Figure 3 Fracture Diagram

Brittle Fracture DOE-HDBK-1017/2-93 BRITTLE FRACTURE MECHANISM Figure 3 is a graph of stress versus temperature, showing fracture initiation curves for various flaw sizes. It is clear from the above discussion that we must operate above the NDT temperature to be Figure 3 Fracture Diagram certain that no brittle fracture can occur. For greater safety, it is desirable that operation be limited above the FTE temperature, or NDT + 60°F. Under such conditions, no brittle fracture can occur for purely elastic loads. As previously discussed, irradiation of the pressure vessel can raise the NDT temperature over the lifetime of the reactor pressure vessel, restricting the operating temperatures and stress on the vessel. It should be clear that this increase in NDT can lead to significant operating restrictions, especially after 25 years to 30 years of operation where the NDT can raise 200°F to 300°F. Thus, if the FTE was 60°F at the beginning of vessel life and a change in the NDT of 300°F occurred over a period of time, the reactor coolant would have to be raised to more than 360°F before full system pressure could be applied. Rev. 0 Page 5 MS-04