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

structures must also provide acceptable safety margins during both normal operation and offnormal
events. Radioactive isotope inventory and release paths are key considerations in designing
for safety. The initial levels of radioactivity of materials on removal from service, and the rate
of decay of the various radioactive isotopes, dictate acceptable storage and disposal methods and
the possibility for recycle or clearing of materials. These issues are major considerations in the environmental
acceptability of fusion.
a significant expansion of the current fusion materials research effort is needed to fully explore
the performance limits of first-generation power plant materials such as RaF/m steels (including
dispersion strengthened ferritic alloys) and tungsten alloys, and to discover the next generation
of high-performance materials. to achieve the widest possible operating temperature window,
the underlying physical mechanisms controlling properties of materials at low, intermediate
and high-temperatures must be determined. a key technical issue is the fundamental relationship
between material strength and ductility or fracture toughness. Present engineering materials
do not exhibit simultaneously high strength and high ductility or fracture toughness. enormous
technological benefits will be accrued far beyond fusion energy if this puzzle can be solved.
its solution will require advances in understanding how materials with high-defect densities deform,
as well as the conditions under which cracks propagate, and in determining the role he and
h make to hardening and non-hardening embrittlement of materials.
another significant issue that has broad applicability beyond fusion energy is microstructural
stability and deformation behavior of materials at high temperatures. severe time-dependent,
thermo-mechanical, high-temperature loading of large and complex fusion structures may be a
grand challenge in itself, not considering radiation damage effects, representing a regime far beyond
the limits of present-day technology. a major scientific challenge is to develop physical models
of high-temperature creep and creep-fatigue interaction mechanisms. current treatments of
these phenomena are largely empirical and material-condition specific. high-temperature design
rules evolved from a body of structural application experience that is enormously less complex,
with fewer interrelated parameters, than in the case of fusion. For example, to move beyond the
current state-of-the-art will require significant advances in models of creep deformation. These
models must simultaneously treat the evolution of complex dislocation, interface and precipitate
structures, stress-driven dislocation motion, the interaction of dislocations with obstacles,
sliding of grain boundaries and diffusionally accommodated creep that accounts for multiple effects
of grain boundary precipitates. The challenge of high-temperature performance will be enormously
amplified by the effects of high concentrations of he, which can degrade performance sustaining
properties, like creep rupture life, by many orders of magnitude.
in addition, plasma facing components (PFcs) experience severe and variable surface heat loads,
damage from energetic ions, and erosion of material by ions (or neutrals) or by redeposited material
from the plasma. These conditions will further complicate their microstructural evolution
and may induce modes of failure that differ from materials elsewhere in the system. Furthermore,
impurities from erosion directly affect plasma stability. Understanding how plasma-surface interactions
affect the design and selection of PFcs and other in-vessel materials is critical. This area
is an interdisciplinary specialization where some aspects of fundamental materials modeling, as
well as experiments, are shared with Thrusts 9, 10 and 11.
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