Structural Integrity Assessment of RPV Under Severe Accident Conditions With Creep Constants Correlation

Creep behavior of nuclear materials is susceptible factor for structural integrity assessment. Particularly, RPV (Reactor Pressure Vessel) under severe accident with a core melting conditions may go through its wall penetration caused by direct contact with corium as well as additional unexpected failure by creep damage. Even though various experiments and analyses were conducted to resolve this special integrity issue, there are still many uncertainties which come from high temperature range, availabilities in only isothermal analysis and so on. In the present study, the state-of-the-art thermal, mechanical and creep properties of a representative RPV material, SA508 Gr. 3 C1. 1 were examined, with which correlation of creep in various loading conditions were determined. Subsequently, a user subroutine which defines the condition-dependent creep constitutive equation was developed and applied to RPV simulation, and relevant Larson-Miller Parameter was also newly fitted. Systematic numerical analyses were conducted by taking into account a typical accident scenario of external reactor vessel cooling. Finally, consequences of the creep effects such as the deformation shape, total strain and rupture time of vessel wall were compared with those of the existing study to enhance the accuracy of numerical analysis.