The influence of thermal-hydraulic cyclic loading on postulated embedded and surface-breaking flaws in the beltline region of a reactor pressure vessel (RPV) are investigated numerically. Over the service life of a nuclear power plant, the RPV is expected to undergo a sequence of cool-down and heat-up thermal-hydraulic transients associated with, for example, scheduled refueling outages (RFOs) or other normal operational transients. With respect to postulated surface or embedded flaws in the RPV wall, these scheduled operational transients produce cyclic, variable-amplitude, nonlinear, multiaxial applied loadings, albeit with possibly long dwell times between the active portions of the cycles. The on-going scoping study indicates that for very large flaws, the driving force increases rapidly with cyclic hardening but tends to saturate after several loading cycles as a stabilized condition is approached; while the driving force tends to keep constant under the cyclic loading for those smaller flaws frequently used in the Pressurized Thermal Shock (PTS) study.

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