ICONE19-43233 Evaluation of Pressurized Thermal Shock in Korean PWR by using Probabilistic Fracture Mechanics

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Plant-specific analyses of the typical pressurized water reactor in Korea are performed to assure the structural integrity of the reactor pressure vessel during transient which is expected to initiate pressurized thermal shock event. The deterministic analysis is performed to determine the critical time interval in the transient during which mitigating action can be effective. Also, the failure probability is obtained by performing probabilistic fracture mechanics analysis. The probabilistic reactor integrity evaluation code, named R-PIE code, is developed in this study. In addition, several sensitivity analyses are performed for warm pre-stressing, plastic zone correction and simulation option to calculate fracture toughness etc. to assess its effect on the failure probability. The critical crack depth and vessel failure probabilities from the deterministic and probabilistic fracture mechanics analyses are obtained, generating the following conclusions. (1) By including WPS effect, critical crack depth is not changed but critical time interval increased about 100 seconds, giving more time for the operator take some mitigating actions. (2) The warm prestressing has a significant effect on the failure probability for SBLOCA by lowering it by more than 50%. (3) Consideration of internal pressure and plastic zone corrections increases about 10% of stress intensity factor and generates more than 200% of increase in the failure probability depending on the fluence level. (4) The simulation option to calculate RTNDT is a very important factor to get the failure probability with the difference of more than 3 orders depending on the simulation option.