MINIMUM PRESSURIZATION-TEMPERATURE CURVES

DOE-HDBK-1017/2-93 Brittle Fracture MINIMUM PRESSURIZATION-TEMPERATURE CURVES MINIMUM PRESSURIZATION-TEMPERATURE CURVES Plant operations are effected by the minimum pressurization-temperature curves. Personnel need to understand the information that is associated with the curves to better operate the plant. EO 1.8 STATE the two bases used for developing a minimum pressurization-temperature curve. EO 1.9 EXPLAIN a typical minimum pressure-temperature curve including: a. Location of safe operating region b. The way the curve will shift due to irradiation EO 1.10 LIST the normal actions taken, in sequence, if the minimum pressurization-temperature curve is exceeded during critical operations. EO 1.11 STATE the precaution for hydrostatic testing. M PT Definition and Basis Minimum pressurization-temperature (MPT) curves specify the temperature and pressure limitations for reactor plant operation. They are based on reactor vessel and head stress limitations and the need to preclude reactor vessel and head brittle fracture. Figure 4 shows some pressure-temperature operating curves for a pressurized water reactor (PWR) Primary Coolant System (PCS). Note that the safe operating region is to the right of the reactor vessel MPT curve. The reactor vessel MPT curve ensures adequate operating margin away from the crack arrest curve discussed above. The curves used by operations also incorporate instrument error to ensure adequate safety margin. Because of the embrittling effects of neutron irradiation, the MPT curve will shift to the right over core life to account for the increased brittleness or decreased ductility. Figure 4 also contains pressurizer and steam generator operating curves. Operating curves may also include surge line and primary coolant pump operating limitations. The MPT relief valve setting prevents exceeding the NDT limit for pressure when the PCS is cold and is set below the lowest limit of the reactor vessel MPT curve. Rev. 0 Page 7 MS-04