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SSCs are subject to thermal and pressure cyclic loadings during normal operation and
anticipated off-normal events such as disruptions/VDEs. Also, systems and components are
subject to vibration loading from motors, cavitation, water/steam hammer, and so on. The
ASME/ANSI design codes or comparable computational methods provide criteria for the evalua-
tion that should use conservative analysis for the number of cycles and service life including the
expected changes in material properties with time. Materials
Material properties used in the analysis of safety-class SSCs must be appropriate for the
operating environment, including off-normal events, and compensated for the degradation of the
material properties with time due to radiation, fatigue, embrittlement, corrosion, or any other
environmental factor. This applies to the relevant properties of safety-class SSCs that perform
specific safety functions. For safety-class SSCs that provide confinement or structural support,
the degradation of yield strength would be an important property to consider in the anticipated
operating environment. For safety-class SSCs that provide a control or monitoring function, the
degradation of insulation or changes in the dielectric behavior would be an important property to
consider in the anticipated operating environment.
a. Radiation--Materials selected should be qualified for the anticipated lifetime in the
anticipated radiation environment. This includes external radiation from the fusion
reaction and component activation and internal radiation due to tritium beta decay.
Conservative end-of-life properties should be used in the design analysis.
b. Thermal--Material properties used in analysis should always be those appropriate for
the given temperature range. If no published property data for a particular tempera-
ture range exist, then materials should be tested for properties at the operating tem-
peratures, or the design analysis should be based on estimated (conservative) mate-
rial properties and the actual component performance should be monitored by formal
in-service testing. For those items to be designed in accordance with ASME 1992,
temperature limits are imposed within the code. If the item will be subjected to tem-
peratures higher or lower than the limit, material properties, such as allowable stress
and creep, used in the analysis should be justified by testing the material at the antici-
pated temperature.
c. Hydrogenic and helium embrittlement--The structural design analysis should base the
material properties on end-of-life hydrogen and helium embrittlement (note He3 is a
product of tritium beta decay). The actual embrittlement of the SSC in the hydrogenic
and helium environment should be determined by a monitoring and testing program.
Where feasible, designers should eliminate embrittlement as a design issue by
considering in the choice of materials a lifetime projection of pressures and tempera-
tures and exposure to hydrogen isotopes and helium.
d. Material compatibility--An SSC may use a variety of materials in close proximity. In
addition to changes in material properties due to external factors, the design should
evaluate and resolve any material compatibility problems within an SSC such as

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