Heat-up and cooldown pressure temperature limit curves according to appendix G to the asme code section III

The technical specifications for light water reactors impose pressure-temperature limits on the reactor coolant pressure boundary during operation to assure protection against non-ductile failure. The operation limit curves are the permissible pressure-temperature relationships that avoid the unstable propagation of a reference crack in the vessel wall during the reactor heat-up and cooldown. These limits are calculated in accordance with the recommendations of Appendix G to the ASME Code Section III which are based upon the principles of linear fracture mechanics. Flaws in the weld metal or in the base material are assumed to be axial oriented and to have a semi-elliptical shape either on the inside or outside surfaces of the vessel. The stress intensity factor is calculated at the tip of the crack for combined thermal and mechanical loads and compared to the stress intensity factor allowed by the code. (J.S.)