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Research Needs for Magnetic Fusion Energy Sciences - US Burning ...

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There is very little experience with steady-state actively cooled PFcs on fusion devices. The database<br />

is insufficient to determine the failure mechanisms and the mean time between failures.<br />

There is an inadequate safety database regarding the loss of coolant and related accidents. There<br />

is also a lack of diagnostics <strong>for</strong> PFc components on existing devices. even with improved diagnostics,<br />

integrated components testing of advanced and innovative PFcs in a fusion nuclear environment<br />

will be required to design <strong>for</strong> demo. adequate design margins should be demonstrated in<br />

the development of PFcs.<br />

minimization of tritium permeation through the PFc to the coolant must be included in the design<br />

of the PFc systems. some materials (e.g., titanium, vanadium, tantalum) are known to be<br />

susceptible to hydrogen embrittlement. tritium retention in PFcs must be limited to avoid safety<br />

issues related to tritium inventory, routine release and release during accidents. Permeation will<br />

only be significant <strong>for</strong> devices that have large tritium throughput or fluence to the PFcs. it can<br />

only be measured on components tested in devices like iteR or ctF. laboratory measurements,<br />

including irradiated samples, could provide the fundamental database.<br />

• helium accumulation at the divertor should be minimized.<br />

• development of remote handling and maintenance equipment will be needed. at the<br />

same time, tailoring the PFcs with precise component alignment should be investigated.<br />

• development of a safety related database <strong>for</strong> the ctF and demo designs will be required<br />

to satisfy licensing authorities.<br />

• all of the above will need to be supported by integrated modeling codes to generate<br />

predictive capability on future PFc designs.<br />

liquid surfaCe deVelopmenT<br />

Can practical liquid surfaces be developed as an option <strong>for</strong> solid surface plasma facing components?<br />

liquid surface PFcs avoid the majority of the deleterious effects of alpha and neutron irradiation,<br />

erosion, and off-normal events. There are no thermal stresses in a liquid so cyclic fatigue and<br />

creep are not an issue. however, the peak operating temperature of a liquid surface is limited by<br />

evaporation from the liquid surface. The precise temperature limit also depends on the transport<br />

of the evaporated material to the plasma, which is uncertain. in general, the expected temperature<br />

limits are below those desired <strong>for</strong> the highest thermal efficiency <strong>for</strong> lithium, but could be acceptable<br />

<strong>for</strong> tin and gallium (with further assessment). For the continuing development of the liquid<br />

surface PFcs, the following requirements will need to be addressed.<br />

• magnetohydrodynamics (mhd) modeling and material transport at high hartmann,<br />

Reynolds, and magnetic interaction numbers with fusion relevant fields, configuration<br />

and spatial and temporal gradients, will be required.<br />

• creative engineering of practical devices <strong>for</strong> injecting, controlling and removing liquid<br />

material will be needed.<br />

• laboratory testing of liquid surface PFcs in relevant magnetic conditions with heat and<br />

particle fluxes <strong>for</strong> the demonstration of operation effects, including wetting, chemical<br />

effects, and corrosive properties, should continue.<br />

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