2. Tritium extraction, inventory, and control in fusion systems Why? Unprecedented amounts of highly mobile, radioactive, elemental tritium are used as fuel in DT fusion systems  ~0.5 kg/day must be bred and extracted from solid/liquid breeder blankets  ~5-10 kg/day or more must be fueled to, recovered and processed from the plasma  Uncertain amounts of trapped inventory can exist in Blanket/PFC components and tritium processing systems. Tritium for new reactor.  Yet, extremely small release limits (~10 Ci/day), mobilization limits, and the desire to recover and utilize valuable tritium fuel require extremely small loss rates and high accountability 1 Tritium Processing Needs (from ReNeW) Parameter State-of- the-art Needed for ITER Needed for DEMO Flowrate1.34 g/m26.8 g/m~100 g/m Time required 24 hr1 hr Tritium inventory 100 gm4000 gm6000 gm Duty Cycle15%5%>50% PowerDesigned for 1000 MW power plant 500 MW2000 MW Tritium breeding NoneTBM experiments Must breed all tritium State-of-the-art based on TSTA, Savanah River Site and CANDU experience Tritium control and management will be one of the most difficult issues for fusion energy development, both from the technical challenge and “public acceptance” points of view. Experts believe the T-control problem is underestimated (maybe even for ITER!)

2. Tritium extraction, inventory, and control in fusion systems Tritium technical issues for fusion:  Fusion plasma are likely to have low tritium burn fraction (a few %) requiring large fueling rates and processing rates  Most fusion blankets have high tritium partial pressure: (at blanket exit) DCLL~100 mPa, HCLL ~ 1000 Pa, DC Flibe ~ 380 Pa, He purge gas in solid breeders ~ 0.6 Pa  The temperature of the blanket coolants and purges are high (500– 700ºC)  Surface area of heat exchanger is high, with thin walls  Tritium is in elementary form. These are perfect conditions for tritium permeation. 2 Scatter in T solubility measurements in PbLi (from Ricapito) Source of variation is still no completely known (technique, surface effects, composition effects, impurity effects…) Uncertainties are large  Tritium fundamental behavior (solubility, diffusivity) in the many materials of blanket, coolants, processing systems not fully known  The effects of multiple processes (transport, dissociation, diffusion, trapping, etc.); multiple materials, coolants and interfaces; and the synergistic effects of radiation are not completely characterized

3 Tritium permeation barrier development is a key to tritium leakage and inventory control, especially in high partial pressure blanket systems  Development and tests of tritium permeation barriers in the EU not conclusive  On PbLi side PRF ~ 15 for HDA tube samples (out-of-pile)  On He side PRF ~30 for oxidized coatings on Eurofer (out-of-pile)  Aluminide barriers in other programs PRF ~ “double digits” in pile, even though out of pile tests had very large values Tritium extraction to high efficiency from coolant, breeder, purge flows with fast flow-thru times also has the potential to reduce permeation concerns,  Transport in the flow media can be the limiting factor and must be included  Methods to achieve high efficiency must be developed Comparisons of permeability of Hot Dip (HD) Aluminization coated tubes in H2 gas and Pb-17Li 2. Tritium extraction, inventory, and control in fusion systems Accountability must ensure tritium is not a threat to workers, the public and the environment, and that the tritium has not be diverted from the facility  Accountability measurements are performed by in-bed calorimeters or off-line P-V-T methods. Processing times are long and accuracies are limited.

4 2. Tritium extraction, inventory, and control in fusion systems Key R&D required Sophisticated modeling tools and supporting database capable of predicting the T- flows in blanket and fuel cycle systems/components  accounting for complexities from geometric factors, temperature dependent properties, concentration/impurity dependent properties, convection effects Continue to develop high performance tritium diffusion barrier and clarify the still existing technological questions:  understanding the sensitivity of the PRF to the quality of coating  crack tolerance and irradiation experiments on coatings  compatibility studies of coatings in flowing conditions at elevated temperatures and in radiation environment Continue to develop efficient tritium recovery system for both the primary and the secondary coolants  Residual partial pressure < 200 mPa Develop instrument capable of detecting tritium on-line down to a very low concentration. Experimental mockup tests in  out-of-pile facilities: real materials, coatings, coolant/breeders/purges, temperatures, geometric complexity, etc.  in-pile: synergistic effect of radiation environment and energetically bred T (e.g. implantation, bubbles, trap sites, radiation dissociation)  in fusion environment such as Test Blanket Modules (TBMs) in ITER/FNSF: full synergistic and combined effects resulting from fusion environment

7. Interactions between plasma operation and blanket/PFC systems Performance and requirements of both the Plasma and Blanket/PFC components are coupled in important ways  Plasma / Surface Interactions – e.g. the plasma particle and energy incident on divertor / first wall surfaces modify the material, while impurities from and fuel retention in the surfaces strongly influence plasma operation  Electromagnetic coupling – e.g. off-normal plasma events can generate large EM forces in blanket and PFC structures, while error fields generated from the use of ferritic steel structures can influence plasma confinement  Spatial coupling and integration – e.g. space around the plasma must be shared by blankets and PFCs that capture energy and breed tritium, and plasma fueling & control systems, without impeding the function of either systems 5 Blanket and PFC components are - inside the vacuum vessel - inside control coils, and in - direct contact with the plasma Example: ARIES-AT

7. Interactions between plasma operation and blanket/PFC systems Challenge – Developing practical systems and strategies that meet BOTH plasma & FNST requirements  Surface energy and force loads in reactors significantly greater than in current devices  Pulse lengths in reactors orders of magnitude larger than current devices  Many aspects of PFCs in current devices do not extrapolate to reactors  Inertial cooling (No active cooling) or low temperature water cooling  Low component and surface temperatures  Thick structures and armors  Use of non-magnetic stainless steel and high thermal conductivity copper  No blankets  Difficulty in simulating fusion conditions outside of a fusion device (thermal and EM loads) Joint understanding of plasma and reactor relevant component behavior is necessary 6 ITER represents a large step forward in capability to investigate and understand Plasma/Blanket/PFC interactions But even ITER uses blanket/PFC designs, materials and temperatures that are not reactor relevant ITERDEMO* P fus GW Q NWL MW/m t burn s IpIp MA B axis T Avail % 150 R m

7. Interactions between plasma operation and blanket/PFC systems State of the art for studying plasma surface interactions and EM coupling effects  Linear plasmas, beam surface experiments, and high heat flux testing experiments  Inertially cooled PFCs in confinement devices  Plasma edge / core / sheath / surface simulations  Plasma equilibria & EM models  ITER PFC R&D and JET ITER-like wall project Required R&D should focus on more prototypic components, materials, coolants, and temperatures, including understanding limits of components and coupling to plasma  Significantly more Integrated Modeling Studies and database focusing on coupled phenomena, especially studying effects of high temperature, error fields, and PMI coupling  More edge, surface and current diagnostics in confinement devices  Fabrication and testing of reactor relevant component structures in simulated conditions (heat flux; EM load; plasma load; prototypic materials, coolants temperatures, designs)  Integrated testing in integrated plasma devices, ultimately including the effects of neutron heating and damage (an FNSF) 7 One example, the PISCES-B linear plasma device