P-T limit curve construction for the reactor pressure vessel : heatup curve

During the startup and shutdown processes of the nuclear power plants, pressure and temperature are to be maintained below the P-T Limit Curve to prevent the non-ductile failure of the reactor pressure vessel. The ASME Sec. XI App. G describes the detailed procedure for constructing the P-T Limit Curve. Recently, several Code Cases as well as more accurate alternative methods were introduced to reduce the excess conservatism in App. G procedure. In this paper, for the startup, or heatup condition, the App. G procedure are reviewed. Then, the effects of the Code Cases on the P-T Limit Curves of the highly embrittled reactor pressure vessel are assessed. The results show that the current App. G procedure should be modified to consider the inner surface flaw under constant heatup rate when constructing the P-T Limit Curve for heatup condition. Also, when the Code Case N-588 is applied, the axial flaw in the less embrittled base metal has significant effect on the P-T Limit Curve in lower temperature range. Overall, the incorporation of the Code Cases greatly widens the allowable operating region during the heatup process