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

gap: Current understanding of strength-ductility/fracture toughness relationships is inadequate to simultaneously
achieve high-strength and high-ductility and fracture toughness.
The lower operating temperature limit for most fusion structural materials is determined by radiation
hardening and embrittlement. at irradiation temperatures less than about 30% of the
absolute melting point the defect structures produced by neutron damage significantly increase
tensile strength, and decrease ductility and fracture toughness. although the experimental parameters
that cause radiation hardening and embrittlement are well known, the fundamental
mechanisms responsible for loss of ductility are not fully understood. improved multi-scale models
coupled with appropriate experiments are needed to determine the causes of ductility loss in
irradiated metals and suggest possible metallurgical solutions to ameliorate this effect.
standard measurement methods of fracture toughness are not adequate for fusion power systems
because the underlying principles of elastic-plastic fracture mechanics are violated for small
specimens or in thin-walled structures with shallow cracks. a new method has been developed to
provide a highly efficient means of acquiring and applying fracture toughness information, but
further work is needed to verify its technical basis and account for embrittlement effects due to
synergistic hardening and non-hardening mechanisms including helium and hydrogen.
gap: Predictive, physics-based, multi-scale models of materials behavior in the fusion environment are
needed for development of advanced materials.
The cost and time required to design, perform and examine materials from reactor irradiation
experiments is high. Further, there is a combinatorial problem in that the broad range of materials,
phenomena, irradiation variables and variable combinations makes a purely experimental
approach intractable for fusion materials development. Robust computational models provide a
means to reevaluate existing data, optimize the design and execution of new experiments, and
interpret the results from those experiments. Physically based multi-scale models describing irradiation
and mechanical damage processes for fusion applications are being developed, but numerous
fundamental details remain to be fully resolved. models of key properties that simultaneously
span spatial and temporal scales ranging from the atomistic to the continuum and from
sub-picosecond to years are urgently needed.
gap: Fundamental understanding of high-temperature deformation mechanisms is lacking.
For fusion to be an economically attractive power source it must possess high thermodynamic
efficiency. This increases the demand for structural materials capable of operation at high temperatures
where materials can plastically deform at stresses well below the elastic limit. This phenomenon
is known as thermal creep and is typically a concern for materials operating at temperatures
greater than about half the absolute melting point. While considerable research has been
performed on the mechanisms of thermal creep, only an elementary knowledge of the rate controlling
processes is currently available. Present models tend to be semi-empirical in nature, do
not fully capture the relevant physics associated with the deformation mechanisms operating at
these temperatures, and generally have limited predictive capability, even for relatively simple
metals and alloys.
154