Under a transient loading like pressurized thermal shock (PTS), the stress discontinuity near the interface between cladding and base metal of a reactor pressure vessel (RPV) is caused by the difference in their thermal expansion coefficients. So the stress intensity factor (SIF) of a surface crack close to the interface should be calculated taking account of the stress discontinuity. Many SIF calculations have to be performed many times in Monte Carlo simulation of the probabilistic fracture mechanics (PFM) analysis. To avoid the time consuming process from the SIF calculation in the PFM analysis, the influence coefficients were developed to calculate the SIF easily and accurately corresponding to the stress distributions in the cladding and base metal. Stress distributions in cladding and base metal are modeled to linear and third-order polynomial expressions, respectively. The non-dimensional SIF coefficients were obtained from FEM analyses. The SIF value at the surface was determined by linear extrapolation of SIF value near the surface. Using the SIF coefficients, the SIF values at the crack tips at both surface and deepest points of a surface crack are evaluated accurately and in a reasonable time.

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