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

There is very little experience with steady-state actively cooled PFcs on fusion devices. The database
is insufficient to determine the failure mechanisms and the mean time between failures.
There is an inadequate safety database regarding the loss of coolant and related accidents. There
is also a lack of diagnostics for PFc components on existing devices. even with improved diagnostics,
integrated components testing of advanced and innovative PFcs in a fusion nuclear environment
will be required to design for demo. adequate design margins should be demonstrated in
the development of PFcs.
minimization of tritium permeation through the PFc to the coolant must be included in the design
of the PFc systems. some materials (e.g., titanium, vanadium, tantalum) are known to be
susceptible to hydrogen embrittlement. tritium retention in PFcs must be limited to avoid safety
issues related to tritium inventory, routine release and release during accidents. Permeation will
only be significant for devices that have large tritium throughput or fluence to the PFcs. it can
only be measured on components tested in devices like iteR or ctF. laboratory measurements,
including irradiated samples, could provide the fundamental database.
• helium accumulation at the divertor should be minimized.
• development of remote handling and maintenance equipment will be needed. at the
same time, tailoring the PFcs with precise component alignment should be investigated.
• development of a safety related database for the ctF and demo designs will be required
to satisfy licensing authorities.
• all of the above will need to be supported by integrated modeling codes to generate
predictive capability on future PFc designs.
liquid surfaCe deVelopmenT
Can practical liquid surfaces be developed as an option for solid surface plasma facing components?
liquid surface PFcs avoid the majority of the deleterious effects of alpha and neutron irradiation,
erosion, and off-normal events. There are no thermal stresses in a liquid so cyclic fatigue and
creep are not an issue. however, the peak operating temperature of a liquid surface is limited by
evaporation from the liquid surface. The precise temperature limit also depends on the transport
of the evaporated material to the plasma, which is uncertain. in general, the expected temperature
limits are below those desired for the highest thermal efficiency for lithium, but could be acceptable
for tin and gallium (with further assessment). For the continuing development of the liquid
surface PFcs, the following requirements will need to be addressed.
• magnetohydrodynamics (mhd) modeling and material transport at high hartmann,
Reynolds, and magnetic interaction numbers with fusion relevant fields, configuration
and spatial and temporal gradients, will be required.
• creative engineering of practical devices for injecting, controlling and removing liquid
material will be needed.
• laboratory testing of liquid surface PFcs in relevant magnetic conditions with heat and
particle fluxes for the demonstration of operation effects, including wetting, chemical
effects, and corrosive properties, should continue.
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