077-05/rs Presented by: Neil B. Morley, Adj. Professor UCLA Fusion Science and Technology Research Needs Workshops Fusion/Fission Hybrid Gaithersburg, MD, Sep 30 – Oct 2, 2009 Summary of Preliminary Conclusions of the ReNeW Fusion/Fission Hybrid Blanket Panel

077-05/rs  David Petti – INL, Lab Fellow, Director R&D for NGNP, Former Fusion Safety Program Leader  Jess Gehin – ORNL, Senior Program Manager Nuclear Technology Systems, Former Leader of Reactor Analysis Group  Jake Blanchard – UW, Professor of Engineering Physics, Thermostructural/EM/Lifetime aspects of fusion structures  Per Peterson – UCB, Professor of Nuclear Engineering, High temperature fission and fusion energy systems, nuclear security and waste management  Mohamed Abdou – UCLA, Distinguished Professor of Mechanical Engineering, Director of the Center for Energy Science and Technology Advanced Research (CESTAR) and the Fusion Science and Technology Center  Neil Morley – UCLA, Adj. Professor of Mechanical Engineering, Fusion Blanket Design and Cooling Technology Contributions from Bill Stacey, Mike Kotschenreuther, Ralph Moir and Wayne Meier are also acknowledged The Hybrid Blanket Panel

077-05/rs Introduce the Panel  Fusion and Fission blanket requirements  Sample of Fusion/Fission Hybrid blanket concepts  Potential advantages of Hybrid blankets  Concerns about Hybrid blankets  Omission, Conclusions and the Parallel Session Outline

077-05/rs 4 Pillars of a Fusion Energy System 1.Confined and Controlled Burning Plasma (feasibility) 2.Tritium Fuel Self-Sufficiency (feasibility) 3.Efficient Heat Extraction and Conversion (attractiveness) 4.Safe and Environmentally Advantageous (feasibility/attractiveness) 5.Reliable System Operation (attractiveness) Yet, keep in mind that no fusion energy relevant first wall and blanket component has ever been built or tested Fusion Nuclear Science and Technology plays the KEY role

077-05/rs 5 Scope of Blanket and Nuclear Technology The scientific issues, technical disciplines, materials, engineering and development of fusion nuclear technology components: From the edge of Plasma to TF Coils: 1. Blanket Components (including FW) 2. Plasma Interactive and High Heat Flux Components ( divertor, limiter, rf/PFC elements) 3. Vacuum Vessel & Shield Components 4. Tritium Processing Systems 5. Remote Maintenance Components 6. Heat Transport, Power Conversion Systems Other Systems / Components affected by the Nuclear Environment: ARIES-AT FNST COMPONENTS

077-05/rs 6 Blanket functions including first wall A.Power Extraction –Absorb plasma radiation on the first wall and convert kinetic energy of neutrons and secondary gamma rays / charged particles into heat –Extract the heat (at high temperature, for energy conversion) B.Tritium Breeding and Extraction –Must have lithium in some form (ceramic, liquid metal, etc) C.Physical Boundary for the Plasma –Physical boundary in contact with the plasma, wall conditioning, Provide access for plasma heating, fueling D.Radiation Shielding of the Vacuum Vessel and Magnets (Usually) E.HYBRID -- Transmutation, Energy and Neutron multiplication, and/or Fissile Fuel Production –Minimize parasitic absorption. Moderation / transmission of fusion neutrons to fission fuel n Plasma p np n np Blanket n ALL FUSION NEUTRONS NEEDED FOR BREEDING TRITIUM, STRONG MULTIPLICATION NEEDED FOR HYBRID

077-05/rs 7 1.D-T fuel cycle tritium self-sufficiency in a practical system 2.Tritium extraction, inventory, and control in solid/liquid breeders and blanket, PFC, fuel processing and heat extraction systems 3.MHD Thermofluid phenomena and impact on transport processes in electrically- conducting liquid coolants/breeders 4.Structural materials performance and mechanical integrity under the effect of radiation and thermo-mechanical loadings in blanket and PFC 5.Functional materials property changes and performance under irradiation and high temperature and stress gradients (including ceramic breeders, beryllium multipliers, flow channel inserts, electric and thermal insulators, tritium permeation and corrosion barriers, etc.) 6.Fabrication and joining of structural and functional materials 7.Fluid-materials interactions including interfacial phenomena, chemistry, compatibility, surface erosion and corrosion 8.Interactions between plasma operation and blanket and PFC materials systems, including PMI, electromagnetic coupling, and off-normal events 9.Identification and characterization of synergistic phenomena and failure modes, effects, and rates in blankets and PFC’s in the fusion environment 10.System configuration and Remote maintenance with acceptable machine down time Summary of Top- Level Technical Issues for Fusion Nuclear Science and Technology

077-05/rs 8 A fusion device has MANY major components Availability required for each component needs to be high DEMO availability of 50% requires: Blanket availability ~88% and blanket MTBF >11 years. (Table based on information from J. Sheffield et al.)

077-05/rs LIFE – IFE based power producer  ODS Ferritic Steel Structural  PbLi First wall coolant  Be multiplier / moderator  Mobile particle (TRISO-like) fission fuel form  Flibe coolant / tritium breeder 9 Courtesy of W. Meier, LLNL

077-05/rs LIFE blanket system with PbLi and Flibe Coolants 10 Courtesy of W. Meier, LLNL Triso-like fuel and MS

077-05/rs SABR Design from Georgia Tech – Tokamak based system with Fusion/Fission blanket inside the TF coils and vacuum vessel 11 Based on ITER size and power levels, and sodium fast reactor fuels Courtesy of W. Stacey, GT

077-05/rs SABR – All sodium cooled blanket, FW, divertor based on ODS ferritic steel structure 12 Courtesy of W. Meier, LLNL

077-05/rs FFTS Concept – Remove the fission blanket completely outside the fusion driver (access & decoupling), design for complete fusion core replacement Courtesy of UT/UCLA

077-05/rs FFTS– normal conducting, replaceable coils and current generation structural materials, SFR blanket Courtesy of UT/UCLA

077-05/rs Process of the Hybrid Blanket Panel  Review past reports, earlier reviews, and papers; particularly focused on recent concepts and blanket / nuclear technology perspective  Summarize some representative example concepts (LIFE, SABR, FFTS)  Many discussions on concept strategies, potential benefits, and concerns – Technical judgement  Writing/revising outcomes of these discussions and summaries of concepts  Draft chapter distributed for comments  Take our lumps at Workshop  Revise chapter, finalize conclusions 15

077-05/rs Potential Benefits to Hybrid Blankets: Possibility of reduced load on the first wall, divertor and plasma control structures (both in neutrons and surface heating)  Lower power plasma operation due to significant energy multiplication behind the first wall in the blanket.  Potential economic and availability benefit from this reduced load if the first wall does not need to be replaced as often or the overall size of the system is made smaller.  Potential R&D, cost and development time benefits if materials requirements in terms of damage (dpa and helium generation) or operating loads could be reduced in favor of more near term materials, while still meeting economic performance goals.  Additionally, if energy in FW, divertor, and other PFC surfaces becomes expendable (a small percentage of overall system power), it may be possible with some acceptable economic penalty to use coolants and temperature regimes most beneficial to their reliability rather than power conversion performance.  NOTE: not all proposed hybrid concepts attempt to reduce the wall loads of pure fusion neutrons 16

077-05/rs Potential Benefit Compared to Fission Systems – Subcritical Fission Blanket operation  Potentially enable the use of a wider range of fission blanket designs and fuels than may be possible for critical systems, –Less need for strong negative power reactivity feedback? –Larger prompt critical margins  There may also be fuel cycle benefits related to potential for increased burn up of fission fuels and transmutation of more difficult to manage fission fuels when compared to critical fission systems (not studied in detail by the blanket panel and conclusions are deferred to the fuel cycle panel). 17

077-05/rs Developing hybrids will require substantially the same types of blanket & materials R&D needed for pure fusion as well as that needed for new fission fuels & safety.  The technology readiness for the fission blankets in hybrids is behind that of the fission analogs  Development and Qualification of these blanket systems would require similar development path (recall earlier slide on pure fusion issues) and integrated test facilities as currently envisioned in both pure fusion and fission development  Adapting the fabrication processes for pin/clad type to cores with more complex toroidal and poloidal geometries in magnetic fusion or the angular and azimuthal geometries in inertial fusion  Particles fuels may not be the traditional TRISO fuel used in high temperature gas reactors, but includes different coating layers whose fabrication is today unknown.  Impact on the fuel of magnetic fields (JxB) forces especially during disruptions and high cycle fatigue associated with the high rep rate of inertial system is not yet known. 18

077-05/rs 19 Theory/Modeling/Database Basic Separate Effects Multiple Interactions Partially Integrated Property Measurement Phenomena Exploration Non-Fusion Facilities A similar science-based Framework for Fusion Fission Hybrid Technology Development will be required Design Codes, Predictive Cap. Component Fusion Env. Exploration Concept Screening Performance Verification Design Verification & Reliability Data Testing in Fusion Facilities (non neutron test stands, fission reactors and accelerator-based neutron sources, plasma physics devices) Experiments in non-fusion facilities are essential and are prerequisites Testing in Fusion Facilities is NECESSARY to uncover unanticipated phenomena, validate the predictive capability, establish engineering feasibility and integration, and qualify components

077-05/rs 20 Integrated Testing Even More Crucial for Fusion Fission Hybrids FNSF (also called VNS, CTF) a small size, low fusion power DT plasma device in which Fusion Nuclear Science and Technology (FNST) 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 3- failure tolerant and designed for fast replacement In MFE: small-size, low fusion power can be obtained in a low-Q (driven) plasma device, with normal conducting Cu magnets Equivalent in IFE: reduced target yield (and smaller chamber radius?)

077-05/rs Whether the development time scale for hybrid is longer or more rapid than pure fusion can not be firmly concluded without further extensive analysis.  Reduced loading on primary fusion structures may reduce risk, number of testing cycles, or material development requirements  But the additional complication related to fission functions and requirements is a concern – achieving RAMI and safety may be much longer than indicated in the hybrid concepts presented.  The safety case burden of proof for the hybrid will be greater than pure fusion given the hazards of the fission blanket, –Increased likelihood of, and complex approaches required to mitigate, loss of coolant accidents (sodium vessel not lifetime component nor low fluence/damage) –the combined energy sources associated with fusion (magnets, plasmas) and fission (afterheat, sodium) –the overall complexity of the system  Several concepts propose use of ODS Ferritic steels as main structural material with high damage limits (200 dpa). ODS steels manufacture and especially joining are still experimental 21

077-05/rs The ability to meet tritium breeding requirements and fission fuel transmutation goals must be based on neutronics analysis including more complete design  Including time variations coming from fuel and lithium burnup and reduced reactivity  Including realistic amounts the structure, coolants, penetrations, plasma fueling/control systems, etc.  The strategy of completely removing the fission blanket to a region outside the TF coils of the fusion device is a paradigm shift from fusion power plants designs that has several potential advantages, but detailed implications must be fully analyzed –power peaking in fission system (magnet system holes) –access for plasma maintenance systems, –ability to meet tritium production requirements, –economics and waste disposal  The strategy to store large amounts of tritium for later in the burn cycle is a safety concern and must be fully analyzed 22

077-05/rs Glaring Omissions  Fission suppressed, fissile fuel production  Differences of other confinement systems  Mobile fuels dissolved in coolants  ?  Blanket/FW/materials area is a key area, the ultimate feasibility, attractiveness, economics of the hybrid will depend heavily on these technological systems. 23 Conclusions

077-05/rs Blanket Parallel Session  Speakers –Bill Stacey – SABR blanket / safety –Bob Woolley – Dissolved fuels and 2 chamber concept –Ralph Moir – fission suppressed fissile fuel production and dissolved fuels –Wayne Meier – LIFE Blanket –Glen Wurden – Other pulsed concepts using molten salt and the benefits of dissolved fuels 24

077-05/rs  New slides added and use throughout the meeting.  Drafts, not in final form… 25

077-05/rs Potential Benefits to Hybrid Blankets: Possibility of reduced load on the first wall, divertor and plasma control structures due to fission energy multiplication  Potential cost/time benefits from this reduced load –if the first wall does not need to be replaced as often or the overall size of the system is made smaller. –if materials requirements are reduced (dpa / helium / TM load / low activation) in favor of more near term materials and test facilities –if energy in FW/divertor becomes expendable so coolants / temperature regimes are chosen that are beneficial to reliability  NOTE: not all proposed hybrid concepts attempt to reduce the wall loads of pure fusion neutrons but use modest power multiplication to boost output power  Some concept pursue this aggressively, either with high keff, low power. 26 Potential Benefits to Hybrid Blankets: Amplification of neutron multiplication for tritium breeding

077-05/rs Potential Benefits to Hybrid Blankets: Opening up the driver space to something that is more easily maintainable, or technologically simpler from blanket perspective  Mirror, others?  Driver panel must evaluate the potential from physics point-of-view  Some concepts have significantly lower current, lower stored energy, smaller size (can cut both ways)  Regimes of conservative plasma operations in regards to disruption frequency and elms  Reduced wall loads leading to less FW flaking into plasma 27 Potential Benefits to Hybrid Blankets: Potential to operate in regime of reduced disruptivity and/or reduced disruption load

077-05/rs Potential Benefit Compared to Fission Systems – Subcritical Fission Blanket operation  Potentially enable the use of a wider range of fission blanket designs and fuels than may be possible for critical systems,  There may also be fuel cycle benefits related to potential for increased burn up of fission fuels and transmutation of more difficult to manage fission fuels when compared to critical fission systems (not studied in detail by the blanket panel and conclusions are deferred to the fuel cycle panel). 28

077-05/rs Other general conclusions/concerns of blanket panel  Developing hybrid blankets will require substantially the same TYPES of blanket & materials R&D needed for pure fusion as well as that needed for new fission fuels & safety.  Integrated testing in a prototype facility remains a serious need  Whether the development time scale for hybrid is longer or more rapid than pure fusion can not be firmly concluded without further extensive analysis and will be concept specific.  The ability to meet tritium breeding requirements and fission fuel transmutation goals must be based on neutronics analysis including more complete design  Blanket/FW/materials area is a key area, the ultimate feasibility, attractiveness, economics of the hybrid will depend heavily on these technological systems. 29

077-05/rs General conclusions of blanket panel  The attempt to put near term fixed fuels / existing fission fast reactor designs inside the fusion vacuum vessel adjacent to the plasma appears very difficult from refueling, LOCA, fuel or coolant interactions with magnetic fields and disruptions.  Mobile fuels may offer benefits to overcome access, geometric restrictions and fuel damage due to fusion conditions. –Concerns exist regarding licensing and proliferation in the current regulatory environment –Significant past work and designs in fission but not currently large MS R&D. Is an option considered for a long time in many fusion systems 30

077-05/rs Today's discussions on blanket (1)  The attempt to put near term fixed fuels / existing fission fast reactor designs inside the fusion vacuum vessel adjacent to the plasma appears very difficult –Access for shuffling the fixed fuel is extremely restricted –LOCAs can not be excluded and afterheat removal from fixed fuel will require active systems –Proximity to plasma disruptions could damage fuels  Fission suppressed, fissile fuel production –Has additional benefit of fuel production. Essentially requires equivalent fusion blanket system / materials as pure fusion –Need for this mission may only materialize down the road (later half of century), but this may be the right time scale for hybrid development anyway. –Proliferation risk 31

077-05/rs Today's discussion on blanket (2)  Mobile fuels offer benefits to overcome hybrid access, geometric restrictions and fuel damage due to fusion conditions  TRISO-like fuels with 99% burnup proposed for LIFE use steel outer shell to contain gases. Other possible fuel failure mechanisms expected at high burnup weren’t discussed  Dissolved fuels in molten salts proposed for several concepts –Pulsed fusion concepts in IFE, MTF, Zpinch already propose MS use, some with thick liquid walls. Requirements on fusion system not reduced by hybrid mission –Recent actinide burning analysis by Ed Chang/Y. Gohar/M. Ubeyli –Advantages: on-line control, no thermomechanical fuel damage, overcome geometrical restrictions, high burnup, reduced MHD issues –Main concerns: licensing and proliferation requires strict accounting for fuel, additional contamination from accidental spills, others?? Why last of GENIV ? 32