduce MHD effects –E.g. CaO maintained by adding 0.5% Ca in Li –Allows for low system pressure Multiple flow passes in the blanket provide the capability for FW surface heat flux ~1 MW/m 2 Lithium provides the advantages of: –High tritium breeding capability, –High thermal conductivity, –Immunity to irradiation damage –Possibility of unlimited lifetime if 6 Li burn-up can be replenished Vanadium alloys offer advantages of: –Low after heat –High temperature and high heat flux capability. –Compatibility with liquid Li Struc. T max =700°C Cool. T max =610°C Cool. P < 1MPa Cycle Eff.=46% Energy Multip. =1.21 Lifetime =15MW-a/m 2

10. 10 Key Material Issues for Lithium and Vanadium Alloy Concept Insulated walls are a must to reduce MHD effects for acceptable pressure drop and heat transfer MAJOR ISSUE –Need to develop reliable and self-healing insulation coating –Compatible with low activation requirements, material interfaces and tritium recovery systems in a fusion environment Chemical reactivity of Li Radiation damage effect on V-alloy from fusion neutron spectrum Fabrication method and cost of V-alloy under the goal of minimizing impurities Joining of V-alloy to another structural material

11. 11 Concepts Utilizing SiC f /SiC Composite as Structural Material Example Self Cooled Pb-17Li + SiC f /SiC Concept: ARIES-ATSimple box design geometry Utilizes 2 cooling passes to uncouple structure temperature from outlet coolant temperatureReasonable design margins as an indication of reliability SiC f /SiC offers advantages of:Safety -Low afterheat: Possibility of passive accommodation of accident scenarios (E.g. LOCA, LOFA) -Low long term activation favorably influences waste disposal requirement (Class C or better)Performance -High temperature operation: possibility of high cycle  SiC f /SiC has been considered with:Self-cooled Pb-17Li (e.g. TAURO and ARIES-AT)He-cooled CB (ARIES-I, DREAM, A-HCPB, and A-SSTR2) Struc. T max =1000°C Cool. T max =1100°C Cool. P =1-1.5 MPa Cycle Eff.=59% Energy Multip. =1.11 Lifetime(?) ~18MW-a/m 2

12. 12 Key Material Issues for Fusion Blanket Concepts with SiC f /SiC Composite Major issue linked to uncertainty about SiC f /SiC behavior and performance at high temperature and under irradiation -Thermal conductivity -Maximum allowable operating temperature -Neutron irradiation effect/Lifetime -Allowable stress -Hermeticity (in particular for He-cooled concept) -FabricationKey issues associated with the breeders are similar to those for other concepts utilizing similar breeding materials

13. 13 Other Concepts Receiving Some Degree of Attention but Generally Less Studied Include: Advanced concepts, e.g. EVOLVE concept with Li evaporation cooling and W alloy -Make use of high latent heat of evaporation of Li -Operation at Li saturation temperature of 1200°C and low pressure -High heat load capable -FW q’’ > 2 MW/m 2 and neutron wall load >10 MW/m 2 -Key material issue: qualification of W alloy under these conditions Struc. T max =1300°C Cool. T max =1200°C Cool. P =0.04 MPa Cycle Eff.>55% Energy Multip. =1.2 Lifetime(?) Struc. T max =550°C Cool. T max =550°C Cool. P =0.5 MPa Cycle Eff.=38% Lifetime =15MW-a/m 2 FLiBe concepts with Ferritic or Other Structural Materials: Advantages of FLiBe -Low chemical activity with air and water -No MHD effect on pressure drop for self-cooled concepts -Compatible with most structural materials to high temperature Issues -Material compatibility issues with transmutation products -Poor heat transfer: Possible MHD effects on heat transfer; need turbulence -Tritium control Limited effort on conceptual design studies for FLiBe concepts in MFE reactors -e.g. FFHR-2 helical-type reactor, with FLiBe + FS blanket concept

14. 14 Substantial Progress Has Been Made in Understanding the Performance and Behavior Of Breeder, Multiplier and Structural Materials Over the Last 10-15 Years Example Accomplishment: Tritium inventory predictions for ceramic breeders Tritium transport in CB is complex process involving several mechanisms Overly conservative T inventory estimate in early studies in the absence of adequate analytical tools and fundamental property data characterization Focused international R&D program including material fabrication and characterization, laboratory and in-reactor purge experiments, and fundamental and integrated model development Intended as a qualitative illustration Specific inventory dependent on parameters which may differ from study to study, Magnitude of CB tritium inventory prediction in blankets has decreased dramatically over the years as a direct result of R&D effort For such classes of blanket, T inventory in other components and materials (such as in Be) are now considered much more problematic Chronology of T Inventory Estimates for CB Blankets from Different Studies

15. 15 However, Many Issues Still Remain for Each Class of Blanket Concept Blanket concepts with the potential for high performance and attractive safety features tend to have higher associated development risk Semi-qualitative subjective classification of different blanket concepts –Attractiveness measure is a subjective assemblage of attractive features, such as cycle efficiency, safety, and lifetime –Measure of development risk includes degree of extrapolation from current material and component performance and complexity and scale of effort required to validate the concept –Individual classification could change over a certain range according to the reviewer –However, the overall classification of choice of structural materials and of breeder materials is unlikely to vary appreciably Example classification of blanket concepts based on attractiveness and development risk

16. 16 Proposed Blanket R&D Strategy (1) The objective of blanket R&D should be to lead at least to the development of a blanket with a minimum acceptable level of performance and attractiveness for a commercial reactor –Lower-bound blanket performance levels which would still result in an acceptably attractive commercial fusion reactor should be developed Blanket concepts with the lowest development risk meeting these performance criteria should be developed and tested –Typically medium-risk medium-performance concepts Representing a fall-back position Provide a reference scale to judge more advanced concepts. –Can be tested in ITER First time operation of full blanket systems in a fusion environment. These tests will give important information on various aspects of blanket component functions But not sufficient (in particular for lifetime) and other approaches would also be required

17. 17 Proposed Blanket R&D Strategy (2) In parallel, critical R&D should be done for the more advanced, higher risk but higher pay off concepts –This R&D is very much material-related –Promises offered by the performance of advanced concepts provides a challenge to the material R&D community to help the blanket design to achieve this Design effort on advanced blanket conceptual design should also be pursued to help guide the material R&D towards high performance material and to provide a vision and a goal for attractive concepts for the future This requires close interaction and coordination between material and design communities, for example, through: – Cross meeting participation, organization of focused workshop e.g. International town meeting on SiC f /SiC at Oak Ridge in Jan. 2000