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

gaps: need to select and test the tritium extraction methods, and demonstrate that tritium can
be reduced to levels that will not challenge containment systems. need to include extraction from
beryllium. testing in concert with 14 mev neutrons, high burn up and high flux is needed.
IN-VESSEL TRITIUM CHARACTERIZATION, RECOVERy AND HANDLINg (NEED 7)
Description: tritium deposition inside the torus is expected. calculations have shown that tritium
can rapidly accumulate in certain iteR conditions. methods are needed to characterize invessel
tritium. also needed are methods to recover in-vessel tritium and handle in-vessel components
that have deposited tritium.
State-of-the-art: experience has been gained with tritium experiments on tFtR and Jet.
stand-alone experiments have shown that tritium buildup on carbon machines is significant and
less so on tungsten machines. higher first-wall temperatures will help.
gaps: Presently there is no tungsten plasma facing component testing data in a demo-like nuclear
environment. There is a need to test the tritium hold-up on the tungsten divertor and first
wall under demo-relevant conditions. There is also a need to test and develop knowledge to increase
the burn-up fraction and recycling coefficient under relevant toroidal plasma conditions.
poWER ExtRactioN
Power extraction is a fundamental challenge for an attractive fusion energy source. The fusion
plasma deposits significant energy in the form of energetic particles and X-rays on the surfaces of
the components that surround the plasma. in addition, neutrons born from the fusion reaction
carry their energy deeper into the components, resulting in strong volumetric heating. The goal of
fusion power extraction is then to capture this energy, transport it away from the burning plasma,
and convert it efficiently to electricity or some other useful form such as hydrogen or process
heat. conversion of this energy at high efficiencies requires that the coolant streams performing
the power extraction are at high temperature.
The element lithium also must capture the same neutrons carrying 80% of the fusion power to
generate (or breed) tritium fuel needed to resupply the plasma. The combined system that captures
these neutrons for both breeding and energy harvesting is called the blanket, and it occupies
about 90% of the surface area surrounding the plasma. it has an integrated first wall facing the
plasma that also captures a portion of the surface energy flux from the plasma. high-temperature
power extraction must be accomplished using strategies, components and materials that do not
damage the potential to continuously breed the tritium fuel. For instance, using thick structures
and plasma facing surfaces to increase strength and absorb energy is not possible because of parasitic
neutron absorption and the resultant decrease in tritium breeding potential.
The remaining portion of the surface heating is typically concentrated on a second power extraction
component called the divertor, designed to take very high surface power loads. For the divertor
(and to a lesser degree the first wall), power extraction issues are integrally connected with
those regarding plasma surface interactions, a topic specifically treated in Theme 3.
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